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Cartilage repair of the knee

119 citationsUpdated Sep 2026

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Overview

Articular cartilage injuries in the knee arise from age-related degeneration, trauma, congenital defects, inflammatory conditions, or infection [2]. Approximately 11% of knee arthroscopies reveal defects suitable for repair [5], though MRI underestimates defect size in roughly 75% of cases [15]. Diagnosis requires concomitant physical examination and advanced imaging to identify the symptom source after nonsurgical measures fail [2]. Indications center on focal, full-thickness cartilage loss with localized symptoms [24]. These procedures are contraindicated in multifocal loss, diffuse arthritis, or inflammatory arthropathy [24]. Unaddressed ligamentous instability, malalignment, or meniscal deficiency also preclude repair [24]. Advanced degenerative joint disease is the primary contraindication for autologous chondrocyte implantation (ACI) [46], and isolated repair is generally not recommended with complete joint space loss [84]. Relative contraindications include limb malalignment, ligamentous insufficiency, and meniscal damage unless concurrently treated [84].

Treatment selection depends on chronicity, severity, and whether the injury is focal or generalized [2]. Key factors include age, lesion size, activity level, alignment, meniscal integrity, and ligamentous stability [15]. Concomitant osteotomies are frequently combined with restoration procedures to correct malalignment and protect the repair site [15, 177, 84]. Bone marrow stimulation techniques, such as microfracture, are single-stage arthroscopic procedures that produce fibrocartilaginous tissue with inferior wear characteristics [24, 15]. They yield good results in 60% to 80% of patients with small defects (<2 to 3 cm²) [15], but long-term clinical deterioration is observed across all ages [24]. Osteochondral autograft transfer (OAT) and allograft transplantation address defects involving subchondral bone loss [24]. OAT is a single-stage procedure using hyaline cartilage plugs, offering durable outcomes with low reoperation rates at 10 years [24, 8, 49]. Allografts are suitable for larger lesions (≥4 cm²) but carry risks of disease transmission and immunological rejection [24, 15].

ACI is a two-stage procedure that creates type II collagen–rich hyaline-like cartilage [216, 15]. It is indicated for medium to large chondral lesions without bony defects [15] and provides durable outcomes, with 71% survivorship at 10 years [3]. Matrix-induced ACI (MACI) allows for single-stage fixation with fibrin glue and even chondrocyte distribution [216]. Allograft cell-based therapies, such as particulated juvenile cartilage, offer single-stage surgery with hyaline-like healing [24]. While these therapies are safe in adolescents [7, 12] and combined with meniscal allografts [48], current treatments often result in mechanically inferior tissue [21]. Condylar lesions demonstrate superior outcomes compared with patellofemoral lesions [15]. Definitive conclusions on optimal treatment remain elusive due to a lack of high-quality comparative studies [164].

Anatomy & Pathophysiology

Etiology and Prevalence

Articular cartilage injuries in the knee arise from age-related degenerative changes, previous trauma or injury, congenital osteochondral defects, inflammatory conditions, infection, and other causes [2]. The predominant reason for localized articular cartilage damage is earlier trauma, which may be a direct impact or a distortion [28]. Osteochondral lesions of the knee are most frequently traumatic in origin [96]. Articular cartilage injury occurs as a result of rotational forces in direct trauma [15]. The etiology of osteochondritis dissecans (OD) remains unknown, with posttraumatic changes and subchondral circulatory disorders currently being discussed [28].

Chondral or osteochondral lesions are present in as high as 61% to 66% of patients undergoing knee arthroscopy [79]. The overall prevalence of focal chondral defects of the knee in athletes has been estimated to be 36% [79]. The true incidence and prevalence of cartilage defects is difficult to determine because a large percentage of defects are asymptomatic [79]. Cartilage damage is often associated with injuries to other anatomic structures of the knee and seen in conjunction with malalignment [79]. Acute anterior cruciate ligament tears and meniscal derangement have been highly correlated with chondral defects [79]. Chondral and osteochondral lesions have been reported in upward of 90% of patients following patellar dislocation [79]. Associated ligamentous or meniscal pathology is reported in 40% of cases of osteochondral lesions of the knee [96]. Women have a different knee chondral lesion pattern and more often have unfavorable conditions related to the cause of injury, site, and activity level [27].

Pathophysiology and Natural History

Articular cartilage and subchondral bone should be viewed as a closely related osteochondral unit [45]. Any disturbance of the osteochondral unit can lead to altered biomechanics and abnormal joint contact pressures, leading to an inflammatory response [45]. This inflammatory response may result in pain and dysfunction with the theoretical risk of widespread joint degeneration [45]. Any disruption of the osteochondral unit may result in altered biomechanics and increased joint contact forces to the surrounding chondral surfaces and subchondral bone [79]. Mechanical wear and loose body formation may initiate an inflammatory response with release of cartilage-degrading enzymes, further leading to joint degeneration [79]. If left untreated, chondral defects can lead to osteoarthritis [79].

Spontaneous healing or regeneration of traumatic cartilage damage in adults is rare due to insufficient proliferation and migration of chondrocytes into the defect [28]. Injury of cartilage together with the adjacent subchondral plate induces a wound clot that may generate fibrous repair tissue [28]. Fibrous repair tissue lacks the biomechanical properties of hyaline cartilage due to a different molecular and textural configuration [28]. Fibrous repair tissue predominantly shows early deterioration and failure, at least in larger defects [28]. Biomechanical studies have demonstrated increased stress concentration on the rim of the osteochondral defect [96]. Larger osteochondral lesions of the knee are associated with symptoms appearing approximately one decade earlier than the degenerative cartilage changes associated with idiopathic osteoarthritis [96].

OCD in adults is usually symptomatic and leads to arthritis if left untreated [15]. Poor prognostic factors for OCD include larger, more severe lesions; older age; discoid meniscus; and mechanical symptoms [15]. Traumatic injury of the patella may progress to arthritis, with osteoarthritic-like degeneration found in all specimens in an experimental animal study [180]. The reversibility of cartilage damage or progression to arthritis is associated with factors such as the intensity and frequency of the trauma [180].

Anatomical and Biomechanical Context

The medial femoral condyle is larger and projects farther posteriorly and distally than the lateral condyle [104]. The lateral femoral condyle projects farther anteriorly and is wider in the medial-lateral direction than the medial femoral condyle [104]. The sulcus terminalis is a small ridge on the lateral femoral condyle just distal to the intercondylar notch that separates the patellofemoral and tibiofemoral articular surfaces [104]. The trochlear groove separates the two condyles anteriorly and constitutes the patellofemoral articulation [104].

The tibial articular surface slopes 7° to 10° in the sagittal plane [104]. The medial tibial plateau is larger than the lateral plateau and is concave in its frontal and sagittal planes [104]. The lateral tibial plateau is smaller and more circular than the medial plateau, concave in the frontal plane and convex in the sagittal plane [104]. The patella has the thickest articular surface in the body, approximately 5 mm in the midportion and 2 mm on the sides [104]. The articular surface of the patella contains a vertical, central ridge that separates the broader lateral facet from the medial facet, and a smaller, more medial facet called the odd facet [104].

The menisci are C-shaped fibrocartilaginous disks that provide shock absorption, allow for increased congruency between joint surfaces, enhance joint stability, and aid in distribution of synovial fluid [55]. If the menisci are not present, the convex femoral condyles articulate with the relatively flat tibial plateaus, decreasing surface area of contact and increasing pressure on the articular cartilage [55]. The medial meniscus is firmly attached to the joint capsule along its entire peripheral edge [55]. The lateral meniscus is attached to the anterior and posterior capsule, but there is a region posterolaterally where it is not firmly attached [55]. The medial meniscus has less mobility than the lateral meniscus and is more susceptible to tearing when trapped between the femoral condyle and tibial plateau [55]. The lateral meniscus is larger than the medial meniscus and carries a greater share of the lateral compartment pressure than the medial meniscus carries for the medial compartment [55].

The knee is a hinge joint that also incorporates both gliding and rolling, which are essential to its kinematics [105]. The "screw-home" mechanism involves the tibia externally rotating 5 degrees in the final 15 degrees of extension [105]. The greatest range of motion in the knee occurs in the sagittal plane, approximately 160° [125]. Knee rotation ranges from 45° in external rotation to 30° in internal rotation [125]. In the frontal plane, the range of motion in both abduction and adduction reaches a maximum of 10° [125]. The normal instant center of the knee joint follows a semicircular path related to the tibiofemoral surface and ligaments crossing the joint [125]. Rupture of the cruciate ligaments or disruption of the tibiofemoral surface, including the menisci, causes a major change in the path of the instant center, leading to articular dysfunction [125].

The anterior cruciate ligament (ACL) is composed of 90% type I collagen and 10% type III collagen [104]. The mean length of the ACL is 33 mm and the mean midsubstance width is 11 mm [104]. The femoral attachment of the ACL is a semicircular area (20 mm long and 10 mm wide) on the posteromedial aspect of the lateral femoral condyle [104]. The tibial attachment of the ACL is a broad, irregular, oval-shaped area (30 mm long and 10 mm wide) slightly medial and anterior to the midline and between the medial and lateral tibial spinous processes [104]. The posterior cruciate ligament (PCL) has a mean length of 38 mm and a mean width of 13 mm [110]. The PCL has a broad, crescent-shaped femoral attachment on the anterolateral medial femoral condyle with a mean length of 30 mm and mean width of 5 mm [110]. The tibial insertion of the PCL onto the posterior central sulcus is 10 to 15 mm distal to the joint line of the knee [110].

The menisci are crescent-shaped, fibrocartilaginous structures with a triangular cross section [110]. Menisci consist of type I collagen fibers arranged obliquely, radially, and vertically [110]. The vascular supply of the menisci is derived from the geniculate arteries, which penetrate into 20% to 30% of the peripheral medial meniscus and 10% to 25% of the peripheral lateral meniscus [110]. The medial meniscus is crescent-shaped and attaches more anterior and posterior [110]. The lateral meniscus is circular in shape and covers a larger proportion of the tibial plateau [110]. The popliteus tendon originates on the posterocentral tibia and inserts anterior and distal to the lateral collateral ligament on the lateral femoral epicondyle [110]. The popliteus tendon has an intra-articular course through the popliteal hiatus [110]. Lateral meniscus mobility is 10 mm, while medial meniscus mobility is 5 mm [110]. A single meniscofemoral ligament is present in 93% of the population, and both ligaments are present in 70% [110]. The ligament of Humphrey is the anterior meniscofemoral ligament, and the ligament of Wrisberg is the posterior meniscofemoral ligament [110]. Meniscofemoral ligaments insert into the substance of the PCL and the medial femoral condyle [110]. Meniscofemoral ligaments originate from the posterior horn of the lateral meniscus [110].

The posterior slope of the tibia is a mean of 10.7° in the medial plateau and 7.2° in the lateral plateau [110]. The medial compartment has a large surface area and contains the convex femoral condyle and concave tibial plateau [110]. The lateral compartment has a smaller surface area than the medial compartment and contains the convex femoral condyle and convex lateral plateau in the sagittal plane [110]. The tibial tuberosity is located slightly lateral to the midline of the knee and is the site of attachment of the patellar tendon [110]. The Gerdy tubercle is located 2 to 3 cm lateral to the tibial tuberosity and is the site of insertion of the iliotibial band [110]. The fibular head is located a mean of 1.5 cm distal to the joint line, with a range of 6 to 32 mm below the joint line [110].

The medial femoral condyle has a large, convex articular surface [110]. The medial epicondyle is the site where the MCL originates on the femoral sulcus approximately 3.2 cm proximal and 4.8 cm posterior to the articular surface of the femur at the knee [110]. The adductor tubercle is a prominence on the medial condyle proximal to the MCL origin and is the site of insertion of the adductor magnus muscle [110]. The lateral femoral condyle has a convex articular surface and a broader mean anterior-posterior dimension compared with the medial femoral condyle [110]. The lateral femoral condyle has a broader mean medial-lateral dimension than the medial condyle [110]. The lateral trochlear facet resists lateral subluxation of the patella [110]. The sulcus terminalis is a transverse ridge extending from the oblique facets of the femoral trochlea that is deeper on the lateral condyle than on the medial condyle [110]. The intercondylar notch varies in width, with the PCL inserting on the anteromedial wall and the ACL inserting on the posterolateral wall [110].

The patella is a large sesamoid bone with a mean thickness of 2.5 cm [110]. The patella has three facets: lateral, medial, and odd [110]. The odd facet is a small facet on the distal medial patella that articulates in deep flexion of the knee [110]. In Wiberg classification Type I patellar morphology, medial and lateral facets are equal in size [110]. In Wiberg classification Type II patellar morphology, which is the most common, the medial facet is smaller and one half the size of the lateral facet [110]. In Wiberg classification Type III patellar morphology, the medial facet is so far medial that the central ridge is barely noticeable [110].

The ACL consists of 90% type I collagen and 10% type III collagen [110]. The mean length of the ACL is 33 mm and mean width is 11 mm [110]. The ACL has a semicircular femoral attachment on the posteromedial aspect of the lateral femoral condyle with a mean length of 20 mm and mean width of 10 mm [110]. The ACL has a broad, irregular, oval-shaped insertion between tibial eminences from anterior to midline [110]. The middle geniculate artery is the primary blood supply to the ACL [110]. The posterior articular branch of the posterior tibial nerve provides innervation to the ACL [110]. The anteromedial bundle of the ACL is tight in knee flexion and the posterolateral bundle is tight in knee extension [110]. The posterolateral bundle of the ACL is responsible for preventing the pivot-shift phenomenon and stabilizes against anterior translation with 30° of knee flexion [110]. The anteromedial bundle of the ACL increases anterior tibial translation at 60° and 90° of knee flexion [110].

The PCL has a mean length of 38 mm and mean width of 13 mm [110]. The middle geniculate artery is the primary blood supply to the PCL [110]. The popliteal artery is near the PCL, and the distance increases with knee flexion [110]. The posterior articular branch of the posterior tibial nerve provides innervation to the PCL [110]. The anterolateral bundle of the PCL is stronger and stiffer than the posteromedial bundle [110]. The anterolateral bundle of the PCL is tight in knee flexion, while the posteromedial bundle is tight in knee extension [110]. Menisci are attached to collateral ligaments via coronary ligaments [110]. The anterior attachment of the lateral meniscus is adjacent to the tibial insertion of the ACL [110]. The popliteus tendon originates on the posterocentral tibia [110]. The popliteus tendon inserts anterior and distal to the lateral collateral ligament on the lateral femoral epicondyle [110]. Lateral meniscus mobility is 10 mm [110]. Medial meniscus mobility is 5 mm [110]. A single meniscofemoral ligament is present in 93% of the population [110]. Both meniscofemoral ligaments are present in 70% of the population [110]. The ligament of Humphrey is the anterior meniscofemoral ligament [110]. The ligament of Wrisberg is the posterior meniscofemoral ligament [110].

Classification

Etiology: Articular cartilage injuries within the knee result from age-related degenerative changes, previous trauma or injury, congenital osteochondral defects, inflammatory conditions, infection, and other causes [2]. The predominant reason for localised articular cartilage damage is earlier trauma, such as a direct impact or distortion [28]. The aetiology of other localised cartilage defects, such as osteochondritis dissecans (OD), remains unknown, though posttraumatic changes and subchondral circulatory disorders are currently discussed as potential causes [28].

Diagnostic Approach: Physical examination must be used concomitantly with radiographic or advanced imaging findings to determine the source of each patient’s symptoms [2]. These combined assessments are also required to determine appropriate surgical intervention when nonsurgical measures have failed [2]. Nonsurgical measures include activity modification, weight loss, nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroid injections, and physical therapy [2].

Biological Response: Spontaneous healing or regeneration in adults is rare, mainly due to insufficient proliferation and migration of chondrocytes into the defect [28]. An injury of cartilage together with the adjacent subchondral plate induces a wound clot that may generate fibrous repair tissue [28]. Such scar tissue lacks the biomechanical properties of hyaline cartilage due to a different molecular and textural configuration [28]. Consequently, this scar tissue predominantly shows early deterioration and failure, at least in larger defects [28].

Other Considerations: The vast majority of cartilage repair procedures were applied in degenerative, non-traumatic cartilage defects [90]. Most patients treated for cartilage defects of the knee were treated for degenerative lesions and lesions with early osteoarthritis [150]. In a recent published multi-centre trial of matrix-induced chondrocyte transplantation, almost 40% of the chondral defects were described as degenerative or chronic [150]. Women have a different knee chondral lesion pattern than men, more often presenting with unfavorable conditions related to the cause of injury, site, and activity level [27]. Women also have lower raw, not standardized, scores for cartilage surgery outcomes [27]. The presence of high-grade cartilage lesions is significantly increased in an ACL-deficient knee when reconstruction is performed more than 12 months after injury [67].

Clinical Presentation

Etiology and Prevalence

Cartilage defects arise from idiopathic causes, trauma, repetitive microtrauma, or a combination of these factors [79]. Approximately 11% of all knee arthroscopies reveal cartilage defects suitable for repair procedures [5]. In adults, osteochondritis dissecans (OCD) is typically symptomatic and progresses to arthritis if left untreated [15]. In a military population undergoing cartilage biopsy, multifocal chondral defects were present in 59% of knees, with the patella being the most common location at 64% [131].

History and Symptoms

A detailed history must capture the onset, quality, duration, tempo, and location of symptoms, along with modifying factors, weight-bearing ability, and trauma history [188]. Patients with nonfocal cartilage loss typically present with knee swelling, locking, catching, or sudden giving way [83]. Isolated cartilage defects are associated with significant deficits in quadriceps muscle strength in the injured leg compared to the uninjured leg [109]. Treatment should prioritize knee function over the cartilage defect itself, as the relationship between the two remains unclear [63].

Physical Examination

Inspection identifies skin abnormalities, evidence of trauma, malalignment, and swelling [188]. Palpation focuses on points of tenderness to detect focal pathologies, such as joint line tenderness, patellar tendon tenderness, or pes anserine bursitis [188]. Peripatellar palpation reveals effusion and/or synovitis [188]. Knee alignment is assessed in both supine and standing positions, as weight-bearing may dynamically alter alignment [188]. When active and passive ranges of motion differ, the clinician must differentiate between pain-related, mechanical, or neuromuscular causes [188]. Hip range of motion is examined to identify referred pain from intra-articular hip pathology [188].

Physical examination for nonfocal cartilage loss often reveals an effusion, joint line tenderness, and positive meniscal signs [83]. These signs include pain or a palpable click with McMurray’s test, pain with Thessaly’s test or Apley’s test, or pain during a deep squat [83].

Imaging

Plain radiographs are the appropriate initial imaging study for most knee conditions, assessing traumatic injury, arthritis, patellofemoral alignment, osteochondral injury, bone neoplasm, and surgical implants [39]. Specific views include: * Weight-bearing AP (extension): Assesses cartilage loss from the distal femur and tibial plateau [39]. * Weight-bearing PA (Rosenberg; flexion): Assesses cartilage loss from the posterior femur and tibial plateau [39]. * Patellofemoral views: Assess patellofemoral alignment (tilt/subluxation), patellar and trochlear morphology, osteochondral injury, and patellofemoral arthritis [39]. * Notch view: Assesses posterior femoral cartilage, notch width, and osteophytes [39].

Radiography may identify subchondral radiolucency for osteochondral defects, most commonly in the medial femoral condyle [39]. MRI identifies the degree of articular cartilage injury (chondrosis, full-thickness loss), associated bone marrow edema, and specific location (medial condyle, lateral condyle, trochlea, patella; anterior, posterior) [39]. No current MRI classification system has been shown to correlate with clinical outcomes after all types of cartilage repair surgery [33], and strong evidence for the reliability of morphological MRI in predicting clinical outcome is lacking [59]. However, increasing preoperative degenerative change, evidenced by a higher WORMS score on preoperative MRI, is associated with inferior patient-reported outcomes at a minimum of 2 years after cartilage restoration surgery [72].

Natural History and Prognosis

Surgical intervention may delay or prevent the progression of degenerative changes in select symptomatic patients at risk for developing osteoarthritis [79]. Cartilage repair surgery prevents the progression of knee degeneration over 6 years compared to non-operated control subjects with initially identical defects [9]. Conversely, nonsurgical treatment of arthroscopically verified focal cartilage lesions yields results equal to most surgical treatments, with a mean KOOS QoL subscore of 58.1 at 19.1 years follow-up [11].

Investigations

Clinical Assessment: Assessment of the knee joint must combine physical examination with radiographic findings, including full-length alignment views, and MRI [16]. The selection of a cartilage repair technique generally accounts for lesion size, activity level, and patient age [26]. Additional factors influencing technique selection include the duration of the condition, as well as the site and depth of the injury [26]. Treatment for focal cartilage lesions depends upon the lesion size, lesion location, and the status of the underlying subchondral bone [16]. Correction of ligamentous instability and limb malalignment is paramount to the success of cartilage restoration procedures and meniscal transplantation [16].

Plain radiography: Radiographic evaluations are essential when diagnosing an osteochondritis dissecans (OCD) lesion of the knee [74]. The notch view is used to assess posterior femoral cartilage, notch width, and osteophytes [39]. Radiography may identify subchondral radiolucency in osteochondral defects, a finding most common in the medial femoral condyle [39]. Supine AP knee radiographs do not adequately estimate the joint space width needed to estimate the degree of osteoarthritis progression [130]. Plain frontal radiographs of the knee may not accurately display the actual joint space due to different cartilage wear patterns, meniscal integrity, or variances in tibial slopes [130]. A 45° standing flexion view was introduced to better evaluate joint space width [130]. The fixed flexion view (FFV) technique uses a fixed X-ray irradiation angle of 10° caudal direction with the limb position fixed relative to the cassette [130]. The Lyon Schuss view (LSV) requires fluoroscopic adjustment of the irradiation angle relative to the medial tibial plateau and is more accurate for measuring actual joint space width than FFV [130]. Goniometer readings of long limb alignment or measured on an FFV correlated well with the angle measured on long limb radiographs, providing an alternative if long limb radiographs are not available [130].

MRI: MRI is the method of choice for the non-invasive evaluation of articular cartilage defects and the follow-up of cartilage repair procedures [88]. It is the most useful study for differentiating osteonecrosis from other conditions such as osteochondritis dissecans, transient osteoporosis, bone bruises, or occult fractures [133]. A serpentine lesion within a well-demarcated border is a specific finding on MRI for osteonecrosis [133]. Bone edema on MRI is a common feature of osteoarthritis, osteonecrosis, cartilage injury, and transient regional osteoporosis [133]. Important aspects of OCD lesions may be better seen with MRI than with radiographic evaluations alone [74]. Compared with arthroscopy, MRI displays moderate sensitivity for detecting and classifying chondral knee injuries [211]. High resolution MRI and well-defined MRI variables are a reliable, reproducible, and accurate tool for assessing cartilage repair tissue [159]. Quantitative MRI had greater sensitivity in diagnosing chondral lesions of the knee compared to other methods, as evaluated in a systematic review and meta-analysis [71]. Subclinical cartilage degeneration can be detected with T1ρ magnetic resonance imaging mapping in young athletes with posterior cruciate ligament injuries who show no degenerative changes on plain radiographs or conventional MRI [223].

CT: Three-dimensional CT with remodeling is used for preoperative planning for reconstruction associated with dysplasia, post-trauma planning, and complex total knee arthroplasty planning [127]. Three-dimensional CT reconstructions may help with preoperative planning for complex intra-articular fractures, multiplanar osteotomy for limb malalignment, and reconstitution of bone loss in joint arthroplasty [39].

Arthroscopy: Arthroscopy can be beneficial for patients with osteoarthritis and mechanical symptoms recalcitrant to conservative care, but this should not be the first-line intervention [16]. Arthroscopic treatment is indicated for débridement, chondroplasty, loose body removal, microfracture, and partial meniscectomy [16].

Other Considerations: Increasing preoperative degenerative change in the knee, as evidenced by a higher WORMS score on preoperative MRI, was associated with inferior patient-reported outcomes at a minimum of 2 years after cartilage restoration surgery [72]. Clinically significant improvements in IKDC scores are associated with a more mature MRI appearance of the autologous chondrocyte implantation graft on postoperative MRI, as indicated by higher MOCART scores [226]. Persistent subchondral alterations were documented at long-term MRI evaluation in patients treated with matrix-assisted chondrocyte transplantation for knee osteochondritis dissecans [196].

Treatment

Non-Operative Management

An initial trial of nonsurgical management is usually warranted for knee cartilage defects, consisting of rest, activity modification, anti-inflammatory medications, physical therapy, bracing treatment, or injections [45]. Surgical intervention is indicated for patients who do not respond to these conservative measures [45]. Weight loss is effective in decreasing pain and minimizing the progression of symptomatic osteoarthritis in patients with a body mass index above 25 kg/m2 [154]. Intra-articular corticosteroid injections are effective for symptomatic management of osteoarthritis of the knee [154]. Oral supplementation with glucosamine and/or chondroitin sulfate has no benefit for managing symptomatic osteoarthritis of the knee [154]. In the absence of mechanical symptoms, knee arthroscopy with débridement is not effective in managing osteoarthritis of the knee [154].

Operative

Indications: Surgical intervention is appropriate for patients who fail nonsurgical care [45]. Arthroscopic procedures, including débridement, chondroplasty, loose body removal, microfracture, and partial meniscectomy, are acceptable treatments for appropriately indicated patients after the failure of nonsurgical care [83]. Patients with mechanical symptoms may specifically benefit from arthroscopic débridement, including partial meniscectomy and chondroplasty [83]. Débridement and chondroplasty are currently recommended for symptomatic lesions [15]. Based on current evidence, an indication for autologous chondrocyte implantation (ACI) is given for symptomatic cartilage defects starting from defect sizes of more than 3-4 cm², or 2.5 cm² in young and active sports patients, while advanced degenerative joint disease is the single most important contraindication [46]. When selecting a procedure, patient and cartilage defect characteristics should be assessed to determine the best technique [158].

Surgical Approach / Technique: Arthroscopic débridement may provide relief from mechanical symptoms in carefully selected osteoarthritis patients but should not be offered as a first-line treatment in lieu of nonsurgical measures [16]. A landmark study by Moseley et al comparing arthroscopic débridement with sham surgery in patients with knee arthritis found no difference in postoperative pain or functional outcomes between groups [83]. Several subsequent studies assessing outcomes after partial meniscectomy versus physical therapy for patients with knee osteoarthritis and a meniscal tear similarly demonstrated no significant difference in outcomes, although about 30% of patients randomized to the physical therapy group crossed over to surgery due to continued pain and achieved good outcomes [83]. Displaced osteochondral fragments can sometimes be replaced and secured with small recessed screws or absorbable pins [15]. Autologous osteochondral grafting involves obtaining small-sized cylindrical osteochondral grafts from a non-weight-bearing area of the knee [22]. ACI is a two-stage process involving biopsy of the patient’s articular cartilage, ex vivo expansion, and subsequent implantation into the defect [15]. Allograft cell-based therapies such as particulated juvenile cartilage or acellular extracellular matrix allow for single-stage surgery and are technically easy [24]. Arthroscopic gel-type autologous chondrocyte implantation is an acceptable, minimally invasive, and technically simple option for the restoration of cartilage defects of the knee [29].

Implant Selection: Osteochondral autograft transfer (OAT) can be used to address medium-sized lesions (2–3 cm²) that include subchondral bone loss, with the lateral trochlea and medial trochlea serving as acceptable harvest locations [15]. The primary indication for mosaic osteochondral transplantation is deep, small defects on the medial femoral condyle [156]. Osteochondral allograft transplant utilizes cadaveric donor plugs and can be used for larger lesions (≥4cm²), especially with bone loss [15]. Osteochondral allografts are still ideally used within 14 to 28 days of donor death [15]. The procedure of combining microfracture and a cell-free polymer-based implant immersed with autologous serum is safe for the treatment of cartilage defects in the knee, with patients showing gradual clinical improvement postoperatively [4]. A cell-free biomimetic scaffold is a safe and effective treatment for cartilage knee lesions, offering positive clinical results at 2 years with a low failure rate [141].

Adjuncts: Concurrent osteotomy significantly increased graft survivorship in ACI patients, with 88% survivorship with osteotomy versus 66% without [53]. Clinical outcomes after combined MAT and cartilage repair/restoration are similar to those after either procedure in isolation [48]. Patellar dysplasia should not be seen as a contraindication for cell-based cartilage repair procedures [157].

Other Considerations: Bone marrow stimulation techniques present the risk of osseous overgrowth that can result in increased joint contact pressures [24]. There are worse outcomes with larger cartilage defects or in patients with high body mass indexes for bone marrow stimulation techniques [24]. Mesenchymal stem cell (MSC) concentration decreases with age, which may render bone marrow stimulation procedures less efficacious in older patients [24]. Good clinical results in small defects (<2 to 3 cm²) are obtained in 60% to 80% of patients undergoing marrow-stimulating techniques [15]. The repair tissue from marrow-stimulating techniques is Type I collagen with inferior wear characteristics [15]. Current clinical evidence does not allow for unequivocal recommendation of enhanced microfracture to treat symptomatic focal grade III/IV knee cartilage lesions [19]. Both BiCRI and microfracture treatments showed significant effectiveness in improving clinical outcomes in patients with small symptomatic articular cartilage defects of the knee, with the BiCRI group demonstrating a superior radiological outcome than microfracture over a five-year period [44]. The treatment of symptomatic cartilage knee defects ≥3 cm2 in size using MACI was clinically and statistically significantly better than with MFX, with similar structural repair tissue and safety [136].

OAT is an effective and durable cartilage restoration procedure for some patients with symptomatic knee cartilage lesions at mid- to long-term follow-up, with a majority of patients demonstrating sustained improvements in clinical outcomes and achieving the MCID [8]. Middle-aged patients with focal, chronic non-traumatic osteochondral lesions of the knee also profit from OAT at a short follow-up [215]. Complications of OAT include donor site morbidity [15].

Osteochondral allograft transplantation allows for precise surface contour matching [24]. Main concerns with osteochondral allografts include the small risk of disease transmission and chondrocyte viability, which has improved with graft preservation techniques [15]. Risks of osteochondral allograft transplantation include immunological rejection or disease transmission [24].

ACI is an effective treatment for full thickness chondral defects of the knee, providing an improvement of clinical outcomes [134]. Treatment of articular cartilage defects of the knee joint leads to satisfactory results concerning everyday activities [14]. Treatment of articular cartilage defects of the knee with ACI in physically active young individuals can return nearly two-thirds of individuals to daily activity with decreased pain and improved function [17]. ACI allows for creation of type II collagen–rich hyaline-like cartilage, with minimal type I collagen, fibrocartilage, present [15]. Improved clinical outcomes following microfracture, OAT, or ACI are seen in well-selected patients, with variable long-term results following microfracture in high-demand patients [15]. Current best available research suggests that for smaller lesions, microfracture, OAT, and ACI have similar recovery periods and functional results [15]. The significantly improved results on 3 outcome measures after 10 years suggest that MACT represents a suitable option in the treatment of local cartilage defects in the knee [41]. MACT is an excellent surgical therapy for full-thickness cartilage defects of the knee, with good long-term results for simple defects [228]. Long-term results suggest that first- and third-generation ACI methods are equally effective treatments for isolated full-thickness cartilage defects of the knee [220]. cMACI showed superior safety compared with pMACI for large cartilage defects, with similarly improved outcomes in approximately 75% of patients [75]. Arthroscopic gel-type autologous chondrocyte implantation presents histologic evidence of regenerating hyaline-like cartilage in the knee with articular cartilage defect [29].

Some studies suggest that prior marrow stimulation procedures such as microfracture may have a detrimental effect on outcomes following ACI [53]. Results demonstrated that 26% of grafts in the prior marrow stimulation group failed compared with 8% in the patients who did not have a prior marrow stimulation procedure [53]. There were significantly more failures associated with ACI after microfracture (7 of 28) than with ACI as a first-line treatment (1 of 28) [53]. Inferior clinical outcome was also associated with ACI after microfracture [53]. In a 2014 study following 210 patients for a mean of 12 years, at least one graft failed in 53 of 210 patients (25%) [53]. In a 20-year follow-up study of 23 patients who underwent first-generation ACI, the 20-year survival rate was 63%, and 79% of patients maintained their native knee and were satisfied at final evaluation [53]. In a study of 104 patients with chronic chondral and osteochondral defects followed for an average of 10.4 years, 27 patients (26%) experienced graft failure at a mean of 5.7 years [53]. Of the 73 patients with surviving grafts in the chronic defect study, 88% reported good to excellent results [53]. In a systematic review of 771 patients treated with ACI followed for an average of 11.4 years, successful outcomes were reached in 82% of patients with a revision surgery rate of 37% [53]. Increased patient age and lesion size greater than 4.5 cm2 were determined to be risk factors for revision surgery and failure in ACI [53]. In a large multicenter study of 110 patients treated with ACI for cartilage defects of the patella followed for at least 4 years, 92% of patients stated they would undergo the procedure again and 86% rated their knees as good or excellent at final follow-up [53]. In a study of 30 patients with isolated chondral lesions of the patella treated with ACI followed for a mean of 7.3 years, knee function was rated as good to excellent in 25 (83%), fair in 4 (13%), and poor in 1 (3%) [53]. There were three failures that occurred at 6.25 years postoperatively in the patellar ACI study, and all of them were in workers compensation patients who were older (average age 42 years) at the time of surgery [53]. Tissue-engineered cartilage implantation is questionable for this indication as a salvage procedure for young patients affected by knee osteoarthritis [34].

Allograft cell-based therapies lack long-term outcome data [24]. Donor-site problems and creation of true articular cartilage at the recipient site are still challenges for cartilage repair procedures [15].

Repair of full-thickness cartilage injury in the knee with a HA-BMAC provides good to excellent clinical outcomes at long-term follow-up in the treatment of small to large lesions [13]. Cartilage repair using HA-BMAC leads to successful medium-term outcomes independent of age or lesion size [140]. This procedure can be proposed as one option for repairing full-thickness cartilage defect of the knee [10]. While approaches using stem cells for cartilage defects are highly promising, there is currently limited evidence of a direct clinical benefit, and further research is required to assess the overall outcome of stem cell therapies for knee cartilage repair [137]. Current treatment modalities vary from conservative to surgical options, but available cartilage regeneration techniques only produce fibrocartilage or fibrohyaline cartilage with poor integrative capacities and higher friability [221]. The near future of cartilage repair will likely involve refinement of current techniques along with incorporation of scientific advances in cartilage biology, potentially leading to a single-stage surgical technique that replicates normal articular cartilage [89]. Existing articular cartilage repair techniques can return the athlete with articular cartilage injury to high-impact sports, but treatment does not produce normal articular cartilage, and this limits the success rate and durability of current cartilage repair in athletes [139]. No definitive conclusion could be made in respect to the best current surgical technique for articular cartilage and osteochondral lesions [158]. The methodologic quality of knee articular cartilage surgery studies was poor overall and also for individual techniques [97]. Scientific analysis of articular cartilage repair methods is difficult due to the lack of controlled, randomized studies and the absence of data on long-term durability [54]. The management of articular cartilage defects continues to be one of the most challenging clinical problems for orthopaedic surgeons [37]. Treatment of knee cartilage defects is a challenge requiring reconstruction of hyaline cartilage to prevent osteoarthritis [91]. Cartilage repair has become a focus of increased interest due to its potential to provide pain relief and alter the progression of degenerative disease, with the hope of delaying or obviating the need for joint replacement in young patients with early osteoarthritis [70]. Existing cartilage treatment options include marrow stimulation, osteochondral tissue transfer or transplantation, cell-free synthetic scaffolds and cell-based repair strategies, but the literature is limited by heterogeneity in surgical procedures and reporting of non-standardised outcome measures [95]. Clinical magnetic resonance imaging (MRI) is the method of choice for the non-invasive evaluation of articular cartilage defects and the follow-up of cartilage repair procedures [88]. Treatment of osteochondral defects at any time had a positive effect on healing compared to no treatment [135].

Complications

General and Arthroscopic

Infection: Infection is the most common complication overall in American Board of Orthopaedic Surgery data from 2003 to 2009 [98]. In a series of 191,584 arthroscopic knee procedures, infection and deep vein thrombosis or pulmonary embolism were the most common complications [98]. The incidence of infection associated with anterior cruciate ligament reconstructions is slightly increased when the reconstruction is performed in conjunction with meniscal repair [98].

Thromboembolism: Deep vein thrombosis is a concern with long, complicated procedures, particularly in patients who are overweight, have a history of DVT, are taking birth control pills, or have been inactive as a result of injury [98].

Stiffness / Arthrofibrosis: The incidence of arthrofibrosis associated with anterior cruciate ligament reconstruction is increased when meniscal repair is performed [98]. Early surgical intervention for ligamentous injuries before regaining muscular tone and motion is associated with arthrofibrosis [98]. Surgical procedures such as medial collateral ligament repair on the femoral side and meniscal repair are associated with arthrofibrosis [98].

Nerve palsy: Saphenous and peroneal nerve injuries are reported with arthroscopic repairs, though the frequency has decreased dramatically with all-inside techniques [98].

Other Considerations: Overall complication rates for knee arthroscopy are generally cited as less than 1% in recent reports [98]. Four large series with a combined total of 191,584 arthroscopic knee procedures reported complications in 1,175 patients (0.6%) [98]. Data from the American Board of Orthopaedic Surgery from 2003 to 2009 showed an overall complication rate of almost 5% for knee arthroscopy [98]. The complication rate for meniscectomy was 2.5% and for PCL reconstruction was 20% in American Board of Orthopaedic Surgery data from 2003 to 2009 [98]. Compensation claims after knee cartilage surgery are rare according to a registry-based study from Scandinavia from 2010 to 2015 [186].

Bone Marrow Stimulation (Microfracture/Abrasion)

Other Considerations: Mesenchymal stem cell concentration decreases with age, which may render bone marrow stimulation procedures less efficacious in older patients [24]. MRI assessment showed that the repair cartilage over microfracture generally was depressed with respect to native cartilage [174]. Propensity for bony overgrowth was most marked in the microfracture group, with loss of adjacent cartilage evident with progressive follow-up [174].

Osteochondral Autograft Transfer (OAT/Mosaicplasty)

Donor Site Morbidity: Complications of osteochondral autograft transfer include donor site morbidity [15]. Donor-site problems and creation of true articular cartilage at the recipient site are still challenges for osteochondral autograft transfer [15].

Osteochondral Allograft

Disease Transmission and Viability: Main concerns for osteochondral allograft transplantation include the small risk of disease transmission and chondrocyte viability [15]. A high short-term failure rate was observed with decellularized osteochondral allograft plugs for treatment of knee cartilage lesions [82]. Decellularized osteochondral allograft plugs should be used with caution in the treatment of osteochondral lesions of the knee due to high short-term failure rates [82].

Autologous Chondrocyte Implantation (ACI/MACI)

Graft Hypertrophy and Overgrowth: Complications related to ACI include chondrocyte overgrowth and periosteal flap hypertrophy [15]. Graft hypertrophy occurred in 63% of autologous chondrocyte implantation surgeries in an MRI assessment study [174].

Graft Failure and Revision: At least one graft failed in 53 of 210 patients (25%) undergoing ACI at a mean of 12 years follow-up [53]. Twenty-seven patients (26%) experienced graft failure at a mean of 5.7 years in a cohort of 104 patients treated with ACI for chronic chondral and osteochondral defects [53]. A revision surgery rate of 37% was reported in a systematic review of 771 patients treated with ACI followed for an average of 11.4 years [53]. Increased patient age and lesion size greater than 4.5 cm² were determined to be risk factors for revision surgery and failure following ACI [53]. 26% of grafts in the prior marrow stimulation group failed compared with 8% in patients who did not have a prior marrow stimulation procedure before ACI [53]. Inferior clinical outcome was associated with ACI performed after microfracture [53].

Surgical Morbidity and Applicability: The morbidity of the second surgical procedure is a complication associated with ACI [15]. ACI requires intact subchondral bone, which is a limitation rather than a direct complication but restricts applicability [24].

Patient-Specific Risk Factors: Female patients and individuals with previous surgeries have an increased risk of reoperation and failure to attain clinically relevant improvement following autologous chondrocyte implantation [194]. Women have lower raw, not standardized, scores after cartilage surgery, though case-control analysis with normalized data showed equal success possibilities as men [27, 100]. Sex does not influence the long-term outcome of matrix-assisted autologous chondrocyte transplantation [165].

Revision and Secondary Failure

Secondary Failure: One of every 4 patients may experience a secondary failure after undergoing a revision cartilage procedure [99]. The histologic appearance of the repair tissue of 3 different failed articular cartilage resurfacing procedures was similar and did not resemble normal articular cartilage [51].

Concomitant Procedures and Context

Other Considerations: Correction of ligamentous instability and limb malalignment is paramount to success of cartilage restoration procedures [16]. Most studies have failed to show improved clinical outcomes in the short term when adding cartilage restoration procedures to high tibial osteotomy [77]. Concomitant osteotomy significantly increased graft survivorship for ACI (88% with osteotomy versus 66% without) [53].

Recovery

Light activity (weeks): The provided evidence does not specify a typical week range for light activity, desk work, driving, or light activities of daily living.

Full activity (months): The provided evidence does not specify a month range for the return to manual work, sport, or full range of motion and strength.

Complete recovery / outcome plateau (months): The provided evidence does not specify a month range for the stabilization of pain, strength, or final functional outcomes.

Rehabilitation protocol: The provided evidence does not detail specific physical therapy phasing, immobilisation duration, weight-bearing or range-of-motion progression, or sling and brace removal timing.

Functional milestones: Validated patient-reported outcome measure trajectories are reported at various follow-up intervals rather than as recovery milestones. The mean KOOS QoL subscore for nonsurgical treatment of arthroscopically verified focal cartilage lesions was 58.1 at 19.1 years follow-up [11]. ACI resulted in improved function in 75% of patients with symptomatic cartilage defects of the knee at a minimum of 10 years after surgery [3]. In a 2014 study, 75% of patients reported improved function at 10 years after ACI [53]. MACT represents a suitable option in the treatment of local cartilage defects in the knee based on significantly improved results on 3 outcome measures after 10 years [41]. A majority of patients undergoing primary OAT demonstrated sustained improvements in clinical outcomes and achieved the MCID [8]. ACI is effective in filling full-thickness chondral defects of the knee, with improvements noted in 86% of patients at 6-year follow-up [86].

Other Considerations: Long-term survivorship and failure rates provide context for outcome expectations. ACI provided durable outcomes with a survivorship of 71% at 10 years [3]. In a 2014 study, survivorship was 71% at 10 years for ACI [53]. The 20-year survival rate was 63% in a study of first-generation ACI [53]. The mean surface area was 11.8 cm2 in a 20-year follow-up study of first-generation ACI [53]. In a 2010 study, 74% of patients reported their status as better or the same as the previous years at a mean follow-up of 12.8 years after ACI [53]. In a 2010 study, 92% of patients were satisfied and would have the ACI procedure again [53]. In a 2014 study, at least one graft failed in 53 of 210 patients (25%) in a study of ACI [53]. Concurrent osteotomy significantly increased graft survivorship to 88% with osteotomy versus 66% without in a 2014 study of ACI [53]. In a 20-year follow-up study of first-generation ACI, 79% of patients maintained their native knee and were satisfied at final evaluation [53]. Twenty-seven patients (26%) experienced graft failure at a mean of 5.7 years in a study of ACI for chronic chondral and osteochondral defects [53]. Of the 73 patients with surviving grafts, 88% reported good to excellent results in a study of ACI for chronic chondral and osteochondral defects [53]. Successful outcomes were reached in 82% of patients in a systematic review of ACI with a revision surgery rate of 37% [53]. Increased patient age and lesion size greater than 4.5 cm2 were determined to be risk factors for revision surgery and failure in a systematic review of ACI [53].

Failure rates vary by lesion type and concomitant procedures. The failure rate for autologous chondrocyte transplantation was 11% among patients who had isolated femoral condylar lesions [20]. The failure rate for autologous chondrocyte transplantation was 14% among patients with osteochondritis dissecans lesions [20]. The failure rate for autologous chondrocyte transplantation was 18% among patients who had the procedure combined with ACL repair [20]. The failure rate for autologous chondrocyte transplantation was 24% among patients treated for patellar lesions [20]. Treatment failure rates for matrix-assisted cartilage repair increase from short-term to midterm follow-up [23]. 11% of patients undergoing matrix-assisted cartilage repair had undergone further surgery at a minimum of 5 years' follow-up [23]. 26% of grafts in the prior marrow stimulation group failed compared with 8% in the patients who did not have a prior marrow stimulation procedure after ACI [53]. Inferior clinical outcome was associated with ACI after microfracture [53].

Clinical outcomes differ by patient demographics and lesion characteristics. Women have lower raw, not standardized, scores after knee cartilage surgery [27]. A case-control analysis with normalized data showed that on equal terms women have the same success possibilities as men after surgical treatment for knee cartilage regeneration [100]. Good-to-excellent results were seen in 85% of patients with femoral condyle defects treated with autologous chondrocyte transplantation [20]. In a large multicenter study, 92% of patients stated they would undergo ACI for patellar cartilage defects again [53]. In a large multicenter study, 86% of patients rated their knees as good or excellent at final follow-up after ACI for patellar cartilage defects [53]. Knee function was rated as good to excellent in 25 (83%) of patients with isolated chondral lesions of the patella treated with ACI at final follow-up [53]. There were three failures that occurred at 6.25 years postoperatively in a study of ACI for isolated chondral lesions of the patella [53]. The clinical outcome in patients with multiple cartilage defects is inferior to that of patients with a single defect after microfracture [62].

Histological and comparative data inform long-term tissue quality and procedure selection. All specimens taken from second-look arthroscopy procedures after autologous chondrocyte transplantation stained positive for cartilage oligomeric matrix protein and aggrecan [20]. Hyaline-like cartilage in autologous chondrocyte transplantation specimens stained positive for type II collagen in the predominant part of the tissue (50%) [20]. The fibrous area in autologous chondrocyte transplantation specimens stained positive for type I collagen [20]. In patients with discrete articular cartilage lesions of the knee and history of failed microfracture, ACI may render favorable clinical outcomes comparable to primary ACI [18]. Nonsurgical treatment of arthroscopically verified focal cartilage lesions of the knee had results equal to those of most surgical treatments [11]. The 20-year cumulative risk of knee arthroplasty after a focal cartilage lesion in the knee was 19% [78]. Mosaicplasty results in a better, clinically relevant outcome than microfracture in articular cartilage defects (2-5 cm2) of the distal femur of the knee in patients aged 18 to 50 years at short, medium, and long term (minimum 15 years) [92]. A 6-mm osteochondral plug placed in a 10-mm defect better preserved the articular surface and contour of the condyle compared to untreated or bone-grafted defects at 6 months and 1 year [85].

Emerging therapies and specific clinical scenarios show variable results. The combination of microfracture and a cell-free polymer-based implant immersed with autologous serum is safe for the treatment of cartilage defects in the knee [4]. Patients treated with microfracture and a cell-free polymer-based implant immersed with autologous serum showed gradual clinical improvement postoperatively [4]. Cell-based regenerative cartilage therapy of the knee has become the standard of care for large and isolated chondral defects [42]. ACI and MACI procedures for the treatment of knee cartilage lesions associated to OA showed long-term success and allowed delaying arthroplasty [102]. Injury origin, sex, symptom duration, lesion size, lesion site, age, and previous surgery might determine the final outcome and can be used as a sort of clinical profiling to guide the surgeon in the choice of this procedure and in giving realistic expectations to patients requiring cartilage treatment [103]. Treatment of osteochondral defects in the ankle and knee joint with a biomimetic scaffold resulted in incomplete cartilage repair and poor subchondral bone repair at 1- and 2.5-year follow-up [173]. Although clinical success in short-term and midterm applications has been suggested for the application of BMAC for the restoration of cartilage defects in lesions of the knee, current study designs are generally of low scientific rigor [181]. The value of AMIC relative to other cartilage repair procedures and to the natural course remains undefined [235].

Key Evidence

• [L4] ACI provided durable outcomes with a survivorship of 71% at 10 years and improved function in 75% of patients with symptomatic cartilage defects of the knee at a minimum of 10 years after surgery. [3] (10.1007/s11999-013-3146-9)
• [L4] The procedure is safe for the treatment of cartilage defects in the knee, with patients showing gradual clinical improvement postoperatively. [4] (10.1007/s00167-011-1763-y)
• [L4] Eleven percent of all knee arthroscopies show cartilage defects that may be suitable for cartilage repair procedures. [5] (10.1177/0363546503259345)
• [L2] Patients who have moderate to large symptomatic chondral knee lesions, significant functional impairment and pain, and failed prior cartilage repair procedures can expect durable and significant functional improvement and symptom reductions following ACI. [6] (10.1016/j.arthro.2008.04.021)
• [L5] Articular cartilage repair techniques appear to be safe in children and adolescents, with no differences in complication rates reported when compared with adult patients. [7] (10.1177/2325967118760190)
• [L4] Primary OAT is an effective and durable cartilage restoration procedure for some patients with symptomatic knee cartilage lesions at mid- to long-term follow-up, with a majority of patients demonstrating sustained improvements in clinical outcomes and achieving the MCID. [8] (10.1177/23259671251399796)
• [L3] Cartilage repair surgery prevents progression of knee degeneration over 6 years compared to non-operated control subjects with initially identical defects. [9] (10.1007/s00167-018-5321-8)
• [L4] This procedure can be proposed as one option for repairing full-thickness cartilage defect of the knee. [10] (10.1007/s00167-013-2521-0)
• [L4] Nonsurgical treatment of arthroscopically verified focal cartilage lesions of the knee had results equal to those of most surgical treatments, with a mean KOOS QoL subscore of 58.1 at 19.1 years follow-up. [11] (10.2106/jbjs.24.00777)
• [L1] Cartilage repair in adolescent knees using ACI provides success across different clinical outcomes measures. [12] (10.1016/j.arthro.2016.03.007)
• [L4] Repair of full-thickness cartilage injury in the knee with a HA-BMAC provides good to excellent clinical outcomes at long-term follow-up in the treatment of small to large lesions. [13] (10.1177/0363546519845362)
• [L4] Treatment of articular cartilage defects of the knee joint leads to satisfactory results concerning everyday activities. [14] (10.1177/0363546515614578)
• [L4] Treatment of articular cartilage defects of the knee with ACI in physically active young individuals can return nearly two-thirds of individuals to daily activity with decreased pain and improved function. [17] (10.1177/2325967117706057)
• [L3] In patients with discrete articular cartilage lesions of the knee and history of failed microfracture, ACI may render favorable clinical outcomes comparable to primary ACI. [18] (10.1177/2325967116s00125)
• [L1] Current clinical evidence does not allow for unequivocal recommendation of enhanced microfracture to treat symptomatic focal grade III/IV knee cartilage lesions. [19] (10.1007/s00167-019-05832-5)
• [L4] [20] (10.1177/03635465020300011601)
• [L4] Current clinical treatments for articular cartilage defects have limited ability to repair tissue and often result in mechanically inferior cartilage; emerging regenerative approaches and strategies informing future treatment options are discussed to address these limitations. [21] (10.3389/fbioe.2021.770655)
• [L4] [22] (10.1007/s00402-013-1680-2)
• [L4] Treatment failure rates for matrix-assisted cartilage repair increase from short-term to midterm follow-up, with 11% of patients having undergone further surgery at a minimum of 5 years' follow-up. [23] (10.1016/j.arthro.2015.07.025)
• [L4] [26] (10.1016/j.injury.2011.06.033)
• [L3] Women have a different knee chondral lesion pattern and more often have unfavorable conditions related to the cause of injury, site, and activity level, and they also have lower raw, not standardized, scores. [27] (10.1177/0363546513480780)
• [Paper] [28] (10.1016/j.injury.2008.01.039)
• [L4] Therefore, it is an acceptable, minimally invasive, and technically simple option for the restoration of cartilage defects of the knee. [29] (10.1007/s00167-019-05572-6)
• [L1] No current MRI classification system has been shown to correlate with clinical outcomes after all types of cartilage repair surgery. [33] (10.1177/0363546513485931)
• [L4] Tissue-engineered cartilage implantation is questionable for this indication as a salvage procedure for young patients affected by knee osteoarthritis. [34] (10.1177/0363546512463675)
• [L1] When selecting a procedure, patient and cartilage defect characteristics should be assessed to determine the best technique for each individual patient. [36] (10.1002/ksa.12525)
• [L5] The management of articular cartilage defects continues to be one of the most challenging clinical problems for orthopaedic surgeons. [37] (10.2106/jbjs.i.00895)
• [L4] The significantly improved results on 3 outcome measures after 10 years suggest that MACT represents a suitable option in the treatment of local cartilage defects in the knee. [41] (10.1177/0363546514548160)
• [L4] Overall, cell-based regenerative cartilage therapy of the knee has shown tremendous development over the last years and has become the standard of care for large and isolated chondral defects. [42] (10.1007/s00167-021-06497-9)
• [L3] Patients in whom treatment is only partially successful can go on to obtain clinical benefit from other cartilage repair options. [43] (10.1007/s00167-014-3295-8)
• [L1] Both BiCRI and microfracture treatments showed significant effectiveness in improving clinical outcomes in patients with small symptomatic articular cartilage defects of the knee, with the BiCRI group demonstrating a superior radiological outcome than microfracture, over a five-year period. [44] (10.1186/s13018-024-05392-6)
• [Paper] Based on current evidence, an indication for ACI is given for symptomatic cartilage defects starting from defect sizes of more than 3-4 cm², or 2.5 cm² in young and active sports patients, while advanced degenerative joint disease is the single most important contraindication. [46] (10.1055/s-0032-1328207)
• [L4] Clinical outcomes after combined MAT and cartilage repair/restoration are similar to those after either procedure in isolation. [48] (10.1016/j.arthro.2010.08.007)
• [L3] OATS remains a durable knee preserving cartilage repair operation with low incidence of reoperation 10 years following index procedure. [49] (10.1177/2325967124s00003)
• [L4] The histologic appearance of the repair tissue of 3 different failed articular cartilage resurfacing procedures was similar and did not resemble normal articular cartilage. [51] (10.1177/0363546507308359)
• [L5] Scientific analysis of articular cartilage repair methods is difficult due to the lack of controlled, randomized studies and the absence of data on long-term durability; future research requires careful basic science investigations and controlled, prospective, randomized clinical trials. [54] (10.1177/03635465980260022701)
• [L1] Strong evidence to determine whether morphological MRI is reliable in predicting clinical outcome after cartilage repair is lacking. [59] (10.1177/0363546512473258)
• [L3] The clinical outcome in patients with multiple cartilage defects is inferior to that of patients with a single defect. [62] (10.1007/s00167-009-0974-y)
• [L3] The prime focus in treatment should be on knee function rather than the cartilage defect as the relationship between the two is unclear. [63] (10.1007/s00167-014-3472-9)
• [L2] The presence of high-grade cartilage lesions is significantly increased in an ACL-deficient knee when reconstruction is performed more than 12 months after injury. [67] (10.1007/s00167-013-2497-9)
• [L4] Cartilage repair has become a focus of increased interest due to its potential to provide pain relief and alter the progression of degenerative disease, with the hope of delaying or obviating the need for joint replacement in young patients with early osteoarthritis. [70] (10.1007/s00167-011-1780-x)
• [L1] [71] (10.1016/j.arthro.2024.01.035)
• [L4] Increasing preoperative degenerative change in the knee, as evidenced by a higher WORMS on preoperative MRI, was associated with inferior patient-reported outcomes at a minimum of 2 years after cartilage restoration surgery. [72] (10.1016/j.asmr.2024.100973)
• [L2] cMACI showed superior safety compared with pMACI for large cartilage defects, with similarly improved outcomes in approximately 75% of patients. [75] (10.1002/ksa.70352)
• [L5] Most studies have failed to show improved clinical outcomes in the short term when adding cartilage restoration procedures to high tibial osteotomy, raising questions about whether longer term studies will show improved efficacy. [77] (10.1016/j.arthro.2023.07.002)
• [L4] The 20-year cumulative risk of knee arthroplasty after a focal cartilage lesion in the knee was 19%. [78] (10.2106/jbjs.22.01174)
• [L4] Based on the high short-term failure rate observed in this study, the authors advise that a decellularized OC allograft plugs implant should be used with caution in the treatment of OC lesions of the knee, as similar outcomes have not been noted with other cartilage restoration techniques. [82] (10.1016/j.arthro.2017.07.018)
• [L5] At 6 months and 1 year, a 6-mm osteochondral plug placed in a 10-mm defect better preserved the articular surface and contour of the condyle compared to untreated or bone-grafted defects. [85] (10.1177/0363546505279914)
• [L4] ACI is effective in filling full-thickness chondral defects of the knee, with improvements noted in 86% of patients at 6-year follow-up, though longer follow-ups are needed to confirm long-term effectiveness. [86] (10.1016/j.otsr.2012.04.019)
• [Paper] Clinical magnetic resonance imaging (MRI) is the method of choice for the non-invasive evaluation of articular cartilage defects and the follow-up of cartilage repair procedures. [88] (10.1016/j.injury.2008.01.043)
• [L5] The near future of cartilage repair will likely involve refinement of current techniques along with incorporation of scientific advances in cartilage biology, potentially leading to a single-stage surgical technique that replicates normal articular cartilage. [89] (10.1016/j.csm.2013.12.003)
• [L4] The vast majority of cartilage repair procedures were applied in degenerative, non-traumatic cartilage defects. [90] (10.1007/s00402-016-2453-5)
• [L4] Treatment of knee cartilage defects is a challenge requiring reconstruction of hyaline cartilage to prevent osteoarthritis. [91] (10.1016/j.otsr.2011.09.007)
• [L1] At short, medium, and long term (minimum 15 years), mosaicplasty results in a better, clinically relevant outcome than microfracture in articular cartilage defects (2-5 cm2) of the distal femur of the knee in patients aged 18 to 50 years. [92] (10.1177/0363546517745281)
• [L5] Recent advancements in cartilage restoration and arthroplasty techniques, along with appropriate patient selection and meticulous surgical technique, have resulted in promising outcomes in patients with patellofemoral cartilage lesions who undergo surgical treatment. [93] (10.5435/jaaos-d-16-00009)
• [L5] Existing cartilage treatment options include marrow stimulation, osteochondral tissue transfer or transplantation, cell-free synthetic scaffolds and cell-based repair strategies, but the literature is limited by heterogeneity in surgical procedures and reporting of non-standardised outcome measures. [95] (10.1136/jisakos-2015-000037)
• [L4] [96] (10.2106/jbjs.j.00813)
• [L4] The methodologic quality of knee articular cartilage surgery studies was poor overall and also for individual techniques. [97] (10.1016/j.arthro.2013.02.023)
• [L4] One of every 4 patients may experience a secondary failure after undergoing a revision cartilage procedure. [99] (10.1177/03635465241260271)
• [L3] However, a case-control analysis with normalized data showed that on equal terms women have the same success possibilities as men after surgical treatment for knee cartilage regeneration. [100] (10.1177/2325967113s00034)
• [L4] ACI and MACI procedures for the treatment of knee cartilage lesions associated to OA showed long-term success and allowed delaying arthroplasty. [102] (10.1007/s00167-022-07030-2)
• [L4] Injury origin, sex, symptom duration, lesion size, lesion site, age, and previous surgery might determine the final outcome and can be used as a sort of clinical profiling to guide the surgeon in the choice of this procedure and in giving realistic expectations to patients requiring cartilage treatment. [103] (10.1177/0363546513518552)
• [L3] Patients with isolated cartilage defects of the knee joint have significant deficits in quadriceps muscle strength of the injured leg compared with the uninjured leg. [109] (10.1177/2325967117703726)
• [L4] Multifocal chondral defects were noted in 59% of knees, and the most common defect location was the patella (64%). [131] (10.1002/ars2.70064)
• [L1] ACI is an effective treatment for full thickness chondral defects of the knee, providing an improvement of clinical outcomes. [134] (10.1007/s00167-010-1050-3)
• [L5] Treatment of osteochondral defects at any time had a positive effect on healing compared to no treatment. [135] (10.1007/s00167-008-0675-y)
• [L1] The treatment of symptomatic cartilage knee defects ≥3 cm2 in size using MACI was clinically and statistically significantly better than with MFX, with similar structural repair tissue and safety. [136] (10.1177/0363546514528093)
• [L4] While approaches using stem cells for cartilage defects are highly promising, there is currently limited evidence of a direct clinical benefit, and further research is required to assess the overall outcome of stem cell therapies for knee cartilage repair. [137] (10.1177/0363546513508744)
• [Paper] Existing articular cartilage repair techniques can return the athlete with articular cartilage injury to high-impact sports, but treatment does not produce normal articular cartilage, and this limits the success rate and durability of current cartilage repair in athletes. [139] (10.1136/bjsports-2015-094772)
• [L2] Cartilage repair using HA-BMAC leads to successful medium-term outcomes independent of age or lesion size. [140] (10.1177/0363546516656179)
• [L3] This cell-free biomimetic scaffold is a safe and effective treatment for cartilage knee lesions, offering positive clinical results at 2 years with a low failure rate. [141] (10.1002/ksa.12402)
• [L4] [150] (10.1007/s00167-016-4047-8)
• [L4] The primary indication is deep, small defects on the medial femoral condyle. [156] (10.1016/j.otsr.2011.08.005)
• [L3] Patellar dysplasia should not be seen as a contraindication for cell-based cartilage repair procedures. [157] (10.1177/03635465231220028)
• [L4] No definitive conclusion could be made in respect to the best current surgical technique for articular cartilage and osteochondral lesions. [158] (10.1016/j.arthro.2016.01.055)
• [L4] High resolution MRI and well-defined MRI variables are a reliable, reproducible and accurate tool for assessing cartilage repair tissue. [159] (10.1016/j.ejrad.2005.08.007)
• [L4] Overall, the various cartilage restoration techniques reported improvements in patient reported outcomes with low complication rates, though definitive conclusions on the optimal treatment remain elusive due to a lack of high-quality comparative studies. [164] (10.1007/s00167-018-5139-4)
• [L2] [165] (10.1002/ksa.12068)
• [L3] OCA transplantation for treatment of large multisurface cartilage defects in the knee resulted in a 94.7% initial success rate when grafts with high viable chondrocyte density (≥70%) were used and when patients strictly adhered to prescribed postoperative rehabilitation protocols. [170] (10.1177/23259671221102452)
• [L4] Treatment of osteochondral defects in the ankle and knee joint with a biomimetic scaffold resulted in incomplete cartilage repair and poor subchondral bone repair at 1- and 2.5-year follow-up. [173] (10.1007/s00167-015-3538-3)
• [L3] [174] (10.1097/01.blo.0000129162.36302.4f)
• [L2] In contrast to other cartilage repair techniques, patients 40 years and older do not have an inferior outcome up to 24 months after ACI for isolated cartilage defects when compared with younger patients. [178] (10.1177/0363546510376742)
• [L5] [180] (10.1007/s001670100248)
• [L1] Although clinical success in short-term and midterm applications has been suggested for the application of BMAC for the restoration of cartilage defects in lesions of the knee, current study designs are generally of low scientific rigor. [181] (10.1016/j.arthro.2018.11.073)
• [L4] [186] (10.1186/s12891-020-03311-4)
• [L3] [194] (10.1007/s00167-023-07615-5)
• [L4] Persistent subchondral alterations were documented at long-term MRI evaluation, suggesting the limits of this approach to regenerate the osteochondral unit in patients affected by knee OCD. [196] (10.1007/s00167-020-06230-y)
• [L3] Compared with arthroscopy, MRI displays moderate sensitivity for detecting and classifying chondral knee injuries. [211] (10.1007/s00167-015-3622-8)
• [L4] Middle-aged patients with focal, chronic non-traumatic osteochondral lesions of the knee also profit from OAT at a short follow-up. [215] (10.1016/j.otsr.2016.06.004)
• [L2] Our long-term results suggest that first- and third-generation ACI methods are equally effective treatments for isolated full-thickness cartilage defects of the knee. [220] (10.1177/0363546520928337)
• [L4] Current treatment modalities vary from conservative to surgical options, but available cartilage regeneration techniques only produce fibrocartilage or fibrohyaline cartilage with poor integrative capacities and higher friability. [221] (10.1530/eor-2024-0083)
• [L4] One should be alert to the possibility of subclinical cartilage degeneration even in asymptomatic patients who show no degenerative changes on plain radiographs or conventional MRI. [223] (10.1007/s00167-014-3469-4)
• [L4] Clinically significant improvements in IKDC scores are associated with a more mature MRI appearance of the autologous chondrocyte implantation graft on postoperative MRI, as indicated by higher MOCART scores. [226] (10.1016/j.jisako.2024.100311)
• [L4] MACT is an excellent surgical therapy for full-thickness cartilage defects of the knee, with good long-term results for simple defects. [228] (10.1177/0363546514526695)
• [L4] The value of AMIC relative to other cartilage repair procedures and to the natural course remains undefined. [235] (10.1007/s00167-011-1840-2)

See Also

• Knee arthroscopy
• Partial meniscectomy
• Knee osteoarthritis
• Meniscal tear
• Meniscal repair
• High tibial osteotomy

References

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