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Bearing surfaces and wear

131 citationsUpdated Sep 2026

For patients: a plain-language version of this topic is available. See the patient guide.

Overview

Bearings in total joint arthroplasty are categorized as hard-on-soft, such as metal-on-polyethylene, or hard-on-hard, such as ceramic-on-ceramic [132]. All articulations produce wear, typically with the harder material wearing the softer counterpart [132]. This process can be accelerated by surface roughening from scratching or the interposition of third bodies like cement fragments [132]. While articulating components should minimize wear particle generation to optimize long-term prosthesis survival [5], contemporary alternative bearing surfaces are not a panacea, and detailed comparative clinical studies remain required to determine factors associated with implant performance and survivorship [3]. Patient-specific wear rates are associated with patients' gait patterns [1].

Metal-on-metal bearings have been associated with higher incidences of failure due to the production of cobalt and chrome debris, leading to their near-total abandonment in hip replacement [132]. Wear and tribocorrosion remain important causes of failure, with metal-on-metal bearings and taper tribocorrosion being prominent clinical concerns due to associated soft tissue inflammatory responses [2]. Analyses by two joint registries indicate that patients receiving metal-on-metal total hip arthroplasty and hip resurfacing are at greater risk for revision than those receiving total hip arthroplasty using a different bearing surface combination [10]. Consequently, the routine use of metal-on-metal hip surface replacement is not justified as proposed advantages over conventional total hip replacement have not been realized, and new serious complications such as pseudotumors have been associated with the procedure [57]. Due to the lack of superiority, increased complications, greater cost, and potential adverse medical consequences, metal-on-metal bearing surfaces should be used with caution [32].

Selection of the bearing surface is often "experience-based" rather than "evidence-based" due to limited direct comparisons at long-term follow-up [6]. Bearing surface choice in primary total hip arthroplasty changed significantly from 2007 to 2015, with metal-on-metal bearing use decreasing as a result of adverse effects [4]. Metal-on-highly cross-linked polyethylene is considered the preferred bearing surface for conventional total hip arthroplasty because of its safety profile and excellent results in the first 10 to 15 years of use [67]. Considering the superior performance of modern bearings, their use is recommended to avoid wear-related complications and revisions [7]. Alternative bearing surfaces with lower wear rates and less particulate debris formation may improve total joint arthroplasty survivorship by decreasing periprosthetic osteolysis, especially in younger, high-demand patients [8]. However, there remains no clear indication which total hip arthroplasty bearing couple is the most biocompatible, especially in young active patients [49].

Anatomy & Pathophysiology

Joint Anatomy and Biomechanics

The hip is a multiaxial joint formed by the articulation between the pelvis and femur, connecting the axial skeleton and the lower extremity [86]. The hemipelvis comprises the ilium, ischium, and pubis, which unite at the triradiate cartilage within the concave acetabulum [86]. The acetabulum consists of an articular crescent-moon–shaped lunate surface and a nonarticular central fossa that serves as the attachment point for the ligamentum teres [86]. The acetabular labrum is a fibrocartilaginous ring attached to the rim of the acetabulum that extends the articulating surface area and increases femoral head coverage [86]. Triangular in cross section, the labrum creates a pressurized seal of the central compartment of the hip during loading [86]. Only the external one-third of the labrum contains blood vessels, leaving the majority of the structure avascular and limiting its healing ability following injury [86].

The femoral head forms two-thirds of a sphere, with a small depression at its center from which the ligamentum teres extends to connect to the acetabular notch [86]. The neck-shaft angle of the femur averages 125°, allowing for greater mobility by placing the head and neck more perpendicular to the acetabulum in a neutral position [86]. Normal version, defined as the head-neck angle in the frontal plane, averages 15 to 20° [86]. The hip is surrounded by a dense fibrous capsule extending from the periphery of the acetabulum to the intertrochanteric line of the femoral neck, which enhances joint stability by preventing translation of the femoral head [86].

Ligamentous Constraints: * Iliofemoral ligament: The thickest and strongest of the three main hip ligaments, functioning to limit external rotation while its lateral arm limits extension of the joint [86]. * Ischiofemoral ligament: Extends from the ischial margin of the acetabulum to the greater trochanter of the femur, providing posterior support and restricting internal rotation motion [86]. * Pubofemoral ligament: Extends from the obturator crest of the pubic bone to the femoral neck and acts to limit abduction of the joint [86].

The hip functions effectively as a fulcrum, resulting in a state of equilibrium between body weight and the opposing abductor muscles [128]. The peak contact force in the hip joint during walking is approximately 2.5 times body weight [128]. The push-off phase in running generates a joint contact force of approximately 5.2 times body weight [128]. The highest calculated forces and torques across the hip joint occur when descending stairs [128]. An increase in femoral offset correlates with a decreased requirement of abductor force to produce a constant net hip moment, thereby decreasing joint reaction forces [128]. Conversely, a decrease in the abductor muscle force disrupts joint stability, triggering a reactive neuromuscular mechanism that increases muscular cocontraction and joint reaction forces [128]. Increasing the joint reaction force at the hip may increase the wear rate of the implant [128].

The acetabulum is normally anteverted 15 degrees and obliquely oriented in the coronal plane 45 degrees caudally [92]. The posterosuperior articular surface of the acetabulum is thickened to accommodate weight bearing [92]. The inferior surface of the acetabulum contains the acetabular (cotyloid) notch, which is bound by the transverse acetabular ligament [92]. The femoral neck is normally anteverted approximately 14 degrees in relation to femoral condyles, with a range of 1 to 40 degrees [92]. The femoral neck-shaft angle averages 127 degrees, beginning at 141 degrees in the fetus [92].

The average range of motion of a normal hip includes approximately 120° of flexion, 30° of extension, 45° of abduction, 20° to 30° of adduction, 35° of internal rotation, and 45° of external rotation [94]. Normal gait function requires hip flexion of 30°, hyperextension of 10°, abduction and adduction of 5°, and internal and external rotation of 5° [94]. The gluteus medius and minimus muscles function together to maintain and abduct the femur during the stance phase of gait [94].

Vascular Anatomy

In adulthood, the major blood supply to the femoral head is from the medial femoral circumflex and lateral epiphyseal arteries [100]. From birth to approximately 4 years of age, the major blood supply to the femoral head comes from the medial and lateral femoral circumflex arteries, with major contributions from the artery of the ligamentum teres [100]. From the age of 4 years to adulthood, the posterosuperior and posteroinferior retinacular arteries from the medial circumflex artery are the major blood supply to the femoral head [100]. The common femoral vessels are the most commonly reported extrapelvic vascular structures injured during total hip arthroplasty [100]. The most common mechanism of injury to the common femoral vessels during total hip arthroplasty is errant retractor placement anterior to the acetabulum [100].

The profundus or deep femoral artery arises from the lateral aspect of the common femoral artery approximately 3.5 cm below the inguinal ligament [100]. The lateral circumflex artery arises from the lateral side of the proximal profundus femoris artery [100]. The medial circumflex artery most commonly comes from the posteromedial profundus femoris artery and traverses between the pectineus and psoas muscles [100]. The superior gluteal vessels are branches of the posterior division of the internal iliac artery and are closest to the hip as they exit from the sciatic notch [100]. The inferior gluteal vessels and internal vessels are branches of the anterior division of the internal iliac artery, exiting the pelvis between the piriformis and coccygeus muscles [100].

The medial femoral circumflex artery is the main blood supply to the femoral head, terminating in the posterior aspect of the extracapsular arterial ring [97]. The lateral group of ascending branches from the extracapsular arterial ring is the main blood supply to the femoral head [97]. The lateral epiphyseal artery penetrates the femoral head and is believed to be the dominant blood supply to the femoral head from the ascending cervical artery system [97]. Fractures that disrupt the ascending blood flow to the lateral epiphyseal vessel have an increased risk of osteonecrosis [97]. The artery of the ligamentum teres arises from either the obturator or medial femoral circumflex artery and does not provide sufficient blood supply to maintain the viability of the femoral head [97].

Wear Mechanisms and Modes

Tribology is the science and technology of friction, lubrication, and wear in interacting surfaces in relative motion [44]. Types of wear include adhesive and abrasive wear, fatigue, and delamination [44]. Adhesive wear predominates in the metal-on-polyethylene bearings used in total hip arthroplasty [44]. Delamination, abrasion, and adhesive wear are commonly seen with total knee arthroplasty [44].

Wear Modes: * Mode 1: Occurs when the two bearing surfaces are articulating against each other in the manner intended by the implant designer [14]. * Mode 2: Occurs when a bearing surface articulates against a non-bearing surface [14]. * Mode 3: Occurs when third-body abrasive particles have become entrapped between the two bearing surfaces [14]. * Mode 4: Occurs when two non-bearing surfaces are wearing against each other [14].

The least wear occurs in Mode 1, whereas severe wear typically occurs in Modes 2, 3, and 4 [14]. Classical wear mechanisms that apply to prosthetic joints include adhesion, abrasion, and fatigue [14]. Wear damage is defined as the change in surface texture or morphology caused by the action of the wear mechanisms [14]. Wear is defined as the removal of surface material by mechanical motion caused by friction, motion, and loading of an interface between materials [82].

Abrasive wear occurs when a rougher, harder surface moves against a softer surface, generating particulate debris from the softer surface [82]. Adhesive wear results between two moving objects in contact whereby a thin layer of material is transferred from one surface to another [82]. Third-body wear results when an additional particle is present between the two main bearing surfaces, leading to friction and loss of material at the contact surface [82]. Friction between two sliding surfaces depends on the applied load, not the area of contact or speed of movement [96]. Normal human joints possess coefficients of friction that are about ten times lower than those of various combinations of prosthesis-bearing materials [96]. Metal on ultra-high molecular weight polyethylene produces a better coefficient of friction than other combinations, which is improved further if the metal is replaced by a ceramic [96]. Synovial fluid reduces the coefficient of friction by forming a fluid film lubrication layer or a molecular-width boundary lubrication coating [96]. Wear is proportional to the load and distance of movement between two surfaces [96].

Adhesive bearing wear is the most important process that generates submicron-sized polyethylene particles [105]. Abrasive wear occurs when a rough femoral head surface causes mechanical scratching of the polyethylene surface with loss of polyethylene material [105]. Third-body particles within the joint space get between the head and polyethylene cup, causing abrasion and removal of polyethylene from the cup surface [105]. Sources of third-body particles include cement debris, metal debris shed from the cup or stem, and metal debris from corrosion at modular metal-metal interfaces [105]. Polyethylene wear comes from bearing wear at the head-cup articulation and backside wear where the polyethylene insert rubs against the metal shell [105]. Backside wear occurs because the polyethylene locking mechanism does not completely inhibit polyethylene micromotion against the metal shell [105]. The more backside micromotion allowed, the more polyethylene debris is generated [105].

Most design parameters influencing wear of contemporary bearings under idealized conditions are well understood, but major confounding considerations arise in vivo from suboptimal component positioning and third-body debris [11]. Neither patient-specific factors nor estimated hip contact force have a major influence on annual wear in DuraLoc cups [39]. The orientation of the acetabular component affects polyethylene wear, with abduction angles of ≥45° associated with a 40% increase in mean linear polyethylene wear compared to angles <45° [68]. Severe acetabular bone defects were predicted by an increased wear rate and increased patient height [37]. Femoral bone defects were predicted by increased wear rate and placement of the cup outside of the true acetabulum [37]. There was a significant difference in linear penetration measurements between AP pelvis and AP hip radiographs, with lower rates recorded using AP pelvis [38]. Deformed acetabular shells produced higher frictional torque than spherical shells [166]. Impaction deformation with consequent friction, wear, and micromotion contributed to the early failure of the Durom acetabular component [167].

A likely cause of squeaking in hip arthroplasty is adverse tribological conditions caused by suboptimal lubrication [71]. Differing audible sounds were detected in total hip arthroplasties with variable bearing surfaces, likely related to differing bearing materials or variable hip kinematic patterns [137]. The dual mobility hip with sequentially crosslinked polyethylene was highly wear resistant under all test conditions [176]. This uncemented acetabular component and particular XLPE had low rates of linear and volumetric wear [193]. This acetabular component and XLPE with large metal heads had low rates of linear and volumetric wear [194]. Hip arthroplasty surgeons may be less concerned about osteolysis-related wear of HXLPE if the femoral offset is slightly increased, allowing focus on joint anatomy reconstruction, hip stability, and leg length [187]. The future of hip bearing development needs to be focused on performance issues with the entire total hip arthroplasty construct rather than on the abrasive wear resistance of the bearing couple per se [75]. Articulating components should minimise the generation of wear particles in order to optimize long-term survival of the prosthesis [5].

Current worldwide guidance for metal-on-metal hip patients is neither evidence-based nor financially sustainable, with most protocols lacking the sensitivity to detect asymptomatic adverse reaction to metal debris lesions [24]. Other surgical, implant and patient factors should be considered when determining the mechanisms of failure of large diameter metal-on-metal hip arthroplasties [158]. Current technology or design of some total hip arthroplasty systems that make use of a large-diameter femoral head may not yet allow the use of modular large heads with a metal-on-metal articulation, especially in young, active male patients [177]. Anterior iliopsoas impingement caused by large-diameter metal-on-metal femoral heads is a potential failure mechanism resulting in persistent groin pain [197]. Extensive soft tissue and abductor muscles dysfunctions were common in revision total hip arthroplasty for failed metal-on-metal hip arthroplasty [170]. A constrained acetabular component with repair of the hip abductors might be beneficial in managing failed metal-on-metal hip arthroplasty [170].

RHA significantly alters hip biomechanics, which may result in altered loading patterns with adaptive remodelling causing neck thinning [112]. An acetabular component inclination of 50° and an anteversion of 25° allowed the most physiologic range of hip motion in metal-on-metal hip resurfacing [131]. High ion levels were associated with an abduction angle of more than 45° and repetitive extreme hip motion in revision cases [163]. Acetabular inclination angle is not a meaningful determinant of metal ion levels in ASR arthroplasties [196]. Fretting and corrosion damage occurs at a variety of modular component interfaces in contemporary metal-on-metal total hip arthroplasties [195]. In vivo metal ion release associated with current like-hardness metal-on-metal systems may be reduced greatly with differential-hardness hip bearing systems [69].

Tribochemical reactions play an important role in the wear of metal-on-metal joints [61]. The generated tribomaterial, which progressively forms by mechanical mixing of the uppermost nanocrystalline zone of the metal surface with proteins from the synovial fluid, governs the wear rate and influences the corrosive behavior of the bearing [61]. Nanometer-sized wear particles may initially originate from the passivation layer covering the implant surface and then detach from this tribolayer [61]. The inflammatory response observed surrounding metal-on-metal implants appears to be lower than that around metal-on-polyethylene implants [61]. Metallic byproducts, which can complex with proteins, may lead to a T lymphocyte-mediated hypersensitivity response [61]. The tribolayer appears to have beneficial effects on the wear of metal-on-metal joints [61].

Alumina ceramic has a surface finish smoother than metal implants due to its high density [58]. Ceramic is harder than metal and more resistant to scratching from third-body wear particles [58]. The liner wear rate of alumina-on-alumina has been shown to be 4000 times less than cobalt-chrome alloy-on-polyethylene [58]. Ceramic wear was measured at less than 0.025 mm/year in a series of patients with a minimum of 18.5 years' follow-up [58]. Ceramic head fracture is more common with smaller head sizes and shorter neck lengths [58]. Application of a ceramic femoral head onto a stem trunnion with wear or surface damage found at revision surgery can produce uneven load distribution within the head and contribute to fracture [58]. Impingement between the femoral neck and rim of the ceramic acetabular component can produce chipping or complete fracture of the acetabular insert [58]. Repetitive contact at extremes of motion can lead to notching of the metal femoral neck by the harder ceramic and initiate failure through this portion of the implant [58]. Ceramic wear has been greater when the acetabular component has been implanted in an excessively vertical orientation [58].

Classification

Wear Modes: Wear in prosthetic joints is classified into four distinct modes based on the surfaces involved and the mechanism of interaction. Mode 1 occurs when two bearing surfaces articulate against each other in the manner intended by the implant designer [14]. This mode results from motion between the intended primary bearing surfaces, such as the prosthetic femoral head against the polyethylene acetabular bearing surface [70]. Mode 2 occurs when a bearing surface articulates against a non-bearing surface [14]. Specifically, this refers to a primary bearing surface moving against a secondary surface that is not intended to move against it [70]. Mode 3 occurs when third-body abrasive particles become entrapped between two bearing surfaces [14]. This mode involves primary surfaces with the interposition of third-body particles [70]. Mode 4 occurs when two non-bearing surfaces wear against each other [14]. This refers to two nonprimary surfaces rubbing together, such as impingement of the prosthetic femoral neck on the rim of the acetabular component [70].

Wear Mechanisms and Severity: Classical wear mechanisms applicable to prosthetic joints include adhesion, abrasion, and fatigue [14]. Wear damage is defined as the change in surface texture or morphology caused by the action of these wear mechanisms [14]. The least wear occurs in Wear Mode 1, whereas severe wear typically occurs in Modes 2, 3, and 4 [14].

Other Considerations: Metal debris generated from taper junctions has a different morphology and composition than debris generated from bearing surfaces [147].

Clinical Presentation

General Wear and Osteolysis

Clinical experience prior to 2000 documented rates of wear and osteolysis ranging from 10% to as high as 70% at 7- to 14-year follow-up [19]. The greatest patient activity and wear occurred during the first 5 years [21]. Regular long-term patient follow-up is necessary to detect evidence of occult polyethylene wear at the earliest opportunity [50]. Early detection of severe polyethylene wear may permit revision of only the femoral head and liner to prevent catastrophic outcomes [29]. Diagnosis and surveillance of wear-related problems should include measurement of wear and imaging methods such as radiographic edge detection, spiral CT, MRI, and radiostereometric analysis to assess the extent and progression of osteolysis [53]. The migration of components and polyethylene wear can be measured without needing specialised radiographs [28]. While three-dimensional analysis detected 10% more wear than two-dimensional analysis, its repeatability was four times worse, resulting in higher patient enrollment requirements for wear detection [52]. Technologies such as whole genome screening and proteomics show promise for identifying biomarkers exclusively associated with wear-induced osteolysis, but standardized protocols are needed to distinguish these markers from non-wear-related pathologies [122].

Metal-on-Metal Bearings

Patients who receive metal-on-metal total hip arthroplasty and hip resurfacing are at greater risk for revision than patients who receive total hip arthroplasty using a different bearing surface combination [10]. The rate of groin pain was 7% after THA with conventional bearing surfaces, 15% with metal-on-metal THA, and 18% with total hip resurfacing [27]. Younger patients were more likely to report groin pain postoperatively and more likely to have metal-on-metal bearing surfaces [27]. Sterile soft tissue lesions appear to be present in a sizeable proportion (N50%) of unexplained painful metal-on-metal hips [23]. Soft tissue lesions in metal-on-metal hips may be asymptomatic and are associated with reactions to metal wear particles on histology [23]. Wasting of the glutei or short external rotators was present almost universally in a population of unexplained painful metal-on-metal hips [23]. A lesion on MARS MRI is not synonymous with the need for intervention, as asymptomatic soft tissue lesions similar in appearance to symptomatic lesions have been identified [23]. Ultrasound examination provides sensitive screening of soft tissue reactions around metal-on-metal bearings and may be useful in monitoring progression and defining treatment for periarticular soft tissue abnormalities [51]. Pseudotumors, masses, and enlarged bursae have been reported in hips with metal-on-metal bearings associated with pain and swelling [114]. Histological analysis supports the formation of pseudotumors from both wear and hypersensitivity reactions [114]. There are currently no definitive blood tests or histopathologic criteria to diagnose metal hypersensitivity [114]. In cases of painful metal-on-metal hip arthroplasty with elevated inflammatory markers, revision and reorientation of the acetabular component with conversion to a non-metal-on-metal bearing can address both mechanical subluxation and metal hypersensitivity when infection is not confirmed [133]. Following 8 dislocations and visible wear in a metal-on-metal hip prosthesis, the patient suffered no additional complications such as osteolysis or black tissues [134]. Increased bearing articulation wear and serum metal ion concentrations in cases with taper interface corrosion support the hypothesis that increased friction in the joint articulation is one of the factors responsible for simultaneous articulation and taper damage [60]. Metal-on-metal bearings produce a greater number of particles than conventional bearing couples because the debris generated is in the nanometer-size range [121]. Nanometer-sized cobalt alloy debris yields a relatively high specific surface area available for dissolution, which may account for substantial elevations in serum and urine cobalt and chromium concentrations [121]. The effect of head size on serum metal levels is not clear, with conflicting data reported in the literature [121]. No unexplained pain or other complication attributable to wear debris or the metal-on-metal articulation was observed in a minimum 5-year follow-up of modular metal-on-metal total hip arthroplasty [25]. All implants were functioning well with no radiographic evidence of component loosening in a cohort of young, active Chinese patients after metal-on-metal hip resurfacing [62]. Anteroposterior and lateral radiographs obtained at least 24 months after index procedure did not show signs of liner wear, periprosthetic osteolysis, or implant loosening in any patient of the 2 investigated groups in a prospective randomized study of metal-on-metal alloarthroplasty [117].

Ceramic Bearings

Both ceramic-on-ceramic and ceramic-on-crossfire-polyethylene bearing surfaces performed well out to 10 years in subjects who were <61 years at time of surgery [16]. Excellent clinical and radiological outcomes were obtained for both metal-on-highly cross-linked polyethylene and ceramic-on-ceramic bearings in a case control study with 5-9-year follow-up [33].

Polyethylene Bearings

Increased patient age, higher BMI, inflammatory arthritis diagnosis, and ceramic femoral heads were associated with decreased wear rates [129]. The larger 'bedding-in' head penetration in contemporary dual mobility heads may be due to the additional convex bearing surface, creating 2 surfaces for deformation/wear [30]. A thigh mass associated with polyethylene wear-induced osteolysis after cementless total hip arthroplasty has been reported [50]. Isolated liner exchange is a viable treatment option in the patient with radiographically demonstrated polyethylene wear in which the acetabular component is well-fixed [59].

Diagnostic Evaluation and Surveillance

A careful examination of the spine and detailed account of the onset of hip pain should be evaluated before discussing revision hip arthroplasty [56]. If there is a history of poor wound healing or pain after a dental/gastrointestinal procedure, particularly pain at rest, the surgeon should consider infection and evaluate this possibility with appropriate testing [56]. Mechanical symptoms should be assessed via history and clinically, as well as an evaluation of the patient’s gait to check for muscle weakness and limping [56]. Surgeons should scrutinize patient radiographs to evaluate for component position, signs of edge loading or impingement, signs of osteolysis, or implant loosening [56]. High cup inclination and large femoral head size have been shown to increase metal ion production secondary to edge loading [56]. Particular attention should be paid to the retroacetabular, ischial, and pubic regions on patient radiographs [56]. Evaluation of a painful metal-on-metal hip arthroplasty should include a critical review of serial plain radiographs focusing on identifying implant type and signs of implant-related complications such as loosening or osteolysis [119]. For hip resurfacing implants, the presence of radiographic sign of impingement, typically an indentation located in the lateral or anterolateral aspects of the femoral neck, should be noted [119]. It is important to measure the acetabular component abduction angle relative to the pelvic horizontal on anteroposterior view, as high inclination angles have been shown to demonstrate elevated serum and joint fluid levels of metal ions and increased wear secondary to edge loading [119]. Excessive acetabular version alone was not associated with an increased in the implant wear [119]. Nonoperative treatment has been advocated for patients with mild and transient symptoms, negative MRI findings, and inconclusive metal ions levels, managed by interval 6-month re-evaluation, follow-up of metal ions levels and MARS-MRIs at 6 months, yearly, and annually thereafter [43]. Patients with trunnionosis should abstain from high impact activities to decrease force load on the prosthesis [43]. During follow-up intervals for trunnionosis, signs of abductor deficiency including Trendelenburg sign and gait evaluation should be sought to identify an underlying progressive soft tissue destructive process [43]. For patients presenting with symptoms suggestive of trunnionosis and a confirmed diagnosis on imaging and laboratory investigations, the next appropriate step would be consideration of revision THA [43]. Preoperative planning for trunnionosis revision starts with careful evaluation of radiographs and MRI images to evaluate prosthetic alignment and the extent of soft tissue involvement [43]. Obtaining previous operative reports to identify prosthetic components and being ready with necessary extraction instruments helps avoid difficult hardware scenarios during surgery [43]. Operative exposure allows for the most accurate evaluation of the extent of local soft tissue damage, particularly if there is any abductor or other muscle deficiency [43]. Any necrotic soft tissue should be appropriately excised during revision for trunnionosis [43].

Investigations

Wear Measurement and Surveillance

Plain radiography: Conventional radiographs remain critical in the initial imaging evaluation of the hip [46]. A complete hip series usually consists of an anterior-posterior (AP) pelvis, a centered AP hip, a lateral view (frog-leg, cross-table, Dunn 45° or 90°), and a false-profile (Lequesne) view [46]. Close radiographic monitoring with determination of linear wear rates is recommended to assess the risk of osteolysis [142]. Multiple radiographic views and determination of linear wear rate are recommended, while CT scans may be needed only when surgical intervention is considered [140]. A single prerevision radiograph appears to be sufficient to assess 2-dimensional in vivo wear [168]. The use of PolyWare and Hip Analysis Suite imaging techniques for measurement of polyethylene wear in the clinical setting appears to be acceptable, provided that their limitations are understood [74]. Radiographic wear data on conventional polyethylene are consistent with laboratory studies showing that radiation-induced cross-linking has a beneficial effect on wear resistance [150].

CT: A clinically available high-resolution CT scanner can estimate 3D displacement of 0.026 ± 0.101 mm, indicating it is a clinically relevant tool for measuring polyethylene wear in total hip arthroplasty [80]. CT overcomes the limitations of radiography by providing three-dimensional assessment of bony morphology and, to some degree, assessment of soft-tissue abnormalities [88]. CT scans are effective for examining cortical and cancellous bone and can be used to create three-dimensional reconstructions of the hip for use in surgical planning [104].

Other Considerations: Patient-specific polyethylene wear rates are associated with patients' gait patterns [1]. Impingement provides a potent mechanism for third-body access to wear-critical central areas of the bearing surface, thus potentiating accelerated/outlier wear and heightened osteolysis propensity [22]. The hip center of rotation can be moved superiorly and/or medially to permit cup inclination below 45° with correct cup coverage [17].

Metal-on-Metal Surveillance

MRI: Metal artifact reduction MRI is advised in all patients with metal-on-metal hip arthroplasties [173]. Most patients with a metal-on-metal total hip replacement who do not undergo early revision have normal MRI scans [157]. A lesion on MARS MRI is not synonymous with the need for intervention [23].

Laboratory: The European multidisciplinary consensus statement recommends safety assessment for all patients with metal-on-metal bearings, with closer follow-up for large head bearings and resurfacing involving x-rays and metal ion measurement [165].

Imaging Modalities

MRI: For patients suspected of soft tissue or intra-articular pathology, MRI is the modality of choice, given its superior sensitivity and specificity [104]. The soft-tissue contrast of MRI is superior to other imaging modalities in assessing both intra-articular and extra-articular hip pathology [88]. Magnetic resonance arthrography (MRA) is more appropriate to determine injuries to the labrochondral structures and the ligamentum teres and identify the presence of loose bodies and synovial chondromatosis [104]. MRI is helpful in assessing complications of conventional and resurfacing hip arthroplasties, particularly those with metal-on-metal bearing systems [118]. Major MRI findings that help predict histologic ALVAL scores include synovial thickening, synovitis, synovial volume, abductor disruption, and soft-tissue edema [118].

Ultrasonography: Ultrasonography can be an effective modality to identify musculotendinous disruptions, effusions associated with intra-articular pathology, or inflammatory conditions, such as bursitis [104]. Ultrasonography provides real-time dynamic assessment of the hip and is useful in diagnosing soft-tissue abnormalities about the hip joint [88].

Treatment

Non-Operative

Nonoperative management is advocated for patients with mild and transient symptoms of trunnionosis, provided MRI findings are negative and metal ion levels are inconclusive [43]. These patients are managed with interval re-evaluation every 6 months, including follow-up of metal ion levels and MARS-MRIs at 6 months, yearly, and annually thereafter [43]. During this surveillance period, clinicians must actively seek signs of abductor deficiency, such as a Trendelenburg sign and gait abnormalities, to identify any underlying progressive soft tissue destructive process [43].

Operative

Indications: Surgical intervention is indicated when patients present with symptoms suggestive of trunnionosis and a confirmed diagnosis on imaging and laboratory investigations, provided infection has been ruled out [43]. In such cases, the next appropriate step is consideration of revision total hip arthroplasty [43]. For adverse wear-related failure, revision surgery using limited debridement and a stable large metal bearing placed in the correct position yields excellent outcomes [171].

Implant Selection: Ceramic-on-ceramic bearings offer superior wear resistance compared with all other available alternative bearing surfaces, making them an excellent option for young and very active patients [66]. Alternative bearing surfaces with lower wear rates and less particulate debris formation may improve total joint arthroplasty survivorship by decreasing periprosthetic osteolysis, particularly in younger, high-demand patients [8]. Intermediate-term data suggest that the prevalence and severity of osteolysis may be reduced with these alternative materials compared with conventional metal-on-polyethylene couples, although long-term data are presently unavailable and future performance awaits clinical validation [34]. Both oxidized zirconium and cobalt chrome articulations have demonstrated polyethylene wear rates well below the threshold for osteolysis [36]. The alumina matrix composite femoral head on an alumina liner provided high survivorship and performed as well as the control device regarding reoperation, clinical, and radiographic outcomes [192].

Conversely, the routine use of metal-on-metal hip surface replacement is not justified because proposed advantages over conventional total hip replacement have not been realized, and new serious complications such as pseudotumors have been associated with the procedure [57]. Analyses of objective patient-oriented outcomes by two joint registries indicate that patients receiving metal-on-metal total hip arthroplasty and hip resurfacing are at greater risk for revision than those receiving total hip arthroplasty with a different bearing surface combination [10]. Consequently, the use of large-head metal-on-metal total hip arthroplasty should be discontinued [135]. Gender factors, potentially hormonal, anatomic, or functional, influence the success of metal-on-metal total hip arthroplasty, leading to expanded contraindications to avoid this device in female patients [130]. Although both ceramic-on-metal and metal-on-metal bearings performed well at short-term follow-up, the ceramic-on-metal group had no wear-related revisions and maintained consistently low metal levels [13]. Bearing surface choice in primary total hip arthroplasty has changed tremendously from 2007 to 2015, with metal-on-metal bearing use decreasing as a result of adverse effects [4].

Revision: When performing isolated head and liner exchange for polyethylene wear, both the liner and head must be exchanged during modular bearing change [108]. The most common postoperative complication of this procedure is dislocation, a risk contributed to by patients generally feeling well and failing to allow adequate soft tissue healing [108]. Not revising poorly positioned implants increases the risk of impingement and instability during isolated bearing exchange [108]. Bone grafting of osteolytic lesions behind the cup is performed with particulate graft through cup holes or a small iliac trap door [108]. Cementing a polyethylene bearing into a fixed porous cup is indicated when there is a damaged or worn locking mechanism or when a replacement polyethylene bearing is not available [108]. To optimize cemented liner exchange, the polyethylene cup position should be optimized to avoid neck impingement, reducing the chance of hip instability [108]. Deep seating of the polyethylene liner into the metal cup maximizes surface contact with cement and minimizes the risk of debonding [108]. Roughening the back side of the polyethylene liner insert and the inside surface of the metal cup shell increases surface area for bonding with cement [108]. Close matching of the polyethylene liner to the metal shell is not important when cementing a polyethylene bearing into a fixed porous cup [108].

Postoperative precautions for isolated acetabular liner exchange include not crossing legs, not flexing the hip >90°, not internally or externally rotating the operated leg, and avoiding low seats for at least 6 weeks [59]. A hinged hip abduction orthosis restricting motion to <90° of flexion may be used for 6 weeks in patients with questionable intraoperative stability or where head size and offset cannot be increased [59]. Caution should be exercised when choosing bearing surfaces for adverse reaction to metal debris revisions [18]. There was no difference in the rate of rerevision comparing different types of the initial revision and comparing different bearing surfaces used for the first revision [35].

Other Considerations: Wear and tribocorrosion remain important causes of failure in joint arthroplasty, with metal-on-metal bearings and taper tribocorrosion currently being prominent clinical concerns due to associated soft tissue inflammatory responses [2]. Determining the optimal bearing surface for extremely young patients continues to be a challenge for orthopedic surgeons as they weigh the risks and benefits of each [31]. The greatest patient activity and wear occurred during the first 5 years following total hip arthroplasty [21]. Clinical experience before the year 2000 included rates of wear and osteolysis from 10% to as high as 70% at 7- to 14-year follow-up [19]. Severe acetabular bone defects were predicted by an increased wear rate and increased patient height, while femoral bone defects were predicted by increased wear rate and placement of the cup outside of the true acetabulum [37]. One should consider replacement of all heads in a failed closed reduction, and those patients successfully reduced should at least be monitored for excessive wear [79]. Obtaining previous operative reports to identify prosthetic components and being ready with the necessary extraction instruments will help avoid difficult hardware scenarios during surgery [43]. A multitude of implants may need to be available for various challenging intraoperative findings, including constrained liners, dual mobility cups, cable plates, cerclage wires, and long femoral stems [43].

Complications

Wear and Osteolysis

Polyethylene wear: Intermediate-term follow-up data suggest that the prevalence and severity of osteolysis may be reduced with alternative bearing materials compared with conventional metal-on-polyethylene bearing surface couples [34]. Impingement provides a potent mechanism for third-body access to wear-critical central areas of the bearing surface, potentiating accelerated or outlier wear and heightened osteolysis propensity [22]. Polyethylene wear can lead to late instability and dislocation, with an average time from initial arthroplasty to dislocation of 9 years (range, 5 to 20 years) in a cohort of 20 patients [154]. Catastrophic failure of a polyethylene liner can result in metallosis, characterized by asymmetric polyethylene wear and femoral head migration [155]. The wear resistance of highly cross-linked polyethylene was not compromised by surface changes that occurred during the first year of in vivo service [73]. Patient-specific factors and estimated hip contact force do not have a major influence on annual wear in DuraLoc cups [39].

Metal-on-Metal Specific Complications

Registry and Revision Risk: Analyses by two joint registries indicate that patients who receive metal-on-metal total hip arthroplasty and hip resurfacing are at greater risk for revision than patients who receive total hip arthroplasty using a different bearing surface combination [10]. Hard-on-hard bearings used in elderly THA patients are associated with no demonstrable benefits and possibly an increased risk of complications at short-term follow-up [20]. Poor implant survivorship and frequent complications were observed at a median of 10 years after metal-on-metal hip resurfacing revision [141].

Clinical Outcomes and Pain: Aseptic loosening was the major reason for failure of Sikomet metal-on-metal prostheses after a mean duration of follow-up of seven years [78]. The rate of groin pain was 15% (4 of 26 patients) with metal-on-metal THA and 18% (7 of 39 patients) with total hip resurfacing, compared to 7% (15 of 217 patients) after THA with conventional bearing surfaces [27]. No unexplained pain or other complication attributable to wear debris or the metal-on-metal articulation was observed in a minimum 5-year study of modular metal-on-metal total hip arthroplasty [25]. The four to seven-year experience with the Metasul metal-on-metal articulation indicates that clinical results are similar to those of total hip replacements with a metal-on-polyethylene articulation [9].

Surveillance and Long-term Data: Additional follow-up is necessary to determine any possible long-term deleterious effects associated with the Metasul metal-on-metal articulation [63]. Rigorous long-term studies are needed to determine if the benefits of metal-on-metal bearings outweigh the associated risks [64]. Bilateral simultaneous metal inlay dissociation from the polyethylene liner of a metal-on-metal hip replacement has been reported, confirming the necessity of periodical follow-up and searching for mechanical complications in the presence of abnormal noise [169].

Ceramic and Polyethylene Specific Complications

Ceramic Bearing Outcomes: Survivorship and function of alumina ceramic-on-ceramic and ceramic-on-conventional polyethylene bearing groups remain comparable at 15 years, while polyethylene wear and osteolysis may represent issues in the future [65]. Complete polyethylene wear-through and secondary breakage of the expansion cup can occur in ceramic-polyethylene total hip arthroplasty [29]. Squeaking in hip arthroplasty is likely caused by adverse tribological conditions caused by suboptimal lubrication [71].

Other Considerations

Trends and Specific Populations: Bearing surface choice in primary THA has changed tremendously from 2007 to 2015, with metal-on-metal bearing use decreasing as a result of adverse effects [4]. The risk of short-term complication (including dislocation) and revision THA were similar among appropriately matched Medicare THA patients regardless of bearing surface [139]. Femoral loosening occurred in 8.7% (4 of 46 hips) of patients with osteonecrosis and femoral-neck fracture occurred in 5.2% (3 of 58 hips) of patients with ankylosing spondylitis following hip resurfacing [153].

Recovery

Other Considerations: The provided evidence base does not contain specific data regarding recovery timelines, rehabilitation protocols, or functional milestones (e.g., weeks to light activity, months to full activity). Consequently, the fields for Light activity, Full activity, Complete recovery / outcome plateau, Rehabilitation protocol, and Functional milestones are omitted. The available data pertains to long-term survivorship, wear characteristics, and clinical outcomes at various follow-up intervals.

Wear and tribocorrosion remain important causes of failure in joint arthroplasty [2]. Metal-on-metal bearings and taper tribocorrosion are prominent clinical concerns due to associated soft tissue inflammatory responses [2]. Articulating components should minimize the generation of wear particles to optimize long-term survival of the prosthesis [5]. Regular long-term patient follow-up is needed to detect evidence of occult polyethylene wear at the earliest opportunity [50].

Bearing surface choice in primary total hip arthroplasty changed tremendously from 2007 to 2015 [4]. Metal-on-metal bearing use decreased from 2007 to 2015 as a result of adverse effects [4]. Contemporary alternative bearing surfaces are not a panacea, and detailed comparative clinical studies are required to determine factors associated with implant performance and survivorship [3]. Long-term data regarding the reduction of osteolysis with alternative bearing materials are presently unavailable [34].

Clinical results of the Metasul metal-on-metal articulation at four to seven years are similar to those of total hip replacements with a metal-on-polyethylene articulation [9]. The ceramic-on-metal bearing group had no wear-related revisions at short-term follow-up [13]. The ceramic-on-metal bearing group maintained consistently low metal levels at short-term follow-up [13]. Clinical and radiographic results of second-generation metal-on-metal bearings continue to be comparable with the results observed for other hard-on-hard bearings [72]. Long-term experiences with metal-on-metal total hip arthroplasty make this combination of implant material the conservative choice for success [77].

Survivorship and function of alumina ceramic-on-ceramic and ceramic-on-conventional polyethylene bearing groups remain comparable at 15-year follow-up [65]. Polyethylene wear and osteolysis may represent issues in the future for ceramic-on-conventional polyethylene bearings [65]. Delta-on-Delta couplings demonstrated to be reliable bearing surfaces in revision settings at a midterm follow-up [144]. A metal-on-metal total hip implant with a modular titanium adapter demonstrates a more favorable mid-term to long-term survivorship compared to other designs [156].

The rate of groin pain was 7% after total hip arthroplasty with conventional bearing surfaces [27]. The rate of groin pain was 15% with metal-on-metal total hip arthroplasty [27]. The rate of groin pain was 18% with total hip resurfacing [27]. The functional outcome of hip resurfacing in patients 40 years old and younger was excellent [145]. Overall survival of hip resurfacing in patients 40 years old and younger was unsatisfactory with a 7-year survival of 90.5% [145]. The 5-year survivorship of metal-on-metal hybrid hip resurfacing was 95.2% with no failures in hips implanted since 2002 [149].

Additional follow-up is necessary to determine any possible long-term deleterious effects associated with metal-on-metal articulation in patients less than fifty years old [63]. It will take decades of close clinical observation to determine if the benefits of metal-on-metal bearings outweigh the associated risks [64].

Key Evidence

• [L3] Patient-specific wear rates are associated with patients' gait patterns. [1] (10.1007/s11999-017-5293-x)
• [L5] Wear and tribocorrosion remain important causes of failure in joint arthroplasty, with metal-on-metal bearings and taper tribocorrosion currently being prominent clinical concerns due to associated soft tissue inflammatory responses. [2] (10.1007/s11999-014-3610-1)
• [L5] Contemporary alternative bearing surfaces are not a panacea, and detailed comparative clinical studies are required to determine the factors associated with implant performance and survivorship. [3] (10.2106/jbjs.f.00453)
• [L3] Bearing surface choice in primary THA has changed tremendously from 2007 to 2015, with metal-on-metal bearing use decreasing as a result of adverse effects. [4] (10.1016/j.arth.2017.07.044)
• [L5] Articulating components should minimise the generation of wear particles in order to optimize long-term survival of the prosthesis. [5] (10.1302/2058-5241.1.000004)
• [L5] Selection of the bearing surface is often 'experience-based' rather than 'evidence-based' due to limited direct comparisons at long-term follow-up. [6] (10.1302/2058-5241.3.180300)
• [L3] Considering the superior performance of modern bearings, their use is recommended to avoid wear-related complications and revisions. [7] (10.1186/s42836-026-00408-4)
• [L4] Alternative bearing surfaces with lower wear rates and less particulate debris formation may have the potential to improve total joint arthroplasty survivorship by decreasing periprosthetic osteolysis, especially in younger, high-demand patients. [8] (10.5435/00124635-199807000-00001)
• [L4] The four to seven-year experience with this articulation surface indicates that the clinical results are similar to those of total hip replacements with a metal-on-polyethylene articulation. [9] (10.2106/00004623-200006000-00005)
• [L2] Analyses conducted on objective patient-oriented outcomes by two joint registries indicate that, overall, patients who receive metal-on-metal total hip arthroplasty and hip resurfacing are at greater risk for revision than are patients who receive total hip arthroplasty using a different bearing surface combination. [10] (10.5435/jaaos-20-06-402)
• [L5] Most design parameters influencing wear of contemporary bearings under idealized conditions are well understood, but major confounding considerations arise in vivo from suboptimal component positioning and third-body debris. [11] (10.5435/00124635-200800001-00020)
• [L3] Ceramic bearing surfaces were associated with fewer dislocations after revision than polyethylene bearing surfaces. [12] (10.1007/s11999-015-4378-7)
• [L1] Although both bearings performed well at short-term followup, the CoM bearing group had no wear-related revisions and maintained consistently low metal levels. [13] (10.1007/s11999-015-4424-5)
• [L5] [14] (10.1016/j.biomaterials.2007.07.040)
• [L4] Ceramic-on-ceramic bearing surfaces can be preferentially considered for revision THA, especially in young patients. [15] (10.1016/j.arth.2009.04.016)
• [L1] Both bearing surfaces performed well out to 10 years in subjects who were <61 years at time of surgery. [16] (10.1016/j.arth.2015.11.043)
• [L3] The hip center of rotation can be moved superiorly and/or medially to permit cup inclination below 45° with correct cup coverage. [17] (10.1016/j.arth.2007.06.008)
• [L3] Caution should be exercised when choosing bearing surfaces for adverse reaction to metal debris revisions. [18] (10.1302/0301-620x.96b12.33473)
• [L4] Clinical experience before the year 2000 included rates of wear and osteolysis from 10% to as high as 70% at 7- to 14-year follow-up. [19] (10.5435/00124635-200800001-00003)
• [L3] Hard-on-hard bearings used in elderly THA patients are associated with no demonstrable benefits and possibly an increased risk of complications at short-term follow-up. [20] (10.1016/j.arth.2012.03.031)
• [L3] The greatest patient activity and wear occurred during the first 5 years. [21] (10.1007/s11999-012-2497-y)
• [L4] This corroborates other recent modalities of evidence that impingement provides a potent mechanism for third-body access to wear-critical central areas of the bearing surface, thus potentiating accelerated/outlier wear and heightened osteolysis propensity. [22] (10.1097/blo.0b013e31815c5a7b)
• [L4] [23] (10.1016/j.arth.2009.11.008)
• [L5] Current worldwide guidance for metal-on-metal hip patients is neither evidence-based nor financially sustainable, with most protocols lacking the sensitivity to detect asymptomatic adverse reaction to metal debris lesions. [24] (10.1016/j.arth.2015.03.009)
• [L3] No unexplained pain or other complication attributable to wear debris or the metal-on-metal articulation was observed. [25] (10.1016/j.arth.2011.07.002)
• [L5] The decision to perform revision hip arthroplasty of a metal-on-metal implant is multifactorial and should be based on documented, objective clinical indications. [26] (10.5435/jaaos-d-14-00183)
• [L4] [27] (10.1007/s11999-010-1356-y)
• [L4] The migration of components and polyethylene wear can be measured without needing specialised radiographs. [28] (10.1302/0301-620x.99b10.bjj-2016-1169.r1)
• [L5] Early detection of severe polyethylene wear may permit revision of only the femoral head and liner to prevent catastrophic outcomes. [29] (10.1007/s00402-009-0843-7)
• [L4] The larger 'bedding-in' head penetration may be due to the additional convex bearing surface, creating 2 surfaces for deformation/wear. [30] (10.1016/j.arth.2018.02.061)
• [L3] Determining the optimal bearing surface for extremely young patients continues to be a challenge for orthopedic surgeons as they weigh the risks and benefits of each. [31] (10.1016/j.arth.2016.01.061)
• [L1] Due to the lack of superiority, increased complications, greater cost, and potential adverse medical consequences, these bearing surfaces should be used with caution. [32] (10.1016/j.arth.2012.05.023)
• [L3] Excellent clinical and radiological outcomes were obtained for both types of bearings. [33] (10.1016/j.otsr.2018.04.016)
• [L4] Intermediate-term follow-up data suggest that the prevalence and severity of osteolysis may be reduced with alternative bearing materials compared with conventional metal-on-polyethylene bearing surface couples, but long-term data are presently unavailable and future performance awaits clinical validation. [34] (10.5435/00124635-200800001-00008)
• [L3] There was no difference in the rate of rerevision comparing different types of the initial revision and comparing different bearing surfaces used for the first revision. [35] (10.1007/s11999-015-4215-z)
• [L3] Both bearing combinations demonstrated wear rates well below the threshold for osteolysis. [36] (10.1016/j.arth.2022.02.099)
• [Paper] Severe acetabular bone defects were predicted by an increased wear rate and increased patient height, while femoral bone defects were predicted by increased wear rate and placement of the cup outside of the true acetabulum. [37] (10.1007/s00264-009-0731-3)
• [L3] There was a significant difference in linear penetration measurements between AP pelvis and AP hip radiographs, with lower rates recorded using AP pelvis. [38] (10.1016/j.arth.2013.07.034)
• [L4] Neither patient-specific factors nor estimated hip contact force have a major influence on annual wear in DuraLoc cups. [39] (10.1016/j.arth.2017.07.027)
• [L4] [43] (10.1016/j.arth.2018.05.035)
• [L2] There remains no clear indication which THA bearing couple is the most biocompatible, especially in young active patients. [49] (10.1302/0301-620x.97b9.34824)
• [L5] The authors emphasize the need for regular long-term patient follow-up to detect evidence of occult polyethylene wear at the earliest opportunity. [50] (10.1007/s00402-009-0979-5)
• [L4] Ultrasound examination provides sensitive screening of soft tissue reactions around metal-on-metal bearings and may be useful in monitoring progression and defining treatment for periarticular soft tissue abnormalities. [51] (10.1016/j.arth.2011.09.015)
• [L4] While three-dimensional analysis detected 10% more wear, its repeatability was four times worse than that of the two-dimensional technique and, as a consequence, patient enrollment requirements for wear detection were higher. [52] (10.2106/00004623-200306000-00020)
• [L5] Diagnosis and surveillance of wear-related problems should include measurement of wear and imaging methods such as radiographic edge detection, spiral CT, MRI, and radiostereometric analysis to assess the extent and progression of osteolysis. [53] (10.5435/00124635-200800001-00005)
• [L5] [56] (10.1016/j.arth.2020.01.011)
• [L4] The routine use of metal-on-metal hip surface replacement is not justified as none of the proposed advantages over conventional total hip replacement have been realised, and new serious complications such as pseudotumors have been associated with the procedure. [57] (10.1302/0301-620x.96b11.34426)
• [L5] [59] (10.5435/00124635-200808000-00010)
• [L4] Increased bearing articulation wear and serum metal ion concentrations in cases with taper interface corrosion support the hypothesis that increased friction in the joint articulation is one of the factors responsible for simultaneous articulation and taper damage. [60] (10.2106/jbjs.m.01199)
• [L5] [61] (10.2106/jbjs.j.01877)
• [L4] All implants were functioning well with no radiographic evidence of component loosening. [62] (10.1016/j.arth.2009.11.019)
• [L4] However, additional follow-up is necessary to determine any possible long-term deleterious effects associated with this metal-on-metal articulation. [63] (10.2106/00004623-200411000-00018)
• [L4] Rigorous long-term studies are needed, and it will take decades of close clinical observation to determine if the benefits of metal-on-metal bearings outweigh the associated risks. [64] (10.1097/01.blo.0000149995.84350.d7)
• [L1] Survivorship and function of the two bearing groups remain comparable; while polyethylene wear and osteolysis may represent issues in the future. [65] (10.1016/j.arth.2017.11.066)
• [L2] Ceramic-on-ceramic bearings have superior wear resistance when compared with all other available alternative bearing surfaces, thereby providing an excellent alternative for young and very active patients. [66] (10.2106/jbjs.i.00342)
• [L4] Metal-on–highly cross-linked polyethylene is considered the preferred bearing surface for conventional total hip arthroplasty because of its safety profile and excellent results in the first 10 to 15 years of use. [67] (10.5435/jaaos-d-15-00754)
• [L4] The orientation of the acetabular component affects polyethylene wear, with abduction angles of ≥45° associated with a 40% increase in mean linear polyethylene wear compared to angles <45°. [68] (10.2106/00004623-200300004-00007)
• [L5] This finding suggests that in vivo metal ion release associated with current like-hardness metal-on-metal systems may be reduced greatly with differential-hardness hip bearing systems. [69] (10.1016/j.arth.2008.05.021)
• [L4] [70] (10.1016/j.arth.2009.01.010)
• [L5] The findings suggest that a likely cause of squeaking in hip arthroplasty is adverse tribological conditions caused by suboptimal lubrication. [71] (10.1016/j.arth.2012.01.023)
• [L4] The clinical and radiographic results continue to be comparable with the results observed for other hard-on-hard bearings. [72] (10.2106/jbjs.m.00748)
• [L5] The wear resistance of the highly cross-linked polyethylene studied was not compromised by surface changes that occurred during the first year of in vivo service. [73] (10.1097/01.blo.0000164407.02998.8d)
• [L4] The use of PolyWare and Hip Analysis Suite imaging techniques for measurement of polyethylene wear in the clinical setting appears to be acceptable, provided that their limitations are understood. [74] (10.2106/00004623-200303000-00017)
• [L5] The future of hip bearing development needs to be focused on performance issues with the entire total hip arthroplasty construct rather than on the abrasive wear resistance of the bearing couple per se. [75] (10.1016/j.arth.2008.06.008)
• [L4] The long-term experiences with metal-on-metal total hip arthroplasty make this combination of implant material the conservative choice for success. [77] (10.1097/01.blo.0000193809.85587.f8)
• [L4] After a mean duration of follow-up of seven years, aseptic loosening was the major reason for failure of Sikomet metal-on-metal prostheses. [78] (10.2106/jbjs.e.00604)
• [L5] One should consider replacement of all heads in a failed closed reduction, and those patients successfully reduced should at least be monitored for excessive wear. [79] (10.1016/j.arth.2008.07.009)
• [L5] The study demonstrated that a clinically available high-resolution CT scanner can estimate 3D displacement of 0.026 ± 0.101 mm, indicating it is a clinically relevant tool for measuring polyethylene wear in total hip arthroplasty. [80] (10.1016/j.arth.2012.03.053)
• [L3] RHA significantly alters hip biomechanics, which may result in altered loading patterns with adaptive remodelling causing neck thinning. [112] (10.1007/s00402-010-1070-y)
• [L4] [114] (10.1007/s11999-010-1372-y)
• [L1] [117] (10.1016/j.arth.2008.07.019)
• [L4] [119] (10.1016/j.arth.2012.03.029)
• [L5] [121] (10.5435/00124635-200902000-00003)
• [L5] Technologies such as whole genome screening and proteomics show great promise for identifying biomarkers exclusively associated with wear-induced osteolysis, but standardized protocols and methods to distinguish these markers from non-wear-related pathologies are needed. [122] (10.5435/00124635-200800001-00014)
• [L3] Increased patient age, higher BMI, inflammatory arthritis diagnosis, and ceramic femoral heads were associated with decreased wear rates. [129] (10.1097/01.blo.0000150112.34736.82)
• [L3] Gender factors, potentially hormonal, anatomic, or functional, influence the success of metal-on-metal THA, leading the authors to expand contraindications to avoid this device in female patients. [130] (10.1016/j.arth.2011.04.012)
• [L5] An acetabular component inclination of 50° and an anteversion of 25° allowed the most physiologic range of hip motion. [131] (10.1016/j.arth.2008.07.021)
• [L4] In cases of painful metal-on-metal hip arthroplasty with elevated inflammatory markers, revision and reorientation of the acetabular component with conversion to a non-metal-on-metal bearing can address both mechanical subluxation and metal hypersensitivity when infection is not confirmed. [133] (10.1016/j.arth.2009.08.015)
• [L4] Following 8 dislocations and visible wear, this patient suffered no additional complications such as osteolysis or black tissues. [134] (10.1016/j.arth.2007.09.007)
• [L4] The authors consider that the use of large-head metal-on-metal total hip arthroplasty should be discontinued. [135] (10.1302/2058-5241.1.160014)
• [L4] Differing audible sounds were detected in all cases, likely related to differing bearing materials or variable hip kinematic patterns. [137] (10.1016/j.arth.2008.01.277)
• [L2] The risk of short-term complication (including dislocation) and revision THA were similar among appropriately matched Medicare THA patients regardless of bearing surface. [139] (10.1007/s11999-010-1262-3)
• [L3] Multiple radiographic views and determination of linear wear rate are recommended, while CT scans may be needed only when surgical intervention is considered. [140] (10.1016/j.arth.2008.02.012)
• [L3] Poor implant survivorship and frequent complications were observed at a median of 10 years after MoMHR revision. [141] (10.1007/s11999-016-4882-4)
• [L2] Close radiographic monitoring with determination of linear wear rates is recommended to assess the risk of osteolysis. [142] (10.2106/00004623-200405000-00037)
• [L3] Delta-on-Delta couplings demonstrated to be reliable bearing surfaces in revision settings at a midterm follow-up. [144] (10.1016/j.arth.2019.04.068)
• [L3] The functional outcome of hip resurfacing in this cohort was excellent, but overall survival was unsatisfactory with a 7-year survival of 90.5%. [145] (10.1007/s00402-012-1640-2)
• [L4] Metal debris generated from taper junctions appears to be of a different morphology, composition and therefore, potentially, immunogenicity to that generated from bearing surfaces. [147] (10.1302/0301-620x.98b7.37029)
• [L4] The 5-year survivorship was 95.2% with no failures in hips implanted since 2002. [149] (10.1016/j.arth.2008.04.017)
• [L3] Radiographic wear data on conventional polyethylene are consistent with laboratory studies showing that radiation-induced cross-linking has a beneficial effect on wear resistance. [150] (10.2106/00004623-200405000-00020)
• [L3] [153] (10.1016/j.arth.2013.05.033)
• [L4] [154] (10.1097/01.blo.0000218751.14989.a6)
• [L5] [155] (10.1016/j.arth.2008.09.002)
• [L3] The results of this study demonstrate a more favorable mid-term to long-term survivorship with this specific MoM implant compared to other designs. [156] (10.1016/j.arth.2022.01.053)
• [L4] Most patients with a metal-on-metal total hip replacement who do not undergo early revision have normal MRI scans. [157] (10.1302/0301-620x.95b8.31377)
• [L3] Other surgical, implant and patient factors should be considered when determining the mechanisms of failure of large diameter metal-on-metal hip arthroplasties. [158] (10.1302/0301-620x.98b7.36554)
• [L3] High ion levels were associated with an abduction angle of more than 45° and repetitive extreme hip motion in revision cases. [163] (10.1016/j.arth.2011.11.009)
• [L5] The consensus statement defines benefits, risks, and uncertain issues related to metal-on-metal bearings, recommending safety assessment for all patients with closer follow-up for large head bearings and resurfacing involving x-rays and metal ion measurement. [165] (10.1016/j.otsr.2013.01.005)
• [L5] Deformed acetabular shells produced higher frictional torque than spherical shells. [166] (10.1016/j.arth.2009.03.020)
• [L5] It is likely that impaction deformation with consequent friction, wear, and micromotion contributed to the early failure of the Durom acetabular component. [167] (10.1016/j.arth.2010.01.029)
• [L4] A single prerevision radiograph appears to be sufficient to assess 2-dimensional in vivo wear. [168] (10.1016/j.arth.2018.03.047)
• [L4] The case confirms the necessity of periodical follow-up and searching for mechanical complications in the presence of abnormal noise after hard-on-hard bearing implantation. [169] (10.1016/j.otsr.2009.07.003)
• [L4] Extensive soft tissue and abductor muscles dysfunctions were common, and a constrained acetabular component with repair of the hip abductors might be beneficial. [170] (10.1016/j.arth.2016.04.033)
• [L4] Revision of adverse wear related failure (AWRF) had an excellent outcome using limited debridement and a stable large metal bearing placed in the correct position. [171] (10.1016/j.arth.2014.01.036)
• [L3] Metal artifact reduction MRI is advised in all patients with metal-on-metal hip arthroplasties. [173] (10.1016/j.arth.2012.05.029)
• [L5] The dual mobility hip with sequentially crosslinked polyethylene was highly wear resistant under all test conditions. [176] (10.1016/j.arth.2012.09.011)
• [L3] Current technology or design of some total hip arthroplasty systems that make use of a large-diameter femoral head may not yet allow the use of modular large heads with a metal-on-metal articulation, especially in young, active male patients. [177] (10.2106/jbjs.j.01885)
• [L2] Hip arthroplasty surgeons may be less concerned about osteolysis-related wear of HXLPE if the femoral offset is slightly increased, allowing focus on joint anatomy reconstruction, hip stability, and leg length. [187] (10.1186/s12891-023-06501-y)
• [L2] The alumina matrix composite femoral head on an alumina liner provided high survivorship and performed as well as the control device in terms of reoperation, and clinical and radiographic outcome. [192] (10.1007/s11999-009-1143-9)
• [L3] This uncemented acetabular component and this particular XLPE had low rates of linear and volumetric wear. [193] (10.1007/s11999-015-4319-5)
• [L3] This acetabular component and XLPE with large metal heads had low rates of linear and volumetric wear. [194] (10.1016/j.arth.2018.02.063)
• [L4] Fretting and corrosion damage occurs at a variety of modular component interfaces in contemporary metal-on-metal total hip arthroplasties. [195] (10.1016/j.arth.2013.05.040)
• [L3] Acetabular inclination angle is not a meaningful determinant of metal ion levels in ASR arthroplasties. [196] (10.1016/j.arth.2013.04.022)
• [L4] Anterior iliopsoas impingement caused by large-diameter metal-on-metal femoral heads is a potential failure mechanism resulting in persistent groin pain. [197] (10.1016/j.arth.2010.10.002)

See Also

• Hip resurfacing
• Total hip replacement
• Adverse reaction to metal debris

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