اوس ایکرومیالی (Os Acromiale)

This is the clinical evidence summary written for health professionals. It is technical, and it lists the research this page was built from. You do not need to read it to understand your treatment or to make a decision about it.

Overview¶

• A symptomatic, unstable os acromiale is relatively rare despite the radiographic appearance of an os acromiale being not uncommon in patients presenting with shoulder pain [1].
• An os acromiale should always be suspected in cases of failed rotator cuff surgery or ongoing shoulder pain after failed treatment [2].
• The prevalence of os acromiale was 2.13% in Thai patients with shoulder problems who required MRI evaluation [3].
• Os acromiale is associated with rotator cuff injuries [7].
• The greater the distance of the acromioclavicular joint from the anterior edge of the acromion, the higher the likelihood of an os acromiale [15].
• The authors recommend that the acromion be carefully examined roentgenographically prior to operation in any patient with a rotator cuff tear [10].
• Surgical treatment is usually not indicated for os acromiale in the professional tennis player [9].
• Operative management of a symptomatic os acromiale that has failed initial nonoperative treatment leads to decreased symptoms and improvement in clinical outcomes [4].
• Surgical options for symptomatic os acromiale include arthroscopic sub-total excision, arthroscopic subacromial decompression of stable fragments, and open reduction and internal fixation of unstable fragments [13].
• Patients with a united os acromiale had a significantly better functional outcome as measured by the Constant score (P = .0169) [12].
• The advantages of arthroscopic internal fixation include improved visualization of the undersurface of the acromion, allowing excellent reduction, the possibility of treating concomitant shoulder pathologies, and to avoid increased morbidity of the open approach [14].
• Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients but resolves spontaneously over time in the majority of patients [5].
• The presence of os acromiale does not appear to have a negative impact on the clinical outcomes after surgery and rTSA remains a safe and effective treatment option [6].
• The outcome of RTSA does not seem to be negatively affected by the presence of an os acromiale [11].
• Ipsilateral os acromiale may be a relative contraindication to the clavicle hook plate [16].

Anatomy & Pathophysiology¶

Bony Anatomy¶

• The acromion has three ossification centers: the metacromion (base), the mesoacromion (middle), and the preacromion (tip) [38].
• Failure of fusion of the acromial ossification centers results in os acromiale [38].
• Os acromiale is defined as incomplete fusion of secondary ossification centers, most commonly between the mesoacromion and meta-acromion [49].
• The unfused segment in os acromiale is most commonly the meso-acromion, a configuration often termed a meso-type os acromiale [22].
• The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch, a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [35].
• The rotator cuff, subacromial bursa, and subdeltoid bursa pass underneath the coracoacromial arch [35].
• The scapula is attached to the axial skeleton by the acromioclavicular and sternoclavicular joints [37].
• The acromion is a flattened bony process that curves forwards from the scapular spine [37].

Prevalence and Associations¶

• In Thai patients with shoulder problems who required MRI evaluation, the prevalence of os acromiale was 2.13% [3].
• The radiographic appearance of an os acromiale is not uncommon in patients presenting with shoulder pain [1].
• A symptomatic, unstable os acromiale is relatively rare [1].

Pathophysiology¶

• Most diagnoses of os acromiale are made incidentally on axillary view radiographs of the shoulder [22].
• Primary shoulder pain is usually unrelated to the unfused os acromiale [22].
• When an os acromiale drives symptoms, the two principal causes are motion at the non-union site or an impingement-type syndrome resulting from flexion of the os fragment during deltoid contraction and arm elevation [22].
• Pain from an os acromiale due to these mechanisms has been reported in a variety of sports, particularly among throwing athletes and swimmers [22].
• Previously stable non-unions can become unstable following an episode of blunt trauma to the region [22].
• The synchondrosis of an os acromiale can be injured following trauma [24].
• Extrinsic impingement occurs when the space available for the rotator cuff is diminished, with examples including acromial fracture or pathologic os acromiale [62].

Epidemiology and Prevalence¶

• Liberson reviewed 1800 shoulder girdles and identified an incidence of os acromiale of 1.4% [21].
• The lesion was bilateral in 62% of patients in Liberson's review of 1800 shoulder girdles [21].

Associated Pathology and Risk Factors¶

• The greater the distance of the AC joint from the anterior edge of the acromion, the higher the likelihood of an os acromiale [15].

Diagnostic Considerations¶

• Awareness of the os acromiale in the young athlete, appropriate clinical examination, and image studies are crucial to confirm diagnosis [19].
• Appropriate radiographic investigation including axillary views is emphasized for the diagnosis of os acromiale injuries [24].

Clinical Presentation¶

• An os acromiale should always be suspected in cases of failed rotator cuff surgery [2].
• An os acromiale should always be suspected in cases of ongoing shoulder pain after failed treatment [2].
• Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients [5].
• Postoperative local tenderness at the os acromiale resolves spontaneously over time in the majority of patients [5].
• The lesion was bilateral in 62% of patients in Liberson's review [21].
• The unfused segment is most commonly the meso-acromion [22].
• Any primary shoulder pain is usually unrelated to the unfused os [22].
• If the os acromiale is driving symptoms, one principle cause is motion at the non-union site [22].
• If the os acromiale is driving symptoms, another principle cause is an impingement-type syndrome resulting from flexion of the os fragment during deltoid contraction and arm elevation [22].
• Pain from an os acromiale by the mechanism of impingement has been reported in a variety of sports [22].
• Pain from an os acromiale by the mechanism of impingement has been reported in particular among throwing athletes and swimmers [22].
• Meta–os acromiale is the rarest subtype of os acromiale [23].

Investigations¶

Prevalence and Demographics¶

• Liberson reviewed 1800 shoulder girdles and identified an incidence of os acromiale of 1.4%, with the lesion being bilateral in 62% of patients [21].
• A multicenter study aimed to determine the prevalence of and factors associated with os acromiale in the Japanese population [8].
• The radiographic appearance of an os acromiale is not uncommon in patients presenting with shoulder pain, but a symptomatic, unstable os acromiale is relatively rare [1].

Radiographic Evaluation¶

• The acromion should be carefully examined roentgenographically prior to operation in any patient with a rotator cuff tear [10].
• Appropriate radiographic investigation for os acromiale includes axillary views [24].
• Awareness of the os acromiale in the young athlete requires appropriate clinical examination and image studies to confirm diagnosis [19].
• The standard shoulder series should include orthogonal views of the shoulder, including a true AP view in the scapular plane, an AP view, an axillary view, and a scapular Y view [60].
• The scapular Y view provides visualization of the coracoacromial arch and can reveal coracoacromial spurs, which have been closely associated with the presence of rotator cuff pathology [60].
• The scapular Y view can also show acromial shape [60].
• At least two X-ray views should be obtained for shoulder imaging: an anteroposterior in the plane of the glenoid and an axillary projection with the arm in abduction to show the relationship of the humeral head to the glenoid [52].
• The purpose of imaging of the shoulder is to help establish the diagnosis, determine the severity of the pathoanatomy, assist in surgical planning, and enable the surgeon to illustrate the condition of the shoulder to the patient [30].
• Standardized plain films are almost always sufficient to garner the information needed for shoulder evaluation [30].
• The first key view for shoulder imaging is the anteroposterior (AP) in the plane of the scapula taken so that the x-ray beam passes through the glenohumeral joint [30].
• The second key view for shoulder imaging is the axillary view taken with the arm in the functional position of elevation in the plane of the scapula and oriented so that both the spinoglenoid notch and the scapular neck are visible [30].
• The axillary view is referred to as the "truth view" because it demonstrates the glenohumeral relationships in the functional position of elevation [30].
• CT scans have the disadvantage of being taken with the arm in the adducted position, unlike the axillary truth view [30].
• The temptation to "overimage" should be resisted, obtaining only the scans or reconstructions that are necessary for the care of the patient [30].

Magnetic Resonance Imaging¶

• In Thai patients with shoulder problems, os acromiale was identified via Magnetic Resonance Imaging evaluation [3].
• MRI is useful to identify labral tears and rotator cuff tears, although the accuracy for these is enhanced by combining the scan with arthrography [52].
• MRI is the modality of choice for evaluating the rotator cuff, biceps, and subacromial/subdeltoid bursa [59].
• T2-weighted MRI provides better visualization of full thickness rotator cuff tears [59].
• MR arthrography is considered the benchmark for evaluation for labral tears and rarely is indicated for evaluation of rotator cuff pathology [59].
• When MRI or MR arthrography is contraindicated, CT arthrography is indicated [59].

Ultrasonography¶

• Ultrasonography is a simple and accurate test for identifying rotator cuff tears and calcific tendinitis [52].
• Ultrasonography is a low-cost alternative to MRI and arthrography for evaluating both skeletal and soft-tissue structures of the shoulder [59].
• Ultrasonography can provide immediate, real-time visualization of the rotator cuff, biceps tendon, and calcific deposits [59].
• Ultrasonography can be used to measure the subacromial space and detect atrophy of rotator cuff muscles [59].
• Ultrasonography is highly operator dependent and is not as useful for evaluating labral tears or rotator cuff tears that are very small or larger than 3 cm [59].
• The most commonly performed joint examination using ultrasonography is the shoulder examination, and accuracy depends on the skill of the scanner operator and an awareness of pitfalls that are encountered [50].

Clinical Associations and Diagnostic Implications¶

• The synchondrosis of an os acromiale can be injured following trauma, though rarely [24].

Treatment¶

Non-Operative¶

• A symptomatic os acromiale in a competitive female fastball pitcher was treated successfully with open reduction and internal fixation [27].

Operative¶

• Symptomatic unstable os acromiale can be effectively treated with autogenous bone-grafting and internal fixation using a rigid tension-band construct and cannulated screws, which results in a high rate of union [65].
• This new arthroscopic technique of fixation of os acromiale with absorbable screws provides promising clinical, cosmetic, and radiologic results with high patient satisfaction [28].
• After 3 to 6 years of follow-up, all 6 shoulders were rated as excellent according to criteria similar to that of the American Shoulder and Elbow Surgeons [18].
• Modified arthroscopic subacromial decompression can provide results similar to standard arthroscopic subacromial decompression for routine impingement [25].
• Meta–os acromiale is the rarest subtype of os acromiale, and special consideration must be given to the type of tension-band construct used to achieve adequate compression and fixation [23].

Complications¶

Post-operative and Surgical Complications¶

• Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients following reverse total shoulder arthroplasty [5].

Diagnostic and Clinical Implications¶

Pathophysiology and Mechanisms of Symptom¶

• Pain from an os acromiale by the mechanism of impingement has been reported in a variety of sports, in particular among throwing athletes and swimmers [22].

Recovery¶

• After 3 to 6 years of follow-up, all 6 shoulders treated with osteosynthesis of an unstable mesoacromion were rated as excellent according to criteria similar to that of the American Shoulder and Elbow Surgeons [18].
• At a two to five year follow-up, all patients treated for fusion of the unstable mesoacromion had fused [69].

Key Evidence¶

• [L4] While the radiographic appearance of an os acromiale is not uncommon in patients presenting with shoulder pain, a symptomatic, unstable os acromiale is relatively rare. [1] (10.1097/00132589-200412000-00006)
• [L4] An os acromiale should always be suspected in cases of failed rotator cuff surgery or ongoing shoulder pain after failed treatment. [2] (10.1097/00132589-200609000-00006)
• [L3] In Thai patients with shoulder problems who required MRI evaluation, the prevalence of os acromiale was 2.13%. [3] (10.1177/23259671221078806)
• [L4] Operative management of a symptomatic os acromiale that has failed initial nonoperative treatment leads to decreased symptoms and improvement in clinical outcomes. [4] (10.1016/j.jse.2019.05.047)
• [L3] Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients but resolves spontaneously over time in the majority of patients. [5] (10.1177/2325967120965131)
• [L4] The presence of os acromiale does not appear to have a negative impact on the clinical outcomes after surgery and rTSA remains a safe and effective treatment option. [6] (10.1016/j.xrrt.2025.01.002)
• [L3] The study supports previous findings that os acromiale is associated with rotator cuff injuries. [7] (10.1016/j.jseint.2025.05.015)
• [L3] This multicenter study aimed to determine the prevalence of and factors associated with os acromiale in the Japanese population. [8] (10.1016/j.jse.2025.01.008)
• [L4] Surgical treatment is usually not indicated for os acromiale in the professional tennis player. [9] (10.1177/2325967118773723)
• [L4] The authors recommend that the acromion be carefully examined roentgenographically prior to operation in any patient with a rotator cuff tear. [10] (10.2106/00004623-198466080-00029)
• [L4] The outcome of RTSA does not seem to be negatively affected by the presence of an os acromiale. [11] (10.1016/j.jse.2017.02.012)
• [L4] Patients with a united os acromiale had a significantly better functional outcome as measured by the Constant score (P = .0169). [12] (10.1016/s1058-2746(98)90008-8)
• [L5] Surgical options for symptomatic os acromiale include arthroscopic sub-total excision, arthroscopic subacromial decompression of stable fragments, and open reduction and internal fixation of unstable fragments. [13] (10.5435/jaaos-d-17-00011)
• [L5] The advantages of this technique are improved visualization of the undersurface of the acromion, allowing excellent reduction, the possibility of treating concomitant shoulder pathologies, and to avoid increased morbidity of the open approach. [14] (10.1097/bte.0000000000000191)
• [L4] Our data suggest that the greater the distance of the AC joint from the anterior edge of the acromion, the higher the likelihood of an os acromiale. [15] (10.1067/mse.2003.128136)
• [L4] Ipsilateral os acromiale may be a relative contraindication to the clavicle hook plate. [16] (10.1186/s12891-021-04841-1)
• [L4] After 3 to 6 years of follow-up, all 6 shoulders were rated as excellent according to criteria similar to that of the American Shoulder and Elbow Surgeons. [18] (10.1016/s1058-2746(99)90004-6)
• [L4] Awareness of the os acromiale in the young athlete, appropriate clinical examination, and image studies are crucial to confirm diagnosis. [19] (10.1016/j.jseint.2020.02.008)
• [L4] [22] (10.1302/2058-5241.4.180100)
• [L4] Meta–os acromiale is the rarest subtype of os acromiale, and special consideration must be given to the type of tension-band construct used to achieve adequate compression and fixation. [23] (10.1177/03635465211028238)
• [L4] This case highlights that the synchondrosis of an os acromiale can be injured following trauma, though rarely, and emphasizes the need for appropriate radiographic investigation including axillary views and a flexible surgical approach. [24] (10.1016/j.jse.2008.02.012)
• [L5] Increased awareness of the diagnosis and improved techniques have shown that modified arthroscopic subacromial decompression can provide results similar to standard arthroscopic subacromial decompression for routine impingement. [25] (10.1097/00132589-200206000-00003)
• [L4] A symptomatic os acromiale in a competitive female fastball pitcher was treated successfully with open reduction and internal fixation. [27] (10.1177/0363546506288305)
• [L4] This new arthroscopic technique of fixation of os acromiale with absorbable screws provides promising clinical, cosmetic, and radiologic results with high patient satisfaction. [28] (10.1016/j.jse.2011.12.011)
• [L4] Symptomatic unstable os acromiale can be effectively treated with autogenous bone-grafting and internal fixation using a rigid tension-band construct and cannulated screws, which results in a high rate of union. [65] (10.2106/00004623-199809000-00011)
• [L4] At a two to five year followup all had fused. [69] (10.1016/s1058-2746(95)80192-8)

References¶

[1] Treatment of the Symptomatic Os Acromiale. Techniques in Shoulder and Elbow Surgery. 2004. DOI: 10.1097/00132589-200412000-00006

[2] Management of Os Acromiale. Techniques in Shoulder and Elbow Surgery. 2006. DOI: 10.1097/00132589-200609000-00006

[3] Prevalence of Os Acromiale in Thai Patients With Shoulder Problems: A Magnetic Resonance Imaging Study. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/23259671221078806

[4] Os acromiale: systematic review of surgical outcomes. Journal of Shoulder and Elbow Surgery. 2020. DOI: 10.1016/j.jse.2019.05.047

[5] Os Acromiale in Reverse Total Shoulder Arthroplasty: A Cohort Study. Orthopaedic Journal of Sports Medicine. 2020. DOI: 10.1177/2325967120965131

[6] Clinical implications of reverse total shoulder arthroplasty with an os acromiale: a systematic review. JSES Reviews, Reports, and Techniques. 2025. DOI: 10.1016/j.xrrt.2025.01.002

[7] Prevalence and factors associated with os acromiale: a multicenter study. JSES International. 2025. DOI: 10.1016/j.jseint.2025.05.015

[8] The prevalence and associated factors of os acromiale: a multicenter study. Journal of Shoulder and Elbow Surgery. 2025. DOI: 10.1016/j.jse.2025.01.008

[9] Os Acromiale in Professional Tennis Players. Orthopaedic Journal of Sports Medicine. 2018. DOI: 10.1177/2325967118773723

[10] Rotator cuff tears associated with os acromiale.. The Journal of Bone & Joint Surgery. 1984. DOI: 10.2106/00004623-198466080-00029

[11] Reverse shoulder arthroplasty in patients with os acromiale. Journal of Shoulder and Elbow Surgery. 2017. DOI: 10.1016/j.jse.2017.02.012

[12] Transacromial approach to obtain fusion of unstable os acromiale. Journal of Shoulder and Elbow Surgery. 1998. DOI: 10.1016/s1058-2746(98)90008-8

[13] Symptomatic, Unstable Os Acromiale. Journal of the American Academy of Orthopaedic Surgeons. 2018. DOI: 10.5435/jaaos-d-17-00011

[14] Arthroscopic Internal Fixation of Symptomatic Os Acromiale. Techniques in Shoulder & Elbow Surgery. 2020. DOI: 10.1097/bte.0000000000000191

[15] Relationship between os acromiale and acromioclavicular joint anatomic position. Journal of Shoulder and Elbow Surgery. 2003. DOI: 10.1067/mse.2003.128136

[16] Os acromiale may be a contraindication of the clavicle hook plate: case reports and literature review. BMC Musculoskeletal Disorders. 2021. DOI: 10.1186/s12891-021-04841-1

[18] Successful osteosynthesis of an unstable mesoacromion in 6 shoulders: A new technique. Journal of Shoulder and Elbow Surgery. 1999. DOI: 10.1016/s1058-2746(99)90004-6

[19] The unstable os acromiale: a cause of pain in the young athlete. JSES International. 2020. DOI: 10.1016/j.jseint.2020.02.008

[21] Types of os acromiale according to Liberson. 2006.

[22] Os acromiale: a review of its incidence, pathophysiology, and clinical management. EFORT Open Reviews. 2019. DOI: 10.1302/2058-5241.4.180100

[23] Rare Symptomatic Meta–Os Acromiale in an Athlete. The American Journal of Sports Medicine. 2021. DOI: 10.1177/03635465211028238

[24] Fracture of an os acromiale with associated rupture of the coracoclavicular ligaments. Journal of Shoulder and Elbow Surgery. 2008. DOI: 10.1016/j.jse.2008.02.012

[25] Arthroscopic Management of the Mesoacromion. Techniques in Shoulder and Elbow Surgery. 2002. DOI: 10.1097/00132589-200206000-00003

[27] Surgical Stabilization of Os Acromiale in a Fast-Pitch Softball Pitcher. The American Journal of Sports Medicine. 2006. DOI: 10.1177/0363546506288305

[28] Arthroscopically assisted internal fixation of the symptomatic unstable os acromiale with absorbable screws. Journal of Shoulder and Elbow Surgery. 2012. DOI: 10.1016/j.jse.2011.12.011

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[69] Successful fusion of the unstable mesoacromion: Technique and report of five cases. Journal of Shoulder and Elbow Surgery. 1995. DOI: 10.1016/s1058-2746(95)80192-8