Os acromiale is a common finding in shoulder surgery. We review the anatomy, prevalence, pathophysiology, and treatment options for this diagnosis. In addition, we report on a case series of 6 patients with a symptomatic meso os acromiale who were treated with a new technique involving arthroscopic acromioplasty in conjunction with the excision of the acromial nonunion site. We have demonstrated this novel treatment method to be a safe and effective technique in this case series. This arthroscopic partial resection of an os acromiale is considered to be an alternative option for treating a symptomatic meso os acromiale.
Key points
- •
An os acromiale can be found at the basi-acromion, meta-acromion, meso-acromion, or pre-acromion level, with a meso-acromion as the most common. The os is named for the most anterior portion on the unstable fragment.
- •
The prevalence of os acromiale is 1% to 30%, with 42% to 61% being bilateral and a higher prevalence in the male and African American population.
- •
Most patients with an os acromiale can be treated nonoperatively, but multiple surgical procedures have been reported in the treatment of a symptomatic os acromiale, including open or arthroscopic excision of the os fragment, open reduction and internal fixation (ORIF) with or without bone grafting, arthroscopic subacromial decompression with acromioplasty, and arthroscopically assisted reduction-internal fixation.
- •
Open fragment excision has limited indications and is recommended for symptomatic pre-acromion with a relatively small fragment or as a salvage procedure after a failed ORIF. In the latter scenario, arthroscopic excision is probably a better option, as it has the possible benefit of less periosteal and deltoid attachment injury, possibly lending to better results than open excision.
- •
ORIF techniques and approaches associated with the most success include those with rigid fixation and preservation of the vascularity of the os acromiale (likely the acromiale branch of the thoracoacromial artery). Even in cases of successful union, patients still may have hardware discomfort requiring hardware removal; however, there are minimal complications that arise from most ORIF cases.
- •
Resection of the synchondrosis without excision of the entire os acromiale has shown promising results in a small number of patients with short-term follow-up and presents a novel approach to patients with a symptomatic os acromiale.
Introduction
Os acromiale is a developmental defect that arises from the lack of an osseous union between the ossification centers of the acromion, resulting in a fibrocartilaginous tissue connection. This anatomic abnormality occurs more frequently in the male and black demographic than in the white and female population. It is common that os acromiale is diagnosed through incidental radiographic findings and has been noted that traumatic events can cause the onset of symptoms from a previously asymptomatic os acromiale. Surgical treatment is typically recommended only after nonsurgical management has failed to relieve symptoms. Procedures commonly used include open or arthroscopic excision of the os fragment, open reduction and internal fixation (ORIF) with or without bone grafting, arthroscopic subacromial decompression with acromioplasty, and arthroscopically assisted reduction-internal fixation. After reviewing the literature, we report on a case series of 6 patients with a symptomatic meso os acromiale treated with a new technique involving arthroscopic acromioplasty in conjunction with the excision of the acromial nonunion site with creation of a 5-mm to 7-mm gap between the anterior and posterior fragments. We have demonstrated it to be a safe and effective technique in this case series. This arthroscopic partial resection of an os acromiale is considered as an alternative option for treating a symptomatic meso os acromiale.
Introduction
Os acromiale is a developmental defect that arises from the lack of an osseous union between the ossification centers of the acromion, resulting in a fibrocartilaginous tissue connection. This anatomic abnormality occurs more frequently in the male and black demographic than in the white and female population. It is common that os acromiale is diagnosed through incidental radiographic findings and has been noted that traumatic events can cause the onset of symptoms from a previously asymptomatic os acromiale. Surgical treatment is typically recommended only after nonsurgical management has failed to relieve symptoms. Procedures commonly used include open or arthroscopic excision of the os fragment, open reduction and internal fixation (ORIF) with or without bone grafting, arthroscopic subacromial decompression with acromioplasty, and arthroscopically assisted reduction-internal fixation. After reviewing the literature, we report on a case series of 6 patients with a symptomatic meso os acromiale treated with a new technique involving arthroscopic acromioplasty in conjunction with the excision of the acromial nonunion site with creation of a 5-mm to 7-mm gap between the anterior and posterior fragments. We have demonstrated it to be a safe and effective technique in this case series. This arthroscopic partial resection of an os acromiale is considered as an alternative option for treating a symptomatic meso os acromiale.
Anatomy
There are 4 centers of ossification of the acromion: the basi-acromion, the meta-acromion, the meso-acromion, and the pre-acromion ( Fig. 1 ). The basi-acromion typically fuses with the scapular spine by age 12, and all 4 centers should unite by ages 15 to 18. However, some do not have complete ossification until as late as age 25 years. Diagnosis of os acromiale should not be finalized until after this time point.
One of the main functions of the acromion is to provide the origin of the deltoid muscle. The meta-acromion provides the origin of the posterior deltoid muscle, the meso-acromion anchors the middle portion of the deltoid, and the pre-acromion supports the anterior deltoid fibers along with the coracoacromial (CA) ligament.
An os acromiale is named by the most anterior ossification center that did not fuse. A meso-acromion involves the failure of the anterior acromial apophysis (including the pre-acromion and meso-acromion) to unite with the posterior portion of the acromion (including the meta-acromion and the basi-acromion). By definition, a pre-acromion exists when the synchondrosis is anterior to the acromio-clavicular joint, a meso-acromion exists when the sychondrosis extends into the acromioclavicular joint, a meta-acromion has the synchondrosis posterior to the acromioclavicular joint, and a basi-acromion occurs in the junction of the acromion and spine of the scapula.
Prevalence
The first instance of os acromiale was defined by Gruber in 1863, when 3 of 100 cadavers presented with os acromiale involving a distinct synovial joint. Prevalence of os acromiale has been reported in 1% to 30% of the general population, with 41% to 62% of cases presenting with bilateral involvement. Genetic causes may attribute to the relatively high 30% rate found in the excavated remains of a Philadelphia congregation from the nineteenth century. Sammarco examined 2367 scapulas from the Hamann-Todd Osteological Collection at the Cleveland Museum of Natural History and discovered more prevalence of os acromiale in the black and male population with 13.2% in black individuals compared with 5.8% in white individuals and 8.5% in males compared with 4.9% in females; 8.0% of the skeletons had os acromiale, of which 33.3% were bilateral. No study has yet to determine if os acromiale occurs more frequently in symptomatic patients with shoulder pain than in the general population.
Pathophysiology
Many os acromiale diagnoses are made incidentally with radiographic imaging. The primary source of shoulder pain is often unrelated to the os acromiale. In symptomatic cases of os acromiale, there are 2 likely etiologies of pain: motion at the nonunion site or an impingement syndrome. Patients often experience localized pain and tenderness at the nonunion site on movement of the unstable fragment if a painful synchondrosis is present. Many times an asymptomatic os becomes symptomatic after a traumatic episode disrupting the fibrous union. Magnetic resonance imaging (MRI) or bone scan may illustrate the inflammatory response at the nonunion site. Alternatively, the subacromial space maybe reduced due to flexion of the anterior fragment with deltoid contraction and elevation of the arm. Symptoms of external impingement are produced as a result of this decrease in the subacromial space with this dynamic process. The presence of a meso-acromion has been associated with rotator cuff pathology, ranging from tendonitis to full-thickness tears of the rotator cuff.
Nonsurgical management
Nonsurgical treatment for a patient who first presents with an isolated symptomatic os acromiale is generally recommended as the initial approach. Physical therapy, in conjunction with nonsteroidal anti-inflammatory drugs, is prescribed similar to a typical impingement treatment protocol. Subacromial corticosteroid injections are also widely used to relieve symptoms and may delay or eliminate the need for surgical intervention. Full-thickness rotator cuff tears have been reported to be associated with an os acromiale as often as 50% of the time; therefore, surgery may be recommended earlier for these patients than our typical patients with external impingement without an os acromiale.
Surgical management
Surgical treatment typically occurs once all nonsurgical means have been exhausted. Multiple surgical procedures have been reported in the treatment of an os acromiale, including open or arthroscopic excision of the os fragment, ORIF with or without bone grafting, arthroscopic subacromial decompression with acromioplasty, and arthroscopically assisted reduction-internal fixation. Depending on the case, certain techniques may be more effective than others; however, each has its benefits and disadvantages. In general, management techniques that address the os acromiale itself (fragment excision or ORIF) are used only when the nonunion site is tender and specifically a cause of pain. Otherwise, attention is focused only on managing the concomitant pathology (impingement or rotator cuff tear) and the os acromiale is ignored.
Fragment Excision
Open fragment excision has had mixed results due to deltoid weakness and dysfunction postoperatively. Mudge and colleagues had 8 patients with rotator cuff tears associated with an os acromiale. Six underwent fragment excision and rotator cuff repair, including suturing of the deltoid to the acromion. Four had excellent results, but the other 2 had poor results.
Armengol and colleagues had a case series of 41 patients with an os acromiale in conjunction with rotator cuff tears. Five patients had an open fragment excision, but all 5 had poor results. Warner and colleagues had 3 patients who underwent fragment excision and only 1 had satisfactory results. The other 2 patients with poor results had meso-acromion fragment excision with lingering weakness and pain. The successful case involved resection of a pre-acromion.
Open fragment excision has limited indications and is recommended for symptomatic pre-acromion with a relatively small fragment or as a salvage procedure after a failed ORIF. In the latter scenario, arthroscopic excision is probably a better option.
In a recent case series reporting on deltoid function after arthroscopic excision of either pre-acromion or meso-acromion, Campbell and colleagues demonstrated no decrease in deltoid function or strength compared with the contralateral arm and found no difference in results when the excision was performed with or without a rotator cuff repair. Additionally, Wright and colleagues reported on 13 patients after an arthroscopic excision of a meso-acromion and had no decrease in anterior deltoid strength and no occurrence of deltoid detachment. Arthroscopic excision has the possible benefit of less periosteal and deltoid attachment injury, possibly lending to better results than open excision.
ORIF
Because complications arise from the fragment excision, many surgeons advocate internal fixation of the unfused os acromiale with bone grafting. Techniques to provide stability include the use of tension-band wires, sutures, or cannulated screws with or without the use of bone graft.
Peckett and colleagues reviewed 26 patients presenting with symptomatic meso os acromiale that were treated with either K-wires or screws and a tension band. Twenty-four had a satisfactory result with 96% union. Average time to union was 4 months. Eight cases had persistent pain postoperatively that was relieved by wire and screw removal. Seventeen of the 26 patients had a concomitant rotator cuff tear, and only 11 of these were repairable. They concluded that ORIF with bone grafting should be used for patients with symptomatic meso os acromiale, but a substantial number of patients require hardware removal.
Warner and colleagues reported on 11 patients who underwent ORIF with iliac crest bone grafting comparing 2 fixation techniques. Each technique incorporated debridement of the nonunion site with incorporation of iliac crest autograft spanning the debrided nonunion site. Four patients (5 shoulders) underwent ORIF with a tension-band procedure including the use of pins and wires. Four of 5 of these procedures resulted in persistent nonunion. The other 7 patients had an ORIF using cannulated screws, and an 18-guage wire passed through the screws in a figure of 8 fashion. Six of 7 were successful unions. Mean time for satisfactory radiographic and clinical union was approximately 9 weeks. Nine of the 12 patients required hardware removal to alleviate postoperative pain. The investigators advocated that stabilization and bone grafting should be performed in conjunction with figure of 8 wires through cannulated screws because there was a higher rate of union.
Hertel and colleagues reported on 15 shoulders in 12 patients who underwent ORIF for unstable os acromiale fragments using tension band wiring without the use of bone grafting. Two surgical approaches were used. An anterior deltoid-off approach was used on 7, whereas the other 8 shoulders were approached trans-acromially to preserve the deltoid origin. Union occurred in 3 of 7 cases approached anteriorly and in 7 of 8 shoulders repaired without detachment of the deltoid. The investigators concluded that fusion was more successful when the vascularity of the acromial epiphysis was maintained, likely through the acromiale branch of the thoracoacromial artery.
Atoun and colleagues reported on arthroscopically assisted internal fixation of the symptomatic unstable os acromiale with absorbable screws. In their series, 8 patients presented with symptomatic meso os acromiale and had satisfactory results 3 to 6 months postoperatively. Two patients experienced hardware irritation that was treated with trimming of the prominent subcutaneous screw. Full union was achieved in 6 patients, partial union in 1 patient, and failed union in 1 patient. The fusion results were all verified by radiographs. This arthroscopic technique was the first of its kind to aid in the fixation of os acromiale.
Techniques and approaches associated with the most success include those with rigid fixation and preservation of the vascularity of the os acromiale. Even in cases of successful union, patients still may have hardware discomfort requiring hardware removal; however, there are minimal complications that arise from most ORIF cases.
Arthroscopic Subacromial Decompression with Acromioplasty
Arthroscopic subacromial decompression is primarily used when impingement with or without a rotator cuff tear is present and the nonunion site is nontender and considered to be incidental. Potential advantages compared with open procedures include more rapid rehabilitation, better range of motion, and shorter surgical times. As with other treatment options presented for this problem, the results are variable.
Jerosch and colleagues analyzed 12 patients with an os acromiale of 122 patients who were all treated with arthroscopic subacromial decompression. At follow-up visits, the patients presenting with os acromiale had slightly better outcomes. Therefore, the arthroscopic subacromial decompression procedure was a recommended alternative to other more invasive and complicated procedures.
Hutchinson and Veenstra had 3 asymptomatic os acromiale patients who underwent arthroscopic decompression for impingement syndrome associated with an unstable os acromiale. All 3 patients were initially satisfied with results postoperatively, but at 1-year follow-up, they all had symptoms return. Two patients even required more surgery. The arthroscopic decompression ultimately failed for all 3 patients. The investigators came to the conclusion that arthroscopic subacromial decompression should not be recommended for impingement secondary to an unstable os acromiale.
Armengol and colleagues reported the results of 42 cases of os acromiale (including 33 patients with meso os acromiale) that were associated with partial or full-thickness rotator cuff tears. The patients were treated in 1 of 3 ways: resection for 5 patients, ORIF for 14 patients, and modified acromioplasty for 22 patients. Their acromioplasty technique involved removal of the acromial spur with preservation of the superior cortex and deltoid fascia. Only half of the patients who had an ORIF had satisfactory outcomes, with 86% needing revision surgery for hardware issues, whereas the modified acromioplasty yielded 86% satisfactory results.
Abboud and colleagues treated 19 patients who had os acromiale associated with rotator cuff tears. Eleven (53%) of the patients had satisfactory results, including 4 who were treated with open acromioplasty and 3 treated with arthroscopic acromioplasty. The remaining 3 patients were treated with ORIF. The 7 patients treated with acromioplasty achieved improved outcome scores in all categories but external rotation. It is important to note that all 3 patients who had workers’ compensation claims did not have satisfactory results with the acromioplasty procedure.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
