Arthroscopic Decompression for an Unstable Os Acromiale
Arthroscopic Decompression for an Unstable Os Acromiale
abstract & commentary
Synopsis: An extended bony decompression of the unstable os acromiale fragment yielded clinical results equivalent to those reported in other series for decompression of impingement for a normal acromion.
Source: Wright RW, et al. Arthroscopic decompression for impingement syndrome secondary to an unstable os acromiale. Arthroscopy 2000;16(6):595-599.
Os acromiale is a failure of fusion of one or more of the outer ossification centers of the acromion to its more medial part. The most common site of fusion failure is at the meso-acromion, occurring in 1-15% of patients. Bilaterality is seen in 62% of the patients. The os acromiale can be symptomatic because of motion at the non fused segment. It can also be symptomatic because of impingement of the rotator cuff and bursa below, aggravated by the downward pull of the deltoid in a dynamic fashion. Treatment results of impingement associated with an unstable os acromiale have been mixed and generally poor. This paper by Wright and colleagues addressed the unstable os acromiale fragment arthroscopically in 13 shoulders over a four-year period. In all cases, the os acromiale was diagnosed on plain radiographs, specifically on the axillary view. All patients underwent at least six months of non-operative treatment involving injections, physical therapy, and anti-inflammatory medications. Diagnostically, an impingement test with an injection of Lidocaine in the subacromial space resulted in complete relief of their pain in all cases. This helped to distinguish impingement as the etiology of pain as opposed to the unstable os acromiale fragment.
The treatment arthroscopically involved a more aggressive and extensive bony decompression of the leading edge in the acromion. Effectively only a thin shell of bone was left remaining superiorly as the majority of the os acromiale fragment was removed with a burr. Leaving this thin shell of bone preserved the deltoid attachment. No attempt was made at fusion of the os acromiale fragment. The postoperative rehabilitation program emphasized early range of motion and rotator cuff strengthening exercises. Five shoulders also had a partial thickness rotator cuff tear but only one of these required repair because of it being more than 50% of the thickness. Patients were evaluated at three, six, and 12 months, as well as the final follow-up at 2½ years. Scoring with the UCLA scoring system averaged 17 preoperatively and 31 at the final follow-up. Overall, 85% of the patients achieved good or excellent results by objective scoring. Full strength of the anterior deltoid and rotator cuff muscles was achieved by all patients six months postoperatively as evaluated by manual muscle testing. Patients’ subjective scores of their shoulders were satisfactory in 12 of 13 cases. In no instance was there detachment of the deltoid or poor cosmetic result or pain at the pseudoarthrosis point.
COMMENT BY DAVID R. DIDUCH, MS, MD
Historically, the treatment of impingement secondary to an unstable os acromiale has been fraught with complications and difficulty. Attempts at fusion yielded mixed results with a high instance of hardware failure and secondary symptoms requiring further operations. Attempts at excision of the os fragment with reattachment of the deltoid to the anterior acromion involve an extensive surgical procedure with prolonged recovery period to allow the deltoid to reattach securely. This has also been fraught with complications. Modified acromioplasty with an open technique has been successful at resecting additional bone over what is conventionally performed for acromioplasty. This paper by Wright et al offers an excellent prospective evaluation of patients with this difficult problem treated with arthroscopic acromioplasty alone. Their resection of the acromion is more extensive than a routine acromioplasty. They basically remove bone sufficient to achieve a flat acromion with a tip that is unable to impinge on the rotator cuff with shoulder motion. Doing this while preserving the deltoid attachment can be technically demanding. To their credit, there were no problems with deltoid detachment in the postoperative period and all patients regained full deltoid strength.
In anticipation of an arthroscopic decompression, one should pay careful attention to the presence of an os acromiale on an axillary radiograph as this would alter the operative plan. It would appear from the results here that an arthroscopic decompression produces results equivalent to patients undergoing the same procedure without the presence of an os acromiale. In comparison to papers in the literature for this difficult problem, it would also seem to offer an advantage over attempts at fusion or excision of the entire fragment. However, prospective, comparative studies would better answer that question.
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