11
Operative Treatment of Symptomatic Os Acromiale
Os acromiale is an uncommon condition of the shoulder, resulting from failure of fusion of the acromial apophysis. The four types of os acromiale are presented in Figure 11–1. Os acromiale are occasionally discovered as an incidental radiographic finding; however, some become symptomatic, causing impingement pain as well as frank rotator cuff pathology. Furthermore, the acromion itself can be a source of pain caused by abnormal motion at the nonunion site.
Historically, treatment alternatives for symptomatic os acromiale have included surgical excision, subacromial decompression alone, and open reduction and internal fixation. Concern has been raised regarding excision of the acromial fragment due to its potential deleterious effect on deltoid function, while the results following isolated subacromial decompression have been associated with recurrent symptoms. Open reduction and internal fixation of the symptomatic os acromiale is a reliable and reproducible technique in which union is achieved and the deltoid attachment and lever arm are preserved.
Indications
1. Symptomatic meso-, meta-, or basi-acromion
2. Preacromion can be simply excised
Contraindications
1. Previous acromioplasty leaving thin, curved acromial fragment unsuitable for fixation
2. Stable fibrous union despite X-ray appearance
Mechanism of Injury
The symptomatic os acromiale is a result of nonunion of the ossification center. A stable fibrous union can be disrupted by direct trauma, leading to late symptoms.
Physical Examination
1. Tenderness and/or acromial motion with direct palpation
2. Pain with forward elevation
3. Impingement sign often positive
Diagnostic Tests
1. Standard shoulder radiographs, including axillary and outlet views (Fig. 11–2), reliably demonstrate the os fragment.
2. If radiographs fail to confirm this diagnosis, computed tomography scanning, with sagittal and axial reconstructions, can ascertain the diagnosis.
3. Technetium-99 bone scans with increased bony uptake at the nonunion site are diagnostic as well.
Differential Diagnosis/Concomitant Injury
1. Acromial fracture from blunt trauma
2. Symptomatic acromioclavicular (AC) joint disease
3. Rotator cuff tear
Special Considerations
If a preacromion fragment is present, simple excision is appropriate. If meso-, meta-, or basi-acromion is present, open reduction and internal fixation is recommended. If impingement is an associated condition, either tilting of the fragment cephalad to increase the subacromial outlet (Figs. 11–3A,B) or combining a decompression with internal fixation is most appropriate.
Preoperative Planning
1. Obtain an adequate outlet view to assess size and tilt of the anterior acromion.
2. If the acromion is thin and curved, one must adjust the surgical technique to achieve adequate bony purchase.
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