Effect of subacromial decompression on laxity of the acromioclavicular joint: biomechanical testing in a cadaveric model.

Subacromial decompression is a well-accepted treatment for impingement syndrome when nonoperative therapies have failed. However, recent clinical data have raised concern that arthroscopic subacromial decompression may lead to laxity of the acromioclavicular joint and, potentially, predispose patients to late postoperative acromioclavicular joint pain. Our goal was to determine whether subacromial decompression with co-planing of the distal clavicle alters the laxity, or compliance, of the acromioclavicular joint in a cadaveric model. Eighteen cadaveric shoulders were dissected and tested in a specially designed rig, driven by a hydraulic materials testing machine. One hundred-Newton loads were applied to the distal clavicle in the superior, posterior, and anterior directions, while acromioclavicular joint motion was recorded with a 3-dimensional infrared optical measurement system. Acromioplasty was performed with a posterior-referenced cutting block technique and included co-planing of the distal clavicle in all specimens. Joint compliance before and after subacromial decompression was compared with the paired t test. Subacromial decompression increased anteroposterior compliance by 13%, from 8.8 +/- 2.9 mm (mean +/- SD) in the intact joint to 9.9 +/- 3.1 mm (P =.001). Subacromial decompression increased superior compliance by 32%, from 3.1 +/- 1.5 mm in the native specimen to 4.1 +/- 1.8 mm (P =.03). These observations may have implications for the technique of acromioplasty. Although the immediate result of acromioplasty with co-planing appears to be an increase in the compliance of the acromioclavicular joint, the clinical significance of these findings has yet to be determined.