The subcoracoid space. An anatomic study.

Soft tissue impingement under the coracoid process has recently been identified as a cause of painful shoulder disability. In this study the normal space between the humeral head and the coracoid process in two functional positions of the arm was measured in an attempt to delineate anatomic risk factors predisposing to subcoracoid impingement. Forty-seven normal shoulders were studied by computerized tomography (CT) in adduction, 20 additionally in forward flexion/internal rotation, which is the position most frequently causing subcoracoid impingement. The distance between the humeral head and the coracoid tip averaged 8.7 mm for the adducted arm and 6.8 mm for the flexed arm. Modifications of the coracohumeral relationship were found to affect the subcoracoid clearance roughly 1.5 times more in flexion than with arm at the side. Subcoracoid impingement appeared particularly likely during forward flexion of a shoulder with a coracoid tip close to the scapular neck and projecting far laterally.