SUPERIOR-INFERIOR STABILITY OF THE SHOULDER - ROLE OF THE CORACOHUMERAL LIGAMENT AND THE ROTATOR INTERVAL CAPSULE

Objective: To study the superior-inferior stabilizing functions of the coracohumeral ligament (CHL) and the rotator interval capsule (RIC) w ith use of a material testing machine. Material and Methods: The axial translations of the humerus with the superior-inferior translation fo rce of 30 N applied were recorded under the following joint capsule co nditions: (1) intact, (2) vented, (3) the CHL sectioned, and (4) the R IC incised in six cadaver shoulders, The order of sectioning was chang ed for conditions 3 and 4 in six other cadaver shoulders. Results: Wit h the arm in internal and neutral rotations, venting the capsule signi ficantly increased the superior inferior translation, which was unaffe cted by further sectioning of the CHL and the RIC. With the arm in ext ernal rotation, only the CHL contributed significantly to inferior sta bility, whereas both this ligament and the RIC contributed to superior stability to a lesser degree. Conclusion: The CHL is a stabilizer in superior-inferior directions with the arm in external rotation, and th e intra-articular pressure that is maintained by the intact RIC is a s tabilizer in superior-inferior directions with the arm in internal and neutral rotations. These findings may provide a scientific background to support closure of the interval space to stabilize the shoulder an d may explain part of the superior instability observed in shoulders w ith rotator cuff tears.