[A biomechanical study on coracoacromial ligament as anterosuperior restraint of shoulder joint].
OBJECTIVE
To determine the change in humeral head anterosuperior migration after releasing the coracoacromial ligament in shoulders from cadavers with simulated intact or irreparable reared rotator cuff, to provide biomechanical basis for preserving the coracoacromial ligament or not during hemiarthroplasty.


METHODS
Twelve fresh-frozen cadaveric glenohumeral joints of adult preserving the scapula, upper 2/3 of the humerus, articular capsule and the coracoacromial ligament, were divided into 2 groups. The suprascapularis was preserved in group A (6 shoulders) and excised in group B (6 shoulders). Positioning the joint in a combination of 30 degrees extension, 0 degree abduction and 30 degrees external rotation, and imposing a 50 N axial compressive load to the humeral shaft, the anterosuperior displacement of the humeral head were measured before and after excising the coracoacromial ligament.


RESULTS
In group A, the displacement of the humeral head was (5.96 +/- 0.77) mm with intact coracoacromial ligament and (6.83 +/- 0.84) mm after transecting the ligament. In group B, the displacement of the humeral head was (8.07 +/- 2.46) mm with intact coracoacromial ligament and (9.92 +/- 3.29) mm after transecting the coracoacromial ligament. So the mean increase of anterosuperior migration of the humeral head was (0.88 +/- 0.34) mm (P < 0.01) in group A, and (1.85 +/- 0.99) mm (P < 0.01) in group B, which was greater than the former (P < 0.05).


CONCLUSIONS
The coracoacromial ligament restrained anterosuperior translation of the humeral head, especially for patients with rotator cuff deficiency, so it should be preserved as far as possible during hemiarthroplasty.
Wang
Juan
J
Department of Orthopaedics, West China Hospital, Sichuan University, Chendu Sichuan, 610041, P.R. China.
Huang
Fuguo
F
D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D017746:Joint Capsule / Q000502:physiology*; D008022:Ligaments / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*