IS THE HUMERAL HEAD'S BARE AREA LARGER IN PATIENTS WITH ANTERIOR INSTABILITY? RESULTS OF A COMPARATIVE ARTHROCT-SCAN STUDY

The bare area of the humeral head is limited in front by the cartilage and backwards by the insertion of the Infra Spinatus tendon. There are few references in the current literature. The aim of this work was to precise the anatomic description of the bare area and to compare the size of this area in patients with anterior shoulder instability and patients without anterior shoulder instability. Material and method We have proceeded first to an anatomic study to precise the limit of the bare area. The second part of this study was a retrospective and prospective comparative arthro CT-scan study in two groups of patients. The first group (group 1) had 48 patients, going to have anterior instability surgery. The second group (group 2) had 38 patients, without shoulder instability. Mean age was respectively 28.2 years (range: 19–48) in group 1; and 39.3 years (16–69) in group 2. The size of the bare area was measured on the axial injected CT cut passing by the larger diameter of the humeral head, The size of the bare area was definite by the angle between the line connecting the centre of the head to the posterior limit of the cartilage and the line connecting the centre of the head to the anterior point of the Infra Spinatus tendon. The reproducibility of the measure has been evaluated by a Bland and Altman test and an intra class correlation test. The measures were realised by two independent surgeons in a blind manner. The results where compared by a Student test with a threshold at 5%. Results In the anatomic part of this study, the average angle of the bare area was 32.7° equal to 13.7mm wide. Mean intraobserver variability was 4° (range: 0 to 20°) (NS) and mean interobserver variability was 4° also (range: 0 to 20°) (NS). Mean size of the bare area was 49.6° eaqual to 19.8mm wide [range 25° to 70°] in group 1 and 33.2° equal to 13.5mm wide [range 21° to 60°] in group 2 (p Discussion Our measures were reproducible. This study confirms our hypothesis: the bare area is significantly larger in shoulders suffering of anterior instability, but we cannot yet tell if this result is a consequence or a risk factor of anterior shoulder instability.