Abstract
Purpose
To describe the geometric variables of the posterosuperior humeral-head (Hill-Sachs) lesion and analyze their relationship with patient clinical variables.
Method
Twenty-eight patients with anteroinferior instability and substantial Hill-Sachs lesions were evaluated using arthro-computer tomography (CT) scans. The images were studied with the OSIRIX software, and the following lesion variables were measured: depth, length, width, volume, surface area, and width/depth ratio. Moreover, the ratio of the humeral heads total volume over the volume under its joint surface was calculated to express the lesions severity as the compromised fraction of the humeral heads articular segment. The above data was statistically analyzed in relation to the total number of instability episodes, the distinction between dislocations and subluxations, and the type of sport played.
Results
The lesions had an mean depth of 7.3 mm, length of 19.9 mm, and width of 19.7 mm. The mean loss in humeral-head surface area was 3.83 cm2. The mean loss in humeral-head volume was 1.4 cm3, which equates to 2.2% of the total volume and 6.9% of the volume fraction under the joint surface. A linear correlation was found between lesion volume and the number of dislocations. Another significant relationship was identified between higher width/depth ratios and the subluxation group. None of the other analyses revealed any statistically significant correlations.
Conclusion
In addition to providing useful descriptive data on Hill-Sachs lesions, this study is the first to demonstrate a significant correlation between lesion severity and the number of instability episodes. It also reveals the occurrence of significantly shallower lesions in the shoulders of subluxators compared to those of dislocators, which (as later studies may show) may have important implications on the therapeutic approach to these distinct types of shoulder instability.
