The Geometry of the Hill-Sachs Lesion (Hsl) and Its Implications in the Acute Injury and Its Effect in Recurrent Episodes

Vidal Barchilon 1 Roy Grinberg 2 Radel Ben Av 2 Meir Nyska 1
1Orthopaedic Surgery, Meir Hospital, affiliated to Sackler School of Medicine, TAU University, Kfar Saba, Israel
2Computer Science, Azrieli College of Engineering, Jerusalem, Israel

Purpose: In order to understand the clinical implications of the geometry of HSL in the acute injury and recurrent episodes of gleno-humeral instability.

Materials and Methods: In 41 consecutive cases of anterior shoulder instability 3D-CT reconstructions of the HSL were analyzed with software.
The following values were calculated: Max. Width is the maximum width of the HSL as a percentage of the diameter of the humeral head. Max. Depth is the maximal depth of the HSL as a percentage of the humeral head radius. Slope is the acute angle between the long axis of the HSL and the longitudinal axis of the humeral head. The Humero-glenoid collision angle, was deduced from the slope. Critical angle is the angle between the most prominent anterior point of the humeral head and the anterior edge of the HSL.

Results: Max. HSL Width was 2.58%±1.32. Max. Depth was 19.70%±7.40. Critical Angle, was 68.12°±17.63. We found two types of HSL according to the slope. Type A (35 cases). Supero-lateral to infero-medial. The angle 30.02°±9.67. Type B (6 cases). Supero-medial to Infero-lateral The angle 29.66°±17.99.

Conclusions: In acute injuries, the collision angle between the humeral head and the anterior Glenoid in type A-HSL may be -30.02° or 149.98°± 9.67 while in type B-HSL It may be 29.66° or 209.66° ± 17.99. The rotation of the humerus at the time of impact was 68.120±17.63.
In recurrent episodes position of the arm in Type A-HSL is 30.02°±9,67 of extension while in Type B-HSL it is 29.66°±17.99 of flexion. The amount of Abduction depends on the proximity of the HSL to the apex of the humeral head.