ACR Codes: 4.4
Anterior dislocations are produced by complex forces acting on the humerus, including abduction and external rotation. The Hill-Sachs fracture results from this anterior dislocation (97% vs. 3%) with compression of posterolateral aspect of the humeral head by the inferior glenoid labrum. Hill-Sachs deformities occur in 35-40% of anterior dislocations and up to 80 % of recurrent dislocations. Hill-Sachs fractures can occur with subluxations, or single or multiple dislocations. The dislocation may also cause a Bankart fracture at the impact site on the glenoid. This is a fracture of the anterior aspect of the inferior rim of the glenoid caused by the anterior movement of the humeral head and is best seen on the anteroposterior projection with the arm in the neutral position. If radiographs at presentation show no dislocation, the presence of either Hill-Sachs deformities or Bankartâ€™s fractures are indicative of a prior dislocation. MRI is the best imaging modality for identifying cartilaginous and osseous Hill-Sachs deformities and associated tears of the anterior glenoid labrum. The contour defect of both cartilage and bone at the superior aspect of the humeral head posterolaterally represents the Hill-Sachs deformity and the high signal intensity separating the cartilaginous labrum from the bony labrum represents the tear â€“ the Bankart lesion.
The younger the patient when the first dislocation occurs, the greater is the probability that dislocation will recur. Thus, patients 20 years old or younger have a 80-90% chance of lifetime recurrence, those 30 or younger have a 60% recurrence rate, and of those 40 and older at time of first dislocation, have a 10-15% probability of recurrence.
Reference(s): Stoller, David W. Magnetic Resonance Imaging in Orthopaedics & Sports Medicine. Lippincott, 1993.
Rogers, Lee. Radiology of Skeletal Trauma. 2nd ed.
Wheeless Textbook of Orthopaedics. â€śAnterior Instability of the Shoulderâ€ť. 1996.
Burkhart, Stephen S. â€śThe Arthroscopic treatment of Traumatic Anterior Instabilityâ€ť. http://www.isakos.com/innovations/antinst.html