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Humeral head defects are commonly present in patients with shoulder instability. The defects are usually small and carry the eponym Hill-Sachs lesion when secondary to anterior instability and reverse Hill-Sachs lesions when secondary to posterior instability.
Although quite ubiquitous in recurrent anterior shoulder instability, the management of large Hill-Sachs defects remains controversial especially in the absence of an associated glenoid defect.
When the glenohumeral joint dislocates, the Hill-Sachs defect can occur at any of a variety of angles as determined by the position of the humerus at the time of dislocation.
Some Hill-Sachs lesions will engage the anterior glenoid rim when the glenohumeral joint is in a position of abduction and external rotation. Burkhart has described these as “engaging” Hill-Sachs lesions. They can be defined as defects in which the long axis of the humeral head defect aligns parallel to the anterior glenoid rim, when the shoulder is in a position of abduction and external rotation.
Such configurations have been found to be particularly prone to recurrent dislocation and subluxation after arthroscopic repair. Furthermore, if a large Hill-Sachs lesion is combined with a glenoid defect, they can be particularly problematic. Hovelius et al. It found significant Hill-Sachs defects in 54% of his study population of 247 individuals with primary anterior instability, and he also found a significantly higher risk of recurrence when a Hill-Sachs defect was present. Rowe et al.
It also suggested that a Hill-Sachs lesion could be a reason for failure after open surgical repair. Other authors however have found that the presence and magnitude of a Hill-Sachs lesion did not influence the outcome after open Bankart repair.
With the “nonengaging” Hill-Sachs lesion, the long axis of the Hill-Sach’s defect crosses diagonally across the glenoid rim with the arm in abduction and external rotation so that it never “engages” the glenoid rim. In these types of defects, there is a continuous smooth articular contact throughout the range of motion.
According to Burkhart, such shoulders with nonengaging Hill-Sachs lesions are not at significant risk for recurrence when repaired arthroscopically, and therefore patients with these types of humeral lesions are good candidates for arthroscopic repair.
Clinically significant, large humeral head defects are fortunately quite rare. They are usually diagnosed by recurrent symptoms of instability, by locking, or by three-dimensional imaging studies. The morphology of the Hill-Sachs defect has been suggested by some as a prognostic factor for the degree of instability.
Burkhart and Danaceau have suggested that the mismatch in the articular arc that occurs with a Hill-Sachs lesion is the important pathoanatomic feature. Most Hill-Sachs lesions are simply ignored at the time of surgery and the anterior capsule and labrum are addressed with an anatomic repair, as discussed previously.
When the bone defect is large, however, the bone defect may need to be addressed. There are unfortunately no guidelines from the literature about what size defect needs surgical treatment. The authors do become concerned when the defect exceeds 20 to 30% of the humeral head as measured on CT scan or when a Hill-Sachs lesion is combined with a glenoid defect.
Surgical options for management of humeral head defects (Hill-Sachs lesions) include reconstructing the humerus with an allograft to restore the humeral articular arc, reconstructing the glenoid with an anterior bone graft to lengthen the glenoid articular arc and prevent the humeral defect from engaging the glenoid rim, or rotating the humeral head with an osteotomy to move the defect so that it does not come in contact with the anterior glenoid.
If there is an associated glenoid defect, the authors recommend that the glenoid be reconstructed first; if the humeral defect is still significant, it can be reconstructed with an allograft. Unfortunately, the evidence for each of these approaches is largely anecdotal and based on small series or case reports.
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