Bony defects of the posterior-superior aspect of the humeral head occur commonly in association with anterior glenohumeral dislocation. One of the first descriptions of these lesions was by Flower¹ in 1861, with many subsequent investigators reporting on these bony defects of the humeral head.^2,3,4,5 In 1940, Hill and Sachs,⁶ two radiologists, reported that these defects were actually compression fractures produced when the posterolateral humeral head impinged against the anterior rim of the glenoid.

Since then, Hill-Sachs lesions have been found to occur with an incidence between 32% and 51% at the time of initial anterior glenohumeral dislocation.^6,7,8,9 In shoulders sustaining a Hill-Sachs lesion at the initial dislocation, there exists a statistically significant association with recurrent dislocation.¹⁰

Although Hill-Sachs lesions are common after anterior glenohumeral dislocations, there are relatively few papers describing specific treatments for these humeral head defects. In general, specific surgical procedures to address Hill-Sachs lesions have not been recommended in the initial surgical management of recurrent anterior dislocations because the majority of these lesions are small to moderate in size and do not routinely cause significant symptoms of instability. In fact, Bankart¹¹ himself did not ascribe any significance to Hill-Sachs lesions observing “nothing can be done about them if they are found.”

Nevertheless, a certain subset of patients exists with more significant bony defects and ongoing symptoms of “instability” and/or painful clicking, catching, or popping, sometimes occurring even after surgical procedures are directed at treating their anterior instability. Rowe et al.¹² found a 76% incidence of Hill-Sachs lesions in patients evaluated for recurrent anterior dislocation of the shoulder after surgical repair, and stated “a Hill-Sachs lesion of the humeral head may play a role in the development of recurrent dislocation after surgical repair.”

The concept of “articular arc length mismatch” has been recently put forth to explain the ongoing sensation of catching or popping arising with the shoulder in the abducted and externally rotated position in patients with large Hill-Sachs lesions.¹³ Furthermore, many of the patients with these symptoms have undergone previous anterior stabilization procedures. This phenomenon occurs mainly in a position of abduction and external rotation of the shoulder. In this position, a large “engaging” Hill-Sachs lesion encounters the anterior glenoid rim, resulting in the rim “dropping into” the Hill-Sachs lesion. This phenomenon can and does occur in the presence of intact or repaired glenohumeral ligaments. The sudden loss of a segment of articular arc on the humeral side of the joint presents an abrupt “flat spot” to the glenoid, causing an uneasy sensation in the patient that feels much like subluxation.

It is also important to differentiate between “engaging” and “nonengaging” Hill-Sachs lesions.¹⁴ In an engaging Hill-Sachs lesion, the long axis of the defect is parallel to the anterior glenoid with the shoulder in a functional position of abduction and external rotation. This leads to the Hill-Sachs lesion engaging or catching the corner of the glenoid. Conversely, a nonengaging Hill-Sachs lesion is one that either fails to engage the glenoid in a functional arm position or engages the glenoid only in a nonfunctional arm position. In the first type of nonengaging lesion, the long axis of the Hill-Sachs lesion is tangential to the anterior glenoid with the shoulder in a functional position of abduction and external rotation. The Hill-Sachs defect passes diagonally across the anterior glenoid with external rotation; therefore, there is continual contact of the articulating surfaces and no engagement of the Hill-Sachs lesion by the
anterior glenoid. In the second type of nonengaging lesion, the Hill-Sachs defect “engages” only in a position that is considered “nonfunctional” (i.e., shoulder in some degree of extension, or in abduction of less than 70 degrees). Since symptoms are greatest if the engagement occurs with the shoulder in a functional position, involving a combination of flexion, abduction, and external rotation, this second group of Hill-Sachs lesions, while technically engaging, has been defined as functionally nonengaging.

Hence, when a patient has symptomatic anterior instability associated with an engaging Hill-Sachs lesion with an articular-arc deficit, treatment must be directed at both repairing the Bankart lesion, if present, and preventing the Hill-Sachs lesion from engaging the anterior glenoid.

We believe that the treatment of symptomatic anterior glenohumeral instability, involving an engaging Hill-Sachs lesion with an articular-arc deficit, can best be accomplished with a technique of anatomic allograft reconstruction of the humeral head using a side and size-matched humeral head osteoarticular allograft. This technique involves an anatomic reconstruction, which eliminates the structural pathology, while maintaining the range of motion of the glenohumeral joint.

The indications for anatomic allograft reconstruction of the humeral head are ongoing symptomatic anterior glenohumeral instability or painful clicking, catching, or popping in a patient with a large engaging Hill-Sachs lesion. We have most commonly used this technique as a secondary procedure in patients who have failed previous soft-tissue stabilization procedures. However, if a large engaging Hill-Sachs lesion is identified prior to undergoing initial surgical treatment, this technique could be performed as part of the primary anterior stabilization procedure. In patients at high risk of redislocation (e.g., epilepsy with recurrent anterior instability and large Hill-Sachs defects) this procedure can be performed at the primary operation.

Contraindications to this procedure include routine medical co-morbidities precluding an elective surgical procedure with general anesthetic, existing infection, or presence of a nonengaging Hill-Sachs lesion.

All patients are initially evaluated with complete history and physical examination. Specifics of the history include questioning for the mode of onset and timing of initial symptoms and for the details of present symptoms including pain, frequency, instability, and level of function. In addition, all previous surgical procedures performed on the shoulder should be noted. Most patients will give a history of recurrent dislocations or multiple surgical attempts to correct the instability. The patients have usually sustained glenohumeral dislocations as a result of significant trauma. Another group of patients that can be encountered is patients with grand mal seizures and recurrent anterior dislocations. These patients usually have fairly large Hill-Sachs defects and significant apprehension about the use of their arms. As a result of the violence of the dislocations, the amount of bone pathology present, and the inability to predict the onset of epileptic events, it is worth considering treating this group of patients with an allograft reconstruction of the humeral head defect at the index procedure as soft tissue repairs alone may not be enough to prevent recurrent injury.

Physical examination should focus on inspection for previous scars, a thorough determination of active and passive range of motion, evaluation of the integrity and strength of the rotator cuff, and a detailed examination for glenohumeral laxity in the anterior, posterior, and inferior directions. Examination for apprehension should be performed in multiple positions as the group of patients with large Hill-Sachs lesions usually exhibits apprehension that often occurs with the arm in significantly less than 90 degrees abduction/ 90 degrees external rotation.

Preoperative imaging includes a comprehensive plain film evaluation with anteroposterior (AP), true AP, axillary, and Stryker Notch views of the involved shoulder (Fig. 19-1). All patients require a preoperative axial imaging study (computed
tomography [CT] or magnetic resonance imaging [MRI]) to more fully define the bony architecture of the glenoid and humeral head and specifically the details of the Hill-Sachs lesion (Fig. 19-2). One must be careful in the interpretation of these studies since the plane of the Hill-Sachs defect is oblique to the plane of the axial image. Therefore, the size of these defects is often underestimated in standard axial imaging. Three-dimensional reconstruction can be a useful tool to aid in more clearly defining the size and location of the defect and to provide an estimation of the amount of the articular surface involved.