Assessment of Humeral Head Bone Loss
A HSL is a compression fracture of the posterolateral humeral head that results from impaction of the humerus on the anterior glenoid rim during an instability event. HSLs are common after anterior shoulder instability events, with an incidence nearing 100% in patients with recurrent instability. In addition to a standard shoulder series, specialized radiographs of the posterolateral humerus may assist in the identification of HSLs. The Stryker notch view is one such projection commonly used for this purpose (Figure 8). The patient is typically standing with the affected side rotated 30 to 45° toward the radiograph tube and the injured arm fully abducted and internally rotated. Although the size of a HSL can be approximated by comparing the depth of the lesion with the radius of the humeral head on an internal rotation radiograph, CT and MRI provide more accurate and reliable quantification (Figure 9).
Patient positioning for a Stryker notch view radiograph (A) with radiograph demonstrating a Hill-Sachs lesion of the posterosuperior humeral head (B). Reference: Pavlov H, Warren RF, Weiss CB, Jr, Dines DM: The roentgenographic evaluation of anterior shoulder instability. Clin Orthop Relat Res 1985:153–158. Rockwood and Green Fractures in Adults, 9th edition.
Anteroposterior radiograph of the shoulder where the maximum depth of the Hill-Sachs lesion (P) is compared with the radius of the humeral head (R) to estimate percent bone loss. Reference: Maio M, Sarmento M, Moura N, Cartucho A: How to measure a Hill-Sachs lesion: a systematic review. EFORT Open Rev 2019;4:151- 157.
As the contribution of humeral head bone loss to glenohumeral instability has been better elucidated, increased emphasis has been placed on using advanced imaging to quantify humeral head defects during the diagnostic workup for patients with shoulder instability. Similar to glenoid bone loss, CT is the current benchmark for localizing and measuring humeral head bone loss and is indicated in patients with recurrent instability, patients with large HSLs on radiographs, and patients who have failed prior shoulder stabilization procedures. 3D CT, in particular, is a reliable, effective, and accurate method for measuring the size of HSLs. Ozaki et al compared humeral head bone loss identified on 3D CT with intraoperative findings and found a sensitivity and a specificity of 76.3% and 100%, respectively. Of the HSLs that were missed on 3D CT, all but one were either chondral lesions or osseous lesions with a depth of less than 6.5%. In addition, high intraobserver reliability was demonstrated with measurements of HSL length, width, and depth.
Overall, few studies have assessed the use of MRI for evaluating HSLs. Early research by Kirkley et al demonstrated only moderate agreement (kappa value 0.44) between preoperative MRI and arthroscopy findings in terms of identifying and quantifying humeral head defects. However, 3D MRI appears to offer enhanced detection of HSLs, allowing for the quantification of humeral head defects comparable with that of 3D CT. As discussed previously, although MRI has the added benefits of allowing for the evaluation of soft-tissue structures and eliminating radiation, 3D MRI is expensive and not yet routinely used in clinical practice.
Quantification of Humeral Head Bone Loss
Although a HSL may have little clinical significance in isolation, recurrent instability can arise through engagement of a HSL with the rim of the glenoid as described by Burkhart and De Beer. HSLs involving less than 25% of the humeral head were thought to pose little risk of recurrence. It is now well understood that both size and location influence the risk of engagement, with larger and medial HSLs more likely to engage the glenoid. Moreover, HSLs are more likely to engage in patients with bipolar bone loss (i.e., bony defects involving both the humeral head and the glenoid). Cho et al described a method of calculating the size of the HSL by using a virtual circle including the articular surface of the humeral head and measuring the depth and width of the defect in multiple planes to determine percent bone loss (Figure 10). The authors observed that in addition to greater size, horizontal orientation of a HSL relative to the humeral shaft also increased the risk of engagement.
J Am Acad Orthop Surg. 2022;30(12):563-572. © 2022 American Academy of Orthopaedic Surgeons