Arthroscopy: The Journal of Arthroscopic & Related Surgery
Level V Evidence With Video IllustrationEvolving Concept of Bipolar Bone Loss and the Hill-Sachs Lesion: From “Engaging/Non-Engaging” Lesion to “On-Track/Off-Track” Lesion
Section snippets
Biomechanical and Anatomic Considerations
It is essential to define the role that the anteroinferior labrum and the bone play in distributing forces across the glenolabral complex during compressive loads, thus guaranteeing an adequate amount of intrinsic stability.
Greis et al.3 showed the effect of progressive labral and bone loss on the articular contact area and pressure across the glenohumeral joint under compressive loads. Loss of the anteroinferior labrum decreased the contact area by 7% to 15% compared with the intact specimens,
The Glenoid Track: Its Relation to Engaging and Non-Engaging Hill-Sachs Lesions
Itoi and associates15 introduced the concept of the glenoid track. Using 3-dimensional (3D) computed tomography (CT) scans, they identified bipolar bone losses that, interacting in different dynamic ways in abduction and external rotation, may require treatment with bone graft. They clarified the contact area of the humeral head and the glenoid from the standpoint of shoulder dislocation. They showed that, as the arm was raised, the glenoid contact area shifted from the inferomedial to the
Bipolar Bone Loss: On-Track Hill-Sachs Lesions Versus Off-Track Hill-Sachs Lesions
The importance of adequate bone as an element of stability has been confirmed; thus its interpretation and evaluation become essential. As mentioned previously, the dynamic interaction of bipolar bone loss assessed at arthroscopy, before Bankart repair, risks reproducing a situation that is only partially reliable because it does not correspond to the anatomic and biomechanical context of a shoulder with an intact capsuloligamentous complex. On the other hand, evaluating the engagement
How to Assess an On-Track/Off-Track Hill-Sachs Lesion by Means of a CT Scan: The Importance of the Hill-Sachs Interval
As previously mentioned, the location of the medial margin of the glenoid track is equivalent to 84% of the glenoid width in cadaveric shoulders15 and 83% in live shoulders (unpublished data, Omori Y, August 2013). For the measurements in live shoulders, a semi-dynamic magnetic resonance imaging (MRI) analysis was used, but the software for this technique is not yet commercially available. We are hopeful that in the near future we can transition from CT scan to MRI scan to obtain our
Arthroscopic Assessment of On-Track/Off-Track Status of Hill-Sachs Lesion
With the foregoing principles in mind, one can systematically evaluate bipolar bone loss arthroscopically to determine whether a Hill-Sachs lesion is on track or off track (Table 1; Video 1, available at www.arthroscopyjournal.org). First, while viewing from an anterosuperolateral portal, one measures the radius of the inferior glenoid by measuring the distance from the bare spot of the glenoid to the posterior glenoid rim (Fig 8). Then, one doubles the radius to obtain the inferior glenoid
The Next Step: A New Paradigm for Addressing Bone Loss in Instability
We believe that anterior instability patients with glenoid bone loss comprising 25% or more of the inferior glenoid diameter, regardless of the size of the Hill-Sachs defect, must be treated with a bone graft to the glenoid. The bone graft will widen the glenoid track to such an extent that in virtually all cases, the Hill-Sachs lesion cannot go off track. If, after grafting of the glenoid, the Hill-Sachs lesion still goes off track when the arm is brought into abduction and external rotation,
Conclusions
On the basis of the foregoing discussion, we prefer to categorize all of our anterior instability patients, regardless of the degree of bipolar bone loss, into 1 of 4 categories (Table 2): group 1, glenoid defect of less than 25% plus on-track Hill-Sachs lesion; group 2, glenoid defect of less than 25% plus off-track Hill-Sachs lesion; group 3, glenoid defect of 25% or more plus on-track Hill-Sachs lesion; and group 4, glenoid defect of 25% or more plus off-track Hill-Sachs lesion. By use of
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The authors report the following potential conflict of interest or source of funding: S.S.B. and G.D.G. receive support from Arthrex.