Glenoid track revisited.

ABSTRACT

The risk of Hill-Sachs lesion (HSL) to cause instability depends not only on the HSL but also on the glenoid size. Clinically, the only method to assess the risk of instability considering the dynamic interaction of both, the HSL together with the glenoid bone loss, is the glenoid track concept. Since it was introduced in a cadaveric study, its clinical efficacy and validity have been reported in the literature. Sometimes, the medial margin of the footprint (lateral margin of the glenoid track) is difficult to identify when a HSL is overriding the footprint. In such cases, we propose a method to draw an imaginary line connecting 2 landmarks. Although 3-dimensional computed tomography is the most accurate and widely used method to assess on/off-track lesions, our interest gradually is shifting toward magnetic resonance imaging (MRI), which has no radiation concern. The current magnetic resonance method is still under way. There are various risk factors influencing the recurrent instability after surgery. The glenoid track concept deals with only 1 of these factors, that is, instability caused by bony lesions. Therefore, the following 2 issues are important 1) how to assess the glenoid track precisely and 2) how to incorporate other risk factors into consideration. The former can be achieved by obtaining the custom-made glenoid track width using not the fixed value of 83%, but more individualized value obtained by measuring the active horizontal extension angle of the opposite shoulder in the sitting position. At the same time, the gray zone (peripheral-track lesion) needs to be clearly defined. The latter can be achieved by incorporating the risk factors other than the bony lesions. One example is the Glenoid Track Instability Management Score (GTIMS), a combination of the glenoid track concept and the instability severity index score. This new scoring system is expected to increase the predictive potential of the scoring system, and accordingly to enhance clinical decision-making.