Glenoid track and subcritical Hill-Sachs lesion

Abstract

Background: We have proposed the concept of glenoid track ("on-track/off-track" lesion) to evaluate the risk of engagement of the Hill-Sachs lesion with the glenoid after arthroscopic Bankart repair. This concept has been widely used and many clinical validation studies have been reported. To measure the glenoid track width, we have recommended to use 3-dimensional computed tomography (CT) images. However, the CT method has the issue of radiation exposure and involves time and effort to make 3-dimensional CT images from 2-dimensional images. For these reasons, there are several reports describing the measurement method using magnetic resonance imaging. Recently, the threshold of the critical glenoid bone loss becomes lower. A zone of bone loss below the critical size is called "subcritical bone loss", which might be related to deterioration of quality of life and bone grafting is recommended. We applied the concept of "subcritical bone loss" to the glenoid track. Patients with "on-track" lesions can be divided into 2 subgroups: those with a "peripheral-track" lesion (most medial 1/4) and those with a "central-track" lesion (the rest 3/4). More recently, similar evaluation methods to evaluate the risk of "off-track" lesions have been reported: ''distance to dislocation'' and "Hill-Sachs interval/glenoid track ratio". Also, similar concept to "peripheral-track" lesion, "near-track" lesion was reported. The concept of "peripheral-track" lesion is a concept of assessing an "on-track" lesion which is very close to the medial margin of the glenoid track (subcritical bone loss).

Methods: Similar evaluation methods to evaluate the risk of "off-track" or "peripheral-track" lesions were proposed in the literature. A review was performed by searching PubMed. Journal articles published between January 2014 and January 2023 were taken into account. They were compared and their differences were explained.

Results: The "near-track" lesion concept is similar to "peripheral-track" lesion. However, the cutoff value is different: Hill-Sachs occupancy ≥ 75% is the "peripheral-track" lesion, whereas "distance to dislocation" < 8 mm is the "near-track" lesion.

Conclusion: We introduced update of the glenoid track concept including the evaluation method, peripheral-track lesion, and its clinical application.

Keywords: Anterior shoulder instability; Central-track lesion; Glenoid track; Hill-Sachs lesion; Off-track lesion; Peripheral-track lesion.

Figure 1

“Peripheral-track” lesion. The glenoid track was divided into 4 zones based on the percentage of Hill-Sachs occupancy: zone 1, < 25%; zone 2, 25% to < 50%; zone 3, 50% to < 75%; and zone 4, ≥ 75%. This Hill-Sachs lesion in zone 4 is called “peripheral-track” lesion.

Figure 2

“Distance to dislocation”. “Distance to dislocation (DTD)” is defined as the distance between the medial edge of the Hill-Sachs lesion and the medial margin of the glenoid track.

Figure 3

“Hill-Sachs interval/glenoid track (H/G) ratio”. H/G ratio is defined as Hill-Sachs interval (A) divided by glenoid track width (B).

Figure 4

Glenoid track, “central-track”, and “near-track” lesion in one shoulder. The width of the glenoid is 25 mm in one shoulder and the glenoid track width is calculated: 25 × 0.83 = 21 mm. The “central-track” width is calculated: 25 × 0.75 = 19 mm. “On-track” lesions with a distance-to-dislocation of < 8 mm is defined as ‘‘near-track” lesion. In this shoulder, if we choose the value of 8 mm to judge a subcritical bone loss, we may overdiagnose it.