Thank you to the AOSSM for the opportunity to present our research. The co-authors' disclosures can be found online. So for over 20 years now, we've been learning about the importance of evaluating bipolar shoulder bone loss and treating shoulder instability. In 2007, Yamamoto et al. introduced the glenoid track concept as a method to evaluate which shoulders are at highest risk of recurrent dislocation following arthroscopic bankart repair by determining whether a shoulder measure is on track or off track. More recently, however, studies have come out to show that not all on-track shoulders are necessarily created the same. Yang et al. in 2018 and Yamamoto et al. looked at a cohort of on-track shoulders who'd undergone bankart repair, looking at the ratio of the Hill-Sacks interval to the glenoid track. And they showed that the higher that ratio, the greater the risk of recurrent dislocation and lower the patient outcome scores. In 2020, Lee et al. introduced the concept of distance to dislocation. This is calculated by subtracting the Hill-Sacks interval length from the glenoid track calculation. And essentially, distance to dislocation tells you how close an on-track shoulder is to being off track. Using receiver operative curve, they determined that at around about 8 millimeters best predicts bankart repair failure. So the purpose of our study was to quantify the rate of recurrent shoulder dislocation in relation to distance to dislocation in patients with on-track Hill-Sacks lesions who'd undergone primary arthroscopic bankart repair. And our hypothesis was that as distance to dislocation approaches zero, the threshold between on-track and off-track, the rate of recurrent dislocation would increase significantly. As a retrospective study, we evaluated 249 patients who'd undergone primary bankart repair from 2007 to 2019. Inclusion criteria included ages 12 to 40 at time of surgery and on-track Hill-Sacks lesions as measured on a preoperative MRI and minimum of two-year follow-up. We excluded patients with greater than 20% going to bone loss prior ipsilateral shoulder surgery, concomitant procedures, a diagnosis of a connective tissue disorder, and less than three-anchor labral repair. The variables we looked at included age, gender, a number of dislocations prior to surgery. Dislocation and collision sports, and the primary outcome was recurrent shoulder dislocation. We measured glenoid track and Hill-Sacks interval on T2 MRIs using the circle method to measure the glenoid bone loss and axial images to measure the largest Hill-Sack interval distance. Our final analysis included 188 subjects with a mean follow-up of 67 months, 15% of which sustained a recurrent shoulder dislocation. If you look at the baseline characteristics broken down by postoperative recurrent dislocation versus no dislocation, the patients who sustained a recurrent dislocation were younger, had had multiple dislocations prior to surgery, and all measures of bone loss, percent glenoid bone loss, Hill-Sacks interval length, and distance to dislocation were all more severe in the failure cohort. Multivariate regression modeling showed that younger age, smaller distance to dislocation, and having multiple dislocations prior to surgery were all predictive of surgical failure. Now here is the failure rate broken down by distance to dislocation at 2 millimeter threshold, and this is the rate of failure below that particular threshold. The key findings when you look at the data in this way are that no patient with a distance to dislocation greater than 24 millimeters sustained a recurrent dislocation. So shoulders that are very on track have a very low risk of recurrent dislocation. However, as our hypothesis predicted, as distance to dislocation decreases, the rate of failure increases significantly. At around a distance to dislocation of about 10 millimeters, that rate of failure begins to increase exponentially. Here's that same concept shown graphically. This is the multivariate regression model data showing the probability of failure for each individual within the study with the best fit line, and again it shows that that best fit line shows that around 10 millimeters of distance to dislocation, the rate of failure begins to increase exponentially as the value approaches zero. We then did subgroup analysis of collision versus non-collision athletes. A key finding here is that if you look at the non-collision athletes, as you would expect, as distance to dislocation increases, the rate of failure in the non-collision athletes decreased significantly, down to zero. So only one non-collision athlete with a distance to dislocation greater than 14 millimeters sustained a recurrent dislocation. However, if you look at the collision sport athletes, their rate of dislocation remained elevated between 13 and 15 percent, and the difference at greater than 14 millimeters distance to dislocation, the rate of dislocation was higher in the collision sport athletes when compared to the non-collision subjects. Limitations to our study include, obviously, it's retrospective data, so there's implicit surgeon bias, possible selection bias. We didn't have accurate patient-reported outcomes or return to sport data. It's not really a limitation, but just be aware that the mean age in our cohort was approximately 20 years, and 33 percent of the patients did participate in collision sports. So it may not be generalizable to all populations when looking at this type of pathology. Conclusions from our study are that as distance to dislocation approaches zero, a patient's risk of recurrent shoulder dislocation increases significantly. So in other words, the closer an on-track shoulder is to being off-track, the higher the risk of recurrent dislocation. At a distance to dislocation of approximately 10 millimeters, that risk begins to increase exponentially as it approaches zero. And perhaps the most important finding is this suggests that the gonad-track concept is perhaps best viewed as a continuum of pathology rather than a binary outcome of on-track versus off-track. In collisions, sport athletes have a higher risk of recurrent dislocation at distance to dislocation values greater than 14 millimeters when compared to non-collision athletes. Thank you.

shoulder instability

glenoid track concept

recurrent dislocation

arthroscopic bankart repair

Hill-Sacks interval