Paper 70: "Distance to Dislocation" as a Predictor of Surgical Failure Following Primary Arthroscopic Anterior Labral Repair: Rethinking the Glenoid Track Concept

OBJECTIVES: Larger amounts of bipolar bone loss have a strong association with shoulder re-dislocation following arthroscopic labral repair. Development of the Glenoid Track (GT) concept has helped propose bone loss cut-offs for shoulders that should not be managed with arthroscopic labral repair alone. Recent literature has suggested the use of the glenoid track as a continuous variable rather than a binary “on-track/off-track” concept. The re-dislocation risk for “on-track” shoulders with smaller distances to dislocation (DTD), or “near-track” shoulders, has not been previously described. We hypothesized that decreasing DTD, or on-track lesions approaching an off-track lesion, would result in an increased risk of failure following arthroscopic Bankart repair alone. METHODS: We performed a retrospective analysis of 197 patients who had undergone primary arthroscopic anterior labral repair between 2007 and 2019 with minimum 2-year follow-up. Glenoid bone loss using a perfect-circle method and Hills-Sachs (HS) interval, were measured from pre-operative MRIs. GT was calculated using previously described methods. Surgical failure was defined as a patient who re-dislocated their shoulder following surgery. DTD was calculated by subtracting the HS measurement from the GT calculation. Patients with “off-track” lesions (negative DTD), and those who had undergone a concomitant arthroscopic remplissage were excluded. We performed a logistical regression model to evaluate the relationship between surgical failure and DTD, glenoid bone loss, Hill-Sachs lesion size, number of anchors used, and patient age. We then created a risk estimator tool that calculates the risk of dislocation with DTD as a continuous variable. RESULTS: Twenty-eight patients (14%) sustained recurrent shoulder dislocations following anterior shoulder labral repair. Average follow up was 7.8 years and there were no demographic differences between those with recurrence and those without (p>0.05). All patients had less than 25% glenoid bone loss (range 0-23%). Increased DTD (p < 0.0005) and glenoid bone loss (p < 0.0005) were independent predictors of surgical failure. After adjusting for glenoid bone loss and patient age, logistic regression modeling showed that for every 1mm decrease in DTD, there was an associated 13.6% increase in re-dislocation risk (p = 0.003). Patient age, Hill-Sachs length, participation in collision sports, and number of anchors used were not significantly associated with failure risk (p>0.05). A DTD <10mm had a 4.26 times greater odds of failure compared to those with DTD >10mm (OR 4.26; 95% CI 1.57-11.65; p = 0.005). The risk estimator tool developed using a logistic regression modeling demonstrated a 19% risk of failure for DTD 10mm, 26% risk for DTD 8mm, 36% risk for DTD 6mm, 49% risk for DTD 4mm, and 67% risk for DTD 2mm after adjusting for glenoid bone loss and patient age (Figure 1). CONCLUSIONS: The main finding of this study was that on-track lesions approaching off-track lesions, the so-called “near track” lesions, are associated with an exponentially increased risk of recurrent dislocation following primary arthroscopic anterior stabilization with labral repair alone. Furthermore, DTD values of <10mm were associated with the highest odds ratios for failure and were 4 times more likely to fail than for patients with DTD values >10mm. All of the patients included in this analysis had “on-track” shoulder lesions and <25% glenoid bone loss. Historically, these values have been identified as “cut-offs” used to identify patients who can be treated successfully with arthroscopic labral repair without a remplissage or other augmentation. DTD is a simple calculation for bipolar bone loss that can be used to predict risk of recurrent dislocation. Our results demonstrate potential pitfalls in making treatment decisions for bipolar bone loss using a binary “on-track, off-track” construct. Rather, the glenoid track concept applied as a continuum may be more useful for optimizing treatment. “On-track” shoulder lesions <10mm with diminishing DTD have a substantially higher risk of surgical failure with arthroscopic labral repair alone. As the DTD approaches 0mm (“off track lesion”), the risk of failure increases exponentially. When making treatment decisions for shoulder instability, bipolar bone loss should be viewed as a continuum rather than discreet “on-track, off-track” entities. For high-risk patients with a DTD approaching 0mm, additional augmentation with remplissage or open approaches should be considered. DTD can be used to estimate patient’s risk of recurrent dislocation following primary arthroscopic anterior labral repair for treatment of anterior shoulder instability. Application of this calculation would help surgeons decide the best surgical treatment for patients following anterior shoulder dislocation and can be particularly valuable for high risk patients. Understanding the association between lower DTD values and failure can also help inform the surgeon and patient regarding the risks and benefits of available treatment options.