The Influence of Laxity on Injury Severity at the Time of Anterior Shoulder Stabilization Surgery

Abstract

Objectives: To determine whether a greater degree of translation measured under anesthesia during anterior shoulder stabilization surgery was associated with greater injury severity, more dislocations in the previous year, and a greater duration of injury. Methods: This study evaluated Multicenter Orthopaedic Outcomes Network (MOON) Shoulder Group shoulder instability participants who underwent anterior shoulder stabilization surgery between October 2012-September 2016. Surgeons measured shoulder mobility under anesthesia following a standardized protocol and graded translation as 0, 1+, 2+ or 3+. Using this measure, translation was defined as having a grade ≥2+. Labral tear length, duration of injury, and number of times dislocated in the previous year were compared between mobility groups using the Wilcoxon Rank Sum Test while categorical variables were compared between groups using the chi-square or exact test. Logistic regression was also used to model the relationship between mobility grade as an ordered variable and presence of >10% bone loss as well as HSL >20%. Age and BMI were compared between groups using t-tests. Results: A total of 679 participants (19% women) with an average age of 24.8±9.5years and BMI of 25.4±4.4 kg/m2were included in analyses. Mobility grade groups <2 had a slightly higher BMI than ≥2 (27.0±5.2 vs 25.0±4.1kg/m2, <0.01) but did not significantly differ in age (26.0±10.7 vs 24.4±9.0yrs, p=0.31) or proportion of women (14% vs 20%, p=0.12), respectively. Labral tear length (median: 126, range: 0-360°) and the proportion with >10% bone loss (5.8% vs 9.8%) did not significantly differ between groups (all p>0.05). However, there was a greater proportion of HSL >20% in the ≥2 (3.2%) vs <2 (0%, p<0.01) groups. In addition, mobility under anesthesia was associated with a larger number of dislocations reported in the previous year (p<0.01), but not a greater duration of injury (p=0.76). A greater proportion of the ≥2 (13.7%) vs <2 (4.7%) mobility groups also had a Beighton score ≥4 (p<0.01). Results were similar looking at EUA grade as an ordinal variable except that an increase in EUA grade was associated with a greater odds of >10% bone loss (OR: 1.51, 95%CI: 1.01-2.27, p=0.046). Labral tear length was significantly greater in individuals who reported at least two dislocations in the previous year (median=144, 0-360°) vs less than two (126, 0-360°, p=0.02). Conclusion: Measures of translation during EUA in patients undergoing anterior shoulder stabilization surgery demonstrated higher likelihood of HSL and increased glenoid bone loss>10% as positive predictors of translation ≥2 intra-operatively. Self-reported number of dislocations and Beighton scores≥4 were also found to be correlated with increasing translation under EUA and may serve as a reliable clinical predictor of patients at risk for recurrent instability.