Poster 142: Capsular Repair Demonstrates Similar Restoration of Resistance to Axial Distraction in Interportal and Periportal Capsulotomies: An In Vivo Propensity Matched Cohort Study

OBJECTIVES: Hip arthroscopy has become increasingly prevalent in the United States for treating young adult hip disorders. The periportal capsulotomy, in comparison to the interportal capsulotomy, has been proposed as a technique for decreasing post-arthroscopy hip instability; however, the effects of this technique are largely theoretical. The objectives of this study were to compare the intraoperative distraction profiles of hip arthroscopy patients undergoing interportal versus periportal capsulotomies. The authors hypothesized the periportal capsulotomy would demonstrate greater resistance to axial distraction at both 1) the capsulotomy and 2) final capsular repair, when compared to the interportal capsulotomy. METHODS: Patients undergoing primary hip arthroscopy by a single surgeon underwent intraoperative axial distraction testing at 25-, 50-, 75-, and 100-pounds force with each axial distraction distance measured by standardized, normalized fluoroscopic evaluation. Demographics, hip radiographic characteristics, and distraction distance measurements were collected on patients undergoing periportal capsulotomy and on a historical control group undergoing an interportal capsulotomy (Figure 1). Propensity matching was conducted using native state distraction, lateral center edge angle, and gender as covariate to achieve balance between groups. Between group comparisons were then conducted across the matched interportal and periportal groups. Student’s T-test for continuous variables and the Fisher exact test for categorical variables. Intragroup comparison was conducted across three capsule states: native, capsulotomy, and repair. Sequential testing of capsular states for each patient was conducted with the paired T-test. RESULTS: Seventy-four interportal capsulotomies and 122 periportal capsulotomies were identified. Propensity matching yielded 74 hips in each group with standard mean differences of <0.03. Demographic and radiographic characteristics were similar between matched cohorts (p > 0.05) (Table 1). Distraction distances were similar between the interportal and periportal groups in both the capsulotomy and repair states (p > 0.05), while the periportal capsulotomy repair demonstrated decreased hip distraction distance when compared to the native state by 1.48mm at 75lbf and 1.54mm at 100lbf (p < 0.001) (Figure 2). CONCLUSIONS: The present study demonstrates that periportal capsulotomy and interportal capsulotomy have similar effects on in vivo hip distractibility. An unrepaired interportal capsulotomy led to an increase in hip distraction of 2.71 mm at 100 lbf (p < 0.001) compared to the native state, while an unrepaired periportal capsulotomy led to an increase in hip distraction of 2.44 mm at 100 lbf (p < 0.001). The periportal capsulotomy technique has been discussed as having the unique advantage of not fully disrupting the iliofemoral ligament and therefore potentially not require a repair; however, the results of the present study indicate that it is biomechanically similar to the interportal capsulotomy in the unrepaired state. Although this finding does not definitively establish a need for capsular repair in all cases when utilizing a periportal capsulotomy, if the surgeon wishes to re-establish native biomechanics, repair should be considered. The present study establishes the in vivo, intraoperative biomechanics of the periportal capsulotomy, for which there were previously no available data. Further, this study establishes that although periportal capsulotomy is a minimally disruptive technique, it has a substantial effect on in-vivo, intraoperative hip stability as measured by hip distraction distance as a result of axial traction forces. While this paper is able to address the biomechanics at the time of surgery, this paper cannot make any conclusions about the healing potential of the capsule when comparing an interportal and a periportal capsulotomy. In conclusion, an unrepaired periportal capsulotomy and interportal capsulotomy have a similar effect on increasing hip axial distraction distance intra-operatively. Performing a capsular repair restores intra- operative resistance to axial distraction in both the periportal and interportal capsulotomy.