The effects of venting and capsulotomy on traction force and hip distraction in hip arthroscopy

This study evaluated the effects of venting and capsulotomy on the ratio of normalized distraction distance to traction force, correlating this trend with patient demographic factors. A ratio was chosen to capture the total effect of each intervention on the hip joint. During primary hip arthroscopy, continuous traction force was recorded, and fluoroscopic images were acquired to measure joint distraction before and after the application of traction, venting and interportal capsulotomy. Distraction-traction force ratios were compared using a one-sided paired t-test. A linear regression model was used to determine the relationship between age, sex and body mass index and pre- and post-intervention distraction-traction force ratios. Seventy-two adult patients and 73 hips were included. There was an increase in hip distraction with a decrease in traction force post-venting and capsulotomy (both P's <0.001). Mean normalized distraction distance increased 1.5% of femoral head size after venting and an additional 2.2% of femoral head size after capsulotomy. Mean traction force decreased 2.2% (14.7 N) after venting and 2.3% (15.3 N) after capsulotomy. Female sex significantly correlated with larger differences in both pre- and post-venting capsulotomy ratios. Venting and capsulotomy both independently improve the ratio of normalized distraction distance to traction force when performed in vivo. However, the effect sizes of each intervention are small and of questionable clinical significance. Specifically, when adequate distraction for safe surgical hip access cannot be obtained despite application of significant traction force, venting and capsulotomy after the application of traction may not afford substantial improvement.