Patient-Specific Parameters Associated with Traction Stiffness in Primary and Revision Hip Arthroscopy

OBJECTIVES: To quantify the force of traction required for adequate distraction of the hip during arthroscopy and explore the relationship between hip joint stiffness and patient-specific demographics, flexibility, and anatomy. METHODS: 101 primary arthroscopy patients (61 females) and 23 patients undergoing revision arthroscopy for capsular repair (all female) were prospectively enrolled. A load cell attached to the traction boot continuously measured traction force. Fluoroscopy images were obtained before and after traction to measure joint displacement. The stiffness coefficient was calculated as the force of traction divided by joint displacement. Primary patients were analyzed in a univariable regression model and re-analyzed separately by gender. Variables significant at p<0.05 were included in a multivariable regression model. Stiffness was compared between female primary and revision patients using independent t-tests. RESULTS: For primary arthroscopy, instantaneous peak force averaged 80 ± 18 kgf, after which the force required to maintain distraction decreased to 57 ± 13 kgf. In univariable regression analysis, gender, alpha angle, hamstring flexibility and Beighton hypermobility score were each correlated to stiffness. However, gender was the only significant variable in the multivariable regression model. Intragender analysis demonstrated increased hamstring flexibility correlated with decreased stiffness in males and higher Beighton scores correlated with decreased stiffness in females. Stiffness was significantly less in the revision cases than the primary cases (p=0.006). CONCLUSION: A substantial force is required to achieve and maintain hip distraction, with males requiring higher forces. Males with increased hamstring flexibility and females with higher Beighton scores are less stiff than their same gender counterparts. Patients indicated for revision capsule repair were less stiff, supporting the importance of the hip capsule on hip stability. These data may be used to identify patients with microinstability and patients where specific focus on capsular repair and/or plication may be warranted.