Introduction

During hip arthroscopy, the extent of hip distraction can vary among patients. Microinstability of the hip is defined as ease of distractibility. The purpose of this study was to evaluate whether acetabular coverage of the femoral head influences the extent of hip distraction.

Methods

This study analyzed prospectively collected data from 251 patients who underwent hip arthroscopy by a single surgeon between January 2018 and April 2019. Patients were excluded because of inappropriate fluoroscopic images for evaluation (11 patients) or a history of operation on the affected hip (24 patients). During the unsterile traction test, one fluoroscopic image of the affected hip was obtained without traction, and the other fluoroscopic image was obtained under maximal traction when no more significant movement of the hip was noted. The lateral acetabulum-to-femoral head gap. The distraction extent was defined as the ratio of the gap under maximal traction to that without traction. The association between the extent of distraction and the lateral center-edge angle (LCEA), as well as the anterior/posterior wall index (AWI/PWI), was evaluated. Other factors potentially influencing the extent of distraction, including age, gender, Tönnis grade, α angle, and the severity of chondrolabral separation, were also analyzed.

Results

A total of 211 patients were included in the final analysis. Univariate analysis revealed that an increased LCEA was significantly associated with a decreased distraction extent at lateral gap (Pearson correlation coefficient -0.242, p<0.001). The extent of lateral gap distraction was the greatest in the group of LCEA <25º, and the most small in the group of LCEA > 40º (p=0.003). Multivariate analysis confirmed that LCEA was significantly associated with the extent of lateral gap distraction (p=0.002). No significant association was observed between other factors and the extent of distraction.

Conclusions

This study demonstrated that a decreased LCEA was associated with an increased extent of lateral gap distraction. The AWI/PWI were not significant factors associated with the extent of distraction.