The diagnosis of hip microinstability is correlated with ease of intra-operative hip distraction

Hip microinstability has emerged as a contributor to young adult, non-arthritic hip pain. There is a paucity of objective clinical data to identify patients with hip microinstability and guide surgical treatment. The purpose of this study was to identify the degree of distractibility in patients with and without microinstability undergoing hip arthroscopy.

A single-surgeon series of hip arthroscopies were retrospectively reviewed from 2014-2020. All procedures were performed with paralysis on a fracture table with a perineal post where 1 turn of fine traction equates to 4 mm of axial traction. Diagnosis was recorded as isolated instability, instability plus femoroacetabular impingement (FAI), and isolated FAI. Operative reports were reviewed to collect patient demographic data, number of turns of traction required for adequate distraction of the femoral head relative to the acetabulum (10 mm), and the presence of residual subluxation after initial traction was released.

A total of 464 patients were identified, 26 (5.6%) with isolated microinstability, 183 (39.4%) with microinstability with FAI anatomy, and 255 (55.0%) with FAI. The concurrent diagnosis of microinstability was associated with decreased turns required to adequately distract the hip. Isolated microinstability patients required 6.9 turns (IQR 4.6-8.8) while those with instability plus FAI required 8.8 turns (IQR 6.5-11) and isolated FAI required 19.1 turns (IQR 15-22). Residual subluxation after removal of negative intra-articular pressure but before performing the hip arthroscopy was more commonly associated with instability, occurring in 84.6% of isolated instability and 86.9% of instability plus FAI as compared with 29.8% in the isolated FAI cohort.

A diagnosis of hip microinstability, with or without features of FAI, is associated with decreased axial traction required to distract the hip. These data support the use of intra-operative ease of distraction as a method of identifying patients with hip microinstability.

Level III.