Abstract
PURPOSE: To define a distraction distance (pull length) cut-off that would differentiate those patients with hip microinstability and those without the disorder, called the Pull-Out Test. METHODS: In total, 100 consecutive patients undergoing hip arthroscopy were included in the study. Patients were separated into a hip microinstability group (HMI) and non-hip microinstability group (NHI) based on the results of Beighton's score, the abduction-extension-external rotation test, hip extension-external rotation examination, and the prone instability test. Inclusion criteria were patients with an magnetic resonance imaging-proven labral tear who did not respond to conservative treatment and underwent hip arthroscopy. Exclusion criteria included those patients undergoing revision hip arthroscopy, had a previous surgery on the ipsilateral hip, or had severe arthritis in the hip. The Pull-Out Test was performed before surgery with the hip in 30° of abduction and the foot in 30° of external rotation. A blinded examiner places gross axial traction on the leg until a firm end point is reached. The distraction distance between the femoral head and acetabulum is the pull length. RESULTS: In total, 32 patients made up the HMI group whereas 68 patients were in the NHI group. The average pull length for the NHI group was 0.9 ± 0.1 cm and 1.7 ± 0.4 cm for the HMI group (P < .001). Subtracting the standard deviation from the HMI group average, when defined a cut off for hip microinstability as 1.3 cm. Using this value, we found the Pull-Out Test to have a sensitivity of 0.91 and specificity of 0.96. The positive predictive value for the Pull Test was 0.91 and the negative predictive value 0.97. CONCLUSIONS: The Pull-Out Test is a useful test in identifying and confirming the presence of hip microinstability in patients undergoing hip arthroscopy. A pull-length of 1.3 cm or greater is consistent with the presence of microinstability with a specificity of 94% and a sensitivity of 96%. LEVEL OF EVIDENCE: Level IV, diagnostic, case-control study.