Diagnostic Accuracy of 3 Physical Examination Tests in the Assessment of Hip Microinstability

Abstract

Background: Hip microinstability is a diagnosis gaining increasing interest. Physical examination tests to identify microinstability have not been objectively investigated using intraoperative confirmation of instability as a reference standard. Purpose: To determine the test characteristics and diagnostic accuracy of 3 physical examination maneuvers in the detection of hip microinstability. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: A review was conducted of 194 consecutive hip arthroscopic procedures performed by a sports medicine surgeon at a tertiary-care academic center. Physical examination findings of interest, including the abduction–hyperextension–external rotation (AB-HEER) test, the prone instability test, and the hyperextension–external rotation (HEER) test, were obtained from prospectively collected data. The reference standard was intraoperative identification of instability based on previously published objective criteria. Test characteristics, including sensitivity, specificity, positive and negative predictive values, and accuracy, were calculated for each test as well as for combinations of tests. Results: A total of 109 patients were included in the analysis. The AB-HEER test was most accurate, with a sensitivity of 80.6% (95% CI, 70.8%-90.5%) and a specificity of 89.4% (95% CI, 80.5%-98.2%). The prone instability test had a low sensitivity (33.9%) but a very high specificity (97.9%). The HEER test performed second in both sensitivity (71.0%) and specificity (85.1%). The combination of multiple tests with positive findings did not yield significantly greater accuracy. All tests had high positive predictive values (range, 86.3%-95.5%) and moderate negative predictive values (range, 52.9%-77.8%). When all 3 tests had positive findings, there was a 95.0% (95% CI, 90.1%-99.9%) chance that the patient had microinstability. Conclusion: The AB-HEER test most accurately predicted hip instability, followed by the HEER test and the prone instability test. However, the high specificity of the prone instability test makes it a useful test to “rule in” abnormalities. A positive result from any test predicted hip instability in 86.3% to 90.9% of patients, but a negative test result did not conclusively rule out hip instability, and other measures should be considered in making the diagnosis. The use of these tests may aid the clinician in diagnosing hip instability, which has been considered a difficult diagnosis to make because of its dynamic nature.