Clinically derived biomechanical criteria for the Trendelenburg test

Background: The Trendelenburg test has been used to assess hip abductor muscle function. A standardized evaluation of the test requires an assessment of both pelvis and trunk coronal plane alignment as the patient stands on one leg for 30 s. Coronal plane biomechanics using motion analysis allows for development of objective criteria to grade the test response. The aim of this study was to develop biomechanical criteria of the pelvis and trunk coronal plane kinematics. Methods: The video of 39 subjects with acetabular hip dysplasia performing the test while instrumented with a full-body modified Plug-In-Gait marker set for three-dimensional kinematic analysis, were evaluated by two orthopedic surgeons and one senior level biomechanist. Reviewers as a group assessed whether the subject had a positive test and noted the reason using guidelines outlined in the literature. Coronal plane trunk and pelvic angles of all subjects were analyzed and Receiver Operating Characteristic curves were used to determine optimal kinematic cutoff values for each positive Trendelenburg test reason. Findings: There were 26/39 patients who reviewers identified as having a positive test. Area under the curve of the receiver operating characteristic curve for trunk and pelvis mean/minimum were greater than 0.75. The curve was used to identify the optimal cut-offs of trunk lean and pelvic obliquity mean/minimum. Interpretation: The biomechanical criteria developed includes clinically derived coronal plane kinematic cut-offs of the pelvic and trunk angles. The criteria can be used within a motion capture setting for the standardization of the grading of the test response.