The resisted torsional stress test in diagnosis of femoral stem loosening in uncemented total hip arthroplasty - first description and retrospective study.

Introduction: Aseptic femoral stem loosening is among the most common causes for revision in total hip arthroplasty (THA). We describe a simple clinical test that triggers pain in the proximal femur in patients with a loose stem. A previously described passive rotation test was associated with a poor sensitivity. The resisted torsional stress test (RTST) was used for several years in our hospital, and this is the first description of its reliability.

Methods: We retrospectively reviewed our database of uncemented stem revisions. Preoperative clinical reports were searched for data on the RTST. A positive RTST was defined as sharp pain felt at the stem level with active internal rotation against a passive external rotation impulse in 90° hip flexion. The definition of stem fixation (fixed vs. loose) was made by readout of the surgery reports.

Results: The RTST was reported in 83 cases and was positive in 32 of the 43 stems, which were found loose intraoperatively and in 9 of the 40 stems, which were well integrated. This leads to an accuracy of classification of 79.5%. The sensitivity was 80% and the specificity was 79.1%. PPV and NPV were 78% and 81%, respectively.

Conclusion: The RTST provides a helpful tool in the clinical assessment of femoral stem fixation in THA with good accuracy and should be included in standard follow-up examinations and in the assessment of painful THAs.