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

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.

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.

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.

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.