Stem subsidence in total hip arthroplasty: retrospective investigation of a short stem using a simple measurement approach.

backgroundUncemented total hip arthroplasty (THA) is a successful treatment for advanced hip joint diseases. More recently, short stems became increasingly popular, but stem subsidence remains a concern. This study investigates early short stem subsidence in a large patient cohort using a simple measurement approach for everyday practice.

methodsThis retrospective, single center, single implant design study included 1000 patients with primary THA. Subsidence was evaluated using standardized weight-bearing radiographs taken 3-5 days and 2-3 weeks postoperatively with full weight-bearing (FWB). A novel Subsidence Index (SID) was introduced to quantify stem subsidence in a simple and reproducible manner. The SID is calculated by averaging four distinct linear measurements between defined anatomical landmarks on the femur and the implant, captured on standard radiographs without additional software.

resultsOut of all analyzed patients 6% (60/1000) had subsidence of more than 3 mm. The mean subsidence was 1.3 mm (range, 0 to 16.25 mm). There were 0.6% (6) who underwent stem revision for symptomatic subsidence. Men and obese patients had greater subsidence. However, patient age, BMI, stems without lateral bone contact and other demographic factors were not associated with subsidence.

conclusionEarly subsidence is relatively frequent with this uncemented short stem, however revisions are rare. Patients with risk factors should be counseled regarding FWB and radiographic controls should be performed. The SID provides an easy, non-invasive and inexpensive tool for early subsidence assessment; however, its simplicity limits its accuracy. Further research is needed in comparison to more elaborate methods.