Changes in bone mineral density of the distal femur after revision total knee arthroplasty with metaphyseal press-fit stem

Background: The effect of postoperative adaptive bone remodeling following a stemmed femoral implant in revision total knee arthroplasty (rTKA) is unknown. The aim of this study was to evaluate bone mineral density (BMD) changes of the distal femur following cemented rTKA with a 100-mm press-fit stem. Materials and methods: Sixteen consecutive patients were included in the study (age range 40-85 years; mean 63.5 years). NexGen® (Zimmer, Warsaw, IN, USA) cemented revision implants were used. All implants had the same press-fit femoral stem length of 100 mm. Clinical examinations with evaluation of the knee function using the Knee Society's Knee Scoring System were used. Measurements of BMD (g/cm²) were performed by dual-energy X-ray absorptiometry (DEXA) using a Norland XR-46 (Norland Corp. Fort Atkinson, WI, USA) bone densitometer. Results: Knee and function scores improved significantly (P = 0.005) from the preoperative values to 1 year of follow-up. In regions of interest (ROI) 1-4, a significant increase in BMD (3.5-6.0%) after 6 months was seen. This increase only remained significant in ROI 4 (4.0%, P = 0.01) at 1 year of follow-up. Conclusions: The increase in BMD is probably the result of increased mobility and load on the extremity after implantation of a well-functioning rTKA.