Change in bone mineral density after cemented and uncemented knee arthroplasty with an asymmetrical tibial component: secondary analysis of a randomized study using dual-energy X-ray absorptiometry

BACKGROUND AND PURPOSE: Total knee arthroplasties (TKA) affect the mechanical loading of the knee joint and may be associated with changes in bone mineral density (BMD). We aimed to evaluate adaptive periprosthetic BMD after cemented and uncemented TKA. METHODS: This is a secondary report of an earlier published RCT. Patients receiving cemented (n = 31) or uncemented (n = 32) TKA were included in a randomized controlled trial (RCT) with a 1:1 allocation. BMD was measured using Dual-energy X-ray Absorptiometry (DEXA) at 1 week and 3, 6, 12, and 24 months postoperatively in 3 regions of interest (ROI) in the femur and tibia. Changes in BMD were assessed using a paired t-test, and between-groups differences using an unpaired t-test. Time-related changes were analyzed using ANOVA. The study was registered at clinicaltrials.gov (NCT03563131) before enrolment. RESULTS: Femoral components: Over 2 years, BMD in ROI I decreased by 33% in the uncemented group and 21% in the cemented group, with a between-group difference of 12.2 percentage points (95% confidence interval [CI] 5.3-19.1; significant). In ROI II, the decrease was 19% vs 13%, with a between-group difference of 6.1 percentage points (CI -1.2 to 13.5; not significant). In ROI III, decreases were 6% vs 7%, with a between-group difference of -0.6 percentage points (CI -4.3 to 3.3; not significant). Tibial components: Changes were small (-4.7 to 3.3%), with significant decreases only in ROI I in the cemented group over 24 months. No significant between-group differences were observed. CONCLUSION: The periprosthetic BMD after TKA decreased both around cemented and uncemented components, particularly in ROI I after using an uncemented femoral component, whereas the decrease under the tibial components was small and of uncertain clinical significans.