Periprosthetic bone mineral density (BMD) may influence implant fixation and subsequent loosening. Unicompartmental knee arthroplasty (UKA) restores normal knee kinematics and load distribution to the surrounding bone. We studied the influence of systemic and periprosthetic BMD of the proximal tibia on migration of the tibial component of cemented medial UKA.
The cohort was dichotomized into a normal BMD group (T-score ≥ -1; n = 37) and a low BMD group (T-score < -1; n = 28) according to World Health Organization criteria. BMD of the proximal tibia and migration of the tibial component were measured with dual X-ray absorptiometry scans and stereoradiographs with 2-year follow-up.
Patients with normal systemic BMD had an 11% to15% higher BMD in all regions of interest (ROIs) compared to patients with low systemic BMD throughout follow-up. Over time, a decrease in periprosthetic BMD in ROI 1-3 was seen for both groups. The operated knees and contralateral knees showed a similar reduction in BMD in all ROIs between preoperative and 24 months. Between 12 and 24 months, the normal BMD group migrated (maximal total point motion) 0.03 mm (95% confidence interval, -0.01, 0.08) and the low BMD group migrated 0.02 mm (95% confidence interval, -0.03, 0.07). Migration over time was not influenced by change in periprosthetic BMD.
Migration of cemented medial tibial UKA was low until 24 months and was neither affected by preoperative systemic BMD nor affected by postoperative change in periprosthetic BMD. This suggests good long-term fixation despite an index difference in proximal tibial BMD.