Periprosthetic tibial bone mineral density changes after total knee arthroplasty: one-year follow-up study of 69 patients.

Background: The critical structure supporting the prosthetic components in total knee arthroplasty (TKA) is tibial trabecular bone. The quality of tibial bone can be evaluated by bone mineral density (BMD) measurements.

Patients and methods: We prospectively measured changes in BMD in the proximal tibia after cemented TKA in osteoarthrotic knees. 69 patients were scanned by dual-energy X-ray absorptiometry (DXA) within a week after surgery, and after 3, 6 and 12 months.

Results: At baseline, the medial region of interest (ROI) BMD was higher in the varus knees than in the valgus aligned knees (p=0.02). The medial metaphyseal ROI showed a decrease in BMD during the follow-up in preoperatively varus knee joints (p<0.001). In preoperatively valgus knees, there was a slight increase in medial compartment BMD which was not significant (p=0.2). Alignment correction in both groups showed bone remodeling giving similar medial and lateral BMD values, suggesting that the bone became equally strong in both compartments of the metaphysis. There was no association between increasing American Knee Society (AKS) scores and bone remodeling.

Interpretation: We suggest that this remodeling is caused by postoperative changes in tibial loading. Our results support the clinical importance of recreating proper valgus alignment of the knee joint in the TKA operation, thus possibly providing better conditions for longevity of the tibial component.