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.
Background and purposeTotal knee arthroplasty (TKA) may cause postoperative periprosthetic bone loss due to stress shielding. Bone also adapts to mechanical alterations such as correction of malalignment. We investigated medium-term changes in bone mineral density (BMD) in tibial periprosthetic bone after TKA.Patients and methods86 TKA patients were prospectively measured with dual-energy X-ray absorptiometry (DXA), the baseline measurement being within 1 week after TKA and the follow-up measurements being at 3 and 6 months, and at 1, 2, 4, and 7 years postoperatively. Long standing radiographs were taken and clinical evaluation was done with the American Knee Society (AKS) score.ResultsThe baseline BMD of the medial tibial metaphyseal region of interest (ROI) was higher in the varus aligned knees (25%; p < 0.001). Medial metaphyseal BMD decreased in subjects with preoperatively varus aligned knees (13%, p < 0.001) and in those with preoperatively valgus aligned knees (12%, p = 0.02) between the baseline and 7-year measurements. No statistically significant changes in BMD were detected in lateral metaphyseal ROIs. No implant failures or revision surgery due to tibial problems occurred.InterpretationTibial metaphyseal periprosthetic bone is remodeled after TKA due to mechanical axis correction, resulting in more balanced bone stock below the tibial tray. The diaphyseal BMD remains unchanged after the initial drop, within 3–6 months. This remodeling process was related to good component survival, as there were no implant failures or revision operations due to tibial problems in this medium-term follow-up.
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