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.

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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.

Undesired bone loss around implants is considered to occur mainly because of a stress-shielding phenomenon. Bone surrounding the total knee arthroplasty (TKA) adjusts its mineral density and structure to meet new mechanical demands. Immobilization, in combination with local operative trauma to the bone and soft tissues, has an additional impact on bone loss. The clinical survival of TKA is associated with the quality and quantity of the surrounding bone environment. Poor bone quality and quantity may predispose to aseptic implant loosening and periprosthetic fractures. We investigated the efficacy of oral bisphosphonate (alendronate, Fosamax) with calcium (Calcichew) for the inhibition of early bone mineral density (BMD) loss after TKA in a prospective, randomized, one-year follow-up study. Periprosthetic BMD changes were measured with fan-beam dual-energy X-ray absorptiometry (DXA) in 19 patients with knee osteoarthrosis. Patients (n = 8) treated with 10 mg alendronate and 500 mg calcium daily maintained distal femoral BMD values close to the baseline values (P > 0.04), while patients receiving only 500 mg of calcium daily (n = 11) showed significant bone loss during the one-year follow-up (P < 0.015). The treatment groups differed significantly in metaphyseal anterior, posterior, diaphyseal, and metaphyseal total regions of interest (ROIs) (repeated measures ANOVA analyses, P = 0.019, P = 0.010, P = 0.022, and P = 0.024, respectively). Our results indicate that oral alendronate reduces early postoperative periprosthetic bone loss significantly. This therapeutic strategy may improve the results and longevity of primary total knee arthroplasties.

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The clinical survival of joint arthroplasties is clearly associated with the quality of surrounding bone environment. Bone mineral density (BMD) is an important measure of bone strength and quality. Periprosthetic BMD can be measured by using dual-energy X-ray absorptiometry (DXA) with special software algorithms. We studied short-term reproducibility of the periprosthetic BMD measurements after total knee arthroplasty (TKA) in 30 patients with primary osteoarthrosis. The operated knees and the contralateral control knees were measured twice and the results were expressed as a coefficient of variation (CV%). The average precision error was 3.1% in femoral regions of interest (ROI) and 2.9% in tibial ROIs after TKA. In the prosthesis-free control knees, CV% were similar; 3.2% and 2.5%, respectively. The best precision was found in the femoral diaphyses above the implant (1.3%), whereas the least reproducible BMD was determined in the patellar region of the TKA knees (6.9%). Our results confirm that DXA measures precisely small bone mineral changes around TKA and makes it possible to follow bone remodeling DXA and may provide a feasible method for monitoring TKA in the future.

Background and Aims: Obesity has been linked to the development of osteoarthritis of the knee and since the incidence of obesity is increasing, the need for total knee arthroplasty (tka) is likely to increase. conflicting findings have been reported concerning the relationship between obesity and tka. it has been shown in several studies, that obese patients have poorer clinical results after operation. On the other hand it has also been reported similar results for obese and non-obese patients. the purpose of this study was to analyze clinically and radiologically the results of total knee artrhoplasty in obese patients.Material and Methods: the study consisted of 48 patients who had a tka. the patients were divided in two groups according their body mass index. patients of bmi over 30 were regarded as obese.Results Conclusions: Obesity has a negative impact on the outcome of tka, assessed by patients' clinical function and satisfaction level.

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