Bone mineral density in the proximal femur and contralateral knee after total knee arthroplasty.

Osteoarthrosis (OA) is often associated with pain and disability, which are relieved after total knee arthroplasty (TKA), but the nature of bone changes associated with OA is controversial. We examined preoperative hip and contralateral knee bone mineral density (BMD) in patients requiring TKA and monitored the BMD changes postoperatively. Sixty-nine patients, scheduled to have TKA for osteoarthrotic knees, had both hips and contralateral knee BMD measured by dual-energy X-ray absorptiometry (DXA) at the time of operation (baseline) and at 1 yr after operation. X-rays of the knee joints were also taken to evaluate the severity of OA. Preoperatively, 27% and 38% of the patients had total hip BMD Z-score more than 1 SD in the operated side and contralateral hips, respectively. In all regions of interest (ROI), the mean baseline BMD of the affected side proximal femur was significantly lower than that of the contralateral side (p < 0.0005-0.019). The severity of OA was not associated with BMD. During 1-yr follow-up, the postoperative knee status and the physical activity of the patients (AKS score) improved. However, neither the hip nor the nonoperated knee BMDs increased. Knee OA is associated with significantly lower BMD values in the affected side compared with the contralateral hip, and these levels remained similar or decreased during a 1-yr follow-up. We conclude that improved mobility after TKA does not improve the effects of preoperative disuse-associated bone loss in the short term.

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.

Periprosthetic femoral bone loss after total knee arthroplasty: 1-year follow-up study of 69 patients.

The clinical survival of joint arthroplasties is related to the quality of the surrounding bone environment. Bone mineral density (BMD) is an important measure of bone strength and quality. The aim of this prospective study was to measure the quantitative changes in BMD in the distal femur after cemented total knee arthroplasty (TKA) in osteoarthrotic knee joints. Sixty-nine patients with TKA were scanned postoperatively using dual-energy X-ray absorptiometry (DXA) within a week of surgery, and at 3-, 6-, and 12-month follow-ups. An average decrease in bone density of 17.1% (mean range of 12.1-22.8%) was measured adjacent to the prosthesis at the 12-month follow-up (repeated measures ANOVA P<0.0005). Bone loss was most rapid during the first 3 months after TKA. The clinical status and function parameters of the knee joint, evaluated by the American Knee Society (AKS) score, had improved significantly on the preoperative values at the three- and 12-month follow-ups (P<0.0005). However, improvement in the AKS score was not associated with periprosthetic BMD change (P=0.204), whereas age (P=0.067) and body mass index (P=0.019) correlated with BMD loss for the total metaphyseal region of interest (ROI), by repeated measures ANOVA. We suggest that the observed periprosthetic bone loss was mainly the result of prosthesis-related stress-shielding.

Glucose, lactate, and pyruvate response in an experimental model of microvascular flap ischemia and reperfusion: a microdialysis study.

Early diagnosis of postoperative perfusion failure is essential in microsurgical tissue transfer. In order to determine if microdialysis could be used in diagnosing flap ischemia, we tested this method in an experimental pig model. Sixty-six flaps (34 myocutaneous and 29 cutaneous) were created in 18 anesthetized pigs. During the experiment, secondary ischemia was induced for 5 h by selective clamping of the artery (20 flaps) or vein (21 flaps). Glucose, lactate, and pyruvate concentrations were measured hourly from the muscular and dermal layers. We found that decreasing glucose levels and increasing lactate concentrations were associated with arterial and venous occlusions from the first hour of ischemia. In venous ischemia, lactate concentrations remained lower than those in arterial ischemia. The increase in lactate-to-pyruvate and lactate-to-glucose ratios was related to ischemia and also discriminated arterial occlusion from venous occlusion. In conclusion, microdialysis can be used to facilitate early detection of ischemia.

Periprosthetic bone loss after cemented total hip arthroplasty: a prospective 5-year dual energy radiographic absorptiometry study of 15 patients.

In this prospective 5-year study, we determined the periprosthetic bone loss after cemented total hip arthroplasty (THA) in 15 patients using dual energy X-ray absorptiometry (DXA). A reduction in the periprosthetic bone mineral density (BMD) of 5-18% occurred in all Gruen regions, or regions of interest (ROI), during the first 3 months after THA. The bone loss continued up to 6 months in almost all ROIs. From 1 to 5 years, we found only minor changes in BMD in periprosthetic bone. After the follow-up, the mean greatest bone loss (26%) was seen in the femoral calcar area. The reduction in mean BMD was 5% in men, and 16% in women. The lower the preoperative BMD, the higher was the postoperative bone loss. We found that after the phase of acute bone loss, further loss was minimal, reflecting merely the normal ageing of bone after uncomplicated THA.