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Knee joint motion appears as a hinge movement around the flexion-extension axis. Corresponding to the rolling-sliding mechanism and alternative models of knee joint kinematics, an instant center pathway must be expected. The current photogrammetric investigation aimed to analyze these pathways when assessed in the sagittal plane in patients with preoperative varus or valgus deformity. A total of 40 patients either with varus or valgus deformity (20 in each group) were examined before and 6 months after implantation of PFC-SIGMA prostheses. Apart from the influence of knee joint deformity, a so-called soft tissue ratio was investigated. Therefore, the relation of thigh and femur as well as lower limb and tibia diameters was calculated and combined in one value. The investigation unit consisted of a standardized chair with passive knee joint movement (90-0 degrees flexion) supported by an electric motor. The position of predefined skin markers was assessed by digital camera with online transmission to a PC. The instant center pathway was then evaluated applying the Reuleaux technique based on the changes of skin marker positions. Results showed the following characteristics: small values of soft tissue ratio were represented by round or oval courses of the pathway whereas increasing ratios led to triangular and slightly increased dimensions of the courses. Varus deformity was primarily combined with an increase of the pathway's dimension and in contrast, valgus deformity showed decreased pathways. In each case, dimensions normalized after prosthesis implantation. The instant center pathway of knee joint motion showed for both patient groups characteristic phenomena. They were clearly associated with constitutional and clinical features of each patient.

Aim: Knee joint motion appears as a hinge movement around the flexion - extension axis. But corresponding to the rolling-sliding-mechanism and alternative models of knee joint kinematics an instant center pathway must be expected. Objective of the study was the comparison of this pathway when assessed in the sagittal plane in patients with preoperative varus or valgus deformity., Method: A total of 40 patients either with varus or valgus deformity (20 in each group) were examined before and 6 months after implantation of PFC(R)-SIGMA prostheses. Apart from the influence of knee joint deformity (35 degrees varus to 24 degrees valgus), a so called soft tissue ratio was investigated. Therefore the relation of thigh and femur as well as lower limb and tibia diameters was calculated and combined in one value. The examination by means of photogrammetry consisted of a standardized chair with passive knee joint movement (90 degrees to 0 degrees flexion) supported by an electric motor. The position of defined skin markers was assessed by digital camara with online transmission to PC. The instant center pathway was then evaluated applying the Reuleaux-technique based on the changes of skin marker positions., Results: Results showed a dependence of the course and dimension of the instant center pathway on the extent of soft tissue ratio as well as knee joint deformity. Small values of the ratio (W = 2.9) were represented by round or oval courses of the pathway whereas increasing ratios (W = 4.0) led to triangular and slightly increased dimensions of the courses. Varus deformitywas primarily combined with an increase of the pathways dimension and in contrast, valgus deformity showed decreased pathways. In each case, dimension normalized after prostheses implantation., Conclusion: The instant center pathway of knee joint motion showed for both patient groups characteristic phenomen. They were clearly combined with constitutional and clinical features of each patient.

The present investigation aims to evaluate periprosthetic bone remodelling after total knee arthroplasty by the use of dual-energy X-ray absorptiometry (DXA). Twelve patients affected by osteoarthrosis of the knee joint underwent primary total knee arthroplasty at an average age of 70.5 years. None of them had received a knee prosthesis before on the contralateral side. Anteroposterior and lateral DXA measurements of the femur, tibia and total knee (both sides) were taken 2 weeks, 3 and 9 months postoperatively. The 2-week measurement was used as an individual reference value to be compared with the 3- and 9-month findings. In addition, the contralateral knee was investigated also in order to estimate how far bone mineral loss was due to implantation or to an individual decline in bone mineral density (BMD). The comparison of BMD values after knee arthroplasty revealed a conspicuous decrease of bone density within 9 months. Bone mineral loss amounted to an average of 9.2% in anteroposterior and 17.8% in lateral DXA measurements. Lateral femur shots showed an average decrease of density of even 21.5%. In contrast, the BMD values of the contralateral knees remained almost unchanged. DXA, especially lateral shots of the femur, promises to be a suitable method for early assessment of periprosthetic bone remodelling after total knee arthroplasty.