Objective To investigate the impact of femoral prosthesis malposition on internal structural strain in unicompartmental knee arthroplasty for osteoporotic knees.Methods A normal bone knee joint model was constructed based on imaging studies(CT,magnetic resonance imaging)of healthy volunteers,and an osteoporotic knee joint model was constructed by altering the elastic modulus.Finite element models of femoral prosthesis malposition in unicompartmental knee arthro-plasty were then established for both normal bone and osteoporotic groups.A vertical static load of 1,000 N was applied to both models,and the peak strain values and distributions were observed in the medial compartment structures(polyethylene gasket,cancellous bone under tibial prosthesis)and lateral compartment structures(meniscus,tibial cartilage)at various malposition angles of the femoral prosthesis.Results The peak strain values of the polyethylene gasket,cancellous bone under tibial prosthesis,meniscus,and tibial cartilage in the osteoporotic group were higher than those in the nor-mal bone group at different varus and valgus angles.In the osteoporotic group,the peak strain values of the polyethylene gasket and cancellous bone under tibial prosthesis increased with the increase in fem-oral prosthesis malposition angle,with a greater increase at valgus angles than at varus angles.Similarly,the peak strain values of the meniscus and tibial cartilage increased with the increase in femoral prosthesis malposition angle,but the increase was greater at varus angles than at valgus angles.The strain concentration area of the polyethylene gasket was located in a circular-like area where the fem-oral prosthesis contacted the gasket,the strain concentration area of the cancellous bone was mainly located in the posterolateral region,the strain concentration area of the meniscus was located near the anterior horn,and the strain concentration area of the tibial cartilage was mainly located in the middle near the intercondylar eminence.Conclusion Osteoporosis may adversely affect the strain on internal structures of the knee joint after unicompartmental knee arthroplasty.Varus malposition of the femoral prosthesis may exacerbate the progression of osteoarthritis in the contralateral compart-ment(lateral compartment),while valgus malposition may increase the risk of prosthesis loosening and revision surgery.

Objective To investigate the impact of femoral prosthesis malposition on internal structural strain in unicompartmental knee arthroplasty for osteoporotic knees.Methods A normal bone knee joint model was constructed based on imaging studies(CT,magnetic resonance imaging)of healthy volunteers,and an osteoporotic knee joint model was constructed by altering the elastic modulus.Finite element models of femoral prosthesis malposition in unicompartmental knee arthro-plasty were then established for both normal bone and osteoporotic groups.A vertical static load of 1,000 N was applied to both models,and the peak strain values and distributions were observed in the medial compartment structures(polyethylene gasket,cancellous bone under tibial prosthesis)and lateral compartment structures(meniscus,tibial cartilage)at various malposition angles of the femoral prosthesis.Results The peak strain values of the polyethylene gasket,cancellous bone under tibial prosthesis,meniscus,and tibial cartilage in the osteoporotic group were higher than those in the nor-mal bone group at different varus and valgus angles.In the osteoporotic group,the peak strain values of the polyethylene gasket and cancellous bone under tibial prosthesis increased with the increase in fem-oral prosthesis malposition angle,with a greater increase at valgus angles than at varus angles.Similarly,the peak strain values of the meniscus and tibial cartilage increased with the increase in femoral prosthesis malposition angle,but the increase was greater at varus angles than at valgus angles.The strain concentration area of the polyethylene gasket was located in a circular-like area where the fem-oral prosthesis contacted the gasket,the strain concentration area of the cancellous bone was mainly located in the posterolateral region,the strain concentration area of the meniscus was located near the anterior horn,and the strain concentration area of the tibial cartilage was mainly located in the middle near the intercondylar eminence.Conclusion Osteoporosis may adversely affect the strain on internal structures of the knee joint after unicompartmental knee arthroplasty.Varus malposition of the femoral prosthesis may exacerbate the progression of osteoarthritis in the contralateral compart-ment(lateral compartment),while valgus malposition may increase the risk of prosthesis loosening and revision surgery.

BACKGROUND:The reasonable implantation range of femoral prosthesis in unicompartmental knee arthroplasty in patients with osteoporosis has not been investigated,and previous studies have often been based on unicompartmental knee arthroplasty models in normal bone,with fewer mechanical studies in models with non-normal bone.Complications after unicompartmental knee arthroplasty have been shown to be highly associated with osteoporosis. OBJECTIVE:To analyze the biomechanical effects of the coronal inclination of the Sled fixed platform femoral prosthesis on unicompartmental knee arthroplasty in patients with osteoporosis and to find the correlation between osteoporosis and mid-and long-term complications after unicompartmental knee arthroplasty. METHODS:Based on the digital imaging technology to obtain the data of the knee joint and prosthesis,a normal bone knee model is then created by using specialized software such as Mimics and Geomagic studio.Based on a validated normal bone knee model,an osteoporotic knee model was created by changing the material parameters.Totally 14 unicompartmental knee arthroplasty finite element models were created using Sled fixed platform femoral prosthesis:standard position(0°),varus and valgus angles:3°,6°,9° in the normal bone and osteoporosis groups.Stress changes on the surface of polyethylene liner,cancellous bone under tibial prosthesis,and cortical bone were calculated and analyzed in all unicompartmental knee arthroplasty models. RESULTS AND CONCLUSION:(1)In the osteoporotic models,the high stress values of the polyethylene liner surface and the cancellous bone under the tibial prosthesis increased with the increase of the tilt angle of the femoral prosthesis,and the high stress values of the cortical bone surface under the tibial prosthesis increased with the increase of the prosthesis valgus angles and decreased with the increase of the varus angles.(2)For the polyethylene liner surface as well as the subcortical bone surface of the tibial prosthesis,the high stress values of the models for each inclination angle in the osteoporosis group were greater than those of the corresponding models in the normal bone group.For the surface of the cancellous bone under the tibial prosthesis,the high stress values of the tilt angle models of the osteoporosis groups were smaller than those of the normal bone groups.(3)Osteoporosis may cause biomechanical abnormalities in the internal structures of the knee after unicondylar replacement,increasing the potential risk of postoperative aseptic loosening of the prosthesis and periprosthetic fractures.Varus and valgus of the femoral prosthesis in the coronal plane should be avoided as much as possible when performing medial unicompartmental knee arthroplasty with a Sled fixation platform in osteoporotic knees.