Abstract: BACKGROUND: Prosthesis misalignment and patient bone condition are important factors affecting the prognosis of unicompartmental knee arthroplasty, and postoperative osteoarthritic progression of the lateral compartment is a major complication leading to its high revision rate. Therefore, this will become a hot research topic in the future.
OBJECTIVE: To analyze the effect of different femoral prosthesis tilt angles on the stress on the structure of the lateral compartment after unicompartmental knee arthroplasty in patients with normal bone and osteoporosis, and to investigate the correlation between osteoporosis and osteoarthritis of the lateral compartment in the postoperative period.
METHODS: Using a validated finite element model of the knee, normal bone (M1) and osteoporotic (M2) unicompartmental knee arthroplasty were modeled. The femoral prosthesis tilt models (normal bone group: varus angles of 3°, 6°, 9°, 12°, and 0°, valgus angles of 3°, 6°, 9°, 12°; osteoporosis group: varus angles of 3°, 6°, 9°, 12°, 0°, valgus angles of 3°, 6°, 9°, 12°) were established respectively, totaling 18 working conditions. The effects of different femoral prosthesis tilt angles on stress magnitude and distribution in the meniscus, tibial cartilage, and femoral cartilage of interstitial compartment were evaluated. 
RESULTS AND CONCLUSION: (1) The high stress values on the meniscus surface and tibial cartilage surface of the healthy lateral compartment of the two models increased with the increase of the prosthesis varus angle, and decreased with the increase of the prosthesis valgus angle. Under the same working conditions, the peak stress on the meniscus surface of the osteoporotic group was greater than that of the normal bone group, but that of the tibial cartilage surface of the osteoporotic group was less than that of the normal bone group. (2) The high stress values on the femoral cartilage of the lateral compartment of the two models increased with the increase of the prosthesis varus and valgus angles. Under the same working conditions, the peak stress on the femoral cartilage of the osteoporotic group was greater than that of the normal bone group. (3) It is indicated that when the fixed-bearing femoral prosthesis is varus, the stresses on the lateral compartment structures after medial unicompartmental knee arthroplasty in normal bone and osteoporotic knees will increase, and the increase in the stresses on the lateral intercondylar structures in osteoporotic knees will be more pronounced. Therefore, special attention should be paid to the placement of the prosthesis during unicompartmental knee arthroplasty to avoid varus and valgus of the prosthesis as much as possible. At the same time, the findings confirm that osteoporosis may exacerbate the progression of lateral compartment osteoarthritis after medial unicompartmental knee arthroplasty.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: knee, osteoarthritis, osteoporosis, unicompartmental knee arthroplasty, femoral component, biomechanics