2022, Vol. 26 ›› Issue (18): 2828-2833

Entry point of an intramedullary rod in knee arthroplasty: determined using singular value decomposition method

Wang Zhen1, Xu Yi1, Tu Yihui2   

Abstract: BACKGROUND: During knee arthroplasty, prosthesis alignment is a key point, which has a great impact on the life span of implants. The role of an intramedullary rod in the intraoperative alignment of prostheses implanted has been verified. Excessive insertion error of the intramedullary rod will increase the probability of prosthesis implantation failure and medial bone collapse. Moreover, the insertion path depends on the determination of anatomical axis.   
OBJECTIVE: To improve the computer-aided method for positioning the anatomical axis based on singular value decomposition, so as to improve the insertion accuracy of intramedullary rod and prolong the life span of prostheses implanted.
METHODS: We processed preoperative computed tomography images from nine patients scheduled for total knee arthroplasty, and reconstructed the three-dimensional model of the femur using MIMICS RESEARCH 17.0. MATLAB2018b software was subsequently used to improve the positioning of the anatomical axis of the femur using singular value decomposition method. Insertion of the intramedullary rod was simulated based on the anatomical axis fitted using multi-point method. After that, the model was introduced into 3-matic, and angle error was measured. Traditional method by which the anatomical axis was fitted by two-point method and the recommended method described above were compared and verified through the simulated insertion of the intramedullary rod.   
RESULTS AND CONCLUSION: The varus and valgus angles measured by the multi-point method were (1.99±1.03)° and (2.35±1.34)°, respectively. The anterior and posterior offset angles were (1.83±0.67)° and (1.60±1.82)°, respectively. Compared with the traditional surgical method, the recommended method could improve the positioning accuracy, by which the average angle error was reduced by 0.41°. Therefore, the recommended method described above helps further improve the accuracy of prosthesis alignment in total knee arthroplasty and prolong the lifespan of prostheses implanted.
Key words: knee arthroplasty, intramedullary rod, singular value decomposition method, three-dimensional reconstruction, computer-aided