Finite element analysis of effects of opening wedge high tibial osteotomy on knee joint and internal fixation stress

Abstract

BACKGROUND: Opening wedge high tibial osteotomy is a well-established method for treating medial compartment knee osteoarthritis with varus deformity. There is still controversy over where the lower limb force correction should be placed after opening wedge high tibial osteotomy. OBJECTIVE: To investigate the mechanical characteristics of the knee joint and the internal fixation device after opening wedge high tibial osteotomy for knee osteoarthritis with varus deformity by finite element analysis of the mechanical loading of different force line patterns on the structures of the knee joint. METHODS: A 57-year-old female volunteer weighing 60 kg, diagnosed with left knee osteoarthritis, was selected. Multislice spiral CT scanning was performed on the left knee joint to obtain imaging data. Finite element analysis software was used for mechanical loading to obtain analysis results. The hinge point of the opening wedge high tibial osteotomy was set approximately 15 mm above the tibial plateau at the fibular head, with a 5 mm lateral tibial cortex preserved at the hinge. The medial cortex osteotomy was positioned 30 mm from the medial tibial plateau, and the osteotomy was opened by 5, 10, and 15 mm. The force line was set to load vertically at 25%, 50%, 62.5%, and 75% of the tibial plateau width. After osteotomy, an 8-hole Tomofix plate (thickness 2 mm) was placed with 8 screws (diameter 4 mm; lengths: 60, 60, 55, 50, 38, 34, 32, 20 mm). The osteotomy gap was filled with cancellous bone. Stress and displacement maps of the knee joint structures were obtained. RESULTS AND CONCLUSION: (1) Before osteotomy, stress was concentrated on the lateral femoral condyle and medial tibial plateau, with meniscal stress concentrated in the medial meniscus body and lateral meniscus anterior horn. As the loading position moved laterally, lateral cartilage and meniscal stress increased while medial stress decreased. (2) In the 5 mm opening model, as the loading position moved from medial to lateral, lateral cartilage and meniscal stress gradually increased; the stress in the graft bone was minimal at the 50% position; titanium plate and screw stress decreased as the loading line moved laterally. (3) With increasing opening height, lateral cartilage and meniscal stress increased, titanium plate stress concentration increased, but screw stress changes were not significant. (4) The posteromedial region of the Tomofix plate and the D-hole and 1-hole screws were prone to fatigue fracture and screw head breakage. (5) Opening wedge high tibial osteotomy effectively transfers medial compartment pressure, but attention should be paid to the increased stress on lateral cartilage and menisci. The posteromedial plate and D-hole/1-hole screws are stress concentration weak zones; intraoperative overcorrection should be avoided and internal fixation design optimized to reduce complications.

1. Introduction

Knee osteoarthritis (KOA) is a prevalent orthopedic condition that profoundly impacts patients' quality of life and imposes a substantial socioeconomic burden [1]. In this context, opening wedge high tibial osteotomy (OWHTO) has re-emerged as a focal point of academic research, recognized as an effective surgical strategy for treating medial compartment KOA [2]. This technique redistributes the abnormal high pressure from the medial compartment to the relatively healthy lateral compartment by adjusting the lower limb mechanical axis, thereby alleviating knee pain, halting osteoarthritis progression, and promoting cartilage repair, while preserving the natural knee structure and extending its functional lifespan [3]. However, the postoperative mechanical state of the tibial plateau is decisive for knee stability and functional recovery. Overcorrection may exacerbate lateral compartment loading, whereas undercorrection fails to adequately relieve medial pain. FUJISAWA et al. [4] suggested that the ideal postoperative weight-bearing axis should be located 30%-40% lateral to the knee center, with 62.5% being commonly used, yet consensus on the optimal position remains debated [5].

Finite element analysis (FEA) has become an indispensable tool in biomechanical research due to its non-invasive nature and ability to simulate multiple loading conditions [6]. By constructing high-fidelity three-dimensional models, FEA quantifies stress and strain distributions in bone, cartilage, and internal fixation systems, particularly excelling in analyzing complex load environments that are difficult to replicate experimentally. In OWHTO research, FEA enables dynamic simulation of different osteotomy angles and their effects on knee cartilage and internal fixation materials, predicting long-term complication risks and providing a theoretical basis for surgical parameter optimization. However, existing studies often focus solely on bone-plate interfaces or isolated structural analyses, lacking comprehensive evaluation of the knee joint combined with internal fixation components (screws/plate).