Biomechanical study on the stress distribution of the knee joint after distal femoral fracture malunion with residual varus-valgus deformity 

Abstract Background: To investigate the effect of residual varus and valgus deformity on the stress distribution of knee joint after distal femoral fracture malunion. Methods: Fourteen adult cadaver specimens with formalin were selected to establish the femoral fractures models, which were fixed subsequently at neutral position (anatomical reduction) and malunion positions (at 3 degrees, 7 degrees, 10 degrees valgus positions and 3 degrees, 7 degrees, and 10 degrees varus positions). The stress distribution on the medial and lateral plateau of the tibia was quantitatively measured using ultra-low pressure sensitive film technology. The change of stress distribution of knee joint after femoral fracture malunion and the relationship between stress value and residual varus varus or valgus deformity were analyzed.Results: Under 400 N vertical load, the stress values on the medial and lateral plateau of the tibia at the neutral position were 1.162±0.114 MPa and 1.103±0.144 MPa, respectively. When compared with the stress values measured at the neutral position, the stress on the medial plateau of tibia were significantly higher at varus deformities and lower at valgus deformities, and the stress on the lateral plateau was significantly higher at valgus deformity and lower at varus deformities (all P<0.05). The stress values on the medial plateau of tibia were significantly higher than the corresponding data on the lateral plateau at neutral and 3 degrees, 7 degrees, 10 degrees varus deformities, respectively (all P<0.05), and significantly lower than the corresponding data on the lateral plateau at 3 degrees, 7 degrees, 10 degrees valgus deformities, respectively (all P<0.05). Conclusions: Residual varus and valgus deformity after femoral fracture malunion can cause obvious changes of the stress distribution of knee joint. Therefore, the distal femoral fracture should be anatomically reduced and rigidly fixed to avoid residual varus-valgus deformity and malalignment of lower limbs.