Biomechanical Study on the Stress Distribution of the Knee Joint After Tibial Fracture Malunion with Residual Varus-Valgus Deformity.

Objective: To investigate the effect of residual varus and valgus deformity on the stress distribution of the knee joint after tibial fracture malunion.

Methods: Fourteen adult cadaver specimens were selected to establish the models of tibial fractures, which were fixed subsequently at neutral position (anatomical reduction) and malunion positions (at 5°, 10°, and 15° valgus positions, and 5°, 10°, and 15° 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 changes in the stress distribution of the knee joint after tibial fracture malunion and the relationship between the stress values and the residual 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 1.137 ± 0.139 MPa and 1.041 ± 0.117 MPa, respectively. When compared with the stress values measured at the neutral position, the stress on the medial plateau of the tibia was significantly higher at varus deformities and lower at valgus deformities, and the stress on the lateral plateau was significantly higher at valgus deformities and lower at varus deformities (all P < 0.05). The stress values on the medial plateau of the tibia were significantly higher than the corresponding data on the lateral plateau at neutral and 5°, 10°, and 15° varus deformities, respectively (all P < 0.05), and significantly lower than the corresponding data on the lateral plateau at 5°, 10°, and 15° valgus deformities, respectively (all P < 0.05).

Conclusion: Residual varus and valgus deformity after tibial fracture malunion can lead to obvious changes of the stress distribution of the knee joint. Therefore, tibial fractures should be reduced anatomically and fixed rigidly to avoid residual varus-valgus deformity and malalignment of lower limbs.