Degenerative arthritis of the knee is a complication of femoral or tibial fractures potentially avoidable by the correction of various degrees of malalignment. To better clarify the malalignment problem, the records of 14 patients (15 limbs), with degenerative arthritis of the knee and a history of tibial or femoral fracture were retrospectively reviewed. The average follow-up was 31.7 years. Static biomechanical frontal plane analyses were evaluated. The calculated increased force on either the medial or lateral tibial plateau, due to the malunion, was strongly associated with presence of a varus or valgus deformity at the knee (p less than 0.0005). A normal tibial plateau force for the malaligned condition multiplied by the time since fracture correlated directly with the amount of subsequent varus or valgus deformity at the knee (p less than 0.01). Lower limb fracture alignment should be restored to as near normal as possible to reduce the likelihood of gonarthrosis.