Valgus knee stress in lumbosacral myelomeningocele: a gait-analysis evaluation

Twenty-five independent community-ambulating patients with lumbosacral-level myelomeningocele (N = 50 limbs) underwent gait analysis. The limbs of these patients were divided into two groups based on thigh-foot angle (TFA): Group I (n = 20) had marked external tibial torsion, TFA > or = 20 degrees, and group II had TFA between 10 and 20 degrees. Ten limbs were excluded because of neutral or internal alignment. Twenty normal limbs with TFA = 10 degrees served as controls. An abnormal internal varus knee stress during stance was identified in all group I limbs and 12 (70%) of 20 limbs group II limbs compared with controls, which demonstrated an internal valgus stress. This internal varus moment was greater in group I limbs than in the abnormal limbs in group II (p < 0.05). Knee flexion was the only other parameter found to correlate with this stress and only in group I limbs. We conclude that (a) in this patient group, increased external tibial torsion is likely to result in an abnormal internal varus knee stress; (b) TFA > 20 degrees appears significantly to increase this stress; and (c) knee flexion is an important related parameter, but only in limbs with TFA between 10 and 20 degrees. We believe that this abnormal stress may predispose the knee to late arthrosis and that derotational osteotomies to normalize the TFA may prove to have a favorable long-term effect.