Background: Fixed knee flexion deformity is common in children with neuromuscular disorders. Anterior guided growth (AGG) of the distal femur can achieve gradual correction in patients who are skeletally immature. Little outcome data are available on this procedure.
Methods: This is a retrospective matched cohort study. Forty-two knees (26 patients) underwent AGG surgery at our institution between 2007 and 2017. All patients underwent instrumented 3-dimensional gait analysis (3DGA). A nonsurgical control group of 49 knees (43 patients) was selected that matched for age, severity of preoperative knee contracture, and 3DGA parameters. Clinical, radiographic, and 3DGA outcomes were assessed and compared.
Results: Average preoperative knee flexion deformity in AGG group was 13±8 degrees. Following AGG, deformity improved by 8±7 degrees (P<0.001) as measured radiographically and by 7±7 degrees (P<0.001) as measured on physical examination. Average rate of correction was 0.7±0.6 degrees per month or 8±8 degrees per year. The 3DGA parameters such as minimum stance phase knee flexion and knee flexion at initial contact were also significantly improved following AGG. In contrast, flexion deformity as measured radiographically worsened by 3±3 degrees (P=0.002) in the control group. Twelve knees (29%) had failure of correction. Predictors of failure included older age, lower level of function, and greater severity of preoperative deformity. The age at time of surgery and the anteroposterior position of plate fixation relative to the distal femoral physis were associated with rate of correction.
Conclusions: In children with neuromuscular disorders, AGG of the distal femur is effective in improving degree of fixed knee flexion deformity as well as objective gait parameters. A significant portion of knees experience inadequate correction. Addressing factors associated with correction failure (ie, age and plate placement) may improve the procedure's success.
Level of evidence: Level III-case control study.