Genu Valgum after Distal Femur Extension Osteotomy in Children with Cerebral Palsy

Background: Distal femur extension osteotomy (DFEO) is a common treatment for knee flexion contracture and crouch gait in patients with cerebral palsy (CP), but skeletally immature patients tend to develop genu valgum deformities after DFEO. This study aimed to report the tendency of valgus changes after DFEO and determine the risk factors for subsequent surgery for excessive genu valgum. Methods: This retrospective case-control study included 25 children with CP who underwent DFEO in 44 limbs for knee flexion contractures ≥15 degrees at a mean age of 11.0 years. Radiologic measurements included the anatomic lateral distal femoral angle (aLDFA), anatomic tibiofemoral angle (aTFA), medial proximal tibia angle, and plate-condyle angle, postoperatively and at the latest follow-up. Age, sex, preoperative knee flexion contracture angle, Gross Motor Function Classification System level, and radiographic measurements were compared between children with and without subsequent guided growth for genu valgum. Results: A significant valgus change was observed at the distal femur in the first postoperative year (aLDFA from 83.6 to 80.1 degrees, P<0.001; aTFA from 176.1 to 172.5 degrees, P<0.01; plate-condylar angle from 5.3 to 9.5 degrees, P<0.001). Valgus changes occurred in 36 of the 44 limbs (82%) by an average of -4.6 degrees in the aLDFA, and subsequent guided growth was performed in 5 patients (20%). Guided growth for genu valgum was associated with a greater postoperative valgus angle (aLDFA: 78.0 vs. 84.9 degrees, P<0.01) but not with age, Gross Motor Function Classification System level, or preoperative flexion contracture. Conclusions: Distal metaphyseal osteotomies and distally placed angled plates near the physis are associated with valgus changes following growth. We recommend making a slight varus alignment during DFEO to compensate for subsequent valgus changes. Level of Evidence: Level III - therapeutic, retrospective comparative study.