Limits of Calcaneal Lengthening for Treating Planovalgus Foot Deformity in Children With Cerebral Palsy

Background: Calcaneal lengthening is used to correct symptomatic planovalgus foot deformity, but outcomes have been less satisfactory in children with cerebral palsy. This study aimed to define limits of calcaneal lengthening by analyzing the risk factors for undercorrection of deformity. Methods: We retrospectively reviewed 20 cases of children with cerebral palsy who underwent calcaneal lengthening of 30 planovalgus feet at a mean age of 11.9 years. Foot deformities were evaluated by the anteroposterior talo-first metatarsal angle (normal, 10 +/- 7.0 degrees), lateral talo-first metatarsal angle (normal, 13 +/- 7.5 degrees), and lateral calcaneal pitch angle (normal, 17 +/- 6.0 degrees) on standing foot radiographs. Among these parameters, a corrected foot was defined as 2 or 3 parameters being corrected to within a normal range, and an undercorrected foot was only 1 or no parameter being corrected to within a normal range. Factors were compared between the corrected group and undercorrected group for significant predictors, and cutoff values of predictors were calculated for use as a clinical guideline. Results: Seventeen planovalgus feet were corrected satisfactorily by calcaneal lengthening, while the other 13 feet were undercorrected. Undercorrected feet had a greater preoperative anteroposterior talonavicular angle (33.7 vs 22.8 degrees, P = .001) and a smaller lateral calcaneal pitch (-1.7 vs 5.6 degrees, P = .03). A talonavicular angle of more than 24 degrees and calcaneal pitch less than -5 degrees were identified as cutoff values using a receiver operating characteristic curve. The predicted probability of undercorrection was 100% (9/9 feet) for 2 positive predictors, 50% (8/16 feet) for 1 positive predictor, and 0 (0/5 feet) for zero predictors. Conclusion: A talonavicular lateral subluxation of more than 24 degrees on the anteroposterior radiograph and a calcaneal pitch angle less than -5 degrees on the lateral radiograph were 2 independent predictors that could be used to identify a planovalgus deformity that would be beyond the corrective capacity of calcaneal lengthening to restore normal alignment.