Tibia vara deformity after below knee amputation and synostosis formation in children.

BACKGROUND: Progressive varus deformity of the tibia in pediatric patients after transtibial and Syme amputations has not been reported in a series. A distal tibia to fibula synostosis, created surgically to minimize the risk of terminal overgrowth or occurring spontaneously, was noted in most patients. The goals of this study are to address the causes of the deformity, the implications for prosthetic wear, and potential treatment options.

METHODS: Twelve patients identified from the juvenile amputee database at 2 centers developed progressive varus deformity of the residual limb. One patient had bilateral involvement. A distal tibia-fibula synostosis was noted in 12 (92%) of the residual limbs, and in one, a fibrous union was suspected. The level of amputation was trans-tibial in 10 patients, and Syme amputation in 3 patients. Two patients had acquired trans-tibial level of amputation from congenital constriction band syndrome. Nine of the patients (75%) were between the ages of 3 and 5 years at the time of injury.

RESULTS: The mean proximal medial tibial angle was 80.5 degrees (range, 75-85 degrees). Ten of the patients underwent procedures to correct the mechanical axis and resolve or prevent problems with prosthetic fitting. Four patients has proximal tibial osteotomies (HTO), 2 oblique closing wedge osteotomies, 1 shaft osteotomy, and 4 lateral proximal tibial hemi-epiphyseodesis. In 2 patients, no correction was recommended.

CONCLUSIONS: The presence of a distal tibia-fibula synostosis in pediatric amputee patients may contribute to the risk of developing a progressive varus deformity and should be monitored during a child's growth. Distal tibiofibular synostosis may disrupt normal differential longitudinal growth and may contribute to this progressive angular deformity. Severe deformity may require prosthetic modifications or operative correction to provide for a normal mechanical axis. Lateral hemiepiphyseodesis of the proximal tibia can be effective if the deformity is detected early. We do not recommend creation of a synostosis in the young child for terminal growth.

LEVEL OF EVIDENCE: Level 4.