Assessment of femoral physeal activity after transitory hemiepiphysiodesis using screws and nonabsorbable filament.

Background: Different techniques for gradual correction of angular deformities of lower limbs exist. Long-term behavior of the growth plate after hemiepiphysiodesis is not yet well understood. We assessed the restoration of normal physeal activity in New Zealand rabbits, after transitory hemiepiphysiodesis, using screws and nonabsorbable filament.

Methods: We performed a lateral distal femoral epiphysiodesis using nonabsorbable filament and screws, in the right knees of 14 New Zealand male rabbits, aged 11 weeks. Two groups were created: in group 1, the suture was cut after 1 month, and in group 2 it was left uncut. Simple plain radiographs were taken at the beginning and at 4, 8, and 12 weeks of follow-up to evaluate lower limb deformity rate and femoral length. The left knee of each rabbit served as controls. Angular deformity and femoral length were compared between the groups.

Results: Eleven rabbits completed the protocol. The control group had no modification in lower limb mechanical axis. On the fourth week, all operated limbs had a significant valgus tibiofemoral angle variation (mean 24 degrees, P<0.05). When the filament was cut, there was complete restoration of the mechanical axis. When the filament was kept, tibiofemoral angle increased its valgus deformity until the eighth week (mean 32 degrees) without changes thereafter. The final femoral length was shorter in group 2 compared with the other 2 groups (P<0.05), whereas group 1 was slightly longer than the control group (P>0.05).

Conclusions: Lateral distal femoral hemiepiphysiodesis with nonabsorbable filament resulted in a valgus deformity on the femur. Once the filament is cut, the femur can restore its normal alignment, while maintaining longitudinal growth. Keeping the physeal tether increases the valgus achieved during the first 8 weeks, and remained stable throughout the study, shortening the bone.

Clinical Relevance: This is an effective alternative for the correction of angular limb deformities that maintains physeal function and may be useful for orthopedic surgeons. It could also represent an adequate model for the study of rebound effect.