Physeal histological morphology after thermal epiphysiodesis using radiofrequency ablation

BACKGROUND: Several treatments have been described for leg length discrepancy. Epiphysiodesis is the most commonly used because of its effectiveness. Thermal epiphysiodesis using radiofrequency ablation (RFA) alters the growth plate morphology without damaging the adjacent articular cartilage; it is a minimally invasive method that has shown excellent results in animal models. This study describes the macro and micro morphology after the procedure.

MATERIALS AND METHODS: Epiphysiodesis using RFA was performed in vivo for 8 min (92-98 °C) at two ablation sites (medial and lateral) in one randomly-selected tibia in eight growing pigs. The contralateral tibia was used as control. After 12 weeks, the pigs were killed and the tibiae harvested. The specimens were studied macroscopically and histology samples were obtained. Physeal morphology, thickness and characteristics were then described.

RESULTS: Macroscopically, the articular cartilage was normal in all the treated tibiae. Microscopically, the physis was detected as a discontinuous line on the treated tibiae while it was continuous in all controls. In the control specimens, the mean thickness of the physis was 625 µm (606-639, SD = 14). All the physeal layers were organized. In the ablated specimens, disorganized layers in a heterogeneous line were observed. Bone bridges were identified at the ablation sites. The central part of the physis looked normal. Next to the bone bridge, the physis was thicker and presented fibrosis. The mean thickness was 820 µm (628-949, SD = 130). No abnormalities in the articular cartilage were observed.

CONCLUSIONS: Thermal epiphysiodesis with RFA disrupts the physeal morphology and causes the formation of bone bridges at the ablation sites. This procedure does not damage the adjacent articular cartilage. The damaged tissue, next to the bone bridges, is characterized by disorganization and fibrosis.