Chronologic change in the growth plate after radiofrequency-induced thermal injury: MRI-histologic correlation.

OBJECTIVE: The purposes of this study were to assess chronologic changes in normal growth plate after radiofrequency-induced thermal injury and to evaluate the feasibility of MRI for revealing alteration of the growth plate.
MATERIALS AND METHODS: Radiofrequency ablation was performed on the right proximal tibia of 13 8-week-old New Zealand White rabbits. An 18-gauge cooled-tip electrode with a 5-mm active tip was placed distal to the physis under fluoroscopic guidance. MRI, including T1- and T2-weighted images, gradient-recalled echo images, and contrast-enhanced T1-weighted images, was performed 2, 4, and 12 weeks after ablation. Rabbits were sacrificed 2 (n = 4), 4 (n = 4), and 12 weeks (n = 5) after ablation. The sequential changes in the ablated zone, the injured physis, and the nonablated portion of the physis were correlated between MRI features and histologic results.
RESULTS: Diameter of the nonenhancing lesion on MR images strongly correlated with the size of the region of coagulation necrosis at gross examination. The intraclass correlation coefficients were 0.98 and 0.94 for the long and short axes (p < 0.001). On gradient-recalled echo images, physial conspicuity was less in the injured physis than in the nonablated portion and less in the ablated than the control tibia. Physial conspicuity was graded for comparison with physial thickness at microscopic examination. The thickness of the physis was less in the ablated than in the control tibia 4 and 12 weeks after treatment (p < 0.05, paired Student t test). The cartilage column of the injured physis was delaminated 2 weeks after treatment, and a bone bridge through the injured physis was detected at 4 weeks.
CONCLUSION: Radiofrequency-induced thermal injury causes early closure of the physis. MRI can depict the extent of radiofrequency-induced thermal injury and alterations in the physis that lead to early closure.