Purpose: To determine the effects of radiofrequency energy on the growth plate in young rabbits for possible future clinical applications in image-guided non-surgical epiphysiodesis
Methods and Materials: 21 8-week old New Zealand rabbits underwent either 21 gauge sham needle placement or RF electrode heating of the proximal tibial growth plate under fluoroscopic guidance. RF was performed with an SMK electrode (Radionics Inc, Burlington, MA) with a 5mm active tip for 2 minutes maintaining the tip tempererature at 80 C. with an RF generator (Cosman coagulator 1, Radionics Inc, Burlington, MA). K-wires were placed in the tibial shafts of both legs as a marker for leg growth. Rabbit leg growth was measured every 2 weeks for 10 weeks using PA radiographs of the lower extremities. Animals were sacrificed at 10 weeks for imaging and histologic analysis. Imaging was performed with a uCT 40 (Scanco USA,Wayne, PA) (30u resolution) and 1mm helically acquired axial images with a multidetector CT (GE Light speed, GE Medical Systems, Milwaukee, WI). Statistical analysis was performed with parametric generalized estimating equations using GENMOD (SAS version 8.2).
Results: Two of the 21 animals died from dehydration due to diarrhea within the first week after the procedure. Endpoint survival was achieved in 7 and 12 animals in the sham and RF group, respectively. 2 of the 12 animals in the RF group were sacrificed at 4 weeks for early histological analysis. Measurements of the entire and proximal tibial growth between the sham and RF group demonstrated a statistically significant (p<.0001) reduction in proximal tibial growth in the RF group by 1.9,3.1,4.4,6.6 and 8.4mm at 2,4 6,8 and 10 weeks, respectively. CT and micro CT analysis showed bridging bars of trabecular bone that spanned the growth plate in the RF group. Histologic analysis confirmed the presence of trabecular bone traversing the growth plate in the RF group.
Conclusion: RF thermocoagulation of the growth plate creates bridging bars of trabecular bone that significantly slows tibial growth in young rabbits. This novel minimally invasive treatment may provide a means of epiphysiodesis in humans with leg length discrepancies. This research was sponsored in part by a small grant from Valley Labs (Boulder, CO). (D. D. is a consultant for and received a grant from Valley lab.)
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