3D Visualization of Vertebral Growth Plates and Disc: The Effects of Growth Modulation.

ABSTRACT

After tethered growth or sham surgery, spinal motion segments underwent microtomography to determine physeal and disc 3-dimensional (3D) morphology. Instrumented and contralateral sides of tether and sham surgical groups were compared. OBJECTIVES: To determine the 3D morphological effects of growth modulation via anterolateral tethering on vertebral physeal and intervertebral disc morphology in a rapidly growing bovine model. SUMMARY OF BACKGROUND DATA Growth modulation acts through physeal loading. Providing a promising alternative to arthrodesis for scoliosis correction, tethering vertebral growth maintains further growth (open/functioning physes) and motion (disc integrity). Standard physeal and disc evaluation using histology reduces 3D geometries to single planar samples. METHODS: Five-week-old calves received anterolateral flexible spinal tethers (n = 6) or sham surgeries (n = 6) followed by 6 months of growth. Individual motion segments were imaged by microtomograph (36 µm). Physeal space and disc space thickness maps were generated from surface reconstructions. Normalized thickness differences were compared between instrumented and contralateral sides of tether and sham groups (analysis of variance, p < .05). Physeal closure was estimated and regions of bony bridging were marked closed. RESULTS: Tethering caused significant physeal thickness reduction on the instrumented side compared with the contralateral side (7.6% ± 2.0%; p = .0002). This reduction was greater (p = .003) in tethered physes than in the sham, which demonstrated no reduction (0.8% ± 3.7%; p = .6). Small regions of physeal closure were observed in sham and tether groups (medians of 1.4% and 0.1% and maximums of 6.8% and 2.7%, respectively). Tethered discs were 29% thinner than sham, but demonstrated no contralateral to instrumented-side thickness difference (5.2% difference; p = .3). CONCLUSIONS: Tethering resulted in thinner physes on the tethered side without notable physeal closure. With no side differences in the sham group, tethering apparently applied instrument-sided compressive forces. Tethering also resulted in thinner discs, although they were apparently. Producing consistent histological samples is difficult; misaligned slices may lead to inaccurate conclusions. Evaluating entire physes or discs produces more robust results.