Abstract
Objective To explore the histological changes of vertebral growth plates under asymmetrical loading in porcine scoliosis model (PSM). Methods A total of 13 female Yorkshire pigs with an age of 6 weeks and a weight range of 6 8 kg were selected.In PSM group, 8 pigs were instrumented and tethered ipsilaterally through 3 separate incisions.After 8 weeks, posterior instrumentation was removed.The animals were observed for 8 more weeks.In control group, internal fixation of spine was performed without tethering.After sacrificing, spines were harvested for histological study.The specimens were embedded in paraffin, decalcified and stained by hematoxylin & eosin (HE) for histomorphometry.The thickness of hypertrophic zone in iliac cartilage, area and number of chondrocytes in cell-nest and number of proliferative chondrocytes were analyzed by Image-Pro Plus. Results In PSM group, 7 pigs developed idiopathic-type scoliosis.The mean coronal Cobb's angle was 27.8 postoperatively and progressed to 59.3 after a tethering period of 8 weeks.The average scoliosis was 55.2 at an average of 8 weeks after tethering removal.No scoliosis was found in control group.In PSM group, the number of chondrocytes of hypertrophic zones was fewer at concave side than that at convex side.And irregular arrangement of chondrocytes was present in hypertrophic zones.In PSM group, inter-side thickness of hypertrophic zone differed significantly (convex: 460.3±26.0 μm, concave: 318.5±72.1 μm, P 0.05). At convex side, average area of cell-nest and average number of cells in cell-nest were larger than those at concave side in PSM group (18 269.6±3 717.4 vs 9 719.0±1 979.7 μm2, P 0.05). In control group, no inter-side difference existed between average area of cell-nest (17 855.2±6 844.0 vs 16 610.0±7 009.9 μm2), average number of cells in cell-nest (12.2±2.0 vs 12.6±2.9) or number of proliferative chondrocytes (127.3±16.3 vs 130.6±31.2)(all P>0.05). Conclusions In porcine scoliosis model, asymmetrical loading contributes to unbalanced bilateral growth and causes vertebral wedging.Growth activity on growth plate at concave side is highly suppressed so that there are significant reductions of cell number and zone height in hypertrophic zone. Key words: Scoliosis; Animal model; Biomechanics
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