An Experimental Study Of Spinal Growth Control With Long-level Shape Memory Alloy Staples

Objective: To evaluate the spinal growth modulation of long-level Staples by contrasting the correction of dual-level versus single-level shape memory alloy Staples in an immature goat model and then observing their histological changes, provide experimental data for the clinical application of Staples in the correction of scoliosis.Background: The technique of Staples is a fiisionless minimally invasion surgery technique in the treatment of idiopathic scoliosis, which is based on the theory of "Hueter-Volkmann" law. This technique can correct the scoliosis in the way of short segmental modulating by asymmetric pressing and tethering to the convex side of the curved spine, and then inducing an asymmetric development of the spine. Animal experiments and clinical tests have indicated that this technique can slow down the progressing of scoliosis or correct early scoliosis. Recent researches focus on its validity and relative animal experiments. However, this technique is developing, and relative pathophysiological, histological and molecular biological results is rare. Relative reports in china are far less. Besides, routine short-level Staple has its limitations in the corection of scolosis, while there is no reports about long-level Staples at home and abroad. Methods: Experimental scoliosis was created in 15 healthy female goats (age, 5-8 weeks; weight, 6-8 kg) in the way of asymmetric tethering using a pedicle screw system and convex rib partial resection. All goats were followed for over 2 months. Goats with progressive scoliosis were randomized into 3 groups for a separate study: All tethers were removed and goats in treated groups underwent followed thoracotomy. Shape memory alloy Staples were lateral implanted into vertebral bodies spanning 4-5 discs close to the apical vertebra, along the convexity (right side) of the maximal curvature, goats in short-level Staple group were implanted Staples spanning one disc each; goats in long-level Staple group were implanted Staples spanning two disc each; goats in control group were just removed the tethers, no treatment were offered. Anterioposterior and lateral plain radiographs were taken right after the surgeries and subsequently every 4-6 weeks to measure the Cobb angles of the spine. All goats were observed for at least 2 additional weeks. At the end of the observation period, superior intervertebral disc of apical vertebra and two adjacent growth plates were harvested. All specimens were sliced undecalcified. The proliferative zonal height and the hypertrophic zonal heigh aolng the growth direction were measured in slides stained with toluidine blue.Results: 14 goats achieved progressive structural scoliosis successfully. Radiographs showed that the 2 treated groups attained an immediate correction right after the surgeries (P<0.05), and the Cobb angles of the scoliosis showed a tendency of decrease with time. Compared with the initial stage of the stapling, the Cobb angles of the treated groups decreased significantly during the observation period (P<0.05), whereas little changes shown in the control group (P>0.05). Both of the treated groups demonstrated an apparent larger virtual correcting angle (immediate angle after surgery minus terminal angle at the end of the observation) (P<0.05), compared with the control group. Goats in long-level Staple group attained larger virtual correcting angle of 17.8°±4.0°than goats in short-level Staple group of 14.0°±7.6°, but there was no distinct difference between the 2 treated groups (P>0.05).The hypertrophic zonal height of the convex side of vertebral growth plates were lower than those of concave side in both treated groups (P<0.05). The convax side mean hypertrophic zonal height in short-level Staple group was 29.2±4.4μm, while the concave side 42.5±8.4μm; the corresponding values was 27.6±1.9μm and 41.2±4.6μm respectively in long-level Staple group. The difference value of the concave side hypertrophic zonal height subtract that of convex side in both short-level Staple group and long-level Staple group were larger than in control group (P<0.05), while there was no difference between the two treated groups (P>0.05). There was no difference between the two sides of the hypertrophic zonal height in the control group (P>0.05), nor among the proliferative zonal height in all three groups (P>0.05). Neither the convex nor the concave side of the hypertrophic zonal height and proliferative zonal height on the plane of vertebral disc nailing the Staple tooth show obvious difference, compared with the plane without the Staple tooth (P>0.05). Conclusions: Both of the 2 types of shape memory alloy Staples can correct scoliosis effectively. long-level Staples can achieve, and even exceed, the effect of short-level Staples, but there was no statistical difference between them.