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Unilateral Pedicle Screw Epiphysiodesis of the Neurocentral SynchondrosisProduction of Idiopathic-Like Scoliosis in an Immature Animal Model
Hong Zhang, MD1; Daniel J. Sucato, MD, MS1
1 Texas Scottish Rite Hospital for Children, 2222 Welborn Street, Dallas, TX 75219. E-mail address for H. Zhang: hong.zhang@tsrh.org
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Texas Scottish Rite Hospital for Children, Dallas, Texas

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Nov 01;90(11):2460-2469. doi: 10.2106/JBJS.G.01493
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Background: The neurocentral synchondrosis plays a role in the growth of the spine. The goal of this study was to determine whether asymmetric epiphysiodesis of this synchondrosis creates a scoliotic deformity in a growing-animal model and to correlate curve magnitude with the degree of closure of the synchondrosis.

Methods: Two-month-old pigs were assigned to three groups. In the control group, two animals received a sham operation without pedicle screw fixation; in the single-screw group, three animals were treated with a single right transpedicular screw placed across the neurocentral synchondrosis from T7 to T14; and in the double-screw group, three animals were treated in the same way as the previous group except that two screws were placed in each pedicle. The animals were killed at six months, and radiographs and axial computed tomography images of the spine were obtained. Histomorphometric analyses were performed to grade the synchondrosis at each level.

Results: A scoliotic curve was seen in none of the animals in the control group, in one of the three in the single-screw group, and in all three in the double-screw group (30°, 42°, and 42°). Vertebral rotation in the axial plane occurred toward the screw side and was significantly greater in the double-screw group (mean, 15.2°) than in the single-screw (mean, 6.1°) and control (0°) groups (p < 0.001). There was no difference in morphology between the left and right pedicles in the control group. The left pedicle was 9% longer than the right (screw-treated) pedicle in the single-screw group, and it was 22% longer than the right pedicle in the double-screw group. Closure of the neurocentral synchondrosis was greatest in the double-screw group (>75% closure) compared with the single-screw group (<50% closure) (p < 0.0001) and the control group (no closure) (p < 0.0001), and closure correlated with the magnitude of the coronal curve (p = 0.001).

Conclusions: Unilateral transpedicular screw fixation that traverses the neurocentral synchondrosis in a growing-pig model can produce asymmetric growth of the synchondrosis to create scoliosis with the convexity on the side of the screw fixation. Double pedicle screws provided a greater epiphysiodesis effect on the neurocentral synchondrosis, which correlated with a greater degree of scoliosis.

Clinical Relevance: This young-animal model demonstrates that asymmetric closure of the neurocentral synchondrosis produces structural scoliosis due to continued growth of the opposite pedicle. This non-fusion strategy may have some role in the treatment of growing patients with spinal deformity.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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