ENDOSCOPIC MECHANICAL SPINAL HEMIEPIPHYSIODESIS MODIFIES SPINE GROWTH

E.J. Wall, M.D.,
D.I. Bylski–Austrow, Ph.D.,
R.J. Kolata D.V.M.,
E. Ballard, M.D.,
A.H. Crawford, M.D.
* (a – Ethicon Endo Surgery)
Children's Hospital Medical Center, Cincinnati, OH, USA

PURPOSE:
Current methods of scoliosis correction are invasive and expensive. Hemiepiphyseal stapling can correct angular deformities in the lower limbs, however, similar methods have previously failed to correct spinal deformities. The purpose of this study was to determine if a simple endoscopic implant is capable of modifying spine growth without fusion.

METHODS:
In eight live skeletally immature domestic pigs, staples were implanted across the growth plates of one side of the mid–thoracic vertebrae just anterior to the rib heads using anterior endoscopic procedures approved by an IACUC. At least 6 staples of a single design were implanted per pig. Five staple designs of successively increasing complexity have been tried. Results were assessed biweekly for 8 weeks with radiographs, and CT scans were obtained postmortem. Coronal sections were cut for histologic analysis. The design variables were staple anatomic location, fixation methods, blade size, and ease of endoscopic implantation.

RESULTS:
Two of the five implant designs resulted in mild (20–25º) to moderate (35–40º) {Fig. 1} increases in curvature within 8 weeks using staples that crossed the invertebral disc and two longitudinal growth plates. Growth plate structure showed graded differences from stapled to unstapled sides and between stapled and unstapled vertebrae in chondrocyte size and organization and in bone density at the metaphyseal margin. Staple blade lengths of nearly half the width of the vertebrae induced physeal changes that gradually decreased across the entire vertebra. Improvements in fixation methods were most effective in increasing spine curvature. The most successful design to date {Fig. 1} included two screws and relatively wide, short, angled, and barbed blades.

CONCLUSION:
In this pilot study spine growth was altered without fusion using surgically relevant, minimally invasive procedures and a simple implant. The mechanism of curvature induction included structural changes to the growth plate consistent with direct physeal compression. The specific design of the staple was crucial to fixation and therefore to the amount of curvature induced.

SIGNIFICANCE:
Endoscopic stapling holds potential for correcting infantile, juvenile, and young adolescent idiopathic scoliosis. Figure 1

* If noted, the author indicates something of value received. The codes are identified as: a–research or institutional support, b–miscellaneous funding, c–royalties, d–stock options, e–consultant or employee.