R-FIX (Rib-FIXation System) for Severe Progressive Spinal Deformity

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Project Summary Early-onset spinal deformity (EOSD) is deformity that begins before 10 years of age. Curvature can be in the lateral direction (scoliosis), anterior direction (hyperkyphosis) or both (kyphoscoliosis). The most common surgical treatment for EOSD is expandable growing rods fixed to the spine with pedicle screws. There are many challenging problems with this technique. Auto-fusion of the vertebrae is common, resulting in stunted spinal growth and sub-optimal pulmonary development. Complication rates are high including proximal fixation failure (pedicle screw pull-out), rod fracture, proximal junctional kyphosis (PJK), and neurological injury. Proximal fixation failure is especially problematic in osteoporotic patients with hyperkyphotic or kyphoscoliotic deformity, and can sometimes make successful treatment of these patients impossible. The VEPTR (Vertical Expandable Prosthetic Titanium Rib) is an alternative device, but it cannot be contoured in the sagittal plane and is contraindicated for hyperkyphosis and kyphoscoliosis. This application proposes a new technique called the rib construct for correcting EOSD. Instead of anchoring rods to the spine with pedicle screws, the rib construct moves proximal fixation to the ribs using a series of hooks. This approach is a conceptual shift in approaching spinal deformity, in that the thorax is manipulated to secondarily reposition the spine. The rib construct allows the surgeon to manipulate the thorax in any combination of both sagittal, coronal, and axial planes, allowing for safer, more effective, and versatile deformity correction. Rib fixation with the rib construct can be achieved with either: 1) off-label laminar hooks, which are already commercially available for spinal fixation to the lamina but can also be used on the ribs, or 2) rib hooks as part of our novel patented R-FIX (Rib-FIXation System). While laminar hooks have performed favorably compared to pedicle screws in our preliminary clinical use, these have been used entirely off-label and there is no commercially available surgical system designed for this technique. There have been issues with loss of fixation under torsional forces, implant prominence, and occasional cases of rib fracture with laminar hooks. The R-FIX System, which originated from a bioengineering lab (one of the applicants' lab) at Clemson University and has been further developed by Apex Orthopaedic Technologies, is designed to resolve these issues. The objective of this proposal is twofold: 1) to prove the overall concept of rib fixation with the rib construct by obtaining basic science data to support the clinical data we have already obtained and 2) to demonstrate the superior performance of R-FIX rib hooks compared to laminar hooks. This research will be conducted over 12 months and the data obtained from this grant proposal will be used in a 510(k) application for FDA clearance and the NIH SBIR Phase II application. Major milestones to be achieved with this grant include 1) ex vivo biomechanical evaluation of R-FIX rib hooks compared to pedicle screws and laminar hooks, and 2) assessment of the safety and efficacy of R-FIX rib hooks compared to pedicle screws and laminar hooks in a pediatric hyperkyphosis porcine animal model.