Clinical and Radiological Outcomes of Posterior Cervical Fusion Supplemented With Interfacet Spacers

Background and Rationale Posterior cervical fusion surgeries are performed for degenerative cervical conditions, cervical deformity, cervical tumors, and cervical trauma. They are preferred over an anterior approach when the pathology is located posterior to the spinal cord or when multiple levels must be addressed. Degenerative cervical spondylosis contributes to loss of disc height, facet arthropathy and hypertrophy, and retrolisthesis of the vertebral bodies, all of which can lead to foraminal stenosis, or narrowing around the exiting nerve roots. This is often accompanied by loss of cervical lordosis. During a posterior fusion operation, the restoration of cervical lordosis can worsen this foraminal stenosis and lead to iatrogenic radiculopathy with and estimated incidence between 2.4-50%. Cadaveric studies have shown the insertion of interfacet spacers in the cervical spine increase foraminal height, and serve to indirectly decompress the exiting nerve roots. Another common complication of cervical spine surgery is C5 palsy, which has been reported in 4.6% of patient undergoing posterior cervical spine decompressive procedures, including decompression and fusion. Patients suffering from iatrogenic C5 palsy have significantly increased recovery times, and often require additional services such as imaging studies (CT, MRI) and increased need for physical and occupational therapy, thus increasing costs. Given the ability to decompress the neuroforamen with interfacet spacers, they could potentially be an effective technique for reducing the incidence of C5 palsy. The use of cervical interfacet spacers (CIS; CORNERSTONE Facet MicroGrafts, Medtronic, Minneapolis, MN) is a relatively novel technique shown to be useful for posterior fusion to address symptomatic pseudoarthrosis (fusion failure) after anterior cervical arthrodesis. CIS have a relatively large osteoconductive surface area and are placed under tension in the interfacet space, which together favorably influence bony fusion. Current techniques for posterior cervical fusion rely on graft placement using bone extenders placed in the posterolateral space, which is not under a compressive load. Wolfe's law dictates that certain amounts of loading of bone grafts is required to achieve bony fusion. Therefore, the use of CIS could potentially increase fusion rates after posterior cervical arthrodesis procedures and reduce or eliminate the need for use of bone graft extenders. Reassuringly, radiologic studies have shown that despite the increase in foraminal height, the use of CIS does not lead to loss of cervical lordosis. Study Objective To date, there have been no prospective studies examining the use of cervical interfacet spacers. The investigators propose to undertake a prospective study to assess fusion rates and cervical sagittal parameters following posterior cervical arthrodesis procedures supplemented with CIS. Primary Outcome Measures The primary outcome measures will include (i) the rate of cervical fusion measured on post-operative radiographs and CT scans performed at 2-years and (ii) cervical sagittal alignment parameters as measured on post-operative radiographs. Secondary Outcome Measures The secondary outcome measures will include post-operative patient reported outcomes including NRS, NDI, and SF-36 RAND. As well, all neurological adverse events will be prospectively collected.