Cervical, Thoracolumbar and Lumbosacral Spine: Novel Internal Fixation Devices

Degenerative lumbosacral stenosis (DLSS), cervical spondolymyelopathy (CSM) and thoracolumbar intervertebral disc protrusion are all chronic debilitating conditions of the canine spine. Multiple disparate treatment modalities have been proposed, primarily constituting decompression and stabilization techniques. A novel intervertebral spacer device (FITS, Fitz Intervertebral Traction Screw, patent pending) has been described for intervertebral distraction and when used with adjunctive fixation elements can distract and stabilize neuroforaminal dimensions and alleviate spinal canal stenosis. Maintenance of clinical improvement following such surgical intervention has been documented for the lumbosacral and cervical regions, and at the time of writing, validation for thoraco-lumbar spinal applications is ongoing. The initial clinical study population of dogs affected by DLSS consisted of 23 dogs presented January 2007 December 2008. Signalment, duration of clinical signs, pre-operative and 12 week postoperative radiography, MRI, complications and one year post-operative clinical and owner visual analog scale (VAS) scores were recorded. All presented with clinical signs attributable to lumbo-sacral and sciatic nerve pain and MRI-documented abaxial neuroforaminal impingement. Standard T2 sagittal and transverse MRI scans were performed in addition to 40-45° angled para-sagittal oblique T2 and T1 images of the neuroforaminae. Standard dorsal laminectomy without facetectomy was followed by intervertebral disc annulectomy and nuclear extirpation. The FITS was inserted manually into the IVD space at the site of annulectomy to a level below the cauda equina nerve roots. Negative profile 2-5-3mm threaded pins were placed across the LS fascets, into the vertebral body of L7 bilaterally and into the sacro-iliac junction bilaterally. All pins were “notched” with an appropriate cutter and enshrouded in a bolus of polymethylmethacrylate cement applied dorsal to L7-S1 with the laminectomy site protected using autogenous muscle/fat. Breeds included Labrador Retriver (30.43%), German Shepherd (21.73 %) and Rottweiler (17.39%). Male dogs constituted 60.86%. The median duration of clinical signs was 3months (range 3 weeks17months). Lumbo-sacral and sciatic nerve pain were present for all cases, whilst abnormal gait or behaviour, lameness, reduced myotactic reflexes, altered tail carriage and micturition functionality varied. All except one dog were able to micturate and defaecate normally by 3 days post-operatively, with one exception taking 10 days to voluntarily urinate. Pelvic limb function deterioration was noted in one patient and resolved over 16 weeks, whilst three others took up to 8 weeks to recover normal ambulation. Mean time to resolution of pain and lameness in 21 dogs, by clinical examination and owner VAS score was 4.2 weeks (range 2-16 weeks). Clinical outcome was evaluated for 15 patients by telephonic interview at mean 495 days postoperatively (range 300 – 780 days). For exercise level, one owner answered that it was sub-optimal, 66.6% answered high (n=10) and 26.6% moderate (n=4). For degree of pain by “whole number” scale of 1 to 10 with 1 being no pain and 10 being severe pain, 60% answered 1 (n=9), 26.66% said 2 (n=4) and 13.3% said 3 (n=2). Radiography performed at twelve weeks postoperatively for all cases revealed mean magnitude of intervertebral distraction 3.4mm (range 2-6mm) and maintenance of distraction position for all cases, with implant integrity for 20 dogs. Three cases were affected by clinically inconsequential migration of a threaded pin, which was removed and one further case was affected by a seroma and superficial licking associated with self-trauma. Surgical intervention for DLSS is indicated when neurologic deficits are present, pain is severe, quality of life is affected or there is no response to medical management or physical therapy. Addressing exit zone impingement of the L7 nerve roots even with radical foraminotomy and a trans-ilial approach is difficult because of propensity for iatrogenic trauma and encroaching soft tissue and bone may grow back over time. Furthermore, without adequate stabilisation, dynamic components of deformity may continue to cause clinically relevant pain, especially with respect to the L7 nerve roots in a definitive subgroup of