Page 606 - WSAVA2017
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An Urban Experience
Although the primary aim of surgical intervention has been cited as acute cauda equina and neuroforamenal decompression, long-term maintenance of decompression and amelioration of pathological
LS instability are important secondary aims. Dorsal decompressive procedures are known to destabilise the lumbar vertebral column, particularly where facetectomy is performed. While lateral foramenotomy is likely to cause minimal additional instability unless the facet
is undermined, in which case fracture could occur,
it may also be challenging to decompress the nerve
root adequately and iatrogenic trauma could occur. It may be necessary to combine a lateral and a dorsal approach to attempt to decompress entry, middle and exit zones. Durability of decompression is also unknown, with osseous or soft tissue re-growth remaining a potential concern, either via post-surgical scarring or in association with recurrent peri-vertebral soft tissue or osseous proliferation as a result of ongoing instability.
Foramenotomy, facetectomy or dorsal stabilisation without distraction (using pins and cement, screws alone or plates and screws) may therefore fail to provide durable resolution of L7 nerve root encroachment in
the entry, middle and exit zones. Our aim over the last decade was to develop an intervertebral spacer screw that could be deployed via dorsal laminectomy and dorsal annulectomy with nuclear extirpation following lateral retraction of the cauda equina. Dorsal fixation elements would then be applied using pins or screws and formerly cement but more recently, rods and clamps (Fitzateur) to produce a dorsal and ventral fixation system akin to anterior-posterior inter-body fusion performed in human patients.
The spacer device has been called a Fitz Intervertebral Traction Screw (FITS). This constitutes a threaded titanium spacer screw with hydroxyapatite coating and is currently available in ten sizes. A 2.4mm screw is driven cranio-ventrally from S1 to L7 through a slot in the FITS device to prevent back-out. The dorsal fixation system is currently available in two sizes. Either 3.5mm or 4.5mm screws are placed on both sides of the L7 vertebra at the bases of the transverse processes and in the alar wings of the sacrum on both sides. A novel slotted polyaxial screw fixation clamp system, which allows multi- directional orientation, permits the L7 and sacral screws to be linked dorsally using rods. The rods are dumb-bell shaped to firmly anchor in the clamps to minimise risk of collapse. The clamps are locked to the spherical stopper ends of the rods using washers and lock-screws.
It should be noted that retraction of the cauda equina and stretching of chronic compressive elements away from the L7 nerve roots is not a benign intervention and risks should be explained to all owners pre-operatively. It should also be noted that other fusion systems such as custom-designed 3D printed plates and screws-rods
designed for human patients have been successfully deployed in other centres. It is likely that other surgical techniques will also be developed for treatment of this difficult condition and they may be equal or superior to the system described.
In a recent case series presented by our facility, thirty- one out of thirty-five patients exhibited improvement
in activity and lameness. Twenty-nine out of thirty-five owners felt quality of life had improved after intervention and two out of thirty-five felt it was equal to pre-surgical levels. Four out of thirty-five owners were indifferent due to complications or failure to improve. All patients were receiving NSAIDs at presentation whereas twenty-five out of thirty-five did not require NSAID therapy post- operatively. Veterinary examination was available for thirty-four out of thirty-five patients. Lameness, pain
and muscle mass scores all improved. On CT scans, significant difference was found between pre-operative and six months’ post-operative measurements of all end- plate distances in sagittal and dorsal planes and also all neuroforamenal dimensions in all zones on both sides. Bone in-growth was observed around the FITS device.
We have performed mechanical testing of the FITS- Fitzateur system wherein instrumented lumbosacral spinal units were subjected to non-destructive 4-point bending under compressive loading. Dorsal laminectomy/ discectomy resulted in a modest increase in the range of motion at L6-L7 and L7-S1 as compared with the intact spine when subjected to compressive loading up to 150N. Application of the spinal instrumentation at L7-S1 resulted in a significant reduction in flexion, extension and lateral bending at L7-S1 as compared with laminectomy alone, but no significant change in motion at the L6-L7 junction.
The FITS-Fitzateur system allows indirect decompression of the neuroforamenae and provides durable long-term stability. This may reduce the propensity for “failed
back syndrome” whereby failure to decompress the components of abaxial encroachment may result in ongoing pain which can be due to static or dynamic compression. Facet joint capsule thickening and osteophyte formation are also potentially addressed by distraction and stabilisation.
In conclusion, in dogs affected by DLSS, conservative management may not be effective in relieving pain and surgical intervention may be needed. Dorsal laminectomy and facetectomy with or without partial discectomy results in increased motion. Foramenotomy may not produce durable neuroforamenal decompression. Pedicle-screw systems have been shown to be effective in restoring stability of the LS junction but traditional mono-axial screws lack versatility. Instrumentation
with the novel spinal system described results in statistically significant reductions in lumbosacral instability in extension, flexion and lateral bending. The

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