Surgical application of a new anchored intervertebral spacer (C-LOX, Rita Leibinger GmbH & Co. KG, Neuhausen, Germany) for the treatment of Canine Cervical Spondylomyelopathy (Wobbler Syndrome)
Author: Winnie Achilles in cooperation with Dr. Günter Schwarz & Prof. Dr. Franck Forterre
Note: Preoperative radiographs are used to make preliminary selection of spacer and screw sizes. It is advisable but not indispensable to use fluoroscopy while performing the distraction-fusion technique with the C-Lox Cage. Fluoroscopy will provide accurate intraoperative assessment of correct implant and screw size, and of the depth and location of spacer and screw placement.
Place the dog in dorsal recumbency with a fulcrum underneath to support the neck. Avoid overextension. A standard approach to the ventral cervical spine is performed.
The affected disc space is identified and exposed, and a window is cut out of the ventral annulus fibrosus using a beaver blade. The width of this window should be minimally larger than the width of the selected spacer. The vertebral endplates delimit the cranial and caudal borders of the opening. Care must be taken not to penetrate the dorsal part of the annulus during discectomy
In order to attach the C-LOX Distractor, vertically oriented 2,5 mm holes are drilled into each of the adjacent vertebrae. These holes must be exactly on the midline and should be located in the caudal half of the cranial and in the cranial half of the caudal vertebrae. Penetration depth should at least be 2/3 of the vertebral body depth in order to avoid tilting when distracting the vertebrae. The crista ventralis marks the median plane of the vertebrae but makes it easy to slide off the midline. Preoperative measurements and fluoroscopy will aid in taking care not to enter the spinal canal.
Insert the C-LOX Distractor into the predrilled holes and open its jaws to widen the intervertebral disc space.
The C-LOX Spinal Disc Broaching Curette is used to carefully remove all remnants of the nucleus pulposus. The dorsal part of the annulus fibrosus can be felt as a more dense structure and should be preserved. The exposed end plates are freed from as much connective tissue as possible, but subchondral bone must be fully preserved.
If a considerable amount of nucleus pulposus material is located within the spinal canal, this can be attempted to remove with the help of fine curettes or delicate arthroscopic biopsy forceps.
The suitable size for the C-Lox implant can be estimated pre-operatively on diagnostic imaging. Attach the C-LOX Implantation Placement Rod to the suitable C-LOX Template and insert it in the intervertebral disc space. Ensure the correct fit. Here again, vertical beam fluoroscopy can be very helpful. If insertion requires energetic forcing or seems to achieve only slight distraction, a slimmer or thicker template should be used.
After establishing optimal fit, the Template is replaced by the corresponding C-LOX Cage. Spikes on the cranial and caudal side will ensure a secure seating of the implant, but can make insertion slightly more difficult compared to the C-Lox Template of the same size. Press the cage firmly down into place.
The cage will be secured with locking screws. Tight contact of the “ears” with the bone is not mandatory, although desirable. If needed, the “ears” can be slightly bent for better bone contact. However, this will change the direction of the screws. After proper seating of the C-Lox Cage, the C-Lox Distractor can be removed and the Implantation Placement Rod is removed from the cage.
Attach the Screw Centering Sleeve to the Implant and use the dedicated 1.8 mm drill bit to prepare the starting points for the Locking Self Drilling Cortex Screws . This drill bit forms a unit with the Screw Centering Sleeve and will just open the ventral cortex and 2 – 3 mm of vertebral body. Due to this security feature, the Screw Centering Sleeve will not create reliable starting points if the “ears” of the C-Lox Cage are not sufficiently adjacent to the vertebral surface. In this case the drill bit can be substituted by a 1,8mm K-Wire. The latter is inserted into the Screw Centering Sleeve until its tip touches the ventral vertebral surface. Then it is advanced at low speed not more than 3-5 mm into the vertebral body. Screw lengths are selected pre-operatively from measurements on the preoperative radiographs. The four Locking Self Drilling Cortex Screws, selected according to cervical spine radiographs in precise latero-lateral projection, are inserted using the hexagonal C-Lox Screwdriver. The screws must be well anchored within the vertebral body and must not penetrate the vertebral end plates or the spinal canal. Again, fluoroscopy can be very helpful in achieving optimal screw placement.
The coupling thread of the C-Lox Cage can be used to directly inject pasteous bone substitutes into the C-Lox Cage for enhanced bone ingrowth. Cancellous bone or bone substitutes can be apposed to the ventral surface of the treated disc space.
Close the soft tissues in a routine manner.