Application of canine pedicle screw and rod fixation system in the lumbar 1 and 2 vertebral body of mongrel dogs

Vertebral fractures and luxation (VFL) is a common spinal cord disorder in dogs, mostly affect the thoracolumbar region. Canine pedicle screw and rod fixation (CPSRF) system is a modified system from pedicle screw and rod fixation system (PSRFS), a device tailored for canine spine that offers a great alternative to commercially available implants. The aims of this study were; (1) to document VFL cases in University Veterinary Hospital, Universiti Putra Malaysia (UVH, UPM), (2) to determine the optimal corridor implantation of CPSRF in medium size dogs and (3) to examine gross and microscopic lesion to the vertebrae and spinal cord after CPSRF system implantation. Retrospective evaluation showed 49% of spinal cord cases were contributed by VFL. Adult, outdoor and intact male dog were prone to VFL. Nearly 40% of VFL cases were represented by local dogs (p <0.01) with the odds of VFL were four times higher than pure breed dogs (OR = 4.21, 95% CI 1.32-13.25). The most common site for VFL were at T13- L2 hence L1 and L2 region were chosen for the experiment. Two screws of 16mm and 20mm and rod of 40mm and 45mm were inserted into the pedicles of L1 and L2 in six dogs. Safe implantation angle for 16mm screw at L1 were 52. 67°±10.40º and at L2 were 58.59°±7.72º. The mean distance of 16mm screw tips to aorta and caudal vena cava at L1 were 9.21±3.67mm and 18.96±5.17mm while average distance for 20mm were 8.91±2.45mm and 20.78±6.32mm. At L2, the distance of 16mm screw tips to aorta and caudal vena cava were 11.32±1.47mm and 19.26±5.12mm while average distance of 20mm were 10.23±2.40mm and 21.15±1.84mm at L2. No gross lesion was found on the vertebrae although minimal microfractures was found in all vertebral samples through histological examination. None of the spinal cord had penetrative or lacerative injury however longer observation period was required to assess the long-term effect of the implant. Findings from computed tomography scan and histological examination suggest that 16mm screw is suitable for medium sized dog with safe implantation corridor between at 58.42°±7.25°. This study had shown that CPSRF is feasible for medium sized dogs however long-term study is required to determine stability and durability of the system.

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