Biomechanical Comparison Between Bicortical Pin and Monocortical Screw/Polymethylmethacrylate Constructs in the Cadaveric Canine Cervical Vertebral Column

Comparison of Cervical Stabilization with Transpedicular Pins and Polymethylmethacrylate versus Transvertebral Body Polyaxial Screws with or without an Interbody Distractor in Dogs

OBJECTIVE

 The main aim of this study was to compare the biomechanical properties of caudal cervical vertebral stabilization using bicortical transpedicular pins with polymethylmethacrylate (PMMA) versus transvertebral body polyaxial screws and connecting rods with or without an interbody distractor.

STUDY DESIGN

 Ten canine cervical vertebral columns (C2-T3) were used. Four models (intact, transvertebral body polyaxial screw with interbody distractor [polyaxial + distractor], transvertebral body polyaxial screw without interbody distractor [polyaxial - distractor] and bicortical transpedicular pins/polymethylmethacrylate [pin-PMMA]) were applied to C6-7 sequentially on the same specimens. Angular range of motion (AROM) in the form of flexion and extension was measured at C4-5, C5-6 and C6-7 in all groups.

RESULTS

 Treated vertebral specimens had significantly less AROM than unaltered specimens. There was no significant difference in AROM between the experimental groups at C6 and C7. Angular range of motion ratio in flexion-extension was 80.8, 72.7 and 78.3% for polyaxial + distractor, polyaxial - distractor and pin-PMMA groups, respectively, which were less than the intact group. There was no significant increase in the range of motion of the adjacent vertebrae after stabilization.

CONCLUSION

 Stabilization obtained with transvertebral body polyaxial screws was comparable to that from the well-established bicortical pins/PMMA construct. Association of an intervertebral distractor did not change AROM of the polyaxial screw constructs.

Long-Term Follow-Up of Dogs and Cats after Stabilization of Thoracolumbar Instability Using 2-0 UniLock Implants

Traumatic vertebral fracture or luxation often results in spinal instability requiring surgical stabilization. This study describes the long-term outcome of spinal stabilization using a unilateral 5-hole 2-0 UniLock implant in eight dogs and two cats with trauma-induced thoracolumbar vertebral luxation/subluxation and presumed instability, as assessed by a combination of preoperative radiographs and MRI using a 3-compartment method. The UniLock plate was secured with four monocortical locking screws in adjacent vertebral bodies. Additional pins and facet screws were used in several patients. Postoperative radiographs and MRI studies showed restoration of the main spinal axis in all patients and satisfactory implantation of the screws in the vertebral bodies, with no intrusion in the vertebral canal or in the adjacent intervertebral disc spaces. Neurological status improved in nine patients six weeks postoperatively. Partial implant failure was detected in three patients with no long-term consequences. After 12 months, seven patients reached full recovery with no neurological deficit, two patients were euthanized (including one owing to an unrelated condition), and one remained paraparetic. The results of this study demonstrate that using a 2-0 UniLock implant to stabilize the thoracolumbar spine results in satisfactory long-term recovery in most dogs and cats with traumatic spinal luxation/subluxation and presumed instability. Complications may occur but do not require revision surgery and do not affect clinical outcomes.

Case Report: Spinal Stabilization Surgery Using a Novel Custom-Made Titanium Fixation System for the Spinal Instability Caused by Vertebral Malformation in a Dog

A 2-year-old Maltese was presented with wobbly gait of the pelvic limbs. Based on imaging examinations, a diagnosis of congenital malformation at T5–T8 and severe kyphosis causing spinal cord compression at T6–T7 was made. Dorsal laminectomy and stabilization of T6 and T7 vertebrae were performed. As the size of the vertebrae was small and they were severely deformed, novel custom-made titanium implants were used for spinal stabilization. Clinical signs were resolved 2 weeks after surgery. Although radiographic examination 373 days after surgery showed slight loosening of implants, post-operative course remained uneventful. This report describes the use of novel custom-made titanium implants for spinal fixation surgery in a dog.

Kinematics of a Novel Canine Cervical Fusion System

OBJECTIVE

 The aim of this study was to determine the biomechanical behaviour of a novel distraction-fusion system, consisting of an intervertebral distraction screw, pedicle locking screws and connecting rods, in the canine caudal cervical spine.

STUDY DESIGN

 Biomechanical study in cadaveric canine cervicothoracic (C3-T3) spines (n = 6). Cadaveric spines were harvested, stripped of musculature, mounted on a four-point bending jig, and tested using non-destructive four-point bending loads in extension (0-100 N), flexion (0-60 N) and lateral bending (0-40 N). Angular displacement was recorded from reflective optical trackers rigidly secured to C5, C6 and C7. Data for primary and coupled motions were collected from intact spines and following surgical stabilization (after ventral annulotomy and nucleotomy) with the new implant system.

RESULTS

 As compared with the intact spine, instrumentation significantly reduced motion at the operated level (C5-C6) with a concomitant non-significant increase at the adjacent level (C6-C7).

CONCLUSION

 The combination of a locking pedicle screw-rod system and intervertebral spacer provides an alternative solution for surgical distraction-stabilization in the canine caudal cervical spine and supports the feasibility of using this new implant system in the management of disc-associated cervical spondylomyelopathy in dogs. The increase in motion at C6-C7 may suggest the potential for adjacent level effects and clinical trials should be designed to address this.

Comparison of the biomechanical performance of a customized unilateral locking compression plate with and without an intervertebral spacer applied to the first and second lumbar vertebrae after intervertebral diskectomy in canine cadaveric specimens

OBJECTIVE

To determine whether a customized unilateral intervertebral anchored fusion device combined with (vs without) an intervertebral spacer would increase the stability of the L1-L2 motion segment following complete intervertebral diskectomy in canine cadaveric specimens.

SAMPLE

Vertebral columns from T13 through L3 harvested from 16 skeletally mature Beagles without thoracolumbar disease.

PROCEDURES

Complete diskectomy of the L1-2 disk was performed in each specimen. Unilateral stabilization of the L1-L2 motion segment was performed with the first of 2 implants: a unilateral intervertebral anchored fusion device that consisted of a locking compression plate with or without an intervertebral spacer. The resulting construct was biomechanically tested; then, the first implant was removed, and the second implant was applied to the contralateral side and tested. Range of motion in flexion and extension, lateral bending, and torsion was compared among intact specimens (prior to diskectomy) and constructs.

RESULTS

Compared with intact specimens, constructs stabilized with either implant were as stable in flexion and extension, significantly more stable in lateral bending, and significantly less stable in axial rotation. Constructs stabilized with the fusion device plus intervertebral spacer were significantly stiffer in lateral bending than those stabilized with the fusion device alone. No significant differences in flexion and extension and rotation were noted between implants.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings did not support the use of this customized unilateral intervertebral anchored fusion device with an intervertebral spacer to improve unilateral stabilization of the L1-L2 motion segment after complete L1-2 diskectomy in dogs.

Surgical management and long-term outcome of dogs with cervical spondylomyelopathy with an anchored intervertebral titanium device

OBJECTIVE

To assess the short- and long-term outcome of an anchored intervertebral titanium device (C-LOX) for the treatment of 10 dogs with disc-associated cervical spondylomyelopathy (DACSM) and 1 dog with osseous-associated cervical spondylomyelopathy.

DESIGN

Retrospective case series.

METHODS

Dogs were included if they were diagnosed with either DACSM or osseous-associated cervical spondylomyelopathy via myelography with or without advanced imaging and underwent surgical distraction and stabilisation of the affected intervertebral disc with a C-LOX implant. Assessment included short-term neurological outcome, radiography immediately and 6 weeks' postsurgery, owner questionnaire and veterinary clinical assessment.

RESULTS

The mean follow-up time was 12 months. Improvement in neurological status was noted in 10 of 11 dogs. Screw loosening or subsidence occurred in five dogs. Revision surgery was performed in two dogs due to implant fracture (n = 1) and recurrence of spinal cord compression due to endplate subsidence around the implant (n = 1). Adjacent segment disease occurred in three dogs (30%) with DACSM at a mean of 11 months postsurgery.

CONCLUSION

The use of the C-LOX implant for dogs with cervical spondylomyelopathy resulted in a high rate of initial neurological improvement; however, there is a moderate incidence of minor and major complications that is comparable to previously described distraction-stabilisation techniques.

Placement of vertebral screws for spinal stabilization and distraction in a dog with disc-associate cervical spondylomyelopathy: case report

ABSTRACT A 10-year-old male Rottweiler was evaluated for a 2-month history of recurrent forelimb weakness. Neurologic examination revealed proprioceptive ataxia, tetraparesis and moderate cervical pain. Disk-associated cervical spondylomyelopathy (CSM) with static lesion at C3-4 was diagnosed based on magnetic resonance imaging (MRI). The dog was surgically treated by a ventral slot procedure and distraction-stabilization of the vertebral bodies through insertion of vertebral screws with transverse connective bars. The patient had favorable clinical outcome. Neurologic assessment performed 120 days after surgery showed absence of neurologic defects. Radiographic assessment performed at the same time indicated adequate spinal cord decompression although vertebral fusion was not achieved. To the authors’ knowledge, this is the first case of distraction-stabilization with vertebral (pedicle) screws to treat CSM in a dog. The treatment was well tolerated with no complications and excellent outcome and can be a viable option for this condition.

Cement plug technique for the management of disc-associated cervical spondylopathy in 52 Dobermann Pinscher dogs

Objectives: To report the radiographic and clinical outcome of an intervertebral bone cement plug technique for the management of disc-associated cervical spondylopathy in Dobermann Pinscher dogs.

Methods: Retrospective study of 52 Dobermann Pinscher dogs.

Results: A variable degree of cement plug subsidence with loss of vertebral distraction was evident in all dogs (n = 40) that were radiographed >6 weeks postoperatively. In no case was there definitive evidence of vertebral body fusion. Eight dogs had a sudden deterioration in neurological status, cervical hyperaesthesia, or both between three days and 12 weeks following surgery that was considered to be implant-associated; six of these dogs were euthanatized. Following surgery, 43/52 dogs were considered to be neurologically normal or to have improved, however, nine of 43 subsequently deteriorated due to adjacent segment disease. At the long-term follow-up, 34 dogs were considered to be neurologically normal or to have improved. Twenty-nine dogs were dead by the end of the study period.

Clinical significance: Intervertebral bone cement plug surgery results in an initial improvement in clinical signs in the majority of Dobermann Pinschers with disc-associated cervical spondylopathy. However, it fails to maintain vertebral distraction or achieve vertebral body fusion, and is associated with acute implant complications, additional cervical disc protrusions or mortality in a significant proportion of cases.

Online Supplementary Material: Please note that online supplementary material for this paper is available at: http://dx.doi.org/10.3415/VCOT-15-09-0160.

Magnetic resonance imaging susceptibility artifacts in the cervical vertebrae and spinal cord related to monocortical screw-polymethylmethacrylate implants in canine cadavers

OBJECTIVE To characterize and compare MRI susceptibility artifacts related to titanium and stainless steel monocortical screws in the cervical vertebrae and spinal cord of canine cadavers. SAMPLE 12 canine cadavers. PROCEDURES Cervical vertebrae (C4 and C5) were surgically stabilized with titanium or stainless steel monocortical screws and polymethylmethacrylate. Routine T1-weighted, T2-weighted, and short tau inversion recovery sequences were performed at 3.0 T. Magnetic susceptibility artifacts in 20 regions of interest (ROIs) across 4 contiguous vertebrae (C3 through C6) were scored by use of an established scoring system. RESULTS Artifact scores for stainless steel screws were significantly greater than scores for titanium screws at 18 of 20 ROIs. Artifact scores for titanium screws were significantly higher for spinal cord ROIs within the implanted vertebrae. Artifact scores for stainless steel screws at C3 were significantly less than at the other 3 cervical vertebrae. CONCLUSIONS AND CLINICAL RELEVANCE Evaluation of routine MRI sequences obtained at 3.0 T revealed that susceptibility artifacts related to titanium monocortical screws were considered mild and should not hinder the overall clinical assessment of the cervical vertebrae and spinal cord. However, mild focal artifacts may obscure small portions of the spinal cord or intervertebral discs immediately adjacent to titanium screws. Severe artifacts related to stainless steel screws were more likely to result in routine MRI sequences being nondiagnostic; however, artifacts may be mitigated by implant positioning.

Canine atlantoaxial optimal safe implantation corridors - description and validation of a novel 3D presurgical planning method using OsiriX™

Background

Canine ventral atlantoaxial (AA) stabilization is most commonly performed in very small dogs and is technically challenging due to extremely narrow bone corridors. Multiple implantation sites have been suggested but detailed anatomical studies investigating these sites are lacking and therefore current surgical guidelines are based upon approximate anatomical landmarks. In order to study AA optimal safe implantation corridors (OSICs), we developed a method based on computed tomography (CT) and semi-automated three-dimensional (3D) mathematical modelling using OsiriX™ and Microsoft®Excel software. The objectives of this study were 1- to provide a detailed description of the bone corridor analysis method and 2- to assess the reproducibility of the method. CT images of the craniocervical junction were prospectively obtained in 27 dogs and our method of OSIC analysis was applied in all dogs. For each dog, 13 optimal implant sites were simulated via geometrical simplification of the bone corridors. Each implant 3D position was then defined with respect to anatomical axes using 2 projected angles (ProjA). The safety margins around each implant were also estimated with angles (SafA) measured in 4 orthogonal directions. A sample of 12 simulated implants was randomly selected and each mathematically calculated angle was compared to direct measurements obtained within OsiriX™ from 2 observers repeated twice. The landmarks simulating anatomical axes were also positioned 4 times to determine their effect on ProjA reproducibility.

Results

OsiriX could be used successfully to simulate optimal implant positions in all cases. There was excellent agreement between the calculated and measured values for both ProjA (ρ_c = 0.9986) and SafA (ρ_c = 0.9996). Absolute differences between calculated and measured values were respectively [ProjA = 0.44 ± 0.53°; SafA = 0.27 ± 0.25°] and [ProjA = 0.26 ± 0.21°; SafA = 0.18 ± 0.18°] for each observer. The 95 % tolerance interval comparing ProjA obtained with 4 different sets of anatomical axis landmarks was [−1.62°, 1.61°] which was considered appropriate for clinical use.

Conclusions

A new method for determination of optimal implant placement is provided. Semi-automated calculation of optimal implant 3D positions could be further developed to facilitate preoperative planning and to generate large descriptive anatomical datasets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0824-3) contains supplementary material, which is available to authorized users.