Abstract
OBJECTIVE
To compare the use of the video telescope operating monitor (VITOM) and use of a conventional unassisted surgical method for treatment of cervical intervertebral disc herniation in dogs.
ANIMALS
39 dogs with cervical intervertebral disc disease.
METHODS
Prospective study. Dogs were prospectively nonrandomly assigned to either the VITOM (n = 19) or conventional surgery (20) group depending on VITOM system availability. Signalment and preoperative neurologic status were recorded for all dogs. Preoperative and postoperative CT myelography was performed to compare intervertebral space location, spinal cord dimensions at the decompression level, ventral slot dimensions, and residual disc material. Surgical complications and postoperative neurologic outcomes were recorded. Data were compared between the 2 groups using fixed-effects or mixed-effects models to consider double reading of CT myelography images.
RESULTS
No significant differences were noted between the 2 groups regarding the decompression ratio (P = .85), vertebral length body ratio (P = .13), ventral slot width ratio (P = .39), residual disc material (P = .30), and sinus bleeding (P = .12). No significant differences were found between the 2 groups regarding postoperative neurologic grade (P = .17).
CLINICAL RELEVANCE
VITOM-assisted ventral slot decompression is equivalent to conventional surgery in treatment of cervical intervertebral disc herniation in dogs. The use of VITOM remains a good alternative to the conventional surgical method.
Introduction
Chondrodystrophic dogs and other small breeds are at a higher risk for intervertebral disc herniation (IVDH).1,2 Medical treatment is usually appropriate for dogs with a first episode of neck pain, whereas surgical treatment is recommended for dogs with recurrent pain or those presenting with neurologic deficits.3 Ventral slot decompression is the surgical method of choice for most cervical IVDH and is often considered more challenging than thoracolumbar hemilaminectomy due to reduced visualization of the spinal cord.2
Conventional ventral slot is the most commonly used technique to remove herniated disc material compressing the cervical spinal cord; however, ventral slot decompression is usually inadequate for removing lateral or foraminal disc extrusions.2,4 In 1 study,5 the incidence of serious immediate surgical complications has been reported to be around 9.9% and include blood loss, ventilatory failure, and cardiac dysrhythmias. Additional postoperative complications, such as infection, vertebral instability, subluxation, and neurologic status worsening, have also been reported. Alternative treatments have therefore been developed in an attempt to improve the intraoperative challenges associated with ventral slot decompression, as well as to improve the postoperative patient. Among these, magnification methods have gained interest in human and veterinary neurosurgery. The use of magnifying binocular lenses, operative microscopes (OMs), and endoscopes has historically been employed in an attempt to improve surgical technique and patient outcomes. These tools have been shown to have several advantages in people as follows: they improve delicate anatomic structure visualization, allow for smaller incisions, reduce soft-tissue damage and operative complications, and shorten hospitalization times.6 An OM occupies a large space in the operating room, limiting the movements of the surgical team; is an expensive piece of equipment; and needs consumable supplies. It also provides an uncomfortable surgical position and a small field of view with a short focal length.6 Because of these limitations and a difficult sterilization protocol, the OM is usually brought into position after spine dissection. The endoscope also has a small field of view, and it is commonly obstructed by surgical instruments. Reports of the use of video-assisted neurosurgery in the veterinary literature is scarce, except for 1 clinical study describing the use of an endoscope-assisted minimally invasive ventral slot technique and 2 cadaveric studies on minimally invasive thoracolumbar neurosurgery in dogs.7–9
The exoscope is a novel alternative to OM and endoscopy, allowing an enhanced visualization with easier access to the operative field and improved ergonomy.10,11 The exoscope is a rigid 0° or 90° scope that sits outside the body cavity (focal distance of 250 to 300 mm) and is held by a mechanical arm that allows for the scope position to be adjusted during surgery.6
The video telescope operating monitor (VITOM) is a recently developed exoscope first described in 2012 to assist human neurosurgeons.6 The VITOM provides high-quality video images, reduces surgeon discomfort, costs less, is easier to use and removable, provides teaching opportunities, and is less obstructive than the OM.6 Use of VITOM recently has been described for cervical IVDH and pituitary adenoma removal in dogs.12,13 In these cases, this system allowed better magnification and illumination while maximizing the comfort of the surgeon and reducing fatigue.13 Despite the great interest in these techniques, little is known about the potential benefits that video-assisted neurosurgery can provide in a veterinary setting.
This prospective study was designed to evaluate the efficacy of the VITOM for ventral slot decompression in dogs with cervical IVDD and compare video-assisted surgery with conventional surgery in terms of spinal cord decompression, ventral slot dimensions, residual disc material, surgical bleeding and complications, and postoperative neurofunctional outcome.
Methods
Ethical consideration
This study was approved by the ethics committee of the National Veterinary School Vetagro Sup (Lyon, France; approval No. 2272). All owners involved in the study signed informed consent for a ventral decompressive surgery but were not told which technique would be chosen.
Study population
All client-owned dogs with cervical IVDD diagnosed by CT myelography from November 2020 to January 2023 at the Centre Hospitalier Frégis in Paris, France, that required a ventral slot decompressive surgery were enrolled in this study. For population homogeneity, only dogs weighing < 20 kg were selected. Dogs whose surgery and postoperative scan could not be done on the same day as the preoperative CT myelography were excluded from the study since radiologists could not accurately perform their measurements because the myelographic contrast media was much less visible after 24 hours.
The minimum number of dogs to enroll in each group for adequate statistical power was calculated considering a mean difference in decompression ratio between groups of 0.18 ± 0.1. The decompression ratio was selected because it directly assessed the effectiveness of VITOM compared to the conventional surgical method. This would be considered a better spinal cord decompression. At least 19 dogs were to be enrolled in each group to achieve an α of 0.05 and power of 90%.
A complete history and the results of physical examination were recorded, including a complete preoperative neurologic examination by a board-certified neurologist (LC) or neurology resident (HF). The neurologic status was graded on the basis of the 5-point scale (0 = normal without any hyperesthesia, 1 = ambulatory, neck pain only, no deficit, 2 = ambulatory tetraparesis with proprioceptive deficits or single thoracic limb lameness, 3 = non-ambulatory tetraparesis, 4 = tetraplegic, and 5 = tetraplegic with respiratory distress) defined by Scott.14–16
Preoperative imaging
All dogs had CT myelography performed prior to decompressive spinal surgery. After premedication with morphine (0.2 mg/kg, IM) and diazepam (Valium; 0.2 mg/kg), anesthesia was induced with propofol (titrated to effect) and maintained with isoflurane in 100% oxygen. Dexamethasone (Dexadreson; 0.2 mg/kg, IV) and cefazoline (Céfazoline; 15 mg/kg, IV) were administered at the time of induction.
Conventional myelography was performed with lumbar injection of 0.1 mL/kg of iohexol (Omnipaque; 350 mgI/mL). CT (BRIVO CT385 16-slice helical CT scanner; GE Healthcare) of the spine extending from the base of the skull to the third thoracic vertebra was performed with the dogs in dorsal recumbency; the long axis of the cervical column was aligned perpendicular to the CT gantry. Positioning of all dogs in the CT scanner was performed by the neurologists. Location of the herniated material was defined as central (no obvious lateralization) or lateralized when the compression had a lateral component in the vertebral canal.
The surgical technique
Ventral slot decompression was performed by 1 of 3 board-certified surgeons and 1 of 2 senior surgery residents under direct supervision of the attending specialist. The surgical technique (ie, use of the VITOM or conventional surgery) was decided at the discretion of the primary surgeon on the basis of VITOM availability (ie, VITOM was unavailable if already used or not yet sterilized from a previous surgery). Dogs were classified into the VITOM or conventional surgery group accordingly. All surgeons performed at least 1 surgery in each group.
Each dog was placed in dorsal recumbency with the neck slightly extended. A conventional ventral midline approach to the cervical spine was performed.2 The affected intervertebral disc space was identified by palpation of the anatomic landmarks. The telescope and high-definition camera system for magnifying and illuminating the surgical site (VITOM; Karl Storz) were used only in the VITOM group, and the installation was adjusted as previously described by Rossetti et al.12
The autoclavable rigid lens telescope was 10 mm in diameter and 10 mm in length and capable of providing up to 16X magnification with high-definition (1080p, HD) quality resolution.17 A 300W xenon fiber optic light source (Xenon Nova 300; Karl Storz) and fiber optic cable were attached directly to the telescope. An autoclavable high-definition digital camera (A3; Karl Storz) with optical zoom was fixed to the telescope, and the resultant image was displayed on medical-grade high-definition video monitors (52 inches) and recorded (AIDATM; Karl Storz). The telescope and camera were sterilized with ethylene oxide or autoclave and did not require a sterile drape or cover. The VITOM system was installed after patient draping, and 1 or 2 remote monitors were placed facing the primary and assistant surgeons. Video assistance was used from the beginning of ventral slot drilling until the end of spinal cord decompression. The occurrence of surgical and anesthetic complications (especially sinus bleeding) were noted. Sinus bleeding severity was considered mild, moderate, or severe if bleeding was controlled in < 5 minutes, between 5 and 10 minutes, and > 10 minutes, respectively (Supplementary Video S1).
A hemostatic sponge (Pangen) was placed over the ventral slot site with an instillation of morphine on the spinal cord (0.1 mg/kg, diluted to 50%) before closure. The conventional surgical technique was performed identically except without the use of the VITOM system.
Postoperative imaging
All dogs had postoperative CT myelography performed immediately after surgery without additional contrast media injection to assess the degree of spinal cord decompression, ventral slot features, and presence of residual disc material.
Evaluation of images and measurements was performed by a board-certified radiologist (EG) and senior resident in radiology (CT; radiologist 1 and radiologist 2, respectively) using a DICOM viewer (Horos; Horos Project). Both radiologists were blinded to the surgical method performed.
Spinal cord dimension measurement
The normal spinal cord area (NSCa) was measured at the widest point cranial to the herniated disc site. The decompressed spinal cord area (DSCa) was measured at the level of the compressive disc site on postoperative images. The spinal cord decompression ratio was calculated using the following formula: 
(Figure 1).12
Sagittal (above) and transverse (below) CT scan view at the level of the herniated disc (yellow arrow) before (left) and after (right) surgical decompression. The normal spinal cord area (NSCa) and decompressed spinal cord area (DSCa) are measured, and the decompression ratio is calculated using the following formula: 
(A).
Ventrodorsal CT scan view at the level of the ventral slot before (left) and after (right) surgical decompression. The postoperative length of the remaining vertebral body (postLVB) and preoperative length vertebral body (preLVB) are measured, and the vertebral body length ratio is calculated using the following formula: 
(B).
Transverse CT scan view at the level of the herniated disc before (left) and after (right) surgical decompression. The slot width (SW) and preoperative width vertebral body (preWVB) are measured, and the width ratio is calculated using the following formula: 
(C).
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.02.0114
The preoperative length of the vertebral body (preLVB) caudal to the herniated disc space was measured from the cranial-to-caudal vertebral endplate on ventrodorsal preoperative images. The postoperative length of the remaining vertebral body (postLVB) was measured at the same location on postoperative images. The vertebral body length ratio was calculated using the following formula: 
(Figure 1).12
The laterolateral width of the vertebral body (preWVB) corresponded, on transverse preoperative image, to the measurement of the space in between the 2 medial imprint of the lateral vertebral artery just caudally to the herniated disc space. The slot width (SW) was measured in between the remainder of the vertebral body on postsurgical images. The width ratio was calculated using the following formula: 
(Figure 1).12 Finally, the ventral slot was defined as lateralized if its axis was not centered on the vertebral body on the transverse section.
Postoperative outcome
During the immediate postoperative period, analgesia was provided through the administration of morphine (0.2 mg/kg, SC) or fentanyl (constant rate infusion, 3 µg/kg/h) as needed for 24 to 48 hours. Dogs were discharged a minimum of 3 days after surgery. A neurologic examination was performed every morning during postoperative hospitalization and at discharge. All dogs were prescribed prednisolone (Dermipred; 0.5 mg/kg, q 12 h, then decreasing dosage for 12 days), tramadol hydrochloride (Tramadol; 5 mg/kg, PO, q 12 h for 5 days), gabapentin (Neurontin; 10 mg/kg, PO, q 8 h for 15 days), and methocarbamol (Lumirelax; 20 to 25 mg/kg, PO, q 12 h for 5 days). Follow-up clinical and neurologic examinations were conducted in all dogs at suture removal 2 weeks after surgery.
Statistical analysis
Recorded clinical data measurements included age, body weight, breed, sex, preoperative and postoperative neurologic status (which was performed at the time of discharge), and bleeding occurrence and duration. The recorded preoperative imaging data included the location of the affected disc space and the location of the disc material within the spinal canal (ventral vs lateral). The recorded postoperative imaging data included the spinal cord diameter and height at the compression site, decompression ratio, ventral slot lateralization, and ventral slot dimension (length, width, and ratio compared with the vertebra).
For descriptive statistics, continuous data were assessed for normal distribution by histogram evaluation and the Shapiro-Wilk test (Gaussian if P > .2).17,18 As none of the data were normal, continuous data were presented using median (minimum–maximum). Categorical data were presented as number of dogs (percentage).
The VITOM and conventional surgery groups were first compared in terms of signalment, preoperative neurologic status, and IVDD location using a Mann-Whitney test for continuous variables (age and body weight), 2-tailed Fisher exact test for unordered categorical variables (sex, breed, and IVDD location), and ordered logistic regression model for ordered categorical variable (preoperative neurologic status). For the latter model, absence of significant violation of the parallel regression assumption was assessed using the Brant test.
The effect of the surgical technique (ie, VITOM vs conventional surgery) on the decompression ratio, vertebral body length ratio, ventral slot width ratio, presence of residual disc material, and postoperative neurologic status was then studied. To take into account repeated measures by the 2 radiologists and the potential confounding effects of herniated disc lateralization, repeated-measures mixed-effects ANOVA models with identity covariance matrix were used, with the dependent variable being the decompression ratio, vertebral body length ratio, or ventral slot width ratio and the independent variables being the surgical technique, radiologist, first-order interaction between the two, and herniated disc lateralization. As presence of residual disc material was an unordered categorical variable, a repeated-measures mixed-effects logistic model was used, with the dependent variable being the presence of residual disc material and the independent variables being the surgical technique, radiologist, first-order interaction between the two, and herniated disc lateralization. Finally, a generalized ordered logistic regression was used to assess the impact of the surgical approach on neurofunctional outcome, with the dependent variable being the postoperative neurologic status and the independent variables being the surgical approach and preoperative neurologic status.
For mixed-effects models, only the fixed-effects results were reported. If significant differences were detected for the first-order interaction between the radiologist and surgical approach, further analyses were conducted using contrasts and predicted margin plots. For mixed-effects ANOVA models, normal distribution and homoscedasticity of the residuals were assessed by graphical assessment of frequency distribution histograms and residual plots, respectively.
Statistical analyses were performed with commercially available software (Stata version 17.0; StataCorp LLC). Values of P < .05 were considered significant.
Results
Study population
A total of 39 dogs were enrolled: 19 in the VITOM group and 20 in the conventional surgery group. Demographic information for the dogs in each group is summarized (Table 1).
Demographic data in conventional surgery and video telescope operating monitor (VITOM) groups.
| Variable | Conventional surgery (n = 20) | VITOM (n = 19) | P value |
|---|---|---|---|
| Age (y) | 5.5 (3–11) | 4.5 (2.5–13) | .95 |
| Body weight (kg) | 11.45 (4.9–16) | 10 (2.3–20) | .41 |
| Sex | .75 | ||
| Male | 12 (60%) | 10 (52.6%) | |
| Female | 8 (40%) | 9 (47.4%) | |
| Breed | .84 | ||
| French Bulldog | 14 (70%) | 12 (63.2%) | |
| Beagle | 0 | 1 (5.3%) | |
| Chihuahua | 0 | 2 (10.5%) | |
| Dachshund | 1 (5%) | 1 (5.3%) | |
| Jack Russel Terrier | 1 (5%) | 1 (5.3%) | |
| Pinscher | 1 (5%) | 0 | |
| Shi-Tzu | 2 (10%) | 2 (10.5%) | |
| Tibetan Spaniel | 1 (5%) | 0 | |
| Affected intervertebral spaces | .22 | ||
| C2-C3 | 2 (10%) | 3 (15.8%) | |
| C3-C4 | 10 (50%) | 5 (26.3%) | |
| C4-C5 | 5 (25%) | 7 (36.8%) | |
| C5-C6 | 1 (5%) | 4 (21.1%) | |
| C6-C7 | 2 (10%) | 0 |
Entries represent median value (minimum–maximum) for continuous variable and number of dogs (percent of dogs) for categorical variables.
There was no significant difference between the VITOM group and conventional surgery group regarding age (P = .95), body weight (P = .41), sex (P = .75), breed (P = .84), and location of the affected intervertebral spaces (P = .22). Preoperative neurologic status was not significantly different between the 2 groups (P = .82) and included dogs with neurologic grades from 1 to 4 in both groups (median grade 1 in both groups).
Decompression ratio
The decompression ratio significantly differed between radiologists (P = .03), although the difference was not significant between the 2 surgical techniques (P = .85) independent of the radiologist and the herniated disc lateralization. A trend toward a better agreement of measurements was found between radiologists within the VITOM group rather than the conventional group (–0.005 and –0.05, respectively; Figure 2).
Predictive margin plots of the relationship between the decompression ratio (A), vertebral body length ratio (B), and ventral slot width ratio (C; on the y-axis) and the surgical approaches (on the x-axis) measured by 2 radiologists (radiologist 1 in blue and radiologist 2 in red). Error bars represent 95% CIs.
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.02.0114
Vertebral body length ratio
Despite a significant difference between radiologists regarding vertebral body length ratio measurement (P = .02), no significant difference was found between the 2 surgical techniques (P = .13) independent of the radiologist and the herniated disc lateralization. A trend toward a significant interaction between the surgical techniques and radiologists was found (P = .09), meaning that the effect of the surgical technique on the vertebral body length ratio was different depending on which radiologist reviewed the CT images. This interaction was explored using contrasts and predicted margins plot. Based on contrasts, the vertebral body length ratio was significantly lower in the VITOM group according to radiologist 2 (P = .04) but not radiologist 1 (P = .13). A trend toward a better agreement of measurements between radiologists in the VITOM and conventional surgery groups was suggested by contrasts (–0.0007 and 0.03, respectively) and by predicted margins plot (Figure 2).
Ventral slot width ratio
While the ventral slot width ratio measurement differed significantly between radiologists (P = .006), there was no significant difference between the 2 surgical techniques (P = .39) independent of the radiologist and herniated disc lateralization. These results were confirmed by predicted margins plot (Figure 2).
Presence of residual disc material
There was no significant difference regarding residual disc material between the 2 surgical techniques (P = .30), independent of the radiologist and disc herniation lateralization.
Occurrence of operative complications
Sinus bleeding was observed in only 1 (5%) dog from the conventional surgical group, whereas it was reported in 5 (26%) dogs within the VITOM group. Some dogs (n = 4) initially assigned to the conventional technique group had surgery stopped due to uncontrolled intraoperative bleeding prior to adequate spinal cord decompression. These dogs were recovered from anesthesia and underwent surgery and postoperative CT scan the next day, but due to the elimination of contrast media 24 hours postinjection, postoperative measurements could not be obtained, resulting in exclusion of these dogs from the study. Sinus bleeding was judged to be mild in the dog in the conventional surgery group. It was considered mild, moderate, and severe in 1 (5%), 2 (10%), and 2 (10%) dogs, respectively, from the VITOM group.
One dog in the conventional surgery group developed discospondylitis at the surgical site and was diagnosed by MRI 3 weeks after surgery. This dog was treated successfully thereafter.
Postoperative neurologic exam
Two weeks after surgery, all dogs achieved a neurologic status of grade 0 to 2, regardless of the surgical technique. There was no significant difference in the postoperative neurologic status between the 2 surgical techniques (P = .17 when comparing grade 0 to grade 1 or 2 and P = .74 when comparing grade 0 or 1 to grade 2) independent of the preoperative neurologic status. The number of dogs achieving a postoperative grade 0 were equivalent in both groups (70% in the conventional group vs 79% in the VITOM group; Supplementary Table S1). Despite an improvement in the neurologic status in dogs of both methods, the greatest neurologic improvements during our follow-up period were observed in the VITOM group (ie, from preoperative neurologic grade 4 to postoperative neurologic grade 1; Figure 3).
Parallel coordinate plots showing the change in neurofunctional status between preoperative (Pre) and postoperative (Post) neurologic examinations in dogs of the conventional surgery and VITOM groups. Neurologic grade is represented on the y-axis.
Citation: Journal of the American Veterinary Medical Association 261, 10; 10.2460/javma.23.02.0114
Discussion
While the feasibility of the VITOM-assisted technique for cervical IVDD has been previously reported, to the authors’ knowledge this is the first prospective clinical study that compared video-assisted surgery with a conventional surgical technique in dogs.12 Results from our study showed no significant differences in terms of spinal cord decompression, ventral slot dimensions, and presence of residual disc material between the 2 surgical techniques. Surgical bleeding and other complications, as well as postoperative neurofunctional outcome, were not statistically different.
Ventral slot decompression can be a challenging procedure to perform because the small, narrow, and deeply located surgical field limits direct visualization of the relevant anatomic structures.19 For this reason, a magnification and illuminating system could theoretically make the procedure less challenging due to improved visualization of these structures; this was also why we expected better outcomes using the VITOM technique. A possible explanation for the lack of difference between the 2 techniques is the extensive experience of the surgeons performing ventral slot decompression in this study, regardless of the surgical method used. Therefore, both the conventional and VITOM-assisted surgeries performed by experienced surgeons provided a good outcome. Despite these results and although all surgeons participating in this study were familiar with the conventional ventral slot surgery technique, they all subjectively reported advantages of the VITOM technique, including improved visibility, recognition of the fine tissue details, and bleeding management. This was most likely due to the high-quality magnified images provided by the VITOM system and digital software.20
Spinal decompression was considered good to excellent in all dogs, regardless of the surgical technique used. Although overall there was no significant difference in decompression ratio, vertebral body length ratio, and ventral slot width ratio in this study, the agreement of measurements between the 2 radiologists tended to be correlated more in the VITOM group than in the conventional surgery group, suggesting that the ventral slot dimensions were more consistent in the VITOM group, which could be explained again by visual magnification of the vertebral body drilling site. The discrepancy in measurements between the radiologists in the conventional group impacted the study of the effect of the surgical technique on the vertebral body length ratio, as the ratio was significantly lower in the VITOM group according to one radiologist but not according to the other.
In comparison with the OM and endoscope, the VITOM is lightweight, inexpensive, and less cumbersome.13 This magnification system can be used during the initial dissection because its placement minimally obstructs the surgeon’s direct view of the operative field; moreover, the surgeon can easily adjust the distance between the scope and the surgical site during the surgery. The focal distance from the telescope lens to the surgical site is approximately 250 mm rather than the 10 to 20 mm that is typical of endoscopes.13 The surgeon is able to operate while standing straight and upright in a comfortable position looking at the screen, minimizing surgical stress and operative fatigue by decreasing the need to lean or bend the neck.6
The learning curve for surgeons who are experienced with laparoscopy or arthroscopy is relatively fast for VITOM-assisted surgery, as perceived by the surgeons of this study.12 Furthermore, it is a tool that is capable of providing optimal teaching conditions since the novice surgeon is able to view the magnified images on the monitor during drilling of the vertebra and decompression of the spinal cord while not interfering with or obstructing the view of the primary surgeon.10 In addition, a surgical assistant can provide more precise help during the surgery, especially with flushing and aspiration of the surgical site.
Some of the previously reported complications, such as seroma, infection, persistent neck pain, worsening of the neurologic status, vertebral instability and reherniation, severe hemorrhage, and death, were not encountered in this study except for the dog in the conventional group that developed discospondylitis 3 weeks postoperatively.
Sinus bleeding is a common complication in this surgery. Major bleeding is rarely a life-threatening complication; however, it has been reported in 1.5% to 25% of dogs undergoing ventral slot decompression.5 Rossmeisl et al5 described that mild to moderate bleeding occurred 18.8% of the time during ventral corpectomy procedures in dogs. Even if mild to moderate bleeding has no clinical significance, it can negatively affect the surgeon’s visualization of the neural tissues and delay progress of surgery until the bleeding is adequately controlled.14,21 Although there was more sinus bleeding with the use of VITOM than with the conventional technique, the bleeding was controlled in all dogs, most likely because of visibility with magnification. An example of the improved bleeding visualization and bleeding control is shown elsewhere (Supplementary Video S1).
Occurrence of sinus bleeding was low in the conventional surgical group due to exclusion of some dogs from the study, as explained in the Results. This exclusion introduced a bias, which significantly underestimated the number and severity of bleeding in dogs in the conventional surgery group. No dog undergoing surgery with the VITOM technique was stopped due to uncontrolled bleeding. Thus, all dogs included in our study had postoperative CT myelography performed immediately after surgery, allowing for adequate assessment of the spinal cord decompression because the residual contrast medium was visible in all dogs.22 No complications secondary to CT myelography have been reported in this study. Another limitation was the use CT myelography instead of MRI, which underestimated the presence of noncalcified disc material and even hemorrhage.
In dogs with cervical IVDD, residual herniated disc material has been reported to be between 57% and 77% after ventral slot decompression with postoperative CT myelography.12,14,23 Although residual disc material was present in both groups, all dogs had improvement of their neurologic status. Residual disc material is not associated with a poor functional outcome.
On the basis of the low OR, the VITOM technique seemed to increase the likelihood of achieving a better postoperative neurologic grade compared to the conventional surgery technique. However, statistical significance was not achieved, likely because of the lack of power due to the small number of dogs enrolled in this study. A larger study is warranted to investigate these results.
Although all surgeons were highly experienced as a specialist or senior resident, a possible limitation of this study was that the surgeries were performed by different surgeons. Another limitation was that the dogs were classified in each group in a nonrandom way on the basis of the availability of the VITOM system. For these reasons, future prospective studies with a larger sample size and improved controls are needed (same surgeon, comparisons of IVDE site, bleedings, and use of an MRI).
In conclusion, no differences were found between the 2 groups in terms of spinal cord decompression, ventral slot dimensions, residual materials, surgical bleeding and complications, and postoperative neurofunctional outcome. Despite this, VITOM assistance subjectively provided good anatomic visualization, allowing for superior bleeding control, more regular ventral slot dimension, and possibly better neurofunctional recovery, although further larger studies are required to confirm these results.
Supplementary Materials
Supplementary materials are posted online at the journal website: avmajournals.avma.org
Acknowledgments
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
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