Skip to main content
NCBI home page
The Canadian Veterinary Journal logoLink to The Canadian Veterinary Journal
. 2014 Oct;55(10):975–980.

Presence of residual material following mini-hemilaminectomy in dogs with thoracolumbar intervertebral disc extrusion

Jonathan L Huska 1, Luis Gaitero 1,✉, Brigitte A Brisson 1, Stephanie Nykamp 1, Jeff Thomason 1, William C Sears 1
PMCID: PMC4187364  PMID: 25320387

Abstract

Presence of residual material following mini-hemilaminectomy in dogs (n = 9) with spontaneous thoracolumbar intervertebral disc extrusion was prospectively investigated. Volume of extruded disc material within the vertebral canal and the proportion of residual material were determined using pre- and post-operative magnetic resonance imaging. The degree of spinal cord compression, proportion of extradural material considered hemorrhage, and invasion of the articular facets were also determined. Residual material was identified in 44% of the mini-hemilaminectomies. The median percentage of residual material calculated was 7.7% of the preoperative volume. No observed effect of surgical side or site, proportion of extradural material considered hemorrhage, patient weight, and duration of clinical signs was detected.

Introduction

Intervertebral disc (IVD) extrusion is a common cause of progressive spinal cord dysfunction in dogs (1–7). Surgical decompression of the spinal cord through removal of extruded compressive IVD material is the treatment of choice for dogs with neurological deficits and/or persistent or recurrent back pain. A successful recovery, defined as return of ambulatory function, ranges between 83% and 100% after surgical decompression in patients with intact deep pain perception. This, however, is considerably less in dogs in which deep pain perception is absent with reports citing recovery in about 50% of cases (8–18). An incomplete recovery, being a lack of improvement or even progressive deterioration, has been reported in dogs with intact deep pain perception in spite of apparently adequate surgical decompression (8–12,19). Potential causes for the latter include progressive myelomalacia, progression of secondary spinal cord injuries, iatrogenic spinal cord trauma, low-grade instability of the vertebral column, post-operative infection, formation of a compressive hematoma, further extrusion of IVD material, and inadequate evacuation of extruded IVD material (5,19–24).

Residual compressive material is frequently present in the thoracolumbar vertebral canal following decompressive hemilaminectomy surgery (19,23–26). This provides an interesting avenue for investigation as any potential to improve evacuation of extruded IVD material, whether that is more inherent with one particular surgical technique than another, could lead to further improvement in post-operative recovery.

Presence of residual material has not been reported for mini-hemilaminectomy in dogs, probably the second most common decompressive surgery after hemilaminectomy used for thoracolumbar IVD herniation, although retrospective studies show similar success recovery rates between both techniques (8–11,16,18,27,28). Hemilaminectomy requires removal of one half of the vertebral arch, including the lamina, pedicle, and the articular processes on 1 side of the vertebrae (29–30). Mini-hemilaminectomy extends over the same length as the hemilaminectomy but preserves the articular processes limiting the procedure to the removal of pedicles ventral to those and adjacent to the intervertebral foramen (28,31–35). This technique is also referred to as extended foraminotomy, lateral spinal decompression, or modified lateral hemilaminectomy (5,28,31–33,35). Proposed benefits of removing less bone by mini-hemilaminectomy are decreased soft tissue dissection, decreased surgical time, reduced impact on the regional biomechanical function, and reduced post-operative morbidity (31,35–37). However, the smaller window created may limit the access to the dorsal and dorsolateral vertebral canal and could lead to a greater tendency for hemorrhage when working around the foramen that could further decrease exposure. The effect this may have on the ability to evacuate extruded IVD material has not been investigated.

The objectives of this study were to investigate, through magnetic resonance imaging (MRI), the presence of residual material in dogs suffering spontaneous thoracolumbar IVD extrusion after surgical decompression by mini-hemilaminectomy.

Materials and methods

Dogs with spontaneous thoracolumbar (T10-L3) IVD extrusion diagnosed on MRI (1.5T, Sigma Scanner; General Electric Medical Systems, Mississauga, Ontario) were prospectively recruited and mini-hemilaminectomy was performed. A post-surgical MRI was performed within 24 h of surgery. Informed client consent was obtained, and the study was approved by the Animal Care Committee of the University of Guelph. Visual confirmation of the presence of extruded IVD material at the surgical site was required for dogs to be included. Exclusion criteria were presence of previously identified neurological disease and deficits unrelated to the present episode, and/or orthopedic disease. Neurological examination was performed immediately prior to surgery, within 72 h following surgery, and at 4- to 6- and 12- to 16-week rechecks; pelvic limbs were functionally graded based on a modification of the Texas Spinal Cord Injury Scale (Table 1) (38).

Table 1.

Modified version of the Texas Spinal Cord Injury Score (score range 0 to 28 after summing results for both pelvic limbs)

Gait
0 No voluntary movement
2 Protraction without ground clearance
4 Protraction with inconsistent ground clearance
6 Ambulatory, falls occasionally, moderate paresis/ataxia
8 Ambulatory, does not fall, mild paresis/ataxia
10 Normal gait
Proprioception
0 Absent
1 Delayed
2 Normal
Deep pain perception
0 No deep pain sensation present
2 Pain sensation present
Open in a new tab

Mini-hemilaminectomy was performed through a dorsolateral approach with the dog positioned obliquely. The intermuscular plane ventral to the longissimus musculature was identified and bluntly dissected to allow identification of the correct surgical sites. Once the desired space was identified, an incision was made through the longissimus muscles, the lateral pedicles were cleared of soft tissues using a periosteal elevator, and the tendinous attachment of the longissimus musculature was transected at its insertion on the accessory process. Mini-hemilaminectomy was performed using a Hall’s pneumatic drill. The accessory process that overlies the dorsal aspect of the foramen was first removed and its most dorsal margin was used to determine the dorsal extent of the mini-hemilaminectomy. Ventral to this, the pedicle was drilled cranial and caudal to the intervertebral foramen over approximately 2/3 of the length of each vertebra. The ventral extent of the mini-hemilaminectomy was the ventral aspect of the intervertebral foramen.

The following image sequences were obtained post- operatively with the same MRI unit while dogs were in dorsal recumbency: T1-weighted, T2-weighted, and T2* in the transverse plane and T2-weighted and T2-weighted myelogram in the sagittal plane. Images in the transverse plane were obtained across the extent of the laminectomy defect with a 3.0-mm slice thickness and 0.2-mm slice gap. Sagittal images were obtained across the length of the thoracolumbar spine and the width of the vertebral column, with a 3.0-mm slice thickness and 0.2-mm slice gap. If residual material was noted within the vertebral canal extending past the cranial and caudal limits of the mini-laminectomy defect on the post-operative sagittal images, further transverse sequences were obtained.

Images were reviewed and analyzed with DICOM viewing software (Advantage Workstation 4.2; General Electric, Milwaukee, Wisconsin, USA). Measurements were performed by 2 reviewers: a neurology resident (JH), and a board-certified veterinary radiologist (SN). Reviewers were blinded to patient and clinical information, though pre- and post-operative images were easily distinguished. Measurements were not performed independently, with both reviewers assessing the images together and agreeing on a single appropriate measure. The cross-sectional area of material within the vertebral canal was measured on each T2-weighted transverse image using a free-hand tool (Figure 1), and reported in mm2. The cross-sectional area was then multiplied by the slice thickness plus the slice gap (3.2 mm), with the sum of these calculations representing the estimated volume of material within the vertebral canal, and reported in mm3. Residual material represented the estimated volume of material within the vertebral canal after surgery. Ratio of residual material was calculated dividing the volume of postoperative material by the volume of pre-operative material and expressed as a percentage. Using the same free-hand tool, the cross-sectional area of the vertebral canal and the cross-sectional area of extruded material were recorded at the transverse image slice with the most evident spinal cord compression in pre- and post-surgical images. Degree of spinal cord compression was then calculated, dividing the estimated area of extruded material by the vertebral canal area. Proportion of extradural material due to hemorrhage was visually estimated based on T2*-weighted images, and subjectively graded through a quantitative score from 0% to 100%. When it was observed that a mini-hemilaminectomy had invaded the articular processes, the extent of invasion was subjectively graded (0 = none, 1 = mild, 2 = moderate, 3 = severe).

Figure 1.

Figure 1

Open in a new tab

Transverse, T2-weighted MRI of the lumbar spine. Free-hand tool measurement of the circumference of extruded material within the vertebral canal (1).

Other data collected included patient signalment and weight on admission, onset and duration of clinical signs, neurological status (on admission, immediately post-operative, and on recheck examinations) using a modified version of the Texas Spinal Cord Injury Scale, surgical site and side along the vertebral column, use of absorbable gelatin sponge (Surgifoam; Ethicon, Somerville, New Jersey, USA) during the surgery, and time elapsed between surgery and the post-operative MRI.

The data were collected in the form of a split-plot design. Sub-sampling was performed to allow a measure of repeatability. Each dog constituted a random blocking variable, while site and side were fixed effects variables. Covariates of weight, duration of clinical signs, elapsed time to post-operative imaging, and hemorrhage were included. For those dogs with residual material, the degree of spinal cord compression, assessed by the ratio of cross-sectional area for material to vertebral canal, was also assessed. The covariates were entered into the model as a linear fixed effect as well as a quadratic effect. All 2-term interactions were included (along with the covariate and quadratic covariate) in the model to start, and then non-significant terms were removed.

To analyze the data, a General Linear Mixed Model was employed using Proc Mixed in SAS (SAS, version 9.2; SAS Institute, Cary, North Carolina, USA). To assess the analysis of variance (ANOVA) assumptions, the residuals were formally tested for normality using the 4 tests offered by SAS (Proc UNIVARIATE): Shapiro-Wilk, Kolmogorov-Smirnov, Cramérvon Mises, and Anderson-Darling tests. The residuals were also plotted against the predicted values as well as all explanatory variables (dog, site, side) to check for possible outliers, assess for equality of variance, or other potential problems. Transformation was performed as required based on residual analysis. P < 0.05 was considered statistically significant.

Results

Nine dogs were included in the study. Relevant individual data are presented in Table 2. Dachshunds were over-represented (n = 4), with the remaining dogs being beagles (n = 2), and 1 each of: cocker/poodle cross, shih tzu/poodle cross, and miniature poodle. Gender distribution was 6 males and 3 females. The mean weight of dogs in the study was 8.1 kg (range: 4.5 to 15 kg). Mean duration of clinical signs prior to surgery was 3.7 d (range: 1 to 8 d).

Table 2.

Patient data (Neurological score: 1 — immediately before surgery, 2 — 72 hours post-surgery, 3 — 4 to 6 weeks post-surgery)

Patient Breed Weight (kg) Surgical site Neurological score (pelvic limbs; range 0 to 28) Residual volume (% of preoperative volume)
1 2 3
1 Dachshund 7.1 T13-L1 24 24 26 0
2 Beagle 7.3 T12-T13 21 18 28 0
3 Cocker/Poodle 12.0 T12-L1 8 16 24 0
4* Shih tzu/Poodle 7.9 T12-T13 26 26 28 0
5* Miniature poodle 5.8 T13-L1 16 15 22 0
6 Dachshund 4.5 T13-L1 4 8 25 6.4 mm3 (11.8%)
7 Beagle 15.0 L2-L3 14 12 21 38.4 mm3 (27.3%)
8 Dachshund 4.5 T13-L1 4 6 NA 76.8 mm3 (18.6%)
9 Dachshund 9.2 L2-L3 0 0 NA 64.0 mm3 (21.9%)
Open in a new tab

NA — not available.

*

Absorbable gelatin sponge remaining at surgical site.

On initial presentation, neurological examination localized a lesion in the T3-L3 spinal cord segment in all patients. The mean neurological score on admission was 13 (range: 0 to 26). Four dogs were ambulatory paraparetic, 2 dogs were non- ambulatory paraparetic, and 3 dogs were paraplegic, 1 in which deep pain perception was absent. The most commonly affected site was T13-L1 (n = 5), followed by T12-T13 (3), L2-L3 (2), and T11-T12 (1). One dog had extruded material extending beyond a single site, requiring decompression of 2 adjacent sites. Five surgeries were performed on the left side of the vertebral column and 4 surgeries were performed on the right side. The mean time between surgery and post-operative MRI was 4.5 h (range: 0.5 to 18 h). The absorbable gelatin sponge was left after surgery in only 2 dogs, in which it was placed ventral to the spinal cord.

Residual material was identified in 44% of the mini-hemilaminectomies. Median volume of preoperative material was 120.8 mm3 [range: 60.9 mm3 to 240 mm3, 95% confidence interval (95% CI): 60.9 mm3 to 240 mm3]. The median percentage of residual material was 7.7% (range: 0% to 27.3%, 95% CI: 4.3% to 13.8%) of the preoperative volume. There was no effect of surgical site and side of the vertebral column, patient weight, or duration of the clinical signs on the percentage of residual material (P > 0.20). Due to the number of variables and small sample size, the effect of time between surgery and post-operative imaging, and the effect of pre-operative material volume on post-operative material volume could not be assessed.

Mean degree of spinal cord compression was 37% (range: 20% to 67%) before surgery and 10.9% (range: 0% to 40%) after surgery. The mean proportion of extradural material considered hemorrhage, using T2* MRI sequences, was 16% (range: 0% to 80%) and 0% for pre- and post-operative MRI, respectively.

On MRI, the ventral aspect of the articular processes appeared to be partially invaded in all of the mini-hemilaminectomy sites, with 4 subjectively graded as moderate invasion and 5 as minimal invasion. Although the low number of cases precluded statistical analysis, there were no trends observed between the grade of articular processes invasion and the calculated ratio of residual material or any other variable assessed.

On follow-up, 3 dogs experienced mild neurological score deterioration of 1 to 4 points during the immediate postoperative period (Table 2). There were no trends subjectively observed between the occurrence of deterioration and the volume of residual material, with only 1 of the 3 having residual material identified (27%). All 3 dogs had clinical signs for at least 3 d prior to surgery. All except 1 dog improved and were ambulatory by the 4- to 6-week recheck examination. The dog that was paraplegic with no deep pain perception showed no improvement within 72 h, but was lost to follow-up after discharge. Upon contact by telephone, the owner reported that the dog had remained paraplegic for 8 mo after surgery.

Discussion

The results of our study confirm that residual material is frequently present following thoracolumbar mini-hemilaminectomy in IVD extrusion, as it has been reported for hemilaminectomy (19,26). As few studies have assessed the occurrence of residual material after decompressive spinal surgery and none involving mini-hemilaminectomy, the clinical relevance of these findings as well as the presence of a correlation between volume of residual material and functional recovery in the dog remains to be elucidated (19,25,26).

These results differ from those of a previous study in which the mean volume of residual material after thoracolumbar hemilaminectomy was approximately 50% on computed tomography (CT), though with a wider range of 2.6% to 155.8% (26). Residual volumes of > 100% were suggested to be the result of complications, such as further disc extrusion or post-operative hemorrhage (26). No dogs in our study had a residual volume > 100%; however, the amount of residual material was assessed using a different imaging modality (CT versus MRI) in each study, and that factor should be taken into consideration.

The volume of residual extradural material was not overestimated by the use of an absorbable gelatin sponge, as postoperative material was not identified in the 2 dogs that had these sponges. An absorbable porcine gelatin sponge is often used to provide hemostasis and prevent the formation of a compressive hematoma or a restrictive laminectomy membrane. While this material tends to be completely reabsorbed within 4 to 6 wk, very little information exists on its MRI signal characteristics and appearance, particularly over time while it degrades and is resorbed (39). In our 2 cases, the gelatin sponge was easily distinguished from the surrounding tissues as a sharply demarcated, geometric shape with high T2-weighted signal material (Figure 2). However, the MRIs were performed at 1 and 1.5 h after surgery and it is unknown whether the sponges would be more difficult to differentiate from tissues or residual disc material after that time frame.

Figure 2.

Figure 2

Open in a new tab

Transverse T2-weighted image after surgery in a case in which an absorbable gelatin sponge (arrow) was placed in the bony defect.

The effect on the functional recovery of any volume of residual material is unknown, as successful recoveries have been previously reported in dogs in which considerable residual material was detected (25,26). Large volumes of compressive material can be tolerated by the spinal cord provided the rate of extrusion and compression are slow (40,41). Considering this and multiple other variables, the investigation of the impact of residual material on functional outcome would require a large sample size. The small sample size (n = 9) herein prevented accurate analysis of several variables using the statistical model, often described as an “over-fitting” of results; therefore, the effect of the amount of residual material on the post-surgical neurological score could not be adequately assessed. However, all cases had improved and were ambulatory by the 4- to 6-week assessment, except for 1 dog in which deep pain perception was absent in the pelvic limbs at presentation. Dogs treated by surgical decompression for thoracolumbar IVD extrusion can require up to 36 wk to recover ambulation, indicating the importance of long-term follow-up (42). The dog that had 21.9% residual material showed an acute onset and rapid deterioration, with the duration of clinical signs being no greater than 24 h. The 2 dogs paraplegic with intact deep pain perception at presentation had a similar duration of clinical signs, and residual material identified on post-operative imaging (11% and 18%), and both had recovered ambulatory function at the 4- to 6-week evaluation.

Venous sinus hemorrhage associated with IVD extrusion is common (43). Intra-operative hemorrhage can also occur typically originating from the venous sinuses or spinal vessels and vessels of the muscular attachments to the articular processes. Hemorrhage can lead to formation of a post-operative compressive hematoma (43). While hemorrhage can have multiple characteristics on MRI, the accuracy of MRI to identify hemorrhage and the ability to distinguish it from other material within the vertebral canal is superior compared to CT when using T2*(gradient echo) sequences (44). Due to the inherent characteristics of T2* sequences, as inferior resolution, and the often dispersed nature of hemorrhage within extruded material, circumferential measurements were deemed too inaccurate for consideration in this study and a subjective visual scale was used instead. Despite the proportion of extradural material considered hemorrhage being a subjective measure, its presence had no effect on the volume of residual material between techniques.

An interesting finding in this study was the invasion of the ventral aspect of the articular facet in 100% of the mini-hemilaminectomy sites. While many reports for the mini-hemilaminectomy technique recommend preserving the articular processes, others suggest altering the dorsal limit of the laminectomy window based on the location of extruded material. Some reports suggest removing the accessory process as the dorsal landmark which would indicate at least partial encroachment of the articular processes (28,31–35). The effect of partial removal of the articular process on vertebral column stability is unknown, although the extent of bone removal could influence the proposed benefits for decreased biomechanical instability with mini-hemilaminectomy. The potential for a larger mini-hemilaminectomy window to have a positive influence on the ability to evacuate compressive material should be considered when results of this study are assessed. Dorsoventral dimensions of the defect created by both hemilaminectomy and mini-hemilaminectomy have been reported in dogs (45). Size of the laminectomy decreased with increasing vertebral canal height (increasing size of dog) regardless of technique, though the difference was greater with the mini-hemilaminectomy. In the current study, laminectomy dimensions were not determined due to the lack of adequate spatial resolution of the MRI. However, the smaller window created by mini-hemilaminectomy did not affect the ability to evacuate extruded material; nor was the volume of residual material affected by patient weight or breed. Additionally, the degree of invasion of the articular processes with mini-hemilaminectomy did not appear to be exclusive to the dogs with lower body weight.

One of the limitations of this study is related to the imaging modality. Magnetic resonance imaging was chosen for its superior contrast resolution; however, spatial resolution is reduced compared to CT. Slice thickness and gap were included in the calculation of volume and may represent an over-estimation, especially in small dogs in which volume averaging is more likely to occur (43).

The Hawthorne effect, a well-described phenomenon in human literature, is suggested to occur when a study participant’s behavior and results are altered by their awareness of being monitored or included in a study, and may even have more influence on outcome measures than the placebo effect (46,47). As surgeons in our study were not blinded to the inclusion of cases, we cannot exclude the influence this may have had on the laminectomy created or the quality of extruded IVD material evacuation. However, surgeons were blinded to the results of post-operative MR imaging in clinical patients, which may have prevented any additional steps being taken to improve their outcomes.

In conclusion, this study identified residual material in dogs with thoracolumbar IVD extrusion that had undergone mini-hemilaminectomy. While variability in the dorsal limits of the mini-hemilaminectomy is evident, the effect this has on vertebral column stability, patient morbidity, and the ability to remove compressive material from the vertebral canal requires more investigation. To the authors’ knowledge this is the first published report of residual IVD material detected by MRI following mini-hemilaminectomy. CVJ

Footnotes

Supported by a grant from the Ontario Veterinary College Pet Trust Fund.

This manuscript represents a portion of a thesis submitted by Dr. Huska to the University of Guelph, Department of Clinical Studies as partial fulfillment of the requirements for a Doctor of Veterinary Science degree.

Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office (hbroughton@cvma-acmv.org) for additional copies or permission to use this material elsewhere.

References

  • 1.Priester W. Canine intervertebral disc disease — occurrence by age, breed, and sex among 8117 cases. Theriogenology. 1976;6:293–303. [Google Scholar]
  • 2.Goggin JE, Li AS, Frante CE. Canine intervertebral disk disease: Characterization by age, sex, breed, and anatomic site of involvement. Am J Vet Res. 1970;31:1687–1692. [PubMed] [Google Scholar]
  • 3.Hansen H. A pathologic-anatomical study on disc degeneration in the dog. Acta Orthop Scand (Suppl) 1952;11:1–117. doi: 10.3109/ort.1952.23.suppl-11.01. [DOI] [PubMed] [Google Scholar]
  • 4.Ball MU, McGuire JA, Swaim SF, Hoerlein BF. Patterns of occurrence of disk disease among registered dachshunds. J Am Vet Med Assoc. 1982;180:519–522. [PubMed] [Google Scholar]
  • 5.Brisson BA, Holmberg DL, Parent J, Sears WC, Wick SE. Comparison of the effect of single-site and multiple-site disk fenestration on the rate of recurrence of thoracolumbar intervertebral disk herniation in dogs. J Am Vet Med Assoc. 2011;238:1593–1600. doi: 10.2460/javma.238.12.1593. [DOI] [PubMed] [Google Scholar]
  • 6.Hoerlein BF. Comparative disc disease: Man and dog. J Am Anim Hosp Assoc. 1979;15:535–545. [Google Scholar]
  • 7.Prata RG. Neurosurgical treatment of thoracolumbar disks: The rationale and value of laminectomy with concomitant disk removal. J Am Anim Hosp Assoc. 1981;17:17–26. [Google Scholar]
  • 8.Aikawa T, Fujita H, Kanazono S, Shibata M, Yoshigae Y. Long-term neurologic outcome of hemilaminectomy and disk fenestration for treatment of dogs with thoracolumbar intervertebral disk herniation: 831 cases (200–2007) J Am Vet Med Assoc. 2012;241:1617–1626. doi: 10.2460/javma.241.12.1617. [DOI] [PubMed] [Google Scholar]
  • 9.Davis GJ, Brown DC. Prognostic indicators for time to ambulation after surgical decompression in non-ambulatory dogs with acute thoracolumbar disk extrusions: 112 cases. Vet Surg. 2002;31:513–518. doi: 10.1053/jvet.2002.36015. [DOI] [PubMed] [Google Scholar]
  • 10.Ferreira AJA, Correia JHD, Jaggy A. Thoracolumbar disc disease in 71 paraplegic dogs: Influence of rate of onset and duration of clinical signs on treatment results. J Small Anim Pract. 2002;43:158–163. doi: 10.1111/j.1748-5827.2002.tb00049.x. [DOI] [PubMed] [Google Scholar]
  • 11.Kazakos G, Polizopoulou ZS, Patsikas MN, Tsimopoulos G, Roubies N, Dessiris A. Duration and severity of clinical signs as prognostic indicators in 30 dogs with thoracolumbar disk disease after surgical decompression. J Vet Med A Physiol Pathol Clin Med. 2005;52:147–152. doi: 10.1111/j.1439-0442.2005.00698.x. [DOI] [PubMed] [Google Scholar]
  • 12.Ruddle TL, Allen DA, Schertel ER, et al. Outcome and prognostic factors in non-ambulatory Hansen type I intervertebral disc extrusions: 308 cases. Vet Comp Orthop Traumatol. 2006;19:29–34. [PubMed] [Google Scholar]
  • 13.Brown NO, Helphrey ML, Prata RG. Thoracolumbar disk disease in the dog: A retrospective analysis of 187 cases. J Am Anim Hosp Assoc. 1997;13:665–672. [Google Scholar]
  • 14.Cudia SP, Duval JM. Thoracolumbar intervertebral disk disease in large, nonchondrodystrophic dogs: A retrospective study. J Am Anim Hosp Assoc. 1997;33:456–460. doi: 10.5326/15473317-33-5-456. [DOI] [PubMed] [Google Scholar]
  • 15.Duval J, Dewey C, Roberts R, Aron D. Spinal cord swelling as a myelographic indicator of prognosis: A retrospective study in dogs with intervertebral disc disease and loss of deep pain sensation. Vet Surg. 1996;25:6–12. doi: 10.1111/j.1532-950x.1996.tb01371.x. [DOI] [PubMed] [Google Scholar]
  • 16.Knecht CD. Results of surgical treatment for thoracolumbar disc protrusion. J Small Anim Pract. 1972;13:449–453. doi: 10.1111/j.1748-5827.1972.tb06872.x. [DOI] [PubMed] [Google Scholar]
  • 17.Laitinen OM, Puerto DA. Surgical decompression in dogs with thoracolumbar intervertebral disc disease and loss of deep pain perception: A retrospective study of 46 cases. Acta Vet Scand. 2005;46:79–85. doi: 10.1186/1751-0147-46-79. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Olby NJ, Harris T, Burr J, Muňana K, Sharp N, Keene B. Recovery of pelvic limb function in dogs following acute intervertebral disc herniations. J Neurotrauma. 2004;21:49–59. doi: 10.1089/089771504772695940. [DOI] [PubMed] [Google Scholar]
  • 19.Forterre F, Gorgas D, Dickomeit M, Jaggy A, Lang L, Spreng D. Incidence of spinal compressive lesions in chondrodystrophic dogs with abnormal recovery after hemilaminectomy for treatment of thoracolumbar disc disease: A prospective magnetic resonance imaging study. Vet Surg. 2010;39:165–172. doi: 10.1111/j.1532-950X.2009.00633.x. [DOI] [PubMed] [Google Scholar]
  • 20.Griffiths IR. The extensive myelopathy of intervertebral disc protrusions in dogs (‘the ascending syndrome’) J Small Anim Pract. 1972;13:425–437. doi: 10.1111/j.1748-5827.1972.tb06870.x. [DOI] [PubMed] [Google Scholar]
  • 21.Olby NJ. Current concepts in the management of acute spinal cord injury. J Vet Intern Med. 1999;13:399–407. doi: 10.1892/0891-6640(1999)013<0399:ccitmo>2.3.co;2. [DOI] [PubMed] [Google Scholar]
  • 22.Funkquist B. Investigations of the therapeutic and prophylactic effects of disc evacuation in cases of thoracolumbar herniated discs in dogs. Acta Vet Scand. 1978;19:441–457. doi: 10.1186/BF03547613. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Dhupa S, Glickman NW, Waters DJ. Reoperative neurosurgery in dogs with thoracolumbar disc disease. Vet Surg. 1999;28:421–428. doi: 10.1111/j.1532-950x.1999.00421.x. [DOI] [PubMed] [Google Scholar]
  • 24.Hettlich BF, Kerwin SC, Levine JM. Early reherniation of disk material in eleven dogs with surgically treated thoracolumbar intervertebral disk extrusion. Vet Surg. 2012;41:215–220. doi: 10.1111/j.1532-950X.2011.00920.x. [DOI] [PubMed] [Google Scholar]
  • 25.Forterre F, Konar M, Spreng D, Jaggy A, Lang J. Influence of intervertebral disc fenestration at the herniation site in association with hemilaminectomy on recurrence in chondrodystrophic dogs with thoracolumbar disc disease: A prospective MRI study. Vet Surg. 2008;37:399–405. doi: 10.1111/j.1532-950X.2008.00394.x. [DOI] [PubMed] [Google Scholar]
  • 26.Roach W, Thomas M, Weh JM, Bleedom J, Wells K. Residual herniated disc material following hemilaminectomy in chondrodystrophic dogs with thoracolumbar intervertebral disc disease. Vet Comp Orthop Traumatol. 2012;25:1–7. doi: 10.3415/VCOT-11-05-0075. [DOI] [PubMed] [Google Scholar]
  • 27.Muir P, Johnson K, Manley P, Dueland RT. Comparison of hemilaminectomy and dorsal laminectomy for thoracolumbar intervertebral disc extrusion in dachshunds. J Small Anim Pract. 1995;36:360–367. doi: 10.1111/j.1748-5827.1995.tb02950.x. [DOI] [PubMed] [Google Scholar]
  • 28.Yovich JC, Read R, Eger C. Modified lateral spinal decompression in 61 dogs with thoracolumbar disc protrusion. J Small Anim Pract. 1994;35:351–356. [Google Scholar]
  • 29.Gage ED, Hoerlein BF. Hemilaminectomy and dorsal laminectomy for relieving compressions of the spinal cord in the dog. J Am Vet Med Assoc. 1968;152:351–359. [PubMed] [Google Scholar]
  • 30.Hoerlein BF. The treatment of intervertebral disc protrusions in the dog. Proceedings of the American Veterinary Medical Association; Atlantic City, New Jersey. 1952; pp. 206–212. [Google Scholar]
  • 31.Bitetto WV, Thacher C. A modified lateral decompressive technique for treatment of canine intervertebral disk disease. J Am Anim Hosp Assoc. 1987;23:409–413. [Google Scholar]
  • 32.Black AP. Lateral spinal decompression in the dog: A review of 39 cases. J Small Anim Pract. 1988;29:581–588. [Google Scholar]
  • 33.Braund KG, Taylor TKF, Ghosh P, Sherwood AA. Lateral spinal decompression in the dog. J Small Anim Pract. 1976;17:583–592. doi: 10.1111/j.1748-5827.1976.tb07005.x. [DOI] [PubMed] [Google Scholar]
  • 34.Jeffery ND. Treatment of acute and chronic thoracolumbar disc disease by ‘mini hemilaminectomy’. J Small Anim Pract. 1988;29:611–616. [Google Scholar]
  • 35.Lubbe AM, Kirberger RM, Verstraete JM. Pediculectomy for thoracolumbar spinal decompression in the dachshund. J Am Anim Hosp Assoc. 1994;30:233–238. [Google Scholar]
  • 36.Eule JM, Breeze R, Kindt GW. Bilateral partial laminectomy: A treatment for lumbar spinal stenosis and midline disc herniation. Surg Neurol. 1999;52:329–338. doi: 10.1016/s0090-3019(99)00102-0. [DOI] [PubMed] [Google Scholar]
  • 37.Thome C, Zevgaridis D, Leheta O, et al. Outcome after less-invasive decompression of lumbar spinal stenosis: A randomized comparison of unilateral laminotomy, bilateral laminotomy, and laminectomy. J Neurosurg Spine. 2005;3:129–141. doi: 10.3171/spi.2005.3.2.0129. [DOI] [PubMed] [Google Scholar]
  • 38.Levine GJ, Levine JM, Budke CM, et al. Description and repeatability of a newly developed spinal cord injury scale for dogs. Prev Vet Med. 2009;89:121–127. doi: 10.1016/j.prevetmed.2009.02.016. [DOI] [PubMed] [Google Scholar]
  • 39.Oto A, Remer EM, O’Malley CM, Tkach JA, Gill IS. MR characteristics of oxidized cellulose (Surgicel) AJR Am J Roentgenol. 1999;172:1481–1484. doi: 10.2214/ajr.172.6.10350276. [DOI] [PubMed] [Google Scholar]
  • 40.Boekhoff TM, Flieshardt C, Ensinger EM, Fork M, Kramer S, Tipold A. Quantitative magnetic resonance imaging characteristics: Evaluation of prognostic value in the dog as a translational model for spinal cord injury. J Spinal Disord Tech. 2012;25:E81–87. doi: 10.1097/BSD.0b013e31823f2f55. [DOI] [PubMed] [Google Scholar]
  • 41.Sparrey CJ, Choo AM, Liu J, Tetzlaff W, Oxland TR. The distribution of tissue damage in the spinal cord is influenced by the contusion velocity. Spine. 2008;33:E812–819. doi: 10.1097/BRS.0b013e3181894fd3. [DOI] [PubMed] [Google Scholar]
  • 42.Olby NJ, Levine J, Harris T, Muňana K, Skeen T, Sharp N. Long-term functional outcome of dogs with severe injuries of the thoracolumbar spinal cord: 87 cases (1996–2001) J Am Vet Med Assoc. 2003;222:762–769. doi: 10.2460/javma.2003.222.762. [DOI] [PubMed] [Google Scholar]
  • 43.Tartarelli CL, Baroni M, Borghi M. Thoracolumbar disc extrusion associated with extensive epidural haemorrhage: A retrospective study of 23 dogs. J Small Anim Pract. 2005;46:485–490. doi: 10.1111/j.1748-5827.2005.tb00277.x. [DOI] [PubMed] [Google Scholar]
  • 44.Tidwell AS, Jones JC. Advanced imaging concepts: A pictorial glossary of CT and MRI technology. Clin Tech Small Anim Pract. 1999;14:65–111. doi: 10.1016/s1096-2867(99)80008-5. [DOI] [PubMed] [Google Scholar]
  • 45.Huska JL, Gaitero L, Brisson BA, Nykamp S, Thomason J, Sears WC. Comparison of the access window created by hemilaminectomy and mini-hemilaminectomy in the thoracolumbar vertebral canal using computed tomography. Can Vet J. 2014;55:449–455. [PMC free article] [PubMed] [Google Scholar]
  • 46.Berthelot JM, Le Goff B, Maugars Y. The Hawthorne effect: Stronger than the placebo effect? Joint Bone Spine. 2011;78:335–336. doi: 10.1016/j.jbspin.2011.06.001. [DOI] [PubMed] [Google Scholar]
  • 47.Fernald DH, Coombs L, DeAlleaume L, West D, Parnes B. An assessment of the Hawthorne Effect in practice-based research. J Am Board Fam Med. 2012;25:83–86. doi: 10.3122/jabfm.2012.01.110019. [DOI] [PubMed] [Google Scholar]

Articles from The Canadian Veterinary Journal are provided here courtesy of Canadian Veterinary Medical Association

RESOURCES