Corpectomy (Imhc) for Treatment of Thoracolumbar Intervertebral Disc Herniation in Large Breed Dogs

Received: 27 February 2015 | Accepted: 12 September 2016 DOI 10.1111/vsu.12616

ORIGINAL ARTICLE

Individualized mini-hemilaminectomy-corpectomy (iMHC) for treatment of thoracolumbar intervertebral disc herniation in large breed dogs

Susanne C. Medl1 | Sven Reese2 | Nikola S. Medl1

1 Small Animal Clinic Dr. Medl, Abstract Babenhausen, Bavaria, Germany 2 Institute of Anatomy, Histology, and Objective: To assess the short-term, mid-term, and long-term results after an individ- Embryology, Department of ualized mini-hemilaminectomy-corpectomy (iMHC) procedure for treatment of acute Veterinary Sciences, Faculty of and chronic thoracolumbar intervertebral disc disease in non-chondrodystrophic Veterinary Medicine, Ludwig- dogs. Maximilians-University, Munich, Study Design: Prospective study. Germany Animals: Client-owned non-chondrodystrophic large breed dogs (n 5 57). Correspondence Susanne C. Medl, Tierärztliche Methods: The iMHC procedure, combining mini-hemilaminectomy (MH) and par- Klinik, Alpenstr. 27, 87727 tial lateral corpectomy, was performed on non-chondrodystrophic dogs with Babenhausen, Bavaria, Germany. thoracolumbar disc disease. Neurological status was evaluated before surgery, for Email: [email protected] short-term outcome on days 1 and 7 after surgery, for mid-term outcome at 6 months after surgery, and for long-term outcome at the conclusion of the study. Prognostic factors were statistically evaluated. P < .05 was considered significant. Results: iMHC was performed on 57 dogs, with minimal intraoperative and postoperative complications. Short-term neurological improvement was observed in 85.7% of dogs. Median hospitalization time after surgery was 2 days (range 0-14) and was significantly shorter for dogs with a chronic history of clinical signs (1 day, range 0- 5) compared to acute onset (3 days, range 0-14) and for those that were ambulatory at initial presentation (1 day, range 0-5) compared to those that were not (3 days, range 0-14). Long-term evaluation included 53 surgeries with a mean follow-up time of 29.4 months. Outcome was excellent in 19 dogs and good in 29 dogs (90.6% success rate). Excellent mid-term and long-term results were significantly more common in the dogs with only 1 affected disc space. Conclusion: The iMHC procedure resulted in a short hospitalization time, minimal postoperative deterioration, and a high success rate.

1 | INTRODUCTION have been proposed to address decompression of the spinal cord. Currently, hemilaminectomy (HL) is the standard pro- Disc herniation is considered the most common cause of spi- cedure used, as there are over 2000 published cases in at nal cord trauma in dogs.1 A variety of surgical approaches least 37 publications. However, a certain degree of spinal cord manipulation is frequently inevitable by HL exposure, *Presented at the European College of Veterinary Neurology with potential untoward neurological sequelae due to verte- 2,3 Annual Symposium, Ghent, Belgium, September 2012, Veterinary bral canal entry from a dorsolateral direction. Deterioration Neurosurgical Society Symposium, Portland, OR, August 2013, of neurological status after surgery has been observed fol- and FECAVA Eurocongress, Munich, Germany, November 2014. lowing HL.3-7

422 | VC 2017 The American College of Veterinary Surgeons wileyonlinelibrary.com/journal/vsu Veterinary Surgery 2017; 46: 422-432 MEDL ET AL. | 423

Surgical treatment by HL typically yields considerably less favorable results in large breed dogs than in small breed dogs.8-10 In a study performed in 1997 on non- chondrodystrophic dogs with thoracolumbar intervertebral disc disease (IVDD), the reported time to recovery after dorsal laminectomy (DL) or HL was 5.6 weeks in dogs that were ambulatory before surgery and 7 weeks in dogs that were non-ambulatory before surgery.10 Another study on small and large breed dogs showed postoperative deterioration in 60% of cases when HL was combined with vertebral stabilization.11 Mini-hemilaminectomy was first described in 1978 by Braund.2 In this procedure, access to the spinal canal by removing the accessory process and enlarging the intervertebral foramen cranially and caudally is gained with minimal removal of bone. The articular facets remain preserved and vertebral column stability, particularly when combined with fenestration, is better maintained than in HL.2,12,13 The FIGURE 1 Computed tomography image of a dog with removal of ventrally located disc material is facilitated and chronic disc extrusion showing the spinal cord wrapped around the risks of iatrogenic spinal cord trauma and laminar mem- the herniated disc material (arrow). The disc material cannot be brane formation are minimized.14 Mini-hemilaminectomy removed by a dorsolateral approach to the spinal canal without has yielded considerably more promising results than HL in considerable manipulation of the spinal cord terms of both postoperative status and recovery time in small and large breed dogs.2,15-17 (iMHC) procedure for the treatment of acute and chronic Due to the pathogenesis of the primarily fibrous disc thoracolumbar IVDD in non-chondrodystrophic dogs. degeneration in non-chondrodystrophic dogs, disc herniations typically begin with annular protrusions. These are pre- 2 | MATERIALS AND METHODS dominantly centrally located18 and over time can progress to extrusions, become hard or calcified, and adhere to the floor In this prospective study, iMHC was performed on all dogs of the spinal canal and/or dura mater. In these cases (Figure selected by the below-mentioned inclusion criteria. The 1), removal of disc material using the dorsolateral approach observational period was a minimum of 6 months. Written to the spinal canal by HL requires considerable manipulation informed consent was obtained from all owners before study of the spinal cord.2,3,9,19 In human neurosurgery, the use of entry. Consecutive clinical cases presented from January evoked motor potentials has revealed that an already com- 2006 to April 2013 were included. Inclusion criteria were promised spinal cord is highly sensitive to surgical manipula- non-chondrodystrophic breed, body weight of 18 kg, com- tion.20,21 Although surgical intervention often is required in pressive thoracolumbar IVDD confirmed by diagnostic imag- cases of compressive IVDD, the surgery by itself should not ing, neurological deficits, and pain consistent with a result in deterioration of clinical signs. Recently, promising neuroanatomical localization from T3 to L4 or recurrent results have been achieved in dogs with chronic disc hernia- back pain that did not respond to pain medication. Exclusion tion with the introduction of partial lateral corpectomy criterion was a postoperative lack of owner compliance. (PLC).19 Portions of the intervertebral disc and adjacent ver- Clinical presentation, breed, body weight, age, and sex of tebral body are removed and the herniated and compressing each dog were recorded. disc material is addressed from a ventral direction, thereby On clinical presentation, general and neurological exami- avoiding surgical manipulation of the spinal cord. nations were performed and the rate of onset, duration of In comparisons of outcomes and recovery times in dogs, clinical signs, and neurological status were noted. The rate of mini-hemilaminectomy (MH) and PLC each have yielded onset of neurological signs was defined as the time from the best results to date.15-17,19,22 The objectives of this study being clinically normal to attaining the worst neurological were to combine both methods to add the advantages of the status and was classified as peracute (<1 hour), acute (1-24 lateral and ventral approach and to minimize the dimensions hours), chronic (>24 hours), or chronic with acute deteriora- of the PLC to the individual needs of each dog, as well as to tion.8,10,23 Duration of clinical signs was defined as the time assess the short-term, mid-term, and long-term outcomes from when the owner first observed neurological dysfunction after this individualized mini-hemilaminectomy-corpectomy until the time of presentation. Based on the severity of 424 | MEDL ET AL.

TABLE 1 Grading system used to assign dogs to 1 of 5 neurologic categories based on the severity of the neurological dysfunction

Grade Ambulatory Deﬁnition # Dogs 1 Yes Back pain without any neurological deﬁcits 1

2 2a Yes Very mild ambulatory paraparesis, mild ataxia, or conscious proprioceptive deﬁcit 0

2b Yes Moderate ambulatory paraparesis 9

2c Yes Severe ambulatory paraparesis 23

3 No Non-ambulatory paraparesis 14

4 No Paraplegia with or without bladder function 13

5 No Paraplegia without deep pain perception 3

neurological dysfunction, dogs were assigned to 1 of 5 neu- diseased side up on a tilting surgery table. A dorsolateral rologic categories.13,23-26 Because grade 2 comprised a wide- approach to the spine was performed at the affected site.28 spread group of dogs with considerable difference in the The area around the intervertebral foramen and adjacent ped- severity of neurological signs, it was further subdivided to icles were freed bluntly from the surrounding musculature allow for a more precise evaluation of the effects of the sur- using a periosteal elevator and the tendinous attachment of gery into grades 2a, 2b, and 2c (Table 1).8,11,27 the longissimus muscle to the accessory process at the The diagnosis of disc herniation and information about its affected site was severed using Metzenbaum scissors (Figure localization and possible lateralization, the number of affected 2A). After completion of the approach, the procedure was sites, and the extent of spinal cord compression were obtained continued under a surgical microscope (Carl Zeiss, Kolpos- using computed tomography (CT; GE High Speed, GE kop Plus, Jena, Germany) that allowed for a 7.5-12-fold Healthcare, Solingen, Germany), cisternal myelography (Sie- magnification of the surgical site. Using a high-speed burr mens Siregraph D, Siemens Healthcare GmbH, Erlangen, that allows for simultaneous continuous irrigation with sterile Germany; Iopamidol, Solutrast 250M, Bracco Imaging, Ger- saline (Microspeed Uni, Aesculap, Tuttlingen, Germany), many), or a combination of both. The evaluation of images iMHC was performed (Figure 2). After completion of MH, was performed using an Osirix 64-bit imaging software work- the dorsal and ventral spinal nerve roots were freed from station (Pixmeo, Bernex, Switzerland). their ligamentous attachments using small pointed scissors Standard blood work, including routine hematology and (Sontec, Centennial, Colorado) and displaced slightly crani- serum chemistry, was performed before anesthesia. Dogs were ally to gain access to the lateral aspect of the intervertebral premedicated IV with diazepam (0.5 mg/kg), xylazine (0.4 mg/ disc. Centered on the intervertebral disc, the PLC was kg), and ketamine (4 mg/kg), anesthetized with propofol (4- enlarged in the cranial, caudal, and medial directions using fl 6 mg/kg IV), and maintained with iso urane in oxygen. Intra- the high-speed burr. The dimensions were kept as small as fl venous crystalloid uids were administered throughout surgery possible but were sufficiently large to achieve decompression (5 mL/kg/h). Metamizole (50 mg/kg IV) was administered pre- of the spinal cord and were thus individualized to the needs operatively and a constant-rate infusion of fentanyl (10 mg/kg/h of each dog (Figure 3). IV) was administered during surgery. Cefalexin (22 mg/kg IV) Lateralized herniations were immediately visualized after was administered 30 minutes preoperatively. Postoperative completion of MH, and after corpectomy could be removed pain was controlled using buprenorphine (0.01 mg/kg IV) and using a nerve hook (Sontec) without manipulating the spinal meloxicam (0.2 mg/kg IV) on the day of surgery. Further cord. For centrally located herniations, PLC was extended pain medication consisted of meloxicam (0.2 mg/kg orally until the herniation underneath the spinal cord came into once daily for 7 days). Antibiotics were not administered sight and sank ventrally as some of the pressure arising from postoperatively. ventrally was already relieved. Fresh, soft disc material was retrieved using the small MH opening by passing the nerve 2.1 | Surgical procedure hook gently underneath the spinal cord (Figure 4). Firm, A single board-certified neurologist, who is also an experi- extruded fibrous material from the annulus fibrosus was bet- enced surgeon (SM), performed all surgeries. Dogs were ter retrieved using the PLC slot (ie, using arthroscopy for- positioned in 308-408 sternal oblique recumbency with the ceps (Dr Fritz, Tuttlingen, Germany; Video Clip S1 and S2). MEDL ET AL. | 425

FIGURE 2 Cadaver study of an individualized mini-hemilaminectomy-corpectomy. A, The vertebral pedicles (P) and the accessory process (A) are freed from the muscular and tendinous attachments. B, After completion of mini-hemilaminectomy, the spinal nerve root (N) is identiﬁed. C, The connecting tissue between the pedicles is severed using small pointed scissors. D, A nerve hook (NH) is passed gently beneath the spinal cord (SC) to explore the spinal canal. E, Using a high speed burr the partial lateral corpectomy (PLC) is created, centered on the intervertebral disc and enlarged cranially, medially, and caudally. F, Disc material is removed from the PLC using a curette or arthroscopy forceps. G, The ﬂoor of the spinal canal sinks ventrally back into position or can be pushed ventrally gently using a nerve hook. Additional disc material can be retrieved from the spinal canal or through the PLC, H, I, View of the completed combined mini-hemilaminectomy—partial lateral corpectomy defect. ST, suction tip; DG, dorsal root ganglion

FIGURE 3 Postoperative computed tomography images of a completed large (A) and small (B) individualized mini- hemilaminectomy-corpectomy (iMHC) at the T13/L1 intervertebral disc space. AP, accessory process; FJ, facet joint 426 | MEDL ET AL.

good outcomes were both rated as successful. Information concerning owner satisfaction was obtained using an owner questionnaire. Quality of life and quality of function were rated on a scale from 1 to 5, with 1 representing the best outcome, and an overall assessment was performed (Table S1).

2.3 | Statistical analysis Data were analyzed using commercial software (SPSS Statis- tics 22, IBM Corp, Munich, Germany and BIAS for Win- dows 10.04, Epsilon-Verlag, Darmstadt, Germany). P < .05 was considered significant for all analyses. After testing for normality using a Kolmogorov-Smirnov test, hospitalization FIGURE 4 Intraoperative view (12-fold magnification) of a times were displayed as median and range and compared ’ completed individualized mini-hemilaminectomy-corpectomy, using a Mann-Whitney U test. Fisher s exact test was used to with the nerve hook (NH) passing gently under the freed nerve evaluate the influences of prognostic factors on the short- root (N) and spinal cord (SC). ST, suction tip; P, pedicle; CE, term, mid-term, and long-term outcomes, and odds ratios partial lateral corpectomy (OR) were calculated. The following prognostic factors were evaluated: signalment (breed, age, sex, and weight); rate of onset, duration of clinical signs, neurological grade at initial Hemorrhage from cancellous bone was controlled with bone presentation, number of affected disc spaces, and lateralized wax (B. Braun Surgical, S.A., Barcelona, Spain), hemor- or central position of herniation. Spearman’s rank correlation rhage from the venous sinuses was controlled by bipolar coefficient rho was calculated for comparison of neurological coagulation (Erbotom T400C, Erbe, Tuebingen, Germany) grade at initial clinical presentation and follow-up examina- and gelatin sponges (Gelita Tampon, B. Braun, Aesculap, tions. A Friedman test followed by post hoc tests according Germany). to Bonferroni-Holm was used to test for differences between Postoperatively dogs were restricted to leash-walks for 6 the time points throughout the observation period. weeks. A formal rehabilitation program was not performed. Complications requiring a second surgery were considered to 3 | RESULTS be major. If no second surgery was necessary complications were considered to be minor. During the study period, 57 dogs met the inclusion criteria. Breeds were German Shepherd (21 dogs), mixed-breed (14), 2.2 | Follow-up Labrador Retrievers (8), Golden Retrievers, Boxers, Dalma- tians, and Canadian Shepherds (2 each), and Great Muenster- Immediate short-term follow-up was performed during the laender, Bobtail, Wachtel, Magyar Vizsla, Border Collie, and first 24 hours after surgery to assess the impact of surgery on Siberian Husky (1 each). A total of 28 dogs were male and neurological status. One week after surgery, a second neuro- 29 were female. The mean weight was 33 kg (range 18-45), logical evaluation was performed to complete the short-term and the mean age was 9 years (range 3-14). follow-up. Neurological status was graded (Table 1). Dogs The onset of clinical signs was peracute in 12 dogs, acute were discharged from the hospital when they were ambula- in 13 dogs, and chronic in 38 dogs. Of the chronic cases, 17 tory without assistance and had urinary control. Hospitaliza- dogs had a history of neurological dysfunction of <6 tion time was recorded. Mid-term follow-up was conducted months, 13 dogs had clinical signs persisting for >6 months, 6 months after surgery by neurological examination at our and 8 dogs had signs for >1 year. Of all chronic cases, 14 clinic or contact with the referring veterinarian. Long-term dogs had a chronic history with acute deterioration. A total follow-up was performed on completion of the study using of 33 dogs were ambulatory, and 30 dogs were non- owner questionnaires (Table S1). Additionally, a separate ambulatory (Table 1). lifelong follow-up was evaluated for the 24 dogs that had died by the end of the study. Mid-term and long-term out- 3.1 | Diagnosis and surgery comes were rated as excellent if no residual pain or neurological deficits were present, as good if only minimal A diagnosis of disc herniation and identification of the site neurological deficits were present (grade 2a), as fair if no or and extent of spinal cord compression were achieved by CT insufficient improvement (grade 2b or worse) was observed, alone in 19 dogs, by myelography alone in 3 dogs, and by a and as poor if the dog’s condition worsened. Excellent and combination of myelography and CT in 41 dogs. A total of MEDL ET AL. | 427

18 months apart). Therefore, each had 2 short-term and 2 mid-term follow-up evaluations. Two dogs with several affected disc spaces underwent 3 iMHC procedures in 2 separate surgical sessions 4 weeks and 5 months apart. One dog received a repeat operation 4 weeks after the first surgery due to recurrence at a different disc space. All but one of the operated disc herniations were extrusions or combinations of extrusions and protrusions.29 In 1 dog that was operated on 3 affected disc spaces simultane- ously, 1 pure protrusion was found. Intraoperative hemorrhage from the venous sinus (Figure 6) was encountered FIGURE 5 Locations of disease in 57 dogs that underwent frequently, but it typically resolved after decompression and, individualized mini-hemilaminectomy-corpectomy at 79 disc due to good visualization, could be controlled using bipolar ff spaces. T13/L1 was the most frequently a ected disc space coagulation and/or gelatin sponges (Gelita Tampon, B. Braun). During 1 iMHC procedure, the ventral spinal nerve 64% of herniations were centrally positioned and 36% were root was injured (1.3%). Seroma formation was the only lateralized (53.6% right and 46.4% left). The thoracolumbar minor postoperative complication in 5 dogs (7.9%) and transition (T13/L1) was the most frequently affected site resolved without intervention. No major postoperative com- (Figure 5). In 28 dogs, 1 disc space was affected and in 29 plications occurred. dogs >1affected disc space (median, 2; range 2-6). Of the 57 dogs, 13 underwent 2 iMHC procedures during 3.2 | Short-term results and time to discharge 1 surgery and 2 dogs underwent 3 iMHC procedures simulta- neously. Six dogs underwent 2 surgeries (3 with operations A total of 63 surgeries in 57 dogs (6 dogs underwent 2 sur- on different disc spaces on 2 occasions spaced 11, 13, and geries) were available for evaluation of the short-term results. At the first postoperative evaluation performed within 24 hours after surgery, the neurological grade was unchanged in 22 dogs (34.9%) and was improved in 38 dogs (60.3%). A total of 24 dogs improved by 1 neurological grade, 12 dogs improved by 2 grades, and 2 dogs improved by 3 grades. Three dogs (4.8%) showed mild transient worsening that resolved 2-5 days after surgery. At the second follow-up 7 days after surgery, 54 dogs (85.7%) showed improvement and 9 dogs (14.3%) remained unchanged compared to their status before surgery. Of the 30 dogs that were non- ambulatory before surgery, 24 (80%) regained ambulation within the first 7 days and 6 dogs regained ambulation within 2 weeks. Short-term outcomes were not influenced by breed, age, weight, sex, lateralized or central position of herniation, neurological score before surgery, or onset of clinical signs. Median hospitalization time for all dogs was 2 days (range 0-14). Median hospitalization time was significantly shorter in ambulatory (1 day; range 0-5) than in non- ambulatory dogs (3 days; range 0-14; P 5 .008) as well as in dogs with chronic onset (1 day; range 0-5) compared with acute onset (3 days; range 0-14; P 5 .005). Seven dogs were hospitalized for >1 week (median, 10 days; range 8-14), all of which were non-ambulatory and had experienced an acute onset or worsening of clinical signs. FIGURE 6 Dorsal T1 weighted magnetic resonance image (3D SST1 dor) of the spinal canal of a German Shepard show- 3.3 | Mid-term and long-term results ing the congested venous sinuses (VS) in the region of the disc herniation (D) between the first (L1) and second (L2) lumbar Mid-term and long-term outcomes could be evaluated in 50 vertebra 1. SC, spinal cord dogs, 3 of which underwent surgery 2 times. Two dogs were 428 | MEDL ET AL. lost to follow-up and 4 died or were euthanatized due to unrelated disease (lymphoma, renal neoplasia, non- regenerative anemia, gastrointestinal disease). In addition, 1 dog was excluded due to poor owner compliance because restriction of the dog was not possible. The mid-term outcome was rated as successful in 90.6% of dogs (48/53), being excellent in 19 dogs (35.8%), good in 29 dogs (54.7%), and fair in 2 dogs (3.8%). The outcome was rated as poor in 3 dogs (5.7%) that had an early recurrence with peracute onset at 4, 6, and 8 weeks after surgery. All 3 dogs were presented and euthanatized elsewhere without any further diagnostic work-up. Long-term follow-up was conducted at the end of the 6 study. The mean observation period for all dogs (n 5 50) FIGURE 7 Mean neurological grades ( SD) at consecutive was 29.4 months (range 6-66). Additionally, a separate life- time points in dogs undergoing individualized mini- long follow-up was evaluated for the 24 dogs that had died hemilaminectomy-corpectomy. The preoperative neurological by the end of the study. Their mean age at death was 13.4 grade was correlated with the postoperative grade. This correla- years (range 10-17) with a mean observation period of 31 tion was gradually lost between week 1 and the 6-month fi months (range 6-64). The proportion of excellent to good follow-up. The average score improved signi cantly between 5 results did not change during the observation period. No dif- follow-ups, independent of the initial score (P .002) ference in outcome was found among the mid-term, long- term, and lifelong follow-up periods. The only factor that surgery. Two dogs were euthanatized elsewhere without fur- significantly influenced mid-term and long-term results was ther diagnostic work-up. the number of affected disc spaces (Figure 4). Dogs with only 1 affected site had a significantly higher likelihood of a successful outcome (OR511.0; P 5 .03) and excellent 3.5 | Owner questionnaire results (OR510.4; P < .001). All dogs with 1 affected site A total of 54 owners (95%) returned the owner questionnaire. had a successful outcome (excellent in 62.5% [15/24] and Whether the dog had an excellent or good result did not have good in 37.5% [9/24]). Of the dogs with >1 disc herniation a significant effect on owner satisfaction (P 5 .072). Quality > or 1 surgery, 82.8% had a successful outcome (excellent in of life was judged as excellent in 77.6% of the dogs, good in 13.8% [4/29] and good in 69.0% [20/29]). The 7 dogs with 18.3%, and fair in 4.1%. The mean (6SD) rating for overall > ff 1a ected site that had not improved by 1 week after sur- outcome was 1.56 (60.58) in dogs with a follow-up of >6 fi gery had a signi cantly lower chance of a successful long- months and 1.85 (60.91) for all dogs, using a scale from 1 5 5 fi term outcome (OR 11.0; P .034). This nding was not to 5. The overall outcome was rated as significantly worse ff observed in dogs with only 1 a ected disc. Breed, age, for dogs with a follow-up period of <6 months (OR 5 94.0; weight, sex, onset, lateralized or central position of the her- relative risk 5 19.6; P < .001), even if the short-term out- niation, neurological score before surgery, or a longstanding come was good and death was not related to disc disease. > ff chronic history 6 months did not a ect the long-term A total of 95% of owners stated that they would opt for outcome. Postoperative neurological grade was correlated the same surgery again and would also choose another sur- fi 5 signi cantly with the preoperative grade (rho 0.714; gery if their dog suffered a new episode. The number of < P .001), but this correlation was lost in the follow-up at 7 affected discs, neurological grade, onset, and number of sur- days to mid-term follow-up at 6 months. Mean neurological geries had no influence on owner satisfaction. grade improved significantly between consecutive follow-up visits, independent of the initial grade (Figure 7; P 5 .002). 4 | DISCUSSION | 3.4 Recurrence The iMHC procedure proved useful for decompression of The overall recurrence rate of disc disease was 14.0% (7/50). the spinal cord in IVDD in large breed dogs, with minimal Five dogs were reimaged at our clinic, and none experienced postoperative deterioration and a short hospitalization time. recurrence at the operated disc space. Four dogs underwent In 90.6% of dogs a successful long-term outcome was an iMHC procedure a second time, 3 recovered with good achieved and the owner satisfaction rate was high. Dogs with long-term outcome, one did not recover from grade 4 and only 1 affected disc space had a significantly better long- was euthanatized. The owners of 1 dog declined a second term result (100% successful and 62.5% excellent). However, MEDL ET AL. | 429 dogs that had more affected disc spaces or received 2 opera- portion of the tuberculum costae is sufficient. The removal or tions still had an 82.8% probability of a successful outcome, luxation of a rib head, which is an important stabilizing factor with 13.8% having excellent results. for the thoracic vertebral column,35 is not necessary. Hemor- Standard surgical decompression techniques, such as DL rhage from the vertebral venous sinus was frequently encoun- and HL, have been reported to be incapable of adequately tered but had a tendency to decrease or stop by itself after decompressing the spinal cord in disc herniations in large decompression. Congestion of the venous sinus caused by the breed dogs, which are primarily centrally located. Difficulties compression due to disc herniation can be seen on MRI (Fig- with these techniques include limited access to the ventral ure 6) and may explain this effect. Venous sinus bleeding aspect of the spinal canal and a wrapping effect of the spinal appeared to be less severe and more easily controlled during cord over the herniated material.2,3,19 Mini-hemilaminectomy the iMHC approach than hemorrhage that occurs when the has been reported to allow superior access to the ventral sinus is lacerated by drilling from the ventral direction, as aspect of the spinal canal.2,15,17 However, a recent publica- described by Salger et al, who examined the use of TLLC tion comparing the slots created by HL and MH reported alone.32 Aiming for complete removal of the dorsal longitudi- that even in MH, a small ventral rim of the pedicle nal ligament, intraoperative complications during the late dril- remains,30 hindering visualization of centrally located hernia- ling phase were described, including pneumothorax in 33% of tions and the removal of hard lateralized, and more so cen- cases, hemorrhage from the vertebral venous sinus in 25% of tral, herniations. Pure PLC provides a ventrolateral approach, cases, injury to the spinal nerve in 8.3%-12% of cases, and but due to restricted visualization, is associated with consid- dural laceration in 5% of disc spaces.31,32 erable intraoperative complications.31,32 The recurrence rate in our study was 14.0%, which is In our cases, the combination of MH and PLC provided similar to those reported in previous studies of decompres- a number of advantages. The true ventrolateral approach sive spinal surgery in large breed dogs (11% and 12%).8,10 In allowed for disc removal with no or only minimal spinal each of the 5 dogs that could be reimaged, recurrence cord manipulation and the created bone window facilitated occurred at a different disc space. visual control of surgical manipulation, evaluation of the The impact of surgery on spinal cord function is reflected extent of the herniation, and assessment of decompression. by the favorable short-term outcome. Within the first 24 The size of the PLC could be kept as restrictive as possible hours after surgery, 60.3% of dogs were improved. Median according to the needs of each case and the height of the hospitalization time, corresponding to the time to ambula- MH slot could be kept very restricted to minimize post- tion, was 2 days and was significantly shorter (1 day) for laminectomy membrane formation.14 Post-laminectomy dogs with a chronic history of clinical signs and for those membrane formation in human medicine is recognized as a that were ambulatory at initial presentation. Recovery times major cause of “failed back surgery syndrome.”33 As no for non-ambulatory dogs (median 3 days) were distinctly technique currently has been proven to prevent scar forma- shorter than those that have been reported for comparable tion, the best strategy seems to be the minimization of the non-chondrodystrophic (up to 7 weeks) and chondrody- bone window size.14,33 Magnification using a microscope strophic (11-28 days) dogs after HL.10,11,36-38 was indispensable, as was the ability to tilt the table (and The results presented here are nearly identical to those therefore the dog) to an optimal viewing angle. An interest- reported by Moissonnier in the first study describing the use ing observation was that chronic extrusions were occasion- of PLC alone or in combination with different laminectomy ally organized and covered by a membrane and could procedures.19 In contrast, Salger et al, employing TLLC initially be mistaken as protrusions (Video Clip S2). In our using extended slot dimensions in combination with com- dogs, 98.7% of herniations were extrusions, or so-called plete removal of the dorsal longitudinal ligament, observed Hansen Type I or mixed Hansen Type I/Hansen Type II her- postoperative worsening in 18.7% of surgeries.32 The combi- niations.18,29,34 This finding is in accordance with observa- nation of anesthesia, myelography, and the surgical tech- tions reported in a previous study.10 We agree with the nique was thought to be responsible for this worsening. In hypothesis that many dogs with type 2 disc protrusions may their study, non-ambulatory dogs were significantly more remain largely subclinical until decompensation of the annu- likely to exhibit post-surgical improvement (44% improved, lus fibrosus occurs and one of these protrusions proceeds to 55.6% unchanged) than ambulatory dogs (67.6% unchanged, extrusion. The chronic histories with acute deterioration 32.4% deteriorated).32 They also found a tendency for chron- observed in 22% of our cases support this theory. icity to negatively influence outcomes. The intraoperative complication rate associated with the In our study, dogs with an acute onset of paraplegia and iMHC procedure was low. The spinal nerve root was clearly several affected disc spaces had a significantly lower proba- visible and was less prone to injury (1.3%) than reported for bility of a successful long-term result if they were not ambu- pure TLLC.31,32 In the thoracic area, the drilling of a small latory 1 week after surgery. Although the number of these 430 | MEDL ET AL. cases (n 5 7) was small, this finding is significant and is in concerning comorbidities were not more stringent. However, agreement with the findings of an earlier study, in these cases provided insights for the improved management which postoperative voluntary motor function was found of complex cases in the future. For example, 2 dogs were to be a favorable prognostic indicator of early return to affected with 5 disc herniations each. After decompression of ambulation.37 the 2 most compressing herniations, neither dog sufficiently For an individual dog the lifelong follow-up is important. improved, and they both underwent further diagnostics and a When the results of the mid-term follow-up were compared second decompressive surgery at an additional disc space. to those of the long-term follow-up and the lifelong follow- One dog achieved a good result and the other had an excel- up, the neurological conditions of the dogs remained stable. lent result. This may lead to the assumption that every com- Consequently, we assume that the outcome at 6 months can pressing disc space should be addressed, preferably in a be accepted as representative of the outcome throughout the single surgery. With the increasing confidence in our ability remainder of a dog’s life. to achieve favorable short-term results, we now re-examine Comparison of our results with those of published studies dogs early for recurrence or insufficient decompression if was hindered by the heterogeneity of the grading systems, they do not improve as expected. This practice is in agree- outcome measures, and follow-up times. Similar to the short- ment with the results of a recent publication reporting that term results, the long-term results are most comparable to delayed postsurgical recovery or deterioration after HL in those reported by Moissonnier in the first study concerning chondrodystrophic dogs is commonly associated with newly PLC.19 The results published in later studies on lateral cor- developed and/or remaining compressive disc material.48 For pectomy performed alone on non-chondrodystrophic dogs dogs with severe bilateral gonarthrosis, a more cautious were not as satisfying,22,32,39 with successful outcomes in prognosis should likely be provided and additional support- 69.2%-76% of cases.22,32 ive physical therapy might be beneficial. Earlier publications reported the effects of facetectomy, Owners currently appear increasingly reluctant to accept pediculectomy, foraminotomy, discectomy, disc fenestration, long, painful recovery periods for their pets. Therefore, in and the influences of muscle forces.12,40-45 Considering the our practice, mildly affected grade 2 and recidivating grade 1 destabilizing effect of discectomy and the importance of dogs increasingly undergo surgery. Still, surgery is an inva- muscle forces, we opted to perform a highly restrictive cor- sive procedure that should not deteriorate the condition of an pectomy and minimal muscle dissection. We did not find animal. For the surgical management of disc disease, 3 main any clinical indications of instability, which is in agreement objectives have been defined: (1) removal of prolapsed disk with the results of 2 recently published studies reporting bio- material and adequate spinal cord decompression; (2) pre- mechanical changes in vitro after PLC alone or in combina- vention of iatrogenic spinal cord injury; and (3) use of effi- tion with MH or HL.46,47 cient prophylactic disc fenestration.2 In our study, iMHC Although the short-term and long-term results observed fulfilled these requirements. To further investigate the effi- in our study were quite favorable, some dogs still had a poor cacy of the iMHC procedure, ideally a prospective study or fair outcome and should be considered specifically. After comparing iMHC to the more conventional approaches like initial improvement, 3 dogs experienced an early recurrence HL should be performed. Decompression of the spinal cord with peracute onset of paraplegia at a few weeks post- with minimal postoperative deterioration, a short hospitaliza- operation, leading to euthanasia. Unfortunately, there was tion time, and a successful outcome rate of 90.6% were likely no way to avoid this outcome although one could obtained using the iMHC procedure. hypothesize that aggressive fenestration of adjacent discs might have prevented recurrence. Both dogs with fair mid- ACKNOWLEDGMENT term and long-term follow-up results as well as the 3 cases We thank Prof. K. Matiasek from the University of Munich that displayed mild transient deterioration immediately after for his help and advice. surgery suffered from distinct spinal or orthopedic comorbidities (4 of them had severe bilateral gonarthrosis). Theoreti- CONFLICT OF INTEREST cally, if orthopedic or spinal comorbidity had been an fl exclusion criterion in our study, then the rate of successful The authors declare no con icts of interest related to this outcomes would have been 94.1% for all dogs and 88.9% for report. those with more than 1 affected disc space. Furthermore, none of the dogs would have shown postoperative deteriora- REFERENCES tion. We intentionally decided not to exclude these dogs [1] Hoerlein BF. Intervertebral disks. In: Hoerlein BF, ed. because we are confronted with them in the clinical setting. Canine Neurology Diagnosis and Treatment. 3rd ed. It may be a drawback of this study that our exclusion criteria Philadelphia, PA: Saunders; 1978:470-560. MEDL ET AL. | 431

[2] Braund KG, Taylor TK, Ghosh P, et al. Lateral spinal [16] Black AP. Lateral spinal decompression in the dog: a decompression in the dog. J Small Anim Pract. 1976;17: review of 39 cases. J Small Anim Pract. 1988;29: 583-592. 581-588. [3] Macias C. Type II thoracolumbar disc disease. What [17] Jeffery ND. Treatment of acute and chronic thoracolum- should we do? In: Proceedings of the 14th ESVOT Con- bar disc disease by mini hemilaminectomy. J Small Anim gress, Munich, Germany, 2008:138-139. Pract. 1988;29:611-616. [4] McKee WM. A comparison of hemilaminectomy (with [18] Bray JP, Burbidge HM. The canine intervertebral disk. concomitant disc fenestration) and dorsal laminectomy Part two: degenerative changes—nonchondrodystrophoid for the treatment of thoracolumbar disc protrusion in versus chondrodystrophoid disks. J Am Anim Hosp dogs. Vet Rec. 1992;130:296-300. Assoc. 1998;34:135-144. [5] Muir P, Johnson KA, Manley PA, et al. Comparison of [19] Moissonnier P, Meheust P, Carozzo C. Thoracolumbar hemilaminectomy and dorsal laminectomy for thoraco- lateral corpectomy for treatment of chronic disk hernia- lumbari ntervertebral disc extrusion in dachshunds. tion: technique description and use in 15 dogs. Vet Surg. J Small Anim Pract. 1995;36:360-367. 2004;33:620-628. [6] Aikawa T, Fujita H, Takahashi T, et al. Assessment of [20] Whittle IR, Johnston IH, Besser M. Recording of spinal post-operative recovery, time to ambulation and urinary somatosensory evoked potentials for intraoperative spinal and faecal incontinence in 831 dogs with thoracolumbar cord monitoring. J Neurosurg. 1986;64:601-612. intervertebral disc disease. Vet Surg. 2012;41:E2. [21] Kitagawa H, Itoh T, Takano H, et al. Motor evoked potential monitoring during upper cervical spine surgery. [7] Aikawa T, Fujita H, Kanazono S, et al. Long-term neuro- Spine. 1989;14:1078-1083. logic outcome of hemilaminectomy and disk fenestration for treatment of dogs with thoracolumbar intervertebral [22] Moissonnier P, Carozzo C, Forterre F. Vertebral lateral disk herniation: 831 cases (2000-2007). J Am Vet Med corpectomy in the Dog. In: Proceedings of the 17th fi Assoc. 2012;241:1617-1626. Annual Scienti c Meeting of European College of Vet- erinary Surgeons, Basel, Switzerland, 2008:535-538. [8] Macias C, McKee WM, May C, et al. Thoracolumbar disc disease in large dogs: a study of 99 cases. J Small [23] Coates JR. Intervertebral disk disease. Vet Clin North Am Anim Pract. 2002;43:439-446. Small Anim Pract. 2000;30:77-110. [24] Griffiths IR. Spinal disease in the dog. In Pract. 1982;4: [9] LeCouteur RA, Grandy JL. Diseases of the spinal cord. 44-52. In: Ettinger S, Feldman E, eds. Textbook of Veterinary Internal Medicine. 7th ed. Philadelphia, PA: Saunders; [25] Scott HW. Hemilaminectomy for the treatment of thora- 2000:608-657. columbar disc disease in the dog: a follow-up study of 40 cases. J Small Anim Pract. 1997;38:488-494. [10] Cudia SP, Duval JM. Thoracolumbar intervertebral disk disease in large, nonchondrodystrophic dogs: a retrospec- [26] Roach WJ, Thomas M, Weh JM, et al. Residual herni- tive study. J Am Anim Hosp Assoc. 1997;33:456-460. ated disc material following hemilaminectomy in chondrodystrophic dogs with thoracolumbar intervertebral [11] Downes CJ, Gemmill TJ, Gibbons SE, et al. Hemilami- disc disease. Vet Comp Orthop Traumatol. 2012;25:109- nectomy and vertebral stabilisation for the treatment of 115. thoracolumbar disc protrusion in 28 dogs. J Small Anim [27] Aikawa T, Fujita H, Shibata M, et al. Recurrent thoraco- Pract. 2009;50:525-535. lumbar intervertebral disc extrusion after hemilaminec- [12] Hill TP, Lubbe AM, Guthrie AJ. Lumbar spine stability tomy and concomitant prophylactic fenestration in 662 following hemilaminectomy, pediculectomy, and fenes- chondrodystrophic dogs. Vet Surg. 2012;41:381-390. tration. Vet Comp Orthop Traumatol. 2000;13:165-171. [28] Johnson KA. The vertebral column. In: Johnson KA, ed. [13] Sharp NJ, Wheeler SJ. Thoracolumbar disc disease. In: Piermattei’s Atlas of surgical approaches to the bones Sharp NJ, Wheeler SJ, eds. Small Animals Spinal Disor- and joints of the dog and cat. 5th ed. St. Louis, MO: ders. 2nd ed. Philadelphia, PA: Elsevier Mosby; 2005: Saunders; 2004:47-115. 121-159. [29] Fardon DF, Williams AL, Dohring EJ, et al. Lumbar disc [14] Thomas WB, Fingeroth JM. What should cover the bone nomenclature: version 2.0: recommendations of the com- defect after laminectomy/hemilaminectomy? In: Fingeroth bined task forces of the North American Spine Society, JM, Thomas WB, eds. Intervertebral Disc Disease in the American Society of Spine Radiology and the Ameri- Dogs and Cats. Ames, IA: Wiley Blackwell; 2015:255- can Society of Neuroradiology. Spine J. 2014;14:2525- 258. 2545. [15] Bitetto WV, Thacher CA. A modified lateral decompres- [30] Huska JL, Gaitero L, Brisson BA, et al. Comparison of sion technique for treatment of canine intervertebral disk the access window created by hemilaminectomy and disease. J Am Anim Hosp Assoc. 1987;23:409-413. mini-hemilaminectomy in the thoracolumbar vertebral 432 | MEDL ET AL.

canal using computed tomography. Can Vet J. 2014;55: [42] Wilke HJ, Claes L, Schmitt H, et al. A universal spine 449-455. tester for in vitro experiments with muscle force simula- [31] Flegel T. Partial lateral corpectomy versus hemilaminec- tion. Eur Spine J. 1994;3:91-97. tomy in thoracolumbar intervertebral disc disease. In: [43] Thevenon A, Delcambre B. Movements of the lumbar Proceedings of the 17th ESVOT Congress, Venice, Italy, spine. A biomechanical study. Rev Rhum Mal Osteoartic. 2014:152-153. 1988;55:367-373. [32] Salger F, Ziegler L, Bottcher€ IC, et al. Neurologic outcome after thoracolumbar partial lateral corpectomy for [44] Schulz KS, Waldron DR, Grant JW, et al. Biomechanics intervertebral disc disease in 72 dogs. Vet Surg. 2014;43: of the thoracolumbar vertebral column of dogs during lat- 581-588. eral bending. Am J Vet Res. 1996;57:1228-1232. [33] Thome C, Zevgaridis D, Leheta O, et al. Outcome after less-invasive decompression of lumbar spinal stenosis: a [45] Shires PK, Waldron DR, Hedlund CS, et al. A biome- randomized comparison of unilateral laminotomy, bilat- chanical study of rotational instability in unaltered and eral laminotomy, and laminectomy. J Neurosurg Spine. surgically altered canine thoracolumbar vertebral motion 2005;3:129-141. units. Prog Vet Neurol. 1991;2:6-14. [34] Hansen HJ. A Pathologic-anatomical study on disc [46] Reves NV, Burki€ A, Ferguson S, et al. Influence of par- degeneration in dogs. Acta Orthop Scand Suppl. 1952; tial lateral corpectomy with and without hemilaminec- 11:1-117. tomy on canine thoracolumbar stability: a biomechanical [35] Takeuchi T, Abumi K, Shono Y, et al. Biomechanical study. Vet Surg. 2012;41:228-234. role of the intervertebral disc and costovertebral joint in stability of the thoracic spine. A canine model study. [47] de Vicente F, Bernard F, FitzPatrick D, et al. In vitro Spine. 1999;24:1414-1420. radiographic characteristics and biomechanical properties [36] Davis GJ, Brown DC. Prognostic indicators for time to of the canine lumbar vertebral motion unit after lateral ambulation after surgical decompression in nonambula- corpectomy, mini-hemilaminectomy and hemilaminec- tory dogs with acute thoracolumbar disk extrusions: 112 tomy. Vet Comp Orthop Traumatol. 2013;26:19-26. cases. Vet Surg. 2002;31:513-518. [48] Forterre F, Gorgas D, Dickomeit M, et al. Incidence of [37] Ferreira AJA, Correia JHD, Jaggy A. Thoracolumbar disc spinal compressive lesions in chondrodystrophic dogs fl disease in 71 paraplegic dogs: in uence of rate of onset with abnormal recovery after hemilaminectomy for treat- and duration of clinical signs on treatment results. ment of thoracolumbar disc disease: a prospective mag- J Small Anim Pract. 2002;43:158-163. netic resonance imaging study. Vet Surg. 2010;39: [38] Ruddle TL, Allen DA, Schertel ER, et al. Outcome and 165-172. prognostic factors in non-ambulatory Hansen Type I intervertebral disc extrusions: 308 cases. Vet Comp Orthop Traumatol. 2006;19:29-34. SUPPORTING INFORMATION [39] Filleur A, Moissonnier P, Cachon T, et al. Benefits of Additional Supporting Information may be found in the online thoracolumbar lateral corpectomy for chronic interverte- version of this article. bral disc disease in dogs: results of a 14 year retrospec- tive study OF 107 dogs in two veterinary teaching hospitals. Vet Surg. 2012;41:E9. [40] Panjabi MM. The stabilizing system of the spine. Part I. How to cite this article: Medl SC, Reese S, and Medl Function, dysfunction, adaptation, and enhancement. NS. Individualized mini-hemilaminectomy-corpectomy J Spinal Disord. 1992;5:383-389. (iMHC) for treatment of thoracolumbar intervertebral [41] Panjabi MM. The stabilizing system of the spine. Part II. disc herniation in large breed dogs. Veterinary Surgery. Neutral zone and instability hypothesis. J Spinal Disord. 2017;46:422-432. doi:10.1111/vsu.12616 1992;5:390-396.