33rd Annual Scientific Meeting proceedings

Introduction
Spinal cord injury is usually regarded as an emergency, mainly because of the notion that swift intervention will mitigate the long-term consequences. Whether this is true depends on many factors, some of which are not clearly understood at present. Having said that, when a decision has been made to pursue surgery then the ideal time to do that would be immediately – why wait unless there are compelling reasons to delay?

However, first there is a need to consider the nature of the spinal cord injury in each patient: there are clear differences between a fracture-luxation and a disc herniation – both may cause spinal cord injury but the opportunities for worsening with delay to surgery may be quite different.

Fracture-luxation
Many fracture-luxations are clearly candidates for surgery and, in such cases, there is a clear rationale for early surgery so as to prevent further trauma to the spinal cord during unconstrained movement by the patient. Nevertheless, alternative means of preventing such damage are available, such as sedation and physical restraint (e.g. attaching animals to rigid boards). One of the problems with rapid surgical treatment for fracture-luxations is that the affected animals have often suffered polytrauma, with multisystem injuries that can be life-threatening and in more urgent need of treatment than the spinal cord injury.

Disc herniation
In veterinary medicine there is much controversy regarding the timing of surgery for acute disc herniation – especially that affecting the thoracolumbar spinal cord. Cervical disc herniations are generally considered less time-sensitive, mainly because dogs present with less severe clinical signs. Dogs with very severe cervical cord injuries may often not survive for long enough to undergo surgery or be poor anesthetic candidates and so decision-making often requires a team approach so as to optimize the probability of recovery. Nevertheless, rapid surgery for cervical cord injury is often justified on humane grounds because of the severe pain these animals suffer, although this can often be managed through antisocial operating hours with opioids, ketamine etc.

The reason for controversy in thoracolumbar disc herniation is that there is a widely held belief that delay is detrimental to the long-term outcome. However, examination of published data suggests that timing of surgery for both deep pain negative and deep pain positive dogs is not associated with likelihood (and, in some instances, rapidity) of recovery. In systematic analyses, deep pain positive and deep pain negative dogs have about a 95% and 50% likelihood of recovery to walk again respectively (Langerhuus and Miles, 2017). The problem with these analyses is that they omit the critical component of what happens to a dog that is deep pain positive but transitions to being deep pain negative before the evaluation takes place. Surprisingly this aspect has rarely been examined. In a manuscript published by Martin et al (2020), the rate of dogs becoming deep pain negative at 24 hours after presenting deep pain positive was examined and found to differ between those that underwent surgery the same day or those that were operated the following day. However, comparison of outcome by whether they recovered to walk again was less statistically persuasive – there were similar outcomes between groups. Furthermore, a reanalysis of the data suggests that the conclusion of advantage of early surgery is not as clear-cut as appears at first sight. Furthermore, in a similar set of data (Lovell et al, 2022) only one dog became deep pain negative after presenting deep pain positive before surgery and in the same dataset one dog became deep pain negative after surgery after presenting deep pain positive.

A logical summary position on the data that is available is that the prognosis for recovery of walking following thoracolumbar disc herniation is (largely, if not totally) determined at the time of injury. If this is true – and there are many reasons why this might not be so – then it would suggest that timing of surgery is not critical. If this is also true (and there are many reasons why this might not be so), then the question could be asked as to whether surgery is required at all! The problem that we face with regard to thoracolumbar disc herniation surgery is that the current consensus has solidified without having a solid evidence base – there has never been a randomized trial of surgery versus conservative therapy for spinal cord injury and so we are on shaky ground when defending surgery as the primary therapy.    

Conclusions
If a dog with a spinal cord injury is determined to have a surgical lesion then it is logical to think that the surgery should be done immediately if there is any doubt as to the effects of delay on outcome. However, there are also many reasons why immediate surgery might not be beneficial overall.

First, in fracture-luxation cases especially, affected animals might not be metabolically or otherwise systemically stable. Clear examples include those with thoracic injuries (after being hit by a car etc) or those with low blood pressure or those that might develop low blood pressure after anesthetic induction (which can occur in acute disc herniations). There is a need to ensure that the animals are likely to survive anesthesia and to reduce the likelihood that anesthesia might exacerbate the injury to the spinal cord (e.g. hypotension).

Second, the availability of the necessary equipment or personnel. Not all surgical centers have availability of cross-sectional imaging 24 hours a day. In some cases, there is a need for this imaging to ensure that surgery is carried out appropriately: the correct patients selected for surgery and the correct site selected in those patients. Mistakes can easily be made without access to appropriate imaging. In similar vein, access to suitable personnel, such as those operating the imaging equipment, or those analyzing CSF, is also important. A prominent differential diagnosis for acute disc herniation, especially in some breeds (such as the dachshund) is acute onset inflammatory disease (meningoencephalomyelitis of unknown origin) and this differential diagnosis requires CSF analysis and MRI imaging.

Third, clinician tiredness requires consideration. Analysis of this issue in human medicine suggests that errors are likely to be made when clinicians are more tired. This may not affect the patient undergoing surgery overnight, but might instead affect the patient receiving poor decisions on the following day when there is less emergency-induced alertness. 

So – all things being equal, spinal surgery should be carried out as soon as possible, but there is surprisingly little evidence in support of doing emergency spinal surgery at any hour of the day and night. At our clinic for instance we have a general rule that if we can’t get an animal into the scanner by 8pm then it waits till the next day.       

References

1. Langerhuus L, Miles J (2017) Proportion recovery and times to ambulation for non-ambulatory dogs with thoracolumbar disc extrusions treated with hemilaminectomy or conservative treatment: A systematic review and meta-analysis of case-series studies.Vet J 220: 7-16. doi: 10.1016/j.tvjl.2016.12.008. 
2. Lovell S, Simon B, Boudreau EC, Mankin J, Jeffery N. (2022) Randomized clinical trial comparing outcomes after fentanyl or ketamine-dexmedetomidine analgesia in thoracolumbar spinal surgery in dogs. J Vet Intern Med 36: 1742-1751. doi: 10.1111/jvim.16514.
3. Martin S, Liebel FX, Fadda A, Lazzerini K, Harcourt-Brown T (2020) Same-day surgery may reduce the risk of losing pain perception in dogs with thoracolumbar disc extrusion. J Small Anim Pract 61: 442-448. doi: 10.1111/jsap.13147.