Just like us, dogs have flexible spines and this flexibility comes from the presence of discs and joints between the back bones (vertebrae). These discs are called intervertebral discs and they are amazing structures made up of layers of fibrous sheets running from back bone to back bone and blob of gelatinous material sitting just off centre. Above the discs is the spinal cord housed within a bony tube called the spinal canal.
Thoracolumbar Disc Disease is premature degeneration of the centre of the disc affecting the discs in the middle of the back at the junction between the ribs and the lumbar spine. The premature degeneration results from a genetic abnormality that is associated with shortening of the limbs and thus is seen mainly in breeds with short, angulated limbs such as Dachshunds, Lhasa Apso and so forth. The premature degeneration leads to extra stresses through the fibrous rings which then tear allowing the degenerate material to move towards the spinal cord.
The signs of Thoracolumbar Disc Disease vary from back pain (which can be chronic and low grade or acute and severe) all the way to causing hindlimb paralysis, where the patient cannot stand or move the limbs. In severe cases patients may not be able to feel their legs at all and some dogs can be incontinent. We use the severity to grade the degree of damage to the spinal cord. This grading system helps in assessing the most appropriate form of management and also the likelihood of recovery.
|Grade 1||Back Pain|
|Grade 2||Back Pain and Hindlimb Weakness|
|Grade 3||Back Pain and Hindlimb Incoordination possibly severe enough to prevent the patient being able to stand.|
|Grade 4||Back Pain, Hindlimb Paralysis (with feeling in the hindlimbs) and Urinary Incontinence.|
|Grade 5||Back Pain, Hindlimb Paralysis (with no feeling in the hindlimbs) and Urinary Incontinence.|
Some patients will have intermittent low grade back pain for a while and may never progress beyond this. Others unfortunately may show no obvious signs at all until they develop neurological signs such as weakness or paralysis with or without incontinence.
These signs result from the push or extrusion of the degenerate centre (nucleus) of the disc into the spinal canal. The severity of the signs relates to the volume and the speed of the material’s entry into the spinal canal. In particular the speed is more important as this influences the energy delivered by its impact on the spinal cord and it is this energy that damages the cord itself. The impact then sets in play a series of chemical events in the cord that continue to cause damage to the cord even after the event. The effect of the impact of the material and the subsequent chemical injury mechanisms in grades 2 and above, is to damage the White Matter of the spinal cord in a way that slows the two way flow of information between the brain and the back legs. This can be likened to the brain and the back legs trying to have a telephone conversation on a poor mobile network. Just as in that case, you may be able to have a meaningful dialogue with difficulty (grade 2 and some grade 3), if the signal quality reduces further, communication may become completely impossible. This would be like a grade 5 injury.
Most patients in the first 4 grades will make a good to excellent recovery from this injury with appropriate management. This recovery however will in many cases take 2-4 months and both outcome and rate of recovery may be influenced by post injury management. In particular it can be extremely beneficial to have qualified physiotherapy support especially in the first month of recovery. Another factor that will influence outcome is the form of management used to deal with the initial injury. It is possible (and still reasonably common) to use non surgical management for patients with spinal cord injuries. Usually there are specific reasons for avoiding surgery such as other health issues, cost, behaviour and so forth. In general however, surgical patients tend to have a smoother and more predictable recovery from injury than non surgically managed cases. The percentage of patients making good to excellent recovery is certainly higher when surgery is used at the outset.
Grade 5 patients may still recover from injury, where surgery is used within the first 48 hours of onset. Unfortunately however patients in this group are always a cause for concern as the rate of recovery is lower than for patients in the lower injury groups.
Before surgery can be performed we need to establish a number of key pieces of information:
The Image above shows the appearance of spinal cord compression on a myelogram. The white lines are the contrast agent and this outlines the spinal cord. You can see where the cord is narrowed directly over the disc. This tells us which disc is compressing the spinal cord.
The two main goals of surgical management are:
We achieve this by making a small hole in the side of the spinal canal and then using a variety of small instruments, retrieving as much of the material from around the spine. The spine is cooled and the canal is flushed during this. Then we make a small window in the side of the disc and scoop out any remaining material from the centre.
The first 24 hours after surgery is all about comfort and our practice pain scoring scheme is used to make sure that this is optimal. After this period, pain management continues of course as we begin to mobilise the patient, assess ability to walk, stand and pass urine and then devise a care plan specific to each patient’s needs. This usually involves Hannah our Physiotherapist as we continually assess recovery and guide our patients towards optimal outcome. Most patients will be hospitalised for 3-7 days after surgery, again this is based on comfort and ability.
We usually try to coordinate discharge with Hannah being available to guide owners to the optimal rehab regime at home. Of course after discharge we ask our owners to keep in touch regularly with updates and most patients are reviewed by the surgeon and Physio on a regular basis.