Caudal cervical spondylomyelopathy (CCSM) causing wobbler syndrome is a condition of young dogs (1 year, Great Dane, Basset Hound) or middle-aged to older animals (6–8 years, Dobermann, Rottweiler). Anatomical abnormalities include stenosis of the cranial apertura of the cervical vertebral canal, vertebral body deformation and asymmetry of the articular facets. Degenerative lesions include intervertebral disc degeneration (IVDD) and Hansen type II fibrinoid disc herniation (protrusion), ligamentous hypertrophy of the dorsal longitudinal ligament (ventral to the spinal cord) and the ligamentum flavum (dorsal to the spinal cord) and joint capsule proliferation.

Wobbler syndrome (syndrome = the clinical description of a complex of signs) is characterised by posterior paresis and ataxia, proprioceptive deficits, forelimb lameness and mild cervical pain. The neurological deficits can eventually progress to the thoracic limbs and evolve into tetraparesis and tetraparalysis. The clinical signs in the wobbler dog can typically be a mix of upper motor neuron disease (spinal cord) and lower motor neuron disease (compression of nerve roots that contribute to the plexus brachialis). CCSM is usually a progressive disease that has a slow onset but neurological deficits may also progress acutely bringing the dog down.

Cervical radiography under sedation or anaesthesia of the C4–T1 region may show spondylosis, vertebral body malformation, tapered cranial cervical apertura, end-plate sclerosis and collapsed intervertebral disc space. Also cervical instability may already be evident on the neutral views but may be evoked by stress views (flexion, extension and linear distraction and compression). The cervical instability shows the dynamic component of the disease: compression on the spinal cord worsens in extension and lessens in flexion. Myelography with stress views (Figure 1) demonstrates the effect of the dynamic compression: unstable vertebrae, ligament hypertrophy and disc protrusion contribute to a ventral and/or dorsal component in the spinal cord compression. Stress views are essential to provide the localisation, and the static or dynamic nature of the spinal cord compression. With the availability of magnetic resonance imaging (MRI) many clinicians have replaced myelography with MRI, but specifically with CCSM the dynamic component of the disease may be missed when MRI is only performed in a neutral position. Myelography followed by computed tomography (CT) (myelo-CT) and scanning in different positions may also be very informative. In the Dobermann usually one junction is involved (C5–C6, C6–C7, C7–T1) and in the Great Dane more vertebrae can be affected (C4–T1).

Since the wobbler dog is a clinical diagnosis the clinician should always be aware of the differential diagnoses. Discospondylitis (infection of the intervertebral disc usually caused by Staphylococcus) or neoplasia (e.g., lymphoma of the vertebral body) in a Dobermann may give exactly the same appearance of wobbler dog as CCSM.

Figure 1. Myelography in an 8-year-old Dobermann with caudal cervical spondylomyelopathy at C6–C7. Neutral (A), extension (B), flexion (C) views.

The Surgical Dilemma

In mild cases of wobbler syndrome medical treatment is the first strategy. Conservative treatment consists of a chest harness for life, bodyweight reduction when applicable, exercise regulation (omit exercises that worsen the ataxia from the daily pattern), physiotherapy (hydrotherapy or exercises for proprioception) and administration of non-steroidal anti-inflammatory drugs or corticosteroids. This will usually lead to some clinical improvement and may slow down the progression.

However, since the disease is progressive there may come a decision point to proceed for surgical treatment. The dilemma in surgery has several aspects. When a dynamic component has been diagnosed a surgical technique such as ventral decompression that only deals with static compression may not be sufficient. In the case of a dynamic component, in addition to decompression, the cervical region needs also to be stabilised but here we have a paradox: the cervical region is a highly flexible region and surgical techniques to stabilise the unstable cervical junction are prone to surgical failure. When spinal segments have been fixated and fused another problem arises in the so-called adjacent segment disease ('domino effect'): stabilisation of one junction may relocate the stress to the next weak link in the chain. Another dilemma is the time point in the disease process to advise surgery: in many textbooks it says that the aim of surgery is to slow down or stabilise the neurological deficits but in that view it may be the best approach to stabilise early in the disease onset.

The goals of surgical treatment are decompression, stability or both. The myelographic examination, myelo-CT or MRI findings usually determine which surgical technique is chosen as the best treatment option.

Ventral decompression ('ventral slot') is indicated in static ventral compressive spinal cord lesions but these are rare in the true wobbler dog. Ventral distraction and stabilisation is indicated in one or multiple dynamic ventral compressive spinal cord lesion(s), e.g., cervical instability, type II disc degeneration and dorsal longitudinal ligamentous hypertrophy. Linear distraction of cervical vertebral bodies results in decompression at the site of the dynamic lesion and (temporary) fixation of the vertebral bodies allows fusion to take place which is promoted by cancellous or corticocancellous bone grafts harvested from the proximal humerus. Surgical techniques that have been performed in the past include: distraction with a cylindrical cortical allograft kept in place with a plastic Lubra plate, distraction with Steinmann pins or screws and fixation with a polymethyl methacrylate (PMMA) bridge, Harrington rod distraction device, screw and washer technique (Figure 2) and the modified distraction-stabilisation technique using an interbody PMMA plug. Arthrodesis of the cervical vertebrae is promoted by packing cancellous bone around the affected cervical junction. Fusion of cervical vertebrae by the surgical techniques listed is usually by ventral spondylosis, as interbody fusion is obstructed by metal implants or PMMA plugs. The ideal spinal fusion would be direct continuous bone bridging at the level of the vertebral bodies and techniques to stimulate this are now reported or under development. Cervical locking plates and interbody titanium cages or smart devices will probably offer a better way to treat cervical instability and promote fusion than the techniques reported in earlier days. However, the paradox between a highly flexible cervical spine and rigid implants remains.

Figure 2. Myelography in an 8-year-old Dobermann with caudal cervical spondylomyelopathy at C5–C6. Before (A) and after screw and washer fixation (B).

Dorsal decompression (e.g., by continuous dorsal laminectomy) is indicated in static or dynamic dorsal compressive spinal cord lesions, e.g., osteophytes around articular facets or interarcuate (flaval) ligamentous hypertrophy.

At Utrecht University 23 dogs (21 Dobermanns and two Great Danes) were surgically treated for CCSM. The surgical procedures included Lubra plate and cortical graft (two dogs), Steinmann pins and PMMA bridge (three dogs), Harrington rod distraction device (four dogs), ventral decompression ('ventral slot', three dogs), dorsal (hemi)laminectomy (one dog) and screw and washer (10 dogs). The Lubra plate and Harrington rod techniques had a high rate of surgical implant failure and the procedures were abandoned. The ventral decompression technique resulted in neurological worsening in two of three dogs. Clinical and neurological stabilisation or improvement was seen with the Steinmann pin and PMMA technique (two of three dogs), the screw and washer technique (eight out of 10 dogs) and following dorsal laminectomy in a Great Dane. Complete surgical arthrodesis by spondylosis of the cervical vertebrae was observed with the screw and washer technique. However, with long-term follow up it was seen that the vertebral bodies collapsed on the washer and the screw tip touched the opposite cortex close to the spinal canal.