Feline Traumatic Spinal Cord Diseases, Clinical Evaluation and How to Achieve Best Outcome
World Small Animal Veterinary Association World Congress Proceedings, 2015
D. Lu, BVetMed, MVM, DECVN, CVA
Peace Avenue Veterinary Clinic, Mongkok, Hong Kong

Following traumatic spinal cord injury (SCI), one of the main concerns from cat-owners is whether their cat can recover (i.e., a "functional pet" that can walk, able to regain urinary/fecal continence). This is a "satisfactory recovery," unfortunately in reality "suboptimal recovery" is more common, where weakness and incontinence persists. It is crucial to communicate well with the owners before any treatment commences to ensure full commitment. Proactively updating and getting the owners to involve in the treatment (e.g., performing physiotherapy) are equally important. Everyone involved should have reasonable and realistic expectation: regarding to cost, time to recovery and be well-prepared for complications during or after treatment, especially in complex cases requiring multiple surgeries.

In general, any SCI patient presented with paraplegia/tetraplegia without deep pain perception (DPP), the prognosis for functional recovery is guarded as the "spinal cord function" is completely blocked or transected at the injured site. Remember that the nociceptive pathways are most resistant to compression and ischemia, any injury capable to interrupt these pathways must be extensive and transverse. Further investigation is necessary to demonstrate the spinal cord integrity. However, a structurally intact spinal cord seen on MR/CT is not equivalent to intact function. A thorough neurological examination is fundamental to evaluate the spinal cord function and provide the client with a reasonable prognosis.

Traumatic animals in shock should be treated prior to assess spinal cord function. Assess airways, breathing, circulation, and remember that multiple organs may be involved. Life-threatening conditions such as hemothorax, tension pneumothorax, hemoabdomen, and uroabdomen should be addressed. Always assume the vertebral column is unstable, thus caution must be endeavored during manipulation or moving the patient. Once vital signs are stabilized, take survey radiographs (2 views, lateral and dorsoventral) of the entire spine, as approximately 20% of SCI patients have multiple vertebral fracture or luxations (VFLs). Overlapping of the vertebral bodies is indicative of complete spinal cord transection and the prognosis of returning of motor function is very guarded to hopeless (one exception is the development of "spinal walker"). Absence of VFLs on radiographs should not be used to definitively exclude their presence.

If the patient is unable to stand or walk, do not force it to. Observe (hands-off examination) if any voluntary movement of the tail and limbs is present. If present, the cat is a Grade 3, and at least a Grade 4 or 5 if plegia (Refer to Table 1 for the grading system the author uses, feel free to use any grading systems but be consistent).

Table 1. Grading system

Grade

Descriptions

1

Normal gait, spinal pain only.

2

Ataxic or ambulatory paresis.

3

Non-ambulatory paresis, voluntary movement observed in the limbs and tail.

4

Plegia (tetra-, hemi-, para-), no voluntary movement in the limbs (tetra = all fours; hemi = half side; para = only hindlimbs) or tail. DPP intact in the plegic limb/tail.

5

Plegia, DPP absent in the plegic limb/tail.

6

Plegia, evidence of ascending and descending myelomalacia.

Assess muscle tone by passively flexing and extending the limbs (floppy limbs = lower motor neurone sign). Following acute SCI, muscle tone can be dramatically reduced despite upper motor neurone (UMN) lesion-localization (i.e., C1–5, T3–L3 segment). Assess these reflexes: patellar, withdrawal and perineal reflexes. Other reflexes are less reliable. DPP assessment is vital; however, the response may be vague or inconsistent (especially if in shock). Use a hemostat and apply gentle pressure on the nail beds/bone, gradually increase pressure until you get a response (Note: withdrawing the limb alone does not indicate intact DPP, some form of behavioral responses from the head are necessary). All digits of the affected limb(s) should be tested, and compare with the unaffected limb. For example, assess the DPP in the hindlimbs and tail in a paraplegic cat, comparing to the forelimbs. From the neuro-exam, try to localize the lesion anatomically to the regions: C1–5, C6–T2, T3–L3, L4–S3 spinal cord segments. Remember simultaneous multiple lesions are possible and may involve more than one region (due to diffuse swelling and hemorrhage).

Following initial stabilization, evaluate the spine (vertebral column, spinal cord, nerve roots and adjacent soft tissues) under general anesthesia: Obtain survey radiography of the entire vertebral column to avoid overlooking a second (or third!) lesion. Complete VFL, or displacement of the vertebral bodies reaches 100%, overriding of vertebral bodies are indicative of spinal cord transection.

The vertebral column can be divided into 3 compartments and instability is evident if any two out of the three compartments are involved:

1.  Ventral 3/4 of the vertebral body and disc, the ventral longitudinal ligament

2.  Dorsal 1/4 of the vertebral body and disc, the dorsal longitudinal ligament

3.  Articular facets, lateral pedicles, dorsal laminae, interarcuate ligaments and spinous processes

If an initial survey spinal radiography doesn't illustrate any obvious VFL, perform flexion and extension views of the atlantoaxial and the lumbosacral joints (with care!).

Proceed to advanced diagnostic imaging using myelography, (CT-myelography) or magnetic resonance imaging (MRI).

Lumbar myelography may demonstrate: presence of dural tear (leakage of contrast media), extradural compression, and extend of spinal cord swelling. However, myelography is unable to demonstrate intra-parenchymal injury and carries risks associated with contrast administration and post-procedure seizures. CT is the imaging modality of choice for bone, and is recommended in patient with suspected unstable VFLs. MRI is superior in imaging soft tissue including the spinal cord parenchyma, intervertebral disks, and nerve roots. In my opinion, small bone fragments can be readily identified by MRI newer sequences (e.g., thin slice 3D-FIESTA, GE). From the imaging, decision can be made whether surgery is necessary; types of surgery required, and to what extent (length of hemilaminectomy necessary).

Different methods and techniques have been described to tackle VFLs and the choice is often a personal preference. Any effective technique must be able: "To decompress the spinal cord, and stabilize the vertebral column by neutralizing the forces acting on the VFL, and be applicable without iatrogenic injury to neural tissue or neighboring structures, using adequate implants to enable bone healing before implants fail."

Below is my favorite technique to repair VFL in the caudal thoracic to lumbar region: If disc prolapse is evident, perform a mini-hemilaminectomy (preserve the articular facet whenever possible) or hemilaminectomy to remove the prolapsed disc.

 Ensure good hemostasis. Use small pieces of Gelfoam (Gelfoam® absorbable gelatin compressed sponge) or Surgicel® (hemostatic agent made of an oxidized cellulose polymer-poly-anhydroglucuronic acid, Ethicon), or macerated epaxial muscle to pack the seeping venous sinus. Cover the exposed spinal cord with saline-soaked Gelfoam. Use bone wax to plug the oozing cancellous lamina.

 Use towel clamps to hold onto the spinous process, one cranial and one caudal to the VFL site. Manipulate carefully to re-align the vertebral column.

 Fixing luxated articular facets results in strong stabilization and ease for placing other implants. The author use acrylic treaded small pins. If possible, fix both facets bilaterally.

 Drill cortical screws into the vertebral bodies. Acquire estimation from pre-operative radiographs and choose the appropriate length and screw size. Ideally the screws (or threaded pins) should penetrate both cortices to provide best implant strength. This is not necessary if implants are placed on both sides of the vertebral body. In general I place 2–4 screws and spread over 2–3 vertebral bodies on each side.

 Use Gelpis to provide adequate exposure for bone cement placement.

 Fill the screw head drives with bone wax (to ease removal of implants in future as the bone wax prevents the bone cement from plugging the drive).

 Prepare bone cement, and encase all implants. Mould the cement and avoid direct placement on the hemilaminectomy site (i.e., on the spinal cord!). Excessive cement causes difficulty in closure if bilateral implants are placed. Joining cement into a U-shape (just one end) or donut-shape (both ends) provide extra strength but is more bulky.

 Irrigate using room-temperature sterile saline until the cement is cured and cooled down completely.

 Routine closure, ensuring normal tension of the fascia. Use tension-releasing incisions if necessary (one or more incisions on the fascia parallel to the vertebral column).

In summary, an accurate clinical/neurological evaluation, good communication skills, and choosing the most appropriate treatment (i.e., surgical or conservative), and good postoperative care (adequate analgesia, thick bedding, turning sides regularly to prevent decubital ulcer, emptying the bladder regularly to prevent retention cystitis, maintain good hygiene and physiotherapy) will lead to best outcome in feline traumatic SCI patients.

References

1.  Olby N. Spinal trauma. In: Platt S, Garosi L, eds. Small Animal Neurological Emergencies. London, UK: Manson Publishing/The Veterinary Press; 2012:383–398.

2.  Jeffery N.D. Vertebral fracture and luxation in small animals. Vet Clin North Am Small Anim Pract. 2010;40(5):809–828.

3.  Sharp NJH, Wheeler SJ. Trauma. In: Sharp NJH, Wheeler SJ, eds. Small Animal Spinal Disorders Diagnosis and Surgery. Edinburgh, NY: Elsevier Mosby; 2005:281–318.

4.  DiFazio J, Fletcher DJ. Updates in the management of the small animal patient with neurologic trauma. Vet Clin North Am Small Anim Pract. 2013;43(4):915–940.

  

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Diane Lu, BVetMed, MVM, DECVN, CVA
Peace Avenue Veterinary Clinic
Mongkok, Hong Kong


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