Sacrocaudal luxation

What it is

Sacrocaudal luxation (or fracture-luxation) is a typical feline injury in which the tail is subjected to violent traction, for example when a car wheel runs over it as the cat flees, when it is caught in a door or when someone pulls it. The joint between the sacrum and the first caudal vertebra, or between the first caudal vertebrae, separates. The bony injury itself is minor; what matters is that the traction is transmitted to the nerve roots of the cauda equina, which are stretched or torn from the spinal cord (avulsion). Depending on the severity, the following may be affected:

• Caudal nerves: paralysis and loss of sensation in the tail.
• Pudendal nerves (sacral segments): loss of tone of the external urethral sphincter and the anal sphincter, and of perineal sensation.
• Pelvic nerves (sacral parasympathetic): loss of contraction of the bladder's detrusor muscle and of rectal motility.

Who it affects

Cats of any age with outdoor access, mainly after road traffic accidents; it is also seen in dogs, though less often.

Anatomy involved

• Sacrum and caudal vertebrae: luxation or fracture at the sacrocaudal junction or between the first caudal vertebrae; a step or gap can be felt at the tail base.
• Cauda equina: in the cat the spinal cord ends further caudally than in the dog, in the sacral region, so the sacral and caudal roots are vulnerable to tail traction.
• Urinary bladder: without detrusor innervation the bladder does not contract, distends and empties only by overflow; sustained overdistension damages the muscle further.
• Rectum and anus: faecal retention or incontinence.

Clinical signs

A flaccid, insensitive tail, often hanging or dragging. Depending on the extent of the injury: urinary retention with a large bladder or incontinence with dribbling of urine, faecal incontinence or constipation, loss of the perineal reflex and anal tone, and loss of perineal sensation. The pelvic limbs usually keep normal function, which distinguishes this injury from more cranial spinal cord lesions.

Diagnosis

• Neurological examination: tail sensation and movement, perineal reflex, anal tone and perineal sensation, palpation of bladder size and ease of manual expression. The overall neurological grade at the first examination is the best guide to prognosis; preserved perineal sensation, anal tone and tail base sensation are good signs, although in the largest series they did not predict recovery of urination on their own.
• Radiographs of the pelvis and sacrocaudal region to confirm the luxation or fracture and rule out concurrent pelvic fractures.
• General evaluation of the trauma patient, including the integrity of the bladder and urethra.

Treatment

The essential step is to keep the bladder empty while the nerves recover: manual expression several times a day or a urinary catheter, to prevent the overdistension that damages the detrusor and to avoid infection. Drugs that relax the urethral sphincter (prazosin, phenoxybenzamine) and, when some function is present, drugs that stimulate bladder contraction (bethanechol) may be used. Constipation is prevented and treated. If the tail remains paralysed, becomes soiled and is injured by dragging, tail amputation is performed, usually once the course of urinary function is clear. Surgical stabilisation of the luxation is rarely needed.

The prognosis depends on the degree of nerve injury: most cats regain voluntary urination, usually within the first weeks; those showing no improvement after about a month are less likely to recover.

Key studies

• Smeak and Olmstead (1985), a retrospective study of 51 cats. 84.3% had other injuries, and 37 of the 51 had temporary or permanent urinary incontinence. The prognosis for urination was good in cats with anal tone and perineal sensation at the first examination, and cats that could not urinate normally one month after the injury did not recover during 2 to 36 months of follow-up.
• Tatton et al. (2009), a prospective study of 21 cats. All 11 cats with pain sensation at the tail base regained urinary control within 3 days; 4 of the 10 without it had still not recovered by day 30. The sample is small.
• Couper and De Decker (2020), a retrospective study of 70 cats. 55 of 61 (90%) regained voluntary urination. A higher neurological grade predicted a less likely and slower recovery, whereas anal tone, perineal sensation, tail base sensation and the degree of displacement were not associated with the urinary outcome. Cats that regained defecatory function lived longer.