34th Annual Scientific Meeting proceedings

There is a close anatomical relationship between the pelvis and important peripheral nerve structures, more specifically the lumbosacral trunk and to a lesser degree the sciatic nerve. It is therefore possible for animals to suffer neurological injury because of pelvic trauma or iatrogenic as a complication of pelvic fracture repair.

The lumbosacral trunk is the largest portion of the lumbosacral plexus and is composed of the ventral branches of the 2 most caudal lumbar and the 2 most cranial sacral nerves. The ventral branches of the sixth and seventh lumbar nerves course over the cranioventral surface of the sacrum, just medial to the sacroiliac joint. They unite with the ventral branches of the first and second sacral nerves to form the lumbosacral trunk. The lumbosacral trunk courses caudally along the medial surface of the ilium. Peripheral nerve injury is most seen in animals with ilial fracture with craniomedial displacement of bone fragments, or from sacroiliac fracture dislocation with cranial displacement of the ilium.  

The sciatic nerve begins when the ventral branch of the second sacral nerve joins the lumbosacral trunk at the level of the greater ischiatic foramen. It starts medial to the ilium and courses caudodorsally and laterally as it exits the pelvic canal. The intrapelvic portion of the sciatic nerve is less vulnerable to direct injury compared to the lumbosacral trunk. It is less closely associated with bone and located in the caudal portion of the ilium and acetabulum. Isolated sciatic nerve injury can be associated with fractures of the acetabulum.

The prevalence of neurological injury in dogs with pelvic fractures is 2.4% to 11%. The clinical signs of animals with pelvic trauma and neurological injury are however similar and can overlap. The occurrence of neurological injury can therefore be masked and easily missed. This underlines the importance of performing an accurate neurological assessment in animals with pelvic trauma. A combination of motor, sensory, and reflex abnormalities can be seen. Special attention should therefore be given to assessment of gait, posture, muscle tone, proprioception, spinal reflexes, tail movement, and anal tone. Sciatic nerve dysfunction typically results in a decreased or absent withdrawal reflex. Peripheral nerve entrapment can be associated with severe pain. This is especially obvious after extension of the hips.

A diagnosis of peripheral nerve in jury is predominantly based on a combination of compatible clinical signs and results of a neurological examination. Basic electrodiagnostic tests might have limited value in detecting acute peripheral nerve trauma. It may take 5 to 7 days after nerve injury before abnormal electromyographic findings can be detected in the muscles. When the lumbosacral trunk has been injured, nerve conduction studies are difficult to perform because the electrode must be placed proximal to the site of the lesion. A severed nerve will further respond to electrical stimulation distal to the site of injury for about 3 days after injury.

Treatment can be surgical or medical. Nerve entrapment can often be relieved when the fracture or luxation is reduced and fixed. In most cases, adequate exposure of the lumbosacral trunk is achieved with a ventrolateral approach to the ilium. Intense physiotherapy and hydrotherapy with or without the use of orthotic devices should be considered in the post-operative phase or as an alternative to surgical intervention. An important goal of physiotherapy is prevention of potentially irreversible complications, such as joint and muscle contractures. Depending on the severity of nerve damage, recovery will be slow and might take several weeks to months. The likelihood and time to recovery will depend on the severity of the injury and distance from the nerve lesion to the muscle to be reinnervated. If no improvement is seen after 3 to 4 months, a poor prognosis should be considered. Incomplete recovery and auto-mutilation can occur.

The outcome of peripheral nerve injury is influenced by the degree of severity and the physical and functional integrity of the nerve trunk. It can be classified as follows:

• Neuropraxia: refers to interruption of nerve conduction without physical disruption of the axon. Recovery is usually spontaneous and complete and occurs within 1-5 weeks.
• Axonotmesis: refers to physical interruption of the axon, but the surrounding supportive tissues remain intact (endoneurium and myelin sheath). Recovery is possible but will be slow. It usually occurs at a rate of 1-4 mm/day.
• Neuronotmesis: refers to complete transection of the nerve trunk and supporting structures. This is the most severe type of injury and recovery is unlikely.

Although of great prognostic importance, it is clinically or electrophysiologically impossible to reliably differentiate between these 3 gradations of peripheral nerve injury. In general, the preservation of nociception in the affected region makes axonotmesis and neuronotmesis unlikely. However, loss of nociception does not rule out neuropraxia and these animals should therefore be given the time and opportunity to improve.