Spinal nerve roots have been implicated in many types of traumatic injuries such as motor vehicle accidents, falls, and sports injury, causing damage to brachial plexus and lumbosacral plexus. They have also been involved in lower back pain, disc herniation or protrusions, sciatica, and traumatic birth delivers such as shoulder dystocia. These roots undergo tension, resulting in traumatic axonal injury (TAI), which is also one of the consequences of traumatic brain injury (TBI). Every year about 2 million cases of TBI are reported nationwide with variable neurological deficits. Thus, it is important to understand the neurophysiological response and injury thresholds of axons when subjected to tensile stress at plausible strain rates that occur during trauma.

The aim of this study was to understand and monitor neurophysiological changes of the spinal nerve root stretched at several strains ranging from low (20mm/sec) to high (800mm/sec). For the current study, L5 dorsal nerve roots were subjected to displacement rates of 20mm/sec, 200mm/sec, and 800mm/sec and neurophysiological parameters such as amplitude, area under the curve and conduction velocity of compound action potential were recorded and analyzed. Recording were taken before and until 6 hours post stretch.

It was observed that <10% strain group showed the least functional deficit followed by 10-20% and >20% strain group for all displacement speeds. It was also observed that 800mm/sec group showed the maximum functional deficit followed by 20mm/sec and then 200mm/sec. Recovery was faster at lower strains and lower strain rates than higher strains and higher strain rates. The 20mm/sec group at <10% strain showed much faster recovery than the 200mm/sec group at <10% strain. Higher strain rates and strains such as 800mm/sec group at 10-20% and >20% did not show any recovery. Partial recovery was shown for 20mm/sec group at >20%, 200mm/sec group at >20%, and 800mm/sec group at <10%.

These findings indicate that functional injury and recovery in the spinal nerve roots shows a strain and strain rate dependency.