Study Design: To examine the innervation of the lumbar spine from patients with lower back pain, and spinal nerve roots from patients with traumatic brachial plexus injuries.
Objectives: To demonstrate the presence of nerve fibres in lumbar spine structures and spinal nerve roots, and determine whether they express the sensory neuronespecific sodium channels SNS/PN3 and NaN/SNS2.
Summary of background data: The anatomical and molecular basis of low back pain and sciatica is poorly understood. Previous studies have demonstrated sensory nerves in facet joint capsule and prolapsed intervertebral disc, but not in ligamentum flavum. The voltagegated sodium channels SNS/PN3 and NaN/SNS2 are expressed by sensory neurones which mediate pain, but their presence in the lumbar spine is unknown.
Methods: Tissue samples (ligamentum flavum n=32; facet joint capsule n=20; intervertebral disc n=15; spinal roots n=8) were immunostained with specific antibodies to protein gene product (PGP) 9.5, a pan-neuronal marker, SNS/PN3 and NaN/SNS2.
Results: PGP 9.5-immunoreactive nerve fibres were detected in 72% of ligamentum flavum and 70% of facet joint capsule but only 20% of intervertebral disc specimens. SNS/PN3-and NaN/SNS2-positive fibres were detected in 28% and 3% of ligamentum flavum and 25% and 15% of facet joint capsule specimens respectively. Numerous SNS/PN3 and NaN/SNS2-positive fibres were found in the acutely injured spinal roots, and some were still present in dorsal roots in the chronic state.
Conclusions: SNS/PN3 and NaN/SNS2-immunoreactivity is present in a subset of nerve fibres in lumbar spine structures, including ligamentum flavum and injured spinal roots. This is the first time that sensory nerve fibres have been demonstrated in the ligamentum flavum, and this raises the possibility that, contrary to the conclusions of previous studies, this unique ligament may be capable of nociception. Selective SNS/PN3 and NaN/ SNS2 blocking agents may provide new effective therapy for back pain and sciatica, with fewer side effects. Other novel ion channels are being studied in these tissues.
