Study design: The segmental levels of dorsal root ganglions innervating the sacroiliac joint in rats were investigated using the retrograde transport method. The pathways and functions of the nerve fibers supplying the sacroiliac joint were determined by immunohistochemical detection of transported tracer.
Objectives: To study the sensory innervation of the sacroiliac joint and to elucidate the neural pathways of low back pain originating from the sacroiliac joint.
Summary of background data: The sacroiliac joint is a possible source of low back pain. The L4-S4 spinal nerves have been regarded as the nerves innervating the sacroiliac joint in humans. However, the origins of nerve fibers have not been analyzed experimentally with tracer methods.
Methods: Cholera toxin B subunit, a neural tracer, was injected into the left sacroiliac joint of adult rats, and the bilateral dorsal root ganglions were immunohistochemically examined 4 days after injection. In another rat group, the dorsal root ganglions were examined using the same methods after resection of the left sympathetic trunk from L2 to the most caudal level. Thus, the pathways of the nerve fibers supplying the sacroiliac joint were investigated.
Results: Labeled neurons were mainly located in the ipsilateral dorsal root ganglions from L1 to S2 of the unsympathectomized rats and in the ipsilateral dorsal root ganglions from L4 to S2 of the sympathectomized rats.
Conclusions: The sacroiliac joint was innervated by sensory neurons in dorsal root ganglions ipsilateral to the joint from L1 to S2. Sensory fibers from the L1 and L2 dorsal root ganglions passed through the paravertebral sympathetic trunk.