Histologic analysis of neural elements in the human sacroiliac joint.

STUDY DESIGN: The posterior ligament of the human sacroiliac joint was examined for nerves and nerve endings using histologic and immunohistochemical techniques. OBJECTIVE: To identify nerve fibers and mechanoreceptors in the posterior ligament. SUMMARY OF BACKGROUND DATA: According to the findings of previous studies, the human sacroiliac joint receives myelinated and unmyelinated axons that presumably conduct pain and proprioceptive impulses derived from mechanoreceptors and free nerve endings in the human sacroiliac joint. METHODS: Tissue obtained from six patients was stained with gold chloride and that obtained from six additional patients was stained using antibodies specific for substance P and protein gene product 9.5. RESULTS: The staining of joint tissue using the gold chloride technique showed myelinated and unmyelinated nerve fibers, two morphotypes of paciniform encapsulated mechanoreceptors, and a single nonpaciniform mechanoreceptor. Analysis using immunohistochemical staining for protein gene product 9.5 did not unequivocally show axons, nerve fascicles, or mechanoreceptors. Similarly, analysis based on immunohistochemical staining for substance P, one of several neurotransmitters known to signal pain from the periphery, showed reactive elements that may have been nerves, but because of background staining, could not be positively identified as such. CONCLUSIONS: The presence of nerve fibers and mechanoreceptors in the sacroiliac ligament demonstrates that the central nervous system receives information, certainly proprioceptive, and possibly pain from the sacroiliac joint. Although it is not known how the central nervous system uses such information, it seems reasonable to speculate that the proprioceptive information is used to optimize upper body balance at this joint. In addition, because the staining techniques used generally to show nerves and nerve elements in periarticular connective tissue are nonspecific, the distinction between neural and nonneural should be made on the basis of both morphologic and staining characteristics.

Correlative changes during early morphogenesis of the sacroiliac complex in squamate reptiles.

We tested the "limb bud" hypothesis, which explains morphogenetic mechanisms of the formation of the sacroiliac skeletal complex in tetrapods. The hypothesis assumes that: 1) the destruction of the embryonal sacral myomeres and the appearance in their place of a sacral gap filled in with mesenchymal cells favor the development of the sacroiliac complex; and 2) the destruction of myomeres takes place under the influence of limb buds. We studied serial hystological sections of embryos from squamate reptiles with large limb buds (sand lizard, Lacerta agilis L.), small and short-living limb buds (slow worm, Anguis fragilis L.) and without limb buds (adder, Vipera berus (L.)). In embryos of the sand lizard, the hypaxial part of the second sacral myomere degenerated, whereas that of the first one survived in its cranial part. Thus, a large sacral gap was formed where two sacral ribs expanded later. They stretched in a manner similar to the sacral gap across the longitudinal axis of the body, the large ilium lying opposite them. In embryos of the slow worm, the sacral gap was of reduced size and was significantly beveled caudally. The only sacral rib and the upper part of the ilium, which lie within the sacral gap, were beveled in the same manner. In embryos of the adder, myomere destruction was not observed, and sacral ribs and the pelvic girdle did not arise. The obtained results generally agree with the limb bud hypothesis; therefore, it can be said that tetrapods possess a simple and effective morphogenetic mechanism by which the hind limbs create their own support on the axial skeleton.

Sensory innervation of the sacroiliac joint in rats.

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.