Immunocytochemical and dye distribution studies of nerves potentially desensitized by injections into the distal interphalangeal joint or the navicular bursa of horses.

To determine whether the distal interphalangeal (DIP) joint directly or indirectly communicates with the navicular bursa (bursa podotrochlearis) and to identify sensory nerves in these synovial structures that might be desensitized by intra-articular injections of anesthetics, Evans blue dye in physiologic saline solution, Luxol fast blue dye with mepivicaine, or commercial latex was injected into the DIP joint (5 ml) or the navicular bursa (3 ml) of 152 digits obtained from horses or ponies at necropsy. The digits were frozen, cut with a band saw, and examined for distribution of dye or latex. Of 122 digits that had injections into the DIP joint, 120 did not have evidence of a communication between the DIP joint and either the navicular bursa or digital flexor tendon sheath. Of 16 digits that had injections into the navicular bursa, 14 did not have evidence of a direct communication with the DIP joint. Injection of dye into the DIP joint resulted in diffusion of dye and staining of other structures, including the synovial linings of the collateral sesamoidean ligaments and of the distal sesamoidean impar ligament and the medullary cavity of the navicular bone. In addition, a blue tinge was observed in the navicular bursa after dye was injected into the DIP joint, suggesting an indirect, and potentially functional, communication between the DIP joint and the navicular bursa. Injection of dye into the navicular bursa resulted in staining only of the bursa's synovial lining. Immunocytochemical analysis revealed nerves immunoreactive for the peptidergic neurotransmitters substance P, and calcitonin gene-related peptide located in structures that were stained after dye was injected into the DIP joint.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptidergic innervation of equine synovial joints.

Immunocytochemical analysis of equine synovial membranes revealed presence of several neuropeptides, including substance P (SP), neurokinin A, and neuropeptide Y, in nerves of the radiocarpal, middle carpal, and metacarpophalangeal (fetlock) joints. Within the subsynovium, these neuropeptides were located perivascularly, whereas in the fronds, only neuropeptide Y was restricted to the vessels of the synovial membrane. Only SP and neurokinin A were found in the intimal layer. The intimal layer of the metacarpophalangeal joint contained more SP-immunoreactive fibers than were observed in the intimal layer of the radiocarpal joint. Substance P also was detected in the synovial fluid from all 3 joints, but mean +/- SD concentrations were significantly different only between the middle carpal joint (37.56 +/- 5.48 fmol/ml; n = 6) and the metacarpophalangeal joint (55.80 +/- 8.33 fmol/ml; n = 5) and between the middle carpal joint and the radiocarpal joint (52.43 +/- 14.60 fmol/ml; n = 7).