The pattern of distribution of PGP 9.5 and TNF-alpha immunoreactive sensory nerve fibers in the labrum and synovium of the human hip joint

To date, there has been no report clarifying the existence of sensory nerve fibers as the origin of the hip joint pain of osteoarthritis. We examined the existence of sensory nerve fibers in osteoarthritis (OA), osteonecrosis of the femoral head (ONFH), and femoral neck fracture of the human hip joint. Ten labra of 10 human hip joints were harvested during a total hip arthroplasty. Each labrum was separated into 12 sections and we used three sections for analysis, which included 2 weight-bearing and 1 non-weight-bearing portion. Protein gene product 9.5 (PGP 9.5) immunoreactive sensory nerve fibers were found in the labrum and synovium harvested from the weight-bearing portion in the OA group. Some of these sensory nerve fibers were also positive for tumour necrosis factor alpha (TNF). The PGP 9.5 immunoreactive sensory nerve fibers existed in the labrum tissue and inflammatory TNF positive cells were observed in the hyperplastic synovium. On the other hand, we could not demonstrate PGP 9.5 or TNF immunoreactive sensory nerve fibers and cells in any of the ONFH group or the non-weight-bearing portion in the OA group. These data suggest that the pain of ONFH and OA of the hip joint have different pathogenetic mechanisms and that the invasion of sensory nerve fibers containing TNF may be involved in the pathogenesis of pain in the human hip joint affected by OA.