Background. To investigate whether the interaction between pre-operative widespread hyperalgesia and radiographic osteoarthritis (OA) was associated with pain severity before and after total hip replacement (THR) and total knee replacement (TKR). Methods. Data were analysed from 232 patients receiving THR and 241 receiving TKR. Pain was assessed pre-operatively and at 12 months post-operatively using the WOMAC Pain Scale. Widespread hyperalgesia was assessed through forearm pressure pain thresholds (PPTs) measured using an algometer. The severity of radiographic OA was evaluated using the Kellgren and Lawrence scheme. Statistical analysis was conducted using linear regression and multilevel models, and adjusted for confounding variables. Results. Pre-operative. In knee patients, there was weak evidence that the effect of PPTs on pain severity was greater in patients with more severe OA compared to patients with less severe OA (Grade 3 OA: ß=0.96 vs Grade 4 OA: ß=4.03). However, in hip patients, the effect of PPTs on pain severity did not differ with the extent of radiographic OA (Grade 3 OA: ß=3.95 vs Grade 4 OA: ß=3.67). Post-operative. Patients undergoing TKR with less severe OA who had lower PPTs (greater widespread hyperalgesia) benefitted less from surgery than patients with higher PPTs (Grade 3 OA: ß=2.28). Conversely, patients undergoing THR with more severe OA who had lower PPTs benefited more from surgery than patients with higher PPTs (Grade 4 OA: ß=−2.92). Conclusion.
A rat model of lumbar root constriction with an additional sympathectomy in some animals was used to assess whether the sympathetic nerves influenced radicular pain. Behavioural tests were undertaken before and after the operation. On the 28th post-operative day, both dorsal root ganglia and the spinal roots of L4 and L5 were removed, frozen and sectioned on a cryostat (8 μm to 10 μm). Immunostaining was then performed with antibodies to tyrosine hydroxylase (TH) according to the Avidin Biotin Complex method. In order to quantify the presence of sympathetic nerve fibres, we counted TH-immunoreactive fibres in the dorsal root ganglia using a light microscope equipped with a micrometer graticule (10 x 10 squares, 500 mm x 500 mm). We counted the squares of the graticule which contained TH-immunoreactive fibres for each of five randomly-selected sections of the dorsal root ganglia. The root constriction group showed mechanical allodynia and thermal hyperalgesia. In this group, TH-immunoreactive fibres were abundant in the ipsilateral dorsal root ganglia at L5 and L4 compared with the opposite side. In the sympathectomy group, mechanical hypersensitivity was attenuated significantly. We consider that the sympathetic nervous system plays an important role in the generation of radicular pain.
