Assessment of chronic trigeminal neuropathic pain by the orofacial operant test in rats.

Classical behavioral tests in animal models of trigeminal neuropathic pain measure reflexive responses that are not necessarily measures of pain. To overcome the problem, we created a chronic constrictive nerve injury (CCI) rat model of pain by ligation of the infraorbital nerve (ION), and applied the orofacial operant test to assess behavioral responses to mechanical and cold stimulation in these rats. Animals were trained to voluntarily contact their facial region to a mechanical or a cold stimulation module in order to access sweetened milk as a positive reward. ION-CCI rats displayed aversive behaviors to innocuous mechanical stimuli, as indicated by a significant decrease in both contact time and the numbers of long contact events in comparison with sham group. For cold stimulation, ION-CCI rats displayed aversive behaviors to both innocuous (17 °C) and noxious cold temperatures (12 °C and 5 °C), as indicated by a significant decrease in both contact time and the numbers of long contact events at the cooling temperatures. The decreases of the contact time and numbers in ION-CCI rats were partially abolished by morphine. Our orofacial operant test demonstrates mechanical allodynia, cold allodynia, and hyperalgesia in rats with chronic trigeminal nerve injury. The neuropathic pain in ION-CCI rats was partially alleviated by morphine. Thus, orofacial operant test provides a desirable behavioral assessment method for preclinical studies of chronic trigeminal neuropathic pain.

Acute atraumatic hip dislocation in an adult with rheumatoid arthritis.

There are no reports of atraumatic hip subluxation and dislocation in the adult patient with rheumatoid arthritis (RA). This rare phenomenon is most prevalent in patients with congenital hip dislocation, von Recklinghausen disease, tumor infiltration, connective tissue disorders, and juvenile rheumatoid arthritis. We report an acute atraumatic dislocation of the hip in an adult patient with RA. We believe that two factors contributed to the patient's atraumatic dislocation: a shallow but appropriately positioned acetabulum and erosive RA with substantiate panus formation. Similar to previous reports, there was a rent or capsular defect that may have contributed to the mechanism of dislocation. Physicians should be aware that, although rare, a de novo atraumatic hip dislocation is a possibility in a patient with a long-standing history of RA and hip pain. Distinguishing features of this case include the acuteness of the dislocation, the absence of previous symptoms, and adult-onset RA.