Pain from conditions such as arthritis remains a major source of disability with substantial personal and socioeconomic impact. It is assumed that pain from the affected joint is transmitted through afferent nerves; however, our understanding of the role of specific nerve endings in the joint capsule remains incomplete. A recent discovery regarding the interrelationships of the anterior and posterior interosseous nerves, which terminate in the anterior and posterior joint capsule of the wrist, has made it possible for the first time to study the role of joint capsule mechanoreceptors in a specific fashion in a human population. This research project will characterize the populations of mechanoreceptors in the wrist joint capsule associated with the anterior and posterior interosseous nerves. The electrical activity of these nerves will then be studied in patients undergoing partial denervation of the wrist for treatment of chronic pain due to arthritis, where both nerves are exposed surgically prior to excision. The potential proprioceptor function of these nerves in a normal volunteer population and patients with wrist arthrosis will be assessed by blocking the activity of the nerves temporarily with a local anesthetic. This information will be used to establish a foundation, upon which further studies of changes that occur in the painful wrist can be made, with likely extrapolation to other articular joints in the human body. The objectives and specific aims of this study are as follows: Study 1. To identify mechanoreceptors in the key wrist ligaments, classify them according to morphology and develop a spatial reconstruction using computer aided three-dimensional reconstruction technology. Hypothesis 1: Specific nerve endings classifiable as mechanoreceptors are found in key wrist ligaments in predictable population locations and can be traced to the anterior (AIN) and posterior (PIN) interosseous nerves. Study 2. To determine if the anterior and posterior interosseous nerves conduct afferent signals related to wrist joint proprioception. Hypothesis 2. The anterior and posterior interosseous nerves contribute to the global sense of wrist joint positioning in space, which is not compromised by arthrosis but altered by surgical denervation. Study 3. To document the specific conduction patterns of the AIN and PIN during wrist movement using microneurography and correlate these to the expected conduction patterns predicted from the mechanoreceptor populations found in the wrist ligaments. Hypothesis 3: Afferent electrical activity can be detected in the anterior and posterior interosseous nerves and is specifically related to direction of displacement of the wrist.
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