EXTRINSIC AND INTRINSIC INNERVATION OF THE GUINEA PIG KNEE JOINT: TOWARD AN ANIMAL MODEL FOR MANIPULATIVE THERAPY

Objectives: Besides spinal conditions, knee joint problems are one of the most common ailments of the musculoskeletal system. Problems with the knee can be classified into (1) poor mechanics, (2) traumatic injury, and (3) arthritic changes. All these problems can produce pain. Conservative treatment such as chiropractic manipulative therapy can be helpful in alleviating some of the pain. The present study was carried out to investigate the extrinsic and intrinsic innervation of the knee joint of the guinea pig in the hope of shedding light on future study of the underlying mechanism of chiropractic manipulative therapy on knee joint pain conditions. Methods: A total of 16 guinea pigs were used in the present study. Microdissection was performed to reveal the gross anatomy of nerve innervation. Histology and immunohistochemistry were also performed to identify nerve endings and immunoreactive fibers in different articular tissues. Results: Gross dissection revealed the general pattern of guinea pig knee joint innervation. By using gold chloride preparations, various kinds of nerves and terminals or endings were identified in these tissues. Immunohistochemistry also revealed immunoreactivities in nerve fibers in different joint tissues. Conclusions: The distribution of the different nerve endings showed a characteristic pattern in different articular tissues. They were considered to be mechanoreceptors (types I, II, and III) and pain receptors (type IV). The structural characteristics and distribution patterns of the different types of nerve endings suggest that the roles of the different nerve endings vary in different parts of the articular tissues. (J Manipulative Physiol Ther 2009;32:223-231)