- Clark, FJ; Horch, KW; Bach, SM; Larson, GF
- Subjects were tested for their ability to correctly detect 5° changes in the angle of their right knee, starting from a position where they perceived their legs to be aligned, and also for the accuracy with which they returned their knee to its initial position after the 5° change. In all the tests, the left leg was fixed in position and the right leg was passively moved. The 5° changes were made sufficiently slowly (less than 1°/min) that no reliable sensations of movement resulted. Rematching movements were made in steps of 0.25-2° at rates about two orders of magnitude greater than the slow movements. Subjects could correctly detect the 5° changes about 85% of the time. Tests were made of the effects of experience, i.e., learning (5 subjects), injecting a local anesthetic into both knee joint spaces (10 subjects), anesthetizing a 15-cm band of skin around the leg being moved (4 subjects), and a combination of skin and joint anesthesia (2 subjects). The learning tests indicated there were no significant changes in performance due to experience. Therefore, it was considered unlikely that any decrements in performance in subsequent tests due to the anesthesia would be masked by improvements due to learning. Neither joint anesthesia, nor skin anesthesia, nor a combination of the two affected the ability of the subjects to correctly detect the flexion, extension, and control trials. Anesthesia did produce a small shift in the mean value of the angle difference between the right and left knees after matching (toward extension of the right leg) compared to the pooled pre- and postinjection data: Δθ = 1.4° for anesthesia of the skin alone, 1.9° for the joint alone, and 0.6° for the combination of skin and joint. This shift in the mean value of the angle difference was significant for the joint injection, but not for the skin or combined anesthesia. Skin anesthesia alone or in combination with joint anesthesia produced a significant decrease in the standard deviation of the angle difference compared to the pooled pre- and postinjection runs: ± 1.7° vs ± 3.0° skin alone and ± 2.0° vs. ± 3.0° for skin and joint combined. No change in standard deviation was seen with anesthesia of the joint alone. The effect on joint receptors of injecting local anesthetic into the joint space was tested in the cat and monkey. The anesthetic abolished nearly all tonic responses in the posterior and medial articular nerves to bending and twisting the joint. In the human, injection of a radiopaque material into the knee joint showed the material to be well distributed throughout the joint space. We conclude that awareness of static knee position does not depend on sensory input from either receptors in the joint or the skin around the joint; however, these receptors may have some minor influence on perceived joint angle, especially during more rapid movements such as those used for rematching.
- January 1, 1979
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