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Comparison of Johnson Anti-Shear Accessory and Standard Dynamometer Attachment for Anterior and Posterior Tibial Translation during Isometric Muscle Contractions.

The purpose of this study was to compare the effectiveness of the Johnson Anti-Shear Accessory (JASA) and the standard dynamometer accessory (SDA) in controlling tibial translation for isometric knee flexion and extension exercise on the Cybex(R) II. The subject was a 26-year-old male with known anterior cruciate ligament (ACL) deficiency of the left knee. The subject performed maximum isometric muscle contractions for JASA and SDA conditions. Medial-lateral roentgenograms were obtained while the subject maintained isometric knee flexion and extension muscle contractions at three positions of knee flexion. JASA and SDA trials were analyzed for one extension position and one flexion position. The authors compared JASA and SDA conditions for magnitude of contact pad force and for degree of tibial translation evidenced on the roentgenograms. Tibial translation was greater and contact pad force was less for the SDA condition than the JASA condition. The results suggest the JASA is useful in protecting ACL surgical reconstructions, the partially torn ACL, and secondary supporting structures of the knee as patients perform isometric exercise on Cybex instrumentation. J Orthop Sports Phys Ther 1990;11(11):547-553.