STRENGTH EVALUATION OF SINGLE RADIUS TOTAL KNEE REPLACEMENT (A CASE STUDY) He Wang 1 , Kathy Simpson 1 , Michael Ferrara 1 , Samatchai Chamnongkich 1 , Steve Casto 1 and Ormonde Mahoney 2 1 Department of Exercise Science, University of Georgia, Athens, Georgia 2 Athens Orthopedic Clinic PA, Athens, Georgia Email: hwang@coe.uga.edu Web: http://www.coe.uga.edu/exs/ INTRODUCTION A successful total knee replacement (TKR) should allow normal knee function. Compared to previous multiaxis TKR designs, the Scorpio TM TKR (Osteonics, Inc.) utilizes one fixed flex/extension (F/E) axis, based on the premise that only one fixed F/E axis exists in intact knees (Elias, et al., 1990; Hollister at al., 1993). The location of the Scorpio F/E axis has been surmised to generate a longer moment arm of the patellar ligament than previous multiaxis designs. Hence, for our participants, would the maximum knee extensor torque of the TKR limb be similar to the non-TKR limb? In addition, it was of interest to observe the effect of a posterior stabilized (PS) TKR design. Thus, would the stabilizing post provide the restraint to replace the posterior cruciate ligament or would the participants exhibit greater quadriceps activity during isolated knee flexion, when the quadriceps serve as an antagonist to assist in posterior displacement stabilization? Therefore, the objective of this case study was to compare the maximum knee F/E torques and the quadriceps co-contraction activity during antagonist actions of the TKR and the non- TKR (N-TKR) limb during isolated knee F/E movements. METHODS Two male participants (55-63 yr.) with a unilateral Scorpio TM PS TKR (P1 = 29 mo; P2 = 31 mo.) took part in this case study. Both were prescreened for health and functional status by the same surgeon who performed the operations. Two days of accommodation practice occurred prior to the actual strength testing. The isometric strength (KIN-COM III TM ) of the quadriceps and hamstring were measured at 60° and 30° of knee flexion, respectively. During isokinetic concentric testing (60°/s), the range of motion was between 10° to 80° of knee flexion. For a given test, the trial exhibiting maximum torque was analyzed. An 8-channel BTS TELEMG TM system was used to collect quadriceps EMG activity. EMG window intervals of 167 ms were used for analysis. Integrated EMG (iEMG) intervals representing quadriceps co-contraction during the hamstring concentric test were normalized to their respective quadriceps concentric EMG interval. As this was a case study with only 2 participants, no statistical analyses were performed. RESULTS The TKR limb compared to the N-TKR limb demonstrated: 1. less maximum concentric (16% and 21% less for P1 and P2, respectively) and isometric (12% and 29%, respectively) quadriceps torque for both participants (Table 1). 2. 14% less maximum hamstrings concentric torque for P1 but 16% greater torque for P2. However, P1 had similar