Assessment of muscle performance is an integral component of patient evaluation. The primary purposes of this study were to examine the relationship between isokinetic dynamometer isokinetic peak force values and hand-held dynamometer isometric peak force values when assessing quadriceps muscle performance in subjects with orthopaedic knee dysfunctions (N = 21) and to test for differences in muscle performance between injured and noninjured lower extremities using a hand-held dynamometer and an isokinetic dynamometer. An analysis of variance was used to compare injured and noninjured extremities for both testing devices. A Pearson product moment correlation was used to examine the relationship between the hand-held dynamometer and isokinetic dynamometer values. No significant difference between extremities at 0 degrees (p = 0.1224) or 60 degrees (p = 0.8267) was revealed when testing with the hand-held dynamometer. The isokinetic dynamometer, however, revealed a significant difference between extremities at 60 degrees/sec (p = 0.0041). Correlations between the two devices were significant, ranging from r = 0.57 to 0.80. We concluded that these correlations were misleading because more force was generated by the quadriceps muscles tested than a tester of average strength could resist. Further research is needed to validate the use of the hand-held dynamometer by a tester of average strength.