The limits of passive motion are variable between and unrelated within normal tibiofemoral joints

Patient-to-patient differences should be accounted for in both clinical evaluations and computational models of knee laxity. Accordingly, the objectives were to determine how variable the laxities are between knees by determining the range of the internal-external (I-E), varus-valgus (V-V), anterior-posterior (A-P), and compression-distraction (C-D) limits of passive motion, and how related the laxities are within a knee by determining whether these limits are correlated with one another. The limits in I-E (± 3 Nm), V-V (± 5 Nm), A-P (± 45 N), and C-D (± 100 N) were measured in 10 normal human cadaveric knees at 0° to 120° flexion in 15° increments using a six degree-of-freedom load application system. The ranges from 15° to 120° flexion of the I-E limits were greater than 3.6°, of the A-P limits were greater than 1.8 mm, and of the varus limits were greater than 1.4°. The ranges from 30° to 120° flexion of the distraction limits were greater than 2.0 mm. Twenty-four of the 28 pair-wise comparisons between the limits had a correlation coefficient less than 0.65. These results demonstrate that a patient-specific approach, including all degrees of freedom of interest, is necessary during clinical evaluations of laxity and when creating and validating computational models of the tibiofemoral joint.