Design and validation of an unconstrained loading system to measure the envelope of motion in the XXXX knee joint.

@entity4610 @entity95 @entity625
An unconstrained loading system was developed to measure the passive envelope of joint motion in an animal model commonly used to study ligament healing and joint @entity625 . The design of the five-degree-of-freedom system allowed for unconstrained knee joint loading throughout flexion with repeated removal and reapplication of the device to a specimen. Seven New Zealand White @entity95 knees were subjected to varus, valgus, internal and @entity4610 loads, and the resulting envelopes of motion were recorded using an electromagnetic tracking device. Intra-specimen reproducibility was excellent when measured in one specimen, with maximal rotational differences of 0.6 and 0.3 deg between the fourth and fifth testing cycles for the varus (VR) and valgus (VL) envelopes, respectively. Similarly, the maximal internal (INT) and @entity4610 ( @entity4610 ) envelope differences were 0.5 and 0.4 deg, respectively, between the fourth and fifth cycles. Good inter-animal envelope reproducibility was also observed with consistent motion pathways for each loading condition. A maximal VR-VL laxity of 17.9 +/- 2.3 deg was recorded at 95 deg flexion for the seven knees tested. The maximal INT- @entity4610 laxity of 75.2 +/- 4.8 deg occurred at 50 deg flexion. Studies on measurement reproducibility of re-applying individual testing components demonstrated a maximal error of 1.2 +/- 0.7 deg. Serial removal and re-application (test-retest) of the complete measuring system to one cadaveric knee demonstrated maximal envelope differences of less than 0.7 deg for VR-VL rotation and 2.1 deg for INT- @entity4610 rotation. Our results demonstrate that the measuring system is reproducible and capable of accurate evaluation of knee joint motion. Baseline in vitro data were generated on normal joint kinematics for future in-vivo studies with this system, evaluating ligament healing and disease progression in @entity625 models.
