Knee's Motion Path Relative to the Passive Coupled Kinematic Envelope

Abstract

Laxity assessments are done before, during, and after intervention of knee injuries to assess potential outcomes. Study objectives were to create a method to define the passive kinematic limits, without artificially constraining coupled motion, and describe motion relative to them. The coupled envelopes of internal/external (IE), varus/ valgus (VV), and anterior/ posterior (AP) motion and a neutral path were used to describe loaded lunges and a simulated walk cycle. The envelopes were created by manual manipulation to motion limits. Lunges with ±3.3 Nm IE torques and ±4.7 Nm VV torque were used to verify the IE-VV coupled kinematic envelope. The IE envelope compared well, while the VV envelope was constantly offset. For six of the eight knees, a repeatable internal-valgus-anterior path relative to the center of laxity was observed for the walk cycle. All eight displayed an average anterior displacement outside the boundary at mid-stance of 4.3 ± 5.0mm.