Kinematic strategies for obstacle-crossing in patients with isolated posterior cruciate ligament deficiency.

The posterior cruciate ligament (PCL) plays an important role in the structural stability and sensory feedback at the knee. Altered structural and proprioceptive function at the PCL-deficient knee may affect the joint motions and the end-point control during functional activities. The current study identified the effects of unilateral PCL deficiency (PCLD) on the end-point control and joint kinematics of the lower limbs during obstacle-crossing. Eighteen patients with unilateral PCLD and eighteen healthy controls were each asked to walk and cross obstacles of heights of 10%, 20% and 30% of their leg lengths, with the affected and the unaffected limb leading, while their kinematic data were measured. Patients with PCLD were found to cross obstacles with significantly increased toe-clearance (p<0.01), increased trailing toe-obstacle distance (p<0.05) and reduced crossing speed (p<0.01) when compared to the controls. Similar end-point control was observed in the PCLD group whether leading with the affected or unaffected limb, which appears to be as a result of bilateral kinematic accommodation to reduce the risk of tripping. To achieve similar toe-clearances, crossing strategies with the unaffected limb leading involved angular changes at more joints than those with the affected limb leading. The PCLD group appeared to adopt a conservative strategy to reduce the risk of tripping over the obstacle during obstacle-crossing, using different joint kinematic changes depending on whether the affected or unaffected limb was leading. It is suggested that monitoring of the kinematic strategies adopted by patients with PCLD during obstacle-crossing may be needed in future rehabilitation programs with the aim of reducing tripping risks during obstacle-crossing.