Kinematic evaluation of the step-up exercise in anterior cruciate ligament deficiency.

Background: Step-up exercise is one of the most commonly utilized exercises during rehabilitation of patients after both anterior cruciate ligament (ACL) injury and reconstruction. Currently, insurance providers increasingly required a trial of intensified rehabilitation before surgical reconstruction is attempted. The purpose of this study was to investigate whether this "safe" rehabilitation exercise in the setting of ACL deficiency can cause altered knee kinematics.

Methods: Thirty patients with unilateral ACL rupture were recruited for this study. The mean time from injury was 3.3 months. Tibiofemoral kinematics were determined during a step-up exercise using a combination of magnetic resonance imaging (MRI), dual fluoroscopy and advanced computer modeling.

Findings: The ACL-injured knee displayed an average 5° greater external tibial rotation than the uninjured knee (P<0.05), during the last 30% of step-up. The ACL-injured knee also demonstrated on average 2.5 mm greater anterior tibial shift during the last 40% of stance phase (P<0.01). In addition, during the last 30% of stance the tibia of the ACL-deficient knee tended to shift more medially (~1 mm) as the knee approached full extension (P<0.01).

Interpretation: The data confirmed the initial hypothesis as it was found that ACL deficient knees demonstrated significantly increased anterior tibial translation, medial tibial translation and external tibial rotation toward the end of the step-up as the knee approached full extension. Intensive rehabilitation utilizing the step-up exercise in the setting of ACL deficiency can potentially introduce repetitive microtrauma by way of altered kinematics.