Quantifying Joint Coordination Variability in Anterior Cruciate Ligament-Reconstructed Individuals During Walking

The knee is the second most common joint to sustain injury. An estimated 200,000 anterior cruciate ligament (ACL) ruptures occur each year in the United States alone, and about 100,000 ACL reconstruction (ACLR) surgeries are performed annually. There is a significant risk of developing osteoarthritis of the knee after incurring an ACL injury, and the incidence of ipsilateral or contralateral injury is six times greater in individuals who have a surgically repaired ACL. Past studies have analyzed kinetic and kinematic characteristics of individual lower extremity joints to reveal differences between subjects with and without ACLR. Despite reports of altered kinematic performance in individuals with ACLR compared to healthy controls, most of the analyses did not evaluate coordinative function, and thus neglected to consider how the lower limb acts as a linked chain. Therefore, the present study used a method based on dynamical systems theory to quantify coordination and account for the interaction between joints in the lower extremity. The purpose of the study was to quantify and compare joint coordination variability and joint coordination patterns between individuals with ACLR and matched controls. Institutional Review Board (IRB) approval was obtained prior to data collection, and all subjects signed an informed consent form. Twenty subjects (nine females, eleven males; body mass index (BMI) 25±3.5 kg/m2) who had undergone unilateral ACLR (thirteen right, seven left) and been cleared to return to full activity were compared to twenty control subjects matched by gender and BMI (nine females, eleven males; BMI 22.4±2.4 km/m2). Kinematic and kinetic data during walking were collected in the UTHSC Motion Analysis Laboratory. A vector coding technique was used to calculate coupling angles for six joint couplings involving the hip, knee, and ankle across four periods within the stance phase. Joint coordination variability was defined as the standard deviation of the coupling angle between trials within a subject, and joint coordination patterns were based on coupling angle magnitude. Individuals with ACLR exhibited increased joint coordination variability and altered joint coordination patterns compared to the matched controls during the stance phase of walking. These results suggested that coordinative function may not be fully restored in individuals with ACLR following rehabilitation. Increased coordination variability from a normal, or optimal amount as well as altered coordination patterns may result from a deficit in sensorimotor control, and represent risk of re-injury. Further investigation that is prospective, focuses primarily on hip-knee coupled motion in frontal and transverse planes, and includes assessment of EMG in addition to kinematics may contribute relevant information for improving ACL injury prevention and rehabilitation