Principal component analysis of knee kinematics and kinetics after anterior cruciate ligament reconstruction.

This study compared the gait of 10 subjects with unilateral anterior cruciate ligament (ACL) reconstruction to a group of 12 height- and weight-matched control subjects. The analysis was based on knee flexion, adduction, and internal rotation angles and moments. The objective was to use principal component analysis (PCA) to identify knees of the ACL reconstructed subjects that fell outside normal ranges as determined by control subjects. Gait data were collected on all subjects in a motion analysis laboratory. Principal component (PC) models were developed for each gait measure based on the control subjects' data and used to assess gait waveforms of ACL reconstructed subjects. PCA allows analysis of entire gait waveforms for comparisons. In a sample of 10 ACL reconstructed subjects (7 years after surgery, on average), six of the ACL reconstructed knees had not returned to normal following surgery and eight of the contralateral knees functioned differently from controls. A majority of the differences were noted to occur in the abduction-adduction knee moment with corresponding infrequency in the differences seen in abduction-adduction rotation. PCA enabled us to identify subjects with abnormal gait waveforms as outliers relative to the normal control group.