The objective of this study was to compare the gait variability of patients with isolated anterior cruciate ligament (ACL) deficiency (experimental group) with that of healthy individuals (control group). The hypothesis was that the gait variability of the experimental group would be higher than the control group. The experimental group consisted of 20 men with an ACL tear and the control group consisted of 20 healthy men without any neurological and/or musculoskeletal pathology or injury. The gait acceleration signal was analysed using the Gait Evaluation Differential Entropy Method (GEDEM). The GEDEM index of the experimental group in the medio-lateral axis was significantly higher than that of the control subjects. A receiver operating characteristic (ROC) analysis was used to assess the diagnostic value of the method and to determine a cut-off entropy value. The GEDEM cut-off value had a 95.6% probability of separating isolated ACL patients from healthy subjects.

An accelerometer system was used to measure the characteristics of the motion of 133 healthy male soccer athletes in a 30-s walking test and the data obtained were analysed using the gait evaluation differential entropy method (GEDEM). GEDEM processes gait acceleration data and calculates an index that provides a quantitative evaluation of a subject's gait, at low cost and with negligible effect on the subject. The GEDEM index was not significantly correlated with age, body weight, body mass index, or the number of years of active training. The GEDEM value for the anterior-posterior axis showed a small negative statistically significant correlation with height and the vertical axis was moderately and statistically significantly positively correlated with the time spent training per week. The triaxial accelerometry system described here is easy for subjects and testers to use, and enables measurements to be made on the sports field to evaluate an athlete's musculoskeletal condition with respect to gait stability.

Change in gait variability at least 6 months after surgical reconstruction of the anterior cruciate ligament (ACL) was assessed in 20 male patients with acute ACL deficiency and compared with preoperative data and that from 20 healthy male controls. Gait was measured using a triaxial accelerometer and data were analysed by the Gait Evaluation Differential Entropy Method (GEDEM) to determine gait variability. Pain was assessed with a visual analogue scale and functional ability with the Oswestry Disability Index and the International Knee Documentation Committee score.Mean gait variability was significantly lower after than before surgery, with values for the anterior-posterior axis being in the normal range of controls after 6 months, whereas in the mediolateral axis mean gait variability remained significantly higher, indicating that some rotational instability remained in the time-frame of the study. Pain and functional ability scores improved after surgery compared with before surgery. The combination of accelerometry and GEDEM may be a useful orthopaedic tool for the post-operative evaluation of patients who have undergone ACL reconstruction.