QUANTITATIVE GAIT ANALYSIS AFTER BILATERAL TOTAL KNEE ARTHROPLASTY WITH 2 DIFFERENT SYSTEMS WITHIN EACH SUBJECT

The functional behavior of two kinematically different knee arthroplas ty systems within each subject was studied by gait analysis (three-dim ensional kinematics, kinetics, dynamic electromyography) in five elder ly patients, 2 to 5 years after bilateral surgery. Clinical results we re good, yet gait velocity was reduced (range, 0.57-1.1 m/s), with a s hortened stride length and a decreased duration of single-limb stance in all subjects. Force plate recordings revealed an undynamic gait wit h slow loading, reduced modulation of the vertical forces, and poor fo re/aft shears. Sagittal plane knee motion during gait was reduced in a ll subjects, with trunk and pelvic compensation patterns for foot clea rance. Muscle activity around the knee was prolonged bilaterally, with activity modulation related to the motion pattern. Although the strid e parameters were quite symmetric, there was a marked asymmetry of the motion pattern, with a side-to-side difference of peak knee flexion d uring stance and swing phase of up to 15 degrees. This finding, howeve r, was not clearly related to the type of prosthesis. Even within one subject, significant side-to-side variability may persist, which leads to asymmetry of the motion pattern, unrelated to the kinematic design of the implant. Other factors, such as the patella-extensor mechanism , ligament balancing, leg-length discrepancy, proprioception, continua tion of a preoperative habit, or a contralateral influence, may explai n part of the asymmetry seen in these subjects.