Co-contraction in RA patients with a mobile bearing total knee prosthesis during a step-up task

• Published in: Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA Vol. 16; no. 8; pp. 734 - 740
• Main Authors: Garling, Eric H., Wolterbeek, Nienke, Velzeboer, Sanne, Nelissen, Rob G. H. H., Valstar, Edward R., Doorenbosch, Caroline A. M., Harlaar, Jaap
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.08.2008; John Wiley & Sons, Inc
• Subjects: Adult; Aged; Aged, 80 and over; Arthritis, Rheumatoid - physiopathology; Arthritis, Rheumatoid - surgery; Arthroplasty, Replacement, Knee; Biomechanical Phenomena; Case-Control Studies; Design; Electromyography; Humans; Joint Instability - physiopathology; Joint replacement surgery; Kinematics; Knee; Knee Prosthesis; Medicine; Medicine & Public Health; Middle Aged; Movement - physiology; Muscle Contraction - physiology; Muscle Strength Dynamometer; Muscle, Skeletal - physiology; Orthopedics; Patients; Polyethylene; Prostheses; Range of Motion, Articular - physiology; Rheumatoid arthritis; Rotation; Netherlands; Knee stability; Co-contraction; Total knee arthroplasty; Mobile bearing knee; Rheumatoid arthritis
• ISSN: 0942-2056; 1433-7347
• DOI: 10.1007/s00167-008-0537-7

It was hypothesized that rheumatoid arthritis (RA) patients with a total knee prosthesis that allows axial rotation of the bearing (MB) will show more co-contraction to stabilize the knee joint during a step-up task than RA patients with a fixed bearing total knee prosthesis (FB) where this rotational freedom is absent while having the same articular geometry. Surface EMG, kinematics and kinetics about the knee were recorded during a step-up task of a MB group ( n  = 5), a FB group ( n  = 4) and a control group ( n  = 8). Surface EMG levels of thigh muscles were calibrated to either knee flexion or extension moments by means of isokinetic contractions on a dynamometer. During the step-up task co-contraction indices were determined from an EMG-force model. Controls showed a higher active ROM during the step-up task than the patient group, 96° versus 88° ( P  = 0.007). In the control group higher average muscle extension, flexion and net moments during single limb support phase were observed than in the patient group. During the 20–60% interval of the single limb support, MB patients showed a significant higher level of flexor activity, resulting in a lower net joint moment, however co-contraction levels were not different. Compared to the control group arthroplasty patients showed a 40% higher level of co-contraction during this interval ( P  = 0.009). Control subjects used higher extension moments, resulting in a higher net joint moment. Visual analysis revealed a timing difference between the MB and FB group. The FB group seems to co-contract approximately 20% later compared to the MB group. RA patients after total knee arthroplasty show a lower net knee joint moment and a higher co-contraction than controls indicating avoidance of net joint load and an active stabilization of the knee joint. MB and FB patients showed no difference in co-contraction levels, although timing in FB is closer to controls than MB subjects. Since visual analysis revealed a timing difference between the MB and FB group, this may express compensation by coordination. Rehabilitation programs for RA patients should include besides muscle strength training, elements of muscle-coordination training.