title: Co-contraction in RA patients with a mobile bearing total knee prosthesis during a step-up task.
abstract: 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 degrees versus 88 degrees (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.
authors.affiliation: Department of Orthopaedics, Leiden University Medical Center, J11-S, 2300 RC Leiden, The Netherlands.
authors.forename: Eric H
authors.initials: EH
authors.lastname: Garling
authors.forename: Nienke
authors.initials: N
authors.lastname: Wolterbeek
authors.forename: Sanne
authors.initials: S
authors.lastname: Velzeboer
authors.forename: Rob G H H
authors.initials: RG
authors.lastname: Nelissen
authors.forename: Edward R
authors.initials: ER
authors.lastname: Valstar
authors.forename: Caroline A M
authors.initials: CA
authors.lastname: Doorenbosch
authors.forename: Jaap
authors.initials: J
authors.lastname: Harlaar
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000503:physiopathology* / Q000601:surgery; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D004576:Electromyography; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology; D007720:Knee Prosthesis; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D053581:Muscle Strength Dynamometer; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation