title: The pendulum test as a tool to evaluate passive knee stiffness and viscosity of patients with rheumatoid arthritis.
abstract: BACKGROUND
  The pendulum test of Wartenberg is a technique commonly used to measure passive knee motion with the aim to assess spasticity. We used this test to evaluate changes of the knee angular displacement, passive stiffness and viscosity in rheumatoid arthritis patients. Stiffness and viscosity represent passive resistances to joint motion associated with the structural properties of the joint tissue and of the muscular-tendon complex. Stiffness can be considered an intrinsic property of the tissues to resist deformation, while viscosity is related to cohesive forces between adjacent layers of tissues. Both parameters may influence the joint range of motion affecting angular displacement.
  
  
  METHODS
  Nine women with rheumatoid arthritis were compared with a group of healthy women. With the subject half-lying, the relaxed knee was dropped from near-full extension and the characteristics of the ensuring damped unsustained knee oscillation evaluated. The kinematics of leg oscillations was recorded using ultrasonic markers (Zebris CMS HS 10) and the kinetic data were calculated from kinematic and anthropometric measures.
  
  
  RESULTS
  Knee stiffness significantly increased (p < 0.001) in patients with respect to the control group, while differences in viscosity were not significant. Moreover, the amplitudes of first knee flexion (the maximal flexion excursion after knee release) and first knee extension (the maximal extension excursion after the first knee flexion) were significantly decreased (p < 0.001). A regression analysis showed that disease severity correlated moderately with stiffness (R2 = 0.68) and first flexion (R2 = 0.78). Using a multivariate regression, we found that increasing stiffness was the main factor for the reduction of flexion and extension motions.
  
  
  CONCLUSIONS
  We showed that the Wartenberg test can be considered a practical tool to measure mechanical changes of knee caused by rheumatoid arthritis. This novel application of Wartenberg test could be useful to follow up the effects of pharmacological and rehabilitative interventions in this disease.
authors.affiliation: Department of Experimental and Clinical Pharmacology, School of Medicine, University of Catania, Catania, Italy. m.valle@unict.it <m.valle@unict.it>
authors.forename: Maria S
authors.initials: MS
authors.lastname: Valle
authors.forename: Antonino
authors.initials: A
authors.lastname: Casabona
authors.forename: Rosaria
authors.initials: R
authors.lastname: Sgarlata
authors.forename: Rosaria
authors.initials: R
authors.lastname: Garozzo
authors.forename: Maria
authors.initials: M
authors.lastname: Vinci
authors.forename: Matteo
authors.initials: M
authors.lastname: Cioni
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D004185:Disability Evaluation; D004576:Electromyography; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology / Q000503:physiopathology*; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D009128:Muscle Spasticity / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D009460:Neurologic Examination / Q000379:methods; D011237:Predictive Value of Tests; D016059:Range of Motion, Articular / Q000502:physiology*; D012021:Reflex, Abnormal / Q000502:physiology; D013583:Synovial Membrane / Q000503:physiopathology; D013710:Tendons / Q000503:physiopathology; D014743:Videotape Recording; D014783:Viscosity