FUNCTIONAL ASSESSMENT OF KNEE JOINT MOBILITY IN ADULT PERSONS WITH DOWN SYNDROME

The Down syndrome (DS) is a common genetic disease characterized by mental retardation and biomechanical deficits. Muscle hypotonia and joint and ligament laxity are typical symptoms of this disorder that reduce movement stability. In this study, we assessed knee joint mobility in adult persons with DS by means of the Wartenberg pendulum test. This test allows to describe the kinematics of knee joint during passive pendular motion of leg under the influence of gravity. We hypothesized that, due to abnormalities of muscles and joints, the knee excursion in the persons with DS would have to be larger than TD persons. Ten adults with DS and ten typically developed (TD) adults performed a series of ten repetition of pendulum test. Surprisingly in persons with DS, angular position, mean velocity and acceleration of the first leg flexion were lower than TD persons and the differences were statistically significant (p < 0.05). Surface EMGs of muscle rectus femoris recorded during the first flexion exhibited large phasic activity in persons with DS, whereas the EMGs of TD controls were characterized by low tonic activity. We compared the total area of EMG with the mean value of acceleration during the first swing and we found that the coefficient of correlation was much higher in persons with DS (r = 0.81) than in TD group (r = 0.35). Thus, the active muscle contraction was the main contributor to the reduction of pendular leg motion. These results suggest that persons with DS react to quick and unpredictable perturbations by automatic muscular contraction which increase joint stiffness and compensate for inherent joint instability.