Increased Joint Stiffness Research Articles

Virtual trajectories of single-joint movements performed under two basic strategies

The framework of the equilibrium point hypothesis has been used to analyse motor control processes for single-joint movements. Virtual trajectories and joint stiffness were reconstructed for different movement speeds and distances when subjects were instructed either to move “as fast as possible” or to intentionally vary movement speed. These instructions are assumed to be associated with similar or different rates of change of hypothetical central control variables (corresponding to the speed-sensitive and speed-insensitive strategies). The subjects were trained to perform relatively slow, moderately fast and very fast (nominal movement times 800, 400 and 250 ms) single-joint elbow flexion movements against a constant extending torque bias. They were instructed to reproduce the motor command for a series of movements white ignoring possible changes in the external torque which could slowly and unpredictably increase, decrease, or remain constant. The total muscle torque was calculated as a sum of external and inertial components. Fast movements over different distances were made with the speed-insensitive strategy. They were characterized by an increase in joint stiffness near the midpoint of the movements which was relatively independent of movement amplitude. Their virtual trajectories had a non-monotonic N-shape. All three arms of the N-shape scaled with movement amplitude. Movements over one distance at different speeds were made with a speed-sensitive strategy. They demonstrated different patterns of virtual trajectories and joint stiffness that depended on movement speed. The N-shape became less apparent for moderately fast movements and virtually disappeared for the slow movements. Slow movements showed no visible increase in joint stiffness. The joint stiffness patterns have been shown to depend upon central control processes rather than on actual values of joint velocity. We conclude that the two basic central strategies have characteristic patterns by which the equilibrium trajectory and joint stiffness are modulated.

Basic Science AND Pathology

Management of intraarticular fractures is often complicated by joint stiffness long after bony healing has occurred. The following experiments provide biomechanical evidence for the effectiveness of CPM in maintaining joint function in stabilized articular injuries. The ankles of ten adolescent New Zealand white rabbits were penetrated by Steinmann pins to create an intraarticular injury. One limb of each animal was immobilized, and the contralateral limb was placed in a continuous passive motion (CPM) machine for three weeks. Joint stiffness of each ankle was quantified with an arthrograph before injury and after three weeks of treatment. Hindlimb volumes were recorded before injury and monitored at weekly intervals using a water-displacement method. Joint stiffness increased 2.6 times the preinjury levels in limbs that were immobilized for three weeks. There was no statistically significant increase in joint stiffness in ankles treated with CPM compared to preinjury values. The posttraumatic difference between the CPM-treated and immobilized limbs was highly significant; limb swelling was not affected by CPM.

The effect of joint velocity on the contribution of the antagonist musculature to knee stiffness and laxity

The electromyographic (EMG) coactivation patterns of the knee flexors and extensors when acting as antagonists were studied as a function of limb velocity to assess their contribution to joint stiffness and laxity. Normalized antagonist coactivation patterns developed from surface EMG recordings from the hamstrings and quadriceps during maximal effort isokinetic extension and flexion, respectively, demonstrated characteristic variations as the joint velocity increased from 15 deg/sec up to 240 deg/sec. The two-tailed t-test (P less than 0.01) was performed on the data obtained from eight normal knees. The results indicate that both hamstrings and quadriceps demonstrate a significant increase (greater than 100%) in their antagonist coactivation pattern during the final 40 degrees of fast extension and flexion movements, respectively, as limb velocity increases. A minor decrease in antagonist activity of the hamstrings (24%) and quadriceps (8%) was evident during the initial phase of the extension and flexion movements, respectively, as joint velocity increased. We concluded that as limb velocity is increased, there is a substantial reflexive (unintentional) increase in the contribution of the antagonist musculature to joint stiffness and reduction of laxity. The results also suggest that strength training of the hamstrings (rather than quadriceps) should be considered as a modality for conservative treatment of ACL deficiencies, as well as an adjunct to surgical reconstruction. Such training can also reduce the risk of high performance athletes in a reflexive manner by increasing joint stiffness.

AGE, EXERCISE AND THE MUSCULO‐SKELETAL SYSTEM

ABSTRACTA striking cultural feature of most of Western society is the expectation that the elderly will become progressively more sedentary, increasingly indolent and gradually more febrile until they are eventually unable to cope for themselves. There is the perception that old people do not need to exercise to any great extent, that exercise may be harmful to the elderly and that older people in exercise are most unattractive. Advertising emphasises that exercise is for the young and encourages a belief that the elderly should take life easily as reward for a lifetime's work.Research into musculo‐skeletal structure and performance has clearly shown the necessity for high levels of exercise activity through the whole life span. Inactivity is associated with a decline in muscle bulk, strength and endurance; an increase in joint stiffness and a decline in the individual's ability to respond to rapid environment change.All of the above changes are markedly improved by exercise, even in the very elderly. This paper discusses current research into the effect of ageing and exercise on the musculo‐skeletal system of the body, and demonstrates the necessity for continued high levels of physical activity into old age.

Contribution of the musculature to rotatory laxity and torsional stiffness at the knee

The relationships between the mean rectified EMG from two muscle groups crossing the knee joint and the rotational stiffness and laxity about the longitudinal axis of the lower leg were investigated. The EMG signals from three of the quadricep muscle group and two of the hamstring muscle group were monitored using surface electrodes. Each subject sustained self-induced muscle activity from specific muscle combinations while the foot was twisted internally and externally by the researcher. Joint rotation was measured using an electrogoniometer. Analyses of the data showed increased joint stiffness with increased numbers of active muscles. The stiffness measurements ranged from 0.16 to 2.54 Nm degree −1 depending upon the combination of active muscles. The stiffnesses measured in different tests were very repeatable with standard deviations ranging from 0.02 to 0.25 Nm degree −1. Increases in joint stiffness of over 400% by activation of these muscles were measured.

Biomechanical and biochemical changes in the periarticular connective tissue during contracture development in the immobilized rabbit knee.

The progressive rabbit knee joint stiffening resulting froin immobilization was studied using biomechanical and biochemical methods. Consistent trends of increase in joint stiffness and decrease in water and total hexosamine content in the periarticular connective tissue were seen as the time of immobilization increased. In addition, positive correlations were found between the total hexosamine loss and the biomechanical measurements in the contracture joints.The correlations demonstrated support of our hypothesis of periarticular connective tissue homeostasis. A cycle of events in which physiological joint forces and motion stimulate fibroblasts to synthesize proteoglycans, which in turn lubricate the collagen fiber interface and allow joints to move easily, is postulated and discussed. These biomechanical and biochemical data, which also detail the rate of contracture development, will provide the requisite basal values in the evaluation of prevention and treatment of experimental contractures by therap...

A study of the effect of cold on joint temperature and mobility.

Exposure to zero and subzero ambient temperatures results in a significant fall in joint temperature, where the knee joint of the cat was used as test object. The fall in rectal, muscle, and “average” skin temperatures for similar exposures is considerably less. Low joint temperature is associated with increased joint stiffness.