PubMed · 7437622
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A W Lettin. 1980. Total joint replacement.. https://pubmed.ncbi.nlm.nih.gov/7437622/
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The mechanical impedance of the ankle joint was estimated in two conditions: during submaximal surface electrical stimulation of the soleus muscle, and with no stimulation applied. Both neurologically intact (n = 5) and spinal cord injured subjects (n = 4) were used. The mechanical impedance was measured by applying angular step and constant velocity (13-100 degrees s-1) perturbations at 10 degrees to the ankle and measuring the resulting changes in torque. A five-element lumped model consisting of an inertial element, a parallel elastic element, and an elastic element in series with a viscous element and a pure tension generator produced a good fit for predicting the compliance characteristics of the ankle for both the relaxed and stimulated conditions. The elastic elements were piecewise linear with different values for the dorsiflexion and plantarflexion directions. The viscous element was velocity-dependent and it decreased in value as the velocity increased. The average torque error between the measured and model's response during soleus stimulation was 10.56% for the dorsiflexed and 11.93% for the plantarflexed perturbations. However, the average error was skewed by several subjects who had excessive error, due to volitional intervention or flexor withdrawal reflex. The average model error for the perturbations without stimulation was 7.12% for dorsiflexed and 5.58% for plantarflexed perturbations.
Incorporation of physiologic muscle tensions to simulate normal in vivo joint loading in cadaveric biomechanical studies has been a challenging problem, especially about the knee, foot, and shoulder. Simulation of muscle contraction requires attachment of tension producing devices to musculotendinous units. To this end, we modified the 'cryo-jaw' device, first described by Riemersma and Schamhardt (1982, J. Biomechanics 15, 619-620) to couple linear actuators to fresh cadaver tendons. These clamps were used in the simulation of 11 different muscles in laboratory investigations of shoulder, elbow, knee, and foot function. The clamps were able to transmit repetitively 3500 N of quadriceps force in eight knees and 2000 N of Achilles force in 11 feet. Overall success rate was 95%.
When the nervous system produces a multi-joint movement it must select a unique set of motor patterns for movement production from a variety of appropriate motor pattern solutions: this is the so-called degrees-of-freedom problem. One strategy which the nervous system could use to simplify the selection of a unique set of motor patterns (i.e. net muscle moments) for movement production would be to constrain the relationships between the net muscle moments of the various joints. Therefore, we addressed the following question: Do the inter-joint relationships of muscle moments and powers become more phase-locked during the acquisition of a novel multi-joint movement. Subjects performed 16 blocks (16 trials per block) of a discrete kicking movement, which involved motion of the hip, knee, and ankle--a weight (1.674 kg) attached to the subject's foot increased movement novelty. Subjects attempted to perform all movements as close as possible to a goal movement time of 400 ms, while maintaining spatial accuracy. An optoelectric imaging system was used to record movement kinematics for the hip, knee, ankle, and toe of the kicking leg, and inverse dynamics were then used to obtain net-muscle-moment profiles. Following learning, inter-joint moments became more closely phase-locked, with hip-flexor and knee-extensor moments being produced simultaneously, as were hip-extensor and knee-flexor moments. This increased phase-locking of inter-joint moment relationships with learning resulted in increased phase-locking of inter-joint power relationships.(ABSTRACT TRUNCATED AT 250 WORDS)