Surface movement errors in shank kinematics and knee kinetics during gait

The movement of surface mounted targets (SMT) on a shell at the mid-shank and of bone mounted targets attached to the distal shank using a Percutaneous Skeletal Tracker (PST) were simultaneously measured during free-speed walking of three adult subjects having different body types. Surface movement errors in shank kinematic estimates were determined by expressing the segmental motion derived from the SMT relative to the PST-based segment coordinate system (SCS) located at the segment center of gravity. The greatest errors were along and around the shank longitudinal axis, with peak magnitudes of 10 mm of translation and 8° of rotation in one subject. Estimates of knee joint center locations differed by less than 11 mm in each SCS direction. Differences in estimates of net knee joint forces and moments were most prominent during stance phase, with magnitudes up to 39 N in the shank mediolateral direction and 9 N.m about the mediolateral axis. The differences in kinetics were primarily related to the effect of segment position and orientation on the expression of joint forces and on the magnitude and expression of joint moments.     

Effect of compressive follower preload on the flexion-extension response of the human lumbar spine.

Traditional experimental methods are unable to study the kinematics of whole lumbar spine specimens under physiologic compressive preloads because the spine without active musculature buckles under just 120 N of vertical load. However, the lumbar spine can support a compressive load of physiologic magnitude (up to 1200 N) without collapsing if the load is applied along a follower load path. This study tested the hypothesis that the load-displacement response of the lumbar spine in flexion-extension is affected by the magnitude of the follower preload and the follower preload path. Twenty-one fresh human cadaveric lumbar spines were tested in flexion-extension under increasing compressive follower preload applied along two distinctly different optimized preload paths. The first (neutral) preload path was considered optimum if the specimen underwent the least angular change in its lordosis when the full range of preload (0-1200 N) was applied in its neutral posture. The second (flexed) preload path was optimized for an intermediate specimen posture between neutral and full flexion. A twofold increase in flexion stiffness occurred around the neutral posture as the preload was increased from 0 to 1200 N. The preload magnitude (400 N and larger) significantly affected the range of motion (ROM), with a 25% decrease at 1200 N preload applied along the neutral path. When the preload was applied along a path optimized for an intermediate forward-flexed posture, only a 15% decrease in ROM occurred at 1200 N. The results demonstrate that whole lumbar spine specimens can be subjected to compressive follower preloads of in vivo magnitudes while allowing physiologic mobility under flexion-extension moments. The optimized follower preload provides a method to simulate the resultant vector of the muscles that allow the spine to support physiologic compressive loads induced during flexion-extension activities.     

Excursion of the flexor digitorum profundus tendon: a kinematic study of the human and canine digits

The most common problem following primary flexor tendon repair is the failure of the tendon apparatus to glide, secondary to the formation of adhesions. Early motion following tendon repair has been shown to be effective in reducing adhesions between the tendon and the surrounding sheath. Therefore, it is important to determine the amount of flexor tendon excursion along the digit during joint motion. In this study, the excursion between the flexor digitorum profundus (FDP) tendon and the sheath was examined in both human and canine digits. Based on roentgenographic measurements and joint kinematic analysis, the motion of the bones, the FDP tendon, and the sheath were measured with respect to joint rotations. It was found that the canine flexor tendon apparatus behaved similarly to that of the human for the motions studied. The amount of tendon excursion was very small in regions distal to the joint in motion (approximately 0.1 mm/10 degrees of joint rotation). There was little displacement of the sheath (0.2-0.3 mm), except at the metacarpal joint region during metacarpophalangeal (MCP) joint motion and at the proximal interphalangeal (PIP) joint region during PIP joint motion. Tendon excursion relative to the tendon sheath was the largest in zone II during PIP joint rotation (1.7 mm/10 degrees of joint rotation). These results suggest that PIP joint motion may be most effective in reducing adhesions following tendon repair in zone II.     

Recovery of locomotion after chronic spinalization in the adult cat

Cats were spinalized (T13) as adults and were trained to walk with the hindlimbs on a treadmill. After 3 weeks to 3 months and up to 1 year depending on the animal, all were capable of walking on the plantar surface of the feet and support the weight of the hindquarters. Interactive training appeared to accelerate the recovery of locomotion and maintain smooth locomotor movements. Despite the obvious loss of voluntary control and equilibrium which the experimenter partially compensated for by maintaining the thorax and/or the tail, the cats could walk with a regular rhythm and a well-coordinated hindlimb alternation at speeds of 0.1-1.2 m/s. Cycle duration as well as stance and swing duration resembled those of normal cats at comparable speeds. The range of angular motion was also similar to that observed in intact cats as was the coupling between different joints. The EMG activity of the hindlimb and lumbar axial muscles also retained the characteristics observed in the intact animal. Some deficits such as a dragging of the foot in early swing and diminution of the angular excursion in the knee were seen at later stages. Thus, the adult spinal cat preparation is considered as a useful model to study the influence of different types of training and of different drugs or other treatments in the process of locomotor recovery after injury to the spinal cord.     

Comparison of the biomechanical effect of posterior condylar offset and kinematics between posterior cruciate-retaining and posterior-stabilized total knee arthroplasty

Background

The effect of the changes in the femoral posterior condylar offset (PCO) on anterior–posterior (AP) translation and internal–external (IE) rotation in cruciate-retaining (CR) and posterior-stabilized (PS) total knee arthroplasty (TKA) remains unknown. The purpose of this study was to compare the kinematics in CR and PS TKA with respect to the difference in prosthetic design and PCO change through a computational simulation.

Deceleration affects anticipatory and reactive components of triggered postural responses

Understanding the physiological and psychological factors that contribute to healthy and pathological balance control in man has been made difficult by the confounding effects of the perturbations used to test balance reactions. The present study examined how postural responses were influenced by the acceleration–deceleration interval of an unexpected horizontal translation. Twelve adult males maintained balance during unexpected forward and backward surface translations with two different acceleration–deceleration intervals and presentation orders (serial or random). “SHORT” perturbations consisted of an initial acceleration (peak acceleration 1.3 m s⁻²; duration 300 ms) followed 100 ms later by a deceleration. “LONG” perturbations had the same acceleration as SHORT perturbations, followed by a 2-s interval of constant velocity before deceleration. Surface and intra-muscular electromyography (EMG) from the leg, trunk, and shoulder muscles were recorded along with motion and force plate data. LONG perturbations induced larger trunk displacements compared to SHORT perturbations when presented randomly and larger EMG responses in proximal and distal muscles during later (500–800 ms) response intervals. During SHORT perturbations, activity in some antagonist muscles was found to be associated with deceleration and not the initial acceleration of the support surface. When predictable, SHORT perturbations facilitated the use of anticipatory mechanisms to attenuate early (100–400 ms) EMG response amplitudes, ankle torque change and trunk displacement. In contrast, LONG perturbations, without an early deceleration effect, did not facilitate anticipatory changes when presented in a predictable order. Therefore, perturbations with a short acceleration–deceleration interval can influence triggered postural responses through reactive effects and, when predictable with repeated exposure, through anticipatory mechanisms.     

Coordination of multiple muscles in two degree of freedom elbow movements

The present study quantifies electromyographic (EMG) magnitude, timing, and duration in one and two degree of freedom elbow movements involving combinations of flexion-extension and pronation-supination. The aim is to understand the organization of commands subserving motion in individual and multiple degrees of freedom. The muscles tested in this study fell into two categories with respect to agonist burst magnitude: those whose burst magnitude varied with motion in a second degree of freedom at the elbow, and those whose burst magnitude depended on motion in one degree of freedom only. In multiarticular muscles contributing to motion in two degrees of freedom at the elbow, we found that the magnitude of the agonist burst was greatest for movements in which a muscle acted as agonist in both degrees of freedom. The burst magnitudes for one degree of freedom movements were, in turn, greater than for movements in which the muscle was agonist in one degree of freedom and antagonist in the other. It was also found that, for movements in which a muscle acted as agonist in two degrees of freedom, the burst magnitude was, in the majority of cases, not different from the sum of the burst magnitudes in the component movements. When differences occurred, the burst magnitude for the combined movement was greater than the sum of the components. Other measures of EMG activity such as burst onset time and duration were not found to vary in a systematic manner with motion in these two degrees of freedom. It was also seen that several muscles which produced motion in one degree of freedom at the elbow, including triceps brachii (long head), triceps brachii (lateral head), and pronator quadratus displayed first agonist bursts whose magnitude did not vary with motion in a second degree of freedom. However, for the monoarticular elbow flexors brachialis and brachioradialis, agonist burst magnitude was affected by pronation or supination. Lastly, it was observed that during elbow movements in which muscles acted as agonist in one degree of freedom and antagonist in the other, the muscle activity often displayed both agonist and antagonist components in the same movement. It was found that, for pronator teres and biceps brachii, the timing of the bursts was such that there was activity in these muscles concurrent with activity in both pure agonists and pure antagonists. The empirical summation of EMG burst magnitudes and the presence in a single muscle of both agonist and antagonist bursts within a movement suggest that central commands associated with motion in individual degrees of freedom at the elbow may be superimposed to produce elbow movements in two degrees of freedom.     

Compartmental Analysis of Breathing in the Supine and Prone Positions by Optoelectronic Plethysmography

Optoelectronic plethysmography (OEP) has been shown to be a reliable method for the analysis of chest wall kinematics partitioned into pulmonary rib cage, abdominal rib cage, abdomen, and right and left side in the seated and erect positions. In this paper, we extended the applicability of this method to the supine and prone positions, typically adopted in critically ill patients. For this purpose we have first developed proper geometrical and mathematical models of the chest wall which are able to provide consistent and reliable estimations of total and compartmental volume variations in these positions suitable for clinical settings. Then we compared chest wall (CW) volume changes computed from OEP( V _CW) with lung volume changes measured with a water seal spirometer (SP) ( V _SP)in 10 normal subjects during quiet (QB) and deep (DB) breathing on rigid and soft supports. We found that on a rigid support the average differences between V _SP and V _CW were –4.2% ± 6.2%, –3.0% ± 6.1%, –1.7% ±7.0%, and –4.5% ± 9.8%, respectively, during supine/QB, supine/DB, prone/QB, and prone/DB. On the soft surface we obtained –0.1% ± 6.0%, –1.8% ± 7.8%, 18.0% ± 11.7%, and 10.2% ± 9.6%, respectively. On rigid support and QB, the abdominal compartment contributed most of the V _CW in the supine (63.1% ± 11.4%) and prone (53.5% ± 13.1%) positions. V _CW was equally distributed between right and left sides. In the prone position we found a different chest wall volume distribution between pulmonary and abdominal rib cage (22.1% ± 8.6% and 24.4% ± 6.8, respectively) compared with the supine position (23.3% ± 9.3% and 13.6% ± 3.0%). © 2001 Biomedical Engineering Society. PAC01: 8763Lk, 8719Uv     

Patterns of coordinated multi-joint movement

In multi-joint reaching movements, the motor system may choose any one of an infinite set of possible joint rotations to move the hand between given start and target positions. In order to find out whether reaching movements are represented in Cartesian hand coordinates or in joint coordinates, it is necessary to measure whether hand paths or joint paths have lower variability. We have measured hand paths and rotations of shoulder, elbow and wrist joints simultaneously in five subjects reaching in four orientations in the horizontal plane. As in earlier studies, we found a preference for nearly straight hand paths, despite different patterns of joint rotation for different orientations of movement. However, movements in three of four orientations showed a single principal joint, which rotated essentially without reversals. This may reflect optimisation in the motor system, preferring the simplest pattern of joint control for a desired hand path. We used generalised Procrustes analysis to quantify the variability in shape of repeated paths in hand space and joint space. Results showed that hand paths were less variable than the joint angles used to realise them, due to the kinematic redundancy of the limb, suggesting that hand paths, rather than joint angles, are directly represented by the motor system. Nevertheless, movements with straighter hand paths, on average, and those requiring coordinated activity at both shoulder and elbow joints also showed more variability in the shape of the hand path. Other orientations such as movement across the body use primarily a single joint and are less variable at the cost of a slightly curved path. These results suggest that coordinating multiple joints to produce a straight hand path has a definite computational cost. The motor system may perform a trade-off between the benefits of planning reaching movements as straight hand paths and the computational simplicity of executing them using patterns of joint rotation which simplify multi-joint coordination.