Ronald F. Zernicke

Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions

Virtually all types of collagenous tissues have been transferred in and around the knee joint for intra-articular and extra-articular ligament reconstructions. However, the mechanical properties (in particular, strength) of such grafts have not been determined in tissues from young adult donors, where age and disuse-related effects have been excluded. To provide this information, we subjected ligament graft tissues to high-strain-rate failure tests to determine their strength and elongation properties. The results were compared with the mechanical properties of anterior cruciate ligaments from a similar young-adult donor population. The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces. Grafts utilizing prepatellar retinacular tissues (as in certain anterior-cruciate reconstructions) and others in which a somewhat narrow width of fascia lata or distal iliotibial tract is utilized are included in this at-risk group. Wider grafts from the iliotibial tract or fascia lata would of course proportionally increase ultimate strength. The semitendinosus and gracilis tendons are stronger, having 70 and 49 per cent, respectively, of the initial strength of anterior cruciate ligaments. The bone-patellar tendon-bone graft (fourteen to fifteen millimeters wide, medial or central portion) was the strongest, with a mean strength of 159 to 168 per cent of that of anterior cruciate ligaments. Patellar tendon-bone units, based on grip-to-grip motions, were found to be three to four times stiffer than similarly gripped anterior cruciate ligaments, while gracilis and semitendinosus tendon preparations had values that were nearly identical to those of anterior cruciate ligaments.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for generalized motor programs using gait pattern analysis.

Human intra limb gait kinematics were analyzed via statistical and structural pattern recognition methods to determine the role of relative timing of limb segments within and between modes of gait. Five experienced runners were filmed while walking (3-6 km/hour) and running (8-12 km/hour) on a motor driven treadmill. Kinematic data consisted of relative timing of the four phases of the Philippson step cycle and intersegmental limb trajectories, determined from angle-angle diagrams. Despite marked decreases in absolute time durations within gaits remained constant over the speeds which were studied. Although a 2-fold increase in locomotor speed occurred in walking and a 1.5-fold speed increase occurred within running, the percentage of time spent in each of the Philippson phases was not significantly changed. However, significant differences in the time percentages and sequences of the step cycle phases were found between walking and running. Correlations between limb segment trajectories occurring in the different gaits showed strong coherence for overall step cycle patterns, but within step cycle phases and across speeds, selective phases displayed little correspondence.

Changes in limb dynamics during the practice of rapid arm movements

In our study we examined Bernsteins hypothesis that practice alters the motor coordination among the muscular and passive joint moments. In particular, we conducted dynamical analyses of a human multisegmental movement during the practice of a task involving the upper extremity. Seven male human volunteers performed maximal-speed, unrestrained vertical arm movements whose upward and downward trajectories between two target endpoints required the hand to round a barrier, resulting in complex shoulder, elbow, and wrist joint movements. These movements were recorded by high-speed ciné film, and myopotentials from selected upper-extremity muscles were recorded. The arm was modeled as interconnected rigid bodies, so that dynamical interactions among the upper arm, forearm, and hand could be calculated. With practice, subjects achieved significantly shorter movement times. As movement times decreased, all joint-moment components (except gravity) increased, and the moment-time and EMG profiles were changed significantly. Particularly during reversals in movement direction, the changes in moment-time and EMG profiles were consistent with Bernsteins hypothesis relating practice effects and intralimb coordination: with practice, motor coordination was altered so that individuals employed reactive phenomena in such a way as to use muscular moments to counterbalance passive-interactive moments created by segment movements.

Strain Gradients Correlate with Sites of Exercise‐Induced Bone‐Forming Surfaces in the Adult Skeleton

Physical activity is capable of increasing adult bone mass. The specific osteogenic component of the mechanical stimulus is, however, unknown. Using an exogenous loading model, it was recently reported that circumferential gradients of longitudinal normal strain are strongly associated with the specific sites of periosteal bone formation. Here, we used high‐speed running to test this proposed relation in an exercise model of bone adaptation. The strain environment generated during running in a mid‐diaphyseal tarsometatarsal section was determined from triple‐rosette strain gages in six adult roosters (>1 year). A second group of roosters was run at a high speed (1500 loading cycles/day) on a treadmill for 3 weeks. Periosteal surfaces were activated in five out of eight animals. Mechanical parameters as well as periosteal activation (as measured by incorporated fluorescent labels) were quantified site‐specifically in 12 30° sectors subdividing a mid‐diaphyseal section. The amount of periosteal mineralizing surface per sector correlated strongly (R2 = 0.63) with the induced peak circumferential strain gradients. Conversely, peak strain magnitude and peak strain rate were only weakly associated with the sites of periosteal activation. The unique feature of this study is that a specific mechanical stimulus (peak circumferential strain gradients) was successfully correlated with specific sites of periosteal bone activation induced in a noninvasive bone adaptation model. The knowledge of this mechanical parameter may help to design exercise regimens that are able to deposit bone at sites where increased structural strength is most needed.

Modulation of limb dynamics in the swing phase of locomotion

Abstract A method was presented for quantifying cat (Felis catus) hind limb dynamics during swing phase of locomotion using a two-link rigid body model of leg and paw, which highlighted the dynamic interactions between segments. Comprehensive determination was made of cat segment parameters necessary for dynamic analysis, and regression equations were formulted to predict the inertial parameters of any comparable cat. Modulations in muscle and non-muscle components of knee and ankle joint moments were examined at two treadmill speeds using three gaits: (a) pace-like walk and trot-like walk, at 1.0 m s−1, and (b) gallop, at 2.1 m s−1. Results showed that muscle and segment interactive moments significantly effected limb trajectories during swing. Some moment components were greater in galloping than in walking, but net joint maxima were not significantly different between speeds. Moment magnitudes typically were greater for pace-like walking than for trot-like walking at the same speed. Generally, across gaits, the net and muscle moments were in phase with the direction of distal joint motion, and these same moments were out of phase with proximal joint motion. Intersegmental dynamics were not modulated exclusively by speed of locomotion, but interactive moments were also influenced significantly by gait mode.

Human patellar-tendon rupture

The first biomechanical analysis of a human patellar-tendon rupture during actual sports competition is reported. Cinematographic data for analysis were collected at a national weight-lifting championship. Dynamic equations to mathematically model the lifter were developed to compute time course and magnitudes of hip, knee and ankle-joint moments of force and of tensile loading of the patellar tendon before and during tendon trauma. Results provided evidence that the range of maximum tensile stress of the tendon may be considerably greater during rapid dynamic loading conditions, as in many sports situations, than maximum tensile stress obtained during static test conditions.

Knee joint dynamics predict patellar tendinitis in elite volleyball players

We quantified the lower extremity dynamics developed during the volleyball spike and block jumps to find out if predictive relations exist between jump dynamics and patellar tendinitis. Lower extremity movement biome chanics were analyzed for 10 members of the 1994 Canadian Mens National Volleyball Team (all right- handed hitters). Based on physical examination, 3 of the 10 players had patellar tendon pain associated with patellar tendinitis at the time of testing. In masked biomechanical and logistic regression analyses, we discovered that the vertical ground-reaction force dur ing the take-off phase of both spike and block jumps was a significant predictor of patellar tendinitis—cor rectly predicting the presence or absence of patellar tendinitis in 8 of 10 players. Deepest knee flexion angle (during landing from the spike jump) predicted 10 of 10 cases correctly for the left knee. The external tibial torsional moment (during the takeoff for the right knee with the spike jump and for the left knee with the block jump) was also a significant predictor of tendinitis. In these players, the likelihood of patellar tendon pain was significantly related to high forces and rates of loading in the knee extensor mechanism, combined with large external tibial torsional moments and deep knee flexion angles.

Understanding movement control in infants through the analysis of limb intersegmental dynamics

One important component in the understanding of the control of limb movements is the way in which the central nervous system accounts for joint forces and torques that may be generated not only by muscle actions but by gravity and by passive reactions related to the movements of limb segments. In this study, we asked how the neuromotor system of young infants controls a range of active and passive forces to produce a stereotypic, nonintentional movement. We specifically analyzed limb intersegmental dynamics in spontaneous, cyclic leg movements (kicking) of varying intensity in supine 3-month-old human infants. Using inverse dynamics, we calculated the contributions of active (muscular) and passive (motion-dependent and gravitational) torque components at the hip, knee, and ankle joints from three-dimensional limb kinematics. To calculate joint torques, accurate estimates were needed of the limbs anthropometric parameters, which we determined using a model of the human body. Our analysis of limb intersegmental dynamics explicitly quantified the complex interplay of active and passive forces producing the simple, involuntary kicking movements commonly seen in 3-month-old infants. our results revealed that in nonvigorous kicks, hip joint reversal was the result of an extensor torque due to gravity, opposed by the combined flexor effect of the muscle torque and the total motion-dependent torque. The total motion-dependent torque increased as a hip flexor torque in more vigorous kicks; an extensor muscle torque was necessary to counteract the flexor influences of the total motion-dependent torque and, in the case of large ranges of motion, a flexor gravity torque as well. Thus, with changing passive torque influences due to motions of the linked segments, the muscle torques were adjusted to produce a net torque to reverse the kicking motion. As a consequence, despite considerable heterogeneity in the intensity, range of motion, coordination, and movement context of each kick, smooth trajectories resulted from the muscle torque, counteracting and complementing not only gravity but also the motion-dependent torques generated by movement of the linked segments.

Predictions for neural control based on limb dynamics

Abstract Knowledge of limb dynamics and joint torques can provide unique predictions about neural mechanisms responsible for the control of limb motions. During unrestrained limb movements, mechanical interactions between articulated limb segments can significantly influence the resultant limb trajectories. To appreciate this mechanical complexity, quantitative modelling is necessary to determine how joint torques are affected by both muscle contractions and interactive forces between limb segments. Examples from non-weight-bearing, stereotypic movements of the cat hindlimb show that muscle contractions can either cause movements or counteract torques arising from mechanical interactions between segments. When interactive torques are substantial, motion-dependent feedback can monitor changes in the limb dynamics. Supraspinal centers, therefore, do not necessarily have to preplan compensatory muscular actions, and feedback at spinal segments allows for neural adaptation of the on-going limb dynamics.

The role of intersegmental dynamics during rapid limb oscillations

The interactive dynamic effects of muscular, inertial and gravitational moments on rapid, multi-segmented limb oscillations were studied. Using three-segment, rigid-body equations of motion, hip, knee and ankle intersegmental dynamics were calculated for the steady-state cycles of the paw-shake response in adult spinal cats. Hindlimb trajectories were filmed to obtain segmental kinematics, and myopotentials of flexors and extensors at each of the three joints were recorded synchronously with the ciné film. The segmental oscillations that emerged during the paw-shake response were a consequence of an interplay between active and passive musculotendinous forces, inertial forces, and gravity. During steady-state oscillations, the amplitudes of joint excursions, peak angular velocities, and peak angular accelerations increased monotonically and significantly in magnitude from the proximal joint (hip) to the most distal joint (ankle). In contrast to these kinematic relationships, the maximal values of net moments at the hip and knee were equal in magnitude, but of significantly lower magnitude than the large net moment at the ankle joint. At both the ankle and the knee, the flexor and extensor muscle moments were equal, but at the hip the magnitude of the peak flexor muscle moment was significantly greater than the extensor muscle moment. Muscle moments at the hip not only acted to counterbalance accelerations of the more distal segments, but also acted to maintain the postural orientation of the hindlimb. Large muscle moments at the knee functioned to counterbalance the large inertial moments generated by the large angular accelerations of the paw. At the ankle, the muscle moments dominated the generation of the paw accelerations. At the ankle and the knee, muscle moments controlled limb dynamics by slowing and reversing joint motions, and the active muscle forces contributing to ankle and knee moments were derived from lengthening of active musculotendinous units. In contrast to the more distal joints, the active muscles crossing the hip predominantly shortened as a result of the interplay among inertial forces and gravitational moments. The muscle function and kinetic data explain key features of the complex interactions that occur between central control mechanisms and multi-segmented, oscillating limb segments during the paw-shake response.