Adaptive changes in running kinematics as a function of head stability demands and their effect on shock transmission

This study aimed to identify adaptive changes in running kinematics and impact shock transmission as a function of head stability requirements. Fifteen strides from twelve recreational runners were collected during preferred speed treadmill running. Head stability demands were manipulated through real-time visual feedback that required head-gaze orientation to maintain within boxes of different sizes, ranging from 21° to 3° of visual angle with 3° decrements. The main outcome measures were tibial and head peak accelerations in the time and frequency domains (impact and active phases), shock transmission from tibia to head, stride parameters, and sagittal plane joint kinematics. Increasing head stability requirements resulted in decreases in the amplitude and integrated power of head acceleration during the active phase of stance. During the impact portion of stance tibial and head acceleration and shock transmission remained similar across visual conditions. In response to increased head stability requirements, participants increased stride frequency approximately 8% above preferred, as well as hip flexion angle at impact; stance time and knee and ankle joint angles at impact did not change. Changes in lower limb joint configurations (smaller hip extension and ankle plantar-flexion and greater knee flexion) occurred at toe-off and likely contributed to reducing the vertical displacement of the center of mass with increased head stability demands. These adaptive changes in the lower limb enabled runners to increase the time that voluntary control is allowed without embedding additional impact loadings, and therefore active control of the head orientation was facilitated in response to different visual task constraints.     

Orientation and location of the finite helical axis of the equine forelimb joints

To reduce anatomically unrealistic limb postures in a virtual musculoskeletal model of a horse's forelimb, accurate knowledge on forelimb joint constraints is essential. The aim of this cadaver study is to report all orientation and position changes of the finite helical axes (FHA) as a function of joint angle for different equine forelimb joints. Five horse cadaver forelimbs with standardized cuts at the midlevel of each segment were used. Bone pins with reflective marker triads were drilled into the forelimb bones. Unless joint angles were anatomically coupled, each joint was manually moved independently in all three rotational degrees of freedom (flexion–extension, abduction–adduction, internal–external rotation). The 3D coordinates of the marker triads were recorded using a six infra-red camera system. The FHA and its orientational and positional properties were calculated and expressed against joint angle over the entire range of motion using a finite helical axis method. When coupled, joint angles and FHA were expressed in function of flexion–extension angle. Flexion–extension movement was substantial in all forelimb joints, the shoulder allowed additional considerable motion in all three rotational degrees of freedoms. The position of the FHA was constant in the fetlock and elbow and a constant orientation of the FHA was found in the shoulder. Orientation and position changes of the FHA over the entire range of motion were observed in the carpus and the interphalangeal joints. We report FHA position and orientation changes as a function of flexion–extension angle to allow for inclusion in a musculoskeletal model of a horse to minimize calculation errors caused by incorrect location of the FHA.     

The effect of hamstring muscle compensation for anterior laxity in the ACL-deficient knee during gait

The hamstring muscles have been recognized as an important element in compensating for the loss of stability in the ACL-deficient knee, but it is still not clear whether the hamstring muscle force can completely compensate for the loss of ACL, and the consequences of increased hamstring muscle force. A two-dimensional anatomical knee model in the sagittal plane was developed to examine the effect of various levels of hamstring muscle activation on restraining anterior tibial translation in the ACL-deficient knee during level walking. The model included the tibiofemoral and patellofemoral joints, four major ligaments, the medial capsule, and five muscle units surrounding the knee. Simulations were conducted to determine anterior tibial translation and internal joint loading at a single selected position when the knee was under a peak external flexion moment during early stance phase of gait. Incremental hamstring muscle forces were applied to the modeled normal and the ACL-deficient knees. Results of simulations showed that the ACL injury increased the anterior tibial translation by 11.8mm, while 56% of the maximal hamstring muscle force could reduce the anterior translation of the tibia to a normal level during the stance phase of gait. The consequences of increased hamstring muscle force included increased quadriceps muscle force and joint contact force.     

Differences in tibial rotation during walking in ACL reconstructed and healthy contralateral knees

This study tested the hypotheses that in patients with a successful anterior cruciate ligament (ACL) reconstruction, the internal–external rotation, varus–valgus, and knee flexion position of reconstructed knees would be different from uninjured contralateral knees during walking. Twenty-six subjects with unilateral ACL reconstructions (avg 31 years, 1.7 m, 68 kg, 15 female, 24 months past reconstruction) and no other history of serious lower limb injury walked at a self-selected speed in the gait laboratory, with the uninjured contralateral knee as a matched control. Kinematic measurements of tibiofemoral motion were made using a previously-described point-cluster technique. Repeated-measures ANOVA (α=0.017) was used to compare ACL-reconstructed knees to their contralateral knees at four distinct points during the stance phase of walking. An offset towards external tibial rotation in ACL-reconstructed knees was maintained over all time points (95%CI 2.3±1.3°). Twenty-two out of twenty-six individuals experienced an average external tibial rotation offset throughout stance phase. Varus–valgus rotation and knee flexion were not significantly different between reconstructed and contralateral knees. These findings show that differences in tibial rotation during walking exist in ACL reconstructed knees compared to healthy contralateral knees, providing a potential explanation why these patients are at higher risk of knee osteoarthritis in the long-term.     

Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using 'interventional' MRI

The aim of this study was to image tibio-femoral movement during flexion in the living knee. Ten loaded male Caucasian knees were initially studied using MRI, and the relative tibio-femoral motions, through the full flexion arc in neutral tibial rotation, were measured. On knee flexion from hyperextension to 120 degrees , the lateral femoral condyle moved posteriorly 22 mm. From 120 degrees to full squatting there was another 10 mm of posterior translation, with the lateral femoral condyle appearing almost to sublux posteriorly. The medial femoral condyle demonstrated minimal posterior translation until 120 degrees . Thereafter, it moved 9 mm posteriorly to lie on the superior surface of the medial meniscal posterior horn. Thus, during flexion of the knee to 120 degrees , the femur rotated externally through an angle of 20 degrees . However, on flexion beyond 120 degrees , both femoral condyles moved posteriorly to a similar degree. The second part of this study investigated the effect of gender, side, load and longitudinal rotation. The pattern of relative tibio-femoral movement during knee flexion appears to be independent of gender and side. Femoral external rotation (or tibial internal rotation) occurs with knee flexion under loaded and unloaded conditions, but the magnitude of rotation is greater and occurs earlier on weight bearing. With flexion plus tibial internal rotation, the pattern of movement follows that in neutral. With flexion in tibial external rotation, the lateral femoral condyle adopts a more anterior position relative to the tibia and, particularly in the non-weight bearing knee, much of the femoral external rotation that occurs with flexion is reversed.     

Sensitivity of the knee joint kinematics calculation to selection of flexion axes

Various flexion axes have been used in the literature to describe knee joint kinematics. This study measured the passive knee kinematics of six cadaveric human knee specimens using two widely accepted flexion axes; transepicondylar axis and the geometric center axis. These two axes were found to form an angle of 4.0 degrees +/- 0.8 degrees. The tibial rotation calculated using the transepicondylar axis was significantly different than the rotation obtained using the geometric center axis for the same knee motion. At 90 degrees of flexion, the tibial rotation obtained using the transepicondylar axis was 4.8 degrees +/- 9.4 degrees whereas the rotation recorded using the geometric center axis at the same flexion angle was 13.8 degrees +/- 10.2 degrees. At 150 degrees of knee flexion, the rotations obtained from the transepicondylar and the geometric center axes were 7.2 degrees +/- 5.7 degrees and 19.9 degrees +/- 6.9 degrees, respectively. The data suggest that a clear definition of the flexion axis is necessary when reporting knee joint kinematics.     

In vitro measurement of the restraining role of the anterior cruciate ligament during walking and stair ascent

The study aimed to test the hypothesis that the restraining role of the anterior cruciate ligament (ACL) of the knee is significant during the activities of normal walking and stair ascent. The role of the ACL was determined from the effect of ACL excision on tibiofemoral displacement patterns measured in vitro for fresh-frozen knee specimens subjected to simulated knee kinetics of walking (n = 12) and stair ascent (n = 7). The knee kinetics were simulated using a newly developed dynamic simulator able to replicate the sagittal-plane knee kinetics with reasonable accuracy while ensuring unconstrained tibiofemoral kinematics. The displacements were measured using a calibrated six degree-of-freedom electromechanical goniometer. For the simulation of the walking cycle, two types of knee flexion/extension moment patterns were used: the more common "biphasic" pattern, and an extensor muscle force intensive pattern. For both of these patterns, the restraining role of the ACL to tibial anterior translation was found to be significant throughout the stance phase and in the terminal swing phase, when the knee angle was in the range of 4 degrees to 30 degrees. The effect of ACL excision was an increase in tibial anterior translation by 4 mm to 5 mm. For the stair ascent cycle, however, the restraining role of the ACL was significant only during the terminal stance phase, and not during the initial and middle segments of the phase. Although, in these segments, the knee moments were comparable to that in walking, the knee angle was in the range of 60 degrees to 70 degrees. These results have been shown to be consistent with available data on knee mechanics and ACL function measured under static loading conditions.     

Contributions of proximal and distal moments to axial tibial rotation during walking and running

The purpose of this study was to determine the cause and effect relationship between tibial internal rotation and pronation of the foot during walking and heel-toe running. This would allow predictions of orthotic effectiveness in reducing knee pain related to excessive internal tibial rotation. Kinematic and force plate data were collected from twenty subjects performing ten running and ten walking trials across a force plate. Using a least-squares algorithm, attitude matrices for each segment in each frame were obtained and the angular velocity vector of the tibia was calculated. The intersegmental moment at the ankle was calculated from ground reaction force and kinematic data, and the power flow from foot to tibia associated with axial tibial rotation was calculated. In walking, all subjects exhibited a clear power flow from tibia to foot during most of the stance phase, indicating that the foot was following the body. This suggests that the use of foot orthoses to reduce knee pain associated with tibial rotation during walking will not be successful. During running, power flow was also mainly proximal to distal, but there were brief periods of opposite power flow. There was more variability between subjects during running, with five subjects having large distal to proximal power flow peaks. These observations may explain and support previous work that has found variable clinical effects of orthoses between patients.     

A finite helical axis as a landmark for kinematic reference of the knee

Reference coordinates based on the finite helical axis for flexion of the knee from 0 to 90 deg are proposed. Six degree-of-freedom tracking allows the use of such a helical axis as a kinematic landmark for knee motion representation. Data from five human subjects in vivo are presented as a path of finite helical axes for flexion of the knee from 20 to 80 deg. The finite helical axis rotates by an average of 11.4 deg, the centrode translates an average of 19.8 mm, and the total axial translation averages 0.1 mm during flexion from 20 to 80 deg. Error due to the transducer was measured on a fixed-pivot pendulum and found to be 1.0 deg and 1.9 mm rms for the helical axis orientation and position, respectively, and 0.1 mm for the axial translation. Reproducibility and soft tissue effects on the measurements were repeatable to 4.0 deg and 2.7 mm rms in orientation and position, respectively, and 0.1 mm for the axial translations. Soft tissue errors averaged 4.9 deg and 3.6 mm in position and orientation, and 0.3 mm in the axial translations.     

Elucidation of a potentially destabilizing control strategy in ACL deficient non-copers.

PURPOSE: The purpose was to differentiate the dynamic knee stabilization strategies of potential copers (individuals who have the potential to compensate for the absence of an ACL without episodes of giving way after return to pre-injury activities) and non-copers (those who have knee instability following ACL rupture with return to pre-injury activities). METHODS: Twenty subjects with ACL rupture were assigned to potential coper (n=10) and non-coper (n=10) groups via a screening examination. Ten active people without lower extremity injury were also tested. Knee angle, tibial position and muscle activity data were collected while subjects stood in unilateral stance on a platform that moved horizontally in an anterior direction. Analysis included the preparation for platform movement; and monosynaptic, intermediate reflex and voluntary response intervals after platform movement. RESULTS: Non-copers showed greater knee flexion than uninjured subjects, and had a posterior tibial position and altered hamstring recruitment compared to the other groups. Potential copers demonstrated greater medial quadriceps activity while maintaining knee kinematics similar to uninjured subjects. Both potential copers and non-copers had greater co-contraction between medial hamstrings and quadriceps than uninjured subjects. All excitatory muscle activation occurred in the intermediate reflex interval. DISCUSSION AND CONCLUSIONS: Non-copers displayed aberrant muscle recruitment that may contribute to knee instability. Potential copers maintained normal tibial position using a strategy that permits quadriceps activation without excessive anterior tibial translation. Muscle recruitment in the intermediate reflex interval suggests neuromuscular training may influence the strategies.     

Partial medial meniscectomy and rotational differences at the knee during walking

Loss of meniscal function due to injury or partial meniscectomy is common and represents a significant risk factor for premature osteoarthritis. The menisci can influence the transverse plane movements (anterior–posterior (AP) translation and internal–external (IE) rotation) of the knee during walking. While walking is the most frequent activity of daily living, the kinematic differences at the knee during walking associated with the meniscal injury are not well understood. This study examined the influence of partial medial meniscectomy (PMM) on the kinematics and kinetics of the knee during the stance phase of gait by testing the differences in anterior–posterior translation, internal–external rotation, knee flexion range of movement, peak flexion/extension moments, and adduction moments between the PMM and healthy contralateral limbs. Ten patients (45±9 years old, height 1.75±0.06 m, weight 76.7±13.5 kg) who had undergone partial medial meniscectomy (33±100 months post-op) in one limb with a healthy contralateral limb were tested during normal walking. The contralateral limb was compared to a matched control group and no differences were found. The primary kinematic difference was a significantly greater external rotation (3.2°) of the tibia that existed through stance phase, with 8 of 10 subjects demonstrating the same pattern. The PMM subjects also exhibited significantly lower peak flexion and extension moments in their PMM limbs. The altered rotational position found likely results in changes of tibio-femoral contact during walking and could cause the type of degenerative changes found in the articular cartilage following meniscal injury.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 2: Analysis of Ligament Function

A three-dimensional model of the knee is used to study ligament function during anterior-posterior (a-p) draw, axial rotation, and isometric contractions of the extensor and flexor muscles. The geometry of the model bones is based on cadaver data. The contacting surfaces of the femur and tibia are modeled as deformable; those of the femur and patella are assumed to be rigid. Twelve elastic elements are used to describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit represented as a three-element muscle in series with tendon. The calculations show that the forces applied during a-p draw are substantially different from those applied by the muscles during activity. Principles of knee-ligament function based on the results of in vitro experiments may therefore be overstated. Knee-ligament forces during straight a-p draw are determined solely by the changing geometry of the ligaments relative to the bones: ACL force decreases with increasing flexion during anterior draw because the angle between the ACL and the tibial plateau decreases as knee flexion increases; PCL force increases with increasing flexion during posterior draw because the angle between the PCL and the tibial plateau increases. The pattern of ligament loading during activity is governed by the geometry of the muscles spanning the knee: the resultant force in the ACL during isometric knee extension is determined mainly by the changing orientation of the patellar tendon relative to the tibia in the sagittal plane; the resultant force in the PCL during isometric knee flexion is dominated by the angle at which the hamstrings meet the tibia in the sagittal plane.     

A Three-Dimensional Musculoskeletal Model of the Human Knee Joint. Part 2: Analysis of Ligament Function

A three-dimensional model of the knee is used to study ligament function during anterior-posterior (a-p) draw, axial rotation, and isometric contractions of the extensor and flexor muscles. The geometry of the model bones is based on cadaver data. The contacting surfaces of the femur and tibia are modeled as deformable; those of the femur and patella are assumed to be rigid. Twelve elastic elements are used to describe the geometry and mechanical properties of the cruciate ligaments, the collateral ligaments, and the posterior capsule. The model is actuated by thirteen musculotendinous units, each unit represented as a three-element muscle in series with tendon. The calculations show that the forces applied during a-p draw are substantially different from those applied by the muscles during activity. Principles of knee-ligament function based on the results of in vitro experiments may therefore be overstated. Knee-ligament forces during straight a-p draw are determined solely by the changing geometry of the ligaments relative to the bones: ACL force decreases with increasing flexion during anterior draw because the angle between the ACL and the tibial plateau decreases as knee flexion increases; PCL force increases with increasing flexion during posterior draw because the angle between the PCL and the tibial plateau increases. The pattern of ligament loading during activity is governed by the geometry of the muscles spanning the knee: the resultant force in the ACL during isometric knee extension is determined mainly by the changing orientation of the patellar tendon relative to the tibia in the sagittal plane; the resultant force in the PCL during isometric knee flexion is dominated by the angle at which the hamstrings meet the tibia in the sagittal plane.     

On the estimation of joint kinematics during gait.

In gait analysis, the concepts of Euler and helical (screw) angles are used to define the three-dimensional relative joint angular motion of lower extremities. Reliable estimation of joint angular motion depends on the accurate definition and construction of embedded axes within each body segment. In this paper, using sensitivity analysis, we quantify the effects of uncertainties in the definition and construction of embedded axes on the estimation of joint angular motion during gait. Using representative hip and knee motion data from normal subjects and cerebral palsy patients, the flexion-extension axis is analytically perturbed +/- 15 degrees in 5 degrees steps from a reference position, and the joint angles are recomputed for both Euler and helical angle definitions. For the Euler model, hip and knee flexion angles are relatively unaffected while the ab/adduction and rotation angles are significantly affected throughout the gait cycle. An error of 15 degrees in the definition of flexion-extension axis gives rise to maximum errors of 8 and 12 degrees for the ab/adduction angle, and 10-15 degrees for the rotation angles at the hip and knee, respectively. Furthermore, the magnitude of errors in ab/adduction and rotation angles are a function of the flexion angle. The errors for the ab/adduction angles increase with increasing flexion angle and for the rotation angle, decrease with increasing flexion angle. In cerebral palsy patients with flexed knee pattern of gait, this will result in distorted estimation of ab/adduction and rotation. For the helical model, similar results are obtained for the helical angle and associated direction cosines.(ABSTRACT TRUNCATED AT 250 WORDS)     

A method to quantify alteration of knee kinematics caused by changes of TKR positioning

Few in-vitro studies have investigated changes in kinematics caused by total knee replacement (TKR) implantation. The advent of surgical navigation systems allows implant position to be measured accurately and the effects of alteration of TKR position and alignment investigated. A test rig and protocol were developed to compare the kinematics of TKR-implanted knees for different femoral component positions. The TKR was implanted and the component positions documented using a navigation system. The quadriceps was tensed and the knees were flexed and extended manually. Torques and drawer forces were applied to the tibia during knee flexion–extension, while recording the kinematics with the navigation system. The implant was removed and replaced on an intramedullary fixation that allowed proximal–distal, and internal–external rotation of the femoral component without conducting a repeated arthrotomy on the knee. The implant was repositioned using the navigation system to reproduce the previously achieved normally navigated position and the kinematics were recorded again. The recorded kinematics of the knee were not significantly different between both normal implantation and intramedullary remounting for tibial internal–external rotation, varus–valgus angulation, or posterior drawer, at any angle of knee flexion examined. Anterior drawer was increased approximately 2.5 mm across the range 20–35° knee flexion (p<0.05), but was otherwise not significantly different. This method of navigating implant components and of moving them within the closed knee (thus avoiding artefactual effects of repeated soft tissue manipulations) can now be used to quantify the effect on kinematics of alteration of the position of the femoral component.     

In vivo kinematic evaluation and design considerations related to high flexion in total knee arthroplasty

In designing a posterior-stabilized total knee arthroplasty (TKA) it is preferable that when the cam engages the tibial spine the contact point of the cam move down the tibial spine. This provides greater stability in flexion by creating a greater jump distance and reduces the stress on the tibial spine. In order to eliminate edge loading of the femoral component on the posterior tibial articular surface, the posterior femoral condyles need to be extended. This provides an ideal femoral contact with the tibial articular surface during high flexion angles. To reduce extensor mechanism impingement in deep flexion, the anterior margin of the tibial articular component should be recessed. This provides clearance for the patella and patella tendon. An in vivo kinematic analysis that determined three dimensional motions of the femorotibial joint was performed during a deep knee bend using fluoroscopy for 20 subjects having a TKA designed for deep flexion. The average weight-bearing range-of-motion was 125 degrees . On average, TKA subjects experienced 4.9 degrees of normal axial rotation and all subjects experienced at least -4.4 mm of posterior femoral rollback. It is assumed that femorotibial kinematics can play a major role in patellofemoral kinematics. In this study, subjects implanted with a high-flexion TKA design experienced kinematic patterns that were similar to the normal knee. It can be hypothesized that forces acting on the patella were not substantially increased for TKA subjects compared with the normal subjects.     

In vivo assessment of the interaction of patellar tendon tibial shaft angle and anterior cruciate ligament elongation during flexion

A potential cause of non-contact anterior cruciate ligament (ACL) injury is landing on an extended knee. In line with this hypothesis, studies have shown that the ACL is elongated with decreasing knee flexion angle. Furthermore, at low flexion angles the patellar tendon is oriented to increase the anterior shear component of force acting on the tibia. This indicates that knee extension represents a position in which the ACL is taut, and thus may have an increased propensity for injury, particularly in the presence of excessive force acting via the patellar tendon. However, there is very little in vivo data to describe how patellar tendon orientation and ACL elongation interact during flexion. Therefore, this study measured the patellar tendon tibial shaft angle (indicative of the relative magnitude of the shear component of force acting via the patellar tendon) and ACL length in vivo as subjects performed a quasi-static lunge at varying knee flexion angles. Spearman rho rank correlations within each individual revealed that flexion angles were inversely correlated to both ACL length (rho = −0.94 ± 0.07, mean ± standard deviation, p < 0.05) and patellar tendon tibial shaft angle (rho = −0.99 ± 0.01, p < 0.05). These findings indicate that when the knee is extended, the ACL is both elongated and the patellar tendon tibial shaft angle is increased, resulting in a relative increase in anterior shear force on the tibia acting via the patellar tendon. Therefore, these data support the hypothesis that landing with the knee in extension is a high risk scenario for ACL injury.     

Resultant lower extremity joint moments in below-knee amputees during running stance

Resultant flexion/extension lower extremity joint moments of four below-knee amputees running between 2.5 and 5.7 m s-1 were computed during stance on their intact and prosthetic limbs. All subjects wore patellar tendon-bearing prostheses with either a SACH or Greissinger foot component. During stance on the prosthesis, the resultant hip extensor moment on the amputated side was greater in magnitude and duration than its counterpart on the intact limb during its corresponding stance period. Since the artificial foot was planted on the ground, such a moment may help control knee flexion and promote knee extension of the residual limb. For the three subjects whose knees continued to flex at the beginning of stance, there was a dominant extensor moment about the knee joint during stance on the prosthesis. By contrast, for the fourth subject whose knee remained straight or hyperextended throughout stance on the prosthesis, a flexor moment was dominant.     

The effect of patella taping on vastus medialis oblique and vastus laterialis EMG activity and knee kinematic variables during stair descent

The purpose of this study was to evaluate the effect of patella taping in normal subjects. Previous work has established positive effects of patella taping on patellofemoral pain syndrome patients, but the mode of action remains unclear. It has been hypothesized that taping brings about subtle changes in the internal physiological environment of the joint. It could be expected that in normal joints taping would bring about a measurable change in function, as the joint is no longer operating in an optimal physiological environment. 10 normal female subject’s (21.4 ± 1.2 years) vastus medialis oblique (VMO) and vastus laterialis (VL) EMG activity and knee kinematics (peak stance flexion angle and angular velocity) were assessed during a step descent, with and without a taped patella. The effect of taping was to significantly decrease VMO and VL EMG activity. Taping also significantly reduced peak stance phase knee flexion and peak stance phase knee flexion angular velocity. In normal asymptomatic subjects patella taping created a situation in which their performance was changed to one similar to that of the pathological patellofemoral pain syndrome population. It would appear that taping caused the joint to function sub-optimally supporting the hypothesis that taping could change the functioning of the patellofemoral joint.