An approach to generate noncontact ACL-injury prone situations on a computer using kinematic data of non-injury situations and Monte Carlo simulation.

ACL-injuries are one of the most common knee injuries in noncontact sports. Kinematic data of injury prone situations provide important information to study the underlying ACL-injury mechanisms. However, these data are rare. In this work an approach is presented to generate injury prone situations for noncontact ACL-injuries on a computer. The injury prone situations are generated by a musculoskeletal simulation model using kinematic data of a non-injury situation and the method of Monte Carlo simulation. The approach is successfully applied to generate injury prone landings in downhill ski racing. The characteristics of the obtained injury prone landings are consistent with video recordings of injury cases.

Relationship between jump landing kinematics and peak ACL force during a jump in downhill skiing: a simulation study.

Recent data highlight that competitive skiers face a high risk of injuries especially during off-balance jump landing maneuvers in downhill skiing. The purpose of the present study was to develop a musculo-skeletal modeling and simulation approach to investigate the cause-and-effect relationship between a perturbed landing position, i.e., joint angles and trunk orientation, and the peak force in the anterior cruciate ligament (ACL) during jump landing. A two-dimensional musculo-skeletal model was developed and a baseline simulation was obtained reproducing measurement data of a reference landing movement. Based on the baseline simulation, a series of perturbed landing simulations (n = 1000) was generated. Multiple linear regression was performed to determine a relationship between peak ACL force and the perturbed landing posture. Increased backward lean, hip flexion, knee extension, and ankle dorsiflexion as well as an asymmetric position were related to higher peak ACL forces during jump landing. The orientation of the trunk of the skier was identified as the most important predictor accounting for 60% of the variance of the peak ACL force in the simulations. Teaching of tactical decisions and the inclusion of exercise regimens in ACL injury prevention programs to improve trunk control during landing motions in downhill skiing was concluded.

Impingement and stability of total hip arthroplasty versus femoral head resurfacing using a cadaveric robotics model.

We identified and compared the impingent-free range of motion (ROM) and subluxation potential for native hip, femoral head resurfacing (FHR), and total hip arthroplasty (THA). These constructs were also compared both with and without soft tissue to elucidate the role of the soft tissue. Five fresh-frozen bilateral hip specimens were mounted to a six-degree of freedom robotic manipulator. Under load-control parameters, in vivo mechanics were recreated to evaluate impingement free ROM, and the subluxation potential in two "at risk" positions for native hip, FHR, and THA. Impingement-free ROM of the skeletonized THA was greater than FHR for the anterior subluxation position. For skeletonized posterior subluxations, stability for THA and FHR constructs were similar, while a different pattern was observed for specimens with soft tissues intact. FHR constructs were more stable than THA constructs for both anterior and posterior subluxations. When the femoral neck is intact the joint has an earlier impingement profile placing the hip at risk for subluxation. However, FHR design was shown to be more stable than THA only when soft tissues were intact.

In vivo evaluation of the persistant and residual antimicrobial properties of three hand-scrub and hand-rub regimes in a simulated surgical environment.

BACKGROUND: The use of antimicrobial formulations for disinfecting hands prior to surgery has been shown to reduce the incidence of surgical site infections. Such formulations must demonstrate an immediate reduction of microbial flora on the hands that persists while the hands are gloved. AIM: This study compared persistent and residual antimicrobial effects of three simulated in-use surgical hand-cleansing procedures, one using a scrub followed by a hand rub with products containing chlorhexidine gluconate (CHG), and two using a scrub with a cleansing soap followed by a hand rub with one of two alcohol-based products. METHODS: The study was executed in two phases. In phase 1, persistent antimicrobial effects versus the resident microbial flora of volunteer subjects' hands were evaluated. In phase 2, the residual antimicrobial effects were challenged with the application of Staphylococcus aureus (ATCC 6538) on to the hands of volunteer subjects. FINDINGS: Phase 1 testing showed that significantly greater reductions of normal flora (P ≤ 0.00) persisted with a scrub with the CHG product followed by alcohol/CHG hand rub, than were achieved by scrubs with soap followed by application of either of the other hand rubs. Through all protocols of phase 2, the CHG scrub and alcohol/CHG hand rub produced significantly greater reductions of the S. aureus population (P ≤ 0.00) than did a soap scrub in combination with the other two hand rubs. CONCLUSION: The combination of a scrub and rub with products containing CHG and alcohol was shown to reduce significantly and persistently both the resident flora and contaminating transient bacteria on skin beneath surgical gloves.

An analytical model for rotator cuff repairs.

BACKGROUND: Currently, natural and synthetic scaffolds are being explored as augmentation devices for rotator cuff repair. When used in this manner, these devices are believed to offer some degree of load sharing; however, no studies have quantified this effect. Furthermore, the manner in which loads on an augmented rotator cuff repair are distributed among the various components of the repair is not known, nor is the relative biomechanical importance of each component. The objectives of this study are to (1) develop quasi-static analytical models of simplified rotator cuff repairs, (2) validate the models, and (3) predict the degree of load sharing provided by an augmentation scaffold. METHODS: The individual components of the repair constructs were modeled as non-linear springs, and the model equations were formulated based on the physics of springs in series and parallel. The model was validated and used to predict the degree of load sharing provided by a scaffold. Parametric sensitivity analysis was used to identify which of the component(s)/parameter(s) most influenced the mechanical behavior of the augmented repair models. FINDINGS: The validated models predict that load will be distributed approximately 70-80% to the tendon repair and approximately 20-30% to the augmentation component. The sensitivity analysis suggests that the greatest improvements in the force carrying capacity of a tendon repair may be achieved by improving the properties of the bone-suture-tendon interface. Future studies will perform parametric simulation to illustrate the manner in which changes to the individual components of the repair, representing different surgical techniques and scaffold devices, may influence the biomechanics of the repair construct.

Helical axes of skeletal knee joint motion during running.

The purpose of this study was to determine the changes in the axis of rotation of the knee that occur during the stance phase of running. Using intracortical pins, the three-dimensional skeletal kinematics of three subjects were measured during the stance phase of five running trials. The stance phase was divided into equal motion increments for which the position and orientation of the finite helical axes (FHA) were calculated relative to a tibial reference frame. Results were consistent within and between subjects. At the beginning of stance, the FHA was located at the midepicondylar point and during the flexion phase moved 20mm posteriorly and 10mm distally. At the time of peak flexion, the FHA shifted rapidly by about 10-20mm in proximal and posterior direction. The angle between the FHA and the tibial transverse plane increased gradually during flexion, to about 15 degrees of medial inclination, and then returned to zero at the start of the extension phase. These changes in position and orientation of FHA in the knee should be considered in analyses of muscle function during human movement, which require moment arms to be defined relative to a functional rotation axis. The finding that substantial changes in axis of rotation occurred independent of flexion angle suggests that musculoskeletal models must have more than one kinematic degree-of-freedom at the knee. The same applies to the design of knee prostheses, if the goal is to restore normal muscle function.

Evaluation of a two dimensional analysis method as a screening and evaluation tool for anterior cruciate ligament injury.

BACKGROUND: Increased knee valgus predicts the risk of anterior cruciate ligament (ACL) injury, particularly in women. Reducing injury rates thus relies on detecting and continually evaluating people with relatively large valgus motions. OBJECTIVES: To examine the potential of a two dimensional (2D) video analysis method for screening for excessive valgus. METHODS: Ten female and 10 male National Collegiate Athletic Association basketball players had three dimensional (3D) knee valgus and two dimensional (2D) frontal plane knee angle quantified during side step, side jump, and shuttle run tasks. 3D valgus was quantified from external marker coordinates using standard techniques, and 2D data were obtained from both the frontal plane projections of these coordinates (2D-Mot) and manual digitization of digital video footage (2D-Cam). A root mean square (RMS) error was calculated between 2D-Mot and 2D-Cam data to evaluate the reliability of the latter. Correlations between 2D-Cam and 3D data (intersubject and intrasubject) were also conducted, and regression slope and r2 values obtained. RESULTS: 2D-Cam and 2D-Mot data were consistent for side step (RMS = 1.7 degrees) and side jump (RMS = 1.5 degrees) movements. Between subjects, 2D-Cam and 3D data correlated well for the side step (r2 = 0.58) and side jump (r2 = 0.64). Within subjects, 2D-Cam and 3D data correlated moderately for the side step (r2 = 0.25 (0.19)) and side jump (r2 = 0.36 (0.27)). CONCLUSIONS: The 2D-Cam method can be used to screen for excessive valgus in elite basketball players, particularly for movements occurring primarily in the frontal plane. This method may also be a useful training evaluation tool when large reductions in dynamic valgus motions are required.

Effect of gender on lower extremity kinematics during rapid direction changes: an integrated analysis of three sports movements.

Anterior cruciate ligament (ACL) injury is a common sports injury, particularly in females. Gender differences in knee kinematics have been observed for specific movements, but there is limited information on how these findings relate to other joints and other movements. Here we present an integrated analysis of hip, knee and ankle kinematics across three movements linked to non-contact ACL injury. It was hypothesised that there are gender differences in lower extremity kinematics, which are consistent across sports movements. Ten female and ten male NCAA basketball players had three-dimensional hip, knee and ankle kinematics quantified during the stance phase of sidestep, sidejump and shuttle-run tasks. For each joint angle, initial value at contact, peak value and between-trial variability was obtained and submitted to a two-way mixed design ANOVA (gender and movement), with movement condition treated as a repeated measure. Females had higher peak knee valgus and lower peak hip and knee flexion, with the same gender differences also existing at the beginning of stance (p<0.05). Peak valgus measures were highly correlated between movements, but not to static valgus alignment. Kinematic differences demonstrated by females for the sports movements studied, and in particular knee valgus, may explain their increased risk of ACL injury. These differences appear to stem largely from subject-specific neuromuscular mechanisms across movements, suggesting that prevention via neuromuscular training is possible.

Foot and ankle forces during an automobile collision: the influence of muscles.

Muscles have a potentially important effect on lower extremity injuries during an automobile collision. Computational modeling can be a powerful tool to predict these effects and develop protective interventions. Our purpose was to determine how muscles influence peak foot and ankle forces during an automobile collision. A 2-D bilateral musculoskeletal model was constructed with seven segments. Six muscle groups were included in the right lower extremity, each represented by a Hill muscle model. Vehicle deceleration data were applied as input and the resulting movements were simulated. Three models were evaluated: no muscles (NM), minimal muscle activation at a brake pedal force of 400 N (MN), and maximal muscle activation to simulate panic braking (MX). Muscle activation always resulted in large increases in peak joint force. Peak ankle joint force was greatest for MX (10120 N), yet this model also had the lowest peak rearfoot force (629 N). Peak force on the Achilles tendon was 4.5 times greater, during MX (6446 N) compared to MN (1430 N). We conclude that (1). external and internal forces are dependent on muscles, (2). muscle activation level could exacerbate axial loading injuries, (3). external and internal forces can be inversely related once muscle properties are included.

Pre-impact lower extremity posture and brake pedal force predict foot and ankle forces during an automobile collision.

BACKGROUND: The purpose of this study was to determine how a driver's foot and ankle forces during a frontal vehicle collision depend on initial lower extremity posture and brake pedal force. METHOD OF APPROACH: A 2D musculoskeletal model with seven segments and six right-side muscle groups was used. A simulation of a three-second braking task found 3647 sets of muscle activation levels that resulted in stable braking postures with realistic pedal force. These activation patterns were then used in impact simulations where vehicle deceleration was applied and driver movements and foot and ankle forces were simulated. Peak rearfoot ground reaction force (F(RF)), peak Achilles tendon force (FAT), peak calcaneal force (F(CF)) and peak ankle joint force (F(AJ)) were calculated. RESULTS: Peak forces during the impact simulation were 476 +/- 687 N (F(RF)), 2934 +/- 944 N (F(CF)) and 2449 +/- 918 N (F(AJ)). Many simulations resulted in force levels that could cause fractures. Multivariate quadratic regression determined that the pre-impact brake pedal force (PF), knee angle (KA) and heel distance (HD) explained 72% of the variance in peak FRF, 62% in peak F(CF) and 73% in peak F(AJ). CONCLUSIONS: Foot and ankle forces during a collision depend on initial posture and pedal force. Braking postures with increased knee flexion, while keeping the seat position fixed, are associated with higher foot and ankle forces during a collision.

Development and validation of a 3-D model to predict knee joint loading during dynamic movement.

The purpose of this study was to develop a subject-specific 3-D model of the lower extremity to predict neuromuscular control effects on 3-D knee joint loading during movements that can potentially cause injury to the anterior cruciate ligament (ACL) in the knee. The simulation consisted of a forward dynamic 3-D musculoskeletal model of the lower extremity, scaled to represent a specific subject. Inputs of the model were the initial position and velocity of the skeletal elements, and the muscle stimulation patterns. Outputs of the model were movement and ground reaction forces, as well as resultant 3-D forces and moments acting across the knee joint. An optimization method was established to find muscle stimulation patterns that best reproduced the subject's movement and ground reaction forces during a sidestepping task. The optimized model produced movements and forces that were generally within one standard deviation of the measured subject data. Resultant knee joint loading variables extracted from the optimized model were comparable to those reported in the literature. The ability of the model to successfully predict the subject's response to altered initial conditions was quantified and found acceptable for use of the model to investigate the effect of altered neuromuscular control on knee joint loading during sidestepping. Monte Carlo simulations (N = 100,000) using randomly perturbed initial kinematic conditions, based on the subject's variability, resulted in peak anterior force, valgus torque and internal torque values of 378 N, 94 Nm and 71 Nm, respectively, large enough to cause ACL rupture. We conclude that the procedures described in this paper were successful in creating valid simulations of normal movement, and in simulating injuries that are caused by perturbed neuromuscular control.

Response time is more important than walking speed for the ability of older adults to avoid a fall after a trip.

We previously reported that the probability of an older adult recovering from a forward trip and using a "lowering" strategy increases with decreased walking velocity and faster response time. To determine the within-subject interaction of these variables we asked three questions: (1) Is the body orientation at the time that the recovery foot is lowered to the ground ("tilt angle") critical for successful recovery? (2) Can a simple inverted pendulum model, using subject-specific walking velocity and response time as input variables, predict this body orientation, and thus success of recovery? (3) Is slower walking velocity or faster response time more effective in preventing a fall after a trip? Tilt angle was a perfect predictor of a successful recovery step, indicating that the recovery foot placement must occur before the tilt angle exceeds a critical value of between 23 degrees and 26 degrees from vertical. The inverted pendulum model predicted the tilt angle from walking velocity and response time with an error of 0.4+/-2.2 degrees and a correlation coefficient of 0.93. The model predicted that faster response time was more important than slower walking velocity for successful recovery. In a typical individual who is at risk for falling, we predicted that a reduction of response time to a normal value allows a 77% increase in safe walking velocity. The mathematical model produced patient-specific recommendations for fall prevention, and suggested the importance of directing therapeutic interventions toward improving the response time of older adults.

Model formulation and determination of in vitro parameters of a noninvasive method to calculate flexor tendon forces in the equine forelimb.

OBJECTIVE: To describe a method to calculate flexor tendon forces on the basis of inverse dynamic analysis and an in vitro model of the equine forelimb and to quantify parameters for the model. SAMPLE POPULATION: 38 forelimbs of 23 horses that each had an estimated body mass of > or = 500 kg. PROCEDURE: Longitudinal limb sections were used to determine the lines of action of the tendons. Additionally, limb and tendon loading experiments were performed to determine mechanical properties of the flexor tendons. RESULTS: The study quantified the parameters for a pulley model to describe the lines of action. Furthermore, relationships between force and strain of the flexor tendons and between fetlock joint angle and suspensory ligament strain were determined, and the ultimate strength of the tendons was measured. CONCLUSION AND CLINICAL RELEVANCE: The model enables noninvasive determination of forces in the suspensory ligament, superficial digital flexor tendon, and distal part of the deep digital flexor (DDF) tendon. In addition, it provides a noninvasive measure of loading of the accessory ligament of the DDF tendon for within-subject comparisons. However, before application, the method should be validated. The model could become an important tool for use in research of the cause, prevention, and treatment of tendon injuries in horses.

Effects of shoe sole construction on skeletal motion during running.

PURPOSE: The purpose of this study was to quantify effects of shoe sole modification on skeletal kinematics of the calcaneus and tibia during the stance phase of running. METHODS: Intracortical bone pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The three-dimensional tibiocalcaneal rotations were determined using a joint coordinate system approach. Three shoe sole modifications were tested with different sole geometry: a lateral heel flare of 25 degrees (flared), no flare 0 degrees (straight), and a rounded sole. RESULTS: The results showed that these shoe sole modifications did not change tibiocalcaneal rotations substantially. The shoe sole effects at the bone level were small and unsystematic (mean effects being less than 1 degrees ) compared with the differences between the subjects (up to 7 degrees ). Shoe eversion measured simultaneously with shoe markers showed no systematic shoe sole effects. A comparison of shoe and bone results showed the total shoe eversion and maximum shoe eversion velocity to be approximately twice as large as the respective measurements based on bone markers (correlations being r = 0.79 for maximum eversion velocity; r = 0.88 for total eversion), indicating that there may be a relationship or coupling effect between the shoes and the bone. CONCLUSIONS: It is concluded that the tibiocalcaneal kinematics of running may be individually unique and that shoe sole modifications may not be able to change them substantially.

Horses damp the spring in their step.

The muscular work of galloping in horses is halved by storing and returning elastic strain energy in spring-like muscle-tendon units.These make the legs act like a child's pogo stick that is tuned to stretch and recoil at 2.5 strides per second. This mechanism is optimized by unique musculoskeletal adaptations: the digital flexor muscles have extremely short fibres and significant passive properties, whereas the tendons are very long and span several joints. Length change occurs by a stretching of the spring-like digital flexor tendons rather than through energetically expensive length changes in the muscle. Despite being apparently redundant for such a mechanism, the muscle fibres in the digital flexors are well developed. Here we show that the mechanical arrangement of the elastic leg permits it to vibrate at a higher frequency of 30-40 Hz that could cause fatigue damage to tendon and bone. Furthermore, we show that the digital flexor muscles have minimal ability to contribute to or regulate significantly the 2.5-Hz cycle of movement, but are ideally arranged to damp these high-frequency oscillations in the limb.

Tibiocalcaneal kinematics of barefoot versus shod running.

Barefoot running kinematics has been described to vary considerably from shod running. However, previous investigations were typically based on externally mounted shoe and/or skin markers, which have been shown to overestimate skeletal movements. Thus, the purpose of this study was to compare calcaneal and tibial movements of barefoot versus shod running using skeletal markers. Intracortical bone pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The subjects ran barefoot, with a normal shoe, with three shoe soles and two orthotic modifications. The three-dimensional tibiocalcaneal rotations were determined using a joint coordinate system approach. Test variables were defined for eversion and tibial rotation. The results showed that the differences in bone movements between barefoot and shod running were small and unsystematic (mean effects being less than 2 degrees ) compared with the differences between the subjects (up to 10 degrees ). However, differences may occur during midstance when extreme shoe modifications (i.e. posterior orthosis) are used. It is concluded that calcaneal and tibial movement patterns do not differ substantially between barefoot and shod running, and that the effects of these interventions are subject specific. The result of this in vivo study contrasts with previous investigations using skin and shoe mounted markers and suggests that these discrepancies may be the result of the overestimation with externally mounted markers.

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.

The influence of orthotic devices and vastus medialis strength and timing on patellofemoral loads during running.

OBJECTIVE: To use a musculoskeletal model and simulation of running to examine: (1) the influence of two commonly prescribed treatments for patellofemoral pain (vastus medialis oblique strengthening and orthoses) and (2) the functional significance of timing differences between vastus medialis oblique and vastus lateralis on lateral patellofemoral joint loads. DESIGN: A three-dimensional musculoskeletal model of the lower extremity was used to simulate running at 4 m/s. BACKGROUND: Repetitive and excessive joint loading is often associated with overuse injuries that require clinical treatments to reduce pain and restore function. Affecting one in four runners, patellofemoral pain is one of the most common injuries in running. Although conservative treatments have been reported to successfully treat patellofemoral pain, the effectiveness is often based on subjective or empirical data, which have generated disagreement on the most effective treatment. METHODS: Nine subject specific running simulations were generated and experiments were performed by applying the treatments and timing differences to the nominal simulations. RESULTS: Both treatments significantly reduced the average patellofemoral joint load and the vastus medialis strengthening also significantly reduced the peak patellofemoral joint load. In addition, when the vastus medialis oblique timing was delayed and advanced relative to the vastus lateralis timing, a significant increase and decrease in the joint load was observed, respectively, during the loading response.Conclusions. Increasing vastus medialis oblique strength yielded more consistent results across subjects than the orthosis in reducing patellofemoral joint loads during running. The effect of orthoses was highly variable and sensitive to the individual subject's running mechanics. Vastus medialis oblique activation timing is an important determinant of lateral patellofemoral joint loading during the impact phase. RELEVANCE: These findings indicate that a reduction in patellofemoral pain may be achieved through techniques that selectively increase the vastus medialis oblique strength. Therefore, future studies should be directed towards identifying such techniques. Additionally, the functional significance of timing differences between the vastus medialis oblique and vastus lateralis is an important consideration in patellofemoral pain treatment and orthoses may be beneficial for some patients depending on their running mechanics.

Movement coupling at the ankle during the stance phase of running.

The purpose of this study was to quantify movement coupling at the ankle during the stance phase of running using bone-mounted markers. Intracortical bone pins with reflective marker triads were inserted under standard local anaesthesia into the calcaneus and the tibia of five healthy male subjects. The three-dimensional rotations were determined using a joint coordinate system approach. Movement coupling was observed in all test subjects and occurred in phases with considerable individual differences. Between the shoe and the calcaneus coupling increased after midstance which suggested that the test shoes provided more coupling for inversion than for eversion. Movement coupling between calcaneus and tibia was higher in the first phase (from heel strike to midstance) compared with the second phase (from midstance to take-off). This finding is in contrast to previous in-vitro studies but may be explained by the higher vertical loads of the present in-vivo study. Thus, movement coupling measured at the bone level changed throughout the stance phase of running and was found to be far more complex than a simple mitered joint or universal joint model.

The influence of foot positioning on ankle sprains.

The goal of this study was to examine the influence of changes in foot positioning at touch-down on ankle sprain occurrence. Muscle model driven computer simulations of 10 subjects performing the landing phase of a side-shuffle movement were performed. The relative subtalar joint and talocural joint angles at touchdown were varied, and each subject-specific simulation was exposed to a set of perturbed floor conditions. The touchdown subtalar joint angle was not found to have a considerable influence on sprain occurrence, while increased touchdown plantar flexion caused increased ankle sprain occurrences. Increased touchdown plantar flexion may be the mechanism which causes ankles with a history of ankle sprains to have an increased susceptibility to subsequent sprains. This finding may also reveal a mechanism by which taping of a sprained ankle or the application of an ankle brace leads to decreased ankle sprain susceptibility.