Knowledge of ligamentous contributions to joint stability is essential to restore normal joint range of motion and functionality through reconstruction procedures. Although, there has been numerous studies on the pathomechanics of the elbow joint, there have been very few rigorous and systematic attempts to characterize the roles of soft tissues during clinically relevant motions.
Five fresh frozen cadaveric elbows from three male subjects were used for this study. In-vitro simulations were performed using a VIVO six degree-of-freedom (6-DOF) joint motion simulator (AMTI, Watertown, MA) capable of virtually simulating the effects of soft tissue constraints (virtual ligaments). This study introduces a unique, hybrid experimental-computational technique for measuring and simulating the biomechanical contributions of ligaments to elbow joint kinematics and stability. In vitro testing of cadaveric joints is enhanced by the incorporation of fully parametric virtual ligaments, which are used in place of the native joint stabilizers to characterize the contribution of elbow ligaments during simple flexion-extension motions using the principle of superposition.
our results demonstrate the importance of AMCL and RCL structures as primary stabilizers under valgus and varus loading respectively. Virtual ligaments demonstrate the ability to restore the VV stability of the joint in the absence of any soft tissues attached to the osseous structures. This demonstrates the effectiveness of “virtual” ligaments for in vitro testing of elbow joint biomechanics, with applications in pre-clinical assessment of elbow implants.
Lateral ankle sprains are common orthopedic injuries and often result in chronic ankle instability (CAI). Studies have shown that the CAI population typically has decreased ankle proprioception and possibly a greater reliance on visual feedback when compared to healthy controls. However, little is known about how the postural control characteristics change in those with and without CAI when external visual feedback is manipulated. Purpose: To compare postural control characteristics of persons with CAI, Copers and healthy adults when performing a single leg balance test with and without external feedback. Method: The definition for CAI used for this study includes persons who have experienced recurrent ankle sprains, in addition to self-reported “feelings of instability” and “giving way,” and a score on the Identification of Functional Ankle Instability (IdFAI) of 11 or greater. 18 participants with CAI, 15 Copers, and 18 healthy controls (mean age of all groups: 22 years) performed the Athlete Single Leg Test on the Biodex Balance System (BBS) at Level 4 which involved a high degree of platform instability. All participants completed 2 trials without and with feedback in that order. Center of pressure position was recorded and the two trial mean was used for further analysis. Overall stability index (OSI) defined as the mean distance of the center of pressure from the center of the platform was obtained from the system. Sway area was calculated using custom Matlab script. Separate 3 (Group) x 2 (Feedback) mixed ANOVAs were run using overall stability index (OSI), and sway area as dependent variables. Results: Significant feedback main effect showed participants had significantly lower (better) OSI value with feedback (1.4±0.1) compared to without feedback (2.6±0.2; P < 0.001) but sway area with feedback (8.61±2.33cm2) was similar to without feedback (10.94±2.43 cm2). There was no significant group main effect or interaction observed for either of the variables. Conclusion: Results suggest that external visual feedback may not play a significant role in helping persons with CAI improve their postural control.
Title: Head Acceleration During Girls Youth Soccer Using Real Time Data
Emily Messerschmidt, Katlyn Van Patten, Ryan Lee, Srikant Vallabhajosula
Purpose/Hypothesis: While the acute effects of concussion have been the focus of research in the past, there is a new emphasis toward following the cumulative effects of sub-concussive head accelerations in athletics. This is especially important in youth athletes because the developing brain is more vulnerable to injury from head trauma in sports like soccer due to techniques such as heading, that can result in numerous head impacts throughout play. There is a current lack of evidence on the magnitude and frequency of head accelerations that occur during real-time youth sports, including soccer, and whether these accelerations have a detrimental cumulative effect. The purpose of the current study was to measure the head acceleration that youth athletes experience during real-time soccer games.
Number of Subjects: 31 under-15 girls club soccer participants. 11 players monitored each game.
Materials/Methods: 3 season games were observed. Triax Smart Impact Monitor headband accelerometers were worn during gameplay to collect real-time head impact data. Forces >10g were recorded. Games were video recorded for further analysis. Head impacts were categorized by type of impact: purposeful header (PH), player to player (PP), player to ground (PG), and ball to head (BH). Data was analyzed using descriptive statistics.
Results: A total of 171 impacts were observed (PH=20, PP=113, PG=36, BH=2). Only one impact recorded was above the concussion threshold of 70g. The majority (77%) of impacts observed were <10g. Of the accelerations recorded, PH resulted in the largest average acceleration (36.8±14.9g) followed by PG (20.5±4.2g), and PP (19.5±4.6g). The maximum accelerations for PH, PG and PP were 73g, 26g and 30g respectively. No BH accelerations were recorded >10g.
Conclusions: While PH yielded the highest average acceleration, it was one of the least frequently occurring impacts. PP impacts were most common however the majority produced little to no head acceleration. While there was variability of head acceleration that occurred within each type of impact, none produced consistently dangerous (≥70g) accelerations.
Clinical Relevance: This study provides preliminary evidence of the impacts sustained during girls youth soccer games for athletic trainers or sports physical therapists who are monitoring athletes for concussions. The findings reveal that the use of headband accelerometers to measure real-time data can be a useful tool to monitor multiple players on the field. There remains a need for further research into the effect of cumulative sub-concussive impacts during soccer in youth athletes with larger sample size. Further studies should investigate the impacts players sustain over multiple seasons to observe if those who experience multiple sub-concussive impacts report concussion-like symptoms or show concussion-like signs. Additionally, this study adds evidence to the existing literature that the use of video analysis to confirm the occurrence of impacts and to correctly categorize them is highly beneficial to ensure reliability in future studies.
The age-associated decline in propulsive push off power generated during walking plays a central role in the reduction of mobility and independence in older adults. Previous work suggests that this population retains an underutilized propulsive reserve during normal walking that dynamometry assessments fail to effectively assess. This is especially notable when assessing plantarflexor mechanical output, which often yield implausible (i.e., ≥100%) values of ‘functional capacity utilized (FCU)’, most frequently defined as the ratio of the peak ankle moment during the push-off phase of walking to that during a maximum isometric voluntary contraction. Therefore, the extent to which we utilize our propulsive capacity, how utilization changes as we age, and the factors that govern utilization and maximum propulsive capacity remain unclear. Utilizing a feedback controlled, motor driven horizontal impeding force system and a novel maximum force condition which systematically increases applied force, we can find a participant’s maximum propulsive capacity. During this condition, we find that younger adults retain a reserve of 48% in terms of ground reaction force, 22% in terms of ankle moment and 43% in terms of ankle power, which may not be effectively predicted using dynamometry assessments. As an important first step, we present data showing that a more functional task, walking with horizontal impeding forces, could potentially more effectively assess propulsive reserves in younger adults.
Even prior to walking slower, older adults walk with a diminished push-off – decreased propulsive forces (FP) accompanied by reduced ankle moment and power generation. The purpose of this study was to identify age-related differences in the joint-level modifications used to modulate FP generation during walking. We posit that there are two possibilities for older adults to enhance FP generation. First, older adults may increase ankle power generation and thereby alleviate compensatory demands at the hip. Alternatively, older adults may opt to exacerbate their distal to proximal redistribution by relying even more on the hip musculature.
10 healthy young adults and 16 healthy older adults participated in this study. Subjects walked at their preferred speed while watching a video monitor displaying their instantaneous FP while instructed to modify their FP to match target values representing normal and ±10% and ±20% of normal. For all trials, we estimated lower extremity joint kinematics and kinetics.
During normal walking, older adults exerted smaller FP and ankle power than young adults. Enhancing FP via biofeedback alleviated mechanical power demands at the hip, without changes in ankle power. Further, older adults walked with increased FP without increasing their total positive joint work. Thus, given the same total requisite power generation, older adults got ‘more bang for their ankle power buck’ using biofeedback.
INTRODUCTION: Cam femoroacetabular impingement (FAI) is characterized by an osseous overgrowth on the femoral head-neck junction [1], leading to pain and limited range of motion (ROM) during daily life activities [2]. Corrective surgery is highly recommended and performed in order to reduce or eliminate pain and further development of osteoarthritis (OA). However, it is still unclear whether it would lead to improved functional mobility. The purpose was to compare kinematic variables of the operated limb between FAI patients when performing a squat task pre-surgery and at around 2-year follow-up. A secondary objective consisted of express the results in a biomechanical functional score to quantify the joint kinematics of FAI patients compared to healthy control (CTRL) participants.
METHODS: Eleven male patients (7 arthroplasty: 34.6±8.1 years, 25.7±3.2 kg/m2; 4 open: 33.3±7.1 years, 24.9±1.9 kg/m2) and 21 CTRL (2F/19M, 33.4±6.7 years, 25.4±3.3 kg/m2) participants were recruited from the orthopaedic surgeon’s clinical practice. Patients were assigned to either an arthroplasty or open FAI surgery correction. The participants signed prior to their participation a consent form approved by the hospital and university ethics board. Patients agreed to undergo motion analysis prior to and 2 years after the surgery. The CTRL were selected based on similar age and BMI as the FAI group and underwent the same motion analysis protocol.
At the local hospital, CT scan was performed in all participants to confirm an alpha-angle higher than 55º and also establish their pelvic and knee bony landmarks. At the motion laboratory, the participants were outfitted with 45 reflective markers and performed a minimum of five trials of deep squat at a self-selected pace. Three-dimensional joint kinematics (200 Hz) of the lower limbs were captured using a ten-camera motion analysis system (Vicon, UK). Kinematics data were processed in Nexus 1.8.3 (Vicon, UK) using a modified Plug-In-Gait model and exported with a custom MATLAB script (Mathworks, USA) to calculate group averages and extract relevant variables. All trials were time-normalized based on a full squat cycle (descent and ascent phases) and individual averages for each participant were calculated across the trials.
Four kinematic variables were included in the analysis: pelvis, hip, knee, and ankle sagittal angles. The normalized root-mean-square deviation (nRMSD) was calculated between the FAI and the CTRL groups for both pre- and post-surgery conditions, expressed by
Falls due to slippery conditions are among the primary causes of disabling workplace injuries. Despite the extensive amount of human slip studies in the literature, only a handful of studies have reported ground reaction forces at the instant of slip initiation. The purpose of this study was to quantify the vertical ground reaction forces (VGRF) at slip initiation during unexpected human slips across different footwear-contaminant conditions. Forty-seven healthy subjects were unexpectedly exposed to a liquid–contaminant, while the vertical force was measured at the moment that the foot began to start slipping. The average VGRF were between 100 and 300 N and varied significantly across the footwear. These forces were significantly less than the typical forces (400-700 N) applied during slip-resistance measurements. This finding may suggest that available coefficient of friction (ACOF) measurements should use lower force levels in order to achieve higher relevance to the onset of slipping.
The relationship between EMG and muscle force changes with muscle fatigue, making interpretation of load sharing between muscles over time challenging. The purpose of this investigation was to evaluate the efficacy of normalizing EMG data to repeated, static, submaximal exertions to mitigate the fatigue artifact in EMG amplitude. Participants completed simulated repetitive work tasks, in 60-second work cycles, until exhaustion and surface EMG was recorded from 11 muscles. Every 12 minutes, participants completed a series of 4 submaximal reference exertions. Reference exertion EMG data were used in 6 normalizing methods including 1 standard (normalized to initial reference exertion) and 5 novel methods: (i) Fatigue Only, (ii) Linear Model, (iii) Cubic Model, (iv) Points Forward, and (v) Points Forward/Backward. EMG data were normalized to each novel methods and results were compared to the Standard Method. The significant differences between the novel methods and the Standard Method were dependent on the muscle and the number of time points in the analysis. Correlation analysis showed that the predicted cubic model points correlated better to the actual data points than the linear predicted values. This novel method to create “fatigue debiased” ratios may better reflect the changing muscular loads during repetitive work. This method was evaluated with a novel data set examining the effects of repetitive shoulder exertions, in multiple axes, on load sharing in the shoulder over time. The normalizing method was effective at distinguishing between the effects of fatigue artifact on EMG amplitude and load sharing between muscles over time.
Over the past years, we have developed a test for postural stability based on the theory of synergies stabilizing salient performance variables. In this study, effects of Parkinson's disease (PD) and dopamine-replacement therapy on multi-muscle synergies stabilizing the center of pressure (COP) coordinate were explored between: (1) a cohort of 11 patients without clinically identifiable postural problems (Hoehn-Yahr stage II) and 11 age-matched controls, and (2) a cohort of 10 patients tested off- and on-medication, with and without postural problems (stage II and III, n = 5 per stage). Participants stood on a force platform and performed cyclical body sway at 0.5 Hz along the anterior-posterior direction. Electromyographic signals from 13 leg and trunk muscles were used to compute: (1) the amount of inter-cycle variance that did not affect (VUCM) and affected (VORT) COP coordinate, and (2) the magnitude of the cycle-to-cycle motion that did not change (motor equivalent: ME) and changed (non-motor equivalent: nME) the COP coordinate. We hypothesized that both methods would produce indices sensitive to PD and dopaminergic medications. Compared to controls, patients showed significantly smaller inter-cycle VUCM and ME components suggesting a less flexible, and hence less stable, behavior. Moreover, inter-cycle variance within/orthogonal to the UCM correlated with ME/nME displacements. Results suggest clinical utility of variance and motor equivalence analyses of postural instability in early stages of PD and quantifying the effects of dopamine-replacement drugs. The analysis of motor equivalence is particularly attractive because it requires only a handful of trials (observations).
Chronic ankle instability (CAI) patients often exhibit altered walking mechanics, due to strength and proprioceptive deficits associated with CAI. Reduced strength and proprioception function may alter walking energetic patterns, by reducing energy absorption and generation capability. It is unclear whether strength and proprioceptive training can affect walking energetics for CAI patients. PURPOSE: To examine the effect of a 6-week ankle and hip rehab program on ankle, knee, and hip joint energetic patterns during walking in CAI patients. METHODS: 15 CAI patients (23 ± 2 yrs, 178 ± 8 cm, 76 ± 9 kg, 83 ± 7% FAAM ADL, 56 ± 10% FAAM Sports, 3.6 ± 1.1 MAII, 4.7 ± 2.0 ankle sprains) performed ankle and hip strength and proprioceptive exercises (i.e., theraband, wobble board, etc.) 3 times per week, for 6 weeks (rehab group). 14 CAI patients (22 ± 2 yrs, 177 ± 9 cm, 75 ± 12 kg, 81 ± 9% FAAM ADL, 56 ± 12% FAAM Sports, 3.4 ± 1.2 MAII, 5.9 ± 3.3 sprains) performed no rehab exercises (control group). We measured ankle, knee, and hip joint power during walking for all patients before and after 6 week duration. Functional statistics (α = 0.05) were used to evaluate the influence of the rehab exercises on joint power for both groups across the entire stance phase of walking. RESULTS: The rehab intervention resulted in up to 0.07 W/kg more positive ankle power (concentric) between 19 and 26% of stance and up to 0.06 W/kg more positive knee power (concentric) between 40 and 48% of stance. No changes were detected in hip joint power during the stance phase of walking. CONCLUSION: Strength and proprioceptive training resulted in an improved gait energetic efficiency via increased ankle and knee power generation during mid-stance. As greater muscular strength can lead to an increase in power absorption and generation, the intervention focusing on strength could be beneficial in improving walking energetics in a CAI population.