Quantitative Analysis of Ball-Head Impact Exposure in Youth Soccer Players.

Since the implementation of the US Soccer heading guidelines released in 2015, little to no research on ball-head impact exposure in the United States youth soccer population has been conducted. The purpose was to compare ball-head impact exposure across sex and age in youth soccer players over a weekend tournament. Ten male and female games for each age group (Under-12 [U12], U13, and U14) were video recorded at a weekend tournament for a total of 60 games. Ball-head impact exposure for each game was then coded following a review of each recording. Male players were 2.8 times more likely to have ball-head impacts than female players, (p < 0.001) particularly in the U14 age group when compared to the U12 age group (p = 0.012). Overall 92.4% of players experienced 0-1 ball-head impacts per game with the remaining players experiencing 2+ ball-head impacts per game. Ball-head impact exposure levels are low in the youth players. Most youth soccer players do not head the soccer ball during match play and those that did, only headed the ball on average once per game. Overall, the difference in ball-head impact exposure per player was less than 1 between all the groups, which may have no clinical meaning.

Identifying Range-of-Motion Deficits and Talocrural Joint Laxity After an Acute Lateral Ankle Sprain.

CONTEXT: Approximately 72% of patients with an ankle sprain report residual symptoms 6 to 18 months later. Although 44% of patients return to activity in less than 24 hours after experiencing a sprain, residual symptoms should be evaluated in the long term to determine if deficits exist. These residual symptoms may be due to the quality of ligament tissue and motion after injury. OBJECTIVE: To compare mechanical laxity of the talocrural joint and dorsiflexion range of motion (DFROM) over time (24 to 72 hours, 2 to 4 weeks, and 6 months) after an acute lateral ankle sprain (LAS). DESIGN: Cross-sectional study. SETTING: Athletic training research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 108 volunteers were recruited. Fifty-five participants had an acute LAS and 53 participants were control individuals without a history of LAS. MAIN OUTCOME MEASURE(S): Mechanical laxity (talofibular interval and anterior talofibular ligament length) was measured in inversion (INV) and via the anterior drawer test. The weight-bearing lunge test was conducted and DFROM was measured. The data were analyzed using repeated-measures analysis of variance, independent-samples t tests, and 1-way analysis of variance. RESULTS: Of the 55 LASs, 21 (38%) were grade I, 27 (49%) were grade II, and 7 (13%) were grade III. Increases were noted in DFROM over time, between 24 and 72 hours, at 2 to 4 weeks, and at 6 months (P < .05). The DFROM was less in participants with grade III than grade I LASs (P = .004) at 24 to 72 hours; INV length was greater at 24 to 72 hours than at 2 to 4 weeks (P = .023) and at 6 months (P = .035) than at 24 to 72 hours. The anterior drawer length (P = .001) and INV talofibular interval (P = .004) were greater in the LAS group than in the control group at 6 months. CONCLUSIONS: Differences in range of motion and laxity were evident among grades at various time points and may indicate different clinical responses after an LAS.

Reactive knee stiffening strategies between various conditioning histories.

Optimizing joint stiffness through appropriate muscular activation is crucial for maintaining stability and preventing injury. Conditioning techniques may affect joint stability by increasing joint stiffness and altering neuromuscular control; however no studies have assessed this in a controlled setting. Fifteen endurance athletes, 12 power athletes, and 15 control subjects sat on a stiffness device that generated a rapid knee flexion perturbation and were instructed to react to the perturbation. Main outcome measures included short-range (0-4°) and long range (0-40°) stiffness and muscle activation from quadriceps and hamstring muscles. Stiffness results revealed greater short-range stiffness in endurance athletes (0.057 ± 0.012 Nm/deg/kg) than controls (0.047 ± 0.008 Nm/deg/kg, p = 0.021); while passive long-range stiffness was greater in power (0.0020 ± 0.001 nm/deg/kg) than endurance athletes (0.0016 ± 0.001 nm/deg/kg, p = 0.016). Endurance athletes had greater reactive stiffness (0.051 ± 0.017 nm/deg/kg) than control (0.033 ± 0.011 nm/deg/kg, p = 0.001) and power (0.037 ± 0.015 nm/deg/kg, p = 0.044) groups. Endurance athletes also displayed greater quadriceps activity during passive and reactive conditions (p < 0.050) compared to power athletes and controls. These findings suggest that power-based training history may be associated with greater passive joint stiffness across the full range of motion, while endurance-based training could positively influence reactive muscular characteristics, as well as resting muscle tone. These unique variations in stiffness regulation could be beneficial to programmes for prevention and rehabilitation of joint injury.

Adaptations of the Shoulder to Overhead Throwing in Youth Athletes.

CONTEXT: The high number of repetitions and high forces associated with overhead throwing lead to anatomical adaptations, such as humeral retrotorsion and posterior-capsule thickness, in elite and professional baseball athletes. However, little is known about the origin and progression of these changes that may account for the increasing trend of chronic shoulder injuries in youth baseball and precipitate subsequent pathologic conditions throughout a young athlete's lifetime. OBJECTIVE: To investigate the relationship of age and upper extremity dominance on humeral retrotorsion, posterior-capsule thickness, and glenohumeral range of motion. DESIGN: Cross-sectional study. SETTING: Research laboratory, local baseball fields, and training facilities. PATIENTS OR OTHER PARTICIPANTS: Thirty-six boys (mean age = 10.94 ± 1.34 years, height = 151.31 ± 12.17 cm, mass = 42.51 ± 10.32 kg) ranging in age from 8 to 12 years and involved in organized youth baseball. MAIN OUTCOME MEASURE(S): Diagnostic ultrasound was used to determine humeral retrotorsion and posterior-capsule thickness. Glenohumeral internal rotation and external rotation were measured using a handheld inclinometer. We used 2 × 2 mixed-model analyses of variance to compare the influence of limb dominance and age on the dependent variables of humeral retrotorsion, posterior-capsule thickness, internal rotation, and external rotation. RESULTS: The dominant shoulders of youth throwers exhibited less glenohumeral internal rotation but greater humeral retrotorsion, posterior-capsule thickness, and glenohumeral external rotation than the nondominant shoulders. Dominant internal rotation was greater in the 8- to 10-year-old group than in the 11- to 12-year-old group, and results trended toward a difference (F1,33 = 4.12, P = .05). Correlations existed between humeral retrotorsion and range of motion (P < .05). CONCLUSIONS: The structural adaptations in the dominant shoulders of younger baseball players were similar to adaptations observed in older baseball athletes, indicating that more examination is needed in younger athletes. We are the first to demonstrate greater posterior-capsule thickness in the dominant shoulders of youth baseball athletes.

Asymmetrical loading affects intersegmental dynamics during the swing phase of walking.

Much of the work related to lower extremity inertia manipulations has focused on temporal, kinematic and traditional inverse dynamics assessments during locomotion. Intersegmental dynamics is an analytical technique that provides further insights into mechanisms underlying linked-segment motion. The purpose of this study was to determine how intersegmental dynamics during the swing phase of walking are altered during asymmetrical lower extremity loading. Participants walked overground at a speed of 1.57 ms(-1) with 0, 0.5, 1.0, and 2.0 kg attached to one foot. Net, interaction, gravitational, and muscle moments were computed. Moment magnitudes at joints of the loaded leg increased systematically with increasing load, whereas unloaded leg moments were unaffected by loading. With increasing load, relative contributions of interaction moments about the knee and hip and gravitational moment about the ankle increased (i.e., 21%, 8%, and 44% increases, respectively), whereas the relative contributions of muscle moments about all three joints declined (i.e., -4%, -13%, and -8% decreases for the ankle, knee, and hip, respectively for unloaded vs. 2.0 kg). These results suggest that altered inertia properties of the limb not only affected the amount of muscular effort required to swing the leg, but also changed the nature of the interaction between segments.

Mechanical effectiveness of lateral foot wedging in medial knee osteoarthritis after 1 year of wear.

The use of lateral foot wedging in the management of medial knee osteoarthritis is under scrutiny. Interestingly, there have been minimal efforts to evaluate biomechanical effectiveness with long-term use. Therefore, we aimed to evaluate dynamic knee loading (assessed using the knee adduction moment) and other secondary gait parameters in patients with medial knee osteoarthritis wearing lateral foot wedging at a baseline visit and after 1 year of wear. Three-dimensional gait data were captured in an intervention group of 19 patients with symptomatic medial knee osteoarthritis wearing their prescribed laterally wedged foot orthoses at 0 and 12 months. Wedge amounts were prescribed based on symptom response to a step-down test. A control group of 19 patients wearing prescribed neutral orthoses were also captured at 0 and 12 months. The gait of the intervention group wearing neutral orthoses was additionally captured. Walking speed and shoes were controlled. Analyses of variance were conducted to examine for group-by-time (between the groups in their prescribed orthoses) and condition-by-time (within the intervention group) interactions, main effects, and simple effects. We observed increased knee adduction moments and frontal plane motion over time in the control group but not the intervention group. Further, within the intervention group, the mechanical effectiveness of the lateral wedging did not decrease. In patients with medial knee osteoarthritis, the effects of lateral foot wedging on pathomechanics associated with medial knee osteoarthritis were favorable and sustained over time.

Dynamic versus radiographic alignment in relation to medial knee loading in symptomatic osteoarthritis.

Dynamic knee alignment is speculated to have a stronger relationship to medial knee loading than radiographic alignment. Therefore, we aimed to determine what frontal plane knee kinematic variable correlated most strongly to the knee adduction moment. That variable was then compared with radiographic alignment as a predictor of the knee adduction moment. Therefore, 55 subjects with medial knee OA underwent three-dimensional gait analysis. A subset of 21 subjects also underwent full-limb radiographic assessment for knee alignment. Correlations and regression analyses were performed to assess the relationships between the kinematic, kinetic and radiographic findings. Peak knee adduction angle most strongly correlated to the knee adduction moment of the kinematic variables. In comparison with radiographic alignment, peak knee adduction angle was the stronger predictor. Given that most epidemiological studies on knee OA use radiographic alignment in an attempt to understand progression, these results are meaningful.

Plantar pressure during running in subjects with chronic ankle instability.

BACKGROUND: It has been suggested that dynamic foot and ankle mechanics predispose individuals with CAI to repetitive episodes of the ankle ``giving way.'' Plantar pressure variations during a walking gait have been detected in those with CAI, but more dynamic conditions for analysis are needed. The purpose of this study was to evaluate plantar pressure distributions during a running gait in individuals with CAI, individuals who suffered a lateral ankle sprain, but did not develop CAI (AS), and subjects with no history of a lateral ankle sprain (CON). MATERIALS AND METHODS: Forty-five subjects [15 in each group, healthy males (18) and females (27), age 18 to 45] were recruited from University communities to participate in this study. Plantar pressure distributions were analyzed on a Tekscan© plantar pressure mat at 66 frames per second during a running gait at a controlled speed. The following variables were obtained: rearfoot medial/lateral (M/L) pressure ratio at foot strike (FS) and center-of-pressure (COP) trajectory during the initial loading response (heel strike to initial peak GRF). Separate one-way ANOVA with Tukey's post-hoc were used to test for group differences. The significance level was defined as p < 0.05. RESULTS: The CAI group had a significantly more lateral ratio (0.97 ± 0.12) at FS when compared to the CON (1.01 ± 0.13) and AS (1.11 ± 0.13) groups. The CAI subjects had a lateral COP trajectory during the loading phase (7.97 degrees ± 11.02), while both the AS (-3.68 degrees ± 10.24) and CON groups (-6.27 degrees ± 9.86) had medial trajectories. The difference was significant between the CAI group and both the AS and CON groups (all significant {\it p} values were less than 0.05). CONCLUSION: Our results confirm that CAI subjects have a more lateral foot positioning and loading pattern during a barefoot running gait when compared to both the CON and LAS groups. CLINICAL RELEVANCE: Clinicians treating patients with CAI should consider providing interventions to decrease the amount of rearfoot inversion at FS and during loading in order to create a more medial COP trajectory upon impact.

Strength asymmetry and osteoarthritis risk factors in unilateral trans-tibial, amputee gait.

Persons with a unilateral, trans-tibial amputation have an increased risk of developing osteoarthritis (OA) in the knee of their intact limb. Between-side strength discrepancies observed in individuals with an amputation may indicate overuse of the intact limb and increased osteoarthritis risk; however, the relationship between lower extremity strength and gait mechanics has not been addressed in previous literature. It was hypothesized that amputee subjects' strength and gait would be more asymmetrical than controls, and that strength asymmetry would positively correlate with gait variable asymmetry and intact side gait variables associated with osteoarthritis risk. Eight persons with unilateral, trans-tibial amputation and eight able-bodied control subjects participated. Three gait variables related to osteoarthritis risk (knee external adduction moment, knee adduction moment load rate, and vertical ground reaction force load rate) were measured bilaterally, along with three strength measures (hip abductors, knee extensors, and knee flexors). Four of the six variables were more asymmetrical in the amputee group than the control group (p<0.05 and/or effect size greater than 0.70). Knee extension strength asymmetry was significantly related to knee adduction moment load rate asymmetry (rho=0.714), and knee flexion strength asymmetry was moderately related to the vertical ground reaction force on the intact limb (rho=0.643). Results suggest that strength asymmetry in unilateral trans-tibial amputees has a moderate relationship with osteoarthritis risk, and may be a useful way to assess gait ability and the need for rehabilitation in this population.

Comparison of methods for kinematic identification of footstrike and toe-off during overground and treadmill running.

When analysing gait, the identification of the period of stance is often needed. Forceplates are typically used, but in their absence kinematic data can be employed. Five kinematic methods have been previously described in the literature. However, these methods have not been compared to each other for overground or treadmill running. Therefore, the purpose of this study was to compare these five kinematic methods of identifying the stance phase with vertical ground reaction force data both during overground and treadmill running. We recruited forty recreational runners (20 males) for this study. Twenty runners underwent an instrumented gait analysis during overground running, and twenty were tested during instrumented treadmill running. All runners ran at 3.35 m/s. Each kinematic method was compared with stance identified from the vertical ground reaction force (gold standard) for overground running. This method was then repeated for treadmill running. Two methods were found to be valid and reliable for determining footstrike. These were the time when the distal heel marker reached a minimum vertical position, and when the vertical velocity of this same marker changed from negative to positive. These methods had absolute errors that ranged from 22.4 ms to 24.6 ms for both modes of running. Toe-off was best identified using peak knee extension, with absolute errors of 4.9 ms for overground running and 5.2 ms for treadmill running. Utilising automated kinematic methods of determining stance will aid researchers studying running when forceplates are unavailable.

Static and dynamic correlates of the knee adduction moment in healthy knees ranging from normal to varus-aligned.

BACKGROUND: Individuals with medial knee osteoarthritis often present with varus knee alignment and ambulate with increased knee adduction moments. Understanding the factors that relate to the knee adduction moment in healthy individuals may provide insight into the development of this disease. Thus, this study aimed to examine the relationships of both static and dynamic lower extremity measures with the knee adduction moment. We hypothesized that the dynamic measures would be more closely related to this moment. METHODS: Arch height index, hip abduction strength and two static measures of knee alignment were recorded for 37 young asymptomatic knees that varied from normal to varus-aligned. Overground gait analyses were also performed. Correlation coefficients were used to assess the relationships between the static and dynamic variables to the knee adduction moment. Hierarchical regression analyses were then conducted using the static measures, the dynamic measures, and the static and dynamic measures together. RESULTS: Among the static measures, the tibial mechanical axis and the distance between the medial knee joint lines were correlated with the knee adduction moment. The best predictive static model (R(2)=0.53) included only the tibial mechanical axis. Among the dynamic variables, knee adduction and rearfoot eversion angles were correlated with the knee adduction moment. Knee adduction and rearfoot eversion, together, were the best dynamic model (R(2)=0.53). The static and dynamic measures together created the strongest of the three models (R(2)=0.59). CONCLUSIONS: These results suggest that dynamic measures slightly enhance the predictive strength of static measures when explaining variation in the knee adduction moment.

Lower extremity walking mechanics of young individuals with asymptomatic varus knee alignment.

Varus knee alignment is associated with an increased risk for developing medial knee osteoarthritis (OA). Medial knee OA is commonly associated with altered walking mechanics in the frontal and sagittal planes, as well as altered ground reaction forces. It is unknown whether these mechanics are present in young, asymptomatic individuals with varus knees. We expected that varus-aligned individuals would generally present with frontal plane mechanics that were similar to those reported for individuals with medial knee OA. The gait mechanics of 17 asymptomatic individuals with varus knees and 17 healthy, normally aligned controls were recorded. Gait parameters associated with medial knee OA were compared between groups. The individuals with varus knees exhibited greater knee external adduction moments, knee adduction, eversion, and lateral ground reaction force than the normally aligned individuals. In addition, those with varus knees also demonstrated increased knee flexion and external knee flexor moments during midstance. These results suggest that individuals with varus knees exhibit some, but not all, of the altered mechanics seen in medial knee OA.

Walking shoes and laterally wedged orthoses in the clinical management of medial tibiofemoral osteoarthritis: a one-year prospective controlled trial.

The purpose of the study was to examine the clinical efficacy of individually prescribed laterally wedged orthoses and walking shoes in the treatment of medial knee osteoarthritis using a prospective, single-blind, block-randomized controlled design. Sixty-six subjects (29 males, 37 females, mean age 62.4 years, mean BMI 33.0 kg/m(2)) were block-randomized to a lateral wedge (treatment) or neutral (control) orthotic group. Both groups were issued a standardized walking shoe for use with the orthoses. Primary outcome measures included the pain, stiffness, and functional limitations subscales of the Western Ontario and McMaster Universities index. Secondary outcome measures included the 6-minute walk distance and pain change, and stair negotiation time and pain change. A significant interaction (p=0.039) favoring the treatment group was observed for pain change during the 6-minute walk. The treatment group demonstrated significant improvements at both 1 month (p<0.001) and 1 year (p<0.001) compared to baseline. The control group only demonstrated significant improvements at 1 year (p=0.017). No other interactions were observed. Both groups were improved at each follow-up in the WOMAC subscales for pain (p<0.001), stiffness (p<0.001), and physical function (p<0.001). Both groups also improved in 6-minute walk test distance (p<0.001), stair negotiation test time (p=0.004), and stair negotiation test pain change (p<0.001). The results suggest that both neutral and laterally wedged orthoses may be beneficial in the management of medial knee osteoarthritis when used with walking shoes. However, the addition of lateral wedging was associated with early improvements in 6-minute walk test pain change not seen in the control group.

Hip and knee frontal plane moments in persons with unilateral, trans-tibial amputation.

Persons with unilateral, lower-extremity amputation are at risk of developing osteoarthritis in their intact limb. Among persons without amputation, knee osteoarthritis disease severity has been linked to elevated frontal plane knee moments. Therefore, the purpose of this study was to examine knee and hip frontal plane moments in persons with unilateral, trans-tibial amputation. We hypothesized that knee and hip internal abduction moments are greater in the intact limb compared to the prosthetic side. Three-dimensional gait mechanics were measured bilaterally from 10 persons with unilateral, trans-tibial amputation during walking to calculate lower-extremity joint moments. The intact limb knee and hip peak internal abduction moments were 46% and 39% greater, respectively, than on the prosthetic side. The intact side knee and hip peak internal abduction moments were 17% and 6% greater, respectively, than normal. Larger moments suggest joint loading is of higher magnitude on the intact side, which may be predisposed to premature joint degeneration, particularly knee osteoarthritis.

Manipulations of leg mass and moment of inertia: effects on energy cost of walking.

PURPOSE: To investigate effects that independent alterations in limb mass and moment of inertia about a transverse axis through the hip have on metabolic and mechanical power of walking and peak electromyography (EMG) amplitude. It was hypothesized that increases in metabolic cost would parallel increases in mechanical power, and that EMG amplitude would increase with greater limb mass or limb moment of inertia. METHODS: Metabolic and mechanical power and lower-extremity EMG were measured on 14 healthy adults walking at 1.5 m.s. Four leg-loading conditions were employed: 1) no load (NL) on the legs; 2) a baseline load (BSLN) condition, with a mean of 2.0 kg per leg distributed on the proximal and distal shank; 3) a load condition with a mean of 2.0 kg per leg distributed on the proximal and distal shank, such that lower-extremity moment of inertia was increased 5% about the hip (MOI5) from the BSLN, but having the same lower-extremity mass as BSLN; and 4) a load condition with a mean of 2.8 kg per leg, concentrated proximally on the shank to increase total lower-extremity mass by 5% (Mass5) from BSLN, but having the same moment of inertia as BSLN. Total subject mass was constant between conditions, as unused leg loads were carried in a waist belt. RESULTS: Changes in mechanical power paralleled changes in metabolic cost as hypothesized. Energy cost increased significantly (4.2%) from NL to BSLN, and from BSLN to MOI5 and Mass5 (3.4 and 4.0%, respectively). EMG did not effectively explain changes in metabolic cost. CONCLUSION: Independent alterations in limb mass and moment of inertia about the hip joint influence energy cost similarly.