Darin A. Padua

Epidemiology of Concussion in Collegiate and High School Football Players

Despite evolutionary changes in protective equipment, head injury remains common in football. We investigated concussion in football and associated epidemiologic issues such as 1) incidence of injury, 2) common signs and symptoms, and 3) patterns in making return-to-play decisions. We received 242 of 392 surveys (62%) that were sent to high school and collegiate certified athletic trainers at the beginning of three football seasons. Of the 17,549 football players represented, 888 (5.1%) sustained at least one concussion, and 131 (14.7% of the 888) sustained a second injury during the same season. The greatest incidence of concussion was found at the high school (5.6%) and collegiate division III (5.5%) levels, suggesting that there is an association between level of play and the proportion of players injured. Players who sustained one concussion in a season were three times more likely to sustain a second concussion in the same season compared with uninjured players. Contact with artificial turf appears to be associated with a more serious concussion than contact with natural grass. Only 8.9% of all injuries involved loss of consciousness, while 86% involved a headache. Overall, 30.8% of all players sustaining a concussion returned to participation on the same day of injury.

Gender Differences in the Incidence and Prevalence of Patellofemoral Pain Syndrome

The purpose of this investigation was to determine the association between gender and the prevalence and incidence of patellofemoral pain syndrome (PFPS). One thousand five hundred and twenty‐five participants from the United States Naval Academy (USNA) were followed for up to 2.5 years for the development of PFPS. Physicians and certified athletic trainers documented the cases of PFPS. PFPS was defined as retropatellar pain during at least two of the following activities: ascending/descending stairs, hopping/jogging, prolonged sitting, kneeling, and squatting, negative findings on examination of knee ligament, menisci, bursa, and synovial plica, and pain on palpation of either the patellar facets or femoral condyles. Poisson and logistic regressions were performed to determine the association between gender and the incidence and prevalence of PFPS, respectively. The incidence rate for PFPS was 22/1000 person‐years. Females were 2.23 times (95% CI: 1.19, 4.20) more likely to develop PFPS compared with males. While not statistically significant, the prevalence of PFPS at study enrollment tended to be higher in females (15%) than in males (12%) (P=0.09). Females at the USNA are significantly more likely to develop PFPS than males. Additionally, at the time of admission to the academy, the prevalence of PFPS was not significantly different between genders.

The Landing Error Scoring System (LESS) Is a Valid and Reliable Clinical Assessment Tool of Jump-Landing Biomechanics The JUMP-ACL Study

Background Anterior cruciate ligament injuries are common in athletes and have serious sequelae. A valid clinical tool that reliably identifies individuals at an increased risk for ACL injury would be highly useful for screening sports teams, because individuals identified as “high-risk” could then be provided with intensive prevention programs. Hypothesis A clinical screening tool (the Landing Error Scoring System, or LESS) will reliably identify subjects with potentially high-risk biomechanics. Study Design Cohort study (Diagnosis); Level of evidence, 2. Methods A jump-landing-rebound task was used. Off-the-shelf camcorders recorded frontal and sagittal plane views of the subject performing the task. The LESS was scored from replay of this video. Three-dimensional lower extremity kinematics and kinetics were also collected and used as the gold standard against which the validity of the LESS was assessed. Three trials of the jump-landing task were collected for 2691 subjects. Kinematic and kinetic measures were compared across LESS score quartiles using 1-way analysis of variance; LESS quartiles were compared across genders using the chi-square test. The LESS scores from a subset of 50 subjects were rescored to determine intrarater and interrater reliability. Results Subjects with high LESS scores (poor jump-landing technique) displayed significantly different lower extremity kinematics and kinetics compared with subjects with low LESS scores (excellent jump-landing technique). Women had higher (worse) LESS scores than men. Intrarater and interrater reliability of the LESS ranged from good to excellent. Conclusion The LESS is a valid and reliable tool for identifying potentially high-risk movement patterns during a jump-landing task.

A Prospective Investigation of Biomechanical Risk Factors for Patellofemoral Pain Syndrome The Joint Undertaking to Monitor and Prevent ACL Injury (JUMP-ACL) Cohort

Background Patellofemoral pain syndrome is one of the most common chronic knee injuries; however, little research has been done to determine the risk factors for this injury. Hypothesis Altered lower extremity kinematics and kinetics, decreased strength, and altered postural measurements will be risk factors. Study Design Cohort study (prognosis); Level of evidence, 2. Methods A total of 1597 participants were enrolled in this investigation and prospectively followed from the date of their enrollment (July 2005, July 2006, or July 2007) through January 2008, a maximum of 2.5 years of follow-up. Each participant underwent baseline data collection during their pre-freshman summer at the United States Naval Academy. Baseline data collection included 3-dimensional motion analysis during a jump-landing task, 6 lower extremity isometric strength tests, and postural alignment measurements (navicular drop and Q angle). Results Risk factors for the development of patellofemoral pain syndrome included decreased knee flexion angle, decreased vertical ground-reaction force, and increased hip internal rotation angle during the jump-landing task. Additionally, decreased quadriceps and hamstring strength, increased hip external rotator strength, and increased navicular drop were risk factors for the development of patellofemoral pain syndrome. Conclusion Multiple modifiable risk factors for patellofemoral pain syndrome pain have been identified in this investigation. To decrease the incidence of this chronic injury, the risk factors for patellofemoral pain syndrome need to be targeted in injury prevention programs. Clinical Relevance Prevention programs should focus on increasing strength of the lower extremity musculature along with instructing proper mechanics during dynamic movements to decrease the incidence of patellofemoral pain syndrome.

Systematic Review of the Balance Error Scoring System

Context: The Balance Error Scoring System (BESS) is commonly used by researchers and clinicians to evaluate balance.A growing number of studies are using the BESS as an outcome measure beyond the scope of its original purpose. Objective: To provide an objective systematic review of the reliability and validity of the BESS. Data Sources: PubMed and CINHAL were searched using Balance Error Scoring System from January 1999 through December 2010. Study Selection: Selection was based on establishment of the reliability and validity of the BESS. Research articles were selected if they established reliability or validity (criterion related or construct) of the BESS, were written in English, and used the BESS as an outcome measure. Abstracts were not considered. Results: Reliability of the total BESS score and individual stances ranged from poor to moderate to good, depending on the type of reliability assessed. The BESS has criterion-related validity with force plate measures; more difficult stances have higher agreement than do easier ones. The BESS is valid to detect balance deficits where large differences exist (concussion or fatigue). It may not be valid when differences are more subtle. Conclusions: Overall, the BESS has moderate to good reliability to assess static balance. Low levels of reliability have been reported by some authors. The BESS correlates with other measures of balance using testing devices. The BESS can detect balance deficits in participants with concussion and fatigue. BESS scores increase with age and with ankle instability and external ankle bracing. BESS scores improve after training.

Gluteal Muscle Activation During Common Therapeutic Exercises

STUDY DESIGN Experimental laboratory study. OBJECTIVES To quantify and compare electromyographic signal amplitude of the gluteus maximus and gluteus medius muscles during exercises of varying difficulty to determine which exercise most effectively recruits these muscles. BACKGROUND Gluteal muscle weakness has been proposed to be associated with lower extremity injury. Exercises to strengthen the gluteal muscles are frequently used in rehabilitation and injury prevention programs without scientific evidence regarding their ability to activate the targeted muscles. METHODS Surface electromyography was used to quantify the activity level of the gluteal muscles in 21 healthy, physically active subjects while performing 12 exercises. Repeated-measures analyses of variance were used to compare normalized mean signal amplitude levels, expressed as a percent of a maximum voluntary isometric contraction (MVIC), across exercises. RESULTS Significant differences in signal amplitude among exercises were noted for the gluteus medius (F5,90 = 7.9, P<.0001) and gluteus maximus (F5,95 = 8.1, P<.0001). Gluteus medius activity was significantly greater during side-lying hip abduction (mean +/- SD, 81% +/- 42% MVIC) compared to the 2 types of hip clam (40% +/- 38% MVIC, 38% +/- 29% MVIC), lunges (48% +/- 21% MVIC), and hop (48% +/- 25% MVIC) exercises. The single-limb squat and single-limb deadlift activated the gluteus medius (single-limb squat, 64% +/- 25% MVIC; single-limb deadlift, 59% +/- 25% MVIC) and maximus (single-limb squat, 59% +/- 27% MVIC; single-limb deadlift, 59% +/- 28% MVIC) similarly. The gluteus maximus activation during the single-limb squat and single-limb deadlift was significantly greater than during the lateral band walk (27% +/- 16% MVIC), hip clam (34% +/- 27% MVIC), and hop (forward, 35% +/- 22% MVIC; transverse, 35% +/- 16% MVIC) exercises. CONCLUSION The best exercise for the gluteus medius was side-lying hip abduction, while the single-limb squat and single-limb deadlift exercises led to the greatest activation of the gluteus maximus. These results provide information to the clinician about relative activation of the gluteal muscles during specific therapeutic exercises that can influence exercise progression and prescription. J Orthop Sports Phys Ther 2009;39(7):532-540, Epub 24 February 2009. doi:10.2519/jospt.2009.2796.

Sagittal-Plane Trunk Position, Landing Forces, and Quadriceps Electromyographic Activity

CONTEXT Researchers have suggested that large landing forces, excessive quadriceps activity, and an erect posture during landing are risk factors for anterior cruciate ligament (ACL) injury. The influence of knee kinematics on these risk factors has been investigated extensively, but trunk positioning has received little attention. OBJECTIVE To determine the effect of trunk flexion on landing forces and quadriceps activation during landing. DESIGN Two (sex) x 2 (task) repeated-measures design. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Forty healthy, physically active volunteers (20 men, 20 women). INTERVENTION(S) Participants performed 2 drop-landing tasks. The first task represented the natural, or preferred, landing strategy. The second task was identical to the first except that participants flexed the trunk during landing. MAIN OUTCOME MEASURE(S) We measured peak vertical and posterior ground reaction forces and mean quadriceps electromyographic amplitude during the loading phase of landing (ie, the interval from initial ground contact to peak knee flexion). RESULTS Trunk flexion decreased the vertical ground reaction force (P < .001) and quadriceps electromyographic amplitude (P < .001). The effect of trunk flexion did not differ across sex for landing forces or quadriceps electromyographic activity. CONCLUSIONS We found that trunk flexion during landing reduced landing forces and quadriceps activity, thus potentially reducing the force imparted to the ACL. Research has indicated that trunk flexion during landing also increases knee and hip flexion, resulting in a less erect landing posture. In combination, these findings support emphasis on trunk flexion during landing as part of ACL injury-prevention programs.

The Effects of Strength Training on the Lower Extremity Biomechanics of Female Recreational Athletes During a Stop-Jump Task

Background Strength training is considered a strategy for anterior cruciate ligament injury prevention. Little is known about the contribution of strength training to knee and hip biomechanics. Hypothesis Lower extremity muscle strength training alters knee and hip biomechanics during a stop-jump task. Study Design Controlled laboratory study. Methods Knee and hip 3-dimensional kinematic and kinetic data were collected for 66 female recreational athletes (33 intervention and 33 control) while performing 3 stop-jump tasks before and after completing a 9-week strength-training program targeting the quadriceps, hamstrings, gluteus medius, and gluteus maximus (intervention) or a 9-week period of no strength training (control). Maximum voluntary isometric contraction strength data were also collected for each subject before the stop-jump tasks in each data collection session. Knee and hip joint angles as well as resultant forces and moments were calculated. Results The intervention group increased in strength (P < .001 for all muscles). No significant differences were observed in knee and hip kinematics and kinetics between groups before and after the strength-training protocol. Conclusions Strength training alone does not alter knee and hip kinematics and kinetics in female recreational athletes. Further research is needed to determine the effect of strength training in combination with other intervention methods on lower extremity biomechanics. Clinical Relevance Strength training as a single intervention method may not be sufficient to reduce the risk of noncontact anterior cruciate ligament injury in female recreational athletes.

Gender differences in leg stiffness and stiffness recruitment strategy during two-legged hopping.

The authors compared leg stiffness (KVERT), muscle activation, and joint movement patterns between 11 men and 10 women during hopping. Physically active and healthy men and women performed continuous 2-legged hopping at their preferred rate and at 3.0 Hz. Compared with men, women demonstrated decreased KVERT; however, after the authors normalized for body mass, gender differences in KVERT were eliminated. In comparison with men, women also demonstrated increased quadriceps and soleus activity, as well as greater quadriceps-to-hamstrings coactivation ratios. There were no significant gender differences for joint movement patterns (p >.05). The relationship between the observed gender differences in muscle recruitment and the increased risk of anterior cruciate ligament injury in women requires further study.

The effects of feedback with and without strength training on lower extremity biomechanics

Background Feedback instruction is a proven modality for the alteration of motion patterns. There are no existing data on the contribution of strength training, when combined with feedback instruction, to the altering of lower extremity biomechanics. Hypothesis Lower extremity muscle strength training provides an increased capacity to alter knee and hip biomechanics during a stop-jump task in response to a feedback protocol. Study Design Controlled laboratory study. Methods Knee and hip 3-dimensional kinematic and kinetic data were collected for 58 female recreational athletes while performing 3 stop-jump tasks after completing a 9-week strength training program (ST-FB; n = 29) or a 9-week period of no strength training (FB; n = 29). Data were then collected for both groups after completing a jump-landing feedback instruction protocol. Knee and hip joint angles, as well as resultant forces and moments, were calculated. Results Across all participants, there were decreased peak vertical ground-reaction forces (P < .001) and increased knee flexion (P = .050), hip flexion (P < .001), and hip abduction (P = .032) angles, subsequent to the feedback protocol. Hip abduction angle (P < .001) increased in the ST-FB group but not the FB group, and peak knee anterior shear force (P = .015) decreased in the ST-FB group but increased in the FB group (P = .009). Conclusion The results indicate that strength training, when used in conjunction with video-assisted feedback, may provide an increased capacity for the alteration of knee and hip biomechanics. Clinical Relevance Programs that include both strength training and movement education through feedback may be necessary to increase the effectiveness of anterior cruciate ligament prevention programs. Strength training may provide an increased capacity for athletes to respond to other intervention modalities used in anterior cruciate ligament injury prevention programs.