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Background: Lower extremity injuries are the most common injuries in professional sports and carry a high burden to players and teams in the National Football League (NFL). Injury prevention strategies can be refined by a foundational understanding of the occurrence and effect of these injuries on NFL players., Purpose: To determine the incidence of specific lower extremity injuries sustained by NFL players across 4 NFL seasons., Study Design: Descriptive epidemiology study., Methods: This retrospective, observational study included all time-loss lower extremity injuries that occurred during football-related activities during the 2015 through 2018 seasons. Injury data were collected prospectively through a leaguewide electronic health record (EHR) system and linked with NFL game statistics and player participation to calculate injury incidence per season and per 10,000 player-plays for lower extremity injuries overall and for specific injuries. Days lost due to injury were estimated through 2018 for injuries occurring in the 2015 to 2017 seasons., Results: An average of 2006 time-loss lower extremity injuries were reported each season over this 4-year study, representing a 1-season risk of 41% for an NFL player. Incidence was stable from 2015 to 2018, with an estimated total missed time burden each NFL season of approximately 56,700 player-days lost. Most (58.7%) of these injuries occurred during games, with an overall higher rate of injuries observed in preseason compared with regular season (11.5 vs 9.4 injuries per 10,000 player-plays in games). The knee was the most commonly injured lower extremity region (29.3% of lower body injuries), followed by the ankle (22.4%), thigh (17.2%), and foot (9.1%). Hamstring strains were the most common lower extremity injury, followed by lateral ankle sprains, adductor strains, high ankle sprains, and medial collateral ligament tears., Conclusion: Lower extremity injuries affect a high number of NFL players, and the incidence did not decrease over the 4 seasons studied. Prevention and rehabilitation protocols for these injuries should continue to be prioritized.

Background: "Research-ready" evidence platforms that link sports data with anonymized electronic health records (EHRs) or other data are important tools for evaluating injury occurrence in response to changes in games, training, rules, and other factors. While there is agreement that high-quality data are essential, there is little evidence to guide data curation., Hypothesis: We hypothesized that an EHR used in the course of clinical care and curated for research readiness can provide a robust evidence platform. Our purpose was to describe the data curation used for active injury surveillance by the National Football League (NFL)., Study Design: Dynamic cohort study., Level of Evidence: Level 2., Methods: Players provide informed consent for research activities through the collective bargaining process. A league-wide EHR is used to record injuries that come to the attention of the teams' athletic trainers and physicians, NFL medical spotters, or unaffiliated neurotrauma consultants. Information about football activities and injuries are linkable by player, setting, and event to other sports-related data, including game statistics and game-day stadium quality measures, using a unique player identification designed to protect player privacy. Ongoing data curation is used to review data completeness and accuracy and is adjusted over time in response to findings., Results: The core data curation activities include monthly injury summaries to team staff, queries to resolve incomplete reporting, and periodic external checks. Experiences derived from producing more than 100 reports per year on diverse topics are used to update coding training and related guidance documents in response to missing data or inconsistent coding that is observed. Roughly 20% more injuries were recorded for the same "reportable" injuries after switching from targeted reporting to an EHR., Conclusion: Research-ready databases need systematic curation for quality and completeness, along with related action plans. More injuries were reported through EHR than through targeted reporting., Clinical Relevance: Evidence-driven decision-making thrives on reliable data fine-tuned through systematic use, review, and ongoing adjustments to the curation process.

Background: Nearly three-quarters of anterior cruciate ligament (ACL) injuries occur as "noncontact" failures from routine athletic maneuvers. Recent in vitro studies revealed that repetitive strenuous submaximal knee loading known to especially strain the ACL can lead to its fatigue failure, often at the ACL femoral enthesis., Hypothesis: ACL failure can be caused by accumulated tissue fatigue damage: specifically, chemical and structural evidence of this fatigue process will be found at the femoral enthesis of ACLs from tested cadaveric knees, as well as in ACL explants removed from patients undergoing ACL reconstruction., Study Design: Controlled laboratory study., Methods: One knee from each of 7 pairs of adult cadaveric knees were repetitively loaded under 4 times-body weight simulated pivot landings known to strain the ACL submaximally while the contralateral, unloaded knee was used as a comparison. The chemical and structural changes associated with this repetitive loading were characterized at the ACL femoral enthesis at multiple hierarchical collagen levels by employing atomic force microscopy (AFM), AFM-infrared spectroscopy, molecular targeting with a fluorescently labeled collagen hybridizing peptide, and second harmonic imaging microscopy. Explants from ACL femoral entheses from the injured knee of 5 patients with noncontact ACL failure were also characterized via similar methods., Results: AFM-infrared spectroscopy and collagen hybridizing peptide binding indicate that the characteristic molecular damage was an unraveling of the collagen molecular triple helix. AFM detected disruption of collagen fibrils in the forms of reduced topographical surface thickness and the induction of ~30- to 100-nm voids in the collagen fibril matrix for mechanically tested samples. Second harmonic imaging microscopy detected the induction of ~10- to 100-µm regions where the noncentrosymmetric structure of collagen had been disrupted. These mechanically induced changes, ranging from molecular to microscale disruption of normal collagen structure, represent a previously unreported aspect of tissue fatigue damage in noncontact ACL failure. Confirmatory evidence came from the explants of 5 patients undergoing ACL reconstruction, which exhibited the same pattern of molecular, nanoscale, and microscale structural damage detected in the mechanically tested cadaveric samples., Conclusion: The authors found evidence of accumulated damage to collagen fibrils and fibers at the ACL femoral enthesis at the time of surgery for noncontact ACL failure. This tissue damage was similar to that found in donor knees subjected in vitro to repetitive 4 times-body weight impulsive 3-dimensional loading known to cause a fatigue failure of the ACL., Clinical Relevance: These findings suggest that some ACL injuries may be due to an exacerbation of preexisting hierarchical tissue damage from activities known to place larger-than-normal loads on the ACL. Too rapid an increase in these activities could cause ACL tissue damage to accumulate across length scales, thereby affecting ACL structural integrity before it has time to repair. Prevention necessitates an understanding of how ACL loading magnitude and frequency are anabolic, neutral, or catabolic to the ligament.

Purpose: The purpose of this study was to determine the effect of concomitant meniscal surgery on the recovery of quadriceps activation and strength at a time when individuals return to sport following anterior cruciate ligament (ACL) reconstruction., Methods: Forty-six individuals that were cleared for participation following ACL reconstruction were invited to participate in this study. Participants were placed into groups according to surgical reports (ACL-only, n = 24; meniscal repair, n = 12; meniscectomy, n = 10). Quadriceps strength was quantified using isokinetic and isometric measures. Isokinetic strength was collected at 60°/s in concentric mode. Isometric strength was collected at 90° of knee flexion. Quadriceps activation was assessed using the burst superimposition technique and quantified via the central activation ratio. One-way ANOVAs were utilized to detect whether differences existed in quadriceps activation and strength between groups. Where appropriate, post hoc Bonferroni multiple comparison procedures were used., Results: Quadriceps activation (P = n.s.) and strength (isokinetic: P = n.s.; isometric: P = n.s.) were not different between groups., Conclusion: Concomitant meniscectomy or meniscal repair did not affect the recovery of quadriceps activation and strength at a time when individuals return to sport following ACL reconstruction. Though group differences in quadriceps function were not detected, all participants demonstrated levels of quadriceps activation failure that are below healthy individuals at a time when they were returned to sport. Given that persistent quadriceps activation failure is detrimental to knee function, rehabilitation protocols that target quadriceps activation failure should be developed and employed post-reconstruction.

Background: The purpose of this study was to evaluate the results of arthroscopic repair of the meniscus in children and young athletes., Methods: Arthroscopic meniscus repairs performed on 49 knees in 31 male and 14 female patients <18 years old were reviewed. All repairs were done using an inside-out technique, and 31 patients required concomitant anterior cruciate ligament (ACL) reconstruction. Age at time of injury, time to surgery, and the extent, type, and location of meniscus tear were noted. All patients underwent postoperative rehabilitation and clinical evaluation. The level of activity at follow-up and postoperative outcomes scores was determined. Analysis included t tests, Wilcoxon tests, χ tests, and Fisher exact tests, with a level of significance of P ≥ 0.05., Results: Excellent clinical outcomes were noted in 43 of 45 patients, with mean length of follow-up of 27 months. Between the groups with and without ACL tears, there were no significant differences in mean age at the time of injury or surgery, or in the distribution of open versus closed physes, medial versus lateral repairs, or level-of-activity at follow-up. However, patients with ACL reconstruction had significantly longer return-to-activity times (mean 8.23 mo vs. 5.56 mo) and significantly lower Tegner scores (mean 6.8 vs. 8.0) than patients without simultaneous reconstruction., Conclusions: The clinical results after arthroscopic meniscus repair in the adolescent were excellent, despite long average time from injury to surgery and a high number of tears in poorly vascularized areas. Meniscal tears in skeletally immature athletes may have greater reparative potential, with and without simultaneous ligament reconstruction. Attempts at repair regardless of time from injury or location of tear should be strongly considered in this age group., Level of Evidence: Level III retrospective cohort series.

Treatment algorithms for posterior cruciate ligament (PCL) injury have evolved over the past two decades as the natural history of these injuries has become clearer. Whether they are isolated injuries or occur with other ligament trauma, PCL ruptures substantially alter knee kinematics. Because of the effects of PCL injury and the less than optimal results after nonsurgical treatment, new surgical techniques have been developed. Several surgical techniques currently are available for reconstruction of the PCL. Most recent reports suggest that the tibial inlay technique is the best choice for restoring posterior tibial stability. Tibial inlay PCL reconstructions can be performed through both open and arthroscopic approaches. Crucial to the outcome of these procedures is detecting all injuries to the secondary restraints, especially the posterolateral corner. Failure to recognize and treat these deficits can compromise the results of PCL reconstruction, emphasizing the need for a detailed, meticulous physical examination when PCL injuries are suspected.

Objective: To review 16 years of NCAA injury surveillance data for women's volleyball and to identify potential areas for injury prevention initiatives., Background: Participation in NCAA women's volleyball has increased greatly over the past 16 years. As with all sports, women participating in volleyball assume an inherent risk of injury each time they practice or participate in a game. In order for clinicians to better understand the risks associated with volleyball, it is critical to gather data that illustrates injury rates and patterns among volleyball athletes. Furthermore, with knowledge of injury mechanisms and risk factors comes the ability to initiate prevention strategies to minimize future injury., Main Results: Over the past 16 years, the rate of injury in a game situation was slightly higher than in practice (4.58 versus 4.10 game injuries per 1000 athlete-exposures, rate ratio = 1.1, 95% confidence interval = -1.0, 1.2, P < .01). A total of 2216 injuries from more than 50 000 games and 4725 injuries from more than 90 000 practices were reported. The lower extremity accounted for more than 55% of all game and practice injuries, with ankle ligament sprains representing 44.1% of game injuries and 29.4% of practice injuries. Approximately 20% of all game injuries involved the upper extremity. The majority of injuries during a game situation occurred while athletes were in one of the front 3 positions. A player landing on another player and contact with the floor each accounted for 21% of game injuries., Recommendations: Ankle injuries appear to be the most common injuries in women's volleyball. Future preventive efforts should focus on preventing first-time ankle sprains and acute traumatic knee injuries, as well as reducing the risk of ankle sprain recurrence.

Background: Athletes often employ prophylactic braces to reduce the risk of ankle injuries., Hypothesis: Ankle braces do not significantly decrease the risk of forced inversion on a standardized one-footed jump landing., Study Design: Controlled laboratory study., Methods: Fourteen healthy men with a mean age of 25.1 years were tested. Three braces, two semirigid (Aircast and Bledsoe) and one lace-up (Swede-O), were fitted to each subject. Forced dynamic ankle inversion of 24 degrees was to be resisted as the subjects landed on one foot with a force of two body weights on a stimulus presented randomly in 5 of 15 jump trial blocks onto a hard, level force plate. Subjects first completed 1 no-brace block of 5 trials to establish baseline performance, then 3 randomly ordered 15-trial blocks testing performance with each of the braces, and then finally a no-brace 5-trial block., Results: The average no-brace success rate was 24%, which demonstrated the challenging nature of the task. All three braces increased the success rate (average, 44%); however, only the two semirigid braces proved to be significantly better than the unbraced state., Conclusion: This test holds promise for evaluating brace efficacy when landing with one foot unexpectedly on an object that acts to forcibly invert the ankle.

Background: Female athletes who participate in sports involving jumping and cutting maneuvers are up to eight times more likely to sustain a rupture of the anterior cruciate ligament than are men participating in the same sports. We tested the hypothesis that healthy young women are able to volitionally increase the apparent torsional stiffness of the knee, by maximally activating the knee muscles, significantly less than are size-matched men participating in the same type of sport., Methods: Twenty-four NCAA (National Collegiate Athletic Association) Division-I athletes (twelve men and twelve women) competing in sports associated with a high risk of injury to the anterior cruciate ligament (basketball, volleyball, and soccer) were compared with twenty-eight collegiate endurance athletes (fourteen men and fourteen women) participating in sports associated with a low risk of such injuries (bicycling, crew, and running). Male and female pairs were matched for age, height, weight, body mass index, shoe size, and activity level. Testing was performed with a weighted pendulum that applied a medially directed 80-N impulse force to the lateral aspect of the right forefoot. The resulting internal rotation of the leg was measured optically, to the nearest 0.25 degrees, at 30 degrees and 60 degrees of knee flexion, both with and without maximal activation of the knee muscles., Results: Maximal rotations of the leg were greater in women than in men in both the passive and the active muscle state (16% and 27% greater [p = 0.01 and p = 0.02], respectively). Moreover, female athletes exhibited a significantly (18%) smaller volitional increase in apparent torsional stiffness of the knee under internal rotation loading than did the matched male athletes (p = 0.014); this was particularly the case for those who participated in sports involving jumping and pivoting maneuvers (42% difference between genders, p = 0.001)., Conclusions: The collegiate female athletes involved in high-risk sports exhibited less muscular protection of the knee ligaments during external loading of the knee than did size and sport-matched male athletes.

Anterior cruciate ligament injury rates are reported to be two to eight times higher in women than in men within the same sport. Because the menstrual cycle with its monthly hormonal fluctuations is one of the most basic differences between men and women, we investigated the association between the distribution of confirmed anterior cruciate ligament tears and menstrual cycle phase. Sixty-nine female athletes who sustained an acute anterior cruciate ligament injury were studied within 24 hours of injury at four centers. The mechanism of injury, menstrual cycle details, use of oral contraceptives, and history of previous injury were recorded. Urine samples were collected to validate menstrual cycle phase by measurement of estrogen, progesterone, and luteinizing hormone metabolites and creatinine levels at the time of the anterior cruciate ligament tear. Results from the hormone assays indicate that the women had a significantly greater than expected percentage of anterior cruciate ligament injuries during midcycle (ovulatory phase) and a less than expected percentage of those injuries during the luteal phase of the menstrual cycle. Oral contraceptive use diminished the significant association between anterior cruciate ligament tear distribution and the ovulatory phase.

In the general population, an estimated one in 3000 individuals sustains an anterior cruciate ligament injury per year in the United States, corresponding to an overall injury rate of approximately 100,000 injuries annually. This national estimate is low for women because anterior cruciate ligament injury rates are reported to be two to eight times higher in women than in men participating in the same sports, presenting a sizable health problem. With the growing participation of women in athletics and the debilitating nature of anterior cruciate ligament injuries, a better understanding of mechanisms of injury in women sustaining anterior cruciate ligament injuries is essential. Published studies strongly support noncontact mechanisms for anterior cruciate ligament tears in women, which make these injuries even more perplexing. Speculation on the possible etiology of anterior cruciate ligament injuries in women has centered on anatomic differences, joint laxity, hormones, and training techniques. Investigators have not agreed on causal factors for this injury, but they have started to profile the type of athlete who is at risk. In the current study the most recent scientific studies of intrinsic and extrinsic risk factors thought to be contributing to the high rate of female anterior cruciate ligament injuries will be reviewed, important differences will be highlighted, and recommendations proposed to alleviate or minimize these risk factors among female athletes will be reported where appropriate.

Anterior cruciate ligament injury rates are four to eight times higher in women than in men. Because of estrogen's direct effect on collagen metabolism and behavior and because neuromuscular performance varies during the menstrual cycle, it is logical to question the menstrual cycle's effect on knee injury rates. Of 40 consecutive female athletes with acute anterior cruciate ligament injuries (less than 3 months), 28 (average age, 23 +/- 11 years) met the study criteria of regular menstrual periods and noncontact injury. Details concerning mechanism of injury, menstrual cycle, contraceptive use, and previous injury history were collected. A chi-square test was used to compute observed and expected frequencies of anterior cruciate ligament injury based on three different phases of the menstrual cycle: follicular (days 1 to 9), ovulatory (days 10 to 14), and luteal (day 15 to end of cycle). A significant statistical association was found between the stage of the menstrual cycle and the likelihood for an anterior cruciate ligament injury (P = 0.03). In particular, there were more injuries than expected in the ovulatory phase of the cycle. In contrast, significantly fewer injuries occurred in the follicular phase. These hormones may be a factor in the knee ligament injury dilemma in women.

The routine use of functional knee braces in the anterior cruciate ligament-deficient, injured, or reconstructed knee, lacks biomechanical support. Although subjective reports favoring bracing are plentiful, objective proof of significant control of tibial translation is not. This in vivo study was designed to assess the effect of six popular braces on anterior tibial translation, isokinetic performance, and neuromuscular function in five chronically unstable anterior cruciate ligament-deficient knees. A knee stress test was performed on a specially designed device that allowed free tibial movement while monitoring anterior tibial translation and muscle function in the quadriceps, hamstring, and gastrocnemius muscles. Results show that braces can decrease anterior tibial translation between 28.8% and 39.1% without the stabilizing contractions of the hamstring, quadriceps, and gastrocnemius muscles. With lower extremity muscle activation and bracing, anterior tibial translation was decreased between 69.8% and 84.9%. Some improvement in spinal level muscle reaction times was seen with brace use, especially in the quadriceps muscle. Unfortunately, most braces appear to consistently slow hamstring muscle reaction times at the voluntary level.

The purpose of this research was to identify possible predisposing neuromuscular factors for knee injuries, particularly anterior cruciate ligament tears in female athletes by investigating anterior knee laxity, lower extremity muscle strength, endurance, muscle reaction time, and muscle recruitment order in response to anterior tibial translation. We recruited four subject groups: elite female (N = 40) and male (N = 60) athletes and sex-matched nonathletic controls (N = 40). All participants underwent a subjective evaluation of knee function, arthrometer measurement of anterior tibial translation, isokinetic dynamometer strength and endurance tests at 60 and 240 deg/sec, and anterior tibial translation stress tests. Dynamic stress testing of muscles demonstrated less anterior tibial translation in the knees of the athletes (both men and women) compared with the nonathletic controls. Female athletes and controls demonstrated more anterior tibial laxity than their male counterparts and significantly less muscle strength and endurance. Compared with the male athletes, the female athletes took significantly longer to generate maximum hamstring muscle torque during isokinetic testing. Although no significant differences were found in either spinal or cortical muscle reaction times, the muscle recruitment order in some female athletes was markedly different. The female athletes appeared to rely more on their quadriceps muscles in response to anterior tibial translation; the three other test groups relied more on their hamstring muscles for initial knee stabilization.

In a previous retrospective study, base sliding was found to be responsible for 71% of recreational softball injuries. As most injuries occurred following rapid deceleration impact against stationary bases, quick-release (breakaway) bases were evaluated as a means to modify this mechanism of injury. Six hundred thirty-three softball games were played on breakaway-base fields and 627 games were played on stationary-base fields. Forty-five sliding injuries (7%) occurred on the stationary-base diamonds and only two sliding injuries (less than 1%) occurred on the breakaway-base fields. Implementing the use of breakaway bases in recreational softball leagues could potentially achieve a significant, cost-effective reduction of injuries.

The care of the pediatric athlete should not be viewed as caring for small adults. Growing bones, tendons, ligaments, and muscles respond differently to stress. Proper training and conditioning can remedy most problems in the immature athlete.