Nagelli, Christopher V.

Objective: Athletes who return to sport after anterior cruciate ligament reconstruction (ACLR) demonstrate persistent biomechanical and neuromuscular deficits of the knee. There is limited evidence on what effect a neuromuscular training (NMT) program has on knee biomechanics in a cohort of athletes with ACLR. Therefore, the primary aim of this study was to quantify the effect of an NMT program on knee biomechanics in a cohort of ACLR athletes. Second, the post-training knee biomechanics were compared between the cohort of ACLR and control athletes. Design: Cohort study. Setting: Controlled laboratory setting. Participants: Eighteen athletes with ACLR and 10 control athletes. Interventions: Neuromuscular training. Main Outcome Measures: Knee kinematics and kinetics during a double-limb jump-landing task. Results: There were no significant interactions (P > 0.05) observed for the athletes with ACLR. However, there was a significant main effect of biomechanics testing session (P < 0.05) for knee flexion angle and moments; athletes with ACLR demonstrated greater knee flexion angle and lower knee flexion moment during the post-training biomechanics testing session. Post-training comparison between the ACLR and control athletes demonstrated no significant interactions (P > 0.05) between the groups. There was a significant main effect of group (P < 0.05) for knee frontal angle, as athletes with ACLR landed with greater knee adduction than the control athletes. Conclusions: Significant improvements in knee sagittal plane biomechanical measures were observed after the NMT program by the athletes with ACLR. In addition, post-training comparison of the ACLR and control groups demonstrates comparable knee biomechanics.

Background: Football has one of the highest injury rates (IRs) in sports, ranging from 4.1 to 8.6 per 1000 athlete-exposures (AEs). Previous research has reported that athletes may be at an increased risk of suffering lower extremity (LE) injuries after a concussion. Purpose/Hypothesis: The purpose of this study was to evaluate the rate of LE injuries in collegiate football athletes after a concussion. We predicted that the overall LE IR would increase after a concussion and that each position group would also demonstrate a similar increase in LE injuries after a concussion. Study Design: Cohort study; Level of evidence, 2. Methods: Daily attendance and injury records were prospectively collected by licensed team medical providers for the 2012 through 2016 college football regular seasons. Each injury report included the date of injury, position group, body part injured, and type of injury. IRs per 1000 AEs with 95% CIs were calculated to evaluate LE injuries at different time points after a concussion (remainder of season, next season, any additional seasons) and by months (<6 months, 6-12 months, >12 months). Mid- P exact tests were utilized to establish injury rate ratios (IRRs) to compare the IR between variables. Results: There was no significant difference in LE IRRs between the athletes post- versus preconcussion ( P = .20) or between the postconcussion and no concussion (control) athletes ( P = .08). There was an increased LE IR beyond 12 months in the postconcussion group (IR, 9.08 [95% CI, 3.68-18.89]) compared with the no concussion group (IR, 2.88 [95% CI, 2.04-3.96]) (IRR, 3.16 [95% CI, 1.21-7.15]; P = .02). Line position players had an increase in LE injuries after a concussion (IRR, 6.22 [95% CI, 1.31-23.68]; P = .03) compared with linemen with no concussion. Conclusion: There was no initial increase in LE IRs immediately after a concussion; however, there was an increased LE IR more than 12 months after a concussion. There was no increase in LE IRs demonstrated by skill and other position groups. Line position players experienced an increased LE IR the next season after a concussion or greater than 12 months after the injury.

Background: The efficacy of a neuromuscular training (NMT) program to ameliorate known hip biomechanical risk factors for athletes with anterior cruciate ligament reconstruction (ACLR) is currently unknown. Purpose/Hypothesis: The purpose was to quantify the effects of an NMT program on hip biomechanics among athletes with ACLR and to compare posttraining hip biomechanics with a control group. The hypotheses were that known hip biomechanical risk factors of anterior cruciate ligament (ACL) injury would be significantly reduced among athletes with ACLR after the NMT program and that posttraining hip biomechanics between the ACLR and control cohorts would not differ. Study Design: Controlled laboratory study. Methods: Twenty-eight athletes (n = 18, ACLR; n = 10, uninjured) completed a 12-session NMT program. Biomechanical evaluation of a jump-landing task was done before and after completion of the program. Repeated measures analysis of variance was performed to understand the effect of NMT within the ACLR cohort. Two-way analysis of variance was used to compare both groups. Post hoc testing was done for significant interactions. Hip biomechanical variables at initial contact are reported. Results: The athletes with ACLR who completed the NMT program had a significant session × limb interaction ( P = .01) for hip external rotation moment and a significant main effect of session for hip flexion angle ( P = .049) and moment ( P < .001). There was a significant change for the involved ( P = .04; 528% increase) and uninvolved ( P = .04; 57% decrease) limbs from pre- to posttraining for hip rotation moment. The ACLR cohort had an increase in hip flexion angle (14% change) and a decrease in hip flexion moment (65% change) from pre- to posttraining. Posttraining comparison for these same hip biomechanical variables of interest revealed no significant interactions ( P > .05) between the ACLR and control cohorts. There was a significant main effect of group ( P = .02) for hip flexion angle, as the ACLR cohort demonstrated greater hip flexion angle than that of the control group. Conclusion: For athletes with ACLR, hip biomechanical measures of ACL injury risk show significant improvements after completion of an NMT program. Clinical Relevance: Athletes with ACLR who are participating in an NMT program may ameliorate known hip biomechanical risk factors for an ACL injury.

Background: Anterior cruciate ligament (ACL) injuries are catastrophic events that affect athletic careers and lead to long-term degenerative knee changes. As injuries are believed to occur within the first 50 milliseconds after initial contact during a rapid deceleration task, impact simulators that rapidly deliver impulse loads to cadaveric specimens have been developed. However, no impactor has reproducibly and reliably created ACL injures in a distribution that mimics clinical observation. Purpose: To better understand ACL injury patterns through a cadaveric investigation that applied in vivo–measured external loads to the knee during simulated landings. Study Design: Controlled laboratory study. Methods: A novel mechanical impact simulator reproduced kinetics from in vivo–recorded drop landing tasks on 45 cadaveric knees. Specimens were exposed to a randomized order of variable knee abduction moment, anterior tibial shear, and internal tibial rotation loads before the introduction of an impulse load at the foot. This process was repeated until a hard or soft tissue injury was induced on the joint. Injuries were assessed by an orthopaedic surgeon, and ligament strain was recorded by implanted strain gauges. Results: The mechanical impact simulator induced ACL injuries in 87% of specimens, with medial collateral ligament (MCL) injuries in 31%. ACL tear locations were 71% femoral side, 21% midsubstance, and 9% tibial side. Peak strain before failure for ACL-injured specimens was 15.3% ± 8.7% for the ACL and 5.1% ± 5.6% for the MCL ( P < .001). Conclusion: The ACL injuries induced by the mechanical impact simulator in the present study have provided clinically relevant in vitro representations of in vivo ACL injury patterns as cited in the literature. Additionally, current ligament strains corroborate the literature to support disproportionate loading of the ACL relative to the MCL during athletic tasks. Clinical Relevance: These findings indicate that the mechanical impact simulator is an appropriate model for examining independent mechanical variables, treatment techniques, and preventive interventions during athletic tasks leading up to and including an ACL injury. Accordingly, this system can be utilized to further parse out contributing factors to an ACL injury as well as assess the shortcomings of ACL reconstruction techniques in a dynamic, simulated environment that is better representative of in vivo injury scenarios.

Background: Anterior cruciate ligament (ACL) injury has a significant psychological effect, and a negative psychological state is a commonly cited reason for a reduction or cessation of sports participation after ACL reconstruction (ACLR) surgery. Purpose: To identify factors that contribute to an athlete’s psychological readiness to return to sport (RTS) after ACLR. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A cohort of 635 athletes (389 male, 246 female) who underwent ACLR and had been cleared to RTS completed the Anterior Cruciate Ligament–Return to Sport After Injury (ACL-RSI) scale at an average 12 months (range, 11-24 months) after surgery. Demographics (age, sex), sporting outcomes (preinjury frequency), surgical timing (injury to surgery interval), clinical factors (laxity), functional measures (single-limb hop symmetry), and symptoms of pain and function (International Knee Documentation Committee subjective) were also taken, and univariate and multiple regression models were used to determine the association between these and the psychological readiness of the athlete to RTS (ACL-RSI scores). Data for the entire cohort were initially analyzed; then, patients were grouped according to whether they had returned to competitive sport, and the analysis repeated for each group (return/nonreturn). Results: Univariate analysis for the entire group showed that all of the following had a positive effect on psychological readiness: male sex (β = 5.8; 95% CI, 2-10), younger age (β = −0.2; 95% CI, –0.4 to 0.01), a shorter interval between injury and surgery (β = −0.1; 95% CI, −0.1 to −0.02), a higher frequency of preinjury sport participation (β = 5.4; 95% CI, 2-9), greater limb symmetry (β = 0.5; 95% CI, 0.3-0.6), and higher subjective knee scores (β = 1.3; 95% CI, 1.1-1.4). In the multivariate model, subjective knee scores and age significantly accounted for 37% of the variance in psychological readiness ( r 2 = 0.37, P < .0001). The only difference between the groups who had and had not returned to sport was that female sex was a significant contributor for the nonreturn group. Conclusion: Self-reported symptoms and function were most associated with psychological readiness to RTS after ACLR surgery. Male patients who participated frequently in sport before ACL injury had higher psychological readiness. Conversely, female patients had a more negative outlook and may therefore benefit more from interventions designed to facilitate a smooth transition back to sport.

Background: Female patients sustain noncontact knee ligament injuries at a greater rate compared with their male counterparts. The cause of these differences in the injury rate and the movements that load the ligaments until failure are still under dispute in the literature. Purpose/Hypotheses: This study was designed to determine differences in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) strains between male and female cadaveric specimens during a simulated athletic task. The primary hypothesis tested was that female limbs would demonstrate significantly greater ACL strain compared with male limbs under similar loading conditions. A secondary hypothesis was that MCL strain would not differ between sexes. Study Design: Controlled laboratory study. Methods: Motion analysis of 67 athletes performing a drop vertical jump was conducted. Kinetic data were used to categorize injury risk according to tertiles, and these values were input into a cadaveric impact simulator to assess ligamentous strain during a simulated landing task. Uniaxial and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect mechanical data for analysis. Conditions of external loads applied to the cadaveric limbs (knee abduction moment, anterior tibial shear, and internal tibial rotation) were varied and randomized. Data were analyzed using 1-way analysis of variance (ANOVA), 2-way repeated-measures ANOVA, and the Fisher exact test. Results: There were no significant differences ( P = .184) in maximum ACL strain between male (13.2% ± 8.1%) and female (16.7% ± 8.3%) specimens. Two-way ANOVA demonstrated that across all controlled external load conditions, female specimens consistently attained at least 3.5% increased maximum ACL strain compared with male specimens ( F 1,100 = 4.188, P = .043); however, when normalized to initial contact, no significant difference was found. There were no significant differences in MCL strain between sexes for similar parameters. Conclusion: When compared with baseline, female specimens exhibited greater values of ACL strain at maximum, initial contact, and after impact (33, 66, and 100 milliseconds, respectively) than male specimens during similar loading conditions, with a maximum strain difference of at least 3.5%. During these same loading conditions, there were no differences in MCL loading between sexes, and only a minimal increase of MCL loading occurred during the impact forces. Our results indicate that female patients are at an increased risk for ACL strain across all similar conditions compared with male patients. Clinical Relevance: These data demonstrate that female specimens, when loaded similarly to male specimens, experience additional strain on the ACL. As the mechanical environment was similar for both sexes with these simulations, the greater ACL strain of female specimens must be attributed to ligament biology, anatomic differences, or muscular stiffness.

Background: Limb asymmetries, as determined through in vivo biomechanical measures, are known risk factors for anterior cruciate ligament (ACL) injury. Previous cadaveric studies have shown a lack of significant differences in ligament strain between contralateral lower extremities when identical kinematics were simulated on specimens. Recent methodological developments have applied in vivo knee kinetics to exert landing forces on cadaveric lower extremities to mimic ACL injury events, but it is unknown whether contralateral limbs fail in a consistent manner during impact simulator testing. Hypothesis: It was hypothesized that contralateral lower extremities would not exhibit side-to-side differences in ligament strains. Furthermore, it was hypothesized that failure loads and failure locations would be independent of limb dominance. Study Design: Controlled laboratory study. Methods: Fourteen pairs of cadaveric lower extremities were obtained from an anatomic donations program (8 female, 6 male; mean ± SD: age, 41.7 ± 8.1 years; mass, 86.8 ± 27.0 kg; body mass index, 29.4 ± 9.0 kg/m 2 ). A mechanical impact simulator was used to re-create the impulse ground-reaction force generated during an in vivo landing task. Ligament strains were recorded by differential variable force transducers implanted on the ACL and medial collateral ligament (MCL). Results: No significant differences were observed in peak ACL or peak MCL strain for 5 loading conditions. Fisher exact tests of independence revealed that limb dominance was independent of both load at failure and failure location. Conclusion: There were no significant differences in ACL and MCL strain values between limb sides during in vitro impact simulation testing. This finding indicates that limb dominance does not influence the failure threshold of the ACL, since there was no significant difference in failure strains. The functional mechanics of the ACL are comparable between contralateral pairs from the same healthy specimen. Clinical Relevance: Injury mechanisms and intra-articular mechanics cannot be ethically studied in an in vivo setting. The current study provides additional insight into limb asymmetry that is observed among athletes in clinical sports medicine settings.

Background: Females are at an increased risk of sustaining noncontact knee ligament injuries as compared with their male counterparts. The kinetics that load the anterior cruciate ligament (ACL) are still under dispute in the literature. Purpose/Hypothesis: The purpose of this study was to determine whether there are differences in knee kinetics between the sexes that lead to greater ACL strain in females when similar external loads are applied during a simulated drop vertical jump landing task. It was hypothesized that female limbs would demonstrate significant differences in knee abduction moment that predispose females to ACL injury when compared with males. Study Design: Controlled laboratory study. Methods: Motion analysis data of 67 athletes who performed a drop vertical jump were collected. The kinematic and kinetic data were used to categorize tertiles of relative risk, and these values were input into a cadaveric impact simulator to assess ligamentous loads during the simulated landing task. Uni- and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect kinetic data and maximum ACL strain for analysis. Conditions of external loads applied to the cadaveric limbs were systematically varied and randomized. Data were analyzed with 2-way repeated-measures analysis of variance and the Fisher exact test. Results: Five kinetic parameters were evaluated. Of the 5 kinetic variables, only knee abduction moment (KAM) demonstrated significant differences in females as compared with males ( F 1,136 = 4.398, P = .038). When normalized to height and weight, this difference between males and females increased in significance ( F 1,136 = 7.155, P = .008). Compared with males, females exhibited a 10.3-N·m increased knee abduction torque at 66 milliseconds postimpact and a 22.3-N·m increased abduction torque at 100 milliseconds postimpact. For loading condition, the condition of “maximum ACL strain” demonstrated a maximum difference of 54.3-N·m increased abduction torque and 74.5-N·m increased abduction torque at 66 milliseconds postimpact. Conclusion: Under the tested conditions, increased external loads led to increased medial knee translation force, knee abduction moment, and external knee moment. Females exhibited greater forces and moments at the knee, especially at KAM, when loaded in similar conditions. As these KAM loads are associated with increased load and strain on the ACL, the sex-based differences observed in the present study may account for a portion of the underlying mechanics that predispose females to ACL injury as compared with males in a controlled simulated athletic task. Clinical Relevance: KAM increases strain to the ACL under clinically representative loading. Additionally, this work establishes the biomechanical characteristics of knee loading between sexes.

Background: The reported rate of second anterior cruciate ligament (ACL) injuries (20%-30%), including graft failure and contralateral ACL tears, after ACL reconstruction (ACLR) or nonoperative therapy indicates that multiple factors may predispose patients to subsequent ACL injuries. Purpose: To determine the incidence of second ACL injuries in a population-based cohort over a 10-year observation period (2001-2010) and to identify factors that contribute to the risk of second injuries. Study Design: Descriptive epidemiological study. Methods: International Classification of Diseases, 9th Revision (ICD-9) codes relevant to the diagnosis of an ACL tear and the procedure code for ACLR were utilized to search the Rochester Epidemiology Project, a multidisciplinary county database, between the years of 2001 and 2010. The complete medical records for all cases were reviewed to confirm diagnosis and treatment details. A total of 914 unique patients with 1019 acute, isolated ACL tears were identified. These patients were stratified by primary and secondary tears, sex, age, activity level, side of injury, sex × side of injury, and graft type of reconstruction. Results: Second ACL tears were recorded in 141 (13.8%) of the 914 patients diagnosed with an ACL tear in Olmsted County, Minnesota, USA, from 2001 to 2010; 50.4% of these occurred in the contralateral knee. A noncontact mechanism was responsible for 76.4% of all ACL injuries. A second ACL injury was influenced by factors of sex × age group, treatment type × age group, and treatment type × activity level. Nonparametric analysis of graft disruption × graft type demonstrated that a higher prevalence of second ACL tears occurred with allografts compared with hamstring autografts ( P = .0054) and patellar tendon autografts ( P = .0001). Conclusion: The incidence of second ACL tears in this population-based cohort was 13.8%, and half occurred to the ACL of the contralateral knee. Statistically, second ACL injuries differed by sex, occurring in female patients younger than 25 years and male patients aged 26 to 45 years. Allografts continued to be associated with a greater risk of second ACL injuries compared with hamstring and patellar tendon autografts. Nonoperative treatment carried more risk of contralateral tears than ACLR.