Publications

BACKGROUND: Anterior cruciate ligament (ACL) injuries are a common cause of time loss in sports. Approximately one-third of ACL reconstructed athletes who return to sport suffer secondary injury. The presence of fatigue during athletic performance has been hypothesized to increase susceptibility to ACL injury. However, the relative role of fatigue in secondary ACL failures remains unexplored.

PURPOSE: To assess how time elapsed within a game and within a season associate with secondary ACL injury occurrence in international professional athletes and American collegiate athletes.

STUDY DESIGN: Retrospective cohort analysis.

METHODS: The public domain was searched for secondary ACL injuries that occurred during competitive matches between 2000-2018. Demographics (age, height, weight), side of injury, type of injury (contact, noncontact), and timing of injury within competition and within season were determined for each case.

RESULTS: Sixty-seven secondary ACL injuries were identified. Within-game, there were no differences in the distribution of ACL injures across each quarter of game time (p = 0.284). This was consistent between sport (p = 0.120-0.448). Within-season, there were no differences in the distribution of secondary ACL injures across each quarter of the season (p = 0.491). This was again consistent between sport (p = 0.151-0.872). Relative risk was not found to be significantly greater for any combination of season and game.

CONCLUSION: The results of the current study indicate that the occurrences of secondary ACL injuries were equally distributed with respect to in-game and in-season timing. Both in-game and in-season timing were not significantly different across each individual sport examined. These results implicate that overall there is not an association between fatigue and secondary ACL injury occurrence in professional athletes.

LEVEL OF EVIDENCE: 3.

PURPOSE: Quadriceps weakness is a common clinical sign following anterior cruciate ligament injury and reconstruction surgery (ACLR). The aim of this study was to compare strength deficits and the limb symmetry index (LSI) from three different types of functional tests: isokinetic dynamometry, hop test, and leg press.

METHODS: A total of 26 subjects with ACLR (average 8.3 months post-operation) participated in the study. The peak knee extension torque was tested with isokinetic dynamometry at 60/180/300 °/s (ISO60/180/300). Hop distance was tested during single hop (SH) and triple hop (TH). Unilateral peak leg power (POWER) was tested during a bilateral leg press test. LSI was calculated as the ratio of the involved limb over the uninvolved limb values. Pearson correlation coefficients and paired t-tests were used to establish relationships among ISO60/180/300, SH/TH, and POWER values and compare these values between the limbs, respectively. Within-subject one-way analysis of variance (ANOVA) with post hoc analyses was used to compare LSI values among different tests.

RESULTS: ISO60/180/300 values were significantly positively correlated with SH/TH and POWER (P < 0.05), while SH/TH and POWER values were not significantly correlated. Significant limb differences were found in all tests (P = 0.001-0.008). ANOVA revealed significant LSI differences among different tests. Specifically, post hoc analyses revealed that LSI during SH was significantly higher than LSI during ISO60. Similarly, LSI during TH was significantly higher than LSIs from ISO60, ISO180, and POWER tests.

CONCLUSIONS: Peak knee extension torque values were positively associated with hop distance and leg power during the leg press test. However, LSI values should be interpreted with caution as hop tests provided significantly higher LSI values than isokinetic testing. Both isokinetic dynamometry and unilateral leg press machine could be used to isolate and strengthen the quadriceps in the involved limb. The current "gold standard" isokinetic testing at slow speed (ISO60) provided the lowest LSI value among all functional tests; therefore, the current study supported a continued use of isokinetic testing when examining individual's readiness and return-to-sport.

LEVEL OF EVIDENCE: III.

BACKGROUND: Altered motor unit (MU) activity has been identified after anterior cruciate ligament (ACL) injury, but its effect on muscle tissue properties is unknown. The purpose of this study was to compare thigh musculature muscle stiffness between control and ACL-injured subjects.

METHODS: Thirty ACL-injured subjects and 25 control subjects were recruited. Subjects completed a randomized protocol of isometric contractions while electromyography (EMG) signals were recorded. Three maximum voluntary isometric contractions (MVIC) determined peak force for 10 and 25% MVIC trials. Shear wave elastography was captured during each 10 and 25% MVIC trials.

RESULTS: Differences in muscle stiffness were assessed between limbs and groups. 12 months post-surgery had higher stiffness for VM 0% MVIC, VL 0 and 10% MVIC, and ST 10 and 25% MVIC (all p ≤ 0.04).

CONCLUSION: Thigh musculature stiffness changed throughout rehabilitation and remained altered at 12 months after ACL reconstruction.

Anterior cruciate ligament (ACL) injury videos estimate that rupture occurs within 50 milliseconds of initial contact, but are limited by imprecise timing and nondirect data acquisition. The objective of this study was to precisely quantify the timing associated with ligament strain during simulated landing and injury events. The hypotheses tested were that the timing of peak strain following initial contact would differ between ligaments and that peak strain timing would be independent of the injury-risk profile emulated during simulated landing. A mechanical impact simulator was used to perform landing simulations based on various injury-risk profiles that were applied to each specimen in a block-randomized order. The ACL and medial collateral ligament were instrumented with strain gauges that recorded continuously. The data from 35 lower-extremity specimens were included for analysis. Analysis of variance and Kruskal-Wallis tests were used to determine the differences between timing and profiles. The mean time to peak strain was 53 (24) milliseconds for the ACL and 58 (35) milliseconds for the medial collateral ligament. The time to peak ACL strain ranged from 48 to 61 milliseconds, but the timing differences were not significant between profiles. Strain timing was independent of injury-risk profile. Noncontact ACL injuries are expected to occur between 0 and 61 milliseconds after initial contact. Both ligaments reached peak strain within the same time frame.

BACKGROUND: Recent studies indicate concussion increases risk of musculoskeletal injury in specific groups of patients. The purpose of this study was to determine the odds of anterior cruciate ligament (ACL) injury after concussion in a population-based cohort.

METHODS: International Classification of Diseases, 9th and 10th Revision (ICD-9, ICD-10) codes relevant to the diagnosis and treatment of a concussion and ACL tear were utilized to search the Rochester Epidemiology Project (REP) between 2000 and 2017. A total of 1653 unique patients with acute, isolated ACL tears were identified. Medical records for cases were reviewed to confirm ACL tear diagnosis and to determine history of concussion within 3 years prior to the ACL injury. Cases were matched by age, sex, and REP availability date to patients without an ACL tear (1:3 match), resulting in 4959 controls. The medical records of the matched control patients were reviewed to determine history of concussion.

RESULTS: 39 patients with a concussion suffered an ACL injury up to 3 years after the concussion. The rate of prior concussion was higher in ACL-injured cases (2.4%) compared to matched controls with no ACL injury (1.5%). This corresponds to an odds ratio of 1.6 (95% CI 1.1-2.4; p = 0.015).

CONCLUSIONS: Although activity level could not be assessed, there are increased odds of ACL injury after concussion in a general population. Based on the evidence of increased odds of musculoskeletal injury after concussion, standard clinical assessments should consider concussion symptom resolution as well as assessment of neuromuscular factors associated with risk of injuries.

BACKGROUND: The incidence of anterior cruciate ligament (ACL) injuries has been estimated at 1 in 3500 individuals in the literature. Second ACL tears represent 7-14% of all ACL tears. The location of ACL tears has been noted to be primarily proximal.

PURPOSE: The purpose of this study was to corroborate previous data as well as to add novel data to the literature regarding the location of ACL tears, risk factors associated with second ACL tears, and correlation between hearing a "pop" at the time of injury and concomitant injuries.

STUDY DESIGN: Epidemiologic Review.

METHODS: A geographic database containing the medical records of individuals in a rural county in Midwest, USA was utilized to identify ACL injuries that occurred in the county from 2011 to 2016. A total of 743 ACL injuries were identified, which were reviewed and stratified by primary and second tears, sex, race, age, activity level, number of "pops" heard at time of injury, side of injury, location of tear, graft type used in reconstruction, location of fixation, and concomitant injuries.

FINDINGS: ACL tear location was noted to be primarily midsubstance (44.1%) or proximal (34.1%). The majority of individuals (56.3%) who reported hearing "multiple pops" at the time of injury sustained multiple types of concomitant injuries. The incidence of second ACL tears was 16.8% of total ACL injuries. Second ACL tears were associated with multiple factors, including tear type (p < 0.015) and tear location (p < 0.022). When comparing primary versus second ACL tears, no significant difference in concomitant injuries was noted.

CONCLUSIONS: The majority of ACL tears (78.2%) occur in the midsubstance or proximal fibers. Hearing multiple "pops" at the time of injury may be associated with more concomitant injuries. The incidence of second ACL tears in this population was comparable to previous studies. Second ACL injuries differed statistically from primary injuries in association with tear type and location.

LEVEL OF EVIDENCE: 2C.

BACKGROUND: The most commonly damaged structures of the knee are the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and menisci. Given that these injuries present as either isolated or concomitant, it follows that these events are driven by specific mechanics versus coincidence. This study was designed to investigate the multiplanar mechanisms and determine the important biomechanical and demographic factors that contribute to classification of the injury outcome.

HYPOTHESIS: Linear discriminant analysis (LDA) would accurately classify each injury type generated by the mechanical impact simulator based on biomechanical input variables (ie, ligament strain and knee kinetics).

STUDY DESIGN: Controlled laboratory study.

METHODS: In vivo kinetics and kinematics of 42 healthy, athletic participants were measured to determine stratification of injury risk (ie, low, medium, and high) in 3 degrees of knee forces/moments (knee abduction moment, anterior tibial shear, and internal tibial rotation). These stratified kinetic values were input into a cadaveric impact simulator to assess ligamentous strain and knee kinetics during a simulated landing task. Uniaxial and multiaxial load cells and implanted strain sensors were used to collect mechanical data for analysis. LDA was used to determine the ability to classify injury outcome by demographic and biomechanical input variables.

RESULTS: From LDA, a 5-factor model (Entropy R2 = 0.26) demonstrated an area under the receiver operating characteristic curve (AUC) for all 5 injury outcomes (ACL, MCL, ACL+MCL, ACL+MCL+meniscus, ACL+meniscus) of 0.74 or higher, with "good" prediction for 4 of 5 injury classifications. A 10-factor model (Entropy R2 = 0.66) improved the AUC to 0.86 or higher, with "excellent" prediction for 5 injury classifications. The 15-factor model (Entropy R2 = 0.85), produced 94.1% accuracy with the AUC 0.98 or higher for all 5 injury classifications.

CONCLUSION: Use of LDA accurately predicted the outcome of knee injury from kinetic data from cadaveric simulations with the use of a mechanical impact simulator at 25° of knee flexion. Thus, with clinically relevant kinetics, it is possible to determine clinical risk of injury and also the likely presentation of singular or concomitant knee injury.

CLINICAL RELEVANCE: LDA demonstrates that injury outcomes are largely characterized by specific mechanics that can distinguish ACL, MCL, and medial meniscal injury. Furthermore, as the mechanics of injury are better understood, improved interventional prehabilitation can be designed to reduce these injuries.

OBJECTIVE: The purpose of this study was to characterize lower extremity passive muscle stiffness in a young, healthy, athletic population. It was hypothesized that males would exhibit greater stiffness than females and that hamstring stiffness would increase with increased passive hamstring stretch.

METHODS: Male (n = 52, age 16.0 ± 1.3 years, height 180.3 ± 7.9 cm, weight 73.1 ± 11.8 kg) and female (n = 89, age 15.6 ± 1.3 years, height 169.7 ± 8.1 cm, weight 65.2 ± 13.2 kg) high school basketball athletes were recruited for this study. Shear wave elastography (SWE) was used to measure shear wave velocity (m/s) of the biceps femoris muscle at three leg positions (40%, 60%, and 80%) of the maximum passive 90-90 straight-leg raise position for each leg. Hamstring stiffness (kPa) was quantified from the SWE elastogram using custom processing software.

RESULTS: Hamstring stiffness was significantly greater for males than females at every position on both the dominant and non-dominant limbs (p < 0.05). Hamstring stiffness was greater on the non-dominant limb than the dominant for females at the 40% position. Stiffness at 60% was greater than stiffness at 40% for males on both the dominant and non-dominant limbs. However, stiffness at 60% was greater than stiffness at 80% on the male non-dominant limb. Females demonstrated higher stiffness at 40% than both 60% and 80% for the dominant and non-dominant limbs.

CONCLUSION: Healthy male basketball players had higher hamstring muscle stiffness than female players. Future studies may investigate what factors contribute to the large variability observed in muscle stiffness, resulting in mixed results on the effects of leg dominance and stretching positions.

BACKGROUND: Non-contact injuries are common in sports as abnormal lower extremity joint mechanics can place athletes at risk for injury. It is important to have reliable, feasible, cost-effective assessment tools to determine lower limb control and injury risk.

HYPOTHESIS/PURPOSE: The purpose of the study was to assess the intra- and inter-rater reliability of a three-tiered anterior cruciate ligament (ACL) injury risk rating assessment of the drop vertical jump using frontal plane, two-dimensional (2-D) motion capture.

STUDY DESIGN: Repeated measures.

METHODS: Twenty male elite basketball athletes performed the drop vertical jump during a 2-D video assessment at Mayo Clinic Sports Medicine Center in Minneapolis, Minnesota. DVJ scores indicated the following: 1 no visible knee valgus, 2 slight wobble, inward motion of the knees, and 3 knee collision or large frontal plane knee excursion. Score assessment from video of the drop vertical jump was obtained by four independent investigators. The four raters then re-examined the same videos 1 month later, blinded to their original scores.

RESULTS: Intra-rater reliability Fleiss Kappa measure of agreement was substantial amongst all four raters at all scoring time points: initial contact (0.672), first landing (0.728), second landing (0.670), and peak valgus (0.662) (p < 0.001). The intra-rater ICC values were good at initial contact (0.809), second landing (0.874), and max valgus (0.885), however were excellent at first landing (0.914) (p < 0.001). Inter-rater reliability Fleiss Kappa measurement scores were slight at initial contact (0.173), fair at max valgus (0.343), and moderate at first landing (0.532) and second landing (0.514; p < 0.001). Inter-rater ICC values were moderate at initial contact (0.588), excellent at first landing (0.919), and good at second landing (0.883) and max valgus (0.882; p<0.001).

CONCLUSION: When comparing scores of the drop vertical jump between four independent raters across two sessions, the study demonstrated substantial Kappa and good to excellent ICC intra-rater reliability. Inter-rater reliability demonstrated slight to moderate Kappa measurements of agreement and moderate to excellent ICC's. Thus, for excellent reliability using this assessment, patients should be scored by one individual. For moderate reliability between multiple raters, the first landing of the DVJ should be scored. Findings indicate that the proposed drop vertical jump assessment may be used for reliable identification of abnormal landing mechanics.

LEVEL OF EVIDENCE: Level 3.