Publications

OBJECTIVE: Fatigue due to game play is often cited as a factor in musculoskeletal injuries; however, it is unclear whether or not this view is supported by published research findings. Given the importance researchers and practitioners place on the potential effects of game play with respect to injury, it is important to understand what inferences can be drawn from the collective research in this realm. This meta-analysis will consider the time of season and segment of the game, as it relates anterior cruciate ligament (ACL), groin, and hamstring injury occurrence.

DATA SOURCES: Database searches were run in PubMed, MEDLINE, SportDiscus, CINAHL, and Ausport, in addition to the inclusion of articles identified manually.

STUDY SELECTION: Search terms were chosen to identify articles related to each of the 3 injuries of interest. There were no date limitations placed on the articles, as such, all published articles listed in the databases up to November 2017 were eligible for selection if they met the search criteria.

DATA EXTRACTION: Initial searches yielded 1349 articles, and this was eventually reduced to 15 articles deemed suitable for inclusion in the meta-analysis, which provided 21 data sets.

DATA SYNTHESIS: Comparing the first half with the second half of the season, there were no differences in ACL, groin, or hamstring injury occurrences [ACL: odds ratio (OR), 1.27; confidence interval (CI), 0.43-3.78, groin: OR, 1.79; CI, 0.63-5.06, and hamstring: OR, 1.16; CI, 0.88-1.53]. Similarly, there were no differences in injury occurrence between the first and second halves of the game for the ACL or hamstring injuries (ACL: OR, 0.43; CI, 0.47-7.92, hamstring: OR, 0.85; CI, 0.58-1.24).

CONCLUSIONS: Findings from this meta-analysis determined that time in season or time in game does not influence risk of the ACL, groin, or hamstring injury. Commonly, many studies did not provide sufficient detail to be included in the meta-analysis. Consequently, it is recommended that future studies report data related to the timing of the injury within the season or game.

BACKGROUND: Frontal plane trunk lean with a side-to-side difference in lower extremity kinematics during landing increases unilateral knee abduction moment and consequently anterior cruciate ligament (ACL) injury risk. However, the biomechanical features of landing with higher ACL loading are still unknown. Validated musculoskeletal modeling offers the potential to quantify ACL strain and force during a landing task.

PURPOSE: To investigate ACL loading during a landing and assess the association between ACL loading and biomechanical factors of individual landing strategies.

STUDY DESIGN: Descriptive laboratory study.

METHODS: Thirteen young female athletes performed drop vertical jump trials, and their movements were recorded with 3-dimensional motion capture. Electromyography-informed optimization was performed to estimate lower limb muscle forces with an OpenSim musculoskeletal model. A whole-body musculoskeletal finite element model was developed. The joint motion and muscle forces obtained from the OpenSim simulations were applied to the musculoskeletal finite element model to estimate ACL loading during participants' simulated landings with physiologic knee mechanics. Kinematic, muscle force, and ground-reaction force waveforms associated with high ACL strain trials were reconstructed via principal component analysis and logistic regression analysis, which were used to predict trials with high ACL strain.

RESULTS: The median (interquartile range) values of peak ACL strain and force during the drop vertical jump were 3.3% (-1.9% to 5.1%) and 195.1 N (53.9 to 336.9 N), respectively. Four principal components significantly predicted high ACL strain trials, with 100% sensitivity, 78% specificity, and an area of 0.91 under the receiver operating characteristic curve (P < .001). High ACL strain trials were associated with (1) knee motions that included larger knee abduction, internal tibial rotation, and anterior tibial translation and (2) motion that included greater vertical and lateral ground-reaction forces, lower gluteus medius force, larger lateral pelvic tilt, and increased hip adduction.

CONCLUSION: ACL loads were higher with a pivot-shift mechanism during a simulated landing with asymmetry in the frontal plane. Specifically, knee abduction can create compression on the posterior slope of the lateral tibial plateau, which induces anterior tibial translation and internal tibial rotation.

CLINICAL RELEVANCE: Athletes are encouraged to perform interventional and preventive training to improve symmetry during landing.

BACKGROUND: Around half of anterior cruciate ligament (ACL) injuries are treated through reconstruction, but the literature lacks mechanical investigation of reconstructions in a dynamic athletic task and rupture environment. The current objective was to ascertain the feasibility of investigating ACL reconstructions in a rupture environment during simulated landing tasks in a validated mechanical impact simulator.

METHODS: Four cadaveric lower extremities were subjected to simulated landing in a mechanical impact simulator. External joint loads that mimicked magnitudes recorded from an in vivo population were applied to each joint in a stepwise manner. Simulations were repeated until ACL failure was achieved. Repeated measures design was used to test each specimen in the native ACL and hamstrings, quadriceps, and patellar tendon reconstructed states.

FINDINGS: ACL injuries were generated in 100% of specimens. Graft substance damage occurred in 58% of ACLRs, and in 75% of bone tendon bone grafts. Bone tendon bone and quadriceps grafts survived greater simulated loading than hamstrings grafts, but smaller simulated loading than the native ACL. Median peak strain prior to failure was 20.3% (11.6, 24.5) for the native ACL and 17.4% (9.5, 23.3) across all graft types.

INTERPRETATION: The simulator was a viable construct for mechanical examination of ACLR grafts in rupture environments. Post-surgery, ACL reconstruction complexes are weaker than the native ACL when subjected to equivalent loading. Bone tendon bone grafts most closely resembled the native ligament and provided the most consistently relevant rupture results. This model advocated reconstruction graft capacity to sustain forces generated from immediate gait and weightbearing during rehabilitation from an ACL injury.

Weaker hamstrings muscular forces and lower ratio of the hamstrings/quadriceps muscular forces in female athletes have been identified as modifiable risk factors for anterior cruciate ligament (ACL) injuries. However, sex differences in athletes' ability to react to visual cues (Choice Visual-Motor Reaction Time: VMRT) and to generate knee muscular forces (rate of force development: RFD) immediately following the visual cues were largely unknown. Therefore, the purpose of the study was to examine sex differences in Choice VMRT and RFD. A total of 50 high school basketball athletes (26F/24 M) participated in the study. Subjects sat in the knee dynamometer chair with their knee secured at 70° of knee flexion and performed knee extension or flexion maximum voluntary isometric contractions immediately after they saw the visual cue: "UP" or "DOWN" arrows, respectively. Choice VMRT was defined as the time between the visual cue and the initiation of muscular force development (>5Newtons). RFD was calculated by dividing the changes in forces over the changes in time at four time points (0-50/100/150/200 ms). Peak muscular forces and RFD were normalized to their body mass. Average of three trials in each direction (flexion and extension) in each leg was used for statistical analyses. Females had significantly slower Choice VMRT (p < 0.001-0.027) and lower knee extension RFD at 100 ms (p = 0.005). In addition, females had significantly higher knee flexion/extension ratio than males in late RFD (150 ms and 200 ms) (p < 0.004). The current study has provided additional sensorimotor characteristics of athletes and sexes in addition to their knee muscular characteristics.

BACKGROUND: Anterior cruciate ligament (ACL) injury reduction training has focused on lower body strengthening and landing stabilization. In vitro studies have shown that quadriceps forces increase ACL strain, and hamstring forces decrease ACL strain. However, the magnitude of the effect of the quadriceps and hamstrings forces on ACL loading and its timing during in vivo landings remains unclear.

PURPOSE: To investigate the effect and timing of knee muscle forces on ACL loading during landing.

STUDY DESIGN: Descriptive laboratory study.

METHODS: A total of 13 young female athletes performed drop vertical jump trials, and their movements were recorded with 3-dimensional motion capture. Lower limb joint motion and muscle forces were estimated with OpenSim and applied to a musculoskeletal finite element (FE) model to estimate ACL loading during landings. The FE simulations were performed with 5 different conditions that included/excluded kinematics, ground-reaction force (GRF), and muscle forces.

RESULTS: Simulation of landing kinematics without GRF or muscle forces yielded an estimated median ACL strain and force of 5.1% and 282.6 N. Addition of GRF to kinematic simulations increased ACL strain and force to 6.8% and 418.4 N (P < .05). Addition of quadriceps force to kinematics + GRF simulations nonsignificantly increased ACL strain and force to 7.2% and 478.5 N. Addition of hamstrings force to kinematics + GRF simulations decreased ACL strain and force to 2.6% and 171.4 N (P < .001). Addition of all muscles to kinematics + GRF simulations decreased ACL strain and force to 3.3% and 195.1 N (P < .001). With hamstrings force, ACL loading decreased from initial contact (time of peak: 1-18 milliseconds) while ACL loading without hamstrings force peaked at 47 to 98 milliseconds after initial contact (P = .024-.001). The knee flexion angle increased from 20.9° to 73.1° within 100 milliseconds after initial contact.

CONCLUSION: Hamstrings activation had greater effect relative to GRF and quadriceps activation on ACL loading, which significantly decreased and regulated the magnitude and timing of ACL loading during in vivo landings.

CLINICAL RELEVANCE: Clinical training should focus on strategies that influence increased hamstrings activation during landing to reduce ACL loads.

BACKGROUND: Eccentric hamstring strength and hamstring/quadriceps strength ratios have been identified as modifiable risk factors of hamstring strains. Additionally, those strength and flexibility characteristics are commonly used as clinical tests to monitor progress of athletes with acute or chronic hamstring strains. Although hamstring strains are common among basketball athletes, normative values of knee strength and flexibility characteristics are scarce. Normative values for these athletes would be important in prevention and management of hamstring strains.

PURPOSE: To establish quadriceps and hamstring isokinetic strength and flexibility values among high school basketball athletes and examine the effects of sex and age.

STUDY DESIGN: Cross-sectional research.

METHODS: Isokinetic knee muscular strength (concentric quadriceps [QuadC], concentric hamstring [HamC], eccentric hamstring [HamE], and strength ratios ([HamC/QuadC and HamE/Quad]), flexibility of hip flexors and quadriceps during a Modified Thomas test, and flexibility of hip extensors and hamstring during passive straight leg raise (SLR) and passive knee extension (PKE) tests were measured. Effects of sex and age were analyzed using t-tests and analysis of variance, respectively with Bonferroni corrected post hoc tests (p≤0.01).

RESULTS: A total of 172 high school basketball athletes (64 males/108 females; mean age (range): 15.7 (14-18) years old) participated in the study. Male athletes were significantly stronger than female athletes (QuadC: p<0.001; HamC: p<0.001) while no differences were observed in strength ratio (HamC/QuadC: p=0.759-0.816; HamE/QuadC: p=0.022-0.061). Among male athletes, a significant effect of age on quadriceps and hamstring strength was observed: older male athletes were stronger than younger male athletes. Contrarily, there were no effects of age on strength among female athletes. There were significant sex differences in quadriceps flexibility, SLR, and PKE (female athletes were more flexible; p=0.001-0.005) while no sex differences were found in hip flexor flexibility (p=0.105-0.164). There were no effects of age for any flexibility variables within male and female athletes (p=0.151-0.984).

CONCLUSION: The current results provide normative values for hamstring strength and flexibility in high school basketball athletes. These normative values may further assist sports medicine specialists to develop screening tests, interventions, and return-to-sport criteria in this population.

LEVEL OF EVIDENCE: 3B.

BACKGROUND: Anterior cruciate ligament (ACL) injuries impair knee extensor and flexor force generation and may alter force variability. Fractal scaling exponents quantify signal complexity and reflect neuromuscular system adaptability. The purpose of this study was to evaluate force variability magnitudes and fractal scaling exponents in persons with ACL injuries.

METHODS: Twenty-four individuals with ACL injury (time from injury: 55 ± 66 days) and 25 uninjured controls completed 10-s isometric knee extension and flexion contractions on a dynamometer at 10%, 25%, 35%, and 50% of peak force. The middle 8-s of data were used to calculate coefficients of variation and fractal exponents. Injured and non-injured limbs as well as dominant and non-dominant limbs in the control group were compared with ANOVA (P < 0.05).

FINDINGS: Peak knee extensor and flexor forces were 19% and 10% lower in the injured limb of ACL-deficient participants (P = 0.014 and P = 0.036, respectively). Fractal scaling exponents of knee extensor force signals at 25% and 35% peak force in injured limbs were higher than in non-injured limbs (P = 0.008 and P = 0.027, respectively). The fractal scaling exponent of knee extensor force signals was greater in injured limbs of ACL-deficient participants than in dominant limbs of the control group at 35% peak force (P = 0.046). The magnitude of variability did not differ between limbs in ACL-deficient participants or between the injured and control groups.

INTERPRETATION: Altered fractal exponents in knee extensor force signals represent sensorimotor and neuromuscular system deficits in individuals with ACL injury. Overall, fractal analysis identified both between-limb and between-group differences.