Scott G. McLean

Fatigue-induced ACL injury risk stems from a degradation in central control.

PURPOSE Fatigue contributes directly to anterior cruciate ligament (ACL) injury via promotion of high risk biomechanics. The potential for central fatigue to dominate this process, however, remains unclear. With centrally mediated movement behaviors being trainable, establishing this link seems critical for improved injury prevention. We thus determined whether fatigue-induced landing biomechanics were governed by a centrally fatiguing mechanism. METHODS Twenty female NCAA athletes had initial contact (IC) and peak stance (PS) three-dimensional hip and knee biomechanics quantified during anticipated and unanticipated single-leg landings, before and during unilateral fatigue accumulation. To induce fatigue, subjects performed repetitive (n = 3) single-leg squats and randomly ordered landings, until squats were no longer possible. Subject-based dependent factors were calculated across prefatigue trials and for those denoting 100%, 75%, 50%, and 25% fatigue and were submitted to three-way mixed-design analyses of covariance to test for decision, fatigue time, and limb effects. RESULTS Fatigue produced significant (P < 0.01) decreases in IC knee flexion angle and PS knee flexion moment and increases in PS hip internal rotation and knee abduction angles and moments, with differences maintained from 50% fatigue through to maximum. Fatigue-induced increases in PS hip internal rotation angles and PS knee abduction angles and loads were also significantly (P < 0.01) greater during unanticipated landings. Apart from PS hip moments, significant limb differences in fatigued landing biomechanics were not observed. CONCLUSIONS Unilateral fatigue induces a fatigue crossover to the contralateral limb during single-leg landings. Central fatigue thus seems to be a critical component of fatigue-induced sports landing strategies. Hence, targeted training of central control processes may be necessary to counter successfully the debilitative impact of fatigue on ACL injury risk.

Pretreatment Health Behaviors Predict Survival Among Patients With Head and Neck Squamous Cell Carcinoma

PURPOSE Our prior work has shown that the health behaviors of head and neck cancer patients are interrelated and are associated with quality of life; however, other than smoking, the relationship between health behaviors and survival is unclear. PATIENTS AND METHODS A prospective cohort study was conducted to determine the relationship between five pretreatment health behaviors (smoking, alcohol, diet, physical activity, and sleep) and all-cause survival among 504 head and neck cancer patients. RESULTS Smoking status was the strongest predictor of survival, with both current smokers (hazard ratio [HR] = 2.4; 95% CI, 1.3 to 4.4) and former smokers (HR = 2.0; 95% CI, 1.2 to 3.5) showing significant associations with poor survival. Problem drinking was associated with survival in the univariate analysis (HR = 1.4; 95% CI, 1.0 to 2.0) but lost significance when controlling for other factors. Low fruit intake was negatively associated with survival in the univariate analysis only (HR = 1.6; 95% CI, 1.1 to 2.1), whereas vegetable intake was not significant in either univariate or multivariate analyses. Although physical activity was associated with survival in the univariate analysis (HR = 0.95; 95% CI, 0.93 to 0.97), it was not significant in the multivariate model. Sleep was not significantly associated with survival in either univariate or multivariate analysis. Control variables that were also independently associated with survival in the multivariate analysis were age, education, tumor site, cancer stage, and surgical treatment. CONCLUSION Variation in selected pretreatment health behaviors (eg, smoking, fruit intake, and physical activity) in this population is associated with variation in survival.

Tibiofemoral Joint Kinematics of the Anterior Cruciate Ligament-Reconstructed Knee During a Single-Legged Hop Landing

Background: Abnormal 3-dimensional tibiofemoral joint kinematics have been identified in anterior cruciate ligament-reconstructed knees during functional gait tasks, which is suggested to directly affect risk of knee osteoarthritis. However, the extent to which similar high-risk abnormalities are present during more demanding maneuvers, such as single-legged hopping, is largely unknown. Hypothesis: When performing a single-legged forward hop landing, the reconstructed knee will demonstrate altered sagittal, frontal, and transverse plane kinematics compared with the contralateral limb. Study Design: Controlled laboratory study. Methods: High-speed biplane radiography was used to quantify bilateral 3-dimensional tibiofemoral joint kinematics in 9 subjects with unilaterally reconstructed anterior cruciate ligaments (mean time after surgery, 4 months) during 3 single-legged, forward hop landing trials. Mean subject-based initial foot contact and maximum stance (0-250 ms) values were calculated for each kinematic variable. Two-tailed paired t tests were subsequently applied to examine for the main effect of limb (reconstructed vs contralateral). Results: The reconstructed knees exhibited significantly greater extension (P = .04), external tibial rotation (P = .006), and medial tibial translation (P = .02) than the contralateral knees at initial contact. Reconstructed knees underwent significantly greater maximum flexion (P = .05), maximum external tibial rotation (P = .01), and maximum anterior tibial translation (P = .02). No significant differences existed between limbs for initial contact (P = .65) or maximum adduction-abduction (P = .55). Conclusion: Tibiofemoral joint kinematics of the anterior cruciate ligament-reconstructed knee are significantly different from those of the uninjured contralateral limb during a single-legged hop landing. This altered kinematic profile, in conjunction with the large impact loads associated with hopping, may further contribute to the risk of posttraumatic knee osteoarthritis. Clinical Relevance: Returning to sports involving dynamic single-legged landings at 4 months after anterior cruciate ligament reconstruction surgery may contribute to accelerated knee joint degeneration.

The Relationship Between Anterior Tibial Acceleration, Tibial Slope, and ACL Strain During a Simulated Jump Landing Task

BACKGROUND Knee joint morphology contributions to anterior cruciate ligament (ACL) loading are rarely considered in the injury prevention model. This may be problematic as the knee mechanical response may be influenced by these underlying morphological factors. The goal of the present study was to explore the relationship between posterior tibial slope (which has been recently postulated to influence knee and ACL loading), impact-induced anterior tibial acceleration, and resultant ACL strain during a simulated single-leg landing. METHODS Eleven lower limb cadaveric specimens from female donors who had had a mean age (and standard deviation) of 65 ± 10.5 years at the time of death were mounted in a testing apparatus to simulate single-limb landings in the presence of pre-impact knee muscle forces. After preconditioning, specimens underwent five impact trials (mean impact force, 1297.9 ± 210.6 N) while synchronous three-dimensional joint kinetics, kinematics, and relative anteromedial bundle strain data were recorded. Mean peak tibial acceleration and anteromedial bundle strain were quantified over the first 200 ms after impact. These values, along with radiographically defined posterior tibial slope measurements, were submitted to individual and stepwise linear regression analyses. RESULTS The mean peak anteromedial bundle strain (3.35% ± 1.71%) was significantly correlated (r = 0.79; p = 0.004; ß = 0.791) with anterior tibial acceleration (8.31 ± 2.77 m/s-2), with the times to respective peaks (66 ± 7 ms and 66 ± 4 ms) also being significantly correlated (r = 0.82; p = 0.001; ß = 0.818). Posterior tibial slope (mean, 7.6° ± 2.1°) was significantly correlated with both peak anterior tibial acceleration (r = 0.75; p = 0.004; ß = 0.786) and peak anteromedial bundle strain (r = 0.76; p = 0.007; ß = 0.759). CONCLUSIONS Impact-induced ACL strain is directly proportional to anterior tibial acceleration, with this relationship being moderately dependent on the posterior slope of the tibial plateau.

ACL Research Retreat V: An Update on ACL Injury Risk and Prevention, March 25–27, 2010, Greensboro, NC

It has been well recognized that multiple factors, whether individually or in combination, contribute to noncontact anterior cruciate ligament (ACL) injury. The ongoing mission of the ACL Research Retreat is to bring clinicians and researchers together to present and discuss the most recent advances in ACL injury epidemiology, risk factor identification, and injury-risk screening and prevention strategies and to identify future research directives. The sixth retreat held March 22–24, 2012, in Greensboro, North Carolina, was attended by more than 70 clinicians and researchers, including representatives from Canada, Iceland, Japan, The Netherlands, Norway, and South Africa. The meeting featured keynote presentations and discussion forums by expert scientists in ACL injury risk and prevention and 34 podium and poster presentations by attendees. Keynotes delivered by Ajit Chaudhari, PhD (The Ohio State University), Malcolm Collins, PhD (Medical Research Council and University of Cape Town, South Africa), and Tron Krosshaug, PhD (Oslo Sports Trauma Research Center, Norway) described their ongoing work related to proximal trunk control and lower extremity biomechanics, genetic risk factors associated with ACL injury, and methodologic approaches to understanding ACL loading mechanisms, respectively. Discussion forums led by Jennifer Hootman, PhD, ATC, FNATA, FACSM (Centers for Disease Control and Prevention) and Scott McLean, PhD (University of Michigan), focused on strategies for implementing injury-prevention programs in community settings and took a critical look at the strengths and limitations of motion-capture systems and how we might continue to refine our research approaches to increase the relevance and influence of our biomechanical research, respectively. Podium and poster presentations were organized into thematic sessions of anatomical, genetic, and hormone risk factors; the role of body position in ACL injury risk; pubertal and sex differences in lower extremity biomechanics; injury-risk screening and prevention; and methodologic considerations in risk factor research. Substantial time was provided for group discussion throughout the conference. From these discussions, the 2010 consensus statement1 was updated to reflect recent advances in the field and to chart new directions for future research. Following is the updated consensus statement. The presentation abstracts organized by topic and presentation order appear online at http://nata.publisher.ingentaconnect.com/content/nata/jat.

Sex and limb differences in hip and knee kinematics and kinetics during anticipated and unanticipated jump landings: implications for anterior cruciate ligament injury

Objectives: In this study, the effects of temporal changes in unanticipated (UN) prelanding stimuli on lower limb biomechanics and the impact of sex and limb dominance on these variables during single-leg landings were determined. It was hypothesised that reductions in the time of prelanding UN stimuli, female sex, and the non-dominant limb would significantly increase high-risk landing biomechanics during UN jump landings. Methods: 26 (13 men and 13 women) had initial contact (IC) and peak stance (0–50%) phase (PS) lower limb joint kinematics and kinetics quantified during anticipated (AN) and UN single-leg (left and right) landings. Postlanding jump direction was governed via one of two randomly ordered light stimuli, presented either before initiation of the jump (AN), or 600 ms (UN1), 500 ms (UN2) or 400 ms (UN3) immediately before ground contact. Results: Statistically significant (p<0.05) differences in IC hip posture and PS hip and knee internal rotation moments occurred in UN compared with AN landings. Differences were not observed, however, among UN conditions for any biomechanical comparisons. Significant (p<0.05) differences in specific IC and PS hip and knee postures and loads occurred between sexes and limbs. Neither of these factors, however, influenced movement condition effects. Conclusion: UN landings induce modifications in landing biomechanics that may increase anterior cruciate ligament injury risk in both men and women. These modifications, however, do not appear overly sensitive to the timing of the UN stimulus, at least within a temporal range affording a successful movement response. Expanding UN training to include even shorter stimulus-response times may promote the additional central control adaptations necessary to manoeuvre safely within the random sports setting.

Investigating isolated neuromuscular control contributions to non-contact anterior cruciate ligament injury risk via computer simulation methods

BACKGROUND Despite the ongoing evolution of anterior cruciate ligament injury prevention methods, injury rates and the associated sex-disparity remain. Strategies capable of successfully countering key control parameters existent within the injury mechanism thus remain elusive. Forward dynamics model simulations afford an expedited means to study realistic injury causing scenarios, while controlling all facets of the movement control strategy. Utilizing these methods, the current study examined the potential for perturbations in key initial contact neuromuscular parameters to injure the anterior cruciate ligament during the stance phase of sidestep cutting maneuvers. METHODS Controlled experiments were performed on optimized and validated subject-specific forward dynamic musculoskeletal sidestep models generated from 10 male and 10 female data sets. Random perturbations (n=5000) were applied to initial contact kinematic and muscle activation parameters in these baseline models and then to those with prescribed systematic modifications in initial hip and knee flexion, hip internal rotation and hip internal rotation velocity postures. The number of injuries via an isolated anterior tibial shear (>2000 N) or knee valgus load (>125 Nm) mechanism was determined for each of the seven model conditions and subsequently compared. FINDINGS Neuromuscular control perturbations produced peak stance phase (0-100 ms) knee valgus loads large enough to induce anterior cruciate ligament injury. Decreases and increases in combined initial contact hip and knee flexion postures and hip internal rotation velocity produced significant increases and decreases in these valgus-induced ACL injury rates respectively. INTERPRETATION Anterior cruciate ligament injury via a valgus load mechanism is more likely during sidestepping when landing in a more extended posture, or with increased hip external rotation velocity. The fact that injury rates are reduced when these control parameters are reversed suggests they should be central to ongoing prevention strategy developments.

Association of Quadriceps and Hamstrings Cocontraction Patterns With Knee Joint Loading

CONTEXT Sex differences in neuromuscular control of the lower extremity have been identified as a potential cause for the greater incidence of anterior cruciate ligament (ACL) injuries in female athletes compared with male athletes. Women tend to land in greater knee valgus with higher abduction loads than men. Because knee abduction loads increase ACL strain, the inability to minimize these loads may lead to ACL failure. OBJECTIVE To investigate the activation patterns of the quadriceps and hamstrings muscles with respect to the peak knee abduction moment. DESIGN Cross-sectional study. SETTING Neuromuscular research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty-one recreationally active adults (11 women, 10 men). MAIN OUTCOME MEASURE(S) Volunteers performed 3 trials of a 100-cm forward hop. During the hop task, we recorded surface electromyographic data from the medial and lateral hamstrings and quadriceps and recorded lower extremity kinematics and kinetics. Lateral and medial quadriceps-to-hamstrings (QratioH) cocontraction indices, the ratio of medial-to-lateral QratioH cocontraction, normalized root mean square electromyographic data for medial and lateral quadriceps and hamstrings, and peak knee abduction moment were calculated and used in data analyses. RESULTS Overall cocontraction was lower in women than in men, whereas activation was lower in the medial than in the lateral musculature in both sexes (P < .05). The medial QratioH cocontraction index (R(2) = 0.792) accounted for a significant portion of the variance in the peak knee abduction moment in women (P = .001). Women demonstrated less activation in the vastus medialis than in the vastus lateralis (P = .49) and less activation in the medial hamstrings than in the lateral hamstrings (P = .01). CONCLUSIONS Medial-to-lateral QratioH cocontraction appears to be unbalanced in women, which may limit their ability to resist abduction loads. Because higher abduction loads increase strain on the ACL, restoring medial-to-lateral QratioH cocontraction balance in women may help reduce ACL injury risk.

Knee joint anatomy predicts high-risk in vivo dynamic landing knee biomechanics

BACKGROUND With knee morphology being a non-modifiable anterior cruciate ligament injury risk factor, its consideration within injury prevention models is limited. Knee anatomy, however, directly influences joint mechanics and the potential for injurious loads. With this in mind, we explored associations between key knee anatomical and three-dimensional biomechanical parameters exhibited during landings. We hypothesized that lateral and medial posterior tibial slopes and their ratio, and tibial plateau width, intercondylar distance and their ratio, were proportional to peak stance anterior knee joint reaction force, knee abduction and internal rotation angles. METHODS Twenty recreationally active females (21.2 (1.7) years) had stance phase three-dimensional dominant limb knee biomechanics recorded during ten single leg land-and-cut tasks. Six anatomical indices were quantified for the same limb via a series of two dimensional (sagittal, transverse and coronal) magnetic resonance images. Linear stepwise regression analyses examined which of these anatomical factors were independently associated with each of the three mean subject-based peak knee biomechanical measures. FINDINGS Lateral tibial slope was significantly (P<0.0001) correlated with peak anterior knee joint reaction force, explaining 60.9% of the variance. Both tibial plateau width:intercondylar distance (P<0.0001) and medial tibial slope:lateral tibial slope (P<0.001) ratios were significantly correlated with peak knee abduction angle, explaining 75.4% of the variance. The medial tibial slope:lateral tibial slope ratio was also significantly (P<0.001) correlated with peak knee internal rotation angle, explaining 49.2% of the variance. INTERPRETATION Knee anatomy is directly associated with high-risk knee biomechanics exhibited during dynamic landings. Continued understanding of multifactorial contributions to the anterior cruciate ligament injury mechanism should dictate future injury screening and prevention efforts in order to successfully cater to individual joint vulnerabilities.

Tumor infiltrating lymphocytes and survival in patients with head and neck squamous cell carcinoma.

Because immune responses within the tumor microenvironment are important predictors of tumor biology, correlations of types of tumor infiltrating lymphocytes (TILs) with clinical outcomes were determined in 278 patients with head and neck squamous cell carcinoma (HNSCC).