Publications

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.

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.

BACKGROUND: Knee abduction moment during landing has been associated with anterior cruciate ligament (ACL) injury. However, accurately capturing this measurement is expensive and technically rigorous. Less complex variables that lend themselves to easier clinical integration are desirable.

PURPOSE: To corroborate in vitro cadaveric simulation and in vivo knee abduction angles from landing tasks to allow for estimation of ACL strain in live participants during a landing task.

STUDY DESIGN: Descriptive laboratory study.

METHODS: A total of 205 female high school athletes previously underwent prospective 3-dimensional motion analysis and subsequent injury tracking. Differences in knee abduction angle between those who went on to develop ACL injury and healthy controls were assessed using Student t tests and receiver operating characteristic analysis. A total of 11 cadaveric specimens underwent mechanical impact simulation while instrumented to record ACL strain and knee abduction angle. Pearson correlation coefficients were calculated between these variables. The resultant linear regression model was used to estimate ACL strain in the 205 high school athletes based on their knee abduction angles.

RESULTS: Knee abduction angle was greater for athletes who went on to develop injury than for healthy controls (P < .01). Knee abduction angle at initial contact predicted ACL injury status with 78% sensitivity and 83% specificity, with a threshold of 4.6° of knee abduction. ACL strain was significantly correlated with knee abduction angle during cadaveric simulation (P < .01). Subsequent estimates of peak ACL strain in the high school athletes were greater for those who went on to injury (7.7-8.1% ± 1.5%) than for healthy controls (4.1-4.5% ± 3.6%) (P < .01).

CONCLUSION: Knee abduction angle exhibited comparable reliability with knee abduction moment for ACL injury risk identification. Cadaveric simulation data can be extrapolated to estimate in vivo ACL strain. Athletes who went on to ACL injury exhibited greater knee abduction and greater ACL strain than did healthy controls during landing.

CLINICAL RELEVANCE: These important associations between the in vivo and cadaveric environments allow clinicians to estimate peak ACL strain from observed knee abduction angles. Neuromuscular control of knee abduction angle during dynamic tasks is imperative for knee joint health. The present associations are an important step toward the establishment of a minimal clinically important difference value for ACL strain during landing.

BACKGROUND/PURPOSE: The number of hip arthroscopies (HAs) performed in the United States is increasing exponentially. Previous authors have shown improvements in short- and mid-term functional outcomes after HA. Despite established overall improvements, functional and objective impairments may persist. In particular, preliminary work demonstrates differences in hip strength between patients who undergo HA when compared to healthy controls at 12- and 24-months post-operative. The purpose of this clinical commentary is to highlight the persistent hip muscle strength and neuromuscular deficits that occur after HA, as well as propose the utilization of neuromuscular electrical stimulation (NMES) as an adjunct to strengthening exercises in early post-operative rehabilitation to address deficits.

DESCRIPTION OF TOPIC: Arthrogenic muscle inhibition (AMI), drives neuromuscular dysfunction and has been shown to occur in peripheral joints. The knee and hip have historically benefited from NMES to aid in improved muscular function, such as in those who have undergone anterior cruciate ligament reconstruction, total hip or knee arthroplasties. Improving muscular strength is a hallmark component of rehabilitation after HA, however, current post-operative HA rehabilitation protocols do not include NMES as a standard treatment intervention. Therapeutic intervention strategies to target muscular inhibition after HA, in particular with the goal to address neural reflex inhibition, have not been thoroughly investigated. This absence of understanding of this important problem yields a critical gap in the treatment of post-operative muscular deficits in patients after HA.

DISCUSSION: The consequence of hip muscle inhibition is likely to include deficits in strength and function, similar to that seen in other muscular groups. Filling the void of current knowledge with regard to muscle inhibition and strength deficits after hip arthroscopy is critical to establish standardized post-operative rehabilitation protocols, as well as to provide targeted training to address muscular inhibition. Ultimately, these strategies could produce improved outcomes guided by robust evidence-based protocols.

LEVEL OF EVIDENCE: 5.

PURPOSE: The sensorimotor system is a subcomponent of the comprehensive motor control system of the body. However, the complex nature of the sensorimotor system makes it difficult to interpret findings for clinical application. The purpose of this study was to utilize principal component analysis (PCA) to identify sex differences and relationships between sensorimotor variables during a dynamic perturbation.

MATERIALS AND METHODS: Thirty physically active individuals (15 males and 15 females) were blindfolded and positioned on an isokinetic dynamometer with their knee flexed to 70°. At random, the dynamometer moved rapidly towards knee extension. Subjects were asked to resist the dynamometer as it would randomly and rapidly move towards knee extension. Torque and position values were used to calculate stiffness values.

RESULTS: PCA revealed sex differences in two principal components (PCs): PC2 in female was comprised from higher position, torque, and time values (p = .038), PC4 in females was comprised from higher active stiffness and lower short-range stiffness values (p = .032) compared to males. Torque at the resting position was correlated to the short-range passive stiffness (ρ = 0.539, p = .002), time to peak torque (ρ = -0.375, p = .003), and reactive stiffness (ρ = 0.526, p = .041).

CONCLUSIONS: Females had later reaction time and lower short-range passive stiffness and they resisted the dynamometer by their voluntary activation compared to the males thus requiring muscle activation for meaningful response. In addition, the higher resting muscle activities may correlate to short-range passive stiffness and quicker active stiffness. Abbreviations: ACL: anterior cruciate ligament; EEG: electroencephalogram; EMG: electromyography; ICC: intraclass correlation coefficient; MDC95: minimally detectable differences at 95% confidence intervals; PC: principal component; PCA: principal component analysis; POS50: position value at 50 ms; POS100: position value at 100 ms; POSprop: position value at TIMEprop; POSpk: position value at TIMEpk; POSprop-pk: position difference between POSprop and POSpk; SEM: standard error of measurements; STIFF50: short-range-stiffness at 50 ms; STIFF100: short-range-stiffness at 100 ms; STIFFreac: reactive knee stiffness (stiffness between TIMEprop to TIMEpk); TIMEprop: threshold-to-detect passive movement as the time point; TIMEpk: time at which peak hamstrings torque occurred; TIMEprop-pk: time between TIMEprop to TIMEpk; TORQ0: torque value at time zero; TORQ50: torque value at 50 ms; TORQ100: torque value at 100 ms; TORQprop: torque value at TIMEprop; TORQpk: torque value at TIMEpk; TORQ50diff: torque difference between TORQ0 and TORQ50; TORQ100diff: torque difference between TORQ0 and TORQ100.

Parkinson's disease is associated with degeneration of neuromelanin (NM)-containing substantia nigra dopamine (DA) neurons and subsequent decreases in striatal DA transmission. Dopamine spontaneously forms a melanin through a process called melanogenesis. The present study examines conditions that promote/prevent DA melanogenesis. The kinetics, intermediates, and products of DA conversion to melanin in vitro, and DA melanogenesis under varying levels of Fe3+, pro-oxidants, and antioxidants were examined. The rate of melanogenesis for DA was substantially greater than related catecholamines norepinephrine and epinephrine and their precursor amino acids tyrosine and l-Dopa as measured by UV-IR spectrophotometry. Dopamine melanogenesis was concentration dependent on the pro-oxidant species and Fe3+. Melanogenesis was enhanced by the pro-oxidant hydrogen peroxide (EC50 = 500 μM) and decreased by the antioxidants ascorbate (IC50 = 10 μM) and glutathione (GSH; IC50 = 5 μM). Spectrophotometric results were corroborated by tuning a fast-scan cyclic voltammetry system to monitor DA melanogenesis. Evoked DA release in striatal brain slices resulted in NM formation that was prevented by GSH. These findings suggest that DA melanogenesis occurs spontaneously under physiologically-relevant conditions of oxidative stress and that NM may act as a marker of past exposure to oxidative stress.

The mechanism underlying non-contact anterior cruciate ligament (ACL) injury is multi-factorial and still an object of debate. Computational models, in combination with in vivo and cadaveric studies, can provide valuable insight into the contribution of the different factors involved. The goal of this study was to validate four knee finite element models (two males and two females) to kinematic and strain data collected in vitro with an impact-driven simulator and use them to assess how secondary external knee loads (knee abduction moment [KAM], anterior shear force, and internal rotation torque [ITR]) affect tibiofemoral contact forces and ACL force during impact. Four subject-specific knee models were developed from specimen computed tomography and magnetic resonance imaging. Patellofemoral and tibiofemoral ligament properties were calibrated to match experimentally measured kinematics and ligament strain. Average root mean square errors and correlations between experimental and model-predicted knee kinematics were below 1.5 mm and 2°, and above 0.75, respectively. Similar errors and correlations were obtained for ACL strain (< 2% and > 0.9). Model-predicted ACL forces were highly correlated with the anterior component of the tibiofemoral contact force on the lateral plateau occurring during impact (r = 0.99), which was increased by larger KAM and ITR through the posterior tibial slope and a larger contact force on the lateral side. This study provides a better understanding of the mechanism through which secondary external knee loads increase ACL injury risk during landing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1730-1742, 2019.

PURPOSE OF REVIEW: Overhand (OH) throwers demonstrate a unique motion profile of the shoulder joint complex. This manuscript reviews normal adaptations in the OH thrower and contrast findings with pathologic motion deficits.

RECENT FINDINGS: Multiple adaptations in range of motion have been associated with increased risk for arm injury. The use of a more conservative cutoff value for glenohumeral internal rotation deficit and horizontal adduction in younger throwers may help reduce injury risk. Deficits in glenohumeral internal rotation, total range of motion, shoulder flexion, and external rotation insufficiency have all been proposed as means to identify OH throwers at risk for arm injury, but conflicting evidence exists. Understanding normal adaptation due to repetitive stress of throwing is essential to effective management of these athletes. Adaptive change in bone and soft tissues is normal and contributes to the unique motion profiles expected in throwers. The causative link between normal adaptation and shoulder and elbow injury remains uncertain.