A Comparison of Inertial Measurement Unit and Motion Capture Measurements of Tibiofemoral Kinematics during Simulated Pivot Landings.

Injuries are often associated with rapid body segment movements. We compared Certus motion capture and APDM inertial measurement unit (IMU) measurements of tibiofemoral angle and angular velocity changes during simulated pivot landings (i.e., ~70 ms peak) of nine cadaver knees dissected free of skin, subcutaneous fat, and muscle. Data from a total of 852 trials were compared using the Bland-Altman limits of agreement (LoAs): the Certus system was considered the gold standard measure for the angle change measurements, whereas the IMU was considered the gold standard for angular velocity changes. The results show that, although the mean peak IMU knee joint angle changes were slightly underestimated (2.1° for flexion, 0.2° for internal rotation, and 3.0° for valgus), the LoAs were large, ranging from 35.9% to 49.8%. In the case of the angular velocity changes, Certus had acceptable accuracy in the sagittal plane, with LoAs of ±54.9°/s and ±32.5°/s for the tibia and femur. For these rapid motions, we conclude that, even in the absence of soft tissues, the IMUs could not reliably measure these peak 3D knee angle changes; Certus measurements of peak tibiofemoral angular velocity changes depended on both the magnitude of the velocity and the plane of measurement.

Loading mechanisms of the anterior cruciate ligament.

This review identifies the three-dimensional knee loads that have the highest risk of injuring the anterior cruciate ligament (ACL) in the athlete. It is the combination of the muscular resistance to a large knee flexion moment, an external reaction force generating knee compression, an internal tibial torque, and a knee abduction moment during a single-leg athletic manoeuvre such as landing from a jump, abruptly changing direction, or rapidly decelerating that results in the greatest ACL loads. While there is consensus that an anterior tibial shear force is the primary ACL loading mechanism, controversy exists regarding the secondary order of importance of transverse-plane and frontal-plane loading in ACL injury scenarios. Large knee compression forces combined with a posteriorly and inferiorly sloped tibial plateau, especially the lateral plateau-an important ACL injury risk factor-causes anterior tibial translation and internal tibial rotation, which increases ACL loading. Furthermore, while the ACL can fail under a single supramaximal loading cycle, recent evidence shows that it can also fail following repeated submaximal loading cycles due to microdamage accumulating in the ligament with each cycle. This challenges the existing dogma that non-contact ACL injuries are predominantly due to a single manoeuvre that catastrophically overloads the ACL.

Levels of ACL-straining activities increased in the six months prior to non-contact ACL injury in a retrospective survey: evidence consistent with ACL fatigue failure.

Introduction: Recent evidence has emerged suggesting that a non-contact anterior cruciate ligament (ACL) tear can result from repetitive submaximal loading of the ligament. In other words, when the intensity of ACL-straining athletic activities is increased too rapidly, microdamage can accumulate in the ligament beyond the rate at which it can be repaired, thereby leading to material fatigue in the ligament and its eventual failure. The objective of this survey-based exploratory study was to retrospectively determine whether the levels of various athletic activities performed by ACL-injured patients significantly changed during the 6 months before injury. Methods: Forty-eight ACL-injured patients completed a survey to characterize their participation in various activities (weightlifting, sport-specific drills, running, jumping, cutting, pivoting/twisting, and decelerating) at three timepoints (1 week, 3 months, 6 months) prior to ACL injury. Activity scores, which summarized the frequency and intensity of each activity, were calculated for each patient at each time interval. A series of linear mixed-effects regression models was used to test whether there was a significant change in levels of the various activities in the 6-month period leading up to ACL injury. Results: Patients who sustained a non-contact ACL injury markedly increased their sport-specific drills activity levels in the time leading up to injury (p = 0.098), while those patients who sustained a contact ACL injury exhibited no change in this activity during the same time period (p = 0.829). Levels of running, jumping, cutting, pivoting/twisting, and decelerating increased for non-contact ACL-injured patients but decreased for contact ACL-injured patients, though not significantly (p values > 0.10). Weightlifting activity significantly decreased leading up to injury among contact ACL-injured patients (p = 0.002). Discussion: We conclude that levels of ACL-straining athletic activities or maneuvers in non-contact ACL-injured patients markedly increased in the 6 months leading up to their injury, providing evidence that changing levels of certain activities or maneuvers may play a role in ACL injury risk. This warrants further investigation of the hypothesis that too rapid an increase in activities or maneuvers known to place large loads on the ACL can cause microdamage to accumulate in the ligament, thereby leading to failure.

Relationship Between Lateral Tibial Posterior Slope and Tibiofemoral Kinematics During Simulated Jump Landings in Male Cadaveric Knees.

Background: It is not known mechanistically whether a steeper lateral posterior tibial slope (LTS) leads to an increase in anterior tibial translation (ATT) as well as internal tibial rotation (ITR) during a given jump landing. Hypothesis: A steeper LTS will result in increased ATT and ITR during simulated jump landings when applying knee compression, flexion, and internal tibial torque of increasing severity. Study Design: Descriptive laboratory study. Methods: Seven pairs of cadaveric knees were harvested from young male adult donors (mean ± SD; age, 25.71 ± 5.53 years; weight, 71.51 ± 4.81 kg). The LTS of each knee was measured by a blinded observer from 3-T magnetic resonance images. Two sets of 25 impact trials of ∼700 N (1× body weight [BW] ±10%) followed by 2 sets of 25 trials of 1400 N (2× BW ±10%) were applied to a randomly selected knee of each pair. Similarly, on the contralateral knee, 2 sets of 25 impact trials of ∼1800 N (2.5× BW ±10%) followed by 2 sets of 25 trials of ∼2100 N (3× BW ±10%) were applied. Three-dimensional knee kinematics, including ATT and ITR, were measured at 400 Hz using optoelectronic motion capture. Two-factor linear mixed effect models were used to determine the relationship of LTS to ATT and ITR as impact loading increased. Results: As LTS increased, so did ATT and ITR during increasingly severe landings. LTS had an increasing effect on ATT (coefficient, 0.50; 95% CI, 0.29-0.71) relative to impact force (coefficient, 0.52; 95% CI, 0.50-0.53). ITR was proportional to LTS (coefficient, 1.36; 95% CI, 0.80-1.93) under increasing impact force (coefficient, 0.49; 95% CI, 0.47-0.52). For steeper LTS, the increase in ITR was proportionally greater than the increase in ATT. Conclusion: In male knee specimens, a steeper LTS significantly increased ATT and ITR during jump landings. Clinical Relevance: Increases in ITR and ATT during jump landings lead to increased strain on the anterior cruciate ligament and are therefore associated with greater risk of ligament failure.

Fatigue-driven compliance increase and collagen unravelling in mechanically tested anterior cruciate ligament.

Approximately 300,000 anterior cruciate ligament (ACL) tears occur annually in the United States, half of which lead to the onset of knee osteoarthritis within 10 years of injury. Repetitive loading is known to result in fatigue damage of both ligament and tendon in the form of collagen unravelling, which can lead to structural failure. However, the relationship between tissue's structural, compositional, and mechanical changes are poorly understood. Herein we show that repetitive submaximal loading of cadaver knees causes an increase in co-localised induction of collagen unravelling and tissue compliance, especially in regions of greater mineralisation at the ACL femoral enthesis. Upon 100 cycles of 4× bodyweight knee loading, the ACL exhibited greater unravelled collagen in highly mineralized regions across varying levels of stiffness domains as compared to unloaded controls. A decrease in the total area of the most rigid domain, and an increase in the total area of the most compliant domain was also found. The results highlight fatigue-driven changes in both protein structure and mechanics in the more mineralized regions of the ACL enthesis, a known site of clinical ACL failure. The results provide a starting point for designing studies to limit ligament overuse injury.

Decreased vestibular efficacy contributes to abnormal balance in Parkinson's disease.

BACKGROUND AND PURPOSE: Abnormal balance is poorly responsive to dopaminergic therapy in Parkinson's disease (PD). Decreased vestibular efficacy may contribute to imbalance in PD. The purpose of this study was to investigate the relationship between vestibular measures of dynamic posturography and imbalance in PD while accounting for confounder variables. METHODS: 106 patients with PD underwent dynamic posturography for the 6 conditions of the sensory integration test (SOT) using the Neurocom Equitest device. All SOT measures, nigrostriatal dopaminergic denervation ((+)-[11C]DTBZ PET), brain acetylcholinesterase ([11C]PMP PET), age, duration of disease, cognitive and parkinsonian motor scores, and ankle vibration sensitivity were used as regressors in a stepwise logistic regression model comparing PD patients with versus without imbalance defined as Hoehn and Yahr (HY) stage 2.5 or higher. RESULTS: The presence of imbalance was significantly associated with vestibular ratio COP RMS (P = 0.002) independently from visual ratio COP velocity (P = 0.012), thalamic acetylcholinesterase activity (P = 0.0032), cognition (P = 0.006), motor severity (P = 0.0039), age (P = 0.001), ankle vibration sensitivity (P = 0.0008), and borderline findings for somatosensory ratio COP velocity (P = 0.074) and visual ratio COP RMS (P = 0.078). Nigrostriatal dopaminergic denervation did not achieve significance. CONCLUSIONS: The inability to efficaciously utilize vestibular information to retain upright stance is a determinant of imbalance in PD independent from visual and somatosensory processing changes and nigrostriatal dopaminergic losses. Thalamic, but not cortical, cholinergic denervation incrementally predicted balance abnormality. Further research is needed to investigate an intrinsic role of the cholinergic thalamus in multi-sensory, in particular vestibular, processing functions of postural control in PD.

The Lateral Femoral Condyle Index Is Not a Risk Factor for Primary Noncontact Anterior Cruciate Ligament Injury.

BACKGROUND: The lateral femoral condyle index (LFCI)-a recently developed measure of the sphericity of the lateral femoral condyle-was reported to be a risk factor for anterior cruciate ligament (ACL) injury. However, issues have been raised regarding how the index was measured and regarding the patient group and the knee in which it was measured. PURPOSE: To investigate the association between the LFCI and the risk of sustaining a primary, noncontact ACL injury, and to examine whether this association was moderated by the posterior-inferior-directed slope of the lateral tibial plateau. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A secondary analysis was conducted of deidentified magnetic resonance images of the uninjured knees of 86 athletes with ACL injury and the corresponding knees of 86 control athletes, matched for sports team, sex, and age. From those images, we measured the LFCI and the posterior-inferior-directed slope of the middle region articular cartilage surface of the tibial plateau's lateral compartment. Conditional logistic regressions were performed to determine whether the LFCI was significantly associated with ACL injury risk and whether the lateral tibial compartment middle cartilage slope moderated this association. Data were analyzed for female and male participants separately as well as for both groups combined. RESULTS: The LFCI was not found to be significantly associated with experiencing a primary, noncontact ACL injury for all analyses. The lateral tibial slope measure was not found to moderate the association between the LFCI and ACL injury. A conditional logistic regression analysis using the LFCI data of the injured knees, instead of the uninjured knees, of the participants with ACL injury revealed that the LFCI was significantly associated with ACL injury. CONCLUSION: In this population of athletically active female and male participants, the LFCI was not found to be a risk factor for noncontact ACL injury, regardless of the geometric features of the lateral tibial slope.

Anterior cruciate ligament microfatigue damage detected by collagen autofluorescence in situ.

PURPOSE: Certain types of repetitive sub-maximal knee loading cause microfatigue damage in the human anterior cruciate ligament (ACL) that can accumulate to produce macroscopic tissue failure. However, monitoring the progression of that ACL microfatigue damage as a function of loading cycles has not been reported. To explore the fatigue process, a confocal laser endomicroscope (CLEM) was employed to capture sub-micron resolution fluorescence images of the tissue in situ. The goal of this study was to quantify the in situ changes in ACL autofluorescence (AF) signal intensity and collagen microstructure as a function of the number of loading cycles. METHODS: Three paired and four single cadaveric knees were subjected to a repeated 4 times bodyweight landing maneuver known to strain the ACL. The paired knees were used to compare the development of ACL microfatigue damage on the loaded knee after 100 consecutive loading cycles, relative to the contralateral unloaded control knee, through second harmonic generation (SHG) and AF imaging using confocal microscopy (CM). The four single knees were used for monitoring progressive ACL microfatigue damage development by AF imaging using CLEM. RESULTS: The loaded knees from each pair exhibited a statistically significant increase in AF signal intensity and decrease in SHG signal intensity as compared to the contralateral control knees. Additionally, the anisotropy of the collagen fibers in the loaded knees increased as indicated by the reduced coherency coefficient. Two out of the four single knee ACLs failed during fatigue loading, and they exhibited an order of magnitude higher increase in autofluorescence intensity per loading cycle as compared to the intact knees. Of the three regions of the ACL - proximal, midsubstance and distal - the proximal region of ACL fibers exhibited the highest AF intensity change and anisotropy of fibers. CONCLUSIONS: CLEM can capture changes in ACL AF and collagen microstructures in situ during and after microfatigue damage development. Results suggest a large increase in AF may occur in the final few cycles immediately prior to or at failure, representing a greater plastic deformation of the tissue. This reinforces the argument that existing microfatigue damage can accumulate to induce bulk mechanical failure in ACL injuries. The variation in fiber organization changes in the ACL regions with application of load is consistent with the known differences in loading distribution at the ACL femoral enthesis.

Clinical-Grade MRI-Based Methods to Identify Combined Anatomic Factors That Predict ACL Injury Risk in Male and Female Athletes.

BACKGROUND: Recently developed multivariate sex-specific statistical models can predict anterior cruciate ligament (ACL) injury risk using various knee anatomic factors. However, screening tools able to identify individuals at an increased injury risk are unlikely to be developed based on these models, given that sophisticated and time-consuming methods were used to measure those factors on research-grade resolution magnetic resonance images (MRIs). PURPOSE: To determine whether simpler methods, amenable to using clinical-grade resolution MRIs, can identify the same knee anatomic factors previously found to contribute to ACL injury risk using sophisticated methods and research-grade resolution images. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: High-resolution 3-dimensional MRIs previously acquired from 87 patients with primary, noncontact, grade III ACL injury and 87 uninjured matched control participants for a series of published studies were downgraded to clinical-grade resolution images. The 4 knee anatomic factors found to contribute to ACL injury risk in women and in men in these published studies-femoral intercondylar notch width at the anterior outlet of the ACL (NW_O), posterior-inferior directed slope of the middle region articular cartilage surface of the tibial plateau's lateral compartment (LatTibMCS), ACL volume, and tibial plateau's lateral compartment posterior meniscus to subchondral bone wedge angle (LatTibMBA)-were measured using clinical-grade resolution MRI-based methods. Stepwise multivariate conditional logistic regressions were used to identify the combinations of factors most highly associated with an ACL injury risk in women and men separately. RESULTS: The multivariate model that best predicted ACL injury risk in the female participants included the LatTibMCS and the NW_O. For the male participants, this model included the ACL volume and the LatTibMBA. These results corroborate the previously published results that reported models with the same knee anatomic factors to best predict injury risk in this group of young women and men. CONCLUSION: Simpler methods using MRIs downgraded to a clinical-grade resolution can identify the same knee anatomic factors previously found to significantly contribute to ACL injury risk using sophisticated methods and research-grade resolution MRIs.

The Anterior Cruciate Ligament Can Become Hypertrophied in Response to Mechanical Loading: A Magnetic Resonance Imaging Study in Elite Athletes.

BACKGROUND: Evidence, mainly from animal models, suggests that exercise during periods of pubertal growth can produce a hypertrophied anterior cruciate ligament (ACL) and improve its mechanical properties. In humans, the only evidence of ACL hypertrophy comes from a small cross-sectional study of elite weight lifters and control participants; that study had methodological weaknesses and, thus, more evidence is needed. PURPOSE: To investigate bilateral differences in the ACL cross-sectional area (CSA) for evidence of unilateral hypertrophy in athletes who have habitually loaded 1 leg more than the other. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: We recruited 52 figure skaters and springboard divers (46 female and 6 male; mean age, 20.2 ± 2.7 years) because the former always land/jump on the same leg while the latter always drive the same leg into the board during their hurdle approach. Sport training for all participants began before puberty and continued throughout as well as after. Using oblique axial- and oblique sagittal-plane magnetic resonance imaging, we measured the ACL CSA and the anteroposterior diameter of the patellar tendon, respectively. In addition, isometric and isokinetic knee extensor and flexor peak torques were acquired using a dynamometer. Bilateral differences in the ACL CSA, patellar tendon diameter, and knee muscle strength were evaluated via 2-sided paired-samples t tests. Correlations between the bilateral difference in the ACL CSA and age of training onset as well as between the bilateral difference in the ACL CSA and years of training were also examined. RESULTS: A significantly larger ACL CSA (mean difference, 4.9% ± 14.0%; P = .041), as well as patellar tendon diameter (mean difference, 4.7% ± 9.4%; P = .002), was found in the landing/drive leg than in the contralateral leg. The bilateral difference in the ACL CSA, however, was not associated with the age of training onset or years of training. Last, the isometric knee flexor peak torque was significantly greater in the landing/drive leg than the contralateral leg (mean difference, 14.5% ± 33.8%; P = .019). CONCLUSION: Athletes who habitually loaded 1 leg more than the other before, during, and after puberty exhibited significant unilateral ACL hypertrophy. This study suggests that the ACL may be able to be "trained" in athletes. If done correctly, it could help lower the risk for ACL injuries.

Complex integrative morphological and mechanical contributions to ACL injury risk.

By failing to consider the integrative impact of key morphological and neuromechanical factors within the anterior cruciate ligament injury mechanism, we consider the current injury prevention model to be flawed. Critical links between these factors continue to be identified, suggesting that a successful prevention model should entrench neuromuscular control strategies that can successfully cater to individual morphological vulnerabilities.

Lower limb muscle activity and kinematics of an unanticipated cutting manoeuvre: a gender comparison.

This investigation compared the amplitude and the timing of the muscle activity of the lower limb, as well as the three-dimensional kinematics of the hip, knee and ankle joints, of male and female elite soccer players performing an unanticipated cutting manoeuvre. These data were recorded for 15 female and 15 male participants for five successful cutting manoeuvres. For this manoeuvre to be performed in an unanticipated manner, the participants were instructed to execute one of three tasks, which were signalled to them with a target board composed of three different coloured lights. Female participants performed the cutting manoeuvre with greater lateral gastrocnemius activity in comparison with the male participants. It was also observed that they contracted their vastus lateralis to a greater extent than their vastus medialis, whereas the men adopted the opposite strategy. These neuromuscular control strategies adopted by the female athletes may elucidate the reasons for which women struck the ground with a more abducted knee during the cutting task. Given that this knee position places greater strain on the anterior cruciate ligament, a restoration of the medial/lateral activation balance of the lower limb muscles may reduce one's risk of injury.

Peripheral neuropathy is associated with more frequent falls in Parkinson's disease.

INTRODUCTION: Peripheral neuropathy is a common condition in the elderly that can affect balance and gait. Postural imbalance and gait difficulties in Parkinson's disease (PD), therefore, may stem not only from the primary neurodegenerative process but also from age-related medical comorbidities. Elucidation of the effects of peripheral neuropathy on these difficulties in PD is important to provide more targeted and effective therapy. The purpose of this study was to investigate the association between lower-limb peripheral neuropathy and falls and gait performance in PD while accounting for disease-specific factors. METHODS: From a total of 140 individuals with PD, 14 male participants met the criteria for peripheral neuropathy and were matched 1:1 for Hoehn & Yahr stage and duration of disease with 14 male participants without peripheral neuropathy. All participants underwent fall (retrospectively) and gait assessment, a clinical evaluation, and [11C]dihydrotetrabenazine and [11C]methylpiperidin-4-yl propionate PET imaging to assess dopaminergic and cholinergic denervation, respectively. RESULTS: The presence of peripheral neuropathy was significantly associated with more falls (50% vs. 14%, p = 0.043), as well as a shorter stride length (p = 0.011) and greater stride length variability (p = 0.004), which resulted in slower gait speed (p = 0.016) during level walking. There was no significant difference in nigrostriatal dopaminergic denervation, cortical and thalamic cholinergic denervation, and MDS-UPDRS motor examination scores between groups. CONCLUSION: Lower-limb peripheral neuropathy is significantly associated with more falls and gait difficulties in PD. Thus, treating such neuropathy may reduce falls and/or improve gait performance in PD.

Association Between Lateral Posterior Tibial Slope, Body Mass Index, and ACL Injury Risk.

BACKGROUND: While body mass index (BMI), a modifiable parameter, and knee morphology, a nonmodifiable parameter, have been identified as risk factors for anterior cruciate ligament (ACL) rupture, the interaction between them remains unknown. An understanding of this interaction is important because greater compressive axial force (perhaps due to greater BMI) applied to a knee that is already at an increased risk because of its geometry, such as a steep lateral posterior tibial slope, could further increase the probability of ACL injury. PURPOSE: To quantify the relationship between BMI and select knee morphological parameters as potential risk factors for ACL injury. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Sagittal knee magnetic resonance imaging (MRI) files from 76 ACL-injured and 42 uninjured subjects were gathered from the University of Michigan Health System's archive. The posterior tibial slope (PTS), middle cartilage slope (MCS), posterior meniscus height (PMH), and posterior meniscus bone angle (MBA) in the lateral compartment were measured using MRI. BMI was calculated from demographic data. The association between the knee structural factors, BMI, and ACL injury risk was explored using univariate and multivariate logistic regression. RESULTS: PTS (P = .043) and MCS (P = .037) significantly predicted ACL injury risk. As PTS and MCS increased by 1°, odds of sustaining an ACL injury increased by 12% and 13%, respectively. The multivariate logistic regression analysis, which included PTS, BMI centered around the mean (cBMI), and their interaction, showed that this interaction predicted the odds of ACL rupture (P = .050; odds ratio, 1.03). For every 1-unit increase in BMI from the average that is combined with a 1° increase in PTS, the odds of an ACL tear increased by 15%. CONCLUSION: An increase in BMI was associated with increased risk of ACL tear in the presence of increased lateral posterior tibial slope. Larger values of PTS or MCS were associated with an increased risk of ACL tear.

New perspectives on ACL injury: On the role of repetitive sub-maximal knee loading in causing ACL fatigue failure.

In this paper, we review a series of studies that we initiated to examine mechanisms of anterior cruciate ligament (ACL) injury in the hope that these injuries, and their sequelae, can be better prevented. First, using the earliest in vitro model of a simulated single-leg jump landing or pivot cut with realistic knee loading rates and trans-knee muscle forces, we identified the worst-case dynamic knee loading that causes the greatest peak ACL strain: Combined knee compression, flexion, and internal tibial rotation. We also identified morphologic factors that help explain individual susceptibility to ACL injury. Second, using the above knee loading, we introduced a possible paradigm shift in ACL research by demonstrating that the human ACL can fail by a sudden rupture in response to repeated sub-maximal knee loading. If that load is repeated often enough over a short time interval, the failure tended to occur proximally, as observed clinically. Third, we emphasize the value of a physical exam of the hip by demonstrating how limited internal axial rotation at the hip both increases the susceptibility to ACL injury in professional athletes, and also increases peak ACL strain during simulated pivot landings, thereby further increasing the risk of ACL fatigue failure. When training at-risk athletes, particularly females with their smaller ACL cross-sections, rationing the number and intensity of worst-case knee loading cycles, such that ligament degradation is within the ACL's ability to remodel, should decrease the risk for ACL rupture due to ligament fatigue failure.© 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2059-2068, 2016.

On the heterogeneity of the femoral enthesis of the human ACL: microscopic anatomy and clinical implications.

BACKGROUND: Most ruptures of the native anterior cruciate ligament (ACL) and ACL graft occur at, or near, the femoral enthesis, with the posterolateral fibers of the native ligament being especially vulnerable during pivot landings. Characterizing the anatomy of the ACL femoral enthesis may help us explain injury patterns which, in turn, could help guide injury prevention efforts. It may also lead to improved anatomic reconstruction techniques given that the goal of such techniques is to replicate the knee's normal anatomy. Hence, the aim of this study was to investigate the microscopic anatomy of the ACL femoral enthesis and determine whether regional differences exist. METHODS: Fifteen human ACL femoral entheses were histochemically processed and sectioned along the longitudinal axis of the ACL at 20, 40, 60, and 80 % of the width of the enthesis. Four thick sections (100 µm) per enthesis were prepared, stained, and digitized. From these sections, regional variations in the quantity of calcified and uncalcified fibrocartilage, the angle at which the ligament originates from the bone, and the shape profile of the tidemark were quantified. RESULTS: At least 33 % more calcified fibrocartilage and 143 % more uncalcified fibrocartilage were found in the antero-inferior region, which corresponds to the inferior margin of the origin of the anteromedial ACL fibers, than all other regions (Ps < 0.05). In addition, the anteromedial fibers of the ACL originated from the femur at an angle six times greater than did its posterolateral fibers (P = 0.032). Finally, average entheseal tidemark profiles correlated bilaterally (Pearson's r = 0.79; P = 0.036), the most common profile being convex with a single re-entrant. CONCLUSIONS: Systematic regional differences were found in fibrocartilage quantity and collagen fiber attachment angles. The marked differences may reflect differences in the loading history of the various regions of the ACL femoral enthesis. These differences, which could affect the potential for injury, should also be considered when developing new ACL reconstruction approaches.

Risk of anterior cruciate ligament fatigue failure is increased by limited internal femoral rotation during in vitro repeated pivot landings.

BACKGROUND: A reduced range of hip internal rotation is associated with increased peak anterior cruciate ligament (ACL) strain and risk for injury. It is unknown, however, whether limiting the available range of internal femoral rotation increases the susceptibility of the ACL to fatigue failure. HYPOTHESIS: Risk of ACL failure is significantly greater in female knee specimens with a limited range of internal femoral rotation, smaller femoral-ACL attachment angle, and smaller tibial eminence volume during repeated in vitro simulated single-leg pivot landings. STUDY DESIGN: Controlled laboratory study. METHODS: A custom-built testing apparatus was used to simulate repeated single-leg pivot landings with a 4×-body weight impulsive load that induces knee compression, knee flexion, and internal tibial torque in 32 paired human knee specimens from 8 male and 8 female donors. These test loads were applied to each pair of specimens, in one knee with limited internal femoral rotation and in the contralateral knee with femoral rotation resisted by 2 springs to simulate the active hip rotator muscles' resistance to stretch. The landings were repeated until ACL failure occurred or until a minimum of 100 trials were executed. The angle at which the ACL originates from the femur and the tibial eminence volume were measured on magnetic resonance images. RESULTS: The final Cox regression model (P = .024) revealed that range of internal femoral rotation and sex of donor were significant factors in determining risk of ACL fatigue failure. The specimens with limited range of internal femoral rotation had a failure risk 17.1 times higher than did the specimens with free rotation (P = .016). The female knee specimens had a risk of ACL failure 26.9 times higher than the male specimens (P = .055). CONCLUSION: Limiting the range of internal femoral rotation during repetitive pivot landings increases the risk of an ACL fatigue failure in comparison with free rotation in a cadaveric model. CLINICAL RELEVANCE: Screening for restricted internal rotation at the hip in ACL injury prevention programs as well as in individuals with ACL injuries and/or reconstructions is warranted.

Quantitative comparison of the microscopic anatomy of the human ACL femoral and tibial entheses.

The femoral enthesis of the human anterior cruciate ligament (ACL) is known to be more susceptible to injury than the tibial enthesis. To determine whether anatomic differences might help explain this difference, we quantified the microscopic appearance of both entheses in 15 unembalmed knee specimens using light microscopy, toluidine blue stain and image analysis. The amount of calcified fibrocartilage and uncalcified fibrocartilage, and the ligament entheseal attachment angle were then compared between the femoral and tibial entheses via linear mixed-effects models. The results showed marked differences in anatomy between the two entheses. The femoral enthesis exhibited a 3.9-fold more acute ligament attachment angle than the tibial enthesis (p<0.001), a 43% greater calcified fibrocartilage tissue area (p<0.001), and a 226% greater uncalcified fibrocartilage depth (p<0.001), with the latter differences being particularly pronounced in the central region. We conclude that the ACL femoral enthesis has more fibrocartilage and a more acute ligament attachment angle than the tibial enthesis, which provides insight into why it is more vulnerable to failure.

Does limited internal femoral rotation increase peak anterior cruciate ligament strain during a simulated pivot landing?

BACKGROUND: Many factors contributing to anterior cruciate ligament (ACL) injury risk have been investigated. Recently, some ACL-injured individuals have presented with a decreased range of hip internal rotation compared with controls. The pathomechanics of why decreased hip range of motion increases risk of ACL injury have not yet been studied. HYPOTHESIS: Peak relative strain of the anteromedial bundle of the ACL (AM-ACL) during a simulated single-leg pivot landing is inversely related to the available range of internal femoral rotation. STUDY DESIGN: Controlled laboratory study. METHODS: A series of pivot landings were simulated in 10 female and 10 male human knee specimens with a testing apparatus that applied a 2-bodyweight impulsive load, inducing knee compression, flexion moment, and internal tibial torque. The range of internal femoral rotation was (1) locked at ~0°, (2) limited with a hard stop to ~7°, (3) limited with a hard stop to ~11°, or (4) free, with rotation resisted by 2 springs to simulate the resistance of the active hip rotator muscles to stretch. The AM-ACL strain was quantified with a differential variable reluctance transducer. A linear mixed model was used to determine whether a significant linear relation existed between peak AM-ACL relative strain and range of internal femoral rotation. RESULTS: Peak AM-ACL relative strain was inversely related to the available range of internal femoral rotation (R (2) = 0.91; P < .001), with strain increasing 1.3% for every 10° decrease in rotation; this represented a 20% increase in peak relative strain, given an average range of femoral rotation of 15° upon landing in healthy athletes. CONCLUSION: Peak AM-ACL relative strain was inversely proportional to the available range of internal femoral rotation during simulated single-leg pivot landings. CLINICAL RELEVANCE: Decreased range of internal femoral rotation results in greater ACL strain and may therefore increase the susceptibility to ACL rupture with athletic cutting and pivoting activities. Screening for a limited range of hip internal rotation should therefore become a component of not only ACL injury prevention programs but also evaluation protocols for those with ACL injuries and/or reconstructions.