Femoral entheseal shape and attachment angle as potential risk factors for anterior cruciate ligament injury

Construction of a physical fitness evaluation index system and model for high-level freestyle skiing aerials athletes in China

OBJECTIVE

This study aims to enhance the competitive level of Chinese freestyle skiing aerials athletes by developing a specialized physical fitness evaluation index system and model tailored for high-level Chinese athletes. This system intends to provide theoretical references and training monitoring schemes in preparation for the 25th Milan Winter Olympics.

METHODS

A study was conducted on 29 high-level Chinese freestyle skiing aerials athletes. Physical fitness test indexes were selected using a literature review, expert interviews, and questionnaire surveys, and athletes were tested. Athletes were ensured to be in optimal physical condition before testing. Based on the test results, the representative indexes of the evaluation system are finally determined by combining R-type clustering analysis, multiple linear regression analysis. Determine index weights through weight questionnaires and normalization, and develop evaluation standards through methods such as percentile counting and weighted scoring.

RESULTS

Physical fitness evaluation system for Chinese freestyle skiing aerialists includes three aspects: evaluation index, index weight, and evaluation standard. The evaluation indexes include 3 first-level, 11 second-level, and 11 third-level indexes of body form, physiological function, and physical quality. In the evaluation weight, physical quality is ranked first, and physiological function and body form rank second and third, respectively. The evaluation standard consists of a scoring evaluation standard and a rating evaluation standard. Based on the index system, this study constructs the general and ideal physical fitness model of China's high-level freestyle aerials athletes.

CONCLUSION

The constructed physical fitness evaluation system effectively represents physical fitness development status of high-level freestyle skiing aerials athletes, providing a basis for creating personalized training plans. The established model serves as a reference for athletes' physical fitness development objectives.

Anatomical Tissue Engineering of the Anterior Cruciate Ligament Entheses

The firm integration of anterior cruciate ligament (ACL) grafts into bones remains the most demanding challenge in ACL reconstruction, since graft loosening means graft failure. For a functional-tissue-engineered ACL substitute to be realized in future, robust bone attachment sites (entheses) have to be re-established. The latter comprise four tissue compartments (ligament, non-calcified and calcified fibrocartilage, separated by the tidemark, bone) forming a histological and biomechanical gradient at the attachment interface between the ACL and bone. The ACL enthesis is surrounded by the synovium and exposed to the intra-articular micromilieu. This review will picture and explain the peculiarities of these synovioentheseal complexes at the femoral and tibial attachment sites based on published data. Using this, emerging tissue engineering (TE) strategies addressing them will be discussed. Several material composites (e.g., polycaprolactone and silk fibroin) and manufacturing techniques (e.g., three-dimensional-/bio-printing, electrospinning, braiding and embroidering) have been applied to create zonal cell carriers (bi- or triphasic scaffolds) mimicking the ACL enthesis tissue gradients with appropriate topological parameters for zones. Functionalized or bioactive materials (e.g., collagen, tricalcium phosphate, hydroxyapatite and bioactive glass (BG)) or growth factors (e.g., bone morphogenetic proteins [BMP]-2) have been integrated to achieve the zone-dependent differentiation of precursor cells. However, the ACL entheses comprise individual (loading history) asymmetric and polar histoarchitectures. They result from the unique biomechanical microenvironment of overlapping tensile, compressive and shear forces involved in enthesis formation, maturation and maintenance. This review should provide a road map of key parameters to be considered in future in ACL interface TE approaches.

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.

Rational Design of Soft-Hard Interfaces through Bioinspired Engineering

Soft-hard tissue interfaces in nature present a diversity of hierarchical transitions in composition and structure to address the challenge of stress concentrations that would otherwise arise at their interface. The translation of these into engineered materials holds promise for improved function of biomedical interfaces. Here, soft-hard tissue interfaces found in the body in health and disease, and the application of the diverse, functionally graded, and hierarchical structures that they present to bioinspired engineering materials are reviewed. A range of such bioinspired engineering materials and associated manufacturing technologies that are on the horizon in interfacial tissue engineering, hydrogel bioadhesion at the interfaces, and healthcare and medical devices are described.

Eight weeks of core stability training improves landing kinetics for freestyle skiing aerials athletes

Freestyle skiing aerials are characterized by technical elements including strength, flexibility and balance. Core stability in aerials can improve sporting performance.

OBJECTIVE

This study aimed to analyze the effect of 8 weeks of core stability training on core stability performance in aerials.

METHODS

Participants were randomly assigned to a control group (CG; n = 4male + 5female; age 15.89 ± 1.54 years; height 163.11 ± 6.19 cm; weight 55.33 ± 5.07 Kg) and a training group (TG; n = 4male+5female; age 16.11 ± 2.47 years; height 161.56 ± 5.25 cm; weight 57.56 ± 8.11 Kg). Body shape, the performance of core stability, and landing kinetics were measured after 8 weeks of core stability training. Independent sample t-tests were used to compare baseline values between groups. A two-way repeated-measures analysis of variance (ANOVA) (time × group) was used.

RESULTS

The TG improved body shape, and waist circumference (t = -2.333, p = 0.020). Performance of core stability, squat (t = -4.082, p = 0.004), trunk flexion isometric test (t = -4.150, p = 0.003), trunk lateral bending isometric test (t = -2.668, p = 0.008), trunk rotation isometric test (t = -2.666, p = 0.008), side bridge (t = -2.666, p = 0.008), back hyperextension (t = -4.116, p = 0.003), single foot triple jump (t = -4.184, p = 0.003), and single-leg balance with eyes closed (t = 4.167, p = 0.003). Performance in landing kinetics, End/Phase (t = -4.015, p = 0.004), sagittal axes (t = -4.598, p = 0.002), frontal axis (t = 3.116, p = 0.014), peak power hip changing range (t = 2.666, p = 0.017), peak power knee changing range (t = 2.256, p = 0.049).

CONCLUSION

Core stability training leads to improvements in body shape, the performance of core stability, and landing kinetics. Therefore, these improvements can improve the sporting performance in aerials competitions.

ACL Graft Matching: Cadaveric Comparison of Microscopic Anatomy of Quadriceps and Patellar Tendon Grafts and the Femoral ACL Insertion Site

BACKGROUND

The optimal graft choice between the bone-patellar tendon-bone (BPTB) and the quadriceps tendon remains controversial. Studies evaluating the microscopic anatomy of the quadriceps tendon-patellar bone (QTB) and BPTB grafts for anterior cruciate ligament (ACL) reconstruction are currently lacking.

HYPOTHESIS

The relationship between post-ACL reconstruction graft bending angle (GBA) and the angle corresponding to the GBA (cGBA) would indicate that the BPTB can bend more than the QTB at the femoral tunnel aperture.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty paired human cadaveric knees fixed at <10° of knee joint flexion (mean age, 82.5 years) underwent histological sectioning and staining with Masson trichrome and toluidine blue. The femoral ACL insertion, QTB graft, and BPTB graft were microscopically analyzed. The width of the direct insertion, thickness of the uncalcified fibrocartilage and calcified fibrocartilage, ligament attachment angle, and cGBA for each group were measured. Eighteen patients who underwent ACL reconstruction with QTB or BPTB autograft were included for the evaluation of GBA using computed tomography images at 1 week postoperatively.

RESULTS

The mean insertion widths of the femoral ACL, QTB, and BPTB were 7.81, 9.07, and 6.54 mm, respectively. The QTB was 16% wider than the ACL, while the BPTB was 16% narrower than the ACL. The mean insertion thicknesses of the femoral ACL, QTB, and BPTB were 0.53, 0.94, and 0.38 mm, respectively. The QTB was 77% thicker than the ACL (P < .001), while the BPTB was 28% thinner than the ACL (P = .017). The mean ligament attachment angles of the femoral ACL, QTB, and BPTB were 20.3°, 30.2°, and 33.3°, respectively, and the QTB and the BPTB were 49% and 64% larger, respectively, than the ACL. The mean cGBAs of the femoral ACL, QTB, and BPTB were 33.9°, 35.1°, and 12.3°, respectively. The BPTB was 64% smaller than the ACL, while there was no significant difference between the QTB and the ACL. The mean GBA was 57.7°.

CONCLUSION

The insertion width and thickness were significantly greater and smaller in the QTB and BPTB grafts, respectively, than in the ACL. The relationship between GBA after ACL reconstruction and cGBA in knee extension indicates that at the femoral tunnel aperture, the BPTB can bend more than the QTB.

CLINICAL RELEVANCE

QTB graft may allow more anatomic ACL reconstruction to be performed.

Enthesis strength, toughness and stiffness: an image-based model comparing tendon insertions with varying bony attachment geometries

Tendons of the body differ dramatically in their function, mechanics and range of motion, but all connect to bone via an enthesis. Effective force transfer at the enthesis enables joint stability and mobility, with strength and stiffness arising from a fibrous architecture. However, how enthesis toughness arises across tendons with diverse loading orientations remains unclear. To study this, we performed simultaneous imaging of the bone and tendon in entheses that represent the range of tendon-to-bone insertions and extended a mathematical model to account for variations in insertion and bone geometry. We tested the hypothesis that toughness, across a range of tendon entheses, could be explained by differences observed in interactions between fibre architecture and bone architecture. In the model, toughness arose from fibre reorientation, recruitment and rupture, mediated by interactions between fibres at the enthesis and the bony ridge abutting it. When applied to tendons sometimes characterized as either energy-storing or positional, the model predicted that entheses of the former prioritize toughness over strength, while those of the latter prioritize consistent stiffness across loading directions. Results provide insight into techniques for surgical repair of tendon-to-bone attachments, and more broadly into mechanisms for the attachment of highly dissimilar materials.

Femoral Intercondylar Notch: Gross Anatomy and Histology of the Connective Tissue Lining of its Roof: A Pilot Study

PURPOSE

We have consistently observed a connective tissue lining over the intercondylar notch's roof (CTLINR) during arthroscopic surgeries of the knee joint. As there is a strong association of the intercondylar fossa with the anterior cruciate ligament (ACL), we believe that this tissue must be having some role in the functioning of the ACL. The purpose of this pilot study was to investigate the anatomic characteristics of the CTLINR.

METHODS

In this observational anatomical study, we have investigated the gross anatomical and histological features of the CTLINR in four knees of two fresh frozen non-embalmed cadavers. We have also studied its ultrastructural characteristics by obtaining an arthroscopic biopsy of the tissue from a patient undergoing ACL reconstruction.

RESULTS

At gross examination, the CTLINR had a typical glistening white surface with transversely oriented fibres. It entirely covered the roof of the intercondylar notch and was soft to touch. Histological examination with haematoxylin-eosin stain revealed fibro-collagenous tissue with intervening blood vessels. Transmission electron microscopy manifested loosely arranged collagen fibres of variable diameter.

CONCLUSION

The histological and electron microscopic characteristics of the tissue differentiate it from the ACL and its femoral enthesis, suggesting that it was a distinct anatomical structure. As it entirely covered the roof of the intercondylar fossa and had a smooth surface and soft consistency, it may protect the reconstructed ACL from graft abrasion. Furthermore, as it had a characteristic arthroscopic appearance, future research can investigate its role in femoral tunnel positioning.

Fiber splay precludes the direct identification of ligament material properties: Implications for ACL graft selection

Anterior cruciate ligament (ACL) injuries typically require surgical reconstruction to restore adequate knee stability. The middle third of an injured patient's patellar tendon (PT) is a commonly used graft for ACL reconstruction. However, many clinicians and researchers question whether it is the best option, as several studies have suggested that it is a stiffer material than the ACL. Still, there is little to no consensus on even the most basic material property of ligaments/tendons: the tangent modulus in the fiber direction, or slope of the linear portion of the uniaxial stress-strain curve. In this study, we investigate the effect of fiber splay (the tendency of collagen fibers to spread out near the enthesis) on the apparent tangent modulus. Using a simplified theoretical model, we establish a quantity we call the splay ratio, which describes the relationship between splay geometry and the apparent tangent modulus. We then more rigorously investigate the effect of the splay ratio on the apparent tangent modulus of the ovine PT and anteromedial and posterolateral regions of the ACL using experimental and computational methods. Both approaches confirmed that splay geometry significantly affects the apparent material behavior. Because true material properties are independent of geometry, we conclude that the macroscopic response of ligaments and tendons is not sufficient for the characterization of their material properties, but rather is reflective of both material and structural properties. We further conclude that the PT is probably not a stiffer material than ACL, but that the PT graft is likely a stiffer structure than either ACL region.

Simulation Analysis of Knee Ligaments in the Landing Phase of Freestyle Skiing Aerial

The risk of knee injuries in freestyle skiing athletes that perform aerials is high. The internal stresses in the knee joints of these athletes cannot easily be directly measured. In order to ascertain the mechanical response of knee joints during the landing phase, and to explore the mechanism of damage to the cartilage and ligaments, a finite element model of the knee joint was established. Three successful landing conditions (neutral, backward, or forward landing) from a triple kicker were analyzed. The results demonstrate that the risk of cruciate ligament damage during a neutral landing was lowest. A forward landing carried medium risk, while backward landing was of highest risk. Backward and forward landing carried risk of injury to the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), respectively. The magnitude of stress on the meniscus and cartilage varied for all three landing scenarios. Stress was largest during neutral landing and least in backward landing, while forward landing resulted in a medium level of stress. The results also provide the basis for training that is scientifically robust so as to reduce the risk of injury and assist in the development of a professional knee joint protector.

An Anterior Cruciate Ligament Failure Mechanism

BACKGROUND

Nearly three-quarters of anterior cruciate ligament (ACL) injuries occur as "noncontact" failures from routine athletic maneuvers. Recent in vitro studies revealed that repetitive strenuous submaximal knee loading known to especially strain the ACL can lead to its fatigue failure, often at the ACL femoral enthesis.

HYPOTHESIS

ACL failure can be caused by accumulated tissue fatigue damage: specifically, chemical and structural evidence of this fatigue process will be found at the femoral enthesis of ACLs from tested cadaveric knees, as well as in ACL explants removed from patients undergoing ACL reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

One knee from each of 7 pairs of adult cadaveric knees were repetitively loaded under 4 times-body weight simulated pivot landings known to strain the ACL submaximally while the contralateral, unloaded knee was used as a comparison. The chemical and structural changes associated with this repetitive loading were characterized at the ACL femoral enthesis at multiple hierarchical collagen levels by employing atomic force microscopy (AFM), AFM-infrared spectroscopy, molecular targeting with a fluorescently labeled collagen hybridizing peptide, and second harmonic imaging microscopy. Explants from ACL femoral entheses from the injured knee of 5 patients with noncontact ACL failure were also characterized via similar methods.

RESULTS

AFM-infrared spectroscopy and collagen hybridizing peptide binding indicate that the characteristic molecular damage was an unraveling of the collagen molecular triple helix. AFM detected disruption of collagen fibrils in the forms of reduced topographical surface thickness and the induction of ~30- to 100-nm voids in the collagen fibril matrix for mechanically tested samples. Second harmonic imaging microscopy detected the induction of ~10- to 100-µm regions where the noncentrosymmetric structure of collagen had been disrupted. These mechanically induced changes, ranging from molecular to microscale disruption of normal collagen structure, represent a previously unreported aspect of tissue fatigue damage in noncontact ACL failure. Confirmatory evidence came from the explants of 5 patients undergoing ACL reconstruction, which exhibited the same pattern of molecular, nanoscale, and microscale structural damage detected in the mechanically tested cadaveric samples.

CONCLUSION

The authors found evidence of accumulated damage to collagen fibrils and fibers at the ACL femoral enthesis at the time of surgery for noncontact ACL failure. This tissue damage was similar to that found in donor knees subjected in vitro to repetitive 4 times-body weight impulsive 3-dimensional loading known to cause a fatigue failure of the ACL.

CLINICAL RELEVANCE

These findings suggest that some ACL injuries may be due to an exacerbation of preexisting hierarchical tissue damage from activities known to place larger-than-normal loads on the ACL. Too rapid an increase in these activities could cause ACL tissue damage to accumulate across length scales, thereby affecting ACL structural integrity before it has time to repair. Prevention necessitates an understanding of how ACL loading magnitude and frequency are anabolic, neutral, or catabolic to the ligament.