Biomechanical Role Research Articles

Biomechanical assessment of myocardial infarction using optical coherence elastography.

Myocardial infarction (MI) leads to cardiomyocyte loss, impaired cardiac function, and heart failure. Molecular genetic analyses of myocardium in mouse models of ischemic heart disease have provided great insight into the mechanisms of heart regeneration, which is promising for novel therapies after MI. Although biomechanical factors are considered an important aspect in cardiomyocyte proliferation, there are limited methods for mechanical assessment of the heart in the mouse MI model. This prevents further understanding the role of tissue biomechanics in cardiac regeneration. Here we report optical coherence elastography (OCE) of the mouse heart after MI. Surgical ligation of the left anterior descending coronary artery was performed to induce an infarction in the heart. Two OCE methods with assessment of the direction-dependent elastic wave propagation and the spatially resolved displacement damping provide complementary analyses of the left ventricle. In comparison with sham, the infarcted heart features a fibrotic scar region with reduced elastic wave velocity, decreased natural frequency, and less mechanical anisotropy at the tissue level at the sixth week post-MI, suggesting lower and more isotropic stiffness. Our results indicate that OCE can be utilized for nondestructive biomechanical characterization of MI in the mouse model, which could serve as a useful tool in the study of heart repair.

Morphometry of talar trochlear surface and its correlation

Background and objectives: The morphometry of talus represents its biomechanical role in transmission of body weight. The objective of the study was to find the shape of trochlea and its correlation with other articular surfaces. Methodology: A total of 160 dry Tali of unknown sex were utilised for this study, its trochlear surface length-anterior, middle and posterior breadth [TSL, TSAB, TSMB and TSPB], calcaneal surface length & breadth [CSL and CSB] and navicular surface length & breadth [NSL and NSB] were measured using digital vernier caliper. Trochlear surface angle [TSA] and depth angle [DA] were calculated using image J software. The mean and standard deviation of the parameters were calculated. Side differences between the parameters were calculated by independent sample t test and the strength of association between the parameters was calculated by Pearson’s correlation coefficient. Results: The results were trochlear surface length, anterior, middle and posterior breadth [29.6 ± 2.7,31 ± 2.5,28.2 ±2.6 and 21.4 ± 2.1mm], navicular surface length & breadth [29.7 ± 2.5 & 20.5 ± 1.7mm] and calcaneal surface length & breadth [30 ± 2.4 &19.8 ± 1.6mm]. The mean trochlear surface and depth angle were 9.7 ± 3.3 and 156 ± 5.1degrees. There was significant correlation between the parameters of the articular surfaces. Conclusion: The present study helps in understanding the morphology of talus and the role of articular surfaces in load transmission.

Angular dimensions and squatting facets in human dry tali of South Indian origin

The angular dimensions of the talus are indicative of its biomechanical role in load transmission. Squatting facets on the neck of the talus are indicative of habitual squatting. The primary objective of this study was to estimate the strength of association between the talar angles and the presence of squatting facets. The secondary objectives were to estimate the side differences in the angular dimensions and to assess the reliability of the method. One hundred and sixty dry tali of unknown sex were studied. The neck angle, vertical angle, torsion angle, trochlear surface angle and depth angle were measured using a photographic method. The presence of squatting facets was noted. The mean and standard deviation of those angles were 108.3 ± 5.23, 89.87 ± 3.97, 37.57 ± 5.62, 9.7 ± 3.3 and 156 ± 5.1 degrees respectively. The neck, vertical and depth angles were significantly higher on the left side. There were significant positive correlations between the neck and vertical angles, the neck and depth angles and the torsion and depth angles. Squatting facets were noted in 90 of the 160 (56%) of the tali. The torsion angle was significantly higher in tali with squatting facets. Intraobserver and inter-observer reliability of the methods were found to be good to excellent. The findings of this study indicate the factors that can possibly influence the magnitude of the talar angles. This data can be useful for designing talar prostheses and analyzing the biomechanical interface of the hind foot bones.

Concussion in Rugby Union and the Role of Biomechanics

Due to the physical and high-impact nature of rugby, head impacts can occur within the game which can result in concussion injuries as well as other moderate-to-severe head injuries 1. Concussion has been defined as “a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces”1 and was found to be one of the more common brain injuries throughout the world.2 This is particularly true in sport; it has been estimated that over half of all concussions are sports related.3 A systematic review of the incidence of concussion in contact sports found that rugby union has a higher incidence rate compared with other sports such as American football and soccer.4
 Unlike other sports injuries, detecting a concussion is difficult as the neuropathological changes cannot be recognized on standard neuroimaging technology.5,6 \Therefore, if a player is suspected of having a concussion, they are removed from play for a Head Injury Assessment (HIA). The HIA is a standardized tool for the medical assessment of concussion injuries in rugby and aims to improve detection and patient education.7 The HIA assesses a range of degenerative concussive symptoms including memory, cognitive ability, balance and player discomfort. This concussion diagnosis protocol therefore relies heavily on side-line medical staff to identify if a player is exhibiting concussive symptoms. A major disadvantage to this is that concussion has a variable natural history, with transient, fluctuating, delayed and evolving signs or symptoms.8) This means that symptoms can take up to 48 hours to become apparent.8 It has therefore been acknowledged that the content of the HIA will be modified as the research around concussion diagnosis evolves.8
 The reliance on side-line medical staff to accurately identify concussive symptoms means that there is a possibility a concussed player may remain on the field; this is one problem that biomechanical research into concussion is trying to overcome. This study will give an overview of concussion in rugby union with a focus on incidence, severity and protection strategies. It will discuss current biomechanical research and further biomechanical research required in the area of concussion injuries in rugby union.

Influence of Short-Term Orthokeratology to Corneal Tangent Modulus: A Randomized Study

ABSTRACTPurpose: Influence of orthokeratology on corneal biomechanics is equivocal using Ocular Response Analyzer, ORA. Implementing indentation method, corneal tangent modulus was measured and monitored in short-term orthokeratology.Materials and Methods: Sixteen young subjects with refractive errors between –4D to –5D sphere and astigmatism within –1.50D were recruited. One randomly selected eye wore orthokeratology lens (treatment), and the fellow eye wore conventional rigid gas permeable lens (control). Lenses were worn for 30 and 60 minutes and one night separately with a week of washout period in between. The first two visits were randomly scheduled and before the overnight visit. Eyes were kept closed during all the lens wearing periods. Corneal radius, thickness, and biomechanics (using both ORA and an indentation device) were compared between eyes prior to each visit, and then before and after lens wear. Associations between baseline corneal biomechanics and central cornea from overnight visit were investigated.Results: Corneal parameters were similar in each visit before lens wear. Significant corneal flattening was observed in treatment eyes, and flattening increased with wearing time. Control eyes showed no significant corneal curvature changes. Corneal resistance factor (CRF) reduced by 0.42mmHg (± 0.68mmHg) after 30 minutes of orthokeratology treatment. Corneal hysteresis (CH) reduced by 0.42mmHg (+/- 0.63mmHg) in control eyes from overnight wear. Both eyes showed stable tangent modulus, E, throughout the study. A lower CH (r = 0.51, p = 0.046) and a higher E (r = 0.53, p = 0.037) at baseline was significantly associated with greater corneal flattening along the flattest meridian in treatment eyes.Conclusions: Short‐term orthokeratology had no significant effect on corneal tangent modulus. Changes in CH and CRF could be related to their intrinsic measurement variability. Corneal tangent modulus provided another measure of corneal biomechanics. Long-term study is required to investigate predictive role of corneal biomechanics in orthokeratology.

Dynamic Mechanical Compression of Chondrocytes for Tissue Engineering: A Critical Review.

Articular cartilage functions to transmit and translate loads. In a classical structure–function relationship, the tissue resides in a dynamic mechanical environment that drives the formation of a highly organized tissue architecture suited to its biomechanical role. The dynamic mechanical environment includes multiaxial compressive and shear strains as well as hydrostatic and osmotic pressures. As the mechanical environment is known to modulate cell fate and influence tissue development toward a defined architecture in situ, dynamic mechanical loading has been hypothesized to induce the structure–function relationship during attempts at in vitro regeneration of articular cartilage. Researchers have designed increasingly sophisticated bioreactors with dynamic mechanical regimes, but the response of chondrocytes to dynamic compression and shear loading remains poorly characterized due to wide variation in study design, system variables, and outcome measurements. We assessed the literature pertaining to the use of dynamic compressive bioreactors for in vitro generation of cartilaginous tissue from primary and expanded chondrocytes. We used specific search terms to identify relevant publications from the PubMed database and manually sorted the data. It was very challenging to find consensus between studies because of species, age, cell source, and culture differences, coupled with the many loading regimes and the types of analyses used. Early studies that evaluated the response of primary bovine chondrocytes within hydrogels, and that employed dynamic single-axis compression with physiologic loading parameters, reported consistently favorable responses at the tissue level, with upregulation of biochemical synthesis and biomechanical properties. However, they rarely assessed the cellular response with gene expression or mechanotransduction pathway analyses. Later studies that employed increasingly sophisticated biomaterial-based systems, cells derived from different species, and complex loading regimes, did not necessarily corroborate prior positive results. These studies report positive results with respect to very specific conditions for cellular responses to dynamic load but fail to consistently achieve significant positive changes in relevant tissue engineering parameters, particularly collagen content and stiffness. There is a need for standardized methods and analyses of dynamic mechanical loading systems to guide the field of tissue engineering toward building cartilaginous implants that meet the goal of regenerating articular cartilage.

The biomechanical role of the chondrocranium and sutures in a lizard cranium.

The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard Salvator merianae. We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite element model to examine strain magnitude and distribution. We find that strains within the chondrocranium are greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocranium unless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending.

Bone Trough Lateral Meniscal Allograft Transplantation: The Tapered Teardrop Technique

The meniscus plays a vital role in knee biomechanics, and its physical absence or functional incompetence (e.g., irreparable root or radial tear) leads to unacceptably high rates of joint degeneration in affected populations. Meniscal allograft transplantation has been used successfully to treat patients with postmeniscectomy syndrome, and there is early laboratory and radiographic evidence hinting at a potential prophylactic role in preventing joint degeneration. We present a technique for lateral meniscal allograft transplantation using the CONMED Meniscal Allograft Transplantation system.

Enthesitis: from pathophysiology to treatment

Entheses are the insertion sites of tendons and ligaments to the bone surface and are essential structures for locomotion. Inflammation of the entheses (enthesitis) is a key feature of psoriatic arthritis and spondyloarthritis. To date, our conceptual understanding of enthesitis remains limited. This Review provides an insight into the pathophysiology of enthesitis, addressing the role of biomechanics, prostaglandin E2-mediated vasodilation and the activation of innate immune cells in the initiation phase of enthesitis, as well as the role of entheseal IL-23-responsive cells that augment inflammation by producing pro-inflammatory mediators such as IL-17A, IL-22 and TNF. In addition, the molecular steps that translate inflammation into resident tissue responses, resulting in new bone formation, are discussed. The second part of the article summarizes the clinical features of enthesitis, and the role of clinical and imaging instruments in detecting enthesitis are discussed together with their challenges and limitations. Finally, the Review summarizes the current treatment possibilities for enthesitis based on the aforementioned pathophysiological concepts, focusing on the role of cytokine-blocking agents.

Role of substrate biomechanics in controlling (stem) cell fate: Implications in regenerative medicine.

Tissue-specific stem cells reside in a specialized environment known as niche. The niche plays a central role in the regulation of cell behaviour and, through the concerted action of soluble molecules, supportive somatic cells, and extracellular matrix components, directs stem cells to proliferate, differentiate, or remain quiescent. Great efforts have been done to decompose and separately analyse the contribution of these cues in the in vivo environment. Specifically, the mechanical properties of the extracellular matrix influence many aspects of cell behaviour, including self-renewal and differentiation. Deciphering the role of biomechanics could thereby provide important insights to control the stem cells responses in a more effective way with the aim to promote their therapeutic potential. In this review, we provide a wide overview of the effect that the microenvironment stiffness exerts on the control of cell behaviour with a particular focus on the induction of stem cells differentiation. We also describe the process of mechanotransduction and the molecular effectors involved. Finally, we critically discuss the potential involvement of tissue biomechanics in the design of novel tissue engineering strategies.

TMIC-09. TOWARDS A FRAMEWORK FOR PREDICTIVE MATHEMATICAL MODELING OF THE BIOMECHANICAL FORCES CAUSING BRAIN TUMOR MASS-EFFECT

GBMs present with different growth phenotypes, ranging from invasive lesions without notable mass-effect to strongly displacing lesions that induce mechanical stresses and result in healthy-tissue deformation, midline shift or herniation. Biomechanical forces, such as those resulting from displacive tumor growth, are recognized to shape the tumor environment and to contribute to tumor progression. We therefore expect that biomechanical forces exerted by lesions on the brain parenchyma have implications on the biophysical level, and that they may affect treatment response and outcome. To better understand the role of biomechanics in the formation of different GBM phenotypes we started developing a framework for the predictive mathematical modeling of mechanical tumor-healthy tissue interaction on the macroscopic level. The tumor’s mass-effect is represented by a solid-mechanics model of brain tissue that computes tumor-induced strain based on local tumor cell concentration. The framework allows to seed tumors at multiple locations in a human brain atlas. It simulates tumor evolution over time and across different brain regions using literature-based parameter estimates for tumor cell proliferation, as well as isotropic motility, and mechanical tissue properties. Despite its simplicity, the mathematical model yielded realistic estimates of the mechanical impact of a growing tumor on intra-cranial pressure. However, comparison to publicly available GBM imaging data showed that asymmetric shapes could not be reproduced by isotropic growth assumptions. Here we present and evaluate an extended version of this mechanically-coupled reaction-diffusion model that takes into account tissue anisotropies based on MRI diffusion tensor imaging (MR-DTI). Structural anisotropies in brain tissue have been found to affect the directionality of tumor cell migration and are critical to mechanical behavior. This makes them likely to play a role also in the development of GBM phenotypes.

TMIC-09. TOWARDS A FRAMEWORK FOR PREDICTIVE MATHEMATICAL MODELING OF THE BIOMECHANICAL FORCES CAUSING BRAIN TUMOR MASS-EFFECT

GBMs present with different growth phenotypes, ranging from invasive lesions without notable mass-effect to strongly displacing lesions that induce mechanical stresses and result in healthy-tissue deformation, midline shift or herniation. Biomechanical forces, such as those resulting from displacive tumor growth, are recognized to shape the tumor environment and to contribute to tumor progression. We therefore expect that biomechanical forces exerted by lesions on the brain parenchyma have implications on the biophysical level, and that they may affect treatment response and outcome. To better understand the role of biomechanics in the formation of different GBM phenotypes we started developing a framework for the predictive mathematical modeling of mechanical tumor-healthy tissue interaction on the macroscopic level. The tumor’s mass-effect is represented by a solid-mechanics model of brain tissue that computes tumor-induced strain based on local tumor cell concentration. The framework allows to seed tumors at multiple locations in a human brain atlas. It simulates tumor evolution over time and across different brain regions using literature-based parameter estimates for tumor cell proliferation, as well as isotropic motility, and mechanical tissue properties. Despite its simplicity, the mathematical model yielded realistic estimates of the mechanical impact of a growing tumor on intra-cranial pressure. However, comparison to publicly available GBM imaging data showed that asymmetric shapes could not be reproduced by isotropic growth assumptions. Here we present and evaluate an extended version of this mechanically-coupled reaction-diffusion model that takes into account tissue anisotropies based on MRI diffusion tensor imaging (MR-DTI). Structural anisotropies in brain tissue have been found to affect the directionality of tumor cell migration and are critical to mechanical behavior. This makes them likely to play a role also in the development of GBM phenotypes.

Effect of muscle soft tissue on biomechanics of lumbar spine under whole body vibration

The object of this study was to simulate effect of muscle soft tissue on resonant frequencies and configuration (deformation and displacement) of lumbar spine in vivo under whole-body vibration (WBV). The three-dimensional (3D) finite element (FE) models of human body including skin, muscle soft tissue, viscera, ligaments, lumbar intervertebral disc (LID) and skeleton were created and validated. Modal analysis was performed by FE method. Results were that muscle soft tissue increased the resonant frequencies of lumbar spine. The first vertical resonant frequency (FVRF) changed greatly with the variation of Young’s modulus of muscle soft tissue in range of 0.01 MPa-0.15 MPa. Muscle soft tissue reduced the modal displacement of the lumbar spine. Especially the modal displacement in the anteroposterior direction was reduced by at least 40%. The risk injury area of lumbar was at low lumbar region under vertical WBV. The conclusions were that muscle soft tissue played a very important role in biomechanics of lumbar spine, and we could contract muscles of whole body for protection of lumbar spine under WBV with high vibration amplitude. The findings could be helpful in understanding the biomechanics of lumbar spine under WBV and offer potential references for spinal disease protection and orthopedics.

A rim-and-spoke hypothesis to explain the biomechanical roles for cytoplasmic intermediate filament networks.

Textbook images of keratin intermediate filament (IF) networks in epithelial cells and the functional compromization of the epidermis by keratin mutations promulgate a mechanical role for this important cytoskeletal component. In stratified epithelia, keratin filaments form prominent radial spokes that are focused onto cell-cell contact sites, i.e. the desmosomes. In this Hypothesis, we draw attention to a subset of keratin filaments that are apposed to the plasma membrane. They form a rim of filaments interconnecting the desmosomes in a circumferential network. We hypothesize that they are part of a rim-and-spoke arrangement of IFs in epithelia. From our review of the literature, we extend this functional role for the subplasmalemmal rim of IFs to any cell, in which plasma membrane support is required, provided these filaments connect directly or indirectly to the plasma membrane. Furthermore, cytoplasmic IF networks physically link the outer nuclear and plasma membranes, but their participation in mechanotransduction processes remain largely unconsidered. Therefore, we also discuss the potential biomechanical and mechanosensory role(s) of the cytoplasmic IF network in terms of such a rim (i.e. subplasmalemmal)-and-spoke arrangement for cytoplasmic IF networks.

All-inside Arthroscopic Meniscal Repair Technique Using a Midbody Accessory Portal

Treatment of symptomatic meniscal tears continues to evolve as we improve our understanding of the biomechanical role of the meniscus and its long-term importance to the health of the knee joint. Suture repair of meniscal tears is challenging, yet the incidence of repairs among our colleagues continues to rise as we aim to preserve meniscal tissue. Many elements of performing a repair are tedious and difficult, including proper meniscal preparation, reduction, mattress suture placement, and fixation. The tear pattern and location present another layer of difficulty. The most widely used all-inside repair devices are harpoon-style devices and present their own challenges in using them without causing harm to the meniscus and surrounding cartilage. In this article, we describe a simple all-inside meniscal repair technique to improve the reproducibility and reliability of meniscal repairs using an accessory midbody meniscal portal and a surgical probe. This ensures proper placement of mattress sutures in a reduced meniscus, with a reduced risk of collateral injury to the meniscus and articular cartilage. Furthermore, this surgical technique is adaptable to any meniscal fixation method to the medial or lateral meniscus.

Tibial tubercle torsion, a new factor of patellar instability

IntroductionExternal torsion of the anterior tibial tubercle (TT), defined as external rotation around a craniocaudal axis with respect to the posterior femoral condylar plane, may induce patellar instability. To our knowledge no studies have focused on this parameter. The present study aimed to perform an MRI analysis of TT torsion. The study hypothesis was that TT torsion correlates with patellar instability and with 3 of its components: tibial tubercle-trochlear groove (TT-TG) distance, axial engagement index of the patella (AEI), and patellar tilt. Material and methodsFour observers performed MRI measurements for 2 groups: 37 patellar instability patients (PI group) with history of at least 2 patellar dislocations, and 50 control patients with meniscal lesion but free from patellofemoral pathology. All measurements were taken from 2 axial slices with the posterior condylar plane as reference. ResultsThe intra-class correlation coefficient (ICC) was 0.88. TT torsion correlated with patellar instability, with a mean 5.8̊ in controls and 17.9̊ in the PI group (P<0.001). There were also excellent correlations between TT torsion and TT-TG distance, patellar tilt and patellar lateralization (measured by AEI), with correlation coefficients greater than 0.85. DiscussionTT torsion is a reproducible measurement, with excellent ICC. It is significantly correlated with patellar instability, with a discrimination threshold of 11.5̊, and correlations with all 3 components of instability. These statistical correlations enable TT torsion to be added to the list of patellar instability factors. Further studies should determine its biomechanical role and assess the contribution of associating TT derotation to medialization or distalization procedures. Level of evidenceIII; case-control study.

The role of biomechanics in aortic aneurysm management: requirements, open problems and future prospects.

Wall stress estimation through biomechanical simulations represents a promising tool to support aneurysm risk stratification and has the potential to provide a more individual risk assessment. Accurate computation of the stress field necessitates the use of robust and biofidelic models based on patient-specific information. A multidisciplinary approach is required to obtain this information, which comprises geometry, boundary conditions, and material properties. The entire workflow encompasses many aspects, ranging from data collection to clinical interpretation of the obtained biomarkers. This review article summarizes and critically analyses the different aspects of the full clinical workflow as they have been described in the latest literature. As such, a critical assessment is provided on where we stand in the process of bringing biomechanical simulations for rupture risk assessment into broad clinical practice. Open problems are discussed and future possibilities identified.

The posterior bundle of the elbow medial collateral ligament: biomechanical study and proposal for a new reconstruction surgical technique.

The medial collateral ligament (MCL) is one of the primary elbows stabilizers. It is composed of an anterior bundle (AB), a posterior bundle (PB) and a transverse bundle. In elbow dislocations, until today MCL reconstruction has addressed the AB only. The purpose of this paper is to understand the biomechanical role of the PB of the MCL and to propose a new surgical technique for the simultaneous reconstruction of the anterior and posterior bundles, preventing the risk of recurrent posterior dislocation or posteromedial rotational instability (PMRI). Sixteen cadaveric elbows were subjected to a force in compression, supination valgus and pronation varus. The residual stability was evaluated in three conditions: intact MCL, sectioned AB and sectioned AB+PB. The tests were performed in collaboration with the Department of Mechanical and Aerospace Engineering of the Politecnico di Torino. In six elbows, the MCL was then reconstructed with the new technique. Complete posterior elbow dislocation does not occur until the PB is sectioned. The section of the AB alone causes elbow instability in valgus stress, but not a dislocation. The reconstruction of the AB and the PB using the described technique allows a good recovery of range of motion and joint stability. The PB of the MCL has a primary role in elbow stability against valgus stress, and it prevents elbow posterior dislocation at all flexion angles. The described reconstruction technique should reduce the risk of residual PMRI.

Bruch´s membrane thickness in relationship to axial length.

PurposeTo assess a potential role of Bruch´s membrane (BM) in the biomechanics of the eye, we measured its thickness and the density of retinal pigment epithelium (RPE) cells in various ocular regions in eyes of varying axial length.MethodsHuman globes, enucleated because of an ocular tumor or end-stage glaucoma were prepared for histological examination. Using light microscopy, the histological slides were histomorphometrically examined applying a digitized image analysis system.ResultsThe study included 104 eyes with a mean axial length of 27.9±3.2 mm (range:22.6mm-36.5mm). In eyes without congenital glaucoma, BM was significantly thickest (P<0.001) at the ora serrata, followed by the posterior pole, the midpoint between equator and posterior pole (MBEPP), and finally the equator. BM thickness was not significantly correlated with axial length (ora serrata: P = 0.93; equator:P = 0.31; MBEPP:P = 0.15; posterior pole:P = 0.35). RPE cell density in the pre-equatorial region (P = 0.02; regression coefficient r = -0.24) and in the retro-equatorial region (P = 0.03; r = -0.22) decreased with longer axial length, while RPE cell density at the ora serrata (P = 0.35), the MBEPP (P = 0.06; r = -0.19) and the posterior pole (P = 0.38) was not significantly correlated with axial length. Highly myopic eyes with congenital glaucoma showed a tendency towards lower BM thickness and lower RPE cell density at all locations.ConclusionsBM thickness, in contrast to scleral and choroidal thickness, was independent of axial length in eyes without congenital glaucoma. In association with an axial elongation associated decrease in the RPE cell density in the midperiphery, the findings support the notion of a biomechanical role BM may play in the process of emmetropization/myopization.

Combined Anatomic Anterior Cruciate Ligament and Double Bundle Anterolateral Ligament Reconstruction

The results of arthroscopic anterior cruciate ligament (ACL) reconstruction are so far satisfactory and improving over time as a result of the improved understanding of the anatomy and biomechanics of the ACL. Rotational instability confirmed by a positive pivot shift is present in more than 15% of cases who underwent successful ACL reconstruction. Persistent rotational instability interferes with performing pivoting sports, and also may lead to meniscal and chondral injuries, or re-rupture of the reconstructed ACL. Surgeons reconsidered the anatomy and biomechanics of the ACL and introduced the double bundle ACL reconstruction technique aiming to achieve a more rotational control by reconstructing the anteromedial and anterolateral bundles of the ACL. To date, the results of double bundle ACL reconstruction are mixed and inconsistent. The improved understanding of the existence, function, and biomechanical role of the anterolateral ligament (ALL) in controlling the rotational instability of the knee has redirected and refocused attention on a supplemental extra-articular reconstruction of the ALL in conjunction with the intra-articular ACL reconstruction so as to restore normal kinematics of the knee. In this Technical Note, we describe a technique that allows for a combined ACL and double bundle ALL reconstruction using autogenous hamstring graft (semitendinosus and gracilis) tendons. This technique is an extension of our previously described technique of a combined anatomic ACL and single bundle ALL reconstruction. The improved understanding of the anatomy of the ALL makes a double bundle ALL reconstruction more anatomic than single bundle ALL reconstruction, as the native ALL is triangular or inverted Y in shape, with a narrow proximal femoral attachment and a broad distal tibial attachment between Gerdy's tubercle and the head of the fibula.