Évaluation clinique et biologique d’un ligament synthétique bioactif chez la brebis

The anterior cruciate ligament, which plays a key role in the knee stabilization, is commonly injured mainly during sport practicing such as soccer or skiing. Although it seems that ligament replacement by a tendon autograft is a better solution, the reconstruction with an artificial ligament provides a shorter recovery time. Polyethylene terephthalate (PET) is the best polymer to fabricate ligament prosthesis but its biocompatibility still needs to be improved. Radical graft polymerization of sodium salt of styrene sulfonate (NaSS) on PET surface was performed using the “grafting from” technique. The grafting ratio is about 5 μmol/g and found to be perfectly reproducible. Polymer grafted ligaments and non-grafted ligaments were implanted in sheep for a 3-month observation. The clinical and biological evaluation of the knee synovial liquid of implanted sheep evidenced an early functional recuperation and an excellent tolerance of pNaSS reflecting a significant absence of articular inflammation.     

A model of anterior cruciate ligament reconstructive surgery: A validation construct and computational insights

This study sought to develop a computational framework that emulates the anterior cruciate ligament reconstruction surgery using transtibial portal technique. The proposed model included the tibia–femoral and patella–femoral joints, articular cartilage and menisci. Key surgical parameters were incorporated including bone-patellar-tendon-bone graft excision and pre-tensioning, tunnel morphology, bone plugs, and bone plug fixation. Several simulation steps were parameterized to reflect the clinically reported surgical procedure. Our focus was to explore the intra-operative effects of variations in tunnel directions on the selected metrics of joint mechanics during Lachman and Anterior Drawer tests. A mathematical construct capable of transforming the limited and heterogeneous experimental and surgical data to evidence-based validation was adopted to ensure the viability of the finite element models. We found that the proposed models, subject to a variation in tunnel directions, resulted in simulation outputs that favor the reported experimental data of Lachman and Anterior Drawer tests under uncertainty. Simulation results for a population of three-dimensional tunnel orientations provided insights into the graft–tunnel contact mechanics and the spatial stress distribution in the graft, insights that have been anecdotally observed in prior experimental studies. The intraarticular graft tension was found to be higher than the estimated in tunnel graft force, and larger differences were found for the least inclined tunnels exhibiting higher contact pressures, transverse bending and twisting of the graft and Von-Mises stress at the graft–femoral tunnel interface. Conversely, tunnels with high inclination angles exhibited higher intraarticular graft tension and Von-Mises stress at the graft–tibial bone plug interface.     

Torsion and bending imposed on a new anterior cruciate ligament prosthesis during knee flexion: an evaluation method

A new composite prosthesis was recently proposed for the anterior cruciate ligament. It is implanted in the femur and the tibia through two anchoring channels. Its intra-articular portion, composed of a fiber mesh sheath wrapped around a silicone rubber cylindrical core, reproduces satisfactorily the ligament response in tension. However, the prosthesis does not only undergo elongation. In addition, it is submitted to torsion in its intra-articular portion and bending at its ends. This paper presents a new method to evaluate these two types of deformations throughout a knee flexion by means of a geometric model of the implanted prosthesis. Input data originate from two sources: (i) a three-dimensional anatomic topology of the knee joint in full extension, providing the localization of the prosthesis anchoring channels, and ii) a kinematic model of the knee describing the motion of these anchoring channels during a physiological flexion of the knee joint. The evaluation method is independent of the way input data are obtained. This method, applied to a right cadaveric knee, shows that the orientation of the anchoring channels has a large effect on the extent of torsion and bending applied to the implanted prosthesis throughout a knee flexion, especially on the femoral side. The study suggests also the best choice for the anchoring channel axes orientation.     

双源CT三维重建前交叉韧带移植物新技术

目的:探讨双源CT(DSCT)三维重建前交叉韧带(anterior cruciate ligament,ACL)重建术后移植物的技术方法。方法:对30例ACL损伤后移植重建术后患者进行DSCT扫描,利用软件三维重建ACL移植物的三维图像,对图像效果进行分析。结果:采用设定的参数和方法,30例患者的ACL移植物均获得三维重现,其中24例获得清晰的移植物图像,6例移植物图像略模糊。结论:DSCT可以重建出移植术后ACL移植物的三维图像,对临床检验、评估重建技术、修正重建方法、实现解剖重建有重大价值。     

Complete one-stage,immediate breast reconstruction with prosthetic material in patients with large or ptotic breasts

Immediate prosthetic breast reconstruction is a relatively simple, quick procedure with no donor site morbidity. This report discusses immediate one-stage breast reconstruction using prostheses in 18 patients (19 breasts) who also required a contralateral reduction or mastopexy. In all cases, an inverted-T pattern was applied to both breasts. The mean age of the patients was 49 years (range, 32 to 62 years), and the mean size of the gel implant used was 330 ml (range, 120 to 550 ml); the implant was inserted in a total submuscular pocket in seven patients and subcutaneously in 11 patients. In two patients with multiple risk factors, the prosthesis extruded, and one patient required removal for a periprosthetic infection. In 10 patients with early stage disease (T1 or T2) with tumors more than 5 cm from the nipple-areola complex, the original areola (n = 3) or nipple-areola complex (n = 7) was retained as a full-thickness skin graft.The breast shape after submuscular prosthesis insertion is different than that of the contralateral breast after a mastopexy or reduction, and nipple-areola complex symmetry was difficult to obtain; thus, this technique was abandoned in favor of the subcutaneous position (using a modified Wise keyhole pattern with a de-epithelialized portion, which still allows two-layer closure).In the subgroup of patients with large breasts or marked ptosis, a single-stage breast reconstruction procedure can be performed with symmetrical incisions. The subcutaneous position allows for symmetrical shape and nipple-areola complex symmetry to be obtained. When the tumors are small and situated in the periphery of the breast, the nipple-areola complex may be retained as a full-thickness graft.     

Tissue engineering of the anterior cruciate ligament using a braid-twist scaffold design

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee. The insufficient vascularization of this tissue prevents it from healing completely after extreme tearing or rupture, creating a need for ACL grafts for reconstruction. The limitations of existing grafts have motivated the investigation of tissue-engineered ACL grafts. A successful tissue-engineered graft must possess mechanical properties similar to the ACL; to date no commercially available synthetic graft has achieved this. To accomplish this goal we have combined the techniques of polymer fiber braiding and twisting to design a novel poly L-lactic acid (PLLA) braid-twist scaffold for ACL tissue engineering. The scaffold is designed to accurately mimic the biomechanical profile and mechanical properties of the ACL. In this study, braid-twist scaffolds were constructed and compared to braided scaffolds and twisted fiber scaffolds. The addition of fiber twisting to the braided scaffold resulted in a significant increase in the ultimate tensile strength, an increase in ultimate strain, and an increase in the length of the toe region in these constructs over scaffolds that were braided. Based on the findings of this study, the braid-twist scaffold studied was found to be a promising construct for tissue engineering of the ACL.     

Results of the surgical reconstruction of the anterior cruciate ligament

Results of the surgical reconstruction of the anterior cruciate ligament (ACL), using as a graft fourfold hamstring tendons (gracilis and semitendinosus) and middle third of the patellar ligament, were compared. In all patients that were participating in this study clinical examination and magnetic resonance showed ACL rupture, and apart from the choice of the graft, surgical technique was identical. We evaluated 112 patients with implemented patellar ligament graft and fourfold hamstring tendons graft six months after the procedure. Both groups were similar according to age, sex, activity level, knee instability level and rehabilitation program. The results showed that there was no significant difference between groups regarding Lysholm Knee score, IKDC 2000 score, activity level, musculature hypotrophy, and knee joint stability 6 months after the surgery. Anterior knee pain incidence is significantly higher in the group with patellar ligament graft (44% vs. 21%). Both groups had a significant musculature hypotrophy of the upper leg of the knee joint that was surgically treated, six months after the procedure. Both grafts showed good subjective and objective results.     

A geometric theory of the equilibrium mechanics of fibers in ligaments and tendons.

This paper presents a theoretical analysis of the equilibrium mechanics of bending and twisting fiber geometries in ligaments and tendons. The theory predicts that the bending of loaded fibers is necessarily accompanied by large transverse pressures and pressure gradients. The predicted pressures are especially large at the bone tunnel entries of ligament grafts, where they can equal or exceed the applied tensile loads. Experimental measurements of internal pressures confirm these predictions.     

Biomechanics of knee ligaments: injury, healing, and repair

Knee ligament injuries are common, particularly in sports and sports related activities. Rupture of these ligaments upsets the balance between knee mobility and stability, resulting in abnormal knee kinematics and damage to other tissues in and around the joint that lead to morbidity and pain. During the past three decades, significant advances have been made in characterizing the biomechanical and biochemical properties of knee ligaments as an individual component as well as their contribution to joint function. Further, significant knowledge on the healing process and replacement of ligaments after rupture have helped to evaluate the effectiveness of various treatment procedures. This review paper provides an overview of the current biological and biomechanical knowledge on normal knee ligaments, as well as ligament healing and reconstruction following injury. Further, it deals with new and exciting functional tissue engineering approaches (ex. growth factors, gene transfer and gene therapy, cell therapy, mechanical factors, and the use of scaffolding materials) aimed at improving the healing of ligaments as well as the interface between a replacement graft and bone. In addition, it explores the anatomical, biological and functional perspectives of current reconstruction procedures. Through the utilization of robotics technology and computational modeling, there is a better understanding of the kinematics of the knee and the in situ forces in knee ligaments and replacement grafts. The research summarized here is multidisciplinary and cutting edge that will ultimately help improve the treatment of ligament injuries. The material presented should serve as an inspiration to future investigators.     

Determination of optimal graft lengths for posterior cruciate ligament reconstruction--a theoretical analysis

Various graft materials have been used in posterior cruciate ligament (PCL) reconstruction. However, it is unclear if these grafts can reproduce the structural behavior of the PCL. This paper analyzed the effect of graft length on the structural behavior of the graft using a minimal deformation energy method. An analytical solution was obtained to determine the optimal effective graft length that can best reproduce the structural behavior of the PCL. This optimal graft length was determined as a function of the axial rigidity of the graft. Two typical grafts, bone-patella tendon-bone (BPTB) and Achilles tendon, were analyzed. The data demonstrated that in order to reproduce the PCL behavior, the effective length of a BPTB graft (10 mm width) should be 34 mm, while the Achilles tendon graft (with a cross sectional area of 55 mn2) needs to be 48 mm in length. Longer grafts result in less resistance and shorter graft increased the graft resistance. An initial graft tension cannot help recreate the overall structural behavior of the PCL. These results suggest that graft length is an important surgical variable in PCL reconstruction. An optimal reconstruction of the PCL should reproduce the structural properties of the PCL by using a graft with an optimal length.     

Spray-painted human fibronectin coating as an effective strategy to enhance graft ligamentization of a polyethylene terephthalate artificial ligament

To enhance graft ligamentization after anterior cruciate ligament (ACL) reconstruction, human fibronectin (FN) was coated on polyethylene terephthalate (PET) ligaments by spray painting. The FN-coated PET ligaments were investigated in vitro using rat mesenchymal stromal cells (MSCs). MSCs cultured on FN-coated grafts resulted in similar cell densities and amounts of proliferating cells with control grafts without coating. The FN-coated group not only gave rise to MSC-derived collagen-like tissues but also enhanced the expression of collagen-I gene. Furthermore, rat ACL reconstruction models were used to evaluate the effect of the FN coating in vivo. The FN coating significantly promoted new ligament tissue regeneration into the graft fibers. In conclusion, sprayed FN coating had a positive effect to enhance graft ligamentization of PET artificial ligament.     

Prefabricated temporalis fascia pedicled flap for previously skin-grafted contracted eye socket

The use of free skin, mucous membrane, or dermis-fat grafts in eye socket reconstruction proved to be unsatisfactory in long-term follow-up because of the progressive contraction of the socket. For achieving eye socket expansion of proper size and shape and a good vascularized lining that can last despite eventual fibrosis, a prefabricated temporalis fascia flap pedicled on the superficial temporal bundle is described in this report. In this technique, a split-thickness skin graft is applied over the termporalis fascia to create a sort of prefabricated flap, on which the proper dimensions of the socket can be fabricated on the grafted temporalis fascia. This study was conducted on 17 patients who had previously undergone eye socket reconstruction with skin graft after posttraumatic enucleation. All patients presented with a contracted eye socket, which manifested clinically by extrusion and migration of the ocular prosthesis. The procedure was performed in two stages. The purpose of prefabrication was to provide the proper shape and size of the newly created socket after release of skin-graft contracture to get a proper fit of the prosthesis, because the flap is thin and can be shaped well. The follow-up period ranged between 1 and 5 years, and the results were good.     

Origin of Twist-Bend Coupling in Actin Filaments

Actin filaments are semiflexible polymers that display large-scale conformational twisting and bending motions. Modulation of filament bending and twisting dynamics has been linked to regulatory actin-binding protein function, filament assembly and fragmentation, and overall cell motility. The relationship between actin filament bending and twisting dynamics has not been evaluated. The numerical and analytical experiments presented here reveal that actin filaments have a strong intrinsic twist-bend coupling that obligates the reciprocal interconversion of bending energy and twisting stress. We developed a mesoscopic model of actin filaments that captures key documented features, including the subunit dimensions, interaction energies, helicity, and geometrical constraints coming from the double-stranded structure. The filament bending and torsional rigidities predicted by the model are comparable to experimental values, demonstrating the capacity of the model to assess the mechanical properties of actin filaments, including the coupling between twisting and bending motions. The predicted actin filament twist-bend coupling is strong, with a persistence length of 0.15-0.4 μm depending on the actin-bound nucleotide. Twist-bend coupling is an emergent property that introduces local asymmetry to actin filaments and contributes to their overall elasticity. Up to 60% of the filament subunit elastic free energy originates from twist-bend coupling, with the largest contributions resulting under relatively small deformations. A comparison of filaments with different architectures indicates that twist-bend coupling in actin filaments originates from their double protofilament and helical structure.     

Outcomes Following Primary Anterior Cruciate Ligament Reconstruction Using a Partial Transphyseal (Over-the-Top) Technique in Skeletally Immature Patients

BackgroundThe incidence of anterior cruciate ligament (ACL) injuries in skeletally immature patients is increasing, with ACL reconstruction preferred in this population due to reported chondroprotective benefits. Due to concerns with growth disturbance following ACL reconstruction in skeletally immature patients, various physealsparing and partial transphyseal techniques have been developed. Currently, there is no consensus on the most effective ACL reconstruction technique in skeletally immature patients. The purpose of the current study was to report the outcomes of a partial-transphyseal over-the-top (OTT) ACL reconstruction in a cohort of skeletally immature patients.MethodsAll patients with radiographic evidence of open tibial and femoral physes that underwent primary ACL reconstruction using a partial-transphyseal OTT technique between 2009-2018 at a single tertiary-care institution with at least twelve months of clinical follow-up were retrospectively reviewed. Patient demographics, physical examination findings, graft ruptures, return to sport, and Tegner activity levels were analyzed. Statistical significance was defined as p<0.05.ResultsOverall, 11 males and 1 female (12 knees) with a mean age of 12.8±1.8 (range: 10-16) years were included in the study. The mean postoperative follow-up of the cohort was 2.3±1.2 (range: 1.1-5.2) years. All ACLs were reconstructed with hamstring autograft with allograft augmentation utilized in a single patient. There were two cases of ACL graft rupture (16.7%). All patients were able to return to the same or higher level of sporting activity at an average of 7.4+2.7 months. There were no cases of clinically significant longitudinal or angular growth disturbance.ConclusionPartial transphyseal ACL reconstruction using a transphyseal tibial tunnel and an extra-articular OTT technique on the femur in skeletally immature patients affords minimal risk of growth disturbance with a graft rupture rate consistent with what has been reported in this high-risk population. All patients were able to return to sport at the same or higher level. Level of Evidence: IV     

Our experience with reconstruction of the breast

Breast reconstruction in female patients undergoing mastectomy for breast cancer (17 patients) or benign breast disease (2 patients), and malformation of breast due to asymmetry (19 patients) was started in 1983. Mastectomy in 10 patients was performed because of the cancer, and in 17 patients due to benign breast disease. Age of patients ranged from 15 to 58 years. Breast reconstruction was performed within 1-12 years following mastectomy. Two different methods of reconstruction were applied: a) flap graft of patient's own skin and muscle from latissimus muscle of the back with silastic prosthesis implanted under graft (12 breasts), and b) implantation of the prosthesis only (28 breasts). Correction of the opposite breast was also made in 3 patients. No complications are seen up-to-date. Esthetic results are also satisfactory.     

Three-dimensional mechanics of eukaryotic flagella.

Equations are derived that account for the contribution of internal structure of cilia and flagella to motion in three dimensions according to a sliding filament model of the motile system. It is shown that for reasonable amounts of bending and twisting, the bending properties of an axoneme can be described by a linear elastic bending resistance, and approximate values for the bending and twisting resistances are computed. Expressions for the shear moments contributed by purely elastic or pinned links between filaments are also derived. It is shown that within the confines of a strict sliding filament model such internal structures cannot by themselves produce twist. Thus planar bending will occur if the internal shear force lies in a plane. Application of an external force, however, will in general produce twisting. Computer simulations of flagellar shape in response to a constant external force applied to the distal end of the axoneme are presented. It is shown that a small amount of twist may arise because of acylindrical bend resistance. Large twists, however, result when the external force is applied to an axoneme with internal shear resistant links.     

Twisting and stretching single DNA molecules

The elastic properties of DNA are essential for its biological function. They control its bending and twisting as well as the induction of structural modifications in the molecule. These can affect its interaction with the cell machinery. The response of a single DNA molecule to a mechanical stress can be precisely determined in single-molecule experiments which give access to an accurate measurement of the elastic parameters of DNA.     

Immediate breast reconstruction with tissue expansion

Between October of 1983 and June of 1985, 31 patients underwent primary breast reconstruction with tissue expansion. Tissue expansion was utilized for breast reconstruction when the remaining muscle and skin following modified radical mastectomy was insufficient to accommodate a prosthesis that matched in size and shape the opposite breast. All expanders were placed beneath an investing muscular pocket created by elevating the pectoralis major and serratus anterior. Postoperative expansion began within 1 week, and the breast was expanded to double the volume of the opposite breast. Twenty-two patients have completed their reconstruction with a mean follow-up in 7 months. There were nine complications, including five deflations and four infections. All patients have remained Baker I or Baker II. Creating ptosis to match the breast was accomplished by placing the expander below the rectus fascia and superiorly advancing this expanded tissue at the time of prosthesis placement. Primary breast reconstruction with tissue expansion following modified radical mastectomy is safe, simple, and produces a breast with excellent shape, size, texture, and patient satisfaction.     

Neuromuscular function after anterior cruciate ligament reconstruction with autologous semitendinosus-gracilis graft.

BACKGROUND: The quadrupled autologous semitendinosus-gracilis graft is the first choice of many orthopaedic surgeons when reconstructing the anterior cruciate ligament. The effect that this procedure has on voluntary muscle control remains unclear. The purpose of this study was to evaluate the effect that anterior cruciate ligament reconstruction with autologous semitendinosus-gracilis graft has on voluntary muscle control by assessing subjects' specificity of muscle action. METHODS: The voluntary muscle control of 10 people (seven males, three females) with acute, isolated ACL ruptures was assessed in the days prior to when they underwent anterior cruciate ligament reconstruction with quadrupled autologous semitendinosus-gracilis grafts and after they had returned to play in sports requiring quick changes of direction and jumping (approximately 6 months later). The experimental protocol included the use of an established target-matching protocol that requires subjects to produce and modulate force with fine control, electromyographic recordings from 11 muscles about the knee, and the use of circular statistics to calculate specificity indices that describe the degree of focus (specificity) associated with the activity pattern of each muscle. Data were analyzed by performing pre-surgery and post-return to sports side-to-side comparisons, as well as, pre-surgery to post-surgery ipsilateral comparisons. RESULTS: Diminished specificity of muscle action was observed in the activity patterns of most of the muscles of the subjects' anterior cruciate ligament deficient knees prior to surgery. The quadriceps muscles were particularly affected. Post-return to sports results indicated that voluntary muscle control had improved in most muscles. There was no significant difference in pre-surgery and post-return to sports semitendinosus and gracilis muscle control. The semimembranosus muscle displayed less specific muscle activity patterns following surgery, which may represent a compensation strategy for minor changes in neuromuscular function. CONCLUSIONS: Voluntary muscle control improved in most muscles following ACL reconstruction with semitendinosus-gracilis autografts. Semitendinosus and gracilis muscle control did not appear to be altered significantly by the procedure.     

Three-dimensional reconstruction using an adaptive simultaneous algebraic reconstruction technique in electron tomography

Three-dimensional (3D) reconstruction of electron tomography (ET) has emerged as an important technique in analyzing structures of complex biological samples. However most of existing reconstruction methods are not suitable for extremely noisy and incomplete data conditions. We present an adaptive simultaneous algebraic reconstruction technique (ASART) in which a modified multilevel access scheme and an adaptive relaxation parameter adjustment method are developed to improve the quality of the reconstructed 3D structure. The reconstruction process is facilitated by using a column-sum substitution approach. This modified multilevel access scheme is adopted to arrange the order of projections so as to minimize the correlations between consecutive views within a limited angle range. In the adaptive relaxation parameter adjustment method, not only the weight matrix (as in the existing methods) but the gray levels of the pixels are employed to adjust the relaxation parameters so that the quality of the reconstruction is improved while the convergence process of the reconstruction is accelerated. In the column-sum substitution approach, the computation to obtain the reciprocal of the sum for the columns in each view is avoided so that the needed computations for each iteration can be reduced. Experimental results show that the proposed technique ASART is better based on objective quality measures than other methods, especially when data is noisy and limited in tilt angles. At the same time, the reconstruction by ASART outperforms that of simultaneous algebraic reconstruction technique (SART) in speed.