Biomechanical study of a computer simulated reconstruction of the anterior cruciate ligament (ACL)

The purpose of the study was to use a computer simulation of various surgical techniques for reconstruction of the anterior cruciate ligament (ACL) to study graft biomechanics. To ensure the normal function of the cruciate ligament and, consequently, normal kinematics of the knee joint, the complex structure of the normal ACL must be built into the graft.

Methods. First the ACL was modeled and then a reconstruction of the ACL was simulated on a computer model of the cadaveric knee. Biomechanical patterns of the ACL and the modeled grafts in different spatial orientations and positions of the femoral attachments were studied. Isometricity of the peripheral and central fibers of the ACL and grafts was measured and the average fiber length change and isometric pattern of fibers in the graft were compared.

Results. None of the ACL fibers is isometric and fiber length change varies with individual fibers of the original ligament or graft. The average length change of graft fibers depends on the position of the femoral attachment in the sagittal plane. It is smaller in anterior positions in relation to the geometric center of the femoral origin of the ACL, and larger in posterior positions. The isometric pattern of fibers in the graft in isometric orientations resembles most closely the pattern of the original ACL.

Conclusions. A computer simulation of various surgical techniques of reconstruction of the ACL can be successfully used for the study of biomechanics. The most significant kinematic characteristics of the ACL is gradual recruitment of graft fibers during knee extension, which can be defined as the pattern of isometricity. The isometric pattern of the graft is primarily influenced by spatial orientation.     

The "epiligament" of the rabbit medial collateral ligament: a quantitative morphological study.

The thin layer of connective tissue covering ligaments--the epiligament--has not been well described. The aim of the present study was to define, describe, and quantify the structure of the epiligament of the rabbit medial collateral ligament (MCL) using polarized light, scanning-electron, transmission-electron microscopy, and computerized histomorphometry. Epiligament was composed of woven bundles of collagen fibers, 3 morphologically-distinct cell types (spinous-shaped cells, cuboidal-shaped cells, and fat cells), and a neurovascular network that periodically arborized into the MCL. The areal fraction of vessels was significantly greater in the epiligament than in the MCL. The epiligament was significantly thicker on the superficial surface of the MCL than the deep surface, and the thickness of epiligament changed significantly during skeletal growth. Based on these structural features we speculate that the epiligament serves several important functions including: (1) protecting the MCL against abrasion, (2) supporting the neurovasculature, (3) controlling water and metabolite flux into the epiligament and possibly the MCL, and (4) being a source of extracellular matrix, cells, and vasculature during ligament growth and during ligament healing.     

A novel,hydroxyapatite-based screw-like device for anterior cruciate ligament (ACL) reconstructions

Background

Rupture of the anterior cruciate ligament (ACL) is one of the most common injuries of the knee. Common techniques for ACL reconstruction require a graft fixation using interference screws. Nowadays, these interference screws are normally made of titanium or polymer/ceramic composites. The main challenge of application of a fixation device made entirely of bioactive ceramic is in relation to the low strength of such materials. The purpose of this study was to evaluate a novel geometry for a fixation device made of pure hydroxyapatite for ACL reconstructions that can overcome some problems of the titanium and the polymer/ceramic screws.

Clinical outcomes of anatomic,all-inside,anterior cruciate ligament (ACL) reconstruction

Background

This paper reports the outcomes of patients undergoing ACL reconstruction using a TransLateral single bundle, all-inside hamstring technique at a minimum of two year follow-up.

Expansion anchors for use in anterior cruciate ligament (ACL) reconstruction: establishing proof of concept in a benchtop analysis

The current method for graft fixation in bone tendon-bone anterior cruciate ligament (ACL) reconstruction is the interference screw. Although this method of fixation provides for adequate graft fixation with respect to strength, intraoperative placement is difficult and the failure rate is high. To address these concerns, we have designed and fabricated prototype expansion anchors that could be expanded to anchor the graft in the bone tunnel. As a first step in assessing the validity of this concept, in the current work, we demonstrate that these systems are of comparable fixation strength (biomechanical pullout testing) to the standard interference screw, are smaller at the time of insertion and thus provide for increased visibility and ease of placement. The increased visibility should result in better placement and reduced failure rates. The increased ease of placement should result in significant savings in decreased OR time.     

Layer-by-layer hyaluronic acid-chitosan coating promoted new collagen ingrowth into a poly(ethylene terephthalate) artificial ligament in a rabbit medical collateral ligament (MCL) reconstruction model

The ideal artificial ligament graft should have favorable biocompatibility to facilitate cell adhesion, proliferation, and collagen regeneration. In this present study, surface modification was performed on a poly(ethylene terephthalate) (PET) artificial ligament graft by layer-by-layer (LBL) self-assembly coating of hyaluronic acid (HA) and chitosan (CS). The surface characterization of the ligament was examined using scanning electron microscopy, atomic force microscopy, and energy-dispersive X-ray spectroscopy. The results of in vitro culturing of human foreskin fibroblast cells supported the hypothesis that the LBL coating of CS-HA could promote the cell proliferation and adhesion on the sheets. A rabbit medical collateral ligament reconstruction model was used to evaluate the effect of this LBL coating in vivo. The final results proved that this LBL coating could significantly promote and enhance new collagen formation among the graft fibers. On the basis of these results, we conclude that such CS-HA assembly coating could enhance PET graft biocompatibility in vitro and in vivo, and a CS-HA-coated PET graft has considerable potential as a desirable substitute for ligament reconstruction.     

Collagenase degradation decreases collagen fibril diameters--an in vitro study of the rabbit medial collateral ligament

Based on the similarity of fibril diameters in healing and grafted ligaments, it has been speculated that all small fibrils represent newly synthesized collagen. Alternatively, small fibrils in grafts could be due to enzymatic degradation of endogenous large fibrils. This study examined the effect of collagenase on collagen fibril diameters in normal NZW rabbit MCLs. Midsubstance MCL slivers were incubated in buffer for 72 or 144 h for comparison with slivers incubated in buffer containing 4 units/ml bacterial collagenase. The samples were examined under TEM for fibril diameter analysis. Mean fibril diameters of 3-day and 6-day collagenase-treated MCLs were significantly reduced, resembling 40-week scar values. These results suggest that collagenase treatment can alter collagen fibril diameter and shape in normal rabbit MCL, thus it is possible that despite their similarity to ligament scars, that at least some small fibrils in ligament grafts may be enzymatically reduced endogenous fibrils.     

Electron microscopic quantification of collagen fibril diameters in the rabbit medial collateral ligament: a baseline for comparison

To establish a normal baseline for comparison, thirty-one thousand collagen fibril diameters were measured in calibrated transmission electron (TEM) photomicrographs of normal rabbit medial collateral ligaments (MCL's). A new automated method of quantitation was used to compare statistically fibril minimum diameter distributions in one midsubstance location in both MCL's from six animals at 3 months of age (immature) and three animals at 10 months of age (mature). Pooled results demonstrate that rabbit MCL's have statistically different (p less than 0.001) mean minimum diameters at these two ages. Interanimal differences in mean fibril minimum diameters were also significant (p less than 0.001) and varied by 20% to 25% in both mature and immature animals. Finally, there were significant differences (p less than 0.001) in mean diameters and distributions from side-to-side in all animals. These mean left-to-right differences were less than 10% in all mature animals but as much as 62% in some immature animals. Statistical analysis of these data demonstrate that animal-to-animal comparisons using these protocols require a large number of animals with appropriate numbers of fibrils being measured to detect small intergroup differences. With experiments which compare left to right ligaments, far fewer animals are required to detect similarly small differences. These results demonstrate the necessity for rigorous control of sampling, an extensive normal baseline and statistically confirmed experimental designs in any TEM comparisons of collagen fibril diameters.     

四象限分区法用于前交叉韧带多纤维束动态受力分析

目的介绍四象限分区法在测量国人前交叉韧带(anterior cruciate ligament,ACL)多纤维束动态受力分析中的应用;并探讨了膝关节活动中ACL多纤维束动态力学特性。方法采集8侧正常国人膝关节标本,评估标本完整性后向ACL胫骨止点中心做斜行骨隧道,游离ACL胫骨侧止点,以四象限法平均分为4个区:1区,后内区;2区,后外区;3区,前外区;4区,前内区。将4个区的附着纤维束分别连接至自制"膝关节交叉韧带测力计"传感器上,连接系统后分别在膝关节屈曲90o位和伸直0o位将ACL各纤维束张力调零后测量膝关节4自由度(屈伸、内外翻、内外旋、前抽屉试验)内各纤维束的动态受力变化。结果2区和3区纤维束在由屈至伸的过程中所受张力逐渐增大,2区纤维束最大为22.52N±8.60N(30o),3区纤维束最大为13.98N±3.47N(0o);3区和4区纤维束在由伸至屈的过程中张力逐渐增大,4区纤维束最大为14.68N±5.29N(90o),3区纤维束最大为9.84N±5.06N(60o)。所有纤维束在外翻、内外旋、前抽屉试验中张力增加。内翻试验中所有纤维束张力增加不明显,1区纤维束在3个膝关节自由度内张力变化不明显。结论膝关节伸直过程中受力承担最大作用的纤维束主要分布在ACL胫骨止点后外分区内,屈曲位的主要承力纤维分布于前内分区,前外分区则有以上两种纤维束的附着,可能为ACL纤维束中动态受力连续变化的中转部分所在位置。四象限分区法测量ACL多纤维束动态受力有助于利用标准分区方法了解ACL多纤维束动态受力连续变化趋势,为进一步深入探讨ACL多纤维束连续动态受力提供了参考依据。     

Viscoelastic and failure properties of two configurations of triple-folded hamstring tendons used for anterior cruciate ligament (ACL) reconstruction

BackgroundHamstring autografts are commonly used for anterior cruciate ligament (ACL) reconstruction. Different folding techniques exist in tripling the semitendinosus. Few anatomical studies exist in evaluating their viscoelastic properties. The purpose of this study was to characterize and compare the viscoelastic and failure properties of two hamstring graft configurations, the “Z” construct and “2” construct.MethodsTen matched pairs of fresh-frozen cadaveric semitendinosus hamstring grafts were used to create the “2” configuration or “Z” configuration. The biomechanical testing consisted of four phases: preconditioning, where graft dimensions (mm) were measured; stress relaxation, where load, displacement and time data were collected and equilibrium relaxation (%) was calculated; dynamic creep, where the total construct elongation was calculated; and ramp-to-failure, where maximum failure load was recorded.ResultsThe “2” configuration demonstrated recorded forces (N) significantly greater at each time point when compared to the “Z” configuration during stress relaxation (p = 0.003). The “2” configuration exhibited significantly less construct elongation (mm) during dynamic creep at 10 cycles (p = 0.008) and 2000 cycles (p = 0.0001). The maximum measured load at failure was significantly greater in the “2” configuration constructs than “Z” configuration (p = 0.013). Moreover, the axial loads at 2, 3 and 4 mm of displacement were, on average, greater in the “2” configuration than “Z” configuration (p = 0.152; p = 0.080; p = 0.012), respectively.ConclusionThe results of this study provide support for folding techniques for tripled grafts to provide higher viscoelastic and failure properties for techniques with less suture interfaces. Future studies can potentially evaluate the clinical significance of these findings.     

人脂肪源干细胞促进前交叉韧带重建后腱骨界面愈合的实验研究

目的　探讨人脂肪源干细胞（human adipose-derived stem cells, hASCs）能否促进前交叉韧带重建后腱骨界面的愈合。 方法　将30只体重2.0~2.5 kg的雌性新西兰大白兔随机分为实验组和对照组,每组各15只。取同侧半腱肌作为供体肌腱,建立单侧下肢前交叉韧带重建动物模型,实验组和对照分别在胫骨和股骨隧道中注射hASCs或等量的生理盐水。分别在术后2、4和8周取材,收集胫骨-移植韧带-股骨标本行大体观察和组织学观察。 结果　HE染色示对照组术后2周腱骨界面主要以炎性细胞浸润为主,4周后炎性细胞减少,8周时腱骨界面可见Sharpey纤维,形成间接止点。实验组术后4周腱骨界面可见纤维软骨细胞及少许骨细胞形成,术后8周可见新骨形成,形成直接止点的结构。 结论　hASCs能促进前交叉韧带重建后腱骨界面的骨化作用,形成直接止点结构,从而促进腱骨界面的愈合。     

The relationship between the medial collateral ligament and the medial meniscus: a topographical and biomechanical study

The functional influence of the medial collateral ligament on the medial meniscus is still discussed controversially. Commonly, a strong fixation of the meniscus by the collateral ligament is described. Injury to the medial meniscus is explained by its reduced mobility due to its strong adherence to the medial collateral ligament. The analysis of 10 plastinated series of the medial femorotibial compartment prove that only few fibres of the ligament radiate into the meniscus. To define the possible contribution of these fibers to the stability of the medial meniscus, experiments on two fresh frozen knee joints were performed. The distal femur was separated by cutting the capsule. The medial collateral ligament was detached carefully from its femoral insertion. The tibial head with both menisci was fixed in a clamping system. A translucent, exact acrylic glass copy of the femoral component to which the medial collateral ligament was reinserted, allowed studying the behaviour of the medial meniscus under axial compression (500 N). Firstly, stress was applied while the collateral ligament was proximally fixed and under tension; then the same experiment was performed after femoral detachment of collateral ligament. All plastinated series revealed only some deep and tender fibrous bundles of the medial collateral ligament radiating into the medial meniscus proximally and posteriorly. The behaviour of medial meniscus was exactly the same in both stress experiment series. The conclusion is that there is no relevant influence of the medial collateral ligament on the stability of the medial meniscus.     

The effect of a longitudinal tear of the medial meniscus on medial meniscal extrusion in anterior cruciate ligament injury patients

PurposeThe purpose of this study was to investigate the effect of a longitudinal tear of the medial meniscus (MM) and its meniscal repair on MM extrusion in anterior cruciate ligament (ACL)-injured patients. The hypothesis underlying this study was that a longitudinal tear of the MM is correlated with MM extrusion, and that the extrusion would persist after ACL reconstruction with concomitant MM repair.MethodsForty-three ACL-injured patients with a concomitant MM longitudinal tear were included in the MM tear group. Thirty-four solely ACL-injured patients without any meniscal injuries were included in the Control group. Medial meniscus extrusion width (MEW) was measured pre-operatively and three months after surgery on magnetic resonance imaging.ResultsPre-operative MEW in the MM tear group was significantly larger than that in the Control group (MM tear group: 1.5 mm, Control: 0.3 mm, P < 0.001). The MEW change in the MM tear group was significantly greater than that in the Control group three months after operation (MM tear group: 0.8 mm, Control: ? 0.2 mm, P < 0.001). The number of sutures required for repair was correlated with MEW both pre-operatively and postoperatively in the MM tear group (pre-operative: P = 0.005, R = 0.42, postoperative: P < 0.001, R = 0.54).ConclusionLongitudinal tear of the MM was correlated with MM extrusion and the MM extrusion persisted after ACL reconstruction with concomitant MM repair in the MM tear group. The initial meniscal tear size was directly correlated with the pre-operative MEW. Therefore, meniscal extrusion after longitudinal tears of the medial meniscus should be taken into careful consideration.     

Biochemical study of collagen and its crosslinks in the anterior cruciate ligament and the tissues used as a graft for reconstruction of the anterior cruciate ligament

Among tissue grafts used for reconstruction of the anterior cruciate ligament (ACL), the pateller tendon (PT) and semitendinosus tendon (ST) are commonly used. It was thought that there were differences in the biochemical composition and process of healing between PT and ST. The aim of this study was to investigate the biochemical difference between ACL and the graft tissues used for reconstruction of the ACL. Hydroxyproline and crosslinks of collagen and elastin were measured from samples of 29 knees from cadavers preserved in formalin solutions. The results of measurements were hydroxyproline: ACL 0.522, PT 0.577, ST 0.463 (micromol/mg dry weight); pyridinoline/collagen: ACL 0.381, PT 0.272, ST 0.244 (mol/mol); and pentosidine/collagen: ACL 0.0434, PT 0.0558, ST 0.0799 (mol/mol). The biochemical properties of PT was not so different from ST. Pentosidine also was measured in the present study to aid in the comparison of the ligament and tendons of the knee joint.     

Analysis of strain distribution in the medial collateral ligament using a photoelastic coating method

The strain distribution over the entire medial collateral ligament (MCL) was measured using a photoelastic coating method. This new approach utilized a polyurethane monomer as a photoelastic coating film. The initial experiments investigating MCL strain measurement showed that this film had a high sensitivity for strain and good adhesion to the ligament. It was confirmed that strain distribution could be obtained qualitatively over the entire ligament using this method. The mechanism of MCL injury was studied by applying this polyurethane coating film to the entire MCL in a femur-MCL-tibia complex. When simple tension was applied to the complex, strain concentrations were centred at the tibial insertion site, and all the specimens ruptured at the MCL tibial insertion site. With application of a valgus bending moment, increased strain was seen in the MCL from the medial femoral condyle to the medial epicondyle. Histological analysis demonstrated midsubstance ligament ruptures in this same region. For both tests, rupture sites and increased strain concentration sites correlated. In addition, an impingement phenomenon of the MCL on the medial femoral condyle can be seen during application of valgus force, and this phenomenon may explain the higher incidence of MCL injuries on the femoral side seen in the clinical setting. This polyurethane coating method allows for direct and visual measurements, and can qualitatively measure the strain behaviour over the entire MCL surface. This new technique represents a significant improvement over previous point-by-point strain measurement methods.     

The migration of cells from the ruptured human anterior cruciate ligament into collagen-glycosaminoglycan regeneration templates in vitro

Guided tissue regeneration of the ruptured anterior cruciate ligament (ACL) offers the potential benefits of retaining the complex footprints of the ACL and the proprioceptive nerve fibers of the tissue. For this approach to be successful, ACL cells must retain the ability to migrate into an adjacent regeneration template, or scaffold, after ligament rupture. Ruptured ACLs were obtained from the knees of four men, ages 25-35, at the time of ACL reconstruction. Explants of ACL tissue were taken from three locations along the longitudinal axis of the remnant: the rupture site, the middle of the remnant, and far from the rupture site. These three areas have been found to be distinct histologically, with the region far from the rupture site having a histologic appearance similar to the intact ligament. Explants from each area were cultured in conventional tissue culture dishes (2-D culture) and on porous collagen-glycosaminoglycan (CG) scaffolds. Two-dimensional outgrowth was measured 3 times a week, and the 3-D explant/scaffold constructs were examined at 1, 2, 3 and 4 weeks to assess outgrowth of cells into the scaffold. The cell number density and expression of a-smooth muscle actin (SMA) were determined at each time point. The decrease in the diameter of the scaffolds and non-seeded controls were determined as a function of time in culture. The outgrowth of cells onto the tissue culture dishes was observed to begin as early as 3 days and as late as 21 days, with outgrowth first detected at an average of 6.8 +/- 2.0 days after explantation. In general, there was a larger area of outgrowth at the 2-week time point from explants with higher cell number density and higher blood vessel density. The 2-week area of outgrowth also correlated with the percentage of SMA-positive cells in the explant. In the experimental constructs with CG scaffolds, fibroblasts were noted to migrate from the human ACL explants into the templates at the earliest time point recorded (I week). The migration and proliferation of cells from the explants in the CG matrices resulted in an increase in the cell density in the scaffolds with time. There was a significant effect of the location from which the explant was taken on cell density in the scaffold, with a higher density of cells migrating from the explants from the rupture site of the ACL specimens. The percentage of cells staining positive for the SMA isoform varied from 0 to 50% of cells in the scaffold. Scaffolds co-cultured with explants showed a reduction in diameter that was significantly affected by time in culture and the location in the ACL from which the explant was taken. The percentage contraction attributed to the cells was 15% at 2 weeks, and increased to 27% for the injury-zone explant at 4 weeks. There was a significant correlation of the cell-mediated contraction of the matrices at 4 weeks with the cell density in the scaffolds, but not with the number of SMA-positive cells in the scaffolds. These data demonstrate that cells in the human ACL retain their ability to migrate into an adjacent CG scaffold in vitro, weeks after complete rupture. Moreover, the ACL-derived cells can express a contractile actin isoform and can contract a CG analog of extracellular matrix.