Anterior Cruciate Ligament Replacement Research Articles

Tissue Engineering of the Anterior Cruciate Ligament—Sodium Dodecyl Sulfate-Acellularized and Revitalized Tendons Are Inferior to Native Tendons

The acellularization of tendons using detergents (sodium dodecyl sulfate, Triton-X, tri-nitro-butyl-phosphate) is a new source of scaffolds for tissue engineering in anterior cruciate ligament (ACL) repair. In vitro testing demonstrated that acellular tendon scaffolds are biocompatible and show good biomechanical properties, but in vivo confirmation of these results is not yet available. Therefore, the aim of this study was to see in vivo if an acellular allogenic construct colonized with autologous fibroblasts improves the quality of ACL reconstruction. ACL replacement was performed in 31 New Zealand White rabbits using a standardized model. Fifteen animals received autologous semitendinosus tendon, whereas 16 animals were treated with a tissue-engineered construct. This construct was made by acellularization of allogenic semitendinosus tendons using sodium dodecyl sulfate and subsequent in vitro colonization with autologous fibroblasts. Eight weeks postoperatively, macroscopic, biomechanical (ultimate load to failure, elongation, stiffness; n = 8/9), and histological (n = 5) examinations were performed. Biomechanical testing showed decreasing strength of the constructs at 8 weeks after implantation compared with the direct postsurgical strength. However, tissue-engineered constructs (F = 19.7 +/- 20.3 N) were significantly weaker than autologous tendons (F = 61.2 +/- 31.2 N). Histologically, the autologous tendons showed signs of partial necrosis and tissue remodeling. The tissue-engineered constructs exhibited an inflammatory reaction and showed both repopulated and acellular regions. In conclusion, in vivo results were much more unfavorable than in vitro results had suggested. Further studies have to be performed to test if modifications of the acellularization process yield better results in vivo.

The Future: Optimizing the Healing Environment in Anterior Cruciate Ligament Reconstruction

The therapeutic use of autologous platelet-rich plasma constitutes a breakthrough in the stimulation and acceleration of soft-tissue healing and bone regeneration. Platelet-rich technologies seek to facilitate anterior cruciate ligament replacement by mimicking the native tissue and improving the adequacy of tissue function with appropriate cues, ultimately leading to better patient care. There are different technical protocols for preparing platelet-rich plasma, and the resultant products are typically heterogeneous; moreover, protocols for administrating the products in patients vary extensively. Poor standardization in the field makes full evaluation of different plasma products and establishing standards for the most beneficial applications of this technology difficult. This article presents the current data on the use of platelet-rich plasma in the reconstruction of the anterior cruciate ligament. Although the findings are not conclusive, the use of autologous platelet-rich plasma is shown to be safe, reproducible, and effective in mimicking the natural processes of soft tissue and bone healing. Platelet-rich technologies offer new opportunities for research and the application of anterior cruciate ligament tissue engineering.

Novel matrix based anterior cruciate ligament (ACL) regeneration

Among the five ligaments in the knee the anterior cruciate ligament (ACL) is among the most important for stability and also the most commonly injured. Due to a lack of vascularization, the ACL has poor healing potential, therefore moderate to severe damage warrants medical intervention. Ligaments are complex, highly organized tissues; they are longitudinally arranged with a great deal of order that begins at the molecular level and carries through to the tissue level. The components of the ligament and their location and orientation heavily influence the tissue's mechanical behavior. ACL replacements have faced a variety of limitations that prevented their extensive use, including implant fatigue or fraying of the device. In the face of these problems, investigators have begun to examine a variety of matrix based techniques to create options for ACL repair, replacement, and regeneration. This article will discuss ACL structure and mechanics, past replacement options and their limitations, and recent tissue engineered options for ACL repair. These techniques employ a wide variety of designs, materials, and methods to heal damaged ACL tissue or regenerate lost tissue in order to regain full ACL strength and mechanics.

Augmentation of Bone Tunnel Healing in Anterior Cruciate Ligament Grafts: Application of Calcium Phosphates and Other Materials

Bone tunnel healing is an important consideration after anterior cruciate ligament (ACL) replacement surgery. Recently, a variety of materials have been proposed for improving this healing process, including autologous bone tissue, cells, artificial proteins, and calcium salts. Amongst these materials are calcium phosphates (CaPs), which are known for their biocompatibility and are widely commercially available. As with the majority of the materials investigated, CaPs have been shown to advance the healing of bone tunnel tissue in animal studies. Mechanical testing shows fixation strengths to be improved, particularly by the application of CaP-based cement in the bone tunnel. Significantly, CaP-based cements have been shown to produce improvements comparable to those induced by potentially more complex treatments such as biologics (including fibronectin and chitin) and cultured cells. Further investigation of CaP-based treatment in the bone tunnels during ACL replacement is therefore warranted in order to establish what improvements in healing and resulting clinical benefits may be achieved through its application.

Navigation System Measures AP and Rotational Knee Laxity in ACL Replacement

We used a non-image-based navigation system to measure anterior and rotational laxity during anterior cruciate ligament replacement. The preoperative and postoperative navigated measurements of anterior laxity were compared with the preoperative and postoperative stress radiographs. There was a significant difference between these 2 measurements, but they were significantly correlated. Navigated anterior laxity measurement can therefore be considered reliable. The intraoperative information about the correction of the anterior laxity may have relevance in controlling the quality of the procedure and improving reproducibility. Information about rotational laxity may be helpful, but its exact significance must be more precisely defined.

In Vivo Matrix Production by Bone Marrow Stromal Cells Seeded on PLGA Scaffolds for Ligament Tissue Engineering

Ligament tissue engineering based on cell-seeded biomechanically functional constructs is a commonly studied strategy toward native anterior cruciate ligament replacement. Little is known about the survival and differentiation of the seeded cells after the transplantation. We applied retroviral genetic marking to trace implanted cells and studied their differentiation by species-specific immunolabeling of the extracellular matrix produced. Goat bone marrow stromal cells were transduced with a MoMuLV-based vector encoding the DeltaLNGFR gene. Transduced cells were seeded onto poly(lactic-co-glycolic acid) (PLGA) fibers and implanted subcutaneously into nude mice and left for various periods up to 6 weeks. Immunohistochemistry for LNGFR expression showed survival of the seeded cells after transplantation for up to 6 weeks. Immunohistochemistry for collagen type I and III showed the production of fibrous tissue inside the scaffolds. Moreover, using a goat-specific anti-collagen type III, donor-derived matrix could be demonstrated. We conclude that bone marrow stromal cells survived in vivo and at least partially differentiated after implantation.

Leeds-Keio 人工靱帯を用いた前十字靱帯再建術の術後成績

Leeds-Keio 人工靱帯を用いた前十字靱帯再建術の術後成績

Evaluation of Knee Stability with Use of a Robotic System

In our research center, we have developed and utilized a novel robotic/universal force-moment sensor testing system to gain quantitative data on multiple-degree-of-freedom kinematics of the knee simultaneously with data on the in situ forces in normal and repaired soft tissues. In particular, we have investigated the complex interaction of the anteromedial and posterolateral bundles of the anterior cruciate ligament as well as several key biomechanical variables in anterior cruciate ligament reconstruction, such as graft selection and femoral tunnel placement (both of which impact knee stability). For example, both the bone-patellar tendon-bone and quadrupled hamstrings tendon autografts restored anterior stability but were insufficient in gaining rotatory stability. In a follow-up study, we have shown that a more laterally placed graft was beneficial and could improve these outcomes. Such findings led to additional investigation in which the biomechanical advantages of double-bundle anterior cruciate ligament reconstruction were demonstrated. However, a more laterally placed autograft at the femoral insertion of the posterolateral bundle also worked well, especially when the knee was nearly at full extension (a position in which the anterior cruciate ligament is needed most). At present, we are moving forward by obtaining in vivo kinematics data and then repeating those kinematics exactly to obtain new data with use of the robotic/universal force-moment sensor testing system in order to gain further insight regarding the function of the anterior cruciate ligament and anterior cruciate ligament replacement grafts in vivo. In parallel, we are developing a mathematical model of the knee and validating the computational model with experimental data. The combined approach will yield new and relevant information, including the stress and strain distribution in the anterior cruciate ligament and anterior cruciate ligament grafts. This will facilitate a better understanding of the function of the anterior cruciate ligament and a scientifically based design of surgical procedures and postoperative rehabilitation protocols that will lead to better patient outcomes.

Functional outcomes and health-related quality of life after robot-assisted anterior cruciate ligament reconstruction with patellar tendon grafts

During a short period of time, surgical robots had been propagated for automated tunnel placement in anterior cruciate ligament (ACL) reconstruction. Clinical outcome data are currently unavailable. Between 2000 and 2003, 152 patients underwent ACL replacement with the assistance of the Computer Assisted Surgical Planning and Robotics system (CASPAR, OrtoMaquet, Germany) at our hospital. After minimal invasive pin placement in both the tibia and femur, computed tomography was used to register anatomical landmarks and to plan graft tunnel alignment. The robot was used to drill tibial and femoral tunnels in an outside-in fashion according to pre-operative planning. There was one procedure-specific Serious Adverse Event (i.e., an intraoperative transection of the posterior cruciate ligament). After IRB approval, all patients were invited for a follow-up examination. Data from 100 patients (35 women, 65 men, mean age 35 [SD 11] years, median follow-up 61 [range 42-77] months) form the basis of this report. Side-to-side differences in anterior laxity were measured with the KT-1000 arthrometer. Patient-centered outcomes included the Lysholm-Score, the lower extremity functional scale (LEFS), and the Short Form 36 (SF36). The mean KT-1000 side-to-side difference was 0.89 [95% confidence interval (CI) 0.52-1.26] mm. Eight and five patients had a positive Lachman and pivot shift test, respectively. The Lysholm-Score averaged 86 (95% CI 83-89) points. Excellent, good, fair, and poor outcomes were reported by 38, 32, 20, and 10 patients. The LEFS averaged 85 (95% CI 82-88) points. The mean SF36 Physical Component Score was 48.4 (95% CI 46.5-50.3), indicating residual deficits compared to the population norm. All tibial graft tunnels did not cross the Blumensaat line, but were placed slightly anterior to the optimal center of 42% reported in previous studies. Compared to literature data, robot-assisted ACL reconstruction with BTB grafts may lead to higher knee stability, but poorer functional outcomes. The immense additional efforts with the procedure did not pay off in a benefit to patients.

Tissue Engineering of the Anterior Cruciate Ligament: The Viscoelastic Behavior and Cell Viability of a Novel Braid–Twist Scaffold

The anterior cruciate ligament (ACL) is the most commonly injured ligament of the knee; it also contributes to normal knee function and stability. Due to its poor healing potential severe ACL damage requires surgical intervention, ranging from suturing to complete replacement. Current ACL replacements have a host of limitations that prevent their extensive use. Investigators have begun to utilize tissue-engineering techniques to create new options for ACL repair, regeneration and replacement. In this study we tested novel braid–twist scaffolds, as well as braided scaffolds, twisted fiber scaffolds and aligned fiber scaffolds, for use as ACL replacements composed of poly(L-lactic acid) fibers. Scaffolds were examined using stress relaxation tests, cell viability assays and scanning electron microscopy. The behaviors of the braid–twist scaffolds were modeled with Maxwell and quasi-linear viscoelastic (QLV) models. In stress relaxation tests, the braid–twist scaffolds behaved similarly to native ACL tissue, with final normalized stresses of 87% and 83% after an 8 N load. There was agreement between the experimental data and the Maxwell model when the model included an element for each structural element in the scaffold. There was also agreement between the experimental data and QLV model, scaffolds with similar braiding angles shared constants. In cell proliferation studies no differences were found between fibroblast growth on the braided scaffolds and the braid–twist scaffolds. SEM images showed the presence of new extracellular matrix. Data from this and previous tensile studies demonstrate that the braid–twist scaffold design may be effective in scaffolds for ACL tissue regeneration.

Transepiphyseal Anterior Cruciate Ligament Reconstruction in Pediatric Patients: Surgical Technique

The prevalence of anterior cruciate ligament (ACL) tears in children and adolescents is relatively low due to anatomic and biomechanical factors that predispose skeletally immature knees to bone injury rather than ligament tears.17 Nevertheless, ACL tears in this age group appear to be increasing.1,7,8,12,14-16,18 Management of these injuries presents a unique challenge; evidence in the literature indicates that the outcome of nonoperative treatment of ACL tears in skeletally immature patients is poor.1,9,11,14,15 Conversely, surgical intervention may cause iatrogenic physeal injury, which can result in leg-length discrepancy or angular deformity.6,11,13,14 Management decisions are complicated by deficiency in the basic science on physeal response to injury and by the limitations of the clinical studies that document surgical treatment for ACL insufficiency in children and adolescents. Despite these uncertainties, a rational approach based on current understanding of normal growth and development can be implemented.2-5 This article describes a technique for transepiphyseal reconstruction of the ACL using autogenous hamstring tendon grafts. The procedure adheres to the generally accepted principles of ACL replacement in adults, but theoretically minimizes the risk of physeal injury by not transgressing either the tibial or femoral physis. The decision as to whether to use this procedure to treat an ACL tear in a child or adolescent can be based on estimates of the relative risk of physeal injury (high, intermediate, or low), which can be determined by assessing the patient’s skeletal and physiological age. The consequences of iatrogenic physeal injury may be severe in children who have a great deal of growth remaining and insignificant in teenagers who have minimal growth remaining in the distal femur and proximal tibial physes. The central issue in treatment of ACL tears in the pediatric age group is the patient’s skeletal age, which determines the potential risk of injurious consequences. The most common method of estimating skeletal age is by comparing an anteroposterior radiograph of the patient’s left hand and wrist with the age-specific radiographs in the Greulich and Pyle Atlas.10 Physiological age can be classified according to Tanner’s staging of sexual maturation.19 Prepubescent patients are categorized in Tanner stages I and II of development, pubescent patients are in Tanner stage III, late pubescent in Tanner stage IV, and postpubescent patients are in Tanner stage V.3-5 The success of transepiphyseal ACL reconstruction, with meniscal repair, without evidence of growth disturbance, supports a recommendation for aggressive treatment of these injuries.2-5 Transepiphyseal replacement is recommended for prepubescent patients in Tanner stage I or II of development, including boys younger than 12 years and girls younger than 11 years; these patients are at high risk of growth disturbance if physeal injury occurs. Pubescent Tanner stage III patients, including boys 13 to 16 years of age and girls 12 to 14 years of age, are at intermediate risk. Transepiphyseal replacement is also recommended in early Tanner stage III patients because the threshold of safety for transphyseal drilling is currently unknown.

Tissue Engineering Options for Ligament Healing

The anterior cruciate ligament (ACL) is one of five ligaments in the knee that are important for stability and kinematics. It is also the most commonly injured ligament of the knee and due to its poor healing potential, severe damage warrants surgical intervention including complete replacement. Ligaments are longitudinally arranged, complex tissues; the mechanical properties of ligaments are a direct result of their components and the arrangement of these components in the tissue. It is these mechanics that have made ligaments so difficult to replace. Past ACL replacements have had many limitations that prevented their extensive use. These limitations range from mechanical fatigue over time to fraying of the device after implantation. In light of these problems, investigators have begun to pursue a host of new techniques to create a range of viable options for the repair, replacement, and/or regeneration of the ACL. These options include tissue engineered scaffolds with novel designs and specially treated transplanted tissues. In this article, the composition, arrangement, and mechanics of the ACL will be discussed in order to elucidate important aspects of ACL repair; past replacements will also be discussed. Afterwards, novel replacement options that look to solve problems faced by older replacement options will be presented. These devices use a wide variety of materials and designs to replicate ligament mechanics and allow for new tissue regeneration.

Biomechanische Untersuchung über die Zugfestigkeit lyophilisierter und tiefgefrorener humaner Achillessehnen nach Gamma- und Ethylenoxid-Sterilisation

By a failed first operation allogenic tissues, as human Achilles tendons are offered for anterior cruciate ligament replacement. The effects of freeze-drying and primary Gamma- or EO-sterilization on the mechanical properties of 62 complete and 74 bisected tendons again fresh frozen controls were investigated under axial tension. A significant decrease of tensile strength for the freeze-dried preparations of 33% for the whole and 43% for the bisected tendons were observed, while Gamma- or EO-sterilizations showed a smaller deleterious effect on the tendons. Considering only the primary mechanical strength complete freeze-dried or complete and bisected irradiated Achilles tendons show sufficient tensile strength for anterior cruciate ligament replacement.

The Risk of Growth Changes During Transphyseal Drilling in Sheep With Open Physes

A sheep model was used to evaluate the risk of growth disturbances of transphyseal drilling and anterior cruciate ligament (ACL) reconstruction. In group A, comprised of six 4-month-old Merino sheep, the ACL was resected and 5-mm tunnels were drilled and left empty. Unilateral ACL reconstruction using an autologous Achilles tendon graft, extracortical fixation, and tunnel diameters of 5 mm was performed in group B. A single-stranded graft with a diameter of 5 mm was used in group B-1 (N = 6) and a 3-mm double-stranded graft in group B-2 (N = 6). Six months after the procedure, the animals were euthanized. Growth changes were evaluated macroscopically, by magnetic resonance imaging, and by histology. Central growth plate lesions on the tibia did not induce growth abnormalities. On the peripheral femur, posterolateral growth plate injuries with empty tunnels led to a shortening of the lateral femur of 8 mm (7 to 10 mm), a valgus deformity of 12.8 degrees (12 degrees to 14 degrees ), and a flexion deformity of 8.6 degrees (5 degrees to 15 degrees ). Histology revealed a strong bone bridge over the physis and an injury to the perichondral structures. Transphyseal ACL replacements did not cause growth disturbances on either the tibia or the femur, even if a drilling injury of the perichondral structures occurred. Despite consistent physeal damage, ACL reconstructions did not lead to clinically relevant growth disturbances. The results suggest that transphyseal ACL reconstruction procedures might yield similar results in children with substantial growth remaining.

Replacement of the anterior cruciate ligament combined with valgization osteotomy of the tibia in incipient medial gonarthrosis with anterior cruciate ligament insufficiency

In 7 patients with chronic, primarily anteromedial instability and incipient medial gonarthrosis a procedure combining valgization osteotomy of the tibia with anterior cruciate ligament replacement was employed. Postoperative examinations after observation periods of between 6 months and 5 years revealed that the results were good to very good, both subjectively and objectively. There was either no recurrence or a definite alleviation of knee joint pain present preoperatively. In view of the good results the authors now regard a combination of valgization osteotomy and anterior cruciate ligament replacement as the treatment of choice in cases with clear insufficiency of the anterior cruciate ligament and simultaneous incipient medial gonarthrosis. The combined procedure improves chances of achieving the goal of therapy. A valgization osteotomy or an anterior cruciate ligament replacement alone ought to be regarded as inadequate treatment in such cases, especially in the longer term.

Lokalisation von TGF-β und PDGF und deren Bedeutung für die Pathogenese der Arthrofibrose

Arthrofibrosis is a disabling complication after knee trauma and surgery and is characterised clinically by joint stiffness. Due to an immune response, the proliferation of fibroblasts and synthesis of extracellular matrix proteins are increased. The cytokines transforming growth factor beta (TGF-beta) and platelet-derived growth factor (PDGF) are critical players in tissue fibrosis, stimulating cell proliferation and the production of various extracellular matrix proteins. Tissue samples from the infrapatellar fat pad and intercondylar synovia of seven patients (age 18-49 years) suffering from arthrofibrosis were taken at surgery. The mean interval between trauma and arthrolysis was 14.3 months. All samples were stained with haematoxylin and eosin, and monoclonal and polyclonal antibodies were applied for immunohistological localisation of TGF-beta and PDGF. The percentage of both cytokines was then analysed using an image analysis system. Tissue samples with no macroscopic pathology of the synovial tissue from eight patients for anterior cruciate ligament replacement served as controls. Immunostaining for TGF-beta and PDGF was found to be increased in arthrofibrotic tissue. Both cytokines could be detected subsynovially around inflammatory cells. The profibrotic cytokines TGF-beta and PDGF play an important role in the pathogenesis of arthrofibrosis. Both cytokines are key mediators of tissue fibrosis.

Artificial biological ligament: Its making, testing, and experimental study on animals

By applying a novel biochemical technique using porcine tendon as the raw material with its antigen minimized, we developed an artificial biological ligament (ABL). We examined and tested its structure, mechanical properties, and biocompatibility and explored the feasibility of reconstructing the anterior cruciate ligament (ACL) with ABL. By means of treating porcine tendon with epoxy crosslinking fixation, diversified antigen minimization process, mechanic enhancement modification, and surface activating process, we fabricated the ABL samples. We then analyzed its in vivo and in vitro performances, respectively, with animal (goat) implantation, histological examination, scanning electron microscope, cells culture, and mechanical tests before and after animal implants. The appearance of ABL was similar to that of normal human ligament. Histological examination showed that the ABL was composed of collagen fibers with no cells. Electron microscope examination revealed that the ABL was composed of hair-appearing and fiber-like objects running uniformly in a certain direction and closely parallel-arranged. Three weeks after xenogenic marrow matrix cells were cultured on the surface of the ABL, it was noted that cells adhered and the matrix secreted by the cells precipitated around the cells. There were no cells found inside the ABL. The average diameter of ABL was 5 mm and the mechanical test at a speed of 100 mm/min showed that its average tensile limit was 927.19 N; the tension-resistant strength was 47.22 N/mm. Those measurements were close to the corresponding parameters of the normal goat ACL. Twelve weeks after ABL replacement of the goat ACL, synovial membrane covering with the ingrowths of small blood vessels was seen on the surface of the implant. Fifty weeks after the replacement, the ABL material was partially replaced by regenerated host ligament-like tissue. Around the ABL material fibers in the bone tunnel close to the joint surface the direct connection mode, ligament-fibro cartilage-calcified cartilage-bone, was seen. As we used the unique biochemical technique and minimized the xenogenic protein immunogenicity of the porcine tendon, ABL showed acceptable biomechanical properties and superior biocompatibility. As a substitute for ligament in the reconstruction of the ACL, ABL has a promising prospect in clinical applications.

Recent Advancements in Ligament Tissue Engineering: The Use of Various Techniques and Materials for ACL Repair

The anterior cruciate ligament (ACL) is important for knee stability and kinematics. Unfortunately, it is also the most commonly injured ligament of the knee and due to its poor healing potential, severe damage warrants surgical intervention including complete replacement. Current ACL replacements have a host of limitations that prevent their extensive use. Thus, investigators have begun to pursue tissue engineering techniques to create new options for the repair, regeneration, and replacement of the ACL. These options involve devices that are mechanically functional tissue engineered scaffolds and as such are designed to withstand normal mechanical loads while promoting ligament development. This article presents background on the ACL and its replacement, novel replacement approaches utilizing natural polymers, synthetic polymers, and natural tissues, and recent patent coverage. Keywords: Anterior cruciate ligament (ACL), silk, poly (L-lactic acid) (PLLA), xenograft, scaffold, polymer, tissue engineering

The Use of Ultrasonication to Aid Recellularization of Acellular Natural Tissue Scaffolds for Use in Anterior Cruciate Ligament Reconstruction

Tissue engineering offers a promising solution to the replacement of anterior cruciate ligament. A decellularized porcine patella tendon scaffold was produced by immersing whole tissues sequentially in hypotonic buffer, 0.1% (w/v) sodium dodecyl sulfate (SDS) in hypotonic buffer, and nuclease solution prior to sterilization with 0.1% (w/v) peracetic acid. Initial studies revealed that primary human tenocytes would attach to, but failed to penetrate into, the decellularized scaffold. A novel use of ultrasonication was therefore developed to allow extrinsic cells to migrate into the acellular scaffold. Various intensities of ultrasonication were tested in order to produce a microscopically more open porous matrix without damaging the overall architecture of the scaffold. Ultrasonication treatment with the intensity of 360 W and a pulse time of 1 s for a total of 1 min was found to be the optimal treatment. This process did not have a significant effect upon the biochemical constituents (collagen, glycosaminoglycans), nor did it denature the collagen. Moreover, the acellular sonicated scaffold retained the essential biomechanical characteristics of the native tissue. Primary human tenocytes penetrated into the center of whole acellular sonicated scaffolds over a 3-week period in static culture. The viability of the cells in the center of the scaffold (depth of circa 2.5 mm) was, however, compromised. To circumvent the problem of nutrient limitation, acellular sonicated scaffolds were split into fascicular scaffolds (500 mum thick). Cells seeded onto the fascicular scaffolds penetrated throughout the scaffold and remained viable after 3 weeks of culture. This study has shown that an acellular biocompatible tendon scaffold can be produced using 0.1% (w/v) SDS and that ultrasonication can provide a novel method to enhance the recellularization of decellularized natural tissues.

Anterior Cruciate Ligament Reconstruction: State of the Art

The rupture of the Anterior cruciate ligament (ACL) belongs to the most common ligament injuries of the human knee joint. ACL rupture results in an increased anterior translation and internal rotation of the tibia. Untreated knee instability causes a disintegration of the roll and sliding movement and a high incidence of secondary meniscus and chondral damages with consecutive or advanced arthritic changes. For deciding on a conservative or operative therapy, it is necessary to develop a high-risk profile. Elderly, inactive patients without instability symptoms can be treated conservatively; younger, active people and complex ligament injuries should receive an ACL replacement. The goal is to eliminate instability by maintaining the physiological kinematics of the knee. Anterior cruciate ligament may be reconstructed arthroscopically assisted by autologous tendons. Predominantly, hamstring- and bone-patellar-tendon grafts are used. No significant differences in knee laxity, clinically and functionally, were observed between both grafts. Various reconstruction techniques, single- or double-bundle techniques, were described. Successful replacement depends on a correct tunnel placement and reconstruction of the physiological band tension, a sufficient mechanical stability of fixation, an impingement-free range of motion and an adequate rehabilitation. A high degree of patient satisfaction in clinical and functional outcome could be evaluated.