A new concept in artificial ligament and tendons modeling : finite element analysis

Reconstruction of the Anterior Cruciate Ligament (ACL) has been a major focus in sports medicine for over twenty years. Severe or unrepairable damage of the ACL due to sport injury is a major problem faced by orthopedic surgeons and engineers. To successfully replace or reconstruct an injured ACL, the mechanical properties as well as the dimensional limitation of the material used must be similar to the biological ligaments. Although excessive literature describes experimental investigation on the mechanical property and clinical application of the ligament material, there is no analytical study that describes strains, stresses, and endurance in the bone/ligament/bone complex. The Finite Element Analysis (FEA) is a method to study this problem. The objectives of the present investigation are (1) to develop a finite element model (FEM) of an artificial ligament yarn, the emphasis is put on the development of the elastic FEM, (2) to analyze stress distribution in the ligament yarn fibers due to various loading conditions and designs, and (3) to compare results obtained from the FEA of the elastic model with results obtained from laboratory tensile test. Results obtained from the FEM model of the ACL prosthesis yarn are confirmed by experimental measurements

Optimal Condition to Create Femoral Tunnel Considering Combined Influence of Knee Flexion and Transverse Drill Angle in Anatomical Single-Bundle ACL Reconstruction Using Medial Portal Technique: 3D Simulation Study

There has been no previous study using three-dimensional (3D) measurement on femoral tunnel characteristics according to the combined influence of various flexion angles of knee and transverse drill angles in single-bundle ACL reconstruction with transportal technique. The purpose of this study was to determine optimal condition of knee flexion angle and transverse drill angle to create secure femoral tunnel in single-bundle ACL reconstruction with transportal technique considering tunnel length, tunnel wall breakage, and graft bending angle. This study was conducted using simulation of 3D computed tomography of thirty subjects. Three variables of femoral tunnel changed according to combined influence of four flexion angles of knee and three transverse drill angles were measured: tunnel length, wall breakage, and graft bending angle. There was no case of short femoral tunnel less than 25 mm at 120° and 130° of flexion. There was no case of breakage of femoral tunnel at 120° of flexion with maximum transverse drill angle (MTA) and MTA-10° and at 130° of flexion. Considering effect on graft bending angle, decrease of flexion angle and transverse drill angle could be appropriate in creating femoral tunnel. Increased flexion angle and transverse drill angle secured femoral tunnel having sufficiently long length without wall breakage. However, avoiding excessive flexion angle and maximum transverse drill angle could be recommended because they tended to cause more acute graft bending angle.ope

Kinematics of the Anterior Cruciate Ligament (ACL) and ACL Graft

The anterior cruciate ligament (ACL) is one of the four main ligaments of the knee and is the most important ligament for knee’s stability. ACL injury has an annual incidence of more than 200,000 cases with approximately 100,000 of these knees having ACL reconstruction annually in the United States alone. However, the behaviors of the ACL and the graft in knees were still debated. There is still no golden standard in choosing appropriate reconstruction techniques, such as the position and orientation of the graft. Tunnel enlargement, and graft failure could happen after reconstruction if the ACL graft was improperly placed. To have better knowledge of the behavior of the intact ACL during flexion-extension and under external loads, this dissertation measured the strain of two bundles of the ACL by using two different measurement methods. This dissertation also measured graft position in the femoral tunnel during knee motions and under different external loadings. This graft position information provides insight into ACL graft behavior and function and may be important for determining appropriate rehabilitation time. Last, a finite element (FE) model was constructed and used to simulate the graft behavior in reconstructed knees with boundary and loading conditions from corresponding cadaveric experiments. The geometry of the tibia and femur were obtained from CT imaging. An isotropic hyperelastic material was used to model the cylindrical graft. Three-dimensional joint kinematics were obtained via a six-degree-of-freedom robotic manipulator and were used for input into the computational model. Graft stress, tension as well as the location of the graft in the tunnel were calculated after the kinematics were applied

The influence of thickness of ACL tendon graft on long-term results of treatment

1. INTRODUCTION: Operative treatment is the treatment of choice for the most severe, third-degree ACL sprain. Many operational techniques exist, including technique using a quadruple-folded semitendinosus tendon and the technique of double-folded semitendinosus and gracilis tendons. Depending on the technique chosen, we can obtain different thicknesses of the grafts used. 2. AIM OF THE STUDY: To find a relationship between the type of surgical technique used and the thickness of the graft, as well as to assess the effect of the thickness of the applied autograft on the long-term outcome of the treatment. 3. MATERIALS AND METHODS: A retrospective study included a group of 43 patients operated on due to ACL injury. In 21 patients, the procedure was performed using the quadruple-folded semitendinosus tendon, whereas in 22 patients the procedure was performed using double-folded semitendinosus and gracilis tendons. The patients were divided into groups based on the thickness of the transplant. A special questionnaire prepared on the basis of the KOOS scale was used to assess the subjective performance of the knee. The type and thickness of the graft was determined based on the analysis of operational protocols. The statistical analysis of the results of the study was performed. The Chi-square compatibility test or chi-square compatibility test in the Yates modification were used to assess the relationship. 4. RESULTS: A relationship was found between the parameters: "general quality of life" (p = 0.01), "pain" (p = 0.005), "sports activity" (p = 0.05), "everyday activities" (p = 0, 01). There is no dependence for the "other symptoms" parameter (p = 0.1). There is no relationship between the technique used and the graft thickness (p = 0.2).  5. CONCLUSIONS: The choice of the surgical technique does not affect the final thickness of the autograft. Overall quality of life, pain, sports activity; everyday activities are the parameters of the KOOS scale, which are affected by the thickness of the transplant

Tibial internal rotation in combined anterior cruciate ligament and high-grade anterolateral ligament injury and its influence on ACL length

BACKGROUND Assessment of combined anterolateral ligament (ALL) and anterior cruciate ligament (ACL) injury remains challenging but of high importance as the ALL is a contributing stabilizer of tibial internal rotation. The effect of preoperative static tibial internal rotation on ACL -length remains unknown. The aim of the study was analyze the effect of tibial internal rotation on ACL length in single-bundle ACL reconstructions and to quantify tibial internal rotation in combined ACL and ALL injuries. METHODS The effect of tibial internal rotation on ACL length was computed in a three-dimensional (3D) model of 10 healthy knees with 5° increments of tibial internal rotation from 0 to 30° resulting in 70 simulations. For each step ACL length was measured. ALL injury severity was graded by a blinded musculoskeletal radiologist in a retrospective analysis of 61 patients who underwent single-bundle ACL reconstruction. Preoperative tibial internal rotation was measured in magnetic resonance imaging (MRI) and its diagnostic performance was analyzed. RESULTS ACL length linearly increased 0.7 ± 0.1 mm (2.1 ± 0.5% of initial length) per 5° of tibial internal rotation from 0 to 30° in each patient. Seventeen patients (27.9%) had an intact ALL (grade 0), 10 (16.4%) a grade 1, 21 (34.4%) a grade 2 and 13 (21.3%) a grade 3 injury of the ALL. Patients with a combined ACL and ALL injury grade 3 had a median static tibial internal rotation of 8.8° (interquartile range (IQR): 8.3) compared to 5.6° (IQR: 6.6) in patients with an ALL injury (grade 0-2) (p = 0.03). A cut-off > 13.3° of tibial internal rotation predicted a high-grade ALL injury with a specificity of 92%, a sensitivity of 30%; area under the curve (AUC) 0.70 (95% CI: 0.54-0.85) (p = 0.03) and an accuracy of 79%. CONCLUSION ACL length linearly increases with tibial internal rotation from 0 to 30°. A combined ACL and high-grade ALL injury was associated with greater preoperative tibial internal rotation. This potentially contributes to unintentional graft laxity in ACL reconstructed patients, in particular with concomitant high-grade ALL tears. STUDY DESIGN Cohort study; Level of evidence, 3

Femoral Graft-Tunnel Angles in Posterior Cruciate Ligament Reconstruction: Analysis with 3-Dimensional Models and Cadaveric Experiments

PURPOSE: The purpose of this study was to compare four graft-tunnel angles (GTA), the femoral GTA formed by three different femoral tunneling techniques (the outside-in, a modified inside-out technique in the posterior sag position with knee hyperflexion, and the conventional inside-out technique) and the tibia GTA in 3-dimensional (3D) knee flexion models, as well as to examine the influence of femoral tunneling techniques on the contact pressure between the intra-articular aperture of the femoral tunnel and the graft. MATERIALS AND METHODS: Twelve cadaveric knees were tested. Computed tomography scans were performed at different knee flexion angles (0°, 45°, 90°, and 120°). Femoral and tibial GTAs were measured at different knee flexion angles on the 3D knee models. Using pressure sensitive films, stress on the graft of the angulation of the femoral tunnel aperture was measured in posterior cruciate ligament reconstructed cadaveric knees. RESULTS: Between 45° and 120° of knee flexion, there were no significant differences between the outside-in and modified inside-out techniques. However, the femoral GTA for the conventional inside-out technique was significantly less than that for the other two techniques (p<0.001). In cadaveric experiments using pressure-sensitive film, the maximum contact pressure for the modified inside-out and outside-in technique was significantly lower than that for the conventional inside-out technique (p=0.024 and p=0.017). CONCLUSION: The conventional inside-out technique results in a significantly lesser GTA and higher stress at the intra-articular aperture of the femoral tunnel than the outside-in technique. However, the results for the modified inside-out technique are similar to those for the outside-in technique.ope

Development and Assessment of a Micro-CT Based System for Quantifying Loaded Knee Joint Kinematics and Tissue Mechanics

Although anterior cruciate ligament (ACL) reconstruction is a highly developed surgical procedure, sub-optimal treatment outcomes persist. This can be partially attributed to an incomplete understanding of knee joint kinematics and regional tissue mechanic properties. A system for minimally-invasive investigation of knee joint kinematics and tissue mechanics under clinically relevant joint loads was developed to address this gap in understanding. A five degree-of-freedom knee joint motion simulator capable of dynamically loading intact human cadaveric knee joints to within 1% of user defined multi-axial target loads was developed. This simulator was uniquely designed to apply joint loads to a joint centered within the field of view of a micro-CT scanner. The use of micro-CT imaging and tissue-embedded radiopaque beads demonstrated high-resolution strain measurement, distinguishing differences in inter-bead distances as low as 0.007 mm. Inter-bead strain measurement was highly accurate and repeatable, with no significant error introduced from cyclic joint loading. Finally, regional strain was repeatably measured using radiopaque markers in four intact, human cadaveric knees to within 0.003 strain in response to multi-directional joint loads. This novel combination of dynamic knee joint motion simulation, tissue-embedded radiopaque markers, and micro-CT imaging provides the opportunity to increase our understanding of the kinematics and tissue mechanics of the knee, with the potential to improve ACL reconstruction outcomes