Computer-Assisted Anatomical Placement of a Double-Bundle ACL through 3D-Fitting of a Statistically Generated Femoral Template into Individual Knee Geometry

Femoral graft placement is an important factor in the success of ACL-reconstruction. Besides improving the accuracy of femoral tunnel placement, Computer Assisted Surgery (CAS) can be used to determine the anatomical Location. This requires a 3D femoral template with the position of the anatomical ACL-center, based on endoscopical measurable landmarks. This study describes the development and application of this method. The template is generated through statistical shape analysis of the ACL-insertion, with respect to the anteromedial- (AMB) and posterolateral bundle (PLB). The data is mapped onto a cylinder and related to the intercondylar notch surface and the cartilage border on the lateral notch wall (n=33). The template was programmed in a computer-assisted system for ACL-replacement and validated. The program allows real-time tracking of the femur and interactive digitization under endoscopic control. In a wizard-like fashion the surgeon is guided through steps of acquiring the landmarks for the template alignment. The AMB-and PLB-center are accurate positioned within 1-3 mm of the anatomic insertion-centers in individual knee

Explicit Finite Element Modeling of Knee Mechanics During Simulated Dynamic Activities

The natural knee is one of the most commonly injured joints in the body due to relatively high loads and motions that can lead to debilitating degenerative diseases such as osteoarthritis. Total knee arthroplasty is a clinically successful method for eliminating pain in the osteoarthritic knee, but is subject to complications that can affect patient satisfaction and long-term implant performance. The work presented in this dissertation is a demonstration of how anatomic three-dimensional (3D) computational knee models can be an effective alternative for investigating knee mechanics when compared to the cost and time prohibitive nature of in-vivo and in-vitro methods. The studies described in this work utilized the explicit finite element (FE) method to investigate varying aspects of soft tissue constraint, implant alignment, and applied dynamic loading on knee mechanics in 3D natural and implanted partial or whole joint knee models. Combined probabilistic and FE methods were used to successfully identify the most important parameters affecting joint laxity in the natural knee and patellar component alignment in the implanted knee. Two model verification studies demonstrated strong agreement between model-predicted and experimental 3D kinematics of specimen-specific isolated patellofemoral and whole joint cadaveric knee models under simulated dynamic loading (deep knee bend and gait) collected in a mechanical simulator. Using one of the single specimen whole joint models, an additional study successfully identified the most important anatomic and implant alignment parameters related to a clinically-relevant complication associated with a particular implant design. Lastly, a new method of efficiently generating 3D natural articular knee surfaces for FE analysis was developed through a combined mesh morphing and statistical shape modeling approach. These studies included several novel methods for investigating knee mechanics under dynamic loading and specimen-specific soft tissue constraint using the explicit FE method that could be used to better reproduce the complex in-vivo knee environment in forward or muscle-driven models and to assist design-phase implant performance evaluation

Individualised Modelling for Preoperative Planning of Total Knee Replacement Surgery

Total knee replacement (TKR) surgery is routinely prescribed for patients with severe knee osteoarthritis to alleviate the pain and restore the kinematics. Although this procedure was proven to be successful in reducing the joint pain, the number of failures and the low patients’ satisfaction suggest that while the number of reoperations is small, the surgery frequently fail to restore the function in full. The main cause are surgical techniques which inadequately address the problem of balancing the knee soft tissues. The preoperative planning technique allows to manufacture subject-specific cutting guides that improves the placement of the prosthesis, however the knee soft tissue is ignored. The objective of this dissertation was to create an optimized preplanning procedure to compute the soft tissue balance along with the placement of the prosthesis to ensure mechanical stability. The dissertation comprises the development of CT based static and quasi-static knee models able to estimate the postoperative length of the collateral lateral ligaments using a dataset of seven TKR patients; In addition, a subject-specific dynamic musculoskeletal model of the lower limb was created using in vivo knee contact forces to perform the same analysis during walking. The models were evaluated by their ability to predict the postoperative elongation using a threshold based on the 10 % of the preoperative length, through which the model detected whether an elongation was acceptable. The results showed that the subject-specific static model is the best solution to be included in the optimized, subject-specific, preoperative planning framework; full order musculoskeletal model allowed to estimate the postoperative length of the ligaments during walking, and at least in principle while performing any other activity. Unlike the current methodology used in clinic this optimized preoperative planning framework might help the surgeon to understand how the position of the TKR affects the knee soft tissue

Epidemiology of injuries in high-level youth sport in Luxembourg [Abstract]

peer reviewe

Musculoskeletal Models in a Clinical Perspective

This book includes a selection of papers showing the potential of the dynamic modelling approach to treat problems related to the musculoskeletal system. The state-of-the-art is presented in a review article and in a perspective paper, and several examples of application in different clinical problems are provided

Insights into the Function on the Knee Meniscus

The knee menisci are understood to have a variety of roles including load transmission and stability of the knee joint. To date, there has been no exploration of the role of radial tears of the menisci in inducing kinematic changes in knee joint movement. Furthermore, the function of proteoglycans in maintaining mechanical meniscus has not been explored.Load was applied to cadaveric knees in the intact state and following both a 50% and 100% radial tear of the medial (5 knees) or lateral (6 knees) meniscus. A coordinate system was developed to allow analysis of joint kinematics. Concurrently,confined compression techniques were used to apply 10% strain to meniscal samples from cadavers (30 samples) and patients suffering osteoarthritis (36 samples) in solutions of varying ionic concentration. 7 samples from an Actifit meniscal scaffold were also tested in deionised water. Resultant relaxation curves were fit using finite element modelling techniques. Human tissue samples were assayed for proteoglycan content.Radial tears of the meniscus did not induce significant changes in knee joint kinematics.Finite element modelling demonstrated that the electrostatic effect of proteoglycans contributed to ~40% of the stiffness of the meniscus. No significant difference in proteoglycan content was observed between solutions. The Actifit meniscal scaffold is stiffer than native meniscal tissue but displays similar permeability.Although radial tears do not alter the kinematics of the knee joint, there is evidence they result in abnormal loading of articular cartilage and it is hence important that they are repaired where possible. Proteoglycans play a critical role in maintaining stiffness of the meniscus - current repair strategies such as meniscal scaffolds do not attempt to recreate this function and hence may not prevent cartilage degradation. The stiffness of the Actifit meniscal scaffold may help protect a nascent meniscal repair but may also contribute to abnormal joint loading; its similar permeability will help mimic meniscal function.The knee menisci are understood to have a variety of roles including load transmission and stability of the knee joint. To date, there has been no exploration of the role of radial tears of the menisci in inducing kinematic changes in knee joint movement. Furthermore, the function of proteoglycans in maintaining mechanical meniscus has not been explored.Load was applied to cadaveric knees in the intact state and following both a 50% and 100% radial tear of the medial (5 knees) or lateral (6 knees) meniscus. A coordinate system was developed to allow analysis of joint kinematics. Concurrently,confined compression techniques were used to apply 10% strain to meniscal samples from cadavers (30 samples) and patients suffering osteoarthritis (36 samples) in solutions of varying ionic concentration. 7 samples from an Actifit meniscal scaffold were also tested in deionised water. Resultant relaxation curves were fit using finite element modelling techniques. Human tissue samples were assayed for proteoglycan content.Radial tears of the meniscus did not induce significant changes in knee joint kinematics.Finite element modelling demonstrated that the electrostatic effect of proteoglycans contributed to ~40% of the stiffness of the meniscus. No significant difference in proteoglycan content was observed between solutions. The Actifit meniscal scaffold is stiffer than native meniscal tissue but displays similar permeability.Although radial tears do not alter the kinematics of the knee joint, there is evidence they result in abnormal loading of articular cartilage and it is hence important that they are repaired where possible. Proteoglycans play a critical role in maintaining stiffness of the meniscus - current repair strategies such as meniscal scaffolds do not attempt to recreate this function and hence may not prevent cartilage degradation. The stiffness of the Actifit meniscal scaffold may help protect a nascent meniscal repair but may also contribute to abnormal joint loading; its similar permeability will help mimic meniscal function