A three-dimensional (3D) knee joint computational model was developed and validated to predict knee joint contact forces and pressures for different degrees of malalignment. A 3D computational knee model was created from high-resolution radiological images to emulate passive sagittal rotation (full-extension to 65°-flexion) and weight acceptance. A cadaveric knee mounted on a six-degree-of-freedom robot was subjected to matching boundary and loading conditions. A ligament-tuning process minimised kinematic differences between the robotically loaded cadaver specimen and the finite element (FE) model. The model was validated by measured intra-articular force and pressure measurements. Percent full scale error between FE-predicted and in vitro-measured values in the medial and lateral compartments were 6.67% and 5.94%, respectively, for normalised peak pressure values, and 7.56% and 4.48%, respectively, for normalised force values. The knee model can accurately predict normalised intra-articular pressure and forces for different loading conditions and could be further developed for subject-specific surgical planning.

Surface texture technique increases the tribological capability and performance of bearing surfaces. This technology has a number of applications, including car engines and golf balls. However, the use of texture surface in artificial hip joints has not been adequately explored. The aim of the study is to investigate the effects of plateau honed surfaces on the tribological performance of metal-on-metal hip joints. Four sets of different plateau honed surfaces and a set of non-textured surface were investigated on a friction simulator with a lubricant having similar viscosity of pseudo-synovial fluid. The results showed 50% and 38% reductions in static and dynamic friction coefficient, respectively, for a honed surface (honed surface 3) compared with those of a non-textured surface after 1 million cycles. There was a number of wear signs, including adhesive and fatigue wear in all of the experimental surfaces. Nevertheless, the wear signs in the honed surface 3 were minor. Lubrication film thickness was thicker, and third body abrasive wear assumed to reduce in the honed surface since wear debris removed through honed channel. Therefore, the performance of a well-designed plateau-honed surface is significant in tribological aspects of metal-on-metal hip joints.

Wear rate and debris are key problems to implanted metal-on-metal hip joints. Surface texture on bearing surfaces is reported to increase tribological performances. Research on the translation of this technology to metal-on-metal hip joint for reduction of friction, wear rate and debris generation is limited. The aim of this study was to investigate, by theoretical predictions and experimental investigations, the tribological properties of simulated metal-on-metal hip joints with different surface textures. Three different honed surfaces were produced with emery paper at controlled load and speed. The experiments were carried out using a computer-controlled friction simulator. Theoretical prediction was carried out using an existing model for textured surfaces. Both experimental and theoretical results demonstrated that honed surfaces had lower friction coefficients during walking and stairs ascent and descent, demonstrating their potential use in metal on metal hip joints for increased implant longevity.

Osteoarthritis (OA) is a degenerative disease of all of the tissues within the diarthrodial joint and one of the leading causes of disability. Knee OA is often caused by lower limb malalignment, high body mass index, and injury to the surrounding soft tissues, resulting in a cyclic degradation of the joint. High tibial osteotomy (HTO) is a realignment surgery to restore knee function and minimise excessive loading. However, the link between malalignment and stress in the knee is not well understood and surgical outcomes by HTO have been unpredictable. Therefore the overarching goal is to develop a three-dimensional virtual surgery finite element (FE) model that integrates subject specific imaging and computational biomechanics to predict the effects of different realignment techniques on knee joint contact stress. FE models of a cadaveric knee joint were created from magnetic resonance images, using Mimics v14 (Materialise, Belgium). Following non-manifold assembly, these 3D models were exported to Abaqus 6.11 to determine the stress distribution within the medial-lateral compartments of the well-aligned knee. A 10° open wedge HTO was performed to simulate the malaligned knee. Boundary conditions of 300N axial load and 12 Nm bending moment were applied to simulate posture in the well aligned and malaligned knee. Peak compressive stress in the malaligned knee was 60% higher than that of the well-aligned knee. This excessive stress is considered a primary factor for the onset and progression of OA. These results highlight the importance of understanding the effects of HTO on the knee joint contact stresses in order to delay OA progression.

Meniscus tears occur in up to one third of all sports injuries and 60% of patients over 65 years. Meniscus tears increase knee joint contact pressure and the risk of developing early osteoarthritis (OA). Integrating juxtaposed meniscus surfaces continues to be a challenge during meniscal repair. Partial meniscectomy is a common surgical procedure for meniscal tear, especially in the non-vascularized white-white zone. Most studies on the effects of size and location of partial meniscectomy on knee joint contact pressures simulated the standing posture and some static angles of flexion (30° and 60°). Information on the safe proportion and location of a partial meniscectomy that would maintain knee joint contact stresses close to those in the healthy joint during dynamic loading is not known. The aim of this study is to investigate the relationship between partial meniscectomy size and location with the corresponding knee joint contact pressures during dynamic loading, emulating activities of daily living. We hypothesize that partial meniscectomy size increases knee joint contact pressure.

Traditional finite element (FE) analysis is computationally demanding. The computational time becomes prohibitively long when multiple loading and boundary conditions need to be considered such as in musculoskeletal movement simulations involving multiple joints and muscles. Presented in this study is an innovative approach that takes advantage of the computational efficiency of both the dynamic multibody (MB) method and neural network (NN) analysis. A NN model that captures the behavior of musculoskeletal tissue subjected to known loading situations is built, trained, and validated based on both MB and FE simulation data. It is found that nonlinear, dynamic NNs yield better predictions over their linear, static counterparts. The developed NN model is then capable of predicting stress values at regions of interest within the musculoskeletal system in only a fraction of the time required by FE simulation.

As a first step to answer this research question, we carried out a comparison study, by finite element methods, on the contact stresses in the tibiofemoral joint of an intact knee and one with a total meniscectomy. Peak compressive stress increases after total meniscectomy. Results of this study show that the meniscectomised knee is subjected to high stress levels which may cause cartilage matrix damage resulting in osteoarthritis (OA).

TIBIAL OSTEOTOMY R. Mootanah, H.J. Hillstrom, A.M. New, C. Imhauser, R. Walker, K. Cheah, E. Blanc, S. Mangeot, C. Daré, C. Mouton, A. Burton, S. Ait Ali, J. Dowell 1. Anglia Ruskin University, Medical Engineering Research Group, Essex, UK; 2. Hospital for Special Surgery, New York, USA; 3. Apogee Engineering Analysis Solutions Limited, Norfolk, UK; 4. Springfield Ramsay Hospital, Essex, UK; 5. Université Henri Poincaré, Nancy, France; 6. Mid-Essex Hospitals Trust, Essex, UK.