Zdenek Horak

Biomechanical factors influencing the beginning and development of osteoarthritis in the hip joint

SummaryOsteoarthritis (OA) can be used as a common name for a group of overlapping pathological conditions when the balance between the processes of degradation and synthesis, in individual parts of the cartilage, is disturbed and leads to gradual cartilage destruction. A preventive approach toward OA helps with a timely diagnosis and subsequent treatment of this disease. One of the significant risk factors affecting development of hip joint OA is the mechanism and magnitude of mechanical loading on the joint. The main motivation for this work was to verify the hypothesis involving a pathologic cycle (overloading – change of locomotion – overloading) as contributory to the development of OA and whether it can be stopped, or at least partly decelerated, by a suitable change of movement stereotypes. Providing that there is a natural balance of muscular action, from the beginning of OA, the development of OA can be significantly decelerated. The return to a natural force balance can be achieved using suitable exercise and strengthening of muscular structures. In order to verify the hypothesis, we undertook experimental measurements of gait kinematics and a computational analysis of the hip joint using the Finite Element Method.

Influence of the method of TM joint total replacement implantation on the loading of the joint on the opposite side

The temporomandibular (TM) joint is one of the most used joints in the human body, and any defect in this joint has a significant influence on quality of life. The objective of this study was to create a parametric numerical finite element (FE) analysis to compare the effect of surgical techniques used for total TM joint replacement implantation on loading the TM joint on the other side. Our hypothesis is that for the optimal function of all total TM joint replacements used in clinical practice it is crucial to devise a minimally invasive surgical technique, whereby there is minimum resection of masticatory muscles. This factor is more important than the design of the usually used total TM joint replacements. The extent of muscle resection influences the mechanical loading of the whole system. In the parametric FE analyses, the magnitude of the TM joint loading was compared for four different ranges of muscle resections during bite, using an anatomical model. The results obtained from all FE analyses support our hypothesis that an increasing extent of the muscle resection increased the magnitude of the TM joint overloading on the opposite side. The magnitude of the TM joint overloading increased depending on the muscle resection to 235% for bite on an incisor and up to 491% for bite on molars. Our study leads to a recommendation that muscle resection be minimised during replacement implantation and to a proposal that the attachment of the condylar part of the TM joint replacement be modified.

The importance of intramedullary hip nail positioning during implantation for stable pertrochanteric fractures: biomechanical analysis.

PurposeProximal femoral fractures are among the most commonly sustained fractures. The current treatment of stable proximal femoral fractures located in trochanteric region primarily involves the use of two systems: extramedullary dynamic hip screws and intramedullary hip nails. Given that these fractures are mainly found in the elderly population, the necessity of a repeat, due to failure of the first, may jeopardize the patient’s life. Decisive factors contributing to the healing of a fracture (or the failure thereof) include fracture pattern, technical implementation of the operation (i.e., position of the implant), implant’s properties and its changes in relation to the surrounding bone tissue during loading. Each screw insertion variant results in damage to various load-bearing bone structures, which can be expected to influence healing quality and stability of newly formed bone.MethodWith the aid of a numerical model and finite element methods, the authors analyzed several different positions of IMHN/PFH-nails in the proximal femur, with the objective of determining positions with an increased risk of failure.Results and conclusionIn model situations, it has been shown that in stable fractures results do not depend on absolutely precise positioning and small deflections in the nails and neck screws positions do not significantly increase the risk of failure for the entire fixation. Damage to load-bearing structures relative to various implant placements does not impact the resultant overall fixation stability. Therefore, it is not necessary to re-introduce implants in the ideal position, which can lead to reduced patient radiation doses during surgery.

Fatigue failure of the sliding hip screw – clinical and biomechanical analysis

Abstract The study was aimed at the clinical and biomechanical analyses of the sliding hip screw breakage with the use of finite element method. We have identified two patients with the sliding screw breakage. In the first patient, the biomechanical analysis revealed the reduced stress values σHMH not exceeding the yield limit or strength limit of the implant. The yield limit was exceeded in second one. Clinical and biomechanical analyses have demonstrated that adherence to technical requirements of the appropriate osteosynthesis implementation is the principal condition of timely healing since it prevents the material failure.

Identification of the critical level of implantation of an osseointegrated prosthesis for above-knee amputees

Abstract The aim of our study was to identify potential critical levels of implantation of an osseointegrated prosthesis for above-knee amputees. The implant used was the OPRA system. It was inserted in the femur at four different amputation heights, characterized by their residual limb ratios (0.299, 0.44, 0.58 and 0.73). The stress and strain distribution was evaluated in the bone-implant system during walking, considering a body mass of 100 kg. Considerably high stimulus (11,489 με) in the tissue near the tip was found at the highest implantation level. All models presented small non-physiologic stress values in the tissue around the implant. The results revealed that the implantation level has a decisive effect on bone-implant performance. Mainly, the analysis indicates adverse biomechanical conditions for implantations in very short residual limbs.

Does mechanical loading influence development of osteoarthritis in hip joint

Osteoarthritis (OA) can be used as a common name for a group of overlapping pathological conditions when the balance between the processes of degradation and synthesis, in individual parts of the c...

Identification of the Changes in Extent of Loading the TM Joint on the Other Side Owing to the Implantation of Total Joint Replacement

Temporomandibular joint is the most used joint of human body. Any defect of it has a significant influence on quality and style of life. If the TM joint is damaged, its treatment is very difficult and, in addition, it is impossible to replace fully this specific joint with a total replacement. In our opinion, the main reason is the method of implantation of existing replacements, when the whole range of masticatory muscles must be removed, and these results in significant change of mechanical loading of the whole system. The objective of this work was to create parametric computational FEM study comparing the effect of surgical procedure while implanting the total replacement of the TM joint on loading of the joint on the other side.

Individual 3D Replacements of Skeletal Defects

In this work several clinical cases of production of individual bone defect replacements will be presented. Special replacements were produced on the basis of 3D geometric models designed from available diagnostic imaging methods (CT and MRI), and their following computer processing. For production of implants by conventional CNC machining were used in clinical practice commonly used biomaterials (titanium, PEEK, UHWMPE), which can be easily machined. The implants were produced for a particular patient individually with millimetre accuracy so that not only fully functional, but also aesthetic defect replacements were achieved