Hybrid materials for meniscus replacement in the knee

The meniscus is cartilage that not only prevents the bones in knee joints to grind together but acts as a joint stabiliser. Many athletes and older people suffer from meniscus tears and degeneration. Meniscal tear treatments have been through meniscal suture or by partial meniscectomy (removal). These treatments may cause changes in loading or decreased contact area and increased contact stress. Consequently, the ultimate result is a total meniscectomy that potentially leads to osteoarthritis (OA). These current surgical strategies have lower success rates in younger patients. There are no successful artificial meniscus replacement devices for young patients, therefore, new materials for meniscus replacement are required. Here, the aim was to develop a novel biomimetic meniscus device made of a silica/polytetrahydrofuran (SiO2/polyTHF) inorganic/organic hybrid material. The device is biomimetic in terms of its structural design, mechanical properties, and integration with the host tissue. The device should delay onset of OA. The hybrid has unique properties in that is a bouncy material which has comparable mechanical properties to knee cartilage. Two pot hybrid synthesis was used to synthesise the SiO2/polyTHF hybrid and casting mould was developed based on the shrinkage factor of the hybrid. The hybrid synthesis modifications were conducted by controlling compositions and drying processes. Biological fixation of the hybrid meniscus was achieved by titanium anchors with gyroid porous architecture which can provide initial mechanical fixation and secondary biological fixation on the tibia. The architecture was designed using Solidworks and Rhinoceros software and printed by the Additive Manufacturing technique of selective laser melting (SLM). Mechanical testing of the device included compression, cyclic loading, shear strength and long-term 90 days in-vitro mechanical testing, tribology against living bovine 2 cartilage, and cell studies. The results suggest that combination of hybrid and Ti gyroid has potential to be meniscus implant due to comparable mechanical properties, low friction coefficient, and non-cytotoxicity.Open Acces

Ankle Syndesmosis Fixation Method

Screw loosening in ankle syndesmosis fixation is a major problem causing permanent arthritis. Loosening is caused by axial and transverse loading, resulting in joint malreduction. Our goal was to develop a fixation method to minimize screw loosening by optimizing screw insertion angles. Finite element analysis, pullout, load-to-failure, and cyclic shear testing were used to find the optimal screw insertion angles. Results indicate 0 deg(*) screws have significantly greater pullout strength than 23* or 45*, 23* screws create a stiffer fixation than 0*, and a two-screw system with 0* and 23* screws is able to withstand greater transverse loads than the current gold standard of two 0* screws. Findings indicate a screw system of 0* and 23* angled screws will provide better fixation

Smart implant: the biomechanical testing of instrumented intramedullary nails during simulated callus healing using telemetry for fracture healing monitoring

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThe purpose of this study is to investigate the effect of loading during long bone fracture healing in-vitro and in-vivo. Fracture healing has until now only been monitored using radiographs and ultrasound. An intramedullary nail instrumented with strain gauges has the potential to monitor loading in-vivo during bone fracture healing. Strain has been previously monitored over time though external fixation devices however there has been no published data about monitoring through a nail. The load carried by a telemetric intramedullary nail during simulated fracture healing is monitored in-vitro with the aid of custom designed jigs, integrated in a biomechanical test frame. Clinically predetermined loading conditions are applied to the construct and synthetic bone composites are used developed to simulate mechanical strength of early to mature osteogenic bone, approximating natural healing processes. Four different synthetic bone composites have been designed and developed to mimic the mechanical properties of granulation tissue, fibrous tissue, cartilaginous tissue and immature bone. Three different generations (GEN I – IIIa) of intramedullary nails were developed and biomechanically tested in-vitro. GEN I and II were purely biomechanical nails that underwent compression, torsional and 4pt bend tests. Different fracture patterns and callus morphology were simulated and tested biomechanically. Circumferential and segmental application of the synthetic materials were applied on the artificial fractured bone instrumented with GEN I. Observations from live animal study provided x-rays from which callus growth patterns were extracted and repeated in-vitro. Cadaveric biomechanical tests and pre-clinical trial of GEN IIIa was conducted. The aim was to repeat the biomechanical tests while at the same time monitoring healing with an instrumented nail implanted in an induced fractured, ovine left hind limb. A loading rig was designed for the in-vivo test. The hypothesis proposed is that forces experienced by an intramedullary nail will progressively decrease as fracture heals. Results from GEN I have shown that strain measurement can be monitored during fracture healing in-vitro. The GEN IIIa nail is yet to be tested in-vivo for the same biomechanical tests for comparison. There is currently no published study on simulating fracture healing with accuracy.Smith & Nephew Plc (S&N) & the Technology Strategy Board (TSB

Tibia Fracture Walking Boot: A Strain Controlling Device

The group designed a non-invasive strain application device that improved upon existing fracture healing devices such as external fixators, casts, and functional braces. The design included combining an AirCast walking boot and patellar tendon bearing (PTB) brace, with the ability to create a gap beneath the heel. Three tests were used to verify the mechanical properties of the analogue bones, the strains at the fracture site produced by various forces, and the forces experienced at different locations on the foot while wearing the device. Through proof of concept, the testing showed that introducing a gap in the device correlates to a dampened force and strain at the fracture site for optimal healing conditions

A New Test Rig for In-Vitro Evaluation of the Knee Joint Behaviour

The evaluation of the knee joint behavior is fundamental in many applications, such as joint modeling, prosthesis and orthosis design. In-vitro tests are important in order to analyse knee behavior when simulating various loading conditions and studying physiology of the joint. A new test rig for in-vitro evaluation of the knee joint behavior is presented in this paper. It represents the evolution of a previously proposed rig, designed to overcome its principal limitations and to improve its performances. The design procedure and the adopted solution in order to satisfy the specifications are presented here. Thanks to its 6-6 Gough-Stewart parallel manipulator loading system, the rig replicates general loading conditions, like daily actions or clinical tests, on the specimen in a wide range of flexion angles. The restraining actions of knee muscles can be simulated when active actions are simulated. The joint motion in response to the applied loads, guided by passive articular structures and muscles, is permitted by the characteristics of the loading system which is force controlled. The new test rig guarantees visibility so that motion can be measured by an optoelectronic system. Furthermore, the control system of the new test rig allows the estimation of the contribution of the principal leg muscles in guaranteeing the equilibrium of the joint by the system for muscle simulation. Accuracy in positioning is guaranteed by the designed tibia and femur fixation systems,which allow unmounting and remounting the specimen in the same pose. The test rig presented in this paper permits the analysis of the behavior of the knee joint and comparative analysis on the same specimen before and after surgery, in a way to assess the goodness of prostheses or surgical treatments

Development of a minimally invasive sliding hip screw

Previously held under moratorium from 30th November 2016 until 30th November 2021.Extracapsular proximal femoral fractures are becoming an increasingly common injury as both the population and average life expectancy increase. Currently sliding hip screws (SHS) are used to treat these fractures; however the surgery to implant these devices causes significant soft tissue damage. This results in long healing times which puts a large financial burden on the health service. Development of an SHS which can be implanted through a minimally invasive technique may reduce healing time for the patients as well as the cost of treating these patients. This study details the development of a new device the minimally invasive Sliding hip screw (MISHS). A finite element (FE) model was developed in order to allow both the current device to be studied and for new designs to be evaluated. Mechanical testing was carried out on the current device in order to validate the model. The results showed that the model behaved similarly to the mechanical test and therefore valid conclusions could be drawn from it. A design process was carried out to evaluate each of the proposed designs, three suitable designs were found and each of these were modelled in order to determine which one should be taken to the prototyping stage. Three prototypes of the chosen design were manufactured for mechanical testing. Both static and cyclic fatigue tests were carried out in order to evaluate the performance of the new design. The results show that the MISHS performed similarly to the SHS in testing. With further development the MISHS has the potential to significantly improve the treatment of extracapsular proximal femoral fractures.Extracapsular proximal femoral fractures are becoming an increasingly common injury as both the population and average life expectancy increase. Currently sliding hip screws (SHS) are used to treat these fractures; however the surgery to implant these devices causes significant soft tissue damage. This results in long healing times which puts a large financial burden on the health service. Development of an SHS which can be implanted through a minimally invasive technique may reduce healing time for the patients as well as the cost of treating these patients. This study details the development of a new device the minimally invasive Sliding hip screw (MISHS). A finite element (FE) model was developed in order to allow both the current device to be studied and for new designs to be evaluated. Mechanical testing was carried out on the current device in order to validate the model. The results showed that the model behaved similarly to the mechanical test and therefore valid conclusions could be drawn from it. A design process was carried out to evaluate each of the proposed designs, three suitable designs were found and each of these were modelled in order to determine which one should be taken to the prototyping stage. Three prototypes of the chosen design were manufactured for mechanical testing. Both static and cyclic fatigue tests were carried out in order to evaluate the performance of the new design. The results show that the MISHS performed similarly to the SHS in testing. With further development the MISHS has the potential to significantly improve the treatment of extracapsular proximal femoral fractures

Adjustable loop femoral cortical suspension devices for anterior cruciate ligament reconstruction: a systematic review

Background: Anterior cruciate ligament (ACL) injury is a common sports injury. Symptomatic knee instability after this injury is usually treated operatively through ACL reconstruction. The surgery involves a tendon graft being fixed in bony tunnels drilled through femur and tibia. The fixation of the graft is of critical importance to achieving good results. One of the commonest devices used to fix the graft in the femoral bony tunnel is a fixed loop cortical suspensory device. More recently, adjustable loop cortical suspension devices have been introduced, and have gained popularity for ACL reconstruction. These allow for adjusting the length of the suspension loop after insertion. There is currently much debate concerning whether the adjustable loop devices are superior or inferior to the fixed loop devices. Purpose: To critique and review the current biomechanical and clinical evidence on the use of adjustable loop devices in hamstring ACL reconstruction. To our knowledge, there have been no previous reviews of this topic. Study Design: Systematic review. Methods: This systematic review was conducted in accordance with PRISMA. Five databases were searched using multiple search terms and MeSH terms where possible. The following limits were applied: papers published in English and papers published in the last 21 years. Results: Eleven laboratory and six clinical studies were reviewed. The laboratory-based studies have frequently shown elongation of adjustable loop devices to more than 3 mm under loading protocols, whereas the clinical studies have not shown any significant differences between the patients with fixed loop and the ones with adjustable loop devices. Clinical Significance: This review shows a discrepancy between laboratory-based and clinical studies. The review of clinical studies in our paper would give future researchers confidence and act as a prompt to construct randomised clinical trials to investigate these devices further. Conclusion: We feel that more robust clinical randomised studies and trials are needed to evaluate these new devices