No abstract

Bone mechanics and traditional implant materials cause a frequent problem for patients of total hip arthroplasty (THA): the bone becomes shielded from the loading. This will result in loosening of the implant, pain, and therefore revision surgery will take place to correct the issue. The current study, a methodology is developed for creating an innovative structural design that extracts volume in the shape of spheres from the samples, in order to focus solely on expected behaviour within the samples and bone. The design decreases extreme stresses carried by samples and pass them onto the remaining bone. Finite element analysis was applied to various models with different complex internal structures that contain hollow spheres close to surface. Moreover, compression test was applied to solid sample and the experimental case containing hollow spheres. This approach was to investigate the effects of spherical hollow structure near the side surface and its bonesample interface. The models containing hollow spheres have smaller young modulus and strength in comparison to the solid sample. The hollow spherical structures reduce the stress shielding and they transfer more stress onto the bone compared to the solid model. This approach also re-structures a hard material such as stainless steel to enhance osseointegration. The reduction of the young modulus and stress directly depends on the volume of the spheres in the models. However, there is a range defined for the volume that could be extracted from solid structure to achieve the most effective outcome.

Hip impingement is a hip associated abnormality and it reduces the activity of those affected and also it can result in osteoarthritis. Current clinical methods in detecting hip impingement known as FADIR test. This is a manual method and relies heavily on surgeons experience and the method is prone to error. The use of computational programmes are known to be more accurate and reliable as the kinematic of contact can easily be studied using the digitised bones of the hip joint assuming that the impingement is determined by bone to bone contact kinematics. Current impingement studies assume that the kinematics of hip joint can be studied by assuming the centre of rotation is fixed for hip joint. For highly conforming joints this assumption is acceptable but for cases where conformity is poor the presence of soft tissue and soft tissue loading becomes very important. The important need in orthopaedics field is to develop a model without too much simplification. All previous work on detecting impingement has ignored the factor of soft tissue. In this paper for the first time the complete computational model of hip with soft tissue has been used to detect the impingement in a specific patient. In this paper the femur, acetabulum, cartilage and ligaments of specific patients were modelled in MIMICs using both MRI and CT scan. 3D hip models with and without soft tissues of normal hip, hip with impingement and hip with impingement after reshaping were modelled. The hip models were imported to detect impingement zone and impingement angle. Our results show that the soft tissue in hip model affects hip impingement angle and hip biomechanics. This finding also shows that, if the boundary condition is closer to the real hip, then the results of computer-aided program will be more reliable.

In recent years new structures have been developed for sustainability as they are lighter, with less material usage while sustaining their mechanical properties to be utilised in the application. One of these structures is a corrugated structure mainly used in the packaging industry but recently has been recognised by many other applications as the structure is known for its capabilities against shock absorption. In this study, BS6655 was used to evaluate corrugated structure in a helmet while an impact occurs to its front. The dynamic responses of the corrugated helmet were compared with a solid helmet. The results showed that the corrugated helmet has a higher ability to absorb the shock and protect the head from injuries in such impact.

There are many aspects that have direct effects on total hip replacement performance (THR), such as material properties, applied loads, surgical approach, femur size and quality, prosthesis design, bone-implant interface etc. One of the purposes to study different structures in THR is reducing the stress shielding. For the current study, an innovative hollow spherical structure is developed for femoral hip stems. The aim is to extract volume in the spherical shape from the stainless-steel hip implant stems, in order to focus solely on correlating with titanium behavior. Internal geometry for the femoral stem is optimized in order to transfer more stress onto the bone. Moreover, the approach involves extracting volume in the spherical shape from the internal structure to reduce stress shielding. A new novel implant is proposed that demonstrated a reduction in stress shielding. The sphered models have a smaller young’s modulus and strength than the solid stainless-steel sample. The spheres in hollowed structures reduce the stress shielding and they transfer more stress onto the bone when compared to the solid stainless-steel models. This approach also involves restructuring a hard material, such as stainless steel, to enhance osseointegration. The reduction of the young’s modulus and stress directly depends on the volume of the hollow spheres in the models; however, there is a certain volume that can be extracted from solid