GUBING WANG
HELLO I'M GUBING
I LOVE SOLVING PROBLEMS
I K J 2.0
Problem Breifing
Through-Knee Amputation (TKA) is becoming advised by surgeons more than Above-Knee Amputation (AKA) because the residual limb provides a longer lever arm about the hip joint. Patella, patella tendon, hamstrings, collateral ligaments and a fraction of the synovial membrane are normally left intact on the femur after the surgery for cushioning. Dave Henson came up with the idea of recreating a fully functioning knee joint by designing an Implantable Knee Joint (IKJ) which utilizes these tendons and ligaments. The objective of this project was to develop the IKJ concept by generating and testing an improved design.
Interviews and Insights
Major. Edwards from Centre for Blast Injury Studies pointed out the low infection rate is vital for a successful surgery, thus ensuring enough skin to cover and pad the implant is as important as the implant itself, and it is included in the design later on.
Total Knee Replacements (TKR) is a well-developed method for replacing the articulating surfaces and ligament augmentation is a common surgery in recent days. Their working mechanisms, surgical procedures and material used provided inspirations to IKJ design. However, instead of being augmented on the tibia that is no longer available after a blast, the tendon and ligaments will be augmented on an artificial tibia. There have been several pieces of research on regenerating synovial membranes and augmenting tendon to biomaterials, but they are only tested on animals. Biomaterials facilitating osteoinduction, osteoconduction and osseointegration are studied and compared.
My task involves: literature review, allocate tasks to group members, organize group meetings, interview Major Edwards, identify design requirements
Final Design
The design process is guided by the design requirements, which are categorised into mechanical, biological, surgical, prosthetic fitting and manufacturing aspects.
The IKJ is composed of a TKR, two tendon grafts, 5Cc BioReadyâ„¢ DBM Putty, two LARSâ„¢ ligaments, 10Cc FGF-2 solution, six titanium soft screws, a silicon skin expander(which are all off-the-shelf implant devices) and an artificial tibia (manufactured using LENSâ„¢ technology).
There are various TKR designs available and a posterior stabilised fix bearing HA-coated TKR is selected in terms of its stability, potential for decreased wear and ease of revision surgery.
The geometry of the artificial tibia is based on an anatomical model and modified to accommodate the tibial tray (attachment with TKR) and augmentation points for tendon, ligaments and synovial membrane. It is a hollow structure with 5mm thickness, made of Ti-6Al-4V with 30 vol% porosity, and HA-coated, so that it is light weight and matched the Young's Modulus of cortical bone, which is essential for avoiding stress shielding. It is 150mm long for providing enough lever arm about the knee joint. The size of the artificial tibia is designed based on the tibial tray size as the sizing system for TKR is well-developed.
Skin expansion was chosen over skin grafts because full-thickness, vascularized skin connected to nerve supply is needed for effective wound closure.
My task involves: tendon attachment design, artificial tibia design, CAD modelling, create FMEA
Prototyping
The artificial tibia was rapid prototyped using Makerbot Replicator and PLA was chosen as the printing material for its good geomteric accuracy. The surgical procedure is simulated on a plastic femour with chosen TKR and using cloth stripes as soft tissues and steel screws as titanium screws.
Proof-of-concept Testing
The geometry testing proved IKJ can achieve knee stability at a wide range of knee flexion angles and loading conditions, and it can achieve the similar level of the range of rotation as a normal knee. The maximum quadriceps force is found to be at a flexion angle of 90 degrees, which provides a starting point for the tendon augmentation strength study in the future.
My task involves: experiment design, data recording
