Machine Intelligence Laboratory

Cambridge University Department of Engineering

Dr Graham Treece, Department of Engineering

F-GMT11-2: Ankle prosthesis alignment from X-rays

The implant location on the tibia and the talus is planned based on a pre-operative CT scan of the patient. A post-operative CT isn't usually available, but X-ray images are. Can the implant axial rotation with respect to the tibia be calculated from these images?

This is a fairly open-ended project largely concerned with matching of CT data to X-ray projections, but it could cover other areas including patient-specific bone models and 3D printing. The motivation is to try to accurately calculate the rotational angle between an ankle replacement implant on the bottom of the tibia (leg bone) and the tibia, measured about the axis of the bone. This angle is very important, since it will determine the relative angle of the foot compared to the leg (imagine looking down at your foot and twisting it right or left). When the implant is attached during surgery, a patient-specific tool is used to try to get the location correct, but it is hard to determine what the best possible angle would be to improve long term outcomes.

Before the operation, there is a 3D Computed Tomography (CT) scan so the patient-specific implant jig can be customised, and this gives the full 3D bony anatomy. After the operation, standard practice only involves the use of X-ray projections. So is it possible to use the pre-op CT data, and the known geometry of the implant, to work out the relative axial rotation from the post-op X-ray images? And, if it is possible, how accurately can this rotation be determined? Errors of 1 or 2 degrees may be clinically relevant.

This is an image analysis / computational geometry / software project, so some experience of writing software is essential, though some of the development could be done using freely available medical image visualisation tools.

The project is being run in conjunction with Tom Turmezei (consultant radiologist, Norfolk and Norwich University Hospital) and David Loveday (consultant orthopaedic surgeon, Norfolk and Norwich University Hospital).

Click here for other medical imaging projects offered by Graham Treece.