Abstract
Many surgical decisions taken in the operating theatre are based on the experience and the expertise of the surgeon. Using biomechanical and computational data can provide additional information for the surgeon. By carrying out biomechanical trials pre-operatively as well as a full three dimensional analysis of the skeletal structure of the patient, it is possible to provide the surgeon with clinical data that can support the decision making with regards of fixation method, type of implant and size to name a few. In the presented project a description is provided of the pre-operative assessment of primary total hip patients in Iceland and how the analysis is helping to prevent periprosthetic fractures.
Over 70 patients undergoing primary total hip arthroplasty in Iceland were recruited for the study1. Gait analysis was performed on the patients using a pressure plate in conjunction with two synchronised video cameras. In addition, EMG was recorded from three muscles: Rectus femoris, Vastus lateralis and Vastus medialis on both the healthy and the operated leg. Finally the patient was CT-scanned with an in-plane resolution of 0.5mm and slice thickness of 1mm. Three dimensional objects of both the femur and muscles were created based on the scans. The material properties were derived from the Hounsfield units. Finite element analysis was carried out on the femur and the fracture risk of press fitting procedure was calculated and areas of weak points in the bone identified. Analysis was carried out on the muscles and the volume distribution between fat, connective tissue and muscle tissue calculated.
The results showed that basing fixation method on age and sex may not necessarily be a good indicator. The three dimensional bone mineral density distribution and the relative volume of cortical bone provided a better indication of which patients should receive cemented implant. Using a strain based failure criteria on the finite element models showed increased number in failed elements with decreased volume of cortical bone. The results of the biomechanical assessment for each patient were finally collected using an automatic report which was presented to the clinician.
Using biomechanical assessment and modelling can help identify an optimal treatment method for total hip patients by giving surgeons quantitative data on which they can build their decision making in the operating theatre. This can eventually lead to reduction in revisions and increased quality of life for the patient.
