A Study of Sizing Accuracy for Digitally Templating the Exeter Hip
The following is a retrospective study of 39 consecutive Primary Exeter total hip replacements (THR) carried out by Dr Grant Shaw, orthopaedic surgeon in Portsmouth, UK to compare the Materialise OrthoView templated prosthesis size with the size used in surgery. The THR procedures were performed by Dr Shaw at Queen Alexandra Hospital in Portsmouth, between August 2016 and May 2017. Of the 39 procedures, 35 were elective hip arthroplasties and 4 were acute total hip replacements undertaken for neck of femur (NOF) fractures. All patients had standard AP Pelvis for Hip x-rays taken with a disc scaling marker placed in the hip plane.
Comparing the templated and actual results, Dr Shaw’s study shows an exact hip stem offset size match in 100%, an exact hip stem match in 85% and an exact acetabular size match in 87% of cases.
Dr Shaw uses pre-operative templating “primarily to predict component size”. The conclusion he draws from this study is “that templating proved to be accurate in between 85 and 100% of cases for all the hip components.” The mismatches were all within one size and equally split between over and under sizing He adds that the size information resulting from a templated surgical plan “can be used during surgery in a number of helpful ways.” which outlines as follows:
”The use of a ‘shopping list’ at the beginning of the day to move components from the theatre store into the operating theatre, saves valuable surgical time by having the correct components ready when they are required.” He continues “It is also occasionally extremely helpful in alerting to a missing component at the beginning of the day, allowing time to rectify the problem.”
“Pre-op size anticipation is helpful for the scrub team as it can be used to predict the size of reamers, rasps and trials. This allows optimization of the instruments on the trolleys and is particularly helpful for junior and training staff who can be overwhelmed by the multitude of different sizes in the full set.”
“I trust templating prediction of component size to be accurate.” States Dr Shaw. “During surgery, if the surgeon finds a component size is different from the plan then careful examination for technical errors should be undertaken, rather than assuming the templating is wrong.” Dr Shaw explains “For example, under-reaming of the femur, resulting in an undersized and mal-positioned femoral component is quite a common technical error. This can be identified in this way and avoided.”
Finally, although Dr Shaw believes that size prediction is the main advantage realised by templating, he also identifies other benefits which are beyond the scope of his study. These include leg length correction, anticipation of issues with bone loss and planning to deal with a dysplastic acetabulum.