The purpose of this study was to determine the reliability of preoperative templating in primary total knee arthroplasty and the influence of the seniority of the surgeon on templating. A retrospective study of 25 randomly selected total knee replacements was undertaken, with templating of preoperative radiographs by four surgical staff members. These included a consultant, a specialist registrar and two senior house officers. Reliability for an exact match between template size and implant actually used was 49% for the femoral component and 67% for the tibial component. The statistical agreement between templated size and actual implant size was classed as only fair to moderate. There was no statistical difference in templating reliability between junior and senior surgical staff. These results indicate that the current system of templating for total knee arthoplasties is prone to error and can only be used as an approximate guide.

Reliability of preoperative templating in total knee arthroplasty.

Total hip arthroplasty (THA) is one of the most common orthopedic procedures. It has proven to be very successful in reducing pain and restoring joint function.1–4 Preoperative templating makes an essential part of the planning process before THA. It prepares an orthopedic surgeon for the procedure by reducing surgical time needed to measure the size of the implant.3,5 Furthermore, it minimizes the cost of the procedure related with inventory control and also helps to avoid postoperative complications.3,6–8

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Accuracy of predictive magnification factor for preoperative templating in total hip arthroplasty

Revision hip arthroplasty is a frequently performed procedure and is projected to increase annually. Removal of a well-fixed acetabular component can involve loss of much needed bone stock. Contemporary instruments allow acetabular removal with minimal morbidity; however, their use requires accurate knowledge of the component size. We describe a technique that allows sizing to be determined accurately, without specialized equipment, in situations where component details are unavailable. Our technique multiplies ratio of head:cup on pre-operative X-ray by the diameter of the index femoral head which is removed intra-operatively to predict index cup size. This novel surgical technique appears accurate in prediction of cup size to guide explant in revision hip arthroplasty.

A Novel Method of Determining Acetabular Component Size to Guide Explant in Revision Hip Arthroplasty.

Templating x-rays of total hip and knee replacements pre-operatively are important to plan surgery. This is usually done using acetate templates of the prosthesis on hard copies of the x-ray. With the change in practice, to use digital x-rays on computer screens instead of hard copies, it is important to assess if acetate templates can be used for digital x-rays on the computer screen. This is a retrospective x-ray study of 19 hip replacements and 30 knee replacements to assess their magnification using the Patient Archiving Computerised System (PACS) software. This study was done to assess the accuracy of magnification, using acetate templates over a computer screen. In total hip replacement, the outer cup diameter was also measured using the digital measurement scale. The mean magnification was 0.59 for the acetabular cup and the femoral stem in total hip replacement and 0.48 for the femoral and tibial implant in total knee replacement. The mean difference in cup diameter comparing to the real size was an excess of 10.21 mm. The study showed over-magnified hip and knee x-rays thus suggesting that acetate templates and measurement scales on PACS was not reliable.

D Prakash

Papers

Magnification error of digital x rays on the computer screen.