Digital templating for THA may increase accuracy

Filmless X-ray templating permits better choice of prosthesis size and eliminates several film problems.

A study of digital preoperative templating to aid in determining correct prosthesis sizes in total hip arthroplasty found the filmless method to be accurate and easy. The use of digital X-rays can eliminate several potential problems, including misplacement of radiographs and ease of measurement of virtually anything on the image.

“Preoperative planning is extremely important in THA. The advantages are that we can improve the surgical accuracy, restore the hip biomechanics, decrease complications such as fractures, reduce OR time and hopefully get a more long-lasting result,” said William J. Murzic, MD, of Orthopaedic Trauma and Reconstructive Associates in Peabody, Mass. “This is especially important with regard to templating press-fit femoral components. We want to avoid oversizing, which may result in fractures as well as inappropriate leg length. And we want to avoid undersizing, causing problems of subsidence and loosening.”

With normal radiographs, physicians can determine the appropriate implant size with acetate overlays. “These give a good estimate of size, they’re easy to use and the results are reproducible. However, there is a problem with magnification, and not all surgeons use magnification markers on their standard X-rays. It can be time consuming, and radiographs as well as the acetate overlays can get lost,” Murzic said.

Femoral component fit

Researchers undertook a retrospective study comparing the standard radiographic technique to the digital technique for THA using specific templating software, with emphasis on femoral component fit. The study’s purpose included determining accuracy of measurements done on a workstation and the time and cost effectiveness of the digital technique.

Murzic and colleagues studied the results for 40 hip replacements, 20 using normal radiographs and 20 using digital templating; demographics were similar across the two groups, and a single surgeon implanted the same components into all 40 cases. Researchers compared the preoperative templated data to the implanted prosthesis; this analysis included femoral component fit, subsidence and complications.

With the digital software, 60% of the hips were implanted the same size as templated, and 35% were within one size. “It was pretty much the opposite for radiographs and acetates: 30% were the same size and 65% were within one size,” Murzic said. He noted that 95% in both groups, though, were within one size of templating. Of the mismatched femoral components, most were undersized rather than oversized.

In terms of femoral component fit, researchers found no significant difference between the two groups (70% excellent, 30% good). No hips had subsidence, there were no intra- or postoperative fractures and there were two dislocations.

“We found that digital templating was safe and effective in this series,” Murzic said. “The study suggests that digital is more accurate, but we were not able to show that with statistical significance. ... Templating software is easy to use, it’s faster than the standard to technique, it’s cost efficient, there are no radiographs to misplace, the data can be transferred electronically to the OR, a permanent record is generated and pretty much anything on the X-ray can be measured accurately.”

For more information:
Murzic WJ, Glozman Z, Lowe PL. The accuracy of digital (filmless) templating in total hip replacement. #148. Presented at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Feb 23-27, 2005. Washington.