Comparison of Digital and Conventional Radiostereometric Image Analysis in an Ankle Phantom Model

Reassessment of computerized wear measurement for total hip arthroplasty with correction for projectional image distortion: a brief follow-up report

BACKGROUND

Wear of the ultra-high molecular weight polyethylene articular surface has been recognized as a major factor threatening the long-term success of total hip arthroplasty. Manual techniques that have been used to measure femoral head penetration into the polyethylene have been plagued with poor reproducibility and limited accuracy. Using a previously described phantom model simulating an unworn total hip arthroplasty, we previously demonstrated significant limitations in the accuracy of several widely used computerized wear measurement programs. A major component of these inaccuracies is projectional distortion of the femoral head and acetabular shell on the radiograph. These inaccuracies can be "corrected for" mathematically.

METHODS

In the present follow-up study, we evaluated a widely used hip wear measurement software program (Hip Analysis Suite version 8.0.3.0) that corrects for these projectional errors with use of our previously described "zero wear" phantom model. A cementless metal-backed acetabular component was evaluated radiographically at three different cephalocaudad locations with respect to a radiopaque centering target. At all three positions, the cup was aligned in three different angles of planar abduction (35 degrees , 45 degrees , 55 degrees ) and four angles of planar anteversion (10 degrees , 20 degrees , 30 degrees , 40 degrees ). The accuracy and reproducibility of Hip Analysis Suite version 8.0.3.0 were determined and compared with the results obtained with the earlier version, Hip Analysis Suite version 4.0.

RESULTS

Hip Analysis Suite version 8.0.3.0 was significantly more accurate than Hip Analysis Suite version 4.0 for determining linear wear and volumetric wear. Hip Analysis Suite version 8.0.3.0 was significantly more accurate for determining femoral head penetration at the different cephalocaudad acetabular positions and over the range of acetabular component anteversion and abduction angles in comparison with Hip Analysis Suite version 4.0.

CONCLUSIONS

With use of the same methodology that was used to evaluate earlier versions of Hip Analysis Suite, the present study showed improvement in the accuracy of wear measurement with Hip Analysis Suite version 8.0.3.0 as compared with Hip Analysis Suite version 4.0.

CLINICAL RELEVANCE

On the basis of the results of the present study, Hip Analysis Suite version 8.0.3.0 appears to fulfill the needs for a user-friendly, efficient, and accurate method of assessment of polyethylene wear following total hip arthroplasty.

Development of an RSA calibration system with improved accuracy and precision

In this study, a new radiostereometric analysis (RSA) calibration cage was developed with the aim of improving the accuracy and precision of RSA. This development consisted of three steps: a numerical simulation technique was first used to design the new cage; a synthetic imaging method was then implemented to predict the performance of the designed cage before it was actually fabricated; and an experimental phantom test was finally conducted to verify the actual performance of the new cage and compare with two currently widely used cages. Accuracy was calculated as the 95% prediction intervals from regression analyses between the measured and actual displacements, and precision was defined as the standard deviation of repeated measurements. The final experimental phantom tests showed that the accuracy and precision of the new calibration cage were improved by about 40% over an existing biplanar cage and by about 70% compared to a uniplanar cage design. This new cage can be used with any skeletal joints, in either static or kinematic examination, which is helpful for the standardization of the RSA application.