Abstract
INTRODUCTION
As computer navigated surgery continues to progress to the forefront of orthopedic care, the application of a navigated total shoulder arthroplasty has yet to appear. However, the accuracy of these systems is debated, as well as the dilemma of placing an accurate tool in an inaccurate hand. Often times a system's accuracy is claimed or validated based on postoperative imaging, but the true positioning is difficult to verify. In this study, a navigation system was used to preoperatively plan, guide, and implant surrogate shoulder glenoid implants and fiducials in nine cadaveric shoulders. A novel method to validate the position of these implants and accuracy of the system was performed using pre and post operative high resolution CT scans, in conjunction with barium sulfate impregnated PEEK surrogate implants.
METHODS
Nine cadaveric shoulders were CT scanned with .5mm slice thickness, and the digital models were incorporated into a preoperative planning software. Five orthopedic shoulder specialists used this software to virtually place aTSA and rTSA glenoid components in two cadavers each (one cadaver was omitted due to incomplete implantation), positioning the components as they best deemed fit. Using a navigation system, each surgeon registered the native cadaveric bone to each respective CT. Each surgeon then used the navigation system to guide him or her through the total shoulder replacement, and implant the barium sulfate impregnated PEEK surrogate implants. Four cylindrical PEEK fiducials were also implanted in each scapula to help triangulate the position of the surrogate implants. Previous efforts were attempted with stainless steel alloy fiducials, but position and image accuracy were limited by CT artifact. BaSO4 PEEK provided the highest resolution on a postoperative CT with as little artifact as possible. All PEEK fiducials and surrogate implants were registered by probing points and planes with the navigation system to capture the digital position. A high resolution post operative CT scan of each specimen was obtained, and variance between the executed surgical plan and PEEK fiducials was calculated.
RESULTS
The PEEK fiducials and surrogate implants that were used are compared with stainless steel fiducials in Figure 1. Figure 2 compares and contrasts the artifact present with BaSO4 PEEK fiducials vs stainless steel fiducials. Figure 3 illustrates the clarity of the reconstructed PEEK surrogate implant and fiducials in 3D space. Using the navigation system, the surgeons implanted the PEEK glenoid components 1.0±1.1mm anterior of center and 0.7±0.9mm superior of center relative to the preoperative plans. The average retroversion was 1.6±1.9° and inclination was 1.0±1.2° relative to the preoperative plans.
CONCLUSION
The increased visible detail and decreased artifact from using a barium sulfate impregnated plastic proved to be a useful tool in determining 3D position of a surrogate implant. This technique could be applied in other biomedical applications beyond orthopedics. The validation technique also showed the accuracy and anticipated clinical benefit of a navigated total shoulder system, as the reported variance of glenoid version post shoulder replacement is ±11°.
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