Development and validation of a new method of 3-dimensional assessment of glenoid and humeral component position after total shoulder arthroplasty.

HYPOTHESIS

This study evaluates the intrarater and inter-rater reliability of 3-dimensional (3D) computed tomography (CT) measurements of component position and alignment after total shoulder arthroplasty (TSA).

MATERIALS AND METHODS

Two patients and one whole-body cadaver with anatomic TSA implants underwent CT scans of the shoulder with a 0.6-mm slice thickness in two different arm positions (supine arm down or lateral decubitus arm up) on the same day. Test-retest reliability of component measurements within and between 5 observers was determined, as were any differences in measurements based on arm position. Precision and 95% confidence intervals were determined for the following measurements: glenoid component position (anterior-posterior, superior-inferior, and medial-lateral), glenoid component orientation (version, inclination, and roll), and humeral-glenoid alignment (HGA). HGA was defined in the anterior-posterior and superior-inferior dimensions.

RESULTS

The range of precision for measurement of the position of the glenoid implant across observers was between 0.2 and 0.5 mm, and for orientation, it was between 1.2° and 1.5°. The range of precision for measurement of HGA across observers was between 0.7 and 1.2 mm. There was no significant difference in the precision of measurements between the two imaged arm positions.

DISCUSSION AND CONCLUSION

The described method of 3-dimensional CT imaging can provide very precise and reproducible assessment of component position after TSA. Ultimately, correlation of these measurements with clinical outcome, anatomic factors, prosthetic design, and surgical factors will allow for better understanding of the causes of implant failure.