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Published on: February 10, 2015
How much does radiographic projection affect the measurement of glenoid inclination?
Mihir Sheth1, Kevin Khoo2, Scott Telfer2
1Anderson Orthopaedic Clinic, Arlington, USA.
Purpose:
The measurement of glenoid and reverse total shoulder arthroplasty (rTSA) inclination has both clinical and research relevance. The purpose of this study was to better understand if and how much radiographic projection and scapula position affect the perception of glenoid inclination.
Materials And Methods:
Twenty computed-tomography (CT) scans of arthritic shoulders were used to create digitally reconstructed radiographs (DRR) through 3° increments of inclination, retraction and protraction on a scapular coordinate system. The reverse total shoulder arthroplasty (rTSA) and total shoulder arthroplasty (TSA) angles were measured on each image.
Results:
The mean range (difference between maximum and minimum values) of rTSA and TSA angle measurements based on simulation of scapula inclination was 14° and 17°, respectively. Nineteen of 20 cases showed a trend towards a higher rTSA and TSA angle with greater forward inclination. With simulated scapula retraction, the maximum difference between rTSA and TSA angle measurements was a mean 11° and 14°, respectively. With simulated scapula protraction, the maximum difference observed for rTSA and TSA angle measurements based was a mean 14° and 11°, respectively. Scapula protraction and retraction did not produce consistent or linear trends in rTSA or TSA angle measurement.
Conclusion:
The radiographic measurement of rTSA and TSA angles is moderately variable based on scapula protraction, retraction and inclination. Forward inclination may increase the perception of superior tilt.
