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Reverse shoulder arthroplasty angle may reliably measure glenoid inclination
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Inclination of the inferior portion of the native glenoid may be reliably measured with the reverse shoulder arthroplasty angle in patients with rotator cuff tear arthropathy, according to published results.
Researchers compared the reverse shoulder arthroplasty angle with the global glenoid inclination (total shoulder arthroplasty angle) among 47 shoulders with rotator cuff tear arthropathy. Researchers defined the reverse shoulder arthroplasty angle as the angle between the inferior part of the glenoid fossa and the perpendicular to the floor of the supraspinatus. Three independent observers made measurements on plain anteroposterior radiographs and reformatted 2-D CT scans and compared these measurements with 3-D software measurements.
Results showed a mean reverse shoulder arthroplasty angle of approximately 25° on plain radiographs, 20° on reformatted 2-D CT scans and 21° on 3-D reconstruction software. On average, researchers found the mean total shoulder arthroplasty (TSA) angle was approximately 10° less than the mean reverse shoulder arthroplasty angle. Researchers observed this difference on radiographs, 2-D CT or 3-D CT and regardless of type of glenoid erosion according to Favard. The difference between TSA angle and reverse shoulder arthroplasty angle was approximately 12° in Favard type E1 glenoids with central concentric erosion.
“Preoperative planning is essential for proper assessment of glenoid erosion and placement of the reverse baseplate tilt,” the authors wrote. “From a surgical standpoint, the [reverse shoulder arthroplasty] RSA angle is useful to ensure a neutral tilt of the glenoid component. By use of 2-D or 3-D planning, this allows measurement of the thickness and the angle of the bone graft or augmented baseplate needed.” – by Casey Tingle
Disclosures: Boileau reports he is a paid consultant for and receives royalties from Wright-Tornier. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
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Mark A. Mighell, MD
In patients undergoing reverse shoulder arthroplasty, unrecognized superior inclination of the glenoid can lead to a cascade of complications resulting from superior baseplate tilt. Mark A. Frankle, MD, and colleagues have previously described the spinospheric angle to determine the position of the baseplate relative to the scapula spine. In this study, significant superior tilt of the implant often resulted in catastrophic failure.
To accurately understand and prevent inferior tilt of the baseplate, the surgeon must have a basic understanding of the Favard classification. Within the classification, the E1 glenoid poses the greatest challenge even to the most experienced arthroplasty surgeon, due to the substantial amount of central erosion. In this pattern of wear, without adequate preoperative planning the baseplate is often placed in superior tilt relative the scapula spine.
Pascal Boileau, MD, PhD, and colleagues describe a new measurement, reverse shoulder arthroplasty angle formed by measuring an angle between line perpendicular to the inferior portion of the glenoid and a line perpendicular to the floor of the supraspinatus fossa. This is of particular importance as the baseplate is usually in contact with the inferior portion of the glenoid.
Total shoulder arthroplasty angle previously described by Alexander Maurer, MD, and colleagues when compared with reverse shoulder arthroplasty resulted in lower angle of correction correlating with more superior inclination of the glenoid. Surgeons should be particularly cautious of the superior inclination especially in patients with central glenoid erosion, which results in the larger difference between the two methods.
In their study, the average reverse shoulder arthroplasty angle was measured to be 21+/-5° in a series of 47 patients with cuff tear arthropathy. The authors included that 15° to 25° of superior inclination needs to be corrected to achieve neutral alignment of the baseplate.
Adequate understanding of glenoid erosion and preoperative planning using either reverse shoulder arthroplasty angle or other alterative techniques are paramount to avoid superior baseplate tilt.
References:
Gutierrez S, et al. J Shoulder Elbow Surg. 2007;doi:10.1016/j.jse.2005.11.008.
Maurer A, et al. J Shoulder Elbow Surg. 2012;doi:10.1016/j.jse.2011.07.010.
University of South Florida
Florida Orthopaedic Institute
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