A comparison of concentric and eccentric glenospheres in reverse shoulder
arthroplasty: a randomized controlled trial.
Author(s): Poon PC, Chou J, Young SW, Astley T.
Affiliation(s): Author information:
Department of Orthopaedic Surgery, North Shore Hospital, Private Bag 93 503,
Takapuna, North Shore City 0740, New Zealand. E-mail address for P.C. Poon:
petercpoon@xtra.co.nz.
Publication date & source: 2014, J Bone Joint Surg Am. , 96(16):e138
BACKGROUND: Inferior scapular notching following reverse shoulder arthroplasty is
due to mechanical impingement and, in some studies, has been associated with
poorer functional scores, lower patient satisfaction, and more limited shoulder
motion. We aimed to test the hypothesis that inferior positioning of the center
of rotation with eccentric glenosphere designs decreases the adduction deficit
before impingement occurs and improves clinical outcome.
METHODS: A randomized, controlled, double-blinded trial was performed. According
to the results of a power analysis, fifty patients undergoing reverse shoulder
arthroplasty for the diagnosis of cuff tear arthropathy were randomized
intraoperatively to receive either a concentric or eccentric glenosphere. The
glenoid baseplate was positioned flush to the inferior border of the glenoid
before the glenosphere was then attached. Notching was assessed using an
anteroposterior radiograph, and clinical outcome was assessed using the visual
analog pain scale score, shoulder function rating, American Shoulder and Elbow
Surgeons score, and Oxford shoulder score. Active forward elevation and external
rotation were assessed. The outcome assessor was blinded to the treatment group.
The mean follow-up period for the groups was forty-three and forty-seven months.
RESULTS: Patient demographics and preoperative scores were similar between the
groups. At the time of the final follow-up, four patients (14.8%) in the
concentric group had developed inferior scapular notching (two with Nerot grade I
and two with Nerot grade II), ranging in size from 1.1 to 7.4 mm, compared with
one patient (4.3%; Nerot grade I) in the eccentric group (p = 0.36). No notching
occurred in any patient with glenoid overhang of >3.5 mm. No significant
difference between the groups was seen with respect to functional outcome scores,
patient satisfaction, or shoulder motion.
CONCLUSIONS: There were no differences in notching rates or clinical outcomes
between concentric and eccentric glenospheres following reverse shoulder
arthroplasty. Inferior glenosphere overhang of >3.5 mm, however, prevented
notching. This may be achieved with a modified surgical technique, but eccentric
glenospheres provide an additional option.
LEVEL OF EVIDENCE: Therapeutic Level I. See Instructions for Authors for a
complete description of levels of evidence.
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