These authors report the clinical and radiographic outcomes of 316 Equinoxe hybrid cage glenoids (below left) compared with an age-matched, sex-matched, and follow-up–matched cohort of 316 Equinoxe cemented all polyethylene peg glenoids (below right) in patients undergoing anatomic total shoulder arthroplasty with 2 years’ minimum follow-up.
These procedures were performed by 13 different fellowship-trained orthopedic surgeons, of whom 10 implanted glenoids in both cohorts. From the time of market introduction of the cage glenoid in 2011, both glenoid options were available in each case for each surgeon and the selection of glenoid type was based on surgeon preference.
The cage glenoid patients had significantly lower rates of radiolucent glenoid lines (9.0% vs.37.6%, P < .0001) and radiolucent humeral lines (3.0% vs. 9.1%, P . .0088) than the all-polyethylene peg glenoid patients.
Comment: This study compares the outcomes of a caged glenoid design with a smooth all-poly glenoid with similar peg configuration. The choice between these two options was made by the surgeons. The reasons for the choice of one design vs the other are not known.
The cage glenoid patients had significantly lower rates of radiolucent glenoid lines (9.0% vs.37.6%, P < .0001) and radiolucent humeral lines (3.0% vs. 9.1%, P . .0088) than the all-polyethylene peg glenoid patients.
In the cage glenoid cohort, 4 cases of aseptic glenoid loosening (1.3%). 4 patients in the cage glenoid cohort experienced a unique complication of polyethylene articular surface disassociation from the central peg. The failure mechanism identified in each case was technique-induced damage to the central cage polyethylene-locking mechanism. An example is shown below in which the central peg was implanted off-axis by 5 degrees relative to the peripheral pegs; this deviation (and bottoming out of the central peg with the medial scapular wall) induced an extra bending moment that led to a failure of the central peg locking mechanism and the reported disassociation.
In the all-polyethylene peg cohort, 12 cases of aseptic loosening (3.8%) occurred. Cage glenoid patients had a significantly lower revision rate than all-polyethylene peg glenoid patients (2.5% vs. 6.9%, P . .0088). Revision was required in 3 of 4 cage glenoid patients with aseptic glenoid loosening, 4 of 4 cage glenoid patients with articular surface disassociation, and 10 of 12 all-polyethylene patients with aseptic glenoid loosening.
The comparison of clinical outcomes is shown below
The authors point out the requirement that the central and peripheral pegs of the caged component be precisely aligned to avoid the risk of articular surface dissociation.
It is not known if a glenoid component with a more flexible ingrowth peg may be more forgiving of small degrees of off axis implantation.
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