Total shoulder - comparison of two Equinoxe glenoid designs

Clinical and radiographic comparison of a hybrid cage glenoid to a cemented polyethylene glenoid in anatomic total shoulder arthroplasty

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. 

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

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 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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We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art"  regarding this radically conservative approach to shoulder arthritis at this link and this link

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How you can support progress in shoulder surgery

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Is intraoperative navigation of value for baseplate fixation of the Equinoxe Reverse Total Shoulder?

Role of intraoperative navigation in the fixation of the glenoid component in reverse total shoulder arthroplasty: a clinical case-control study

These authors point out that fixation of the glenoid baseplate in reverse total shoulder arthroplasty (rTSA) is an important factor in the success of the procedure. They state that although aseptic loosening comprises 1.1%to 5% of the postoperative complications for rTSA it accounts for 18.2% of revisions.

They sought to determine whether computed tomography–based computer navigation improved the glenoid base plate fixation of the Exactech baseplate that uses an ingrowth central peg and angled peripheral screws.

Patients undergoing rTSAs using navigation (NAV, N = 27) and manual technique (MAN, N= 23) from January 2014 to July 2017 were analyzed in a case-control design. Screw purchase length and central cage perforation were assessed using multiplanar computed tomography. Central cage perforation was defined as a breach in the scapular wall in any plane.

Median screw purchase length was significantly longer in the NAV group for both anterior (20 mm vs. 15 mm, P <.01) and posterior screws (20 mm vs. 13 mm, P <.01), but not for the superior and inferior screws.

The NAV group displayed significantly reduced incidence of central cage perforation (17.7% vs. 52.4%, P . .04).

The authors concluded that for the Exactech baseplate, the use of computer-assisted navigated rTSA contributes to significant alterations in screw purchase length, screw angulation, and central cage perforation of the glenoid baseplate compared with non-navigated methods.

Comment: This is an interesting retrospective investigation that applies specifically to the prosthesis system studied. Some additional data would be helpful in assessing the value of the "NAV" system: (1) what is the incremental cost of implementing and using the NAV?, (2) has it been demonstrated that even a small amount of scapular penetration by the central peg affects the stability of the Equinoxe baseplate?, (3) how much is the fixation of the baseplate compromised by the observed changes in screw length and angulation" (4) are the clinical results different for those shoulders in which NAV is used?

For this prosthesis, restricting micromotion between the base plate and the underlying bone to below 150 micrometers is considered ideal for encouraging bony ingrowth. For other systems that do not require bone ingrowth and that have different methods for fixation (such as that shown below) the case for navigation may be less compelling.

===

We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art"  regarding this radically conservative approach to shoulder arthritis at this link and this link

Use the "Search" box to the right to find other topics of interest to you.

How you can support progress in shoulder surgery

You may be interested in some of our most visited web pages   arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'