UW Shoulder and Elbow Academy: The hybrid glenoid

Hybrid Glenoid Designs in Anatomic Total Shoulder Arthroplasty:A Systematic Review

Hybrid glenoid components have been designed with the aim of combining the initial stability provided by cementing a polyethylene component with the long-term potential of biologic fixation through ongrowth of metal components. These components are marketed in the hope that they will provide better clinical outcomes and lower revision rates than standard all polyethylene glenoid components in total shoulder arthroplasty (TSA)

These authors sought to systematically review the literature for studies that assessed outcomes of TSA performed using hybrid glenoid components.

Their hypothesis was that hybrid glenoid components offered greater initial stability and had lower complication rates than all-polyethylene and metal-backed glenoid components.

They found seven studies with 593 shoulders for inclusion in this review. The mean age of patients was 65 ± 1 years, and 46% of the population was male. Mean follow-up was 50 months (4.2 years).

The overall complication rate was 7% and rate of revision was 2.5%; glenoid radiolucency was present in 33% of shoulders at mean follow-up of 50 months.

Mean improvements in forward elevation, external rotation, internal rotation score, and abduction were 49°, 28°, 2 points, and 42°, respectively. Mean improvements in Constant, American Shoulder and Elbow Surgeons (ASES), and University of California, Los Angeles (UCLA) scores were 36 points,

52 points, and 17 points, respectively.

The rate of complications was reported by 6 studies with a total of 548 shoulders. Complications occurred in 38 shoulders giving an overall complication rate of 7%. The most common complications were rotator cuff tears in 6 shoulders (1%) and infection in 5 shoulders (1%). Regarding complications specifically related to the glenoid component, glenoid aseptic loosening and glenoid fracture each occurred in 4 shoulders (0.7%). There was 1 case of the polyethylene component shearing off the post at the screw-in mechanism. Other complications included articular surface dissociation, postoperative pain, nerve injuries, clavicular fractures, aseptic humeral loosening, acromioclavicular joint injuries, and hematomas.

Five studies with radiographic follow-up for 351 shoulders reported the percentage of

shoulders with radiolucency. Of these shoulders, 33% had some degree of radiolucency.

There were 15 reported revisions in this review resulting in an overall rate of revision of 2.5%. The reasons for revision were aseptic glenoid loosening (4), articular surface dissociation (8), posterior instability (1), glenoid fractures (3) rotator cuff tear plus polyethylene wear (1), and 1 case of the polyethylene component shearing off the post at the base of the screw-in mechanism.

Three cohort studies compared TSA performed with hybrid glenoid components and all polyethylene glenoid components; all found that improvements in ROM and patient-reported outcome scores were not inferior to those found in all-polyethylene glenoid components

Comment: This is an interesting review of the hybrid glenoid.

The article points out that the hybrid glenoid has some unique failure modes not seen with conventional all-polyethylene glenoid components: articular surface dissociation, shearing of the poly off the post, and glenoid fracture.

It appears that the authors' did not find evidence to support the hypothesis " that hybrid glenoid components offered greater initial stability and had lower complication rates than all-polyethylene and metal-backed glenoid components."

Here are a few articles related to hybrid glenoids:

Uncemented fixation of a monoblock ingrowth polyethylene glenoid: early follow-up

These authors reviewed their experience with uncemented fixation of a hybrid cage monoblock
polyethylene glenoid component in 51shoulders with a minimum follow-up of 2 years.

Twelve glenoid components (24%) had radiolucent lines. Glenoid lines were rated grade 1,grade 2, and grade 5 (6, 4, and 2 shoulders, respectively). Six shoulders (12%) had humeral lucent lines. Two shoulders (4%) underwent reoperation, only 1 of these occurring due to isolated failure of the glenoid component. As a group, mean ROM and PROMs improved significantly compared with preoperative values and exceeded the minimal clinically important difference.

One patient had failure of the glenoid after a motorcycle accident

Comment: The clinical and radiographic outcomes of this glenoid do not appear to be superior to those with a standard all-polyethylene glenoid component.

See below for a discussion of another recent paper describing the use of this component.

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 Exactech hybrid cage glenoids below left) to an age-matched, sex-matched, and follow-up–matched cohort of 316 Exactech cemented all polyethylene glenoid (below right) in patients undergoing anatomic total shoulder arthroplasty with 2 years’ minimum follow-up.

The Exactech 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 Exactech all-polyethylene peg glenoid patients. In the cage glenoid cohort, 4 cases of aseptic glenoid loosening (1.3%) and 4 cases of articular surface dissociation (1.3%) occurred as shown below.

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).

Comment: These authors point out the importance of exact alignment of the drilled holes and the direction of impaction required by the metal-coated pegs.

The required direction and accuracy may be difficult to achieve because of challenges with exposure, especially in retroverted glenoids.

Failure to achieve the desired alignment of the holes with the reamed bony surface can result in failure of the component as shown below.

In contrast to the all-polyethylene component with smooth pegs used in this study, we prefer a component with a fluted central peg.

This component has several advantages, including (1) the flexibility of the pegs that can better accommodate minor degrees of malalignment in comparison to the more rigid hybrid pegs and (2) the fluted central peg that allows bone ingrowth which cannot occur with the smooth pegs used in this study.