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Glenoid component loosening is a significant concern in total shoulder arthroplasty. In fact, it’s the number 1 reason for revision procedures.

Manufacturers often modify their implants to combat problems like this, with designs, for example, that reduce the risk of glenoid component failure by reducing radiolucent lines at the bone-cement interface, or that improve fixation by making the implant more stable.

Research has demonstrated these efforts can help in identifying better options for the glenoid component in total shoulder arthroplasty. For instance, all-polyethene components have been shown to be more reliable than metal-backed components, and all-polyethylene glenoid components with biaxial pegs have been found to be superior to an inline keeled glenoid design.

In a more recent study from the Florida Orthopaedic Institute, researchers took a 2-pronged approach to evaluating a newer implant design:

• Biomechanical evaluation of a self-pressurizing peripheral peg glenoid component versus a traditional polyethylene pegged glenoid component
• Retrospective radiographic and clinical review of patients who had received one or the other of these 2 implants

Their findings have been published online ahead of print by the Journal of Shoulder and Elbow Surgery.

Study Methodology: Biomechanical

The researchers had 2 working hypotheses for the biomechanical evaluation:

• The amount of effort needed for insertion of the self-pressurizing glenoid would be different that for insertion of the traditional glenoid.
• The use of the self-pressurizing peripheral pegs would reduce micromotion under physiologic load, improving the stability of that implant.

They selected 2 glenoid components manufactured by DJO Surgical to test their hypotheses:

• A newer self-pressurizing component that has 3 peripheral pegs with larger, outer diameter fins (trilobe lock) and 1 central peg with barbed features (AltiVate)
• A traditional component that has 3 peripheral pegs with ribbed features and 1 central peg with barbed features (Turon)

A single surgeon implanted all glenoid components according to the manufacturer’s recommended surgical technique. The components were implanted in various testing conditions:

• Uncemented
• Cemented in the central peg hole only (partially cemented)
• Cemented in all peg holes (fully cemented)

Video cameras were set to record the implantation in each testing condition, from which the researchers calculated the amount of time to seat the component, the number of hammer hits to seat the component, the effort to seat the component (resistance-to-seat), and estimated the force required to fully seat the implant.

Mechanical testing was performed according to ASTM F2028-14:

• Subluxation test, in which the researchers applied shear force at a rate of 50 mm/minute until the humeral head subluxed
• Rocking horse test, in which the researchers applied a compressive force and cyclically displace the humeral head along the superior-inferior axis of the glenoid to 90% of subluxation distance for 50,000 cycles

The average of the last 5 cycles for each time point represented the component motion.

Study Methodology: Clinical

In the clinical analysis, the researchers included 431 Florida Orthopaedic Institute patients who had received either the traditional glenoid component (n=206) between January 2014 and December 2016 or the self-pressurizing glenoid component (n=225) between January 2017 and December 2019. All patients were diagnosed with primary glenohumeral osteoarthritis and had at least 3 months of follow-up visits.

A fellowship-trained orthopaedic surgeon specializing in shoulder and elbow surgery performed a blinded review of the radiographs that were taken of the study participants at 3 months, 1 year, and 2 years after surgery, noting the presence of radiolucent lines (modified Franklin grade and Lazarus grade) and glenoid seating at these timepoints. Radiographic views included:

• Anteroposterior (AP)
• AP Grashey
• Velpeau (modified axillary lateral)
• Scapular Y

Each patient also had a 2-dimensional CT scan to assess glenoid morphology and assign a Walch classification.

The researchers recorded preoperative and postoperative clinical outcomes data:

• American Shoulder and Elbow Surgeons (ASES) questionnaire
• Simple Shoulder Test (SST)
• Visual analog scale (VAS) assessments of shoulder pain at rest and with strenuous activity

Study Findings: Biomechanical

In the biomechanical arm of the study, the researchers found that overall, it took more time and more effort (more mallet hits with greater force per mallet strike) to fully seat the self-pressurizing glenoid than for the traditional glenoid.  Moreover, the traditional glenoid component was found to have less resistance-to-seat.

The researchers said the greater resistance-to-seat was likely due to the non-uniform thickness of the pegs for the self-pressurizing glenoid compared with the traditional design, with the difference in this geometric feature causing greater frictional resistance between the pegs and bony interface. As a result, the surgical technique needed to fully seat the self-pressurizing glenoid was different than for a traditional design.

This is important, the researcher said: Understanding when a surgical technique needs to be altered to accommodate the differences in a newer implant is crucial for ensuring that the implant is fully seated. This will help to reduce early glenoid component loosening.

The uncemented and partially cemented glenoid components did not survive the full 50,000 cycles, with both types of implants failing at 4000 cycles in the uncemented group and at 7000 cycles for the self-pressurizing implant and at 8000 cycles for the traditional implant in the partially cemented group. The self-pressurizing design had significantly less motion than the traditional design for both groups. For the fully cemented group, both implants successfully completed the 50,000 cycles, with so difference in motion.

The results of the biomechanical tests of micromotion under physiologic loads “provide evidence that glenoid component fixation can reliably be achieved with improved geometry and appropriate cement technique,” the researchers said.

Study Findings: Clinical

More patients who had received the self-pressurizing glenoid component showed radiographic evidence of eccentric wear patterns than those who had received the traditional implant; however, initial postoperative radiographs showed less radiolucency in the self-pressurizing glenoid group than in the traditional glenoid group (0.005% radiolucency vs 45% radiolucency, respectively).

At 2 years after surgery, no patient in either group had undergone revision total shoulder arthroplasty. In addition, the researchers saw no differences between groups in the clinical outcome scores (ASES, SST, VAS).

The superior biomechanical stability of the self-pressurizing glenoid component “correlated with a reduction of radiolucent lines,” the researchers said, “and we anticipate this will lead to a reduction in glenoid component loosening.”

Source

Melvani R, Diaz MA, Wilder L, Christmas KN, Simon P, Cronin KJ, Mighell MA, Frankle MA. Improved mechanical fixation of an all-polyethylene glenoid reduces postoperative radiolucent lines. J Shoulder Elbow Surg. 2022 Mar 23;S1058-2746(22)00301-9. doi: 10.1016/j.jse.2022.02.016. Online ahead of print.