Bony ongrowth in stemless reverse total shoulder arthroplasty components.

Abstract

Background: Stemless shoulder arthroplasty utilizes epiphysometaphyseal fixation, eliminating the need for humeral canal reaming. Extending stemless technology to reverse total shoulder arthroplasty (rTSA) introduced distinct biomechanical challenges. In the absence of diaphyseal support, concerns regarding humeral component subsidence, varus tilting, and aseptic loosening arise. In the United States, stemless rTSA remains investigational, with the Fx Easytech Reversed system currently under evaluation through an Investigational Device Exemption clinical trial.

Methods: Explanted components were submitted to an independent orthopaedic laboratory for systematic, non-destructive analysis comprising high-magnification microscopy. Bony ongrowth was assessed using a non-standardized, semi-quantitative grading scale applied across four fixation surface quadrants (Q1-Q4), estimating tissue coverage from 0 (none) to 4 (75-100%).

Results: Bony ongrowth was observed on all three titanium-hydroxyapatite (Ti/HA)-coated humeral anchor bases across implantation durations ranging from 39 days to 3 years and 8 months, with semi-quantitative scores of Q1: 2-4, Q2: 4, Q3: 3-4, Q4: 3. No case was revised for fixation failure.

Conclusion: Ti/HA-coated stemless humeral components demonstrated osseointegration under the compressive-dominant loading environment of rTSA. Bony ongrowth was evident as early as 39 days postoperatively. Larger retrieval series and long-term follow-up are necessary to confirm the durability of stemless humeral implants.

Level of evidence: Level IV, Case Report.