The polyethylene on bone articulation, as occurs with scapular notching, is associated with osteolytic potential

Abstract Introduction Scapular notching is a common finding following reverse total shoulder arthroplasty. Severe notching can extend beyond the inferior baseplate screw or post and is therefore unlikely to be the result of isolated mechanical impingement. It is highly likely that the cause of this bone loss is biologically mediated osteolysis, but the driver of this osteolysis is unknown. We completed in vitro polyethylene on bone wear testing, as occurs with scapular notching, to characterize the osteolytic potential of this articulation. Methods Physiologically relevant wear testing was performed with 18 polyethylene pins articulating against cortical bone, cancellous bone, and cobalt-chrome pucks. Pins were cycled up to 1,000,000 times, or until failure, and incremental material loss was determined to calculate polyethylene and bone wear rates. Polyethylene particles were extracted from the associated lubricant and evaluated using scanning electron microscopy. To validate the model, wear patterns on polyethylene pins were compared to those on 24 explanted reverse prostheses. Results Polyethylene wear rates were significantly higher on cortical bone (3.5-times, P = .040) and cancellous bone (10,700-times, P = .015) than on cobalt-chrome. Cortical bone wear rates decreased over time (P = .003). Electron microscopy demonstrated that polyethylene on cortical and cancellous bone both produced submicron polyethylene particles, the size necessary to induce biologically mediated osteolysis. Analysis of explanted reverse polyethylene components with impingement demonstrated similar wear patterns to what was seen in vitro. Conclusion The polyethylene on bone articulation, as occurs with scapula notching, has potential to be an osteolytic driver as it is marked by high polyethylene wear rates and produces particles small enough to cause macrophage-mediated osteolysis, as has been demonstrated following total hip arthroplasty. Level of evidence Basic Science Study