These authors remind us that loosening of the glenoid component is a primary reason for failure of an anatomic shoulder arthroplasty.
They reviewed 330 total shoulder arthroplasties using a cemented, all-polyethylene, in-line pegged glenoid component evaluated with an average clinical follow-up of 7.2 years.
At most recent follow-up, 30 glenoid components had been revised for aseptic loosening. Of 287 glenoid components, 113 glenoid components (39%) had a clear shift in position. A total of 120 glenoid components (42%) had either a complete 1.5-mm or greater radiolucent line involving the pegs or had shifted in position, signifying radiographic failure as shown by comparing the immediate postoperative to the followup x-rays below.
Severe pre surgical glenoid erosion (Walch A2, B2, C) and patient age <65 years were risk factors for radiographic failure. Late humeral subluxation was associated with radiographic failure, with a loosening rate of 33.8% in shoulders without late subluxation compared with a rate of 48.4% in shoulders with late subluxation.
Comment: It is of note (as shown by the charts below) that clinical and radiographic glenoid failure were not evident until after the usual two year followup period. It is also of note that revision rate is not a reliable indication of radiographic failure. Evidently many patients choose to cope with the symptoms of glenoid failure rather than undergoing another surgical procedure.
Secondly, humeral subluxation was a common feature among the failures suggesting a rocking horse loosening mechanism. See Rocking horse loosening in total shoulder arthroplasty
Finally, these authors are careful to point out that these results relate to a specific glenoid component design with in-line non-ingrowth pegs. Other results may apply to other designs such as that shown below.
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