Friday, July 28, 2017

How long do total shoulders last? The Great Paradox

Survival of the pegged glenoid component in shoulder arthroplasty: part II

Theses authors point out that loosening of the glenoid component is a primary reason for failure of an anatomic shoulder arthroplasty. These authors evaluated the midterm clinical and radiographic survival of an in-line pegged glenoid component and identified risk factors for radiographic loosening and clinical failure at an average clinical follow-up of 7.2 years

287 had presurgical, initial postsurgical, and late postsurgical radiographs (mean radiographic follow-up, 7.0 years). At most recent follow-up, 30 glenoid components had been revised for aseptic loosening. The rate of glenoid component survival free from revision for all 330 shoulders of 99% at 5 years and 83% at 10 years. 

Of 287 glenoid components, 120 (42%) were considered loose on the basis of radiographic evaluation. Four humeral components were considered loose. Component survival (Kaplan- Meier) free from radiographic failure at 5 and 10 years was 92% and 43%. 

Severe presurgical glenoid erosion (Walch A2, B2, C) and patient age <65 years were risk factors for radiographic failure. Late humeral head subluxation was associated with radiographic failure.

Comment: This paper shows the importance of longer term followup. Both radiographic failure and the need for surgical revision for this component was not apparent until after five years - a time well after the usual 2-year followup required for publication in most journals. 

This article also points out that the rate of revision at any time point after surgery underestimates the rate of radiographic glenoid failure.

A case example from this paper shows late loosening of an initially well-fixed glenoid component

 The late followup x-ray shows superior displacement of the humeral head with superior angulation of the glenoid component.
This is the type of component loosening that has been associated with rotator cuff failure via the 'rocking horse' mechanism.

The authors point out that their results with this peg configuration were inferior to those they achieved with the corresponding keeled fixation.
One of the challenges we face in clinical orthopaedic research what we refer to as the Great Paradox: the long term data we have relates to components that are no longer in use.

The authoring surgeons have moved on to other designs for which 10 year outcomes are not available:

Nevertheless, the problem of glenoid component failure retains its position as a leading cause of poor total shoulder outcomes. Some of the risk factors for failure identified in this study are likely to remain in effect with any glenoid component design: young age, advanced glenoid erosion, and glenohumeral instability. 

Finally, an understanding of the factors associated with component failure may be most reliably obtained from national registry data such as that provided by the Australian Orthopaedic Association 

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