Saturday, December 29, 2012

Metal back glenoid component failure

Results of total shoulder arthroplasty with a monoblock porous tantalum glenoid component: a prospective minimum 2-year follow-up study

This article presents the two year results of 19 shoulders having arthroplasty by an expert surgeon using a "novel", porous, tantalum-backed glenoid component, with a minimum 2 years of follow-up.

Interestingly, the components were implanted using a small amount of cement to remain with the FDA approval for this component.

At followup, 18 shoulders had complete bone ingrowth, but four components had failed by fracture at the keel-glenoid face junction and another had prosthetic instability requiring revision to a reverse total shoulder. As pointed out previously, the cost of these revisions need to be included in the value equation for this particular prosthesis.

Seven humeral components had lucent lines of 2 mm or more.  Of those, 2 humeral components were considered to be at risk by the criteria of Sperling. The relationship between these lucent lines and glenoid component failure is not presented.

The authors conclude that "caution should be exercised in the use of novel implants with an unproven clinical track record".

While there seems to be intense interest in exploring metal backed glenoid components, as pointed out in a previous post and in this review article, the major issue with metal-backed glenoid components is not the fixation of the metal to bone, but rather the dissociation and wear of the polyethylene attached to the metal base plate.   Metal backed glenoid component are discussed in previous reports and here.

See also 

Survival of the glenoid component in shoulder arthroplasty.

Mid-term results of a metal-backed glenoid component in total shoulder replacement.
Total shoulder arthroplasty with an uncemented soft-metal-backed glenoid component.

It seems possible that in all polyethylene components the flexibility of high density polyethylene is protective against failure of fixation and fatigue fracture of the metal that may arise from the eccentric loading inherent in glenohumeral contact.
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