Sunday, December 30, 2012

Cementless metal back glenoid

Midterm results of a total shoulder prosthesis fixed with a cementless glenoid component

This is a level IV report of 65 shoulders having total shoulder arthroplasty with a cementless glenoid component.

While on average the Constant score and active range of motion improved, glenoid component loosening occurred in 5 cases because of breakage of the cage screw. 6 patients required revision after a mean of 68 months.  All the revision cases showed massive PE and metal wear intraoperatively, demanding meticulous synovectomy.

The authors reference a multicentric study of 158 total shoulders with  this component 61 of which required revision. 

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 and here.

See also 

The authors of this study consider possible reasons for the failure of metal backed glenoids, including (1) metal trays that were too thick with thinner polyethylene inserts, (2) overstuffing of the joint leading to excessive wear, (3) poor initial fixation of the implant, (4) breakage of screws and pegs causing metal debris, and (5) dissociation of the polyethylene insert from the metal tray.

We suggest that because all glenoid components are loaded eccentrically, it is likely that the flexibility of  all polyethylene components is protective against failure of fixation and fatigue fracture that has been repeated shown to be a problem with metal backed components.

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