Saturday, June 25, 2011

Shoulder arthritis articles from the June JBJS - glenoid preparation, rocking horse loosening

The June issue of the JBJS provides a "specialty update" on 'What's New in Shoulder and Elbow Surgery'.
The authors state that 'asymmetric reaming to correct glenoid retroversion is commonly performed, but is thought to decrease the glenoid bone available for component implantation'. This is a critical point, since preservation of glenoid bone is a key element of glenohumeral arthroplasty - overzealous reaming sacrifices this precious commodity as shown below.

 It turns out that soft tissue balance, and not glenoid version, is the key element of shoulder arthroplasty stability. Thus our approach is to accept a substantial amount of retroversion, if necessary, to preserve the glenoid bone stock, as shown below, and achieve stability by soft tissue balancing.

The authors of this review suggest that it is preferable to insert a smaller sized glenoid component in less retroversion. Our experience is the opposite: shoulders are more stable with a larger glenoid component - inserted in retroversion if necessary - coupled with soft tissue balancing.

The authors of this review go on to comment on the amount of retroversion that can be 'corrected' before a pegged glenoid component would penetrate the vault. Actually, penetration of the glenoid vault by fixation pegs is not a critical consideration, in that the support of the component comes primarily from the accuracy of the contouring of the surface on which the component is placed as demonstrated by our fellow David Collins in his study on eccentric loading 

This review also comments on the use of computer-assisted technology to 'improve the accuracy of glenoid implantation'. While computer assistance yielded 'correct' glenoid version more consistently, there is no evidence presented that 'correcting' glenoid version improved stability or the clinical result. It did signficantly lengthen operative time, however.

Finally, the authors point to a randomized comparison of pegged versus keeled glenoid components. After 26 months, the keeled components had a 46% glenoid lucency rate as compared to a 15% lucency rate for the pegged components. This replicated the results of our fellow Mark Lazarus published in 2002. The superiority of peg fixation may be in part due to the unique positioning of component on the glenoid surface reamed around the central radial peg as shown below. Such precise positioning is more difficult to accomplish with a keeled component.
The superiority of pegs over keels may also be due to the ability of pegs that are not all in line to resist the 'lift off' seen with rocking horse loosening of the glenoid component.


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