Tuesday, March 1, 2016

Total shoulder and short stems: less is not more.

Radiographic evaluation of short-stem press-fit total shoulder arthroplasty: short-term follow-up

The authors performed 158 consecutive shoulder arthroplasties using a short-stem press-fit humeral component of which two year followups were available for 73 (46%).  Four underwent revision before 2 years' follow-up; one of the revisions was for aseptic humeral loosening. Sixty-nine shoulders had at least 24 months of radiographic follow-up, and 62 had radiographic and clinical follow-up. Of the 69 shoulders, 5 underwent revision for humeral loosening: 1 for aseptic loosening and 4 for infection. Two other shoulders with humeral loosening were asymptomatic, and the patients refused revision surgery. The overall revision rate for humeral loosening was 8.2% (6 of 73 shoulders). Radiolucent zones of any size were seen in 71.0%, with 8.7% of these shoulders identified as having humeral stems at risk of future loosening.

The authors conclude that the overall rates of loosening and revision for the humeral implant examined in this study were higher than those noted in other recent studies evaluating press-fit stems.

Comment: The Introduction to this paper begins with the statement that "Humeral loosening is an uncommon etiology for revision shoulder arthroplasty." Their results indicate an increased loosening rate in short stemmed prostheses. 

One of the issues with short stems, as shown in the figure below, is that there is less lateral endosteal cortex available to resist the tendency of the component to subside in varus.

While the authors concluded "Our results showed a concerning number of cases of earlybone resorption radiographically and humeral loosening in the short-term postoperative period. It is unclear if the results were due to stress shielding from distal fixation or from lack of bony ongrowth. Even though we had good clinical results, future research and designs are worth investigating. Such improvements may include a shorter stem and a proximal coating". It is difficult to see the logic for short or shorter stems in comparison to what can be achieved using a standard prosthesis with impaction grafting as shown in this link and here and below.

We have previously posted on short stems here and here.

This article points out the problem of unintended consequences when trying to address an "uncommon etiology for revision shoulder arthroplasty"

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