Monday, January 19, 2015

Infection in shoulder arthroplasty - are we winning the battle?

Periprosthetic shoulder infection in the United States: incidence and economic burden

These authors used the Nationwide Inpatient Sample from 2002 to 2011 to study hemi, total and reverse total shoulder arthroplasty with specific reference to periprosthetic joint infection (PJI). They found that the rate of PJI remained essentially constant at 1% over this period. The risk of PJI was heightened by (1) weight loss/nutritional deficiency, (2) drug abuse, and (3) anemia from blood loss  or iron deficiency - each with an odds ratio of about 2. The risk was also increased in younger and male patients. Doing the math, the authors concluded that the increasing incidence of shoulder arthroplasty and a constant infection rate will result in greater overall shoulder PJI burden.

Comment: The concern with these numbers is that they are very likely to underestimate the actual rate of periprosthetic infections after shoulder arthroplasty. The authors used a methodology similar to that employed in identifying infection rates in the hip and knee arthroplasty population using the NIS database by identifying shoulder PJI from ICD-9 diagnosis code 996.66 (prosthetic infection) in conjunction with the shoulder prosthesis codes (81.80, 81.81, 81.88, 80.01). While this methodology captures cases diagnosed with PJI during the primary arthroplasty hospitalization as well as those that underwent arthrotomy and removal of arthroplasty hardware for diagnosis of infection, it is unlikely to capture periprosthetic infections with Propionibacterium (the most common organism cultured from failed arthroplasties) because these cases are frequently thought to represent 'aseptic' failure of the arthroplasty and because they often present late after the index joint replacement.  It seems likely that a substantial number of these cases would not be coded 996.66.  This problem does not exist (at least to the same extent) in hip and knee infections where Propionibacterium is relatively rarely identified.

The bottom line is that the problem of shoulder PJI is distinct from that in hip and arthroplasty where we appear to be winning the battle; in the shoulder, the battle is just beginning.

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