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AAOS Now

Published 6/1/2011

Second Look—Clinical News and Views

If you missed these Headline News Now items the first time around, AAOS Now gives you a second chance to review them. Headline News Now—the AAOS thrice-weekly, online update of news of interest to orthopaedic surgeons—brings you the latest on clinical, socioeconomic, and political issues, as well as important announcements from AAOS.

FDA clears MRSA/MSSA identification test
The U.S. Food and Drug Administration (FDA) has cleared a test designed to quickly identify whether a strain of Staphylococcus aureus is methicillin-resistant (MRSA) or methicillin-susceptible (MSSA). The test takes about 5 hours to reach a determination and does not require any specific instruments beyond blood culture equipment. FDA based its clearance on a clinical study of 1,116 blood samples evaluated at four major U.S. hospital centers and found the MRSA determination to be 98.9 percent accurate (178/180) and the MSSA determination to be 99.4 percent accurate (153/154).

Be aware of groin pain after THA
A study in Journal of Bone & Joint Surgery—American (JBJS-A) (May) suggests that groin pain after total hip arthroplasty (THA) may be associated with local reactions or component loosening that may not yet be clinically apparent. The prospective study of 279 patients who underwent either metal-on-metal (MOM) THA with a 28-mm–diameter femoral head (n=85), THA with a different large-diameter femoral head (n=89), or hip resurfacing (n=105) found that 41 patients reported groin pain at 24-month follow-up. Of these, 23 did not seek further evaluation or treatment, 9 had revision surgery, and 9 thought the pain was substantial enough to warrant further evaluation and treatment.

MOM vs COP implants
According to a study in JBJS-A (May 4), MOM hip implants may have better radiographic and long-term survival results than ceramic-on-polyethylene (COP) in young, active patients. The case-control study of 78 THA patients (mean age: 41 years, range: 15–49 years) who were given either MOM (n = 39) or COP (n = 39) implants found no revisions in the MOM group at mean 13-year follow-up and only one hip (3 percent) with asymptomatic acetabular osteolysis. In the COP group, 18 hips (46 percent) had osteolysis and 11 hips (28 percent) had been revised because of wear or osteolysis. The 12-year survival rate (with reoperation for any reason as the end point) was 100 percent in the MOM group and 70 percent in the COP group. MOM patients had a median cobalt concentration in the whole blood of 0.95 µg/L (0.4 µg/L –4.8 µg/L) and a median chromium concentration of 1.2 µg/L (0.1 µg/L –5.6 µg/L).

Highly cross-linked polyethylene wear
A study in the JBJS-A (April 20) compares the use of highly cross-linked polyethylene against conventional ultra-high molecular weight polyethylene for total hip arthroplasty (THA). Patients (n = 54) were randomized to undergo THA with either conventional ultra-high molecular weight polyethylene acetabular liners or highly cross-linked polyethylene liners. At minimum 7-year follow-up, the mean steady-state wear rate of highly cross-linked polyethylene was 0.005 mm/year, compared with 0.037 mm/year for conventional ultra-high molecular weight polyethylene. No patient in the highly cross-linked polyethylene group had a wear rate above the osteolysis threshold of 0.1 mm/year, but 9 percent of patients in the ultra-high molecular weight polyethylene group did.

THA LOS and readmission
A study in the Journal of the American Medical Association (JAMA) (April 20) finds that hospital length-of-stay (LOS) after THA has decreased while readmission rates have increased during the same period. The observational cohort study of 1,453,493 Medicare Part A beneficiaries who underwent primary THA, along with an additional 348,596 who underwent revision THA between 1991 and 2008, found that, for primary THA patients, mean hospital LOS decreased from 9.1 days in 1991–1992 to 3.7 days in 2007–2008. The proportion of THA patients discharged to skilled care increased from 17.8 percent to 34.3 percent, and the 30-day all-cause readmission rate increased from 5.9 percent to 8.5 percent. Trends were similar for patients undergoing revision THA.

Long-term PPI use and fracture risk
A study in the Archives of Family Medicine (May/June) suggests that use of proton pump inhibitors (PPIs) may be associated with increased risk of fracture. The meta-analysis of 5 case-control studies, 3 nested case-control studies, and 3 cohort studies that examined fracture risk against long-term use of PPIs and histamine 2 receptor antagonists (H2RAs) found that long-term use of PPIs increased risk of any fracture and of hip fracture risk. Long-term H2RA use was not significantly associated with fracture risk.