AAOS Now

Published 4/1/2010

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.

Gram-negative HAIs increasing
An article in the New York Times (Feb. 26) looks at concerns over the rising incidence of Gram-negative bacteria in American hospitals. Although much research has been conducted on antibiotics to combat Gram-positive bacteria such as methicillin-resistant Staphylococcus aureus, many Gram-negative bacteria strains are resistant to all modern antibiotics. Doctors treating patients with resistant strains of Gram-negative bacteria may be forced to offer a choice between taking antibiotics such as colistin or polymyxin B—both of which were largely abandoned decades ago due to association with kidney and nerve damage—or no antibiotics at all. Authorities in Europe estimate that Gram-negative infections account for two-thirds of the 25,000 deaths caused there each year by hospital-acquired infections (HAIs). HAIs from all types of bacteria combined cause or contribute to 99,000 deaths each year in the United States.

Toxicity of bupivacaine anesthetic
The potentially toxic effects on articular cartilage following a single injection of bupivacaine may be difficult to detect clinically, according to a study in Journal of Bone & Joint SurgeryAmerican (JBJS-A) (March). The research team injected 48 Sprague-Dawley rats with 100-µL of sterile 0.9 percent saline solution (negative control) into one stifle joint and either 100 µL of preservative-free 0.5 per- cent bupivacaine (experimental group) or 0.6 mg/mL monoiodoacetate (positive control) into the contralateral joint. The rats were killed and examined at 1 week, 4 weeks, 12 weeks, or 6 months. Specimens injected with bupivacaine had intact chondral surfaces under gross and histologic examination. No differences in superficial chondrocyte viability or modified Mankin scores were found between the saline-solution and bupivacaine groups. A quantitative histologic analysis of the bupivacaine-treated knees at 6 months revealed an up to 50 percent reduction in chondrocyte density compared with that of the saline-solution–treated knees. Monoiodoacetate injection resulted in death of up to 87 percent of the superficial chondrocyte cells at 1 week and chondrolysis at 6 months.

Metal foam in implant designs?
According to research in Materials Science and Engineering: A (March 25), scientists have developed a “metal foam” with a similar modulus of elasticity to that of bone. Modulus of elasticity is a measure of a material’s ability to deform when pressure is applied and then return to its original shape when the pressure is removed. Loosening of orthopaedic implants can occur if the modulus of elasticity is too great, causing the implant to take on the bulk of the load bearing. Researchers suggest that devices manufactured from the foam would reduce the effects of such “stress shielding” and that the porosity of the foam would promote the growth of bone into and around the implant.

Lasofoxifene, fracture risk and VTE risk
A study in the New England Journal of Medicine (Feb. 25) finds that lasofoxifene may reduce the risk of fracture in postmenopausal women with osteoporosis. However, the drug is associated with an increased risk of venous thromboembolic (VTE) events. The prospective, randomized, placebo-controlled trial of 8,556 women between the ages of 59 and 80 years with bone mineral density T scores of –2.5 or less at the femoral neck or spine found that patients who were given 0.5 mg lasofoxifene per day had reduced risk of both vertebral fractures (13.1 cases vs. 22.4 cases per 1,000 person-years) and nonvertebral fracture (18.7 vs. 24.5 cases per 1,000 person-years)compared to placebo at 5-year follow-up. Patients in the lasofoxifene group had an increased incidence of VTE events (2.9 cases vs. 1.4 cases per 1,000 person-years respectively).

HAIs cost money, lives
Healthcare-associated septic infections impose substantial clinical and economic costs, according to an article in Archives of Internal Medicine (Feb. 22). Hospital discharge records from the Nationwide Inpatient Sample database were used to identify sepsis and pneumonia cases among 69 million discharges from hospitals in 40 U.S. states between 1998 and 2006. Cases of sepsis associated with invasive surgery had a mean length of stay of 10.9 days, costs of $32,900, and mortality of 19.5 percent. Sepsis cases not associated with invasive surgery had an estimated mean length of stay of 1.9 to 6.0 days, costs of $5,800 to $12,700, and mortality of 11.7 percent to 16.0 percent. Hospital-acquired pneumonia and sepsis resulted in 48,000 deaths and increased U.S. healthcare costs by $8.1 billion in 2006.

Apixaban an alternative to enoxaparin after TKA
Apixaban may be more effective than enoxaparin for preventing VTE after total knee arthroscopy (TKA), according to a study in The Lancet (March 6). In a multicenter, randomized, double-blind trial of 3,057 patients undergoing elective unilateral or bilateral TKA, 1,528 patients received 2.5 mg of oral apixaban twice daily and 1, 529 patients received 40 mg of subcutaneous enoxaparin once daily. Overall, 1,973 patients were eligible for primary efficacy analysis. Of those, the primary outcome (composite of asymptomatic and symptomatic DVT, nonfatal PE, and all-cause death during treatment) was reported in 147 (15 percent) of 976 apixaban patients and 243 (24 percent) of 997 enoxaparin patients (p < 0.0001). Major or clinically relevant nonmajor bleeding occurred in 53 (4 percent) of 1,501 patients receiving apixaban and 72 (5 percent) of 1,508 patients treated with enoxaparin (p=0.09).

Mobile compression device prevents bleeding events after THA
A study in JBJS-A (March) finds that use of a mobile compression device may be more effective than low-molecular-weight heparin for prophylaxis against VTE events following total hip arthroplasty (THA). The prospective study of 410 patients (414 hips) randomized to receive either a mobile compression device and up to 81 mg of aspirin daily or low-molecular-weight heparin after THA found that 0 percent of patients in the compression group and 6 percent of patients in the heparin group had had major bleeding events at 12 weeks follow-up. Based on bilateral lower-extremity duplex ultrasonography, 3 percent of patients in the compression group had distal deep venous thrombosis (DVT) and 2 percent had proximal DVT, compared to 3 percent of the patients in the heparin group with distal DVT and 1 percent with proximal DVT. Within the 12-week follow-up period, one patient in the compression group had two events (one DVT and one pulmonary embolus[PE]), even though an ultrasonography on postoperative day 12 had negative findings. No difference between groups with regard to the prevalence of VTE was found.

Osteoporosis drug for rotator cuff healing?
According to a rat study presented at the AAOS 2010 Annual Meeting, a synthetic version of parathyroid hormone (teriparatide) may reduce healing time and improve outcomes for patients with torn rotator cuffs. Rats with surgically repaired rotator cuffs injected with teriparatide had more bone and cartilage cells, the organization of the tissue more closely resembled normal tissue, and tendon stiffness had increased at 4 to 8 weeks postoperative. Teriparatide is approved for the treatment of osteoporosis, and further study is needed to determine its safety and efficacy in treating rotator cuff tears.

THA/TKA patients have high expectations
A study released at the AAOS 2010 Annual Meeting found discrepancies between physician and patient expectations of arthroplasty outcomes, despite physician efforts to encourage realistic expectations. Surveys of 42 THA or TKA patients and their physicians at a single center found clinically meaningful disagreement between 68 percent of the patients and their physicians; nearly 54 percent of the patients’ expectations exceeded their surgeons’ expectations.