Blood Clot Prevention in Fracture Patients: No Difference for Aspirin vs LMWH

SAN DIEGO — For patients with traumatic bone fractures, there was no difference between oral aspirin and low-molecular-weight heparin (LMWH) injections as a bleeding prevention strategy, a subpopulation analysis of the randomized PREVENT CLOT trial showed.

Among over 12,000 patients in 11 high-risk groups, there were no differences in the prevention of pulmonary embolism, proximal deep vein thrombosis (DVT), or bleeding complications between those treated with aspirin 81 mg twice daily or LMWH 30 mg twice daily, reported Sandip Tarpada, MD, of NYC Health + Hospitals/Harlem, at the American Academy of Orthopaedic Surgeons annual meeting.

Three groups who took aspirin did have a higher rate of distal DVT compared with those who received LMWH — those with head injury and an Abbreviated Injury Scale (AIS) score >2 (5.5% vs 1.1%, P=0.02), those with thoracic injury with an AIS score >2 (2.2% vs 0.8%, P=0.04), and those with severe injury (Injury Severity Score [ISS] >16; 3.3% vs 1.6%, P=0.03), but the researchers determined this was not significant after correcting for multiple comparison (P<0.0001).

As for the initial primary endpoint of 90-day mortality, two groups who received LMWH had higher rates versus those who received aspirin — those with head injury with an AIS score >2 (3.7% vs 0.5%, P=0.03) and those with spine injury with an AIS score >2 (6% vs 0%, P=0.04), but there was no statistically significant difference among the 11 groups overall (P=0.63).

“These findings are largely consistent with [results from the primary analysis of PREVENT CLOT] and provide further evidence of the viability of aspirin to prevent blood clots in orthopedic trauma, even those with additional risk factors,” co-author Nathan O’Hara, PhD, MHA, of the University of Maryland School of Medicine in Baltimore, told MedPage Today.

In their original study, the researchers concluded that aspirin was noninferior to LMWH for all-cause mortality at 90 days, bleeding complications, and nonfatal pulmonary embolism. Only rates of DVT were significantly worse with aspirin.

“Venous thromboembolism, which include pulmonary embolism and deep vein thrombosis, remain common complications after orthopedic trauma,” noted O’Hara. “Most clinical guidelines recommend that patients take LMWH while in hospital and often after discharge for several weeks to prevent blood clots after orthopedic trauma.”

However, he added, “there is growing evidence that aspirin might provide similar protection against venous thromboembolism in this patient population. Assuming similar clinical outcomes, patients strongly prefer aspirin, a small oral tablet, over LMWH, which requires a needle injection into the abdomen.”

O’Hara said it was unclear to many surgeons if these results applied to various orthopedic trauma subpopulations with additional risk factors for venous thromboembolism, which led to his team launching this analysis.

“With a conservative interpretation, we found no evidence that aspirin or LMWH provided superior protection against the five outcomes in any of the 11 key subpopulations,” he said. “However, with a less conservative interpretation, aspirin was superior to LMWH in preventing death in orthopedic trauma patients with an additional head or spine injury. Similarly, LMWH was superior to aspirin in preventing distal DVT in patients with an additional head injury, chest injury, or multi-trauma patients.”

Why wouldn’t LMWH have more of an impact than aspirin? “The medications have different mechanisms, but it isn’t entirely clear how that explains the findings,” O’Hara noted. “Overall, the blood clot rates in both groups are lower than some previous research, suggesting that both medications are effective in reducing clots.”

As for choosing between the two options, O’Hara said “10% to 20% of orthopedic trauma patients do not have health insurance, and there is a strong health equity argument in favor of aspirin for this population.”

Ian Harris, PhD, MSc, MBBS, of the University of New South Wales School of Clinical Medicine in Sydney, told MedPage Today that “no study has shown that the death rate is different.”

Harris also highlighted his 2022 randomized trial that found a “significantly higher” rate of symptomatic venous thromboembolism within 90 days in patients who took aspirin versus LMWH.

The current subpopulation analysis included 12,211 patients in 11 high-risk groups — head injury and an AIS score >2 (n=371), abdominal injury and an AIS score >2 (n=352), spine injury and an AIS score >2 (n=140), thoracic injury and an AIS score >2 (n=1,196), severe injury with an ISS >16 (n=1,596), obesity (n=4,234), previous VTE (n=89), isolated upper extremity fracture (n=800), isolated lower extremity fracture (n=6,289), isolated pelvic fracture (n=1,256), and age >65 with femur fracture (n=731).

The researchers noted that their statistical correction for multiple comparison may have been overly conservative, which was a study limitation.

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