Risk-stratified thromboprophylaxis effects of aspirin versus low-molecular-weight heparin in orthopaedic trauma patients: a secondary analysis of the PREVENT CLOT trial.

BACKGROUND: The PREVENT CLOT trial concluded that thromboprophylaxis with aspirin was noninferior to low-molecular-weight heparin (LMWH) in preventing death after orthopaedic trauma. However, it was unclear if these results applied to patients at highest risk of thrombosis. Therefore, we assessed if the effect of aspirin versus LMWH differed based on patients' baseline risk of venous thromboembolism (VTE).

METHODS: The PREVENT CLOT trial enrolled 12,211 adult patients with fractures. This secondary analysis stratified the study population into VTE risk quartiles: low (<1%) to high (>10%) using the Caprini Score. We assessed stratum-specific treatment effects using the win ratio method, in which each patient assigned to aspirin was paired with each assigned to LMWH. In each pair, we compared outcomes hierarchically, starting with death, then pulmonary embolism, deep vein thrombosis, and bleeding. The secondary outcome added patients' medication satisfaction as a fifth composite component.

RESULTS: In the high risk quartile (n = 3052), 80% had femur fracture, pelvic, or acetabular fractures. Thoracic (47%) and head (37%) injuries were also common. In the low risk quartile (n = 3053), most patients had a tibia fracture (67%), 5% had a thoracic injury, and less than 1% had head or spinal injuries. Among high risk patients, thromboembolic events did not differ statistically between aspirin and LMWH (win ratio, 0.94; 95% CI, 0.82-1.08, p = 0.42). This result was consistent in the low (win ratio, 1.15; 95% CI, 0.90-1.47, p = 0.27), low-medium (win ratio, 1.05; 95% CI, 0.85-1.29, p = 0.68), and medium-high risk quartiles (win ratio, 0.94; 95% CI, 0.80-1.11, p = 0.48). When medication satisfaction was considered, favorable outcomes were 68% more likely with aspirin (win ratio, 1.68; 95% CI, 1.60-1.77; p < 0.001).

CONCLUSION: Thromboembolic outcomes were similar with aspirin or LMWH, even among patients at highest risk of VTE. Aspirin was favored if medication satisfaction was also considered.

LEVEL OF EVIDENCE: Level I, (therapeutic/care management).