Individualized Thromboprophylaxis in Patients with Lower-Leg Cast Immobilization—A Validation and Subgroup Analysis in the POT-CAST Trial

Abstract

Background A small subgroup of patients treated with lower-leg cast immobilization develops venous thromboembolism (VTE).

Objectives (1) Identify risk factors for VTE in patients with cast immobilization, (2) assess the effectiveness of thromboprophylaxis in low- and high-risk groups, and (3) validate the performance of the L-TRiP(cast) score.

Methods Data from the POT-CAST trial were used. A total of 1,519 patients with lower-leg cast immobilization were randomized to a prophylactic dose of low-molecular-weight heparin or no treatment. Primary outcome: symptomatic VTE within 3 months. Absolute risks (ARs) were determined for low- and high-risk subgroups. For several risk factors, relative risks (RRs) for VTE were estimated with corresponding 95% confidence intervals (CIs). For validating the L-TRiP(cast) score, a discrimination and calibration analysis were performed.

Results Patients with a body mass index of > 30 kg/m² and those with a VTE in their family history had an increased VTE risk, RR 3.8 (95% CI, 1.5–9.4) and RR 2.4 (95% CI, 1.0–5.6), respectively. Concerning injury-specific risk factors, patients with an Achilles tendon rupture or those who were surgically treated had the highest risk of VTE, AR at 8.5% (95% CI, 3.7–16.1) and AR 3.5% (95% CI, 1.3–7.5), respectively. There were no subgroups in which thromboprophylaxis was effective for prevention of symptomatic VTE. The area under the curve for the L-TRiP(cast) score was 0.69 (95% CI, 0.58–0.80).

Conclusion Thromboprophylaxis was not effective for VTE prevention following lower-leg cast immobilization in any risk category. Low- and high-risk individuals could be identified using the L-TRiP(cast) score. The best treatment strategy for these patients is yet to be determined.

Keywords

prophylaxis - venous thrombosis - orthopaedics - risk factors

Authors' Contributions

B.N. and S.C. designed the analysis. B.N. and R.v.A. included patients. B.N. and S.L.C. performed the statistical analyses. B.N. wrote the first manuscript draft. All authors were involved in writing and revision of the manuscript. All authors read and approved the final manuscript.

Ethical Approval

All participants provided written informed consent. This study was approved by the Medical Ethical Committee of the Leiden University Medical Center in Leiden, The Netherlands.

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