Duplex Ultrasound of the Left Leg
The next best step is duplex ultrasound of the left leg. 1
Clinical Reasoning for Immediate Imaging
This 65-year-old woman presents with high pretest probability for deep vein thrombosis based on multiple Wells criteria components: recent major surgery (hip replacement 6 weeks ago), entire leg swelling with 2+ pitting edema, and current reduced mobility despite physical therapy. 1 The American College of Chest Physicians explicitly recommends complete duplex ultrasound (CDUS) as the preferred initial test for patients with high pretest probability of DVT (Grade 1B). 1
Hip replacement surgery is a major risk factor for DVT, with thrombosis risk persisting for up to 2 months post-operatively, making this patient still within the high-risk window. 1 The presence of entire leg swelling (not just localized to the surgical site) suggests venous obstruction beyond local surgical trauma from the hematoma alone. 1
Why Not the Other Options
D-dimer Testing is Inappropriate
Do not delay imaging for D-dimer results in high-probability patients, as this only postpones definitive diagnosis (Grade 1B). 1 D-dimer has utility in low-probability patients to rule out DVT, but in high-probability scenarios like this one, a negative D-dimer would not exclude DVT and a positive result would still require imaging. 2, 1
Empiric Heparin is Premature
Do not start anticoagulation empirically when diagnostic testing is available, especially with a large hematoma present that could expand with anticoagulation. 1 While the American College of Chest Physicians does recommend starting parenteral anticoagulation immediately in high clinical suspicion cases, this applies when diagnostic testing will be delayed. 3 Given that ultrasound is readily available and the presence of a large hematoma creates bleeding risk, confirming the diagnosis first is the safer approach. 1
CT Venography is Unnecessary
CT venography is not the first-line test for lower extremity DVT. 2 Duplex ultrasound is preferred due to its non-invasive nature, lack of radiation exposure, absence of contrast-related nephrotoxicity risk (relevant given her diabetes and multiple medications), and excellent diagnostic accuracy for proximal DVT. 1 CT venography is reserved for situations where ultrasound is technically inadequate or when evaluating central veins. 2
Specific Imaging Protocol Required
The Society of Radiologists in Ultrasound recommends complete duplex ultrasound from the inguinal ligament to the ankle, including posterior tibial and peroneal veins in the calf, with compression performed at 2-cm intervals. 1 Whole-leg ultrasound is particularly appropriate for this patient given her severe symptoms (2+ pitting edema of the entire leg). 1
Post-surgical patients are at risk for both proximal and distal DVT, making whole-leg ultrasound the preferred diagnostic approach rather than limited proximal compression ultrasound. 1
Critical Pitfall to Avoid
Do not assume the hematoma explains all findings. 1 While the large thigh hematoma may contribute to some swelling, entire leg pitting edema extending beyond the hematoma site strongly suggests concurrent venous thrombosis requiring anticoagulation. 1 The absence of focal tenderness and redness in the lower leg does not exclude DVT, as these findings are neither sensitive nor specific. 1
Management After Positive Ultrasound
If proximal or whole-leg ultrasound is positive for DVT, treatment should be initiated immediately without confirmatory venography (Grade 1B). 1 For provoked DVT following surgery, the American College of Chest Physicians recommends 3 months of anticoagulation (Grade 1B). 2, 3 The presence of the hematoma will require careful monitoring during anticoagulation, but DVT treatment takes priority given the mortality risk from untreated proximal DVT and potential pulmonary embolism. 3