An older adult two weeks post‑total hip arthroplasty on thromboprophylaxis presents with sudden severe lateral and medial knee pain and posterior knee bruising that started while sleeping; what is the most likely diagnosis and immediate management?

Spontaneous Hemarthrosis/Intramuscular Hematoma Secondary to Thromboprophylaxis

This patient has developed a spontaneous bleeding complication (likely hemarthrosis or intramuscular hematoma in the thigh/knee region) from anticoagulation therapy, and immediate management requires stopping all pharmacologic anticoagulation, assessing hemoglobin levels, and preparing for potential surgical evacuation if compartment syndrome develops. 1

Immediate Diagnostic Assessment

The clinical presentation—sudden severe pain (10/10) in the knee with posterior bruising while on thromboprophylaxis two weeks post-hip arthroplasty—strongly suggests bleeding into the joint or surrounding soft tissues rather than deep venous thrombosis. 1

Key immediate actions:

• Stop all anticoagulation immediately regardless of VTE risk, as active bleeding takes priority over thrombosis prevention 1
• Check hemoglobin urgently using point-of-care analyzers to quantify blood loss 1
• Assess for compartment syndrome by examining for severe pain disproportionate to findings, tense swelling, and neurovascular compromise (pulses, sensation, motor function) 1
• Monitor vital signs for hypotension and tachycardia indicating hemodynamic instability 1

Diagnostic Imaging

Obtain ultrasound or CT scan to confirm the diagnosis and differentiate between superficial wound bleeding versus deep joint/muscle bleeding, and to quantify hematoma size 1. The posterior knee bruising with severe pain suggests significant hemorrhage tracking from the thigh or knee joint posteriorly.

Transfusion Strategy

The American Academy of Orthopaedic Surgeons provides clear thresholds:

• Transfuse if hemoglobin <8 g/dL with symptoms (pain, tachycardia, hypotension, fatigue) 1
• Transfuse if hemoglobin <7 g/dL even without symptoms 1
• Use packed red blood cells as the primary transfusion product 1
• Avoid transfusing based solely on hemoglobin number without considering clinical symptoms 1

Reversal of Anticoagulation

If the patient was on warfarin with INR >2.0, administer vitamin K 1. For patients on direct oral anticoagulants (DOACs) or low-molecular-weight heparin, specific reversal agents may be considered in severe bleeding, though guidelines prioritize supportive care and time for drug clearance.

Surgical Intervention Indications

Surgical evacuation is indicated for:

• Progressive bleeding despite cessation of anticoagulation 1
• Development of compartment syndrome with neurovascular compromise 1
• Infected hematoma 1

Do not delay surgical consultation if any of these features develop, as compartment syndrome can lead to permanent neurovascular damage 1.

Resumption of VTE Prophylaxis

This represents a critical clinical dilemma. The American College of Chest Physicians emphasizes that thromboprophylaxis should be used in hip arthroplasty patients 2, 1, but this must be balanced against bleeding complications.

Resume pharmacologic prophylaxis only after:

• Bleeding has stopped for 24-48 hours 1
• Hemoglobin has stabilized 1
• No signs of ongoing hemorrhage or compartment syndrome 1

Once acute bleeding resolves, the risk of fatal pulmonary embolism generally outweighs ongoing bleeding risk 1, making resumption of some form of prophylaxis essential. Consider mechanical prophylaxis (intermittent pneumatic compression) as a bridge until pharmacologic agents can be safely restarted 2, 1.

Common Pitfalls

• Do not continue anticoagulation in the setting of active bleeding, even if concerned about VTE risk—bleeding takes priority 1
• Do not assume this is DVT based solely on leg pain in a post-arthroplasty patient on anticoagulation; the posterior bruising is pathognomonic for bleeding 1
• Do not delay imaging if clinical examination suggests large hematoma or if the bleeding source is unclear 1

Risk Stratification for Future Management

Extended prophylaxis up to 35 days is recommended for hip arthroplasty 3, but may need to be shortened in patients with bleeding complications 1. When restarting prophylaxis, consider using the lowest effective dose and closest monitoring, or switching to aspirin if the patient was on more potent anticoagulation 4.