What is the evaluation and management for a non-tender groin mass in a patient with a history of total hip arthroplasty (THA) and a reported allergy to watermelon?

Evaluation and Management of a Non-Tender Groin Mass After Total Hip Arthroplasty

The most appropriate initial evaluation for a non-tender groin mass in a patient with recent total hip arthroplasty (THA) is radiography of the hip followed by ultrasound of the groin mass. 1

Initial Evaluation

• Plain radiographs of the hip should be the first imaging modality to assess for complications related to the recent THA, including component positioning, loosening, or periprosthetic fracture 1
• Ultrasound should be performed as the next step to characterize the groin mass, as it can effectively differentiate between various etiologies including hernia, fluid collection (seroma/hematoma), lymphadenopathy, and vascular pathology 2
• The timing of the mass appearance (9 days post-THA) suggests a potential relationship to the recent surgery, making post-surgical collections a primary consideration 3

Differential Diagnosis

Post-THA Related Causes:

• Seroma or hematoma: Common finding after THA, detected in up to 33% of patients on ultrasound examination within weeks after surgery 3
• Iliopsoas bursitis: Can develop due to mechanical irritation from the prosthesis 1
• Prosthetic joint infection: Though typically associated with pain, fever, and other systemic symptoms (which this patient denies) 1
• Adverse reaction to metal debris (ARMD): Can present as a soft tissue mass or pseudotumor, particularly with metal components 1

Non-THA Related Causes:

• Inguinal or femoral hernia: Common cause of groin masses that may be asymptomatic 4
• Lymphadenopathy: May be reactive due to recent surgery or indicate other pathology 2
• Vascular pathology: Including femoral aneurysm or pseudoaneurysm 1

Diagnostic Algorithm

1. Hip radiographs: Evaluate prosthesis position, signs of loosening, osteolysis, or periprosthetic fracture 1

2. Ultrasound of the groin mass: Characterize the mass and determine if it's solid, cystic, or mixed 2

   • If cystic collection (seroma/hematoma): Monitor if asymptomatic, consider aspiration if large or symptomatic 3
   • If hernia: Surgical referral may be indicated 4
   • If solid mass or complex collection: Further imaging warranted 5

3. Additional imaging based on ultrasound findings:

   • MRI with metal artifact reduction: If suspicion for periprosthetic complication or ARMD 1
   • CT: If ultrasound is inconclusive and further characterization is needed 1
   • Image-guided aspiration: If infection is suspected or for diagnostic purposes 1

Management Recommendations

For Post-THA Collections (Seroma/Hematoma):

• Observation is appropriate for asymptomatic, small collections 3
• Serial ultrasound to monitor resolution 2
• Aspiration only if the collection is large, symptomatic, or suspicious for infection 1

For Inguinal Hernia:

• Surgical consultation for repair if confirmed, particularly if symptomatic 4
• Watchful waiting may be reasonable for asymptomatic hernias in men 4

For Iliopsoas Bursitis:

• Conservative management with activity modification and anti-inflammatory medications 6
• Ultrasound-guided aspiration and steroid injection may be considered if symptomatic 6

Special Considerations

• The patient's reported watermelon allergy is unlikely to impact the diagnostic workup but should be noted when considering contrast agents for advanced imaging 1
• The recent THA (within 9 days) significantly increases the likelihood of a post-surgical collection rather than a primary hernia 3
• The absence of pain, fever, or other systemic symptoms makes infection less likely but does not exclude it entirely 1

Follow-up Recommendations

• Repeat clinical examination in 2-4 weeks to assess for changes in the mass 3
• Follow-up imaging based on initial findings and clinical course 1
• Patient education regarding warning signs that would warrant urgent evaluation (increasing pain, redness, fever, expansion of the mass) 7