What is the recommended treatment for a patient with knee pain and MRI findings indicating potential cartilage or bone issues, as well as pes anserine bursitis?

Treatment for Knee Pain with Bone Marrow Edema and Pes Anserine Bursitis

This patient requires conservative management with NSAIDs and activity modification for the bone marrow lesion (likely subchondral insufficiency fracture), combined with targeted treatment of the pes anserine bursitis using local corticosteroid injection under ultrasound guidance.

Understanding the MRI Findings

Bone Marrow Signal Changes in Medial Femoral Condyle

• The ill-defined intermediate T2 signal change in the anterior medial femoral condyle with contralateral tibial plateau involvement is highly suggestive of subchondral insufficiency fracture, which most commonly affects the medial femoral condyle in middle-aged to elderly females 1
• These lesions represent what was previously termed "spontaneous osteonecrosis of the knee" and are now recognized as stress-related bone injuries 1
• MRI identifies these fractures earlier than radiographs, which are often initially normal and may later show articular surface fragmentation, subchondral collapse, and progressive osteoarthritis 1
• Bone marrow lesions (BMLs) are associated with increased knee pain, and new or increasing BMLs correlate with worsening symptoms 1

Pes Anserine Bursitis

• The 5.6 cm fluid collection wrapping around the medial tendons in the posteromedial knee is consistent with pes anserine bursitis 2, 3
• This condition involves inflammation of the bursa located between the medial tibia and hamstring muscles 3
• Pes anserine bursitis commonly occurs in patients with degenerative knee arthritis and can significantly affect quality of life 2

Treatment Algorithm

For the Bone Marrow Lesion (Subchondral Insufficiency Fracture)

Activity Modification and Protected Weight-Bearing:

• Reduce mechanical loading on the affected knee to prevent progression to articular collapse 1
• Consider assistive devices (cane, crutches) if pain is significant during ambulation 1
• Avoid high-impact activities and prolonged standing 1

Pharmacologic Management:

• Initiate oral NSAIDs for pain control and anti-inflammatory effect 4
• For acute pain: Naproxen 500 mg initially, followed by 500 mg every 12 hours or 250 mg every 6-8 hours (maximum 1250 mg first day, then 1000 mg daily thereafter) 4
• For chronic management: Naproxen 250-500 mg twice daily, using the lowest effective dose 4
• Use caution in elderly patients and those with renal impairment; dose adjustment may be necessary 4

Monitoring:

• Serial radiographs may be indicated if symptoms worsen to assess for progression to articular collapse 1
• Some patients may eventually require total knee arthroplasty if progressive osteoarthritis develops 1

For Pes Anserine Bursitis

First-Line Treatment: Local Corticosteroid Injection

• Ultrasound-guided injection of triamcinolone acetonide into the pes anserine bursa is the preferred treatment 3
• This approach provides direct delivery to the inflamed bursa with excellent response rates 3
• Ultrasound guidance ensures accurate needle placement and confirms bursal distension 3

Alternative Conservative Measures (if injection declined or unavailable):

• Aspiration of bursal fluid if significant distension is present 5
• Rest, ice, and immobilization of the affected area 5
• Oral NSAIDs (already prescribed for bone marrow lesion) provide additional benefit 2
• Physical therapy focusing on hamstring stretching and strengthening once acute inflammation subsides 2

Novel Approach (if standard treatment fails):

• Mesotherapy with diclofenac (subcutaneous injections) has shown efficacy in reducing pain and ultrasonographic evidence of bursitis, with effects lasting 30-90 days 2
• This technique may reduce systemic NSAID exposure and associated adverse effects 2

Clinical Pitfalls to Avoid

Do Not Misdiagnose the Bone Marrow Lesion:

• The preserved cartilaginous layer and intact menisci/ligaments help distinguish this from acute trauma or meniscal pathology 1
• Do not assume this is simple osteoarthritis—subchondral insufficiency fractures require activity modification to prevent collapse 1
• If symptoms worsen despite conservative treatment, consider repeat imaging to assess for progression 1

Do Not Overlook Bursal Rupture:

• Pes anserine bursa can rupture, mimicking deep vein thrombosis with acute unilateral lower leg swelling 6
• If sudden worsening of swelling occurs, consider ultrasound to evaluate for rupture 6

Do Not Use Imaging Alone for Treatment Decisions:

• While MRI identified both pathologies, treatment response should be monitored clinically 1
• Decreasing bone marrow lesions correlate with reduced knee pain, so symptom improvement is the key outcome 1

Do Not Delay Injection for Bursitis:

• Pes anserine bursitis typically responds well to conservative treatment but can persist for 10 days to 36 months without intervention 2
• Early corticosteroid injection provides faster relief and better quality of life outcomes 2, 3

Expected Outcomes

• Pes anserine bursitis should respond within days to weeks after corticosteroid injection 3
• Bone marrow lesions may take months to resolve, and some patients develop progressive osteoarthritis requiring eventual arthroplasty 1
• Pain relief from NSAIDs typically begins within 1 hour for acute symptoms 4