Pes Anserine Bursitis

Inflammation of the bursa lying between the medial tibial plateau and the combined insertion of the sartorius, gracilis and semitendinosus tendons (the pes anserinus), about 5 to 6 cm distal to the medial joint line. Much of what is labelled bursitis is tendinopathy of the same insertion, and the two coexist.

• It causes medial knee pain with tenderness, and is commonly mistaken for medial meniscal or medial collateral ligament injury.
• Risk factors: obesity, female sex, age over 50 years, knee osteoarthritis (especially varus deformity), type 2 diabetes, flat feet, tight hamstrings, valgus knee alignment, and overuse in runners, swimmers (breaststroke) and cyclists.
• Direct trauma, rheumatoid arthritis, and gout are less common causes.
• Prevalence is up to 2 to 3% of the general population, and it accounts for a large share of medial knee pain in obese older women with osteoarthritis.

• Medial knee pain, aching or sharp, worse on stair climbing, getting out of a chair, walking uphill and at night, with morning stiffness that is short lived.
• Focal tenderness over the anteromedial proximal tibia, distal to the joint line. Mild swelling may be palpable. Pain is reproduced by resisted knee flexion with the hip externally rotated, or by resisted internal rotation of the tibia.
• No joint line tenderness, no effusion, no locking, and a stable joint with normal ligament tests.
• Differential diagnosis: medial meniscal tear, medial collateral ligament sprain, osteoarthritis of the medial compartment, stress fracture of the medial tibial plateau, saphenous nerve entrapment, medial plica syndrome, referred hip pain, osteonecrosis, tumour, and infection.
• Red flags: warmth, fever and marked swelling (septic bursitis), night pain with weight loss, inability to bear weight, and history of cancer.
• Complications: chronic pain, gait alteration and recurrence.

• Clinical, from the site of maximal tenderness.
• X-ray of the knee (standing anteroposterior and lateral) to assess osteoarthritis, alignment, and exclude a stress fracture or an osteochondroma.
• Ultrasound shows bursal fluid and tendon thickening, and guides injection. MRI if the diagnosis is uncertain or if a meniscal, ligamentous or bony lesion is suspected.
• Check glucose or HbA1c, urate and CRP when diabetes, gout or inflammatory arthritis is possible. Aspirate and culture if infection is suspected.

• Conservative treatment for 4 to 8 weeks:
  • Relative rest from running, stairs and aggravating movements, and avoidance of crossing the legs.
  • Ice for 10 to 15 minutes, 3 times daily, early on.
  • Paracetamol 1 g orally 6 hourly, with ibuprofen 400 mg orally 8 hourly with food, or naproxen 500 mg 12 hourly, for 1 to 2 weeks if no contraindication. Topical diclofenac 1% gel 2 to 4 g up to 4 times daily is an alternative in older adults.
  • Weight loss when overweight.
  • Physiotherapy: hamstring, adductor and calf stretching, quadriceps and hip abductor strengthening, and correction of foot mechanics (insoles for flat feet).
  • A pillow between the knees at night.
• Corticosteroid injection for pain that persists after 4 to 6 weeks: methylprednisolone acetate 20 to 40 mg or triamcinolone acetonide 20 to 40 mg with lidocaine 1% 2 to 4 mL, into the bursa at the point of maximal tenderness under ultrasound guidance when available. Relief lasts weeks to months. Do not inject into the tendon. Maximum 2 to 3 injections per year. Warn about skin atrophy, depigmentation, and a transient rise in glucose for 3 to 5 days in diabetes.
• Extracorporeal shock wave therapy, 3 weekly sessions, for refractory cases (evidence limited).
• Treat osteoarthritis and its alignment contribution, and consider a medial wedge free or valgus unloading approach under orthotic guidance. Evidence for knee braces is limited.
• Surgery is rarely needed. Bursectomy and tendon release for failure of 6 to 12 months of treatment, after imaging excludes other causes.
• Special groups:
  • Diabetes: monitor glucose after injection, and treat the neuropathy and obesity contribution.
  • Pregnancy: rest, physiotherapy and paracetamol. Avoid NSAIDs after 20 weeks and avoid injection unless essential.
  • Elderly: favour exercise and topical NSAIDs, and avoid repeated steroid injection.
  • Renal impairment and gastrointestinal disease: avoid oral NSAIDs.
  • Anticoagulation: use a fine needle with ultrasound guidance and apply pressure for 5 to 10 minutes.
• Follow up: review at 6 weeks. Refer to orthopaedics or sports medicine for no improvement by 3 months or diagnostic doubt.