Pes Anserinus Bursitis

Pes anserinus bursitis is an inflammatory condition of the medial aspect of the knee causing pain inferomedial to the knee joint. It is also called anserine or pes anserine bursitis.

A buras is a small synovial tissue lined structure between two surfaces which functions to provide space for gliding and reducing friction between two surfaces.

The exact incidence of pes anserinus bursitis is unknown. It is common in individuals involved in sports, obese middle-aged women, and elder patients with osteoarthritis of the knees.

Runners and basketball, soccer, and racket sports have higher incidence of pes anserinus bursitis. It has also  been reported in swimmers.

Relevant Anatomy and Pathophyhsiology

Pes anserinus means goose’s foot in Latin and the name is derived from webbed foot like shape of conjoined tendon of the sartorius, gracilis, and semitendinosus muscles. The pes anserinus inserts superficial to the insertion of the superficial medial collateral ligament of the knee on tibia.

Pes anserinus bursa is located between the conjoined hamstring tendons and underlying superficial collateral ligament.

The musculi sartorii bursa, located between sartorius and the conjoined tendons of the gracilis and the semitendinosus muscles is independent bursa but considered collectively as the pes anserinus bursa.

The sartorius, gracilis, and semitendinosus muscles are primary flexors of the knee and cause internal rotation of the tibia and protect the knee against rotary and valgus stress. Repeated injuries or contusion may cause bursa to become inflamed and painful.

Causes of Pes Anserinus Bursitis

Pes anserinus bursitis can result from acute trauma to the medial knee, athletic overuse, or chronic diseases like osteoarthritis of the knee.

Pes anserineus bursitis either results from tight hamstrings [and thus conditions which cause spasm of hamstrings may be associated with pes anserinus bursitis], which extra pressure on the bursa or direct injury to the bursa.

Pes anserinus bursitis is a common finding in

• Osgood-Schlatter syndrome
• Suprapatellar plical irritation
• Medial meniscal tears
• Patellofemoral arthritis
• Degenerative joint disease of the knee
• Obesity (especially in middle-aged women)
• Valgus knee deformity
• Pes planus [flat foot]
• Sportspersons who engage in sports requiring side to side movement
• Exostosis

Presentation of Pes Anserinus Bursitis

The patient complains of mild to moderate pain over the medial aspect of knee which is more often when arising from a seated position, with ascending or descending. Usually the pain is not present on level surface walking. The pain is generally diffuse and site of pain may vary due to presence of other associated pathologies. Night pain may be present due to extension of knee on lying down.

Examination reveals tenderness over the pes anserinus [slightly distal to the tibial tubercle and about 4 cm medial to it]. The bursa may not be palpable unless effusion and thickening are present. Noticeable bursal swelling is less frequent.

Palpable crepitus consistent with bursitis occasionally is noted. Pain in these patient may also be in joint line as the joint pathologies may coexist.

Hamstring Popliteal Angle

It measures hamstring tightness. Flex the hip to 90° and then passively extend the leg. The angle formed between a perpendicular line to the femoral shaft and the tibial shaft is the hamstring-popliteal angle.

Flexion or extension of the knee usually does not elicit pain. Valgus stress may reproduce the symptoms [This sign is also present in medial collateral ligament injuries]

Differential Diagnoses

• Medial Collateral Knee Ligament Injury
• Medial Synovial Plica Irritation
• Myofascial Pain
• Osgood-Schlatter Disease
• Osteoarthritis
• Patellofemoral Syndrome
• Prepatellar Bursitis
• Stress Fracture
• Fibromyalgia
• Gout
• Pseudogout
• Hamstring Strain
• Jumper’s Knee
• Osteochondritis Dissecans

The diagnosis of pes anserinus bursitis usually is made on clinical grounds but further studies may be required for cases where diagnosis cannot be made with certainty.

Laboratory Studies

The lab tests are needed if there is a suspicion of infection CBC, ESR and CRP are measured as work up for infection.

Aspiration of bursa may be subjected to cell count, Gram staining, culture, and polarized light microscopy as required.

Imaging

As a rule, radiography of the knee is not indicated for bursitis but is useful for ruling out a proximal tibial stress fracture, other bony pathologies, and arthritis.

MRI shows by increased signal intensity and fluid around the area of the pes anserinus bursa but fluid filled bursae have been found in asymptomatic knees too.

Treatment of Pes Anserinus Bursitis

Pes anserinus bursitis is primarily a self-limiting condition and nonoperative methods are quite effective in treating these patients.

The treatment includes

• Rest – Cutting back or eliminating the offending activities
• Ice massage – especially after the activity
• NSAIDs for pain relief
• Physical therapy – stretching and strengthening of the hip addujctor-abductors, quadriceps and stretching of the hamstrings
• Ultrasonography and electrical stimulation can be used as adjunct treatment.
• Intrabursal injection of local anesthetics, corticosteroids.
  • Second line of treatment in refractory cases
  • No more than 3 injections/year
  •  > 1 month period between injections.

Usually the patients respond within 6-8 weeks

Surgical management of pes anserinus bursitis is very rarely needed. In required cases, excision of the bursa and any bony exostosis if present are done.