Pes Anserine Bursitis
Introduction and prevalence
Pes anserine bursitis (PAB) is the inflammation of the pes anserine bursa and a common cause of medial knee pain. It is most prevalent among obese individuals, those with osteoarthritis, females, and those with previous knee injury. The prevalence of PAB is difficult to assess as many cases are misclassified as patellofemoral pain syndrome, however some studies show that almost 20% of individuals with knee OA suffer from PAB.
Etiology and Pathophysiology
Pes anserine refers to the conjoined tendons of the sartorius, gracilis, and semitendinosus inserting on the anteromedial proximal tibia; PAB is related to repetitive stress or direct trauma to the bursa. The condition is associated with knee OA, Osgood-Schlatter Syndrome, plical irritation, patellofemoral arthritis, obesity, hamstring tightness, valgus knee, and activities requiring lateral movements, such as basketball and tennis, are significant contributors.
Clinical presentation
Medial knee pain, worsened by activities including rising from a seated position, using the stairs, or sitting with legs crossed can be suggestive of PAB. The patient may endorse trauma to the knee, OA, or sport activities. PAB coexisting with MCL injury is not uncommon.
Physical examination
Physical examination should include a full examination of the knee, including for joint line tenderness, effusion, and crepitus. Tenderness over the pes anserine bursa, usually 5-7 cm below the anteromedial knee joint margin while the knees are extended, is a good test for PAB. To test for hamstring tightness, the hip joint should be flexed to 90° and the knees extended; a flexion angle greater than 20° indicates hamstring tightness.
Investigations
PAB is diagnosed clinically, however Pes Anserine Bursal injection with lidocaine and corticosteroid can have both therapeutic and diagnostic value. Plain radiograph can be used to assess arthritis and bony abnormalities, US for assessment of swelling, and MRI for assessing intra-articular pathologies.
Management
Conservative therapy includes rest, ice, NSAIDs, and physical therapy, including stretching and strengthening adductors, abductors, quadriceps, and hamstrings. Special focus should be put on enhancing the last 30° of knee extension. Weight management and corrective orthopedic measures have also been found to be helpful. Newer management strategies include ultrasound therapy for swelling reduction, extracorporeal shock wave therapy for reduction of pain, and kinesio-taping for management of pain and swelling. Intra-bursal injection of local anesthetics and corticosteroids, or with PRP, has been shown effective in treatment of severe PAB. Patients should be notified that steroid injections risk tissue atrophy, skin pigmentation, and tendon rupture.