Pes anserine bursitis is a common cause of medial knee pain. The pes anserine bursa lies beneath the pes anserine tendon, which is the insertional tendon of the sartorius, gracilis, and semitendinosus muscle to the medial side of the tibia (Fig. 147.1). The bursa serves to cushion and facilitate sliding of pes anserine tendon over the tibia. The bursa is subject to inflammation from a variety of causes with acute trauma to the knee and repetitive microtrauma being the most common. Acute injuries to the bursa can occur from direct blunt trauma to the medial knee as well as from overuse injuries including running on hills or sudden increases in the distance that one runs. If the inflammation of the bursa is not treated and the condition becomes chronic, calcification of the bursa with further functional disability may occur. Gout and other crystal arthropathies may also precipitate acute pes anserine bursitis as may bacterial, tubercular, or fungal infections.

The patient suffering from pes anserine bursitis most frequently presents with the complaint of pain in the medial knee, which may radiate inferiorly over the medial tibia. The patient may find any activity that involves flexion or external rotation of the knee such as getting in and out of cars increasingly difficult. Physical examination of the patient suffering from pes anserine bursitis will reveal point tenderness over the medial knee just below the medial knee joint. If there is significant inflammation, rubor and color may be present, and the entire area may feel boggy or edematous to palpation. At times, significant effusion may be present, which can be quite distressing to the patient (Fig. 147.2). Active resisted flexion and passive external rotation of the affected knee will often reproduce the patient’s pain. Sudden release of resistance to active flexion will markedly increase the pain. If calcification or gouty tophi of the bursa and surrounding tendons are present, the examiner may appreciate crepitus with active extension of the knee, and the patient may complain of a catching sensation when moving the affected knee, especially on awaking. Often, the patient will not be able to sleep on the affected side. Occasionally, the pes anserine bursa may become infected, with systemic symptoms, including fever and malaise, as well as local symptoms, with rubor, color, and dolor being present.

Plain radiographs are indicated in all patients who present with knee pain to rule out occult bony pathology (Fig. 147.3). Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound imaging of the affected area may also confirm the diagnosis and help delineate the presence of other knee bursitis, calcific tendonitis, tendinopathy, tendonitis, or other knee pathology (Fig. 147.4). Rarely, the inflamed bursa may become infected, and failure to diagnose and treat the acute infection can lead to dire consequences.

There is significant intrapatient variability in the size of the pes anserine bursa. The pes anserine bursa lies between the combined tendinous insertion of the sartorius, gracilis, and semitendinosus muscles and the medial tibia (see Fig. 147.1). The bursa is subject to the development of inflammation after overuse, misuse, or direct trauma. The medial collateral ligament often also is involved if the medial knee has been subjected to trauma. The medial collateral ligament is a broad, flat, band-like ligament that runs from the medial condyle of the femur to the medial aspect of the shaft of the tibia, where it attaches just above the groove of the semimembranosus muscle. It also attaches to the edge of the medial semilunar cartilage. The medial collateral ligament is crossed at its lower part by the tendons of the sartorius, gracilis, and semitendinosus muscles.

The benefits, risks, and alternative treatments are explained to the patient and informed consent is obtained. The patient is then placed in the supine position with the knee slightly flexed and supported by a rolled up towel (Fig. 147.5). The skin overlying the medial knee and medial proximal tibia is then prepped with antiseptic solution. A sterile syringe containing 4.0 mL of 0.25% preservative-free bupivacaine and 40 mg


of methylprednisolone is attached to a 1½-inch, 22-gauge needle using strict aseptic technique. A high-frequency linear ultrasound transducer is placed over the medial knee joint space in the oblique longitudinal plane with the superior portion of the ultrasound transducer turned about 20 degrees toward the patella (Fig. 147.6). A survey scan is taken, which demonstrates the characteristic appearance of the medial joint space with the hyperechoic medial margins of the femur and the tibia with the thick hyperechoic filaments of the medial collateral ligament overlying the triangular-shaped medial meniscus (Fig. 147.7). The medial meniscus is visualized as a triangular-shaped hyperechoic structure resting between the bony medial margins of the femur and tibia (see Fig. 147.7). After the structures of the medial joint space and proximal tibia are identified, the ultrasound transducer is slowly moved inferiorly while slowly rotating the superior border of the transducer clockwise when imaging the right medial knee and counterclockwise when imaging the medial left knee until
the pes anserine tendon is visualized as it is passing over the medial collateral ligament (Figs. 147.8, 147.9 and 147.10). The pes anserine bursa lies just beneath the pes anserine tendon at this level. When the pes anserine tendon and pes anserine bursa are identified, the needle is placed through the skin ˜1 cm above the middle of the superior aspect of the longitudinally placed transducer and is then advanced using an out-of-plane approach with the needle trajectory adjusted under real-time ultrasound guidance until the needle tip passes through the pes anserine tendon and lies in between the tendon and the tibia (Fig. 147.11). When the tip of needle is thought to be in satisfactory position, a small amount of local anesthetic and steroid is injected under real-time ultrasound guidance to confirm that the needle tip is outside the substance of the
tendon and correctly placed between the tendon and the tibia within the pes anserine bursa. There should be minimal resistance to injection. After needle tip placement is confirmed, the remainder of the contents of the syringe are slowly injected. If synechiae, loculations, or calcifications are present, the needle may have to be repositioned to ensure that the entire intra-articular space is treated. The needle is then removed, and a sterile pressure dressing and ice pack are placed at the injection site.