Recalcitrant knee pain just below the medial tibial plateau? Worse with sprints, hills and after running a while? It may be the pes anserine insertion(s).

Made up of the tibial insertions, from anterior to posterior, of the sartorius, gracilis and semitendinosis which lie superficial to the distal tibial insertion of the superficial medial collateral ligament. This structure is named from the way it looks, like a goose's foot (anserine pes), rather than its anatomical location. The pes anserine bursa usually lies between it an the tibia (most of the time), sometimes between it an the MCL (about 20% of the time) and occasionally interspersed between the individual tendons. it can be subject to compressive forces if compromised in some way, by injury or pathomechanics

The muscles of the pes anserine arise from three different compartments in the thigh. The sartorius originates from the anterior compartment,  the gracilis from the medial compartment and the semitendinosus, the posterior compartment. Their varied origins, paths, and actions, as these muscles approach their insertion all add stability to the medial aspect of the knee.

During an ideal gait cycle, the sartorius fires from toe off through nearly terminal swing, the semitendinosus from mid swing through nearly loading response, with a brief firing at toe off  and gracilis tonically throughout stance phase with bursts from terminal swing through initial contact and again from pre swing to initial swing.

We remember that the abdominals should initiate thigh flexion with the iliopsoas, rectus femoris, tensor fascia lata and sartorius perpetuating the motion. Sometimes, when the abdominals are insufficient, we will substitute other thigh flexors, often the psoas and/or rectus femoris, but sometimes sartorius, especially in people with excessive midfoot pronation. Think about all of the medial rotation occurring at the knee during excessive midfoot pronation and when overpronation occurs, the extra compensatory external rotation that must occur to try and bring the knee back into the sagittal plane. The sartorius is positioned perfectly for this function, along with the semitendinosus which assists and external rotation and closed chain with the innocent pes anserine bursa directly beneath. This is complemented by the compressive forces of this gracilis firing because of the increased coronal plane motion occurring at the pelvis.

The sartorius is easily accessed as it is superficial in the anterior thigh, just under the skin (skin and you are in), running from the ASIS, coursing lateral to medial and inserting at the pes, at its most superior aspect, just overlying the gracilis. Since it is an external rotator, knee flexor and assists in thigh abduction, you can easily locate it by placing the patient in a "figure 4" position and having them resist as you pull downward on the leg, Be careful of the subsartorial canal (ie Hunters canal) lying just beneath it in the middle 1/3 of the thigh, from the apex of the femoral triangle to the adductor hiatus in the adductor magnus. It houses the femoral artery and vein, as well as the saphenous nerve and nerve to the vastus medialis. Use only enough needle (15-20mm) to get the job done, as it is immediately below the skin.

The gracilis is another superficial "skin and you are in" muscle on the medial thigh, running from the the pubic symphisis and upper pubic arch to the pes, sandwiched between the sartorius and semitendinosis. Again, a small needle (15-20 mm) will usually suffice.

The semitendinosis is the most superficial of the hamstrings and originates between the biceps femoris, with which it shares a common tendinous attchment, which is anterior and slightly lateral and the semimembranosis which is just beneath it and slightly medial. It is fusiform and the muscle body ends about mid thigh, before becoming a long "piano string" and ultimately inserting most inferiorly of the trio, below the gracilis, on the pes. This one is superficial as well and is suited best to a shorter needle.

Call it pes anserinus bursitis or pes anserine tendinitis but they both add up to medial knee pain when the thigh needs help flexing. Look to this troublesome trio the next time you have recalcitrant medial knee pain. You have a needle,  you know how to use it. What are you waiting for?

Keep on needling,

Ivo

Imani F, Rahimzadeh P, Abolhasan Gharehdag F, Faiz SH. Sonoanatomic variation of pes anserine bursa. Korean J Pain. 2013;26(3):249-54. 

Gupta, Aman & Saraf, Abhinesh & Yadav, Chandrajeet. (2013). ISSN 2347-954X (Print) High-Resolution Ultrasonography in PesAnserinus Bursitis: Case Report and Literature Review. 1. 753-757. 

Gray H:  Anatomy of the Human Body  Lea and Febiger, Phildelphia and New York 1918

https://www.anatomy-physiotherapy.com/knee/articles/systems/musculoskeletal/lower-extremity/knee/test-your-knowledge-the-pes-anserinus

 Michaud T: in Foot Orthoses and Other Forms of Conservative Foot Care Williams & Wilkins, 1993 Pp. 50-55

 Michaud T: in Human Locomotion: The Conservative Management of Gait-Related Disorders 2011