Pes anserinus: who is driving the bus?

We all see medial knee pain located just below the medial tibial plateau. It often results from running, or substitute work of hamstring but sometimes with jumping sports as well. these people are often diagnosed with an MCL type injury, but when you examine them further, they do not really fit into the diagnosis box . All the ligaments are stable and there is no tenderness at the joint line. The is often tenderness at the pes anserine. Now who is driving ?

The Sartorius:The sartorius originates from the anterior compartment of the thigh. the sartorius fires from toe off through nearly terminal swing[3] during ideal gait cycle.We remember that the abdominals should initiate thigh flexion with the iliopsoas, rectus femoris, tensor fascia lata .

Sometimes, when the abdominals are insufficient to produce force , ,there will substitute other thigh flexors works , but people with excessive midfoot pronation Sartorius works as substitute sometime.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 function along with the semitendinosus which assists and external rotation in closed chain. This is the reason it is often implicated as the culprit in many cases of pes bursitis (1-2) it is utilized more in crossing or cutting maneuvers while changing directions during running (4).

Many times , It can often be overlooked in adductor strains. It can also be avulsed during sprints, particularly in adolescents (5) and because of its course of the lateral femoral cutaneus nerve beneath it, may be the cause of meralgia paresthetica (6). It is proprotionally smaller in females (along with the gracilis and short head of the biceps femoris) (7).

The sartorius is superficial in the anterior thigh region , just under the skin, running from the ASIS. It runs lateral to medial and inserting at the upper third of tibia on superior medial aspect ,just overlying the gracilis. Since it is an external rotator, you can easliy locate it by placing the patient in a “figure 4” position and having them resist as you pull downward on the leg. Be careful if you are needling this muscle because 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.

So think about Sartorius muscles when you have patient with tenderness on U/3 of tibia.During diagnosis you May find tightness hip flexors , poor lumbopelvic stability and tightness in TA .

Treatment :

1. Activate the obliques
2. Release the psoas , Gastrocnemius
3. Improve lumbopelvic stability
4. strengthning sartorious

Referance

1. Imani F, Rahimzadeh P, Abolhasan Gharehdag F, Faiz SH. Sonoanatomic variation of pes anserine bursa. Korean J Pain. 2013;26(3):249-54. 
2. 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. 
3. Michaud T: in Human Locomotion: The Conservative Management of Gait-Related Disorders 2011
4. Rand MK, Ohtsuki T. EMG analysis of lower limb muscles in humans during quick change in running directions. Gait Posture. 2000 Oct;12(2):169-83.
5. Manning CJ, Singhai S, Marshall P. Synchronised sartorius avulsions in adolescent sprinter. BMJ Case Rep. 2016 Jul 13;2016.
6. Hsu CY, Wu CM, Lin SW, Cheng KL. Anterior superior iliac spine avulsion fracture presenting as meralgia paraesthetica in an adolescent sprinter. J Rehabil Med. 2014 Feb;46(2):188-90. doi: 10.2340/16501977-1247.
7. Behan FP, Maden-Wilkinson TM, Pain MTG, Folland JP. Sex differences in muscle morphology of the knee flexors and knee extensors. PLoS One. 2018 Jan 23;13(1):e0190903.
8. Cleather DJ. An important role of the biarticular hamstrings is to exert internal/external rotation moments on the tibia during vertical jumping. J Theor Biol. 2018 Oct 14;455:101-108