Medial Knee Pain: Pes Anserine Anatomy & the Associated Fascia
Muscular anatomy of the pes anserine
The pes anserine is composed of the:
Sartorius (proximal).
Gracilis.
Semitendinosus (distal).
Each individual pes anserine tendon is attached in an almost linear fashion at the lateral edge of the pes anserine bursa (LaPrade et al 2009) with the fascia lata being adherent, less elastic and fixed to the tendons’ insertions of the pes anserinus (Biz et al 2022). Whilst the fascia lata is thinner in the medial region muscle fibres from the vastus medialis and fibers from the posterior fascia of the sartorius makes this fascia become wider and assume a crisscrossed texture as it forms the medial retinaculum along with the quadriceps aponeurosis (Biz et al 2022) and medial joint capsule (and deep medial collateral ligament) (refer layer III) (Wymenga et al 2006).
Sartorius
Origin: ASIS
Insertion: (1) joins to the pes anserine tendon below the tibial tuberosity. (2) Below and medial to the medial tibial tuberosity. (3) Deep fascia of the crus. (Dziedzic et al 2013).
Action (Dziedzic et al 2013):
Initialises hip and knee flexion from the phase of full extension.
Weak external rotator and abductor of the hip joint.
Rotates the tibia and fibula internally with the knee joint flexed.
Gracilis
Origin: pubis, inferior pubic ramus, ischial ramus.
Insertion: upper part of the medial surface of the tibia.
Additional attachments: deep fascia of the lower leg and medial head of the gastrocnemius.
Actions: adducts, flexes and medially rotates the leg. When the foot is fixed the gracilis rotates the femur and pelvis laterally on the tibia.
Semitendinosus
Origin: ischial tuberosity, joint tendon of the biceps femoris and an aponeurosis connecting these two muscles.
Insertion: upper medial surface of the tibia behind the sartorius and distal to the gracilis. At its termination it is united to the gracilis tendon.
Additional attachments: deep fascia of the leg, gracilis, sartorius (Lee et al 2014), medial head of gastrocnemius and biceps femoris.
Action:
Hip extension.
Knee flexion.
With the hip extended an internal rotator of the thigh.
Pes anserine bursa
The pes anserine bursa is located at the upper medial aspect of the tibia, at the insertion of the conjoined tendon of the pes anserine muscles. LaPrade et al (2009) found each individual pes anserine tendon was attached in an almost linear fashion at the lateral edge of the pes anserine bursa. The sartorius tendon attaches more proximally, followed by the gracilis tendon and then the semitendinosus tendon most distally. They also found attachments of the superficial medial collateral ligament to the pes anserine bursa.
The bursa separates the pes anserine tendons from the distal portion of the tibial collateral ligament and the bony surface of the medial tibial condyle. It does not communicate with the knee joint.
The shape of the anserine bursa is of an irregular circular. Lee et al (2014) found its boundaries to be:
Superior: the proximal line of the tibia (around the level of the tibial plateau), and sometimes above this.
Medial: follows the line of the sartorius muscle.
Inferior: 16mm from the inferomedial point of the tibial tuberosity and in relation to the pes anserine tendon.
Sometimes the infrapatellar nerve (from the saphenous nerve) lies near the bursa. Hemler et al (1991) presented a case of a patient with symptoms of medial tibial stress syndrome cured by an injection of the pes anserine bursa. They attributed this to an entrapment neuropathy of the saphenous nerve from a pes anserine bursitis.
Fascial layers of the medial knee
Wymenga et al (2006) identified three layers of the fascia in the medial knee:
Layer I: superficial fascia
The superficial fascia is fascia lata and deep crural fascia.It blends with the pes anserine and tibial periosteum. The superficial portion of layer I adheres to the sartorius. The deep portion of layer I adheres to the gracilis and semitendinosus tendons (Wymenga et al 2006).
In the patellar region, the fascia lata’s interdigitations with the periosteum, peritenon, quadriceps aponeurosis and capsular structures of the deep layers make it difficult to separate the fascia lata from the deep structures i.e. deep medial collateral ligament as a thickening of the medial joint capsule (refer to layer III) (Biz et al 2022) as they blend into one and join the medial retinaculum (Wymenga et al 2006).
The fascia lata envelopes the vastus medialis and sartorius being thinner in this medial region as muscle fibres from the vastus medialis insert into its inner side. Running distal to the insertion of the vastus medialis on the proximal-medial corner of the patella, this fascia becomes wider and assumes a crisscrossed texture due to fibres joining it from the posterior fascia of the sartorius. This wider, crisscrossed part of the fascia, which is adherent to the quadriceps aponeurosis, is the medial retinaculum. The medial retinaculum continues on the medial leg surface, becoming thicker due to the deep interdigitations with the distal insertion of the sartorius muscle and fibres coming from the posterior region of the leg and adhering to the hamstring tendons and fascia. At the pes anserinus level, the fascia is quite adherent, less elastic and fixed to the tendons’ insertions of the pes anserinus (Biz et al 2022).
Layer II: superficial medial collateral ligament
The superficial medial collateral ligament extends from just proximal and posterior to the medial femoral epicondyle to the anteromedial tibial crest 5–7 cm below the joint line. LaPrade (2009) found a majority of the distal attachments of the superficial medial collateral ligament to be to the semimembranosus and pes anserine bursa rather than the tibia. But Biz et al (2022) found it to attach slightly posterior to the insertion of the pes anserinus to which it was connected by fibrous bundles.
Posteriorly these fibres are continuous with the oblique fibres of layer III although this was disputed by LaPrade (2009) who found no clear connection. Anterior to the femoral attachment the superficial medial collateral ligament is continuous with the medial patellofemoral ligament (medial femoral epicondyle —> medial patella). As well as being attached to the superficial medial collateral ligament the medial patellofemoral ligament also receives fibrous expansions from the distal tendinous insertion of the vastus medialis (Biz et al 2022).
Tuncay et al (2007) found the semitendinosus and gastrocnemius tendons to lie between layer I and II.
Just as the superficial portion of layer I adheres to the sartorius, the deep portion of layer I adheres to the gracilis and semitendinosus tendons. Tuncay et al (2007) found two fascial bands associated with the semitendinosus:
Dense 3–4-cm band around the gracilis and semitendinosus tendons approximately 8–10 cm proximal to their tendon insertion.
Fascial band originating from the semitendinosus and extending to the gastrocnemius fascia.
The superficial (and deep) medial collateral ligament resists valgus strain and internal rotation between 0-90º flexion < 30º. The superficial medial collateral ligament also resists external rotation at 0-90º flexion (Requicha & Comley 2021).
Layer III: the true capsular layer and mid-third medial capsular ligament (deep medial collateral ligament)
Layer III thickens and forms the deep medial collateral ligament as a thickening of the medial joint capsule.
The deep medial collateral ligament (layer III) separates the superficial medial collateral ligament (layer II) from the medial meniscus.
The deep medial collateral ligament extends from just distal and posterior to the medial femoral condyle to the meniscus (meniscofemoral fibers); and from the meniscus to a fan-wide tibial attachment (meniscotibial fibers). It’s adherent to the articular capsule (Requicha & Comley 2021).
Proximally the deep medial collateral ligament attachment merges into the superficial medial collateral ligament fibres, but sometimes it has a distinct attachment 0.5 cm distally.
The meniscotibial attachment of the deep medial collateral ligament is clearly separated from the superficial medial collateral ligament but blends with it posteriorly.
Anterior to the superficial medial collateral ligament layer III is thin and loose blending with layer I (fascia lata attachments from the vastus medialis and fibers from the posterior fascia of the sartorius) into the retinaculum.
Conjoint attachments of layers II and III
The conjoined tissue of layers II and III forms the posteromedial capsule. The posteromedial capsule is composed of (Ramos et al 2021):
Posterior oblique ligament.
Posterior horn of the medial meniscus.
Capsular joint.
Semimembranosus tendon insertion. The posteromedial capsule is also known as the ‘semimembranosus corner’ since all the structures in this region are directly related to it.
A condensation of fibres within the posteromedial capsule forms the posterior oblique ligament. This ligament extends from the semimembranosus tendon being orientated obliquely to blend with the posterior margin of the superficial medial collateral ligament and attaches to the posterior-medial surface of the proximal tibia. It posteriorly reinforces the articular capsule. It is an important stabiliser of the medial side of the knee < extension with internal rotation and external rotation at 0-30º of flexion (Requicha & Comley 2021).
The femoral attachment of the posteromedial capsule is located at the adductor tubercle. It attaches to the posterior horn of the medial meniscus and tibia tightening in extension to contribute to the control of posterior tibial translation (Requicha & Comley 2021).
The posteromedial capsule is augmented by:
Semimembranosus tendon: inserts into the medial and posteromedial tibia just below the joint line and creates an “octopus-like weave” with several expansions to the posteromedial capsule and posterior medial meniscus (along with the deep medial collateral ligament). This enables it to function as a dynamic stabiliser against external rotation and anterior translation of the tibia (Requicha & Comley 2021) and valgus strain (Ramos et al 2021).
Adductor magnus tendon: LaPrade et al (2009) found the distal-medial aspect of the adductor magnus tendon had a thick fascial expansion, which fanned out posteromedially and attached to the medial gastrocnemius tendon, the capsular arm of the posterior oblique ligament and the posteromedial capsule.
Gastrocnemius: as well as a thick fascial attachment to the adductor magnus the medial gastrocnemius has a thin fascial band extending to the capsular arm of the posterior oblique ligament (LaPrade et al 2009).
Fascia of the sartorius, gracilis & semitendinosus (Stecco 2015 pg 335)
Medially the myofascial expansions of the sartorius, gracilis and semitendinosus form the pes anserinus superficialis. The myofascial expansion of the semimembranosus form the pes anserine profundis.
Tendons of the gracilis and semitendinosus have longitudinal fascial expansions that fuses with the crural fascia. The semimembranosus has myofascial expansions that attach on to the crural fascia covering the medial head of the gastrocnemius.
Due to the considerable tension from the sartorius, semitendinosus, semimembranosus and gastrocnemius these myofascial expansions may act as fascial tensors stabilising the medial knee when weight bearing.
Fibers from the posterior fascia of the sartorius form the retinaculum, along with the vastus medialis fibers insertion on to the fascia lata (Biz et al 2022) and medial joint capsule (and deep medial collateral ligament) (refer layer III) (Wymenga et al 2006).
References
The fascial band from semitendinosus to gastrocnemius: the critical point of hamstring harvesting An anatomical study of 23 cadavers (2007) Ibrahim Tuncay, Hudaverdi Kucuker, Ibrahim Uzun and Nazim Karalezl
The Anatomy of the Medial Part of the Knee (2009). Robert F. LaPrade, Anders Hauge Engebretsen, Thuan V. Ly, Steinar Johansen, Fred A. Wentorf, Lars Engebretsen
Wymenga AB, Kats JJ, Kooloos J, Hillen B. (2006). Surgical anatomy of the medial collateral ligament and the posteromedial capsule of the knee.
Anatomy and Biomechanics of the Medial Side of the Knee and Their Surgical Implications (2015) Matthew D. LaPrade, Mitchell I. Kennedy, Coen A. Wijdicks, and Robert F. LaPrade
Anatomy of sartorius muscle (2013). D. Dziedzic, U. Bogacka, B. Ciszek
Pes anserinus and anserine bursa: anatomical study (2014). Je-Hun Lee, Kyung-Jin Kim, Young-Gil Jeong, Nam Seob Lee, Seung Yun Han, Chang Gug Lee, Kyung-Yong Kim, and Seung-Ho Han
Saphenous Nerve Entrapment Caused by Pes Anserine Bursitis Mimicking Stress Fracture of the Tibia (1991) Douglas E. Hemler, Wendy K. Ward, Kent W. Karstetter, Phillip M. Bryant
The fascial band from semitendinosus to gastrocnemius: the critical point of hamstring harvesting An anatomical study of 23 cadavers (2007). Ibrahim Tuncay, Hudaverdi Kucuker, Ibrahim Uzun & Nazim Karalezli.
Stecco C (2015). Functional anatomy of the human fascial system.
Requicha F, Comley A (2021). Medial soft-tissue complex of the knee: Current concepts, controversies, and future directions of the forgotten unit
Ramos LA, Ciancio BA, Barbosa MA, Miyashita GK, Yamashita JL. (2021). Semimembranosus Tendon Advancement for the Anteromedial Knee Rotatory Instability Treatment.
Biz C, Stecco C, Crimì A, Pirri C, Fosser M, Fede C, Fan C, Ruggieri P, De Caro R. (2022). Are Patellofemoral Ligaments and Retinacula Distinct Structures of the Knee Joint? An Anatomic, Histological and Magnetic Resonance Imaging Study
