Entrapment neuropathy of the saphenous nerve in the subsartorial (adductor) canal can account for:
- Anteromedial thigh and shin symptoms.
- Knee medial joint line pain.
- Restless leg syndrome (Lewis 1991).
- Medial tibial pain (Hemler et al 1991).
- Upper region of the popliteal fascia (Satoh et al 2016). These authors found the popliteal fascia innervated by either the posterior femoral cutaneous or saphenous nerve.
Outlined is a review of the anatomy of the subsartorial canal including its associated anatomical structures including:
- Fascia Lata.
- Medial Intermuscular septum.
- Sartorius fascia.
- Vastofemoral and Vastoadductor membrane.
- Fascia overlying the Obturator Externus and Adductor Magnus.
Subsartorial (adductor) canal
Standring (2015) identified the subsartorial (adductor) canal as a intermuscular tunnel occupying the distal two thirds of the medial aspect of the thigh.
The boundaries of the subsartorial canal include:
- Proximal: apex of the femoral triangle.
- Distal: distal attachment of the tendon of the adductor magnus.
- Roofed: Sartorius muscle and its fascia and the vastoadductor membrane (Oliveira et al 2009).
- Posterior: (proximal) Adductor Longus and (distal) Adductor Magnus (and its fascia that continues over the Obturator Externus. Kumka, 2010).
- Anterolateral: Vastus Medialis.
The contents of the subsartorial canal include:
- Superficial femoral artery.
- Femoral vein.
- Femoral nerve (Saphenous nerve and nerve to the Vastus Medialis)
Oliveira et al (2009) found the connective tissue of the adductor canal continuous with the outer layer of the vessels. They identified this as a cause of inhibiting the vessels from sliding freely during movement and causing a dynamic compression mechanism.
Soft tissues associated with the subsartorial canal
The soft tissues associated with the Subsartorial canal are:
The deep investing fascia which envelopes the muscles of the thigh is known as the Fascia Lata. It splits into two distinct layers at several locations in the thigh, either to enclose muscles such as Gluteus Maximus and Tensor Fascia Lata, or to create openings such as the saphenous opening for the great saphenous vein.
Proximally the fascia lata has a complete attachment to the pelvic bone: anteriorly to the pelvic rami and inguinal ligament, laterally to the iliac crest (with a thickening at the iliac tubercle) and posteriorly to the ischial tuberosity, sacrotuberous ligament, sacrum and coccyx (Huang et al 2013).
Lyte (1979) found at the level of the inguinal ligament:
- The fascia iliaca descends, attaching to the lateral third of the inguinal ligament, to then blend with the fascia lata.
- The fascia lata blends with the transversalis fascia at the anterior wall of the femoral sheath.
- The fascia lata forms the Lacunar (Gimbernat's) ligament (inguinal ligament --> pectineal ligament).
(No author, 1835) found the part of the fascia lata attaching on to (and forming) part of the Lacunar ligament and forming the anterior part of the femoral canal is stretched when the thigh is extended and rotated outwards. The author found this produced a stretch on the crural arch (inguinal ligament) drawing it downwards without producing much effect upon the Lacunar ligament. By flexion and rotation inwards of the thigh the opposite effect was produced.
Stecco et al (2013) found the fascia lata continuous with the gluteus fascia and the crural fascia. It is thicker laterally and posterolaterally. They found it's not adhered to the muscles of the thigh due to a loose connective tissue between the fascia lata and the muscles. There are three exceptions:
(1) In the distal thigh the fascia lata gives origin to some fibers of the vastus lateralis and vastus medialis.
(2) Where the fascia lata gives a myofascial origin to the bicep femoris.
(3) There is a complete adhesion of the vastus medialis to the fascia lata along its entire course.
Fourie (2011) found the distal attachments of the fascia lata to be:
(1) Patellar retinaculum.
(2) Medial and lateral collateral ligaments of the knee.
(3) Crural fascia.
The fascia lata forms the medial and lateral intermuscular septum:
(1) Medial intermuscular septum: described below. It seperates the Vastus Medialis from the Adductor Longus and Magnus. It attaches to the linea aspera and medial supracondylar ridge (Burnet et al 2004).
(2) Lateral intermuscular septum: it seperates the anterior and posterior compartments of the thigh. It lies between the Vastus Lateralis and Bicep Femoris and attaches to the linea aspera of the femur (Fairclough et al 2006). Fibers from the lateral intermuscular septum run from the femur to the iliotibial band. These form the horizontal fibers of the iliotibial band (Evans 1979)
As well as the vastus lateralis, vastus medialis and the bicep femoris the fascia lata also receives muscular insertions from the gluteus maximus. These muscle fibers attach onto the iliotibial band and the lateral intermuscular septum.
The iliotibial band is merely a lateral expansion of the fascia lata and made up of three layers: superficial, middle and deep.
Superficial and middle layer: encloses the tensor fascia lata anchoring it to the iliac crest. These layers unite at the distal end of the tensor fascia lata to form a tendon for the muscle. These two united layers receives fibers from the gluteus maximus and runs down the lateral thigh. As it courses down the lateral thigh Fairclough et al (2006) found the Iliotibial band continuous with the strong lateral intermuscular septum, which was firmly anchored to the linea aspera of the femur. Evans (1979) found fibers from the lateral intermuscular septum form the horizontal fibers of the iliotibial band. Distally, after coursing through the Biceps Femoris and Vastus Lateralis, Fairclough et al (2006) found the iliotibial band attached to the region of, or directly to, the lateral epicondyle of the femur by strong fibrous ‘tendonous’ strands and then more ‘ligamentous’ strands between the lateral epicondyle of the femur and Gerdy's tubercle on the tibia. Conversely to popular belief no bursa was found between the tendonous fibrous bands of the Iliotibial band and femur just adipose tissue. Evans (1979) found additional attachments to the patella retinaculum and lateral meniscus. Additional muscular attachments to the Iliotibial Band include the Biceps Femoris and Vastus Lateralis.
Deep layer: The deep layer of the iliotibial band merges where the superficial and middle layers fuse distal to the tensor fascia lata (Putzer et al 2017). From here it runs deep attaching to the vastus lateralis and rectus femoris fascia. Coursing deeper still it follows the iliofemoral ligament to attach to the supraacetabular fossa between the tendon of the reflected head of the rectus femoris and the hip joint capsule. It resists hip extension.
With reference to the subsartorial canal the fascia lata's importance lies in its attachments to the Adductor Longus, Adductor Magnus, it's strong attachments to the Vastus Medialis and Medial Intermuscular Septum. The importance of these are discussed below.
Burnet et al (2004) describes a fascial envelope around the Sartorius in the upper thigh which in a majority of cases continues distally in the lower part of the muscle. Fourie (2011) found the upper third of the sartorius adhered to its fascia by septa passing between the deep surface of the fascia and the muscle fascicles. The middle third showed a transition between the tight adherence of the proximal part of the muscle to the fascia and the loose relation of the distal third.
Posteriorly this is reinforced by the thick aponeurotic roof of the subsartorial canal: the vastofemoral and vastoadductor membrane.
Vastofemoral and Vastoadductor membrane
The Vastofemoral and Vastoadductor membrane are two membranes in the subsartorial canal. They can be continuous with each other or discontinuous. Oliveira et al (2009) describes the Vastoadductor membrane as being the roof of the subsartorial canal.
(a) Vastofemoral membrane
Vastofemoral membrane lies proximal in the subsartorial canal. It runs between the Vastus Medialis and femoral artery (Elazab & Elazab 2017).
(b) Vastoadductor membrane
Tubbs et al (2007) found the vastoadductor membrane to originate from the medial intermuscular septum. Elazab & Elazab (2017) found the fibers of the vastoadductor membrane to originate from the adductor magnus tendon and the fascia overlying the adductor magnus. This fascia runs:
- Proximally: from the adductor magnus over the obturator externus (Kumka 2010).
- Distally: from the adductor magnus tendon a thick fascial expansion fans out attaching to the medial gastrocnemius tendon, the capsular arm of the posterior oblique ligament, and the posteromedial knee capsule (LaPrade et al 2009).
The vastoadductor membrane lies distally to the Vastofemoral membrane in the subsartorial canal. It bridges from the adductor longus proximally and adductor magnus distally to the vastus medialis (Elazab & Elazab 2017)
Tubbs et al (2007) measured the vastoadductor membrane 7.6cm long. They measured 28cm from the ASIS to the proximal boarder of the vastoadductor membrane and 10cm from the adductor tubercle to the distal boarder.
Subsartorial (adductor) canal
All ready described above this intermuscular canal is bound on all sides by muscular and fascial tissue capable of causing an entrapment neuropathy and vascular claudication.
Medial Intermuscular Septum
From superficial to deep the medial intermuscular septum joins the fascia lata superficially before travelling deep through the thigh seperating the Vastus Medialis in the anterior compartment and the Adductor Longus and Magnus in the posterior compartment. Travelling deeper still it attaches to the medial lip of the linea aspera of the femur and its medial supracondylar ridge (Burnet et al 2004).
Tubbs et al (2007) found the medial intermuscular septum to give origin to the vastoadductor membrane. This membrane bridges across the medial intermuscular septum from the vastus medialis to the adductor longus (proximally) and adductor magnus (distally). In contrast Elazab & Elazab (2017) found the vastoadductor membrane to originate from the adductor magnus tendon and fascia.
Satoh et al (2016) found the popliteal fascia to be a potential source of pain from its relation to the saphenous nerve.
These authors found the popliteal fascia to be a single aponeurotic sheet acting as a three-layered retinaculum:
- Layer one. The superficial layer of the popliteal fascia. Strongly interwoven with the epimysium of biceps femoris along its lateral aspect and with that of the semimembranosus along its medial aspect. This ensures that the flexor muscles remained in their correct positions.
- Layer two. The intermediate layer: arose from the medial side of biceps femoris and merged medially with the superficial layer.
- Layer three. The deep layer: stretched transversely between the biceps femoris and the semimembranosus.
These authors found this fascia was innervated by the posterior femoral cutaneous or saphenous nerve. These nerves are closely related and distributed to densely packed collagen fibers in layer one (superficial layer) as free or encapsulated nerve endings. Therefore this fascia could be a source of pain in the upper region of the popliteal fossa.
Pes anserine bursitis
Lee et al (2014) found 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 injection of the pes anserine bursa. They attributed this to an entrapment neuropathy of the saphenous nerve from a pes anserine bursitis.
Considerations in the myofascial treatment of the Subsartorial canal
Obturator Externus & Adductor Magnus
Elazab & Elazab (2017) found the fascia of the Obturator Externus and the Adductor Magnus gives origin to the Vastoaddutor membrane. The Adductor Magnus also forms a boundary for the Subsartorial canal.
Origin: the external bony margin of the obturator foramen and a few fibres from the obturator membrane.
Insertion: Trochanteric fossa with some fibres extending towards the piriformis fossa.
Action: primary function of external rotation with the hip in flexion.
With the hip in extension the Obturator Externus does not function as an external rotator. In fact the Obturator Externus stretches slightly when extended and externally rotated (Gudena et al 2015).
Stretching the obturator externus
The mean efficiency of stretching the muscle in internal rotation is (Gudena et al 2015):
(1) Most effective in hip extension.
(2) Secondly most effective in 90 degrees hip flexion.
(3) Thirdly most effective in a neutral hip position.
Vaarbakken et al (2015) found the most effective way to stretch the Obturator Externus was in extension/abduction/internal rotation.
As well as forming an opposing border for the Subsartorial canal with the vastus medialis the vastus medialis obliquus attaches to the adductor magnus tendon.
Origin: pubis to the ischium
Insertion: a point between the greater trochanter and the linea aspera, down the linea aspera to the medial condyle (adductor tubercle) of the femur.
The superior fibers that run horizontally to the more proximal part of the linea aspera flex the the thigh
The fibers that attach to the linea aspera laterally rotates the thigh.
The fibers that attach distally on the femur at the adductor tubercle medially rotates the thigh (Reimann et al 1996).
The more vertical fibers that run more distally on the linea aspera and adductor tubercle extend the thigh.
As well as forming a boundary for the Subsartorial canal the Vastus Medialis is an attachment for the vastoadductor membrane. The more distal Vastus Medialis Obliquus (as opposed to the proximal Vastus Medialis Longus) attaches on the adductor magnus tendon.
Origin: femur and adductor magnus tendon.
Insertion: patella tendon
Action: Pulls the patella medially and has a minimal roll in knee extension. Mixed results if the Vastus Medialis activates with joint hip adduction and knee extension.
The Vastus Medialis muscle fibers run at an almost horizontal angle (50 to 55 degs to the shaft of the femur) giving it a minimal function in knee extension (Miao et al 2015). Studies are mixed supporting the activation of the Vastus Medialis with simultaneous knee extension and hip adduction with Miao et al (2015) finding only in patellofemoral pain did this actively recruit the Vastus Medialis.
The Adductor Longus forms a boundary for the Subsartorial canal.
Origin: ramus superior of the pubic bone and deep portion of the anterior pubic ligament.
Insertion: linea aspera
van de Kimmenade et al (2015) found the muscle a relatively thin muscle.
The adductor longus forms a continuous 'complex' with the abdominal muscles (Schilders et al 2017):
- Pyramidalis: the Adductor Longus has attachments to the pyramidalis and deep anterior pubic ligament.
- External oblique and anterior rectus sheath: via the superficial anterior pubic ligament the aponeurosis of the external oblique and anterior rectus sheath connects with the fascia lata over the adductor area.
Action: flexion, adduction and internal rotation and external rotation of the femur.
Flexion and abduction intensifies the lateral rotating function of the Adductor Longus. Extension and adduction intensifies the internal rotating function of the Adductor Longus (Reimann et al 1996).
The Sartorius fascia attaches to the Vastoadductor membrane.
Insertion: (1) joins to the pes anserine tendon below the tibial tuberosity. (2) Below and medial to the medial 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.
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