Stecco et al (2009) found the crural fascia composed of three layers of parallel, collagen fibre bundles separated by a thin layer of loose connective tissue. Only a few elastic fibres were found.
The arrangement of the collagen fibres gives the crural fascia different degrees of strength in different directions and a non-linear elastic behaviour.
- Superiorly: continuous with the fascia lata, patella, ligamentum patella, tibial tuberosities, tibial condyles and head of the fibula.
- Posteriorly: covers the popiliteal fossa (aka popliteal fascia) and the calf.
- Anteromedially: blends with the periosteum of the tibia.
- Anterolaterally: blends with the head of fibula and lateral malleolus.
- Inferiorly: continuous with the flexor and extensor retinaculum and the Achilles tendon.
Soft tissue attachments
Muscular attachments to the crural fascia include:
- Biceps Femoris.
- Sartorious, Gracilis, Semitendinosus & Semimembranosus.
- Tibialis Anterior & Extensor Digitorium Longus.
The Iliotibial band also strongly attaches to the crural fascia (which intern attaches to the fascia of the peroneal longus) (Wilke et al 2016). The authors found strain to the Iliotibial band caused local movement in the crural fascia and the underlying fascia of the peroneal muscle.
Stecco et al (2014) found the crural fascia to be a structure that can transmit muscular forces at a distance connecting different segments of the limb.
The crural fascia forms the intermuscular septums:
- Anterior intermuscular septum: attached to the anterior border of the fibula.
- Posterior intermuscular septum: attached to the posterior border of the fibula.
Anatomy of the transverse intermuscular septum
- Fibrous stratum extending transversely from the medial margin of the tibia to the posterior border of the fibula.
- Superiorly it is attached to the fascia of the popliteus, which is, in effect, an expansion of the tendon of the semimembranosus.
- Inferiorly continuous with the flexor and superficial fibula retinacula.
The transverse intermuscular septum divides the superficial and deep muscles of the calf.
- Superficial: crural fascia.
- Posteriorly: interosseous surfaces of the tibia and fibula and the interosseous membrane.
- Laterally: anterior intermuscular septum.
- Tibialis Anterior.
- Extensor Digitorium Longus
- Extensor Hallucis Longus.
- Peroneal Tertius.
- Anterior fibulocalcaneus: Lambert and Atsas (2010) identified this anomalous muscle originating from the fibula, anterior intermuscular septum, and the investing fascia of the peroneal tertius to pass anterior to the lateral malleolus and insert on the calcaneus.
Innervation: deep peroneal nerve
Stecco et al (2014) found the fascia in the anterior compartment to be stiffer than in the posterior compartment. This can explain why anterior compartment syndrome is more common than posterior compartment syndrome. However stretching the crural fascia for 120 secs decreases the stress of the crural fascia by 40%.
- Anteriorly: anterior intermuscular septum.
- Posteriorly: posterior intermuscular septum.
- Laterally: crural fascia.
- Medially: lateral surface of fibula.
- Peroneal Longus.
- Peroneal Brevis.
Innervation: superficial peroneal nerve.
- Superficial: crural fascia.
- Laterally: posterior intermuscular septum.
- Posteriorly: fibula, tibia and interosseous membrane.
- Divided into the superficial and deep compartments by the transverse intermuscular septum.
Superficial posterior compartment:
Whilst the crural fascia does not integrate with the calf muscle it does join with the Achilles paratenon 4cm proximal to its calcaneal attachment (Mattiussi et al 2016). Stecco et al (2014) found the crural fascia divides to envelope the Achilles tendon and give origin to the Achilles paratenon.
Deep posterior compartment
- Flexor Hallucis Longus.
- Flexor Digitorium Longus.
- Tibialis Posterior.
- Fibulocalcaneus (peroneocalcaneus) internus (PCI) muscle (of MacAlister): Lambert et al (2011) identified this anomalous muscle arising from the distal third of the fibula, posterior intermuscular septum of the leg, and flexor hallucis longus muscle. This muscle inserted into the inferior surface of the medial calcaneus distal to the coronoid fossa. This insertion differs from the documented insertion of this muscle that attaches to the inferior surface of the sustentaculum tali of the calcaneus or distal to the sustentaculum tali into the medial aspect of the calcaneus.
Innervation: tibial nerve
Stecco et al (2014) examined the macroscopic and microscopic characteristics of the achilles paratendineous tissues (paratenon, epitenon and endotenon) as forming a sheath around the Achilles.
The crural fascia splits to encircle the Achilles tendon and gives origin to its paratenon. Mattiussi et al (2016) found the crural fascia to join with the Achilles paratenon 4cm proximal to the Achilles tubercle on the calcaneus.
In patients with tendonitis a substantial increase in the paratenon is present. This could support the relationship of paratendineous tissue and the crural fascia in the aetiology and pathology of tendonitis (Mattiussi et al 2016).
Neurological relations of the crural fascia
Anatomy of the Peroneal Nerve
Common peroneal nerve
Originates from the dorsal branches of L4-L5 and ventral rami of S1-S2.
Runs from the lateral popliteal fossa between the tendon of the biceps femoris, to which it is bound by fascia, and the lateral head of the gastrocnemius.
Passes into the anterolateral compartment of the leg through a tight opening in the thick fascia overlying the tibialis anterior.
Curves lateral to the neck of the fibula into the fibular tunnel. The floor of the tunnel is formed from the bone and the roof from the musculoaponeurotic arch of the soleus and peroneous longus (Ryan et al 2003). From here the nerve divides into the superficial peroneal and deep peroneal nerve.
Common peroneal nerve innervates the knee and superior tibiofibular joint. The cutaneous branches (lateral sural and sural communicating branches. Innervates the skin on the anterior, posterior and lateral surfaces of the lateral leg.
Superficial peroneal nerve
The nerve runs deep to the the peroneal longus. Sandwiched between this muscle and the peroneal brevis and extensor digitorium longus.
Pierces the crural fascia anywhere from half way down to the distal third of the leg.
The nerve the nerve becomes superficial, crossing the distal fibula from posterior to anterior on average 11cm proximal to the tip of the fibula and usually within 6 – 12 cm of the lateral malleolus tip (Asp et al 2014).
Superficial peroneal nerve innervates: peroneal longus, peroneal brevis and skin of anterolateral leg.
Asp et al (2014) and Tomaszewski et al (2017) found great anatomical variations in the superficial peroneal nerve.
Deep peroneal nerve
The nerve runs deep to the peroneal longus coursing obliquely anteriorly deep to the extensor digitorium longus.
Runs down the interosseous membrane descending with the anterior tibial artery.
Deep peroneal nerve innervates: tibialis anterior, extensor hallucis longus, extensor digitorium longus and peroneal tertius. Ankle joint.
Lateral terminal branch: innervates extensor digitorium brevis. Tarsal and 2-4 Mt-Phl joints
Medial terminal branches: innervates the cutaneous interosseous area between 1-2 toes and 1 Mt-Phl joint.
Points of entrapment
- Sural nerve: perforates the popliteal fascia.
- Common peroneal nerve: Jaeyeon et al (2016) identified the main sites of entrapment of the common peroneal nerve as: between the two heads of the peroneus longus, between the peroneus longus and the posterior intermuscular septum, between the peroneal and tibialis anterior muscles in the anterior intermuscular septum, in the thick tendinous fascia superficial to the soleus and between the origin of the soleus and peroneus longus as an anatomical anomaly.
- Common and superficial peroneal nerve: Hiramatsu et al (2016) identified the peroneal longus as a source of entrapment after an inversion strain. The authors identified the peroneal longus as a source of entrapment at the fibula tunnel and as the superficial peroneal nerve ran behind the peroneous longus.
- Superficial peroneal nerve: Tzika et al (2015) found an entrapment site of the superficial peroneal nerve due to mechanical compression of the nerve at its exit from the crural fascia.
- Accessory superficial peroneal nerve: Paraskevas et al (2014) found the superficial peroneal nerve presents great anatomic variability. They reported a case where an accessory superficial peroneal sensory nerve was encountered. The nerve originated from the main superficial peroneal nerve trunk, proximal to the superficial peroneal nerve emergence from the crural fascia, and followed a subfascial course. After fascial penetration the nerve was distributed to the skin of the proximal dorsum of the foot and lateral malleolar area. A potential entrapment site of the nerve was observed as the accessory nerve travelled through a fascial tunnel at the lateral malleoli area while perforating the crural fascia.
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Acute Achilles Paratendinopathy following Major Injury of the Crural Fascia in a Professional Soccer Player: A Possible Correlation? (2016). Gabriele Mattiussi, Michele Turloni, Pietro Tobia Baldassi, and Carlos Moreno
Common peroneal nerve palsy due to deep tendinous fascia superficial to the soleous muscle: a case report (2018) Jaeyeon Kim, Hak-Cheol Ko, Byung-Chul Son
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