Ligaments 12
Anteromedial and posterolateral bundles.
- Origin
- Medial surface of the lateral femoral condyle, in the posterior part of the intercondylar fossa.
- Insertion
- Anterior intercondylar area of the tibia, anterior and lateral to the medial tibial spine.
- Function
- Restrains anterior translation and internal rotation of the tibia.
Thicker and stronger than the ACL; anterolateral and posteromedial bundles.
- Origin
- Lateral surface of the medial femoral condyle, in the anterior part of the intercondylar fossa.
- Insertion
- Posterior intercondylar area of the tibia, on the posterior surface about 1 cm below the plateau.
- Function
- Restrains posterior translation of the tibia.
Humphrey anterior to the PCL, Wrisberg posterior. Possible pseudotear of the posterior horn on MRI.
- Origin
- Posterior horn of the lateral meniscus.
- Insertion
- Lateral surface of the medial femoral condyle.
- Function
- Stabilize the posterior horn of the lateral meniscus; secondary restraints to posterior tibial translation.
On MRI it can mimic a tear of the anterior horn of the lateral meniscus.
- Origin
- Anterior horn of the medial meniscus.
- Insertion
- Anterior horn of the lateral meniscus.
- Function
- Connects and stabilizes the anterior horns of the menisci.
Deep to the pes anserinus; the deep layer is attached to the medial meniscus.
- Origin
- Medial epicondyle of the femur.
- Insertion
- Superficial layer: medial tibial metaphysis, about 5–6 cm below the joint line. Deep layer: tibial margin below the joint line, through the meniscofemoral and meniscotibial ligaments.
- Function
- Primary restraint to valgus; secondary restraint to external rotation of the tibia.
Extracapsular; part of the posterolateral corner.
- Origin
- Lateral epicondyle of the femur.
- Insertion
- Lateral surface of the fibular head, anterior to the apex.
- Function
- Primary restraint to varus; limits external rotation of the tibia.
Associated with the Segond fracture.
- Origin
- Lateral femur, near the epicondyle.
- Insertion
- Anterolateral tibia, between Gerdy tubercle and the fibular head.
- Function
- Controls internal rotation of the tibia.
Key component of the posterolateral corner.
- Origin
- Popliteus musculotendinous junction.
- Insertion
- Apex of the fibular head.
- Function
- Restrains external rotation of the tibia and varus.
Expansion of the semimembranosus.
- Origin
- Semimembranosus tendon, near its posteromedial tibial insertion.
- Insertion
- Posterior capsule, obliquely toward the lateral femoral condyle.
- Function
- Reinforces the posterior capsule; limits hyperextension and external rotation.
Frequently torn in patellar dislocation.
- Origin
- Femur, between the adductor tubercle and the medial epicondyle.
- Insertion
- Medial margin of the patella (upper two thirds).
- Function
- Main passive restraint to lateral displacement of the patella, especially in early flexion.
Fibrous expansion of the vastus medialis and the fascia.
- Origin
- Vastus medialis and deep fascia.
- Insertion
- Medial margins of the patella and patellar tendon, down to the tibia.
- Function
- Stabilizes the patella medially.
Stronger than the medial; its tightness favors lateral patellar tilt.
- Origin
- Vastus lateralis and iliotibial tract.
- Insertion
- Lateral margins of the patella and patellar tendon, down to the tibia.
- Function
- Stabilizes the patella laterally.
Muscles 24
Biarticular muscle; the belly continues into a tendinous sheet that forms the superficial layer of the quadriceps tendon.
- Origin
- Direct head: anterior inferior iliac spine. Reflected head: supra-acetabular groove (acetabular roof) and hip capsule.
- Insertion
- Base of the patella through the quadriceps tendon and, through the patellar tendon, tibial tuberosity.
- Function
- Extends the knee; flexes the hip.
Deep to the rectus femoris; forms the deep layer of the quadriceps tendon.
- Origin
- Anterior and lateral surfaces of the upper two thirds of the femoral shaft.
- Insertion
- Base of the patella through the deep layer of the quadriceps tendon and, through the patellar tendon, tibial tuberosity.
- Function
- Extends the knee. Its deepest fibers (articularis genus) lift the suprapatellar recess during extension.
The distal oblique fibers (VMO) insert on the medial margin of the patella and counteract its lateral displacement.
- Origin
- Lower part of the intertrochanteric line, spiral line, medial lip of the linea aspera, medial supracondylar line, medial intermuscular septum and adductor magnus tendon (oblique fibers, VMO).
- Insertion
- Medial margin of the patella and quadriceps tendon; medial patellar retinaculum; through the patellar tendon, tibial tuberosity.
- Function
- Extends the knee; the VMO is the main dynamic medial stabilizer of the patella.
The largest head of the quadriceps. Its distal fibers, more oblique, reach the superolateral margin of the patella; its tendinous sheet merges into the lateral margin of the quadriceps tendon.
- Origin
- Upper part of the intertrochanteric line, anterior and inferior margins of the greater trochanter, gluteal tuberosity, lateral lip of the linea aspera, lateral intermuscular septum.
- Insertion
- Lateral margin of the base of the patella and quadriceps tendon; lateral patellar retinaculum; through the patellar tendon, tibial tuberosity.
- Function
- Extends the knee.
With the gracilis and semitendinosus it forms the pes anserinus, a common insertion on the anteromedial tibia about 4 cm below the joint line: the sartorius is its most anterior and superficial component, and its expansion covers the other two tendons.
- Origin
- Anterior superior iliac spine.
- Insertion
- Medial surface of the proximal tibia (pes anserinus), anterior to the gracilis and semitendinosus; expansion to the crural fascia.
- Function
- Flexes the knee and, with the knee flexed, internally rotates the tibia; flexes, abducts and externally rotates the hip.
With the sartorius and semitendinosus it forms the pes anserinus, on the anteromedial tibia: the gracilis inserts between the sartorius (in front) and the semitendinosus (below). Harvested with the semitendinosus for ACL reconstruction.
- Origin
- Body of the pubis (lower half, near the symphysis) and ischiopubic ramus.
- Insertion
- Medial surface of the proximal tibia (pes anserinus), between the sartorius and semitendinosus.
- Function
- Adducts the hip; flexes the knee and internally rotates the tibia.
With the sartorius and gracilis it forms the pes anserinus, on the anteromedial tibia; its long distal tendon is the lowest component.
- Origin
- Ischial tuberosity, with a tendon shared with the long head of biceps femoris.
- Insertion
- Medial surface of the proximal tibia (pes anserinus), posterior and distal to the gracilis.
- Function
- Flexes the knee and internally rotates the tibia; extends the hip.
- Origin
- Ischial tuberosity (superolateral facet).
- Insertion
- Main: posteromedial surface of the medial tibial condyle. Expansions: anterior arm under the MCL, oblique popliteal ligament, posteromedial capsule and popliteus fascia.
- Function
- Flexes the knee and internally rotates the tibia; extends the hip; tenses the posterior capsule and stabilizes the posteromedial corner.
Common tendon with the short head on the fibular head, together with the LCL.
- Origin
- Ischial tuberosity, with a tendon shared with the semitendinosus; sacrotuberous ligament.
- Insertion
- Fibular head (lateral surface, anterior to the apex), with a tendon shared with the short head; expansions to the lateral tibial condyle and the crural fascia.
- Function
- Flexes the knee and externally rotates the tibia; extends the hip.
- Origin
- Lateral lip of the linea aspera, lateral supracondylar line and lateral intermuscular septum.
- Insertion
- Fibular head, with a tendon shared with the long head.
- Function
- Flexes the knee and externally rotates the tibia (monoarticular: no action on the hip).
The femoral vessels pass through the adductor hiatus and become the popliteal vessels.
- Origin
- Adductor portion: ischiopubic ramus. Ischiocondylar portion: ischial tuberosity.
- Insertion
- Adductor portion: gluteal tuberosity, linea aspera and medial supracondylar line. Ischiocondylar portion: adductor tubercle of the femur, through the distal tendon.
- Function
- Adducts the hip; the adductor portion flexes it, the ischiocondylar portion extends it.
The bursa of the Baker cyst lies between its tendon and the semimembranosus. Typical site of strain (tennis leg).
- Origin
- Posterior surface of the femur above the medial condyle and adjacent joint capsule.
- Insertion
- Posterior surface of the calcaneus, through the calcaneal (Achilles) tendon shared with the lateral head and the soleus.
- Function
- Plantar flexion of the ankle; flexes the knee (biarticular).
A fabella (sesamoid bone) may be present in its tendon of origin.
- Origin
- Lateral surface of the lateral femoral condyle, lower part of the lateral supracondylar line and adjacent joint capsule.
- Insertion
- Posterior surface of the calcaneus, through the calcaneal (Achilles) tendon.
- Function
- Plantar flexion of the ankle; flexes the knee (biarticular).
Small belly above the lateral head of the gastrocnemius; long, thin tendon between the gastrocnemius and soleus down to the calcaneus.
- Origin
- Lower part of the lateral supracondylar line of the femur and oblique popliteal ligament.
- Insertion
- Posterior surface of the calcaneus, medial to the Achilles tendon or merged with it.
- Function
- Negligible action: assists the gastrocnemius in ankle plantar flexion and knee flexion.
The tendon, intracapsular but extrasynovial, passes through the popliteal hiatus of the lateral meniscus.
- Origin
- Lateral surface of the lateral femoral condyle (below the epicondyle), through an intra-articular tendon; accessory fibers from the lateral meniscus and the fibular head (popliteofibular ligament).
- Insertion
- Posterior surface of the tibia, above the soleal line.
- Function
- At the start of flexion it internally rotates the tibia (or externally rotates the femur with the foot planted), “unlocking” the extended knee; posterolateral stabilizer.
The tendinous arch of the soleus, between the fibula and the tibia, is crossed by the popliteal vessels and the tibial nerve; deep to the gastrocnemius, with which it forms the triceps surae.
- Origin
- Posterior surface of the head and proximal third of the fibula, soleal line and middle third of the medial border of the tibia, tendinous arch of the soleus.
- Insertion
- Posterior surface of the calcaneus, through the calcaneal (Achilles) tendon.
- Function
- Plantar flexion of the ankle (monoarticular); stabilizes the leg in standing and acts as a venous muscle pump.
Anterior compartment.
- Origin
- Lateral condyle and upper half of the lateral surface of the tibia, interosseous membrane and crural fascia.
- Insertion
- Medial and plantar surfaces of the medial cuneiform and base of the 1st metatarsal.
- Function
- Ankle dorsiflexion and foot inversion; supports the medial longitudinal arch.
Anterior compartment.
- Origin
- Lateral condyle of the tibia, upper three quarters of the medial (anterior) surface of the fibula, interosseous membrane.
- Insertion
- Through four tendons on the dorsal aponeurosis of the 2nd–5th toes, to the middle and distal phalanges.
- Function
- Extends the 2nd–5th toes; assists ankle dorsiflexion and foot eversion.
Lateral compartment; the common fibular nerve passes between the muscle and the fibular neck.
- Origin
- Head and upper two thirds of the lateral surface of the fibula; intermuscular septa.
- Insertion
- Base of the 1st metatarsal and medial cuneiform (plantar side), after crossing the sole in the groove of the cuboid.
- Function
- Everts the foot and plantar flexes the ankle; supports the transverse and longitudinal arches.
The deepest muscle of the posterior compartment; its tendon passes behind the medial malleolus.
- Origin
- Interosseous membrane and adjacent posterior surfaces of the tibia (below the soleal line) and fibula.
- Insertion
- Navicular tuberosity and medial cuneiform; plantar expansions to the other cuneiforms, the cuboid and the bases of the 2nd–4th metatarsals.
- Function
- Foot inversion and plantar flexion; main dynamic stabilizer of the medial arch.
Deep posterior compartment: it runs medial to the tibialis posterior and passes behind the medial malleolus.
- Origin
- Posterior surface of the tibia, medially, below the soleal line.
- Insertion
- Bases of the distal phalanges of the 2nd–5th toes.
- Function
- Flexes the lateral four toes; assists plantar flexion and foot inversion.
Deep posterior compartment, laterally; the tendon then crosses toward the medial malleolus.
- Origin
- Lower two thirds of the posterior surface of the fibula and interosseous membrane.
- Insertion
- Base of the distal phalanx of the great toe (plantar surface).
- Function
- Flexes the great toe; assists plantar flexion and supports the medial arch at push-off.
Anterior compartment: between the tibialis anterior and the extensor digitorum longus, which cover it proximally.
- Origin
- Middle third of the medial surface of the fibula and interosseous membrane.
- Insertion
- Base of the distal phalanx of the great toe (dorsal surface).
- Function
- Extends the great toe; assists ankle dorsiflexion.
Lateral compartment, deep to the fibularis longus; its origin begins about 12 cm below the fibular head. The model stops at mid-leg: only the proximal part of the belly is visible.
- Origin
- Lower two thirds of the lateral surface of the fibula; intermuscular septa.
- Insertion
- Tuberosity of the base of the 5th metatarsal.
- Function
- Everts the foot and plantar flexes the ankle.
Arteries 8
In the adductor canal, under the sartorius, between the vastus medialis and the adductor magnus; it becomes the popliteal artery at the adductor hiatus. In the popliteal fossa it is the deepest structure of the neurovascular bundle, on the popliteal surface of the femur and on the capsule, posterior to the oblique popliteal ligament (it does not pierce it); it divides at the lower border of the popliteus, under the soleal arch.
Arises from the femoral artery in the adductor canal; it gives articular branches to the genicular network and a saphenous branch.
Superior and inferior, medial and lateral (the middle genicular artery, supplying the cruciate ligaments, is not shown): periarticular anastomotic network, target of genicular artery embolization.
Branches of the popliteal artery to the heads of the gastrocnemius, the soleus and the plantaris.
Arises from the popliteal artery and passes anteriorly over the interosseous membrane, descending into the anterior compartment.
From the anterior tibial artery it ascends anteriorly and anastomoses with the inferior genicular arteries.
Continuation of the popliteal artery in the deep posterior compartment; gives rise to the fibular artery.
Arises from the posterior tibial artery and descends along the fibula in the deep posterior compartment.
Veins 5
Superficial to the artery and deep to the tibial nerve; receives the small saphenous vein. A common site of DVT, to be ruled out with Doppler ultrasound.
Usually paired (a single one here); joining the anterior tibial veins they form the popliteal vein.
Accompany the anterior tibial artery, over the interosseous membrane (usually paired, a single one here); at the lower border of the popliteus they join the posterior tibial veins to form the popliteal vein.
Ascends posteriorly on the calf between the heads of the gastrocnemius and drains into the popliteal vein (saphenopopliteal junction, variable level).
Subcutaneous along its whole course: at the knee it passes behind the medial femoral condyle, superficial to the pes anserinus tendons; below the knee it is accompanied by the saphenous nerve.
Nerves 9
Descends in the posterior thigh deep to the long head of biceps femoris, on the adductor magnus; it divides into the tibial and common fibular nerves, usually at the apex of the popliteal fossa (variable level, sometimes more proximal).
The most superficial structure of the popliteal neurovascular bundle; it descends deep to the gastrocnemius and under the soleal arch.
Follows the medial margin of the biceps femoris and winds around the fibular neck, where it is superficial: vulnerable to fractures, compression and trauma (foot drop).
Arises at the fibular neck, deep to the fibularis longus, and descends in the lateral compartment between the fibular muscles and the extensor digitorum longus; it supplies the fibular muscles. It becomes subcutaneous in the distal third of the leg: sensation to the dorsum of the foot.
Pierces the anterior intermuscular septum, passes deep to the extensor digitorum longus and descends on the interosseous membrane, lateral to the anterior tibial artery, between the tibialis anterior and the extensor digitorum longus (further down, the extensor hallucis longus); it supplies the extensor muscles.
Sensory branch of the femoral nerve: in the adductor canal and then behind the sartorius; on the medial side of the knee it pierces the fascia between the sartorius and gracilis tendons, becomes subcutaneous and descends with the great saphenous vein.
Sensation of the anterior skin below the patella; at risk in medial surgical and arthroscopic approaches.
From the tibial nerve, it descends between the heads of the gastrocnemius with the small saphenous vein and contributes to the sural nerve.
From the common fibular nerve; sensation of the posterolateral skin of the leg.
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