General

• The anterior compartment of the leg is responsible for extension of the toes, dorsiflexion at the talocrual joint, and inversion/eversion at the subtalar joints.

Fascial specializations

• crual fascia - investing fascia making up the anterior boundary of the anterior compartment
• Anterior intermuscular septum attaches to fibula - separates the anterior from the lateral compartment
• Interosseous membrane - separates the anterior from the posterior compartment
• Extensor retinaculum supports redirection of extensor tendons, tendon sheaths

Boundaries

• Superior - crual fascia knee joint capsule
• Inferior - continuous with dorsum of foot
• Anterior - crual fascia
• Posterior - interosseous membrane
• Lateral - anterior intermuscular septum and fibula
• Medial - lateral contour of tibia

contents and relationships

• Muscles - from medial to lateral
  • tibialis Anterior - origin from tibia and insertion on plantar side of 1st cuneiform and navicular
    • dorsiflexion of talocrural joint and inversion of subtalar joints
  • extensor hallucis longus - origin from tibia/interosseous membrane to extensor hood of great toe
    • extends the great toe, dorsiflexes the talocrural joint, inversion of subtalar joints
  • extensor digitorum longus- origin from fibula/interosseous membrane to extensor hood of toes 2-5
    • extends toes 2-5, dorsiflexes talocrural joint
  • peroneus tertius - origin from lower third of fibula to base of fifth metatarsal
    • eversion of subtalar joints, dorsiflexion of talocrural joint
• Nerves
  • Deep peroneal nerve - pierces posterior and anterior intermuscular septa (crual fascia)
    • crosses lateral aspect of the neck of the fibula prior to entering anterior compartment
    • pierces posterior and anterior intermuscular septa
    • applies to anterior surface of interosseous membrane and deep to extensor hallucis longus
    • runs along lateral aspect of anterior tibial artery
    • supplies cutaneous innervation to space between toes 1 and 2
• Vasculature
  • anterior tibial artery - from posterior tibial artery within posterior compartment, enters anterior compartment at superior free edge of interosseous membrane
  • fibular circumflex artery - superior in compartment
  • peroneal artery (posterior compartment) - inferior, branches pierce interosseous membrane
  • branches of the malleolar anastomosis

Support of the arches of the foot

• tibialis anterior supports the medial longitudinal arch as "suspension" element
• Peroneus tertius supports the lateral longitudinal arch as "suspension" element

Injury

• Damage to the anterior compartment would cause the foot drop due to unopposed flexors of the talocrural joint (posterior compartment). The medial and lateral longitudinal arches are weaken. The pulse at the dorsalis pedis is weakened due to compression within the anterior compartment. Paraesthesia is expected between the first and second toes. Decompression might require cutting the crural fascia.

Bones and Articulations

• Synovial hinge joint between the femoral and tibial condyles.
• Tibial plateau is cupped by the medial and lateral menisci.
• Femoral condyles
• Patella articulates anteriorly as a sesamoid bone in the quadriceps tendon.

ligaments

• Medial collateral ligament (attached to medial meniscus).
  • medial femoral epicondyle to the medial tibial condyle.
  • resists abduction of tibia.
• Lateral collateral ligament (interval between lateral meniscus and ligament transmits popliteus m.
  • From lateral femoral epicondyle to the head of the fibula
  • resists adduction of tibia.
• Anterior cruciate ligament
  • from lateral posterior femoral condyle to anterior aspect of tibial intercondyler eminence.
  • resists forward displacement of the tibia.
• Posterior cruciate ligament.
  • from posterior medial femoral condyle to posterior aspect of tibial intercondyler eminence.
  • resists posterior displacement of tibia.
• Oblique popliteal and arcuate ligaments strengthen the posterior joint capsule.
• coronary, transverse genicular, and meniscofemoral ligaments secure the menisci.

Cavities and bursae

• Synovial joint cavity
  • attaches to edges of menisci - articular surface is intrasynovial
  • Alar folds anterior to anterior crucial ligament - posterior limit of midsaggital synovial cavity
  • reflections of the synovial membrane along the intercondylar fossa - cruciate ligaments are extrasynovial.
  • continuous with suprapatellar bursa (quadriceps bursa)
• prepatellar bursa
• infrapatellar bursa

Capsular joint cavity

• ligaments making up the capsule (above)
• intercondylar area is extrasynovial
• popliteus tendon within cavity

Muscles, movements and limitations of movement

• Primarily flexion and extension (hinge joint).
• Some rotation (30-40 degrees) is possible when the knee is flexed.
• Flexion is primarily by the hamstrings, short head of biceps, gracilis, and sartorius.
  • innervated by tibial portion sciatic, peroneal portion sciatic, obturator, and femoral nerves respectively.
  • minor flexion by popliteus, gastrocnemius, and plantaris.
  • flexion is limited by quadriceps, cruciate ligaments, and by opposing soft tissues (calf and thigh).
• Extension is primarily by the quadriceps and tensor fascia lata.
  • innervation by femoral nerve and superior gluteal nerve.
  • extension is limited by hamstrings, cruciate ligaments, collateral ligaments, posterior joint capsule.
• Medial rotation of tibia is primarily by popliteus, semitendonosus, gracilis, and sartorius.
  • innervation by tibial nerve, tibial portion sciatic, obturator, and femoral nerves respectively.
  • limitation of movement by collateral ligaments
• Lateral rotation of tibia is primarily by biceps femoris.
  • innervation by tibial and peroneal portions of sciatic nerve.
• limitation of movements by collateral ligaments.
  • Abduction and adduction is limited by the medial and lateral collateral ligaments.

Fascial specializatons

• patellar retinaculum
• iliotibial tract
• investing fascia

Vascular supply

• Genicular anastomosis
  • Superior and inferior, medial and lateral genicular arteries, and middle genicular from the popliteal artery.
  • descending genicular artery from femoral artery and descending branch from lateral femoral circumflex artery
  • Fibular circumflex artery, and anterior and posterior tibial recurrent arteries from the anterior and posterior tibial artery
  • Accompanying veins

Innervation (Hilton's Law)

• small branches of the femoral, obturator, and sciatic, and tibial nerves pierce the joint capsule.

"Screw Home"

• Consider when the knee is extended with the foot planted on the ground. In this case, the tibia is fixed by virtue of the planted foot. Thus, rotation of the knee occurs as movement of the femur. The femur rotates medially as the knee "locks" in extension. The lateral femoral condyle is smaller than the medial femoral condyle. As the knee is extended the smaller condyle moves through its arc before the medial condyle. Thus, movement stops at the lateral condyle while the femoral medial condyle continues to move further posteriorly. This movement results in a medial rotation of the femur.
• This medial rotation torques the joint capsule and it's ligamentus specializations (medial and later collateral ligs). The "twisting" of the capsular ligaments causes the region to tighten. This firmly approximates the femoral condyles to the tibial plateau and "locks" the knee. The femur "screws" medially onto the tibial plateau due to the larger medial condyle and the twisting of the capsular ligaments. On extension, the knee goes through a "screw home" rotation that results in "close packing."
• The final medial rotation of the femur is driven by the line of gravity moving anterior to the axis of the knee joint. Thus, locking the knee is driven by gravity. Unlocking the knee requires muscular involvement. The popliteus, having lateral superior to medial inferior attachments, posterior to the axis of the knee, can to lateral rotate the femur (reverse origin and insertion) and, thus, unlock the knee joint.

Pericardial Cavity and Sac

• Within the middle mediastinum
• The pericardial cavity is a collapsed serous cavity within the pericardial sac that surrounds, but does not containing, the heart
• The content of the pericardial cavity is, under nonpathological conditions, a small amount of serous fluid
• Provides reduced friction to accomodate movement of the heart

Layers of the sac and cavity

• Fibrous layer of parietal pericardium - outermost
• Serous parietal pericardium - lining the inner surface of the fibrous parietal pericardium
• Visceral pericardium (epicardium) - outer surface of myocardium

Relationships, Stabilization, and Reflections

• Superior - Superior mediastinum and contents
  • Support by attachments to great vessels and by arterial mesocardium
  • Reflections at the arterial mesocardium help to define the transverse sinus
• Inferior - diaphragm
  • Support by the central tendon and the inferior vena cava
• Anterior - anterior mediastinum
  • Support by pericardiosternal ligaments
  • Thymus
  • Internal thoracic, musculophrenic, and anterior intercostal vessels
  • Sternocostal recesses
• Posterior - posterior mediastinum and contents (esophagus, aorta, and much more)
  • Support by contents of posterior mediastinum
  • Reflections at the venous mesocardium define the oblique sinus
• Lateral (left and right) - pleural cavities
  • Within the adjacent endothoracic fascia - pericardiacophrenic vessels, phrenic nerves, vagus nerves,
  • Sternocostal recesses

Vascularization

• Fibrous pericardium - based on location, the pericardicophrenic, internal thoracic, anterior intercostal, musculophrenic, bronchial, esophageal, and superior phrenic vessels
• Visceral pericardium - based on loction, the coronary arteries and branches

Lymphatic Drainage

• mediastinal nodes - bronchopulmonary nodes - paratracheal nodes - bronchomediastinal lymph truncks
• parts of fibrous paracardium drain to parasternal nodes
• Parasternal and paratracheal drainages combine to form the bronchomediastinal lymph trunks
• right - right lymph duct into brachiocephalic v.
• left - thoracid duct or independently into left brachiocephalic

Innervation

• Fibrous pericardium - somatic (sharp pain) innervation by phrenic and intercostal nerves
• Visceral pericardium - visceral (dull pain) innervation by superficial and deep cardiac plexuses which, in turn, are formed by cardiac nerves derived from the vagus nerves and from the sympathetic trunks
• Anatomic pathways for pain sensation (visceral) from the visceral pericardium follow - cardiac plexuses, splanchnic nerves, rami communicantes, spinal nerve ventral ramus (intercostal nerve), dorsal root (dorsal root ganglion at T2), spinal cord at T2 (T1-4)

Cardiac Tamponade

• Fluid in the pericardial sac limits movement of the heart and, thus, compromises cardiac output.