Ligaments:Knee joint:Cruciate ligaments (anterior & posterior)

Cruciate ligaments are in an extrasynovial but intracapsular location

Anterior cruciate ligament

* Multiple separate fascicles which spiral laterally from femur to tibia (fibers rotate externally 90°); fatty tissue is seen between fibers
* **Origin of ACL:** Posteriorly from lateral femoral condyle at intercondylar notch
* **Insertion of ACL:** Anteromedial tibial spine and adjacent plateau; bundles fan out at tibial attachment, forming "foot"
* **Function:**
	+ Primary restraint to anterior tibial translation
	+ Major secondary restraint to internal rotation, minor secondary restraint to external rotation
	+ Minor secondary restraint to varus/valgus at full extension
* **Blood supply:** Middle geniculate artery (pierces posterior capsule from popliteal); lesser supply from fat pad (inferior medial and lateral geniculates)
* **Nerve:** Posterior articular (branch of posterior tibial)

Posterior cruciate ligament

* Appears as a single round ligament but consists of two major parts; rotates 90° from an antero-posterior alignment at femoral origin to medial-lateral insertion at posterior tibia
	+ Anterolateral bundle: Bulk of ligament, taut in flexion, lax in extension
	+ Posteromedial (oblique) bundle: Taut in extension, lax in flexion
* **Origin of PCL:** Mid portion of medial femoral condyle at intercondylar notch
* **Insertion of PCL:** Mid posterior tibia, 1 cm below joint line, where it blends in with posterior capsule
* **Function:** Primary restraint against posterior translation
* Meniscofemoral ligaments
	+ Both arise from posterior horn lateral meniscus and insert on medial femoral condyle; at least one present 70% of time
	+ Posterior (Wrisberg) lies posterior to PCL
	+ Anterior (Humphrey) lies anterior to PCL; intact ligament of Humphrey may mimic an intact PCL
	+ May play a role in secondary restraint to posterior instability; may stabilize lateral meniscus during flexion
* **Blood supply:** Middle geniculate artery proximal and middle thirds; geniculate and popliteal artery base; capsular vessels through entire length.

 Posterior Capsule

* Complex fibrous structure, augmented by extensions of adjacent tendons
* Incomplete, pierced centrally by neurovascular structures
* Proximal attachment: Vertical fibers attached to posterior margins of femoral condyles and intercondylar fossae
* Distal attachment is to posterior margins of tibial condyles and intercondylar areas
* Tendons/ligaments attach to posterior capsule to provide reinforcement
	+ Proximally (medially and laterally): Tendinous heads of gastrocnemius
	+ Posteromedial corner: Semimembranosus and posterior oblique ligament
	+ Posterolateral corner: Arcuate ligament and iliotibial tract
	+ Posterior central: Oblique popliteal ligament

Spaces Within Cruciate/Posterior Capsule

* Synovial membrane surrounds anterior, medial, and lateral portions of cruciates, but is reflected posteriorly from PCL to adjoining parts of joint capsule
* Results in a potential space (PCL bursa or recess)
	+ Seen only when fluid-filled, best on coronal and sagittal planes
	+ Seen posterior to PCL and adjacent to lateral aspect of medial femoral condyle
	+ No contact between PCL recess and the proximal third of the PCL (fat is interposed)
	+ Communicates with medial (femorotibial) compartment of knee
	+ Does not communicate with lateral compartment
	+ If ligament of Wrisberg is present, it lies posterosuperior to PCL recess
* Intercruciate recess
	+ Localized potential fluid collection between ACL and PCL, best seen on sagittal and axial planes
	+ Communicates with either lateral or medial (femorotibial) compartments