Ligaments:Knee joint:Collateral ligaments (medial & lateral)

Medial Supporting Structures

* Medial capsuloligamentous complex has 3 layers that vary from anterior to mid to posterior; highly complex, with layers merging at different sites
* Primary stabilizers of femorotibial joint in valgus motion; secondary stabilizers to rotation
* Primary stabilizer against lateral subluxation/dislocation of patella

Superficial Layer (Layer 1)

* Primarily consists of **crural fascia**
* Anteriorly and superiorly, this crural fascia is continuous with fascia overlying vastus medialis
* Sartorius muscle/tendon enveloped by this fascia and is part of superficial layer
* Semimembranosus, semitendinosus, and gracilis are immediately deep to sartorius and superficial fascia
* Tendons of semitendinosus and gracilis blend with fascia of layer 1 and fibers of MCL as they insert distally on tibia
	+ This means semitendinosus and gracilis cross just superficial to MCL (layer 2) and are between layers 1 and 2
	+ Sartorius, semitendinosus, and gracilis together form pes anserinus at their insertion on anteromedial tibia, approximately 5 cm below joint line
		- Sartorius crosses medial knee joint anterior to gracilis, which in turn is anterior to semitendinosus
		- Sartorius has the broadest and most anterior insertion on tibia
		- Gracilis inserts directly adjacent to sartorius, with semitendinosus directly posterior and slightly inferior to gracilis

Middle Layer (Layer 2)

* Anteriorly, superficial (longitudinal) fibers of MCL (layer 2) merge with crural fascia (layer 1)
* Mid knee: Superficial fibers of MCL form layer 2
	+ Vertical fibers
	+ 12 cm long, 1-2 cm wide, 2-4 mm thick
	+ *Origin:* Medial epicondyle
	+ *Course:* slightly anteriorly to insert on tibia approximately 5 cm below joint line
	+ Layer of fat containing medial inferior genicular artery lies between superficial MCL and tibia
* Posteriorly, superficial MCL has a posterior oblique component
	+ Oblique fibers extend from layer 2 posteriorly and fuse with layer 3
	+ Attaches closely to posteromedial portion of meniscus; this conjoined structure is termed the posterior oblique ligament

* Semimembranosus
	+ Complex insertion, involving both middle and deep layers
	+ Main portion inserts on posteromedial tibial plateau
	+ Other attachments
		- Tibia beneath MCL
		- Posteromedial capsule
		- Oblique popliteal ligament
		- Superficial fibers of MCL

Deep Layer (Layer 3)

* Anterior
	+ Continuous with capsule along suprapatellar recess
	+ Patellomeniscal ligament extends anteriorly from meniscus to patella margin
* Mid knee: Capsular layer, sometimes termed deep fibers of MCL
	+ Capsule thickens to form these two ligaments
	+ **Meniscofemoral**
		- 1-2 cm long
		- Extends from outer superior aspect of body of medial meniscus obliquely and proximally
		- Attaches to either superficial MCL or femur
	+ **Meniscotibial (coronary ligament)**
		- Short (1 cm)
		- Extends from outer inferior aspect of body of medial meniscus to tibia just distal to joint line
		- Slightly more posterior than meniscofemoral
	+ Capsular layers fuse posteriorly with oblique fibers of superficial MCL (no fat interposed) to form posterior oblique ligament
* Posteriorly, primarily capsule, but receives fibers from
	+ Semimembranosus
	+ Oblique fibers of superficial MCL (in the form of posterior oblique ligament)
	+ Oblique popliteal ligament
		- Receives fibers from semimembranosus, superficial MCL (posterior oblique ligament), and synovial sheath
		- Envelops posterior aspect of femoral condyle to become a posterior structure

Lateral Supporting Structures:

* Combination of muscles, tendons, and ligaments which contribute to lateral stability of knee

* **Muscles:**
	+ Iliotibial tract
		- Origin: Strong band of deep fascia composed of the fusion of aponeurotic coverings of
			* Tensor fascia lata
			* Gluteus maximus
			* Gluteus minimus
		- Above knee, IT tract has insertion arms to
			* Supracondylar tubercle of lateral femoral condyle
			* Blends with intermuscular septum
		- Main insertion
			* Gerdy tubercle (anterolateral tibia near plateau)
			* Small other attachments to patella and patellar ligament
	+ Biceps femoris
		- Long head joined by short head above knee
		- Main insertion site is head and styloid process fibula
		- Several tendinous and fascial insertional components, including a portion that inserts on posterior edge of IT tract
		- Anterior oblique fibers of conjoined tendon arise from anterior bundle of short head biceps and insert on tibia
	+ Popliteus
		- Tendinous attachment at popliteal sulcus of lateral femoral condyle
			* Inferior and deep to origin of LCL
		- Extends posteromedially through popliteal hiatus (runs deep to fabellofibular and arcuate ligaments)
		- Popliteus muscle attaches to posteromedial aspect of proximal tibial metaphysis
		- Function of popliteus muscle
			* Assist with flexion of knee
			* Internally rotates tibia on femur (at initiation of flexion of knee)
			* Protects posterior horn lateral meniscus by withdrawing it from joint space during flexion and rotation
			* Stabilizes posterolateral corner from rotatory instability
* **Posterolateral Capsule**
	+ Arcuate ligament fibers contribute to capsule laterally
	+ Popliteal tendon (intra-articular but extrasynovial) firmly attached to posterior capsule
	+ Popliteal recess may extend deeply behind tibia (in front of capsule); may have continuity with proximal tibiofibular joint
	+ Lateral gastrocnemius muscle contributes fibers to capsule

Lateral Support System Consists of 3 Layers

* Layer 1 (superficial)
	+ Anteriorly, IT tract
	+ Posterolaterally, superficial portion of biceps
* Layer 2 (middle)
	+ Anteriorly, lateral retinaculum
	+ 2 ligamentous thickenings originate from lateral patella
		- Proximal one terminates at lateral intermuscular septum
		- Distal one terminates at femoral insertion of posterolateral capsule and lateral head of gastrocnemius tendon
* Layer 3 (deep)
	+ Forms lateral part of capsule
	+ Contains several thickenings that function as discrete structures
		- Lateral (fibular) collateral ligament
		- Arcuate complex, consisting of multiple ligaments
	+ Posterolateral corner ligament anatomy is extremely complex

* Posterolateral Corner Structures
	+ All insert on fibular head and provide posterolateral support
	+ Not all are seen with equal reliability on imaging
	+ Posterolateral corner structures may be divided into superficial and deep
		- Superficial: Long and short heads of biceps femoris, and LCL
		- Deep: Posterolateral reinforcements of fibrous capsule, including fabellofibular, arcuate, oblique popliteal, and popliteofibular ligaments
	+ Long head of biceps femoris
		- 2 major tendinous components
			* Direct arm inserts on fibular head
			* Anterior arm inserts just anterior to direct arm on fibular head and continues distally as the anterior aponeurosis that extends anterolaterally around leg
	+ Short head of biceps femoris
		- 2 tendinous components
			* Direct arm inserts on fibular head anterior to styloid process and medial to long head biceps
			* Anterior arm passes medial to lateral collateral ligament and inserts into superolateral edge of lateral tibial condyle, approaching Gerdy tubercle
	+ **The lateral (fibular) collateral ligament** is a cord-like ligament on the lateral aspect of the knee. It originates from the lateral femoral epicondyle and has an oblique course, is joined by the biceps femoris tendon forming the conjoint tendon, which inserts at the head of the fibula.Unlike the medial collateral ligament, it is not attached to the knee capsule or lateral meniscus and as such is more flexible and less susceptible to injury.
		- The tendon of the popliteus (through the popliteal hiatus), a bursa and the lateral inferior geniculate vessels and nerve run deep to the lateral collateral ligament. Proximal attachment is slightly proximal and anterior to sulcus for origin of popliteus tendon
	+ Arcuate ligament
		- Y-shaped
		- Arises from fibular styloid process, just deep to fabellofibular ligament
		- Lateral limb courses straight upward along lateral knee capsule to reach lateral femoral condyle
		- Medial limb crosses over posterior surface of popliteal tendon and attaches to posterior knee capsule
			* Medial limb, along with superior popliteomeniscal fascicle, forms bowed roof of popliteal hiatus
			* At insertion on posterior knee capsule, medial limb arcuate merges with fibers from oblique popliteal ligament
		- Arcuate may be dominant when fabellofibular is absent (or may contain fibers of fabellofibular ligament)
		- Inferior lateral geniculate artery passes anterior relative to arcuate