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Structure

Knee joint

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This is the date the draft was written, not a medical review date.

The knee is the largest and most complex synovial joint, a modified hinge with limited rotation. It comprises the tibiofemoral and patellofemoral articulations and relies on ligaments and menisci rather than bony shape for stability.

Terminologia Anatomica (Latin): Articulatio genus · Open in the 3D atlas

Location

It lies between the distal femur, proximal tibia and the patella. The popliteal fossa behind contains the popliteal vessels and the tibial and common fibular nerves.

Structure

Medial and lateral menisci (C-shaped fibrocartilage) deepen the tibial plateau. The anterior cruciate ligament (ACL) prevents anterior tibial translation and the posterior cruciate ligament (PCL) prevents posterior translation; the medial (tibial) and lateral (fibular) collateral ligaments resist valgus and varus stress. The medial meniscus is attached to the medial collateral ligament.

Blood supply

The genicular anastomosis is formed by the superior, middle and inferior genicular branches of the popliteal artery, the descending genicular artery, the anterior and posterior recurrent tibial arteries and the descending branch of the lateral circumflex femoral artery. Menisci receive a direct blood supply only at their periphery (roughly the outer 10 to 30%).

Innervation

Femoral (via nerves to vasti), tibial, common fibular and obturator nerves supply the joint. Knee pain may therefore reflect hip disease.

Function

Flexion and extension with small rotation in flexion. The screw-home mechanism (medial rotation of the femur on the tibia in terminal extension) locks the knee, and the popliteus unlocks it. Quadriceps extend; hamstrings, gastrocnemius and popliteus flex.

Clinical correlations

ACL rupture (anterior drawer, Lachman test) typically follows twisting injuries; the classic combined injury (the unhappy triad) involves the ACL, medial collateral ligament and medial meniscus, although this pattern is debated. Meniscal tears cause locking and joint-line tenderness. Other conditions: osteoarthritis, patellar dislocation and bursitis (prepatellar, infrapatellar).

Common exam points

  • ACL: anterior drawer and Lachman tests; PCL: posterior drawer, posterior sag.
  • Medial meniscus is attached to the medial collateral ligament and is injured more often than the lateral.
  • Popliteus unlocks the knee at the start of flexion.
  • Genicular anastomosis supplies the joint; popliteal artery is vulnerable in posterior dislocation.
  • Common fibular nerve winds around the fibular neck and may be injured in lateral knee trauma.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Netter FH. Atlas of Human Anatomy. Elsevier — Tier 3 (textbook)

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