Knee Joint Anatomy and Related Conditions

Knee Joint Articulation

  • Formed by the articulation of the femur, tibia, fibula, and patella.
  • Articulations include:
    • Femur and patella (patello-femoral joint).
    • Femur and tibia (tibio-femoral joint).
    • Tibia and fibula (tibio-fibular joint).

Distal Femur

  • The femur expands to form two articular condyles.
  • Epicondyles allow attachment for ligaments and muscles.
  • Condyles linked anteriorly by the patellar surface and separated posteriorly by the intercondylar fossa.

Proximal Tibia

  • Widened proximal ends form condyles.
  • Each condyle has flattened articular surfaces called tibial plateaus.
  • Plateaus separated by the intercondylar eminence, which includes medial and lateral intercondylar tubercles (attachments for cruciate ligaments).

Fibula

  • Long, thin, lateral bone of the lower leg.
  • The medial border of the head articulates with the lateral condyle of the tibia.
  • Proximal tibiofibular joint is a synovial plane joint.

Patella

  • Largest sesamoid bone, embedded in the quadriceps tendon.
  • Flat, triangular shape with a flattened base superiorly.
  • The posterior surface has thick articular cartilage and articulates with femoral condyles.
  • The base has attachments for 2 quadriceps muscles.

Ossification Sites

  • Distal femur: 3-6 months.
  • Tibial plateau: Usually present at birth.
  • Tibial tuberosity: 10-12 years.
  • Fibular head: 2-4 years.
  • Patella: Variable, 1-3 ossification sites appear between 3-5 years.

Knee Stability

  • Structures that strengthen and support the knee:
    • Joint capsule.
    • Menisci.
    • Ligaments.
    • Muscles.

Joint Capsule and Menisci

  • Joint Capsule: A tough, fibrous membrane strengthened by extracapsular ligaments, blending anteriorly with the quadriceps tendon.
  • Menisci: "C" shaped fibrous membranes between tibial plateaus and femoral condyles, acting as cushions.

Bursae

  • Small, fluid-filled sacs that reduce friction; approximately 10 in the knee.
  • Suprapatellar bursa: Large extension of the joint capsule, between the distal femur and the quadriceps tendon.

Ligaments of the Knee

  • Extracapsular: Support and strengthen the joint capsule.
  • Intracapsular: Provide stability to the femur and tibia.

Extra-Capsular Ligaments

  • Medial & Lateral Collateral ligaments: Support medial and lateral aspects.
  • Patellar Ligament: Continuation of the quadriceps tendon, attaching to the tibial tuberosity.

Cruciate Ligaments

  • Intra-capsular ligaments.
    • Anterior: From medial intercondylar tubercle to postero-medial aspect of the lateral femoral condyle.
    • Posterior: From posterior aspect of intercondylar eminence to antero-medial aspect of the medial femoral condyle.

Muscles of the Knee & Leg

  • Anterior: Extensor and peroneus groups.
  • Posterior: Flexor muscles (Divided into deep and superficial groups).

Arterial Supply

  • Femoral artery becomes the popliteal artery at the knee.
  • Popliteal artery bifurcates into the anterior & posterior tibial arteries.

Venous Drainage

  • Great saphenous vein drains into the femoral vein.
  • Small saphenous vein drains into the popliteal vein.
  • Anterior & posterior tibial veins merge to form the popliteal vein.

Lipohaemarthrosis

  • Blood and fat fluid levels within the suprapatellar bursa, indicating intraarticular fracture.
  • Bone marrow separates from blood, forming a fat layer on top.

Tibial Plateau Fractures

  • Often associated with significant damage to cruciate ligaments and medial collateral ligaments.
  • 80% involve the lateral tibial plateau.

Patellar Fractures

  • Direct blow can cause vertical, transverse, or comminuted fractures.
  • Violent contraction of the quadriceps can cause transverse fractures.

Bipartite Patella

  • Normal variant (2% of the population).
  • Caused by an unfused secondary ossification center, commonly supero-lateral.

High-Riding Patella

  • The distance between the tibial tubercle and the inferior pole of the patella exceeds the length of the patella by more than 20%.
  • Causes: Abnormal patellar ligament or rupture of the patellar ligament.

Segund Fracture

  • Avulsion fracture from the lateral aspect of the tibial plateau.
  • Associated with tear of the anterior cruciate ligament and damage to the meniscus.

Periosteal Reactions (Periostitis)

  • Can be solid, onion-skin, or spiculated.
  • Useful in determining the aggressiveness of a lesion.

Periosteal Reactions (Periostitis)

  • Onion-skin: Multiple, concentric layers of new bone, indicating variable growth potentially due to acute osteomyelitis or Ewing’s sarcoma.
  • Spiculated: Indicates rapid bone growth; strong indication of malignancy.

Zone of Transition

  • Border between a bone lesion and normal bone.
    • Narrow zone = benign.
    • Wide zone = Aggressive.
  • Only useful in lytic lesions on plain film imaging.