Joints of the knee

Question 1

Tibiofemoral joint

Answer 1

• Synovial biaxial condylar joint
• Distal femoral condyles articulate with the medial + lateral condyles of the tibia
• The two directions of movements are:
  
  • sagittal plane - flexion/extension
  • horizontal plane - medial & lateral rotation

Tibiofemoral joint - articular surfaces distal femur
- asymmetrical condyles
- medial femoral condyle is convex with longer articulation surface than the lateral femoral condyle

Tibiofemoral joint – articular surfaces tibia
- Tibial condyles – asymmetrical – medial has a longer, concave articular surface

Question 2

Patellofemoral joint

Answer 2

• Multiaxial plane joint
• Articulation b/w the posterior surface of the patella + the anterior patellar surface of the distal femur
• Patella is a sesamoid bone located within the tendon of the quadriceps muscle group
• a fat pad sits on the anterior tibia proximal to the insertion of the patellar tendon

Question 3

Knee joint capsule

Answer 3

• Composed of muscle tendons + their expansions, further reinforced by ligaments. Lined by synovial membrane
• Postero-superiorly: capsule attaches to the articular surface (popliteal surface) of femur, + extends laterally to attach to the head of the fibula
  Posteriorly reinforced by:
• Oblique popliteal ligament (OPSM) expansion of semimembranosus tendon
• Arcuate popliteal ligament (posterolaterally)
• Gastrocnemius
• Laterally: the joint capsule is reinforced by the ITB
• Medially: the joint’s capsule is reinforced by MCL
• Anteriorly: thin, partly deficient due to the patella
  - reinforced by capsular ligaments – medial + lateral patellar retinaculum

Question 4

Knee joint capsule - plicae and bursae

Answer 4

• plicae are folds within synovial layer of the joint capsule, with several located around the knee joint
• bursae: the popliteal, suprapatellar + medial head of gastro bursa communicate with the synovial cavity

Question 5

OKC + CKC tibiofemoral joint movts

Answer 5

Sagittal
- OKC knee flexion: tibia flexes relative to the femur
- CKC knee flexion: femur flexes relative to the tibia
- OKC knee ext: tibia extends relative to the femur
- CKC knee ext: femur extends relative to the tibia
Horizontal/transverse
- OKC knee medial rot:

Question 6

Tibiofemoral joint motion – locking

Answer 6

• Energy efficient mechanism, whereby medial rot of the femur on the tibia, or lateral rot of the tibia on the femur, occurs at the end of knee extension range (~ last 0-20° ext), creating increased knee joint stability.
• 3 important features:
  
  1. Longer curved medial femoral condyle
  2. Tibial medial condyle more concave
  3. MCL stretched less rapidly than LCL
• The ligaments become taut, + menisci are tightly wedged, creating a close-packed position
• Lateral rot of the femur on the tibia must then occur before the knee can flex again. The popliteus muscle helps to ‘unlock’ the knee

Question 7

Tibiofemoral joint motion – locking mechanism

Answer 7

• Last 20-30° of knee extension (in CKC position):
• ACL (first) then PCL (resists the post translation of femur), MCL, LCL are taut
• Hamstrings, gastroc, ITB providing both active or passive tension
• Anterior horn of medial meniscus supports the PCL to resist ant translation
  “Locked out knee”: when ACL and LCL/MCL are fully taut