Knee Joint Complex Anatomy and Motion

Knee Joint Complex

• The knee is an intermediate joint in the lower limb, exhibiting a condylar structure.
• The knee joint has both femoral condyles (convex) and tibial glenoids (concave).
• It primarily has one degree of freedom, but also involves accessory movements.
• The knee joint comprises femoro-patellar and femoro-tibial joints.
• The femoro-patellar joint involves the patella and femoral trochlea, along with pre-patellar cartilage.
• Menisci are fibrocartilage structures that act as compression transmitters.

Range of Motion

• Flexion:
  • Active flexion with extended hip: 120°
  • Active flexion with flexed hip: 140°
  • Estimated passive flexion with extended hip: unknown
  • Estimated passive flexion with flexed hip: 160°
• Extension:
  • Active extension: 0°
  • Passive extension: 0°
• Internal Rotation: 30°
• External Rotation: 60°

Main Knee Muscles

• Quadriceps: The primary extensor muscle group.
• Sartorius: Involved in flexion and internal rotation.
• Hamstrings:
  • Semitendinosus: contributes to flexion and internal rotation.
  • Semimembranosus: contributes to flexion and internal rotation.
  • Femoral biceps: contributes to flexion and external rotation.
• Popliteal: Involved in flexion and internal rotation.

Tests

• Lunge Test: Patient performs a lunge, assessing for valgus collapse, internal rotation, and adduction of the hip, as well as knee valgus and external tibial torsion. It clinically assesses hip separator and knee internal rotator hyperactivity.
• Squat Test: Patient does a squat, observing for abnormalities like posterior pelvic tilting and "bat wing" characteristics. This test helps identify issues related to hamstring tension.
• Vastus Medialis and Adductor Magnus Co-Contraction Test: Patient performs knee extension while pressing a ball between the knees. Abnormal results can indicate hypotonia in the vastus medialis.
• Monopodal Support Test with Fitball: Patient performs a monopodal stance with a fitball. This tests spring extension of the knee and compensations for vastus medialis hypotonia.
• Antero-medial Lunge: Patient performs a lunge directed medially, assessing the number of repetitions in 30 seconds and internal/external hip rotator weakness/strength.
• Balance Sit and Reach: Involves a monopodal stance with a reach for the opposite heel. Instability and repetition counts within 30 seconds assess gluteus medius and vastus medialis strength.