Knee

Anatomy

• Complex joint:
• No rotary motion in full extension.
• Rotation enabled on flexion: up to 40 degree of rotation at 90° flexion (relaxes tendons)
• Above Knee:
  • Vastus medialis - pulls patella medially (prevents lateral dislocation)
  • Vastus intermedius
  • Vastus lateralis
• Medial:   (Aka Pes anserinus)
  • Sartorius
  • Gracilis
  • Semitendinosus
    • Tendon inserts on the oblique popliteal ligament. Adding posterior mobility to the ligament and medial meniscus during flexion.
• Lateral:
  • Iliotibial tract
  • Tendon of biceps femoris.

• Static Stabilizers (Ligaments).
  • MCL
    • Most commonly injured ligament.
    • Ligament is taught only in extension.
    • Limit forward glide of tibia on femur and limit rotation + abduction.
  • Collaterals are twice as effective in limiting rotational laxity as cruciate ligaments.
  • LCL
  • Posterior Capsule (prevents against anteromedial or anterolateral rotatory instability).
  • Cruciate ligaments:
    • Extend from intercondylar fossa of femur to intercondylar eminence of tibia.
    • Named on basis of their tibial attachment.
    • ACL
      • Prevents anterior displacement of tibia and excessive lateral mobility in flexion or extension.
      • Prevents hyperextension of knee.
      • ACL tears are rarely isolated, often associted with MCL tears.
      • Plentiful vascular supply.
      • When ruptures, hemarthrosis is almost always present!
    • PCL
      • Primary static knee stabilizer against rotation.
      • if ruptured, anteposterior and mediolateral instability can occur.
      • If ruptured, rarely isolated, usually associated with serious knee injuries.
• Dynamic Stabilizers (Tendons/muscles)
  • Quadriceps tendon - dynamic stabilizer
    • Combination of tendons: vastus medialis, intermedialis, lateralis, and rectus femoris. 
    • Primary dynamic stabilizer of knee.
    • Attaches to patella and continues distally to tibial tubercle as patellar tendon.
  • Pes anserinus  (medial)
    • Conjoined tendons:
      • Gracilis, sartorius, and semitendinosus.
    • Stabilize against excessive rotary and valgus motion.
  • Semimembranosis (lateral)
    • Tendon has three extensions:
      • To posterior capsule (posterior oblique ligament), and tightens the capsule when stressed.
      • Posterior horn of medial meniscus (pulls posteriorly during flexion)
      • Medial tibial condyle - serving to flex and internally rotate the knee.
  • Other Lateral Stabilizers
    • 1. Iliotibial band - inserts lateral tibial condyle.
    • 2. Biceps femoris - lateral stability, knee flexion + external rotation.
    • 3. Popliteus muscle (posterir muscle inserting with a Y-shaped tendon called arcuate ligament, another limp inserts into posterior portion of lateral meniscus providing posterior mobility of lateral meniscus during flexion). 
  • 

• Imaging:
  • AP
  • Lateral
  • Oblique (for tibial plateau and spines).
  • Otherviews:
    • Skyline (patellar view of supine patient with knees slightly flexed - beam down to feet).
      • See Patella relationship to femoral condyles.
    • Tunnel view  (patient lying prone, knee flexed to 40° from vertical)
      • See intercondylar notch.

Ottawa Knee Rules

Proximal Tibia Fractures

• Fractures can be classified:
  • Intra-articular - "Condylar" (tibial plateau)
  • Extra-articular
    • Tibial spine
    • Tubercle
    • Subcondylar Regions
• Classification:
  • Schatzker classification:
    • NOTE: tibial plateau fracture defined as  >4mm of inferior displacement.
    • Types I to III result of low energy trauma
    • Types IV to VI is high energy.
  • Type 1 - lateral condyle (aka splint fracture)
    • typically young patients because bone resists depression.
    • Suggests lateral menistal injury
  • Type II - lateral condyle + depression (aka split-depression)
    • Usually people >30yo bc subchondral bone is weaker.
  • Type III - Depression of lateral condyle.
    • Likely joint is unstable.
  • Type IV - Medial condyle (need higher force to fracture medial condyle)
    • High energy - high incidence of cruciate ligaments and popliteal artery injuries.
    • May be associated with # of intercondylar eminence.
  • Type V - Bicondylar
    • Possess varying articular depression and displacement.
    • Medial is usually split, and lateral is often depression (can be split)
  • Type VI - Bicondylar + fracture between diaphysis-metaphysis
    • High energy, often comminuted.
  • 
• Mechanism:
  • Fall from height (20%)
  • Automobile-pedestrian where car bumper strikes over proximal tibia. (50%)
  • Lateral Tibial plateau #'s: abduction force on the leg.
  • Medial plateau: adduction
• Imaging:
  • If clincally suspected but negative xrays: do CT!
  • Can do tibial plateau view (tibial plateau slopes down anatomically)
  • Look for avulsion fractures:
    • fibular head
    • femoral condyles
    • intercondylar eminence
  • Look for widened joint space (fracture of opposite condyle)
  • Look for knee effusion (occult fracture, peripheral meniscus, ACL/PCL, patellar dislocation)
    • Knee effusion appears as distance between two fat pads just superior to patella on lateral view
  • 
• Tx
  • Immobilize with long-leg posterior mold
  • Need operative fixation.
  • (CAN treat non-operatively, but very high degree of complications)
• Complications:
  • Loss of ROM (prolongued immobilization)
  • Degenrative arthritis
  • Angular deformity

Tibial Spine Fractures

• Isolated uncommon: usually 8-14yo.

Patellofemoral

• Atraumatic
• Mid-ROM pain 45-90° flexion.
• Sitting long periods.
• Pain with walking down stairs.
• Mechanism:  Young people that grow rapidly, associated with patellar maltracking.
• Exam:
  • Can squat, but mid-ROM pain.
  • J-sign: sitting on bench - extend knee and it goes laterally.
  • Lean on Patella pushing it laterally --> pain.
  • "Clarke's Test" put hand on quad tendon.. push down against quads and ask patient to contract quad --> pain.