The Knee Joint

Anatomy

  • The knee is more complex than a simple hinge joint.
  • It is made of three articulations, the patellofemoral, the tibiofemoral, and the tibiofibular joints.
  • The ligamentous components of the joint are the lateral collateral ligament (LCL), medial collateral ligament (MCL), the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL).
  • The extensor mechanism includes the quadriceps tendon, the patella, and the patellar ligament.
  • The important cartilaginous structures are the medial and lateral menisci.
  • The medial meniscus is connected with the MCL; the lateral menicus is not.

Management
Prehospital

  • Prehospital care entails immobilization to prevent further neurovascular injury, elevation and ice.

History

  • The emphasis is on mechanism.
  • The following are classical injuries associated with common mechanisms of injury: The Knee Joint
  • Head on traffic collision
    		•  Posterior cruciate ligament injury
  • Twisting injury (i.e., skier)
    		•  Anterior cruciate ligament tear
  • Contact with lateral force
    (i.e., football player)
    		•  MCL tear, medial meniscus tear and ACL tear
    (aka O�Donaghue�s triad)
  • Hyperextension
    		•  ACL injury followed by PCL injury
  • Turn with tibia rotated
    in opposite direction
    		•  Patellar dislocation

Physical Exam

  • Neurovascular exam is crucial especially if knee dislocation is suspected.
  • If dislocation has occurred, immediate reduction with sedation and analgesia is recommended.
  • After reduction, neurovascular exam must be reevaluated.
  • Inspect for areas of swelling, tenderness, and ecchymosis. The presence of an acute effusion suggests hemarthrosis and possible ACL tear.
  • Aspiration of the knee may reveal clues to the underlying injury.
  • Hemarthrosis is highly associated with cruciate ligament tears. Fat suggests the presence of fracture.
  • All lacerations in the vicinity of the knee joint must be considered to involve the joint space until proven otherwise.
  • Assess the stability of the knee joint by evaluating the ligaments and the menisci.
  • The Lachman test is the most sensitive test for determining ACL disruption. It is performed in 15� to 30� of flexion. The proximal tibia is pulled anterior relative to the tibia.
  • Excessive movement relative to the opposite side is considered positive. Anterior and posterior drawer tests in 90� flexion also help to diagnose ACL and PCL injuries respectively.
  • The medial and lateral collateral ligaments can be tested by assessing the joint under valgus and varus stress respectively.


    Figure 8.3. The Lachman test. (From Rockwood and Green, fort fourth ed., pg 2070)

  • The medial and lateral menisci can be tested by performing the McMurray or grind test although the specificity and sensitivity are low.
  • Examine the knee for range of motion, both active and passive. Always remember to identify other injuries by examining the femur, tibia, and patella.

Radiography

  • Plain Films
  • The Ottawa Knee Rules were described in order to delineate which patients require plain films.
  • Standard views are the AP and lateral.
  • Other views may be helpful to elucidate individual injuries if suspected:
  • Cross-table lateral
    		•  May detect fat-fluid level, pathognomonic of fracture
  • Oblique views
    		•  Fracture or loose foreign body
  • Notch view
    		•  Osteochondral fracture
  • Sunrise view
    		•  Patellar injuries
  • Plateau view
    		•  Tibial plateau fracture
  • CT and MRI are rarely used in emergency imaging of the knee.
  • MRI provides superior visualization of soft tissue structures including menisci and cruciate ligaments, but is usually performed by the primary care or orthopedist in a nonurgent setting.

    Knee Joint


A knee X-ray series is only required for knee injury patients with any of these findings:
  1. age 55 yr or older, or
  2. isolated tenderness of patella*, or
  3. tenderness at head of fibula, or
  4. inability to flex to 90�, or
  5. inability to bear weight both immediately and in the emergency department (4 steps).** * No bone tenderness of knee other than patella.

** Unable to transfer weight twice onto each lower limb regardless of limping.

Figure 8.4. Ottawa Knee Rule for use of radiography in acute knee injuries. From Stiel et al. Implementation of the Ottawa Knee Rule for the use of radiography in acute knee injuries. JAMA 1997; 278:2075-2079.

Table Classification of ligament sprains
STRETCH-GRADE I
A first-degree sprain is really a microscopic tear and can be treated with rest, ice, and
protection with crutches and/or a splint.
PARTIAL-GRADE II
A second-degree sprain should be immobilized to prevent the ligament from tearing
completely.
COMPLETE TEAR-GRADE III
Third-degree sprains may require surgery. Therapy is somewhat controversial.
Classification, Treatment and Disposition
Soft Tissue Injury
Injury Classification Treatment Disposition
Anterior Grades I-III Compressive dressing orthopedic emergencies
Cruciate from midthigh to referral for grade III.
Ligament (ACL), midcalf. May include 24 h
Posterior Cruciate Ice, Elevation recheck
Ligament (PCL)
Collateral Grades I-III Knee immobilizer Grades I and II follow
Ligament tears. and crutches. with primary care
(MCL and PCL) Ice compression physician. Grade III
elevation and rest. requires orthopedic referral
Meniscus NA Reduction of �locked Orthopedic referral.

       
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