Boniform

The bones of your calf (the tibia and fibula) get moved compared to the bone of your thigh (femur). The bones of your knee are held together by strong bands of tissue, called ligaments. For a knee dislocation to happen, these bands have to tear.

The positional classification system was developed by Kennedy and describes 5 major types of positional dislocation, which are illustrated in Media file 1:



Types of knee dislocation.
• Anterior: Anterior dislocation often is caused by severe knee hyperextension. Cadaver research has shown that approximately 30 degrees of hyperextension is required before dislocation will occur.
• Posterior: Posterior dislocation occurs with anterior-to-posterior force to the proximal tibia, such as a dashboard type of injury or a high-energy fall on a flexed knee. Media file 2 shows a radiograph of a posterior dislocation.



Posterior knee dislocation.
• Medial, lateral, or rotatory: Medial, lateral, and rotatory dislocations require varus, valgus, or rotatory components of applied force. A lateral dislocation is illustrated in Media file 3.


Lateral knee dislocation.
• More than half of all dislocations are anterior or posterior, and both of these have a high incidence of popliteal artery injury. Twenty to thirty percent of all knee dislocations are complicated further by open joint injury (see Media file 4).



Open knee dislocation.

The anatomical classification system was developed by Schenck and modified by Wascher. It describes the injury by its ligamentous/anatomical involvement as follows:
• KD I - Multiligamentous rupture with either cruciate intact
• KD II - Bicruciate rupture with both collaterals intact (rare)
• KD IIIM - Bicruciate and medial collateral ligament (MCL) rupture
• KD IIIL - Bicruciate and lateral collateral ligament (LCL) rupture
• KD IV - Panligament rupture
• KD V - Knee dislocation with periarticular fracture
• C (added to above) - Arterial injury included
• N (added to above) - Nerve injury included

The knee is a very stable joint generally requiring high-energy trauma to produce dislocation. At least 3 major ligaments typically rupture for dislocation to occur. Common mechanisms of injury include the following:
• Motor vehicle collisions
• Auto-pedestrian impact
• Industrial injuries
• Falls
• Athletic injuries