What is a Dashboard Knee Injury and it's Effect on the PCL? February 04, 2016 12:16
A dashboard injury occurs almost always occurs during flexion of the knee. When the is bent knee recieves a direct blow to the top of the shinbone, the tibia can get pushed backwards with enough force to inflict damage to the PCL.
Posterior View Of PCL / Back of Right Knee
A dashboard injury refers to an injury caused to the PCL or posterior cruciate ligament, which is one of the major ligaments found in the human knee. The posterior cruciate ligament lies deep within the knee and gets its name because it attaches the posterior, or back, of the tibia to the femur. This configuration helps the PCL resist backward motion of the lower leg or tibia.
A posterior cruciate ligament injury can occur when the knee is bent and the upper tibia suffers direct impact causing the shinbone to be pushed backwards below the knee. With enough force, this can result in a tear or rupture of the PCL as the tibia is pushed back too far. This type of injury is often called a dashboard injury as it can occur during car accidents as the driver's or passenger's bent leg suffers a direct blow into the dashboard causing posterior cruciate ligament damage. Dashboard type injuries can also occur during sporting activity when an athlete falls or gets tackled on a bent knee or when the bent knee collides with an immovable object.
PCL injuries can vary dramatically in the degree on damaged inflicted and range from minor injuries that are difficult to assess and diagnose to more serious cases which show obvious signs of physical injury and severe knee instabilities.
One of the indicators of possible injury to the posterior cruciate ligament is often a divot or 'dent' in the subjects patella tendon. A posterior sag test can help confirm whether PCL damage exists or not. The test is performed as the subject lays flat on their back and lifts the injured leg in the air, flexed at a 90-degree angle. A positive sign of injury will result in the posterior sag of the tibia and an indent in the patella tendon caused by gravitational pull.
The protocol for the rehabilitation of a PCL injury will depend on the degree of damage and whether surgery is recommended or not. Frequently, rehab is often recommended over surgery with PCL injuries but as always one should consult the advice of a medical professional.
Posterior View of the Knee and PCL
As shown in the diagram above, the PCL is an extremely large and strong ligament and therefore a lot of force is required to rupture it completely. It is 1.5 to 2 times the size of the more commonly injured and discussed anterior cruciate ligament or ACL.