Knee dislocation

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Ahmad H. Othman, M.D.[2]

Synonyms: Patellofemoral dislocation.

Overview

Tibiofemoral joint dislocation is a rare orthopedic condition because of the considerable force required to cause it i.e. road accident. For the same reason, this condition is often associated with concurrent cruciate and one or both lateral collateral ligaments injury. It is a true orthopedic emergencies requiring urgent Orthopedic consultation and intervention because of the high-risk of vascular and nerve injury and are thus potentially limb-threatening injuries.. Immediate reduction followed by careful neurovascular assessment is necessary.

Types

Tibiofemoral dislocations are classified based on the direction of the tibia in relation to the femur. There are five types, with posterior and anterior dislocations being the most common:

1. Posterior – Result from a direct blow to the proximal tibia that displaces it posterior to the distal femur.
2. Anterior – Result from a hyperextension injury to the knee that tears the posterior structures and drives the distal femur posterior to the proximal tibia.
3. Medial – Result from valgus forces to the proximal tibia.
4. Lateral – Result from varus forces to the proximal tibia.
5. Rotatory – Result from indirect rotational forces, usually caused by the body rotating in the opposite direction of a planted foot. Rotatory dislocations are subdivided into anteromedial, anterolateral, posteromedial, and posterolateral. Posterolateral dislocations are irreducible by closed reduction.

Tibiofemoral dislocations are also divided into open and closed based on the presence or absence of lacerations at the knee joint, and as reducible or irreducible.

Complications

The Popliteal artery is tethered across the Popliteal space like a bowstring, making it susceptible to injury during knee dislocation. Up to 40 percent of patients with knee dislocations sustain an associated vascular injury.

The Peroneal nerve winds around the fibular neck. It provides sensation to the dorsum of the foot and controls ankle dorsiflexion. The Peroneal nerve is injured in up to 20 percent of patients with knee dislocations.

Clinical Features

Pain and swelling often limit the physical examination at the initial presentation, but the direction of the dislocation can often be assessed clinically. Often a significant hemarthrosis and ecchymosis are present in addition to the swelling.. The circulation in the foot must be examined because the Popliteal aretery maybe obstructed or injured. This doesn't station and movement should be tested to exclude nerve injury. Be wary, the dislocation may spontaneously reduce but vascular injury may still occur in these cases.

Imaging

Knee X-ray

At least 2 views knee X-ray will assist in classifying the type of dislocation. In addition to the dislocation, the films occasionally reveal tibial spine fracture due to ligament avulsion. If vascular injury is suspected, attempted closed reduction should not be delayed awaiting imaging.

CT Angiography

If there is any doubt about the circulation, such vascular studies are essential to detect and delineate any vascular injury.

See also

• Knee
• Knee examination
• knee pain/swelling