Knee dislocation
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Ahmad H. Othman, M.D.[2]
Synonyms: Tibiofemoral 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:
- Posterior – Result from a direct blow to the proximal tibia that displaces it posterior to the distal femur.
- Anterior – Result from a hyperextension injury to the knee that tears the posterior structures and drives the distal femur posterior to the proximal tibia.
- Medial – Result from valgus forces to the proximal tibia.
- Lateral – Result from varus forces to the proximal tibia.
- 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
Popliteal artery injury is the most dangerous potential complication following tibiofemoral dislocation. 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. Of note, popliteal artery lesions or thrombosis may not become clinically apparent for up to several weeks following the acute knee 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.
Other potential short-term complications include compartment syndrome of the leg and deep vein thrombosis. Complications may also include pseudoaneurysm, instability, arthrosis, stiffness, and chronic pain. Associated fractures may occur, including injuries of the tibial plateau, tibial shaft, and the proximal fibula.
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 artery maybe injured or obstructed. Distal senstation 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 and reduction planning. 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.
Treatment
Contraindications and precautions
Posterolateral dislocations are irreducible by closed reduction. Whenever this type is identified, the patient should be transferred to the operating room and an open reduction should be performed promptly.
Analgesia and sedation
Provide appropriate analgesia. Generally this means procedural sedation. If the clinical condition allows, general anesthesia may be contemplated because the muscle relaxation will ease the reduction especially in patients with delayed presentation where the soft tissue swelling and muscle spasm might hinder the reduction.
Method of reduction
Closed reduction of the dislocated knee should be performed immediately and must not be delayed if there is any sign of vascular impairment. Only patients with good peripheral pulses may undergo pre-reduction imaging.
Generally two clinicians are required to reduce the knee. The principle of traction and counter-traction is employed with vertical traction being sufficient most of the time and if unsuccessful, reverse mechanism of injury may be employed i.e. vertical and medial force applied to the tibia in a lateral knee dislocation.
For isolated anterior or posterior dislocations, the knee should reduce easily with a satisfactory clunk. Special care should be taken to avoid applying any pressure at the popliteal fossa during reduction to avoid further injury to the popliteal artery.
If there is an open wound, or vascular damage which needs operation, the opportunity is taken to repair the capsule and ligaments. Otherwise, these structures are left undisturbed.
Postreduction Management
Initial care and evaluation - Immediately after the tibiofemoral joint is reduced, look closely for signs of vascular injury. Meticulous evaluation of the extremity's circulatory status includes palpating the distal and popliteal pulses, measuring an ankle-brachial index (ABI), and performing a screening duplex ultrasound, if available. Obtain emergent bedside consultation by a vascular surgeon if the limb manifests ANY sign of vascular compromise. Such signs may include diminished or absent pulses, pale or dusky skin, paresthesias, and paralysis.
Once reduction is achieved the limb is arrested on a backslap with the knee bent in 15° of flexion. When swelling has subsided, a cast is applied and worn for 12 Weeks. Thigh muscles exercises are practiced from the start. Weight-bearing in the plaster is permitted as soon as the patient can lift the leg. knee movement is regained once the plaster is removed.
Imaging - Obtain anteroposterior and lateral radiographs to confirm reduction
In either case, consult vascular surgery emergently should any arterial injury be identified. For patients without apparent vascular injury at the time of the initial evaluation, close surveillance, including daily vascular checks, must be performed for several days.
After a thorough vascular assessment, magnetic resonance imaging (MRI) may be obtained to determine the extent of injury following knee dislocation. MRI allows for the identification of ligamentous injury as well as injuries to the joint capsule, meniscus, and articular cartilage. Bone marrow edema, occult fractures, and bruising may also be found. Identifying the full spectrum of injury assists surgical planning. If multiple ligamentous injuries were not anticipated but are identified on MRI, immediate imaging of the popliteal artery should be performed considering the severity of the injury.
Follow-up Care
After postreduction radiographs are performed, the patient is admitted to the hospital overnight for close monitoring of the limb's vascular function. Serial reassessment of the neurovascular status is of the utmost importance, and exams should be performed every three to four hours for a minimum of 24 hour.
One-week interval XR may be performed to confirm reduction. Close Orthopedic follow-up is necessary to assess the extent of ligamentous injury and the need for surgical reconstruction.
Upon discharge, patient should be educated about signs of vascular compromise and instructed to return to the ER if they experience any of the symptoms.
External Links
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC535529/
http://acldoc.org/Files/knee%20dislocate744.pdf
http://journals.lww.com/jcat/Abstract/2009/01000/Extensor_Mechanism_Injuries_in_Tibiofemoral.27.aspx
See also