The patellar dislocation pearl was the less serious cousin to this one: tibiofemoral (or true knee joint) dislocation reductions.

In general, tibiofemoral dislocations are a high energy traumatic injury BUT can be seen in patients with minimal trauma. The usual mechanisms are high velocity contact sports, motor vehicle accidents (knee vs dashboard), and falls. Men are more commonly affected. Knee dislocations are rare, making up 0.02% of orthopedic injury presentations. 50% will self-reduce prior to evaluation, so it is very important to keep a high index of suspicion when patients present with a knee injury.

Knee dislocations are a true surgical emergency. These injuries are fraught medicolegally; the injury is rare, the diagnosis is often delayed or missed due to self-reduction, and they have very high rates of serious neurovascular injury/compartment syndrome often leading to amputation. 86% of patients who experience lower extremity ischemia for more than six hours following a knee dislocation ultimately require above the knee amputation. Obese patients are at significantly higher risk of neurovascular injury and missed diagnosis despite suffering dislocations more often than those without an elevated BMI.

Considerations:

Anterior and posterior dislocations are the most common, but lateral, medial, and rotational are all possible

25% of knee dislocations will have a nerve injury, most commonly the common peroneal/fibular nerve which controls dorsiflexion of the foot and toes
Up to 40% of patients will have associated vascular injuries, most commonly the popliteal artery.

Posterior and open dislocations carry the highest risk.
Vascular surgery should be immediately consulted with diminished/absent pulses, pale/dusky limb, paresthesias/paralysis

It is imperative to assess all lower extremity pulses including PT, DP, and popliteal in patients with a suspected dislocation
Absent or diminished pulses require immediate reduction (if joint is still dislocated) - do not wait for x-ray if the dislocation is obvious
The presence of pulses does not fully exclude vascular injury.

Collateral circulation can mask a popliteal artery occlusion.
Ankle-brachial index (ABI) is mandatory to rule in the diagnosis and should be obtained on all patients with a suspected knee dislocation

ABI is calculated by dividing the systolic blood pressure at the ankle by the systolic blood pressure in the upper arm. Normally the pressure is higher in the lower extremities (giving an ABI >1.0).

An ABI of less than 0.9 is suggestive of a vascular injury and warrants an immediate vascular surgery consultation and CTA.

Exam findings are usually notable for gross joint instability when the knee is fully extended or with varus/valgus stress and drawer tests– be careful as the unstable joint may slip and cause/worsen a vascular injury.

Swelling and joint effusions may obscure finding or make exam difficult

X-ray and CT/CTA are necessary to look for fractures and to assess for vascular injuries

Consent:

Risks: pain, vascular injury, damage to nerves/vessels/cartilage/bones, iatrogenic fractures, development of compartment syndrome, knee instability, need for repeat procedures, need for operative management, development of post traumatic arthritis
Alternatives: operative management
Contraindications: open fracture/dislocation, “dimple” or “pucker” sign showing entrapment of skin/soft tissues (indicating an irreducible rotational dislocation), evidence of skin necrosis, failure of reduction after multiple attempts

Relative contraindications: extreme obesity, unstable fractures, significant concomitant injury

Supplies:

Your healing hands
Procedural sedation

Blocks may be inadvisable as it can obscure important exam findings

Multiple assistants
A long leg knee immobilizer with a hinge or supplies to place a long leg posterior splint

How to do it:

Knee dislocations tend to be unstable due to the disruption of multiple stabilizing ligaments in the joint. These will reduce easily but can quickly re-dislocate
Position patient supine or reclined on a stretcher
Apply longitudinal traction/countertraction to the leg

One clinician holds the ankle or lower leg and applies continuous axial/distal traction
Assistant holds the upper leg at mid-thigh to provide countertraction
This is usually sufficient to reduce

Alternative method for posterior dislocation

Stand at the foot of the bed
Place on hand on the femoral condyles and stabilize the femur by applying steady proximal axial pressure
Hold the lower leg with one hand and pull, providing continuous distal axial traction
While continuing to apply distal axial traction, use the hand on the lower leg to pull the tibia upwards and reduce

If longitudinal traction alone does not reduce:

For anterior dislocations:

Apply traction/countertraction as above
The assistant should apply continuous axial traction on the lower leg
Clinician begins applying countertraction to the upper leg as above and slowly lift the femur to reduce

For posterior dislocations:

Apply axial traction/countertraction as above

Have the clinician who is holding the lower leg use one hand to continue applying axial traction
Take other hand and place behind the proximal tibia
While continuing to apply traction on the ankle, use the second hand behind the tibia to apply upward pressure/lift the tibia to reduce

For medial/lateral dislocations

Apply axial/longitudinal traction and counter traction as above with the clinician providing the traction on the lower leg and the assistant providing counter traction on the upper leg
The hand should apply traction on the ankle while the second hand is placed at the proximal tibia
Pressure is applied to the proximal tibia in the opposite direction of the dislocation (apply medial pressure for a lateral dislocation, lateral for a medial)

Post Reduction Care:

Pulses/ABIs should be repeated post reduction and frequently monitored while in the ED
Compartment syndrome can develop – have a high suspicion if the patient is complaining of increasing pain after reduction
Knee should be immobilized with the joint in 20-30 degrees of flexion to prevent re-dislocation – use a hinged knee immobilizer or a long leg splint with appropriate flexion at the knee
These patients are generally admitted for serial vascular checks and compartment monitoring
Patients will always need surgery

Surgery will be emergent if vascular injury compromise or nerve impingement is present
In uncomplicated cases that have been stable with no change in neurovascular exam and well controlled pain, patients may be sent home after an observation period for outpatient surgery in a few weeks.
Non operative management and longer wait times to operation have been associated with worse functional outcomes and increased complications

References:

Videos:

https://www.youtube.com/watch?v=aN7zDxtyHy8 – posterior dislocation reduction
https://www.youtube.com/watch?v=MkTLo6imnR0&t=174s – anterior dislocation reduction, patient has a common peroneal nerve palsy on exam, reduction part starts at 2:45 or so
https://accessemergencymedicine.mhmedical.com/MultimediaPlayer.aspx?MultimediaID=16604696 – anterior reduction