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Knee Dislocation | Diagnosis & Treatment

Knee dislocation is a relatively rare occurrence, but it can pose a serious threat to the limb due to potential damage to blood vessels. Because of this vascular risk, immediate orthopedic attention is essential.

The exact frequency of this injury might be underestimated since a substantial portion (20-50%) of dislocations resolve on their own without medical intervention. The occurrence of a knee dislocation requires significant harm to the surrounding soft tissues, including the tearing of at least three or four major ligaments within the knee joint.

In most instances, both the anterior and posterior cruciate ligaments (ACL and PCL) are affected, alongside varying levels of harm to collateral ligaments, capsule components, and menisci. There’s also a chance of injury to the common peroneal nerve and popliteal blood vessel. Additionally, it’s common to find associated fractures involving the tibial eminence, tibial tubercle, fibular head or neck, as well as capsule avulsions.

See Also: Knee Meniscus Anatomy

Mechanism of Injury

The majority of knee dislocations stem from high-energy incidents. The orientation of the dislocation is influenced by the atypical force direction.

Mechanisms of injury and techniques for reducing knee dislocations:

Type of DislocationInjury MechanismReduction Approach
AnteriorForceful hyperextension of the knee beyond -30°Employ axial limb traction in conjunction with varus/valgus stress, lifting the distal femur
PosteriorApplication of posterior-directed force to the proximal tibia of a flexed knee, akin to a ‘dashboard’ injuryCombine axial limb traction and knee extension, while elevating the proximal tibia
Medial/lateralVarus force that disturbs lateral supporting structures / Valgus force that disrupts medial supporting structuresBlend axial limb traction with lateral/medial translation of the tibia
RotatoryVarus/valgus force with a rotational element involving derotation of the tibiaCombine axial limb traction with derotation of the tibia

Clinical Evaluation

Knee joint dislocation diagnosing is typically straightforward; however, because some dislocations can spontaneously reduce, the patient might present with a knee that appears relatively normal. Subtle indicators of injury, such as minor abrasions, slight swelling, or complaints of knee pain, might be the only noticeable irregularities. If an obvious dislocation is present, immediate reduction should be initiated.

Arterial damage can occur in up to 32% of dislocations, often in association with posterior dislocations. Signs of arterial injury include a cold, bluish foot with absent pulses in the pedal vessels, as well as tenderness, swelling, and bruising in the popliteal fossa. These signs necessitate prompt arterial assessment and management. After any reduction procedure, repeat assessments of neurovascular status are important due to the potential for vasospasm or thrombosis resulting from an unexpected tear in the artery lining, which could lead to delayed ischemia hours or even days after reduction. Injury to the popliteal vein is uncommon.

Nerve damage occurs in 16–43% of dislocations, usually in connection with the posterolateral type. The peroneal nerve is more frequently injured than the tibial component. Such injuries often involve neurapraxia, although complete transection is a rare possibility. The extent of ligamentous injury correlates with the degree of displacement, typically occurring when the displacement exceeds 10–25% of the ligament’s resting length. Pronounced instability following reduction indicates considerable disruption of the soft tissues.

See Also: Knee Meniscus Tear

Radiology Evaluation

Knee dislocation presents a potential threat to the limb’s integrity. As a result, immediate reduction is sometimes advised even prior to conducting X-ray assessments. Once the reduction is performed, it’s essential to obtain anteroposterior (AP) and lateral views of the knee. These images serve to confirm the successful realignment and to identify any accompanying injuries. Radiographs might reveal irregular or asymmetric joint gaps, avulsion fractures in the lateral ligaments causing lateral capsular avulsions, as well as osteochondral defects like the Segond sign which is an avulsion fracture affecting the lateral tibial plateau.

If the knee joint spaces appear unusually widened, it could suggest the presence of soft tissue between the joint components, indicating a potential requirement for a more invasive open reduction procedure. Following the initial reduction, an MRI scan becomes valuable for assessing any ligament or meniscus damage, concealed fractures, lesions in the articular cartilage, and disruptions in the joint’s capsule. The insights provided by the MRI are crucial for planning any necessary ligament reconstruction surgeries, aiding in decisions such as determining the number of allografts needed for the procedure.

Knee Dislocation Classification

Types of knee dislocation is classified primarily by the direction of the dislocated tibia in relation to the femur (anterior, posterior, medial, lateral and rotatory). Rotary dislocations are designated further as anteromedial, anterolateral, posteromedial or posterolateral. The description should include open vs closed and reducible vs irreducible. It may be classified as occult, indicating a knee dislocation that has spontaneously reduced.

Kennedy classification for Knee Dislocation

It’s based on direction of displacement of the tibia.

Anterior (30-50%)– most common
– due to hyperextension injury
– usually involves tear of PCL
– arterial injury is generally an intimal tear due to traction
Posterior (25%)– 2nd most common
– due to axial load to flexed knee (dashboard injury)
– highest rate of vascular injury (25%) based on Kennedy classification (direction of dislocation)
– highest rate of complete tear of popliteal artery
Lateral (13%)– due to varus or valgus force
– usually involves tears of both ACL and PCL
– highest rate of peroneal nerve injury
Medial (3%)– varus or valgus force
– usually disrupted PLC and PCL
Rotational (4%)– posterolateral is most common rotational dislocation
– usually irreducible
– buttonholding of femoral condyle through capsule
Kennedy classification for Knee Dislocation
Kennedy classification for Knee Dislocation

Schenck Classification for Knee Dislocation

It’s based on pattern of multiligamentous injury of knee dislocation (KD).

KD IMultiligamentous injury with involvement of ACL or PCL
KD IIInjury to ACL and PCL only (2 ligaments)
KD IIIInjury to ACL, PCL, and PMC or PLC (3 ligaments). KDIIIM (ACL, PCL, MCL) and KDIIIL (ACL, PCL, PLC, LCL). KDIIIM has highest rate of vascular injury (31%) based on Schenck classification
KD IVInjury to ACL, PCL, PMC, and PLC (4 ligaments)
KD VMultiligamentous injury with periarticular fracture
See Also: Knee PCL Injury

Knee Dislocation Treatment

Immediate closed reduction is crucial right at the accident site. Avoid applying direct pressure to the popliteal space during or after the reduction process. Following the reduction, it’s important to aspirate any haemarthrosis and immobilize the knee in full extension. Regularly assess the neurocirculatory status over a span of 5-7 days.

Posterolateral dislocations often become “irreducible” due to the medial femoral condyle pushing through the medial capsule, causing a Dimple sign on the limb’s inner side. This situation necessitates an open reduction.

Dimple sign knee dislocation
Dimple sign
See Also: ACL Injury

Subsequent to the reduction, ligament injuries can be treated non-surgically or through surgical repair. Non-surgical management involves wearing a brace that keeps the knee extended for 6 weeks. External fixation is recommended if the reduction is unstable, if subluxation occurs during brace immobilization, in obese patients, in cases of open injuries, in polytrauma patients with or without head injuries, and when vascular repair has been performed. An alternative is to place a large transarticular pin through the femur’s intercondylar notch into the tibia’s intercondylar eminence to provide immediate stability. Most experts suggest opting for repair of torn structures as non-surgical treatment has shown worse outcomes compared to surgical intervention.

Emergency surgery for knee dislocation is warranted in instances of vascular injury, open fractures, open dislocations, irreducible dislocations, and compartment syndrome. Restoring vascular integrity takes precedence. Vascular injuries call for external fixation and vascular repair using a reverse saphenous vein graft from the opposite leg. Delays of over 8 hours in restoring circulation have led to amputation rates as high as 86%. In cases of limb ischemia, a fasciotomy should accompany vascular repair to prevent compartment syndrome.

The timing of ligamentous repair following knee dislocation is a subject of debate. Delaying surgery is argued for reasons such as observing vascular conditions and reducing the risk of arthrofibrosis. However, current literature leans towards promptly repairing posterolateral structures, capsular structures, and avulsion fractures once the patient’s condition and limb allow. Combined ACL and PCL reconstruction and management of meniscal injuries can be performed later with satisfactory outcomes. Postoperative rehabilitation protocols for knee dislocation should incorporate range-of-motion exercises as soon as soft-tissue repair, vascular repair, and ligament reconstruction permit.

References & More

  1. Conwell HE, Alldredge RH. Complete dislocations of the knee joint: a report of 7 cases with end-results. Surgery, Gynecology and Obstetrics 1937;64:94.
  2. Roman PD, Hopson CN, Zenni EJ Jr. Traumatic dislocation of the knee: a report of 30 cases and literature review. Orthopedic Reviews 1987;16:917.
  3. Twaddle BC, Hunter JC, Chapman JR, et al. MRI in acute knee dislocation: a prospective study of clinical, MRI, and surgical findings. Journal of Bone and Joint Surgery (British) 1996;78B:573. PubMed
  4. Mercer’s Textbook of Orthopaedics and Trauma, Tenth edition.
  5. Bistolfi, A., Massazza, G., Rosso, F. et al. Non-reducible knee dislocation with interposition of the vastus medialis muscle. J Orthopaed Traumatol 12, 115–118 (2011). https://doi.org/10.1007/s10195-011-0134-2
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