Orthopaedic Surgery - Knee Dislocation

Basics

Knee dislocation is an orthopaedic emergency because of the substantial risk of associated vascular, neurologic, and multiligament injury.

Most cases result from high-energy trauma, although sports injuries and even low-energy falls can also cause dislocation.

A knee that has spontaneously reduced before evaluation may appear relatively normal despite having sustained a major injury. For this reason, the diagnosis should be considered whenever there is evidence of severe multiligament instability or a compatible mechanism.

Classification by Direction

Knee dislocations are classified according to the position of the tibia relative to the femur.

Anterior Dislocation

The tibia is displaced anteriorly relative to the femur.

Posterior Dislocation

The tibia is displaced posteriorly.

Posterior dislocations are particularly concerning for injury to the popliteal artery because of the close relationship between the vessel and the posterior knee.

Medial Dislocation

The tibia is displaced medially relative to the femur.

Lateral Dislocation

The tibia is displaced laterally.

Rotary Dislocation

Rotational injuries can be further described as:

Anteromedial, anterolateral, posteromedial, or posterolateral.

Classification by Injury Energy

The injury may also be classified according to the amount of energy involved.

High-Energy

High-energy dislocations typically result from:

Motor vehicle collisions, falls from height, or other major trauma.

These injuries have a greater risk of:

Vascular disruption, extensive soft-tissue damage, fractures, open wounds, and compartment syndrome.

Low-Energy

Low-energy knee dislocation may occur during sports, twisting injuries, or moderate trauma.

Ultralow-Energy

Some dislocations occur after seemingly minor trauma, particularly in patients with substantial obesity or ligamentous vulnerability.

Even these injuries can cause serious neurovascular damage.

Epidemiology

Knee dislocation is uncommon, historically reported in fewer than 0.02% of musculoskeletal injuries.

The true incidence is probably higher because many dislocations spontaneously reduce before the patient is examined and may therefore be missed.

Sex

Historical series report a male predominance of approximately 2.5:1.

Associated Injuries

Knee dislocation frequently damages multiple structures.

Important associated injuries include:

Popliteal artery injury, common peroneal nerve injury, tibial or femoral fractures, rupture of the cruciate ligaments, rupture of the collateral ligaments, posterolateral corner injury, and extensive capsular disruption.

Diagnosis

History

The mechanism and amount of energy involved should be determined whenever possible.

Important questions include:

Direction of force, presence of twisting, direct impact, speed of injury, open wounds, loss of sensation, weakness, and whether the knee appeared deformed before spontaneously reducing.

Signs and Symptoms

A classic unreduced knee dislocation presents with:

Gross deformity, severe pain, swelling, inability to move the knee, and inability to bear weight.

However, deformity may be absent if the joint has reduced spontaneously or was reduced before orthopaedic evaluation.

Neurovascular Injury

Careful assessment of vascular and neurologic function is essential in every suspected knee dislocation.

Popliteal Artery Injury

Historical series report popliteal artery injury in approximately 32–45% of knee dislocations.

Because the artery is tethered proximally and distally around the knee, major displacement can produce:

Intimal tearing, thrombosis, transection, or stretch injury.

Peroneal Nerve Injury

Nerve injury occurs in approximately 16–40% of cases in older series.

The common peroneal nerve is the nerve most frequently affected.

Vascular Red Flags

Urgent vascular evaluation is required when there is:

Absent or diminished pulse, asymmetric pulses, cool or cyanotic foot, delayed capillary refill, expanding hematoma, popliteal ecchymosis, active bleeding, or loss of motor or sensory function.

Physical Examination

Trauma Assessment

High-energy injuries should first undergo a complete trauma evaluation according to standard trauma priorities.

Inspection

Examine for:

Deformity, swelling, bruising, open wounds, skin tenting, and evidence of associated fracture.

Vascular Examination

Document:

Dorsalis pedis and posterior tibial pulses, capillary refill, foot temperature, skin color, and symmetry with the opposite limb.

A Doppler examination may be used when pulses are difficult to palpate.

Important Point

The presence of palpable distal pulses does not completely exclude vascular injury.

An intimal flap can preserve flow initially and subsequently thrombose.

Ankle-Brachial Index

An ankle-brachial index (ABI) should be obtained when appropriate.

An abnormal or asymmetric ABI increases concern for occult arterial injury and may prompt CT angiography or vascular consultation.

Neurologic Examination

Motor and sensory function should be documented before and after reduction.

Particular attention should be given to the:

Common peroneal and tibial nerves.

Peroneal Nerve

Assess:

Ankle dorsiflexion, great-toe extension, foot eversion, and sensation over the dorsum of the foot.

Tibial Nerve

Assess:

Plantarflexion, toe flexion, and plantar foot sensation.

Ligament Examination

The knee should be assessed systematically for injury to the:

ACL, PCL, MCL, LCL, and posterolateral corner.

Laxity involving two or more major ligaments strongly suggests that a knee dislocation has occurred, even if the joint is reduced at presentation.

Compartment Syndrome

Patients require repeated examination because compartment syndrome can develop after vascular injury, reperfusion, fracture, or severe soft-tissue trauma.

Warning Signs

Particularly concerning findings include:

Severe pain out of proportion to the injury and pain with passive stretch of the ankle or toes.

Other findings such as tense compartments, weakness, or sensory changes may occur later.

Imaging

Plain Radiographs

Obtain:

AP and lateral radiographs of the knee.

Radiography should not delay immediate reduction when an obvious dislocation is present.

Post-reduction radiographs are required to confirm alignment and identify associated fractures.

CT Angiography

CT angiography is useful when there is:

Abnormal perfusion, pulse asymmetry, abnormal ABI, suspicious examination findings, or uncertainty regarding vascular integrity.

MRI

MRI is useful for defining:

Cruciate ligament tears, collateral ligament injuries, posterolateral corner injuries, meniscal damage, cartilage injury, and other soft-tissue abnormalities.

It is usually obtained after the acute emergency has been stabilized rather than before reduction or vascular evaluation.

Schenck Classification of Multiligament Knee Injury

The Schenck system classifies knee dislocation according to the ligament structures disrupted.

KD I

One cruciate ligament plus a collateral ligament or posterolateral structure is injured.

KD II

Both the ACL and PCL are torn, with collateral structures relatively preserved.

KD III-M

The ACL, PCL, and MCL are injured.

Additional medial or posteromedial structures may also be involved.

KD III-L

The ACL, PCL, LCL, and posterolateral corner are injured.

KD IV

All four major ligament groups are disrupted:

ACL, PCL, MCL, and LCL/posterolateral corner.

KD V

A knee dislocation occurs in association with a periarticular fracture, producing a fracture-dislocation.

Moore Classification of Knee Fracture-Dislocations

The Moore classification describes associated tibial plateau fracture patterns.

Type I

Split fracture involving the medial or lateral plateau.

Type II

Complete fracture separating essentially an entire medial or lateral plateau.

Type III

Rim avulsion fracture.

Type IV

Rim compression fracture.

Type V

Four-part fracture pattern.

Differential Diagnosis

Conditions that may mimic or accompany knee dislocation include:

Patellar dislocation, isolated vascular injury, femoral fracture, tibial fracture, isolated ligament injury, and fracture-dislocation around the knee.

Treatment

Immediate Reduction

An unreduced knee dislocation should be reduced urgently.

The goal is to restore:

Alignment, vascular perfusion, nerve function, and soft-tissue tension.

Reduction Principles

Reduction should be performed using:

Gentle longitudinal traction and controlled correction of the deformity.

Forceful focal pressure should be avoided because it may worsen vascular, neurologic, or soft-tissue injury.

Anterior Dislocation

Reduction generally involves:

Longitudinal traction with controlled posterior translation of the tibia and manipulation of the femur as necessary.

Posterior Dislocation

Reduction typically uses:

Longitudinal traction with anterior elevation of the proximal tibia while the knee is carefully extended.

Medial and Lateral Dislocations

Traction is combined with controlled correction of the medial or lateral displacement.

Post-Reduction Care

After reduction:

Repeat and document the complete neurovascular examination.

Then obtain appropriate radiographs and vascular assessment.

Irreducible Knee Dislocation

Some knee dislocations cannot be reduced by closed manipulation.

Dimple Sign

A skin dimple over the medial joint line between the medial femoral condyle and medial tibial plateau suggests that the medial femoral condyle has buttonholed through the medial capsule, trapping soft tissue such as the MCL within the joint.

This finding strongly suggests an irreducible dislocation.

Management

Irreducible dislocations usually require open surgical reduction.

Repeated forceful attempts at closed reduction should be avoided.

Immobilization

After reduction, the knee is stabilized with either:

A well-padded splint or a spanning external fixator, depending on stability and associated injuries.

Indications for Spanning External Fixation

External fixation may be required when there is:

Persistent gross instability, vascular repair requiring protection, open injury, severe soft-tissue compromise, polytrauma, or inability to maintain reduction in a splint.

Vascular Injury

Any confirmed or strongly suspected arterial injury requires emergency vascular surgery evaluation.

Revascularization

Repair may require:

Primary repair, thrombectomy, patch angioplasty, bypass, or interposition grafting, often using autologous saphenous vein.

Timing

Limb viability is closely related to ischemia time.

Delays approaching or exceeding 8 hours have historically been associated with a dramatic increase in amputation risk.

For this reason, suspected vascular injury must be treated urgently.

Fasciotomy

Fasciotomy may be necessary when there is:

Compartment syndrome, prolonged ischemia, substantial reperfusion injury, or severe swelling after vascular reconstruction.

Open Dislocation

An open knee dislocation requires urgent operative management including:

Irrigation, debridement, reduction, stabilization, antibiotic therapy, and treatment of associated ligamentous or vascular injury.

Nonoperative Treatment

Nonoperative treatment may be considered when:

There is no vascular injury, the patient has low functional demands, advanced age, major medical comorbidities, or surgical reconstruction is contraindicated.

Immobilization

Protected immobilization may continue for approximately 6–8 weeks, although prolonged immobilization increases the risk of stiffness.

Surgical Treatment

Definitive ligament repair or reconstruction is commonly considered after initial stabilization.

Timing depends on:

Soft-tissue swelling, vascular repair, open wounds, associated fractures, overall patient condition, and surgeon strategy.

Historically, reconstruction has often been performed after approximately 10–14 days, once swelling has decreased, although staged and earlier approaches are also used.

Ligament Reconstruction

Surgical strategy depends on which structures are injured.

Accurate restoration of:

Joint alignment, cruciate stability, collateral stability, and posterolateral stability

is necessary to restore functional knee mechanics.

The sequence of reconstruction is important and should be individualized according to the pattern of injury.

Activity

Nonoperative Patients

Protected immobilization is generally maintained initially.

Quadriceps-setting exercises can often begin while the patient remains immobilized.

Operative Patients

Postoperative activity depends on:

Which ligaments were repaired or reconstructed, meniscal or cartilage injury, associated fractures, and vascular procedures.

Range of Motion

Progressive active or assisted range of motion commonly begins after the initial protective period.

Some protocols begin earlier when fixation and reconstruction are sufficiently stable.

Physical Therapy

Rehabilitation is essential.

Early goals include:

Edema control, quadriceps activation, protection of reconstructed structures, and prevention of excessive stiffness.

Later phases emphasize:

Progressive range of motion, strengthening, proprioception, gait training, and functional retraining.

Return to Activity

Recovery is prolonged.

Historical approximate timelines include:

Sedentary work: around 2 months

Heavy labor: approximately 6–9 months

Return to sport: approximately 9–12 months or longer

Actual timing depends on injury severity and reconstruction.

Follow-Up

Patients should be followed closely, often at approximately 4–6 week intervals during recovery, until stability, motion, strength, and function have plateaued.

Referral

An orthopaedic surgeon should be consulted emergently for any suspected knee dislocation.

A vascular surgeon should be involved immediately when arterial injury is suspected or confirmed.

Prognosis

Outcome depends heavily on:

Energy of injury, vascular damage, nerve injury, number of ligaments torn, cartilage injury, associated fracture, and success of reconstruction.

High-energy injuries generally have worse functional results.

Vascular Prognosis

When arterial injury is present, the likelihood of limb salvage declines as ischemia time increases.

Historical data reported an amputation rate as high as approximately 86% when ischemia persisted beyond 8 hours.

Arthrofibrosis

Loss of knee motion is one of the most common long-term problems.

Nonoperative Treatment

Residual stiffness may provide some stability in a chronically ligament-deficient knee but can substantially impair function.

Operative Treatment

Reconstruction may itself increase stiffness risk, particularly when prolonged immobilization is required.

Stable reconstruction that permits controlled early motion helps reduce this risk.

Motion Loss Patterns

Loss of extension may occur after ACL reconstruction, whereas loss of flexion can occur after PCL reconstruction.

Neurologic Deficit

Common peroneal nerve injury is a frequent sequela.

Recovery can take:

Months to years, and prognosis varies according to whether the injury represents neurapraxia, axonal disruption, or complete nerve injury.

Persistent foot drop may require bracing, tendon transfer, or other reconstructive procedures.

Chronic Instability

Residual instability may occur because of incomplete healing or reconstruction of the damaged ligaments.

True redislocation after definitive treatment is uncommon.

Post-Traumatic Arthritis

Articular cartilage injury at the time of dislocation can lead to progressive degenerative disease.

Historical studies have reported post-traumatic arthritis in a large proportion of patients, in some series approaching 87%.

Patient Monitoring

Patients require careful monitoring during both the acute and recovery phases.

Important parameters include:

Distal perfusion, pulses, ABI when indicated, motor and sensory function, compartment status, skin condition, wound healing, ligament stability, range of motion, and radiographic alignment.

Particular attention should be paid to detecting:

Delayed vascular thrombosis, compartment syndrome, arthrofibrosis, persistent instability, nerve dysfunction, and post-traumatic arthritis.