Knee Dislocation

A knee dislocation is disruption of the tibiofemoral articulation associated with major multiligament injury.

Many knee dislocations spontaneously reduce before hospital arrival, so a normal looking knee does not exclude a limb threatening injury.

A patient with significant injuries to two or more major knee ligaments should be assessed as a potential reduced knee dislocation.

The immediate threats are:

• Popliteal artery disruption
• Common peroneal nerve injury
• Compartment syndrome
• Irreducible dislocation
• Severe instability

The popliteal artery is tethered proximally at the adductor hiatus and distally near the soleus arch, making it vulnerable to traction and intimal disruption.

Palpable distal pulses do not completely exclude arterial injury because collateral circulation can maintain flow.

Kennedy classification

Based on direction of tibial displacement relative to the femur.

Anterior

Usually hyperextension.

Often associated with PCL disruption.

Arterial injury can result from traction and intimal tearing.

Posterior

Often dashboard type axial load to a flexed knee.

Particularly associated with popliteal artery disruption.

Medial

Tibia displaced medially.

Usually severe collateral and cruciate injury.

Lateral

Tibia displaced laterally.

Usually ACL and PCL plus collateral injury.

Rotational

Posterolateral rotational dislocation is particularly important.

The medial femoral condyle can buttonhole through capsule and soft tissue, producing the dimple sign.

This injury may be irreducible by closed methods.

Schenck classification

Based on multiligament injury pattern.

KD I

One cruciate ligament remains intact with multiligament injury involving the opposite cruciate plus collateral structures.

KD II

Both ACL and PCL disrupted, collateral structures largely intact.

KD III

Both cruciates plus one collateral side disrupted.

KD IIIM

ACL + PCL + medial collateral or posteromedial complex injury.

KD IIIL

ACL + PCL + lateral collateral or posterolateral corner injury.

KD IV

ACL + PCL + medial and lateral collateral complexes disrupted.

Extremely unstable.

KD V

Multiligament knee injury associated with periarticular fracture.

Modifiers are often added:

• C for arterial injury
• N for significant nerve injury

A grossly dislocated knee is obvious.

A spontaneously reduced knee may present only with:

• Massive swelling
• Ecchymosis
• Instability
• Peroneal nerve deficit
• Abnormal vascular findings

Vascular assessment

Perform before and after reduction:

• Dorsalis pedis pulse
• Posterior tibial pulse
• Capillary refill
• Skin temperature
• Ankle brachial index

Hard vascular signs

• Active haemorrhage
• Expanding haematoma
• Absent distal perfusion
• Cold pale limb
• Obvious arterial disruption

These require immediate vascular intervention.

A normal pulse examination alone is insufficient.

ABI

After reduction:

ABI below 0.9

Requires vascular imaging, usually CT angiography.

ABI at least 0.9 with symmetric normal pulses

Allows close serial vascular examinations in a reliable patient without other concerning findings.

ABI below 0.9 has very high specificity for significant arterial injury.

Continue serial examinations because intimal injury can thrombose later.

Neurological assessment

The common peroneal nerve is particularly vulnerable in posterolateral injuries.

Assess:

• Ankle dorsiflexion
• Great toe extension
• Foot eversion
• First web space sensation
• Dorsum of foot sensation

Assess tibial nerve function as well.

Complete peroneal palsy has a worse prognosis than incomplete injury.

Obtain AP and lateral radiographs before reduction if this does not delay treatment of a threatened limb.

In a neurovascular emergency, reduce immediately.

Obtain post reduction films to confirm a concentric joint.

CT angiography: obtain for:

• ABI below 0.9
• Abnormal pulses
• Soft vascular signs
• Concerning high energy injury
• Equivocal vascular assessment

MRI knee: obtained after reduction and initial stabilisation to define:

• ACL
• PCL
• MCL
• LCL
• Posterolateral corner
• Menisci
• Cartilage
• Tendons

MRI is not the immediate priority when limb perfusion is threatened.

Immediate reduction

Reduce the knee urgently using longitudinal traction with correction of displacement.

Avoid repeated forceful attempts.

After reduction:

• Repeat pulses
• Repeat ABI
• Repeat neurological examination
• Confirm radiographically
• Immobilise in a well padded brace or splint

Irreducible dislocation

Posterolateral dislocation with medial skin puckering or a dimple sign may indicate medial femoral condyle buttonholing.

Do not persist with multiple forceful closed attempts.

Proceed to urgent open reduction.

Pulseless or ischaemic limb

Immediately reduce the knee.

If perfusion does not return, proceed directly to vascular exploration and repair.

Do not delay arterial restoration for MRI.

Temporary vascular shunting can be used when:

• Ischaemia time is prolonged
• Orthopaedic stabilisation is needed before definitive vascular repair

A stable knee spanning external fixator can protect the vascular reconstruction.

Popliteal artery repair

Repair options include:

• Primary repair in a small clean defect
• Interposition graft
• Bypass, often using reversed autologous great saphenous vein

Perform four compartment leg fasciotomy liberally when:

• Ischaemia has been prolonged
• Revascularisation has occurred
• Major swelling exists
• Compartment pressure is concerning

Temporary external fixation

Use a knee spanning external fixator when:

• Vascular repair requires protection
• Open dislocation
• Severe soft tissue injury
• Gross instability cannot be maintained in a brace
• Fracture dislocation
• Polytrauma prevents immediate reconstruction.

Pins should be positioned outside future ligament reconstruction tunnels where possible.

Definitive ligament treatment

Nonoperative management is mainly reserved for:

• Frail patients
• Low functional demand
• Major comorbidity
• Selected incomplete ligament injuries

Most active patients with true KD III or KD IV injury benefit from operative reconstruction.

The primary objective is restoration of:

• Central pivot, ACL and PCL
• Medial stability
• Posterolateral stability

Failure to recognise posterolateral corner injury is a major cause of cruciate reconstruction failure.

Repair versus reconstruction

Collateral avulsions

Acute repair may be appropriate when:

• Ligament is avulsed from a clearly repairable attachment
• Tissue quality is good
• Surgery occurs early

Midsubstance collateral or cruciate disruption

Reconstruction is usually more reliable than simple suture repair.

Timing

Definitive multiligament reconstruction is individualised.

Early surgery within approximately 3 weeks can improve stability and functional outcomes but carries a greater risk of arthrofibrosis.

Delay or stage reconstruction when there is:

• Vascular repair
• Major soft tissue injury
• Open wound
• Severe swelling
• Fracture requiring healing
• Significant loss of knee motion

A common staged strategy uses temporary stabilisation followed by reconstruction after soft tissue recovery, often around 3 to 6 weeks in severe injuries.

Peroneal nerve injury

Observe incomplete palsies with serial examination because recovery can occur.

Complete palsy requires careful assessment.

Explore when there is:

• Open injury
• Nerve transection suspected
• Entrapment
• Progressive neurological deterioration

Persistent foot drop may eventually require:

• Nerve reconstruction in selected cases
• Posterior tibial tendon transfer
• Ankle foot orthosis

Rehabilitation

Rehabilitation must balance:

• Prevention of stiffness
• Protection of reconstructed ligaments
• Restoration of quadriceps function

Early controlled range of motion is generally preferable to prolonged rigid immobilisation once the knee is stable.

Weight bearing progression depends on:

• Ligaments reconstructed
• Meniscal repair
• Fracture
• Vascular repair
• External fixation

Major complications include:

• Limb loss from missed arterial injury
• Popliteal thrombosis
• Compartment syndrome
• Peroneal nerve palsy
• Arthrofibrosis
• Chronic instability
• Graft failure
• Heterotopic ossification
• Post traumatic osteoarthritis