Dislocation of the Knee

Overview

Knee dislocation represents one of the most severe injuries that can occur to the knee joint, accounting for less than 0.2% of all orthopedic injuries but carrying significant potential for long-term disability. Unlike the more common patellar (kneecap) dislocation, true knee dislocation involves complete displacement of the tibia from the femur, requiring tremendous force that typically damages multiple stabilizing structures. The severity of this injury extends beyond the bones and ligaments, as the proximity of major blood vessels and nerves makes vascular and neurological complications a primary concern in the acute management phase.

The knee joint's stability depends on a complex network of ligaments, including the anterior and posterior cruciate ligaments (ACL and PCL) and the medial and lateral collateral ligaments (MCL and LCL). In a complete knee dislocation, at least three of these four major ligaments are typically torn, along with potential damage to the joint capsule, menisci, and surrounding soft tissues. The popliteal artery, which runs directly behind the knee, is at particular risk during dislocation, with vascular injury occurring in up to 40% of cases. Similarly, the peroneal nerve can be stretched or torn, leading to foot drop and sensory deficits.

The classification of knee dislocations is based on the direction of tibial displacement relative to the femur: anterior (most common), posterior, lateral, medial, or rotatory. Each type carries different risks and mechanisms of associated injuries. While many knee dislocations spontaneously reduce before medical evaluation, making diagnosis challenging, the presence of multi-ligamentous injury with gross instability should raise suspicion for a reduced dislocation. The long-term prognosis depends on prompt recognition, appropriate acute management including vascular assessment, and comprehensive rehabilitation to restore knee function and stability.

Symptoms

The symptoms of knee dislocation are typically severe and immediate, reflecting the extensive damage to the joint structures. Recognition of these symptoms is critical for prompt treatment and prevention of complications.

Primary Symptoms

• Knee pain - severe, immediate, and often described as the worst pain ever experienced
• Knee swelling - rapid onset, massive swelling of the entire knee region
• Knee stiffness or tightness - complete inability to bend or straighten the knee
• Obvious deformity of the knee joint
• Complete inability to bear weight on the affected leg

Vascular Symptoms (Emergency Signs)

• Absent or diminished pedal pulses (foot pulses)
• Cold foot or lower leg
• Pale or bluish discoloration of the foot
• Delayed capillary refill in toes
• Increasing pain in the calf (compartment syndrome)

Neurological Symptoms

• Numbness or tingling in the foot or lower leg
• Inability to move toes or ankle (foot drop)
• Loss of sensation on the top of the foot
• Weakness in ankle or toe movements
• Electric shock sensations down the leg

Associated Symptoms

• Feeling or hearing a "pop" at the time of injury
• Immediate feeling of the knee "giving out"
• Extensive bruising developing within hours
• Muscle spasms around the knee
• Skin tenting or dimpling over displaced bones
• Open wounds (in cases of open dislocation)

Systemic Symptoms

• Signs of shock (rapid pulse, low blood pressure, sweating)
• Nausea or vomiting from severe pain
• Lightheadedness or fainting
• Anxiety or sense of impending doom
• Difficulty concentrating due to pain

Causes

Knee dislocation requires significant force to overcome the strong ligamentous structures that stabilize the joint. Understanding the mechanisms of injury helps in prevention and recognition of associated injuries.

High-Energy Trauma

• Motor vehicle accidents:
  • Dashboard injuries where the knee strikes the dashboard
  • Motorcycle accidents with direct knee impact
  • Pedestrian struck by vehicle
  • High-speed collisions causing twisting forces
• Falls from height:
  • Construction or industrial accidents
  • Falls from ladders or scaffolding
  • Rock climbing or mountaineering accidents
  • Landing with knee hyperextended or twisted

Sports-Related Injuries

• Contact sports:
  • Football tackles with direct knee impact
  • Rugby scrums with twisting injuries
  • Wrestling takedowns gone wrong
  • Ice hockey collisions
• High-velocity sports:
  • Skiing accidents with twisting falls
  • Snowboarding with fixed bindings
  • Motocross or BMX crashes
  • Wakeboarding or water skiing injuries

Low-Energy Mechanisms

• Ultra-low velocity dislocations:
  • Morbid obesity (BMI >40)
  • Simple falls in obese individuals
  • Stepping wrong or pivoting
  • Rising from squatting position
• Pathological dislocations:
  • Connective tissue disorders (Ehlers-Danlos)
  • Previous multiple ligament injuries
  • Neuromuscular conditions
  • Joint laxity syndromes

Directional Mechanisms

• Anterior dislocation (30-40%): Hyperextension injuries, dashboard impact
• Posterior dislocation (25%): Direct blow to anterior tibia with flexed knee
• Lateral dislocation (13%): Varus force with rotation
• Medial dislocation (3%): Valgus force with rotation
• Rotatory dislocation (4%): Combined rotational and translational forces

Risk Factors

While knee dislocation typically results from significant trauma, certain factors increase susceptibility to this severe injury.

Anatomical Risk Factors

• Joint laxity: Generalized ligamentous laxity
• Previous knee injuries: Prior ACL/PCL tears or repairs
• Bone geometry: Shallow femoral notch or tibial plateau
• Muscle imbalances: Quadriceps/hamstring weakness
• Alignment issues: Significant varus or valgus deformity

Activity-Related Risk Factors

• High-risk occupations:
  • Construction workers
  • Military personnel
  • Professional athletes
  • Stunt performers
• Sports participation:
  • Contact sports without proper protective gear
  • Extreme sports enthusiasts
  • Weekend warriors with poor conditioning
• Transportation risks:
  • Motorcycle riding
  • Not wearing seatbelts
  • Aggressive driving behaviors

Medical Conditions

• Connective tissue disorders:
  • Ehlers-Danlos syndrome
  • Marfan syndrome
  • Benign joint hypermobility syndrome
  • Osteogenesis imperfecta
• Metabolic conditions:
  • Morbid obesity (special risk for low-energy dislocation)
  • Vitamin D deficiency
  • Chronic kidney disease affecting bone health

Environmental Factors

• Hazardous work conditions
• Icy or slippery surfaces
• Poor lighting in activity areas
• Inadequate safety equipment
• High-traffic accident areas

Diagnosis

Diagnosis of knee dislocation requires urgent evaluation with particular attention to vascular and neurological status. Many dislocations spontaneously reduce before medical evaluation, making diagnosis challenging.

Emergency Assessment

• Primary survey:
  • ABCs (Airway, Breathing, Circulation)
  • Assessment for other life-threatening injuries
  • Hemodynamic stability evaluation
  • Pain assessment and management
• Vascular examination:
  • Palpation of dorsalis pedis and posterior tibial pulses
  • Ankle-brachial index (ABI) measurement
  • Doppler ultrasound if pulses unclear
  • Capillary refill assessment
  • Temperature and color comparison

Physical Examination

• Inspection:
  • Obvious deformity or abnormal positioning
  • Skin integrity and wounds
  • Swelling pattern and extent
  • Ecchymosis development
  • Comparison with uninjured knee
• Neurological testing:
  • Peroneal nerve function (ankle dorsiflexion)
  • Tibial nerve function (ankle plantarflexion)
  • Sensation testing in all distributions
  • Motor strength assessment
• Ligament assessment (after reduction):
  • Anterior/posterior drawer tests
  • Varus/valgus stress testing
  • Dial test for posterolateral corner
  • Assessment for multi-ligament injury

Imaging Studies

• Plain radiographs:
  • AP and lateral views mandatory
  • May show obvious dislocation or subluxation
  • Associated fractures in up to 50% of cases
  • Avulsion fractures indicating ligament tears
• CT angiography:
  • Gold standard for vascular assessment
  • If ABI <0.9 or clinical suspicion
  • Evaluates popliteal artery integrity
  • Can identify intimal tears
• MRI (once stable):
  • Comprehensive ligament evaluation
  • Meniscal and cartilage assessment
  • Posterolateral corner injuries
  • Surgical planning tool

Classification Systems

• Kennedy classification: Based on direction of tibial displacement
• Schenck classification:
  • KD-I: Single cruciate + collateral
  • KD-II: Both cruciates intact
  • KD-III: Both cruciates + 1 collateral
  • KD-IV: All 4 major ligaments
  • KD-V: With periarticular fracture

Treatment Options

Treatment of knee dislocation requires immediate emergency management followed by definitive surgical reconstruction and extensive rehabilitation. The approach must address all damaged structures while preventing complications.

Emergency Management

• Immediate reduction:
  • Gentle longitudinal traction
  • Conscious sedation usually required
  • Avoid forceful manipulation
  • Document neurovascular status before and after
  • Immobilization in slight flexion (20-30°)
• Vascular management:
  • Emergency vascular surgery if indicated
  • Revascularization within 6-8 hours critical
  • Fasciotomy for compartment syndrome
  • Serial vascular examinations
  • Anticoagulation as appropriate

Surgical Treatment

• Timing of surgery:
  • Emergency: Vascular injury, open dislocation, irreducible
  • Urgent (24-48 hours): Nerve injury, compartment syndrome
  • Delayed (10-21 days): Most ligament reconstructions
  • Staged: Complex multi-ligament injuries
• Ligament reconstruction:
  • ACL reconstruction with autograft or allograft
  • PCL reconstruction techniques
  • MCL/LCL repair or reconstruction
  • Posterolateral corner reconstruction
  • Combined procedures for multiple ligaments
• Associated procedures:
  • Meniscal repair or debridement
  • Cartilage restoration procedures
  • Fracture fixation if present
  • Capsular repair
  • Nerve exploration or repair

Non-Surgical Management

• Immobilization:
  • Hinged knee brace locked in extension initially
  • Progressive range of motion as healing allows
  • External fixation for severe instability
  • Cast immobilization rarely used
• Conservative treatment indications:
  • Elderly or low-demand patients
  • Significant medical comorbidities
  • Partial injuries with good stability
  • Patient preference after informed consent

Rehabilitation

• Early phase (0-6 weeks):
  • Pain and swelling control
  • Protected weight bearing
  • Gentle range of motion exercises
  • Quadriceps activation
  • Modalities for pain relief
• Intermediate phase (6-12 weeks):
  • Progressive range of motion
  • Strengthening exercises
  • Proprioception training
  • Stationary cycling
  • Pool therapy
• Advanced phase (3-6 months):
  • Advanced strengthening
  • Sport-specific training
  • Plyometric exercises
  • Return to activity protocols
  • Functional testing
• Return to sports (6-12 months):
  • Completion of functional testing
  • Physician clearance
  • Sport-specific drills
  • Psychological readiness
  • Ongoing maintenance program

Pain Management

• Acute phase:
  • Multimodal analgesia approach
  • Regional nerve blocks
  • Patient-controlled analgesia
  • Ice and elevation
• Ongoing management:
  • NSAIDs for inflammation
  • Acetaminophen for baseline pain
  • Muscle relaxants for spasms
  • Topical analgesics

Complications

Knee dislocation carries a high risk of complications, both immediate and long-term. Early recognition and management of these complications is crucial for optimal outcomes.

Immediate Complications

• Vascular injury (20-40%):
  • Popliteal artery injury
  • Intimal tear or complete transection
  • Limb ischemia
  • Compartment syndrome
  • Need for amputation if delayed
• Nerve injury (25-35%):
  • Common peroneal nerve palsy
  • Tibial nerve injury (less common)
  • Permanent foot drop
  • Sensory deficits
  • Complex regional pain syndrome

Early Complications

• Deep vein thrombosis: Due to immobility and vascular injury
• Infection: Surgical site or deep joint infection
• Skin necrosis: From severe swelling or vascular compromise
• Heterotopic ossification: Abnormal bone formation
• Arthrofibrosis: Excessive scar tissue limiting motion

Long-term Complications

• Chronic instability:
  • Persistent ligamentous laxity
  • Recurrent giving way episodes
  • Inability to return to sports
  • Need for revision surgery
• Post-traumatic arthritis:
  • Develops in 25-50% of patients
  • Progressive joint degeneration
  • Chronic pain and stiffness
  • May require joint replacement
• Persistent stiffness:
  • Loss of terminal extension
  • Flexion contracture
  • Need for manipulation or lysis
  • Permanent motion loss

Prevention

While many knee dislocations result from unavoidable high-energy trauma, certain measures can reduce risk and severity of injury.

Sports Safety

• Proper conditioning:
  • Quadriceps and hamstring strengthening
  • Balance and proprioception training
  • Flexibility exercises
  • Sport-specific conditioning
  • Gradual return after injury
• Protective equipment:
  • Properly fitted knee braces for at-risk athletes
  • Appropriate footwear with good traction
  • Sport-specific protective gear
  • Playing surface maintenance
• Technique training:
  • Proper landing mechanics
  • Cutting and pivoting techniques
  • Fall training in martial arts
  • Tackling technique in contact sports

Vehicle Safety

• Always wear seatbelts properly
• Adjust seat position to prevent dashboard injury
• Motorcycle protective gear including knee guards
• Defensive driving practices
• Vehicle safety features maintenance

Occupational Safety

• Fall protection equipment at heights
• Non-slip surfaces in work areas
• Proper lifting techniques
• Safety training and protocols
• Regular equipment inspection

Medical Management

• Treatment of joint hypermobility conditions
• Weight management for obese individuals
• Bone health optimization
• Management of neuromuscular conditions
• Regular screening for at-risk populations

When to See a Doctor

Call 911 immediately for:

• Obvious knee deformity or dislocation
• Severe knee pain with inability to move leg
• No feeling or movement in foot
• Foot appears cold, pale, or blue
• No pulse felt in foot
• Rapidly expanding knee swelling
• Open wound with visible bone or joint

Seek urgent medical care for:

• Severe knee injury with immediate swelling
• Complete inability to bear weight
• Feeling of knee "giving out" completely
• Numbness or tingling below the knee
• Severe knee stiffness after injury
• Multiple "pop" sounds during injury

See a doctor promptly for:

• Significant knee injury with instability
• Persistent pain and swelling after trauma
• Difficulty straightening or bending knee
• Feeling of looseness in the knee
• Previous knee injury with new trauma

Related Conditions

• ACL Injury
• PCL Injury
• Patellar Dislocation
• Knee Fracture
• Compartment Syndrome
• Popliteal Artery Injury
• Multi-ligament Knee Injury

References

1. Medina O, Arom GA, Yeranosian MG, et al. Vascular and nerve injury after knee dislocation: a systematic review. Clin Orthop Relat Res. 2014;472(9):2621-2629.
2. Levy BA, Dajani KA, Whelan DB, et al. Decision making in the multiligament-injured knee: an evidence-based systematic review. Arthroscopy. 2009;25(4):430-438.
3. Howells NR, Brunton LR, Robinson J, et al. Acute knee dislocation: an evidence based approach to the management of the multiligament injured knee. Injury. 2011;42(11):1198-1204.
4. Schenck RC Jr. The dislocated knee. Instr Course Lect. 1994;43:127-136.
5. Fanelli GC, Stannard JP, Stuart MJ, et al. Management of complex knee ligament injuries. J Bone Joint Surg Am. 2010;92(12):2235-2246.