Knee dislocation (tibiofemoral dislocation) is a limb-threatening orthopedic emergency defined by complete displacement of the tibiofemoral articulation, involving disruption of at least two major knee ligaments. The critical concern is popliteal artery injury (occurring in ~10–18% of cases) and common peroneal nerve injury (~19–25%), which mandate immediate reduction and serial neurovascular assessment. [1-3]
1. History
- Mechanism: High-energy trauma (MVC, pedestrian struck, fall from height) or sports-related contact injury; increasingly recognized in morbidly obese patients from low-energy falls ("ultra-low-velocity" knee dislocations) [1]
- Immediate severe knee pain, inability to bear weight, gross deformity (if still dislocated)
- ~50% of knee dislocations spontaneously reduce before ED arrival — maintain a high index of suspicion in any patient with a grossly swollen, unstable knee after significant trauma [4]
- Ask about paresthesias, numbness in the foot (peroneal nerve distribution), and any transient deformity witnessed at the scene
- Timing of injury, prior knee surgery, anticoagulant use
2. Alarm Features
- Absent or asymmetric distal pulses (dorsalis pedis, posterior tibial) — suggests popliteal artery injury
- Expanding popliteal hematoma or hard signs of vascular injury (active hemorrhage, bruit/thrill, pulsatile mass)
- Pale, cool, or mottled foot — limb-threatening ischemia
- Foot drop — common peroneal nerve palsy (inability to dorsiflex ankle/toes)
- Tense calf compartments — evolving compartment syndrome
- Open wound communicating with the joint
- "Dimple sign" on the medial skin — pathognomonic for irreducible posterolateral dislocation [5]
- Irreducible dislocation requiring emergent OR [1][6]
3. Medications
- Procedural sedation for closed reduction (ketamine, propofol, or etomidate per institutional protocol)
- Parenteral analgesia: IV opioids (fentanyl, morphine) and/or regional nerve block
- Anticoagulation: systemic heparin may be indicated if vascular repair is planned (per vascular surgery)
- Tetanus prophylaxis if open injury
- Antibiotics for open dislocations (first-generation cephalosporin ± aminoglycoside per open fracture protocols)
- Avoid NSAIDs acutely if surgical intervention is anticipated (bleeding risk)
4. Diet
- NPO if surgical intervention is anticipated (vascular repair, open reduction, or external fixation)
- No specific long-term dietary considerations unique to this injury
5. Review of Systems
- Vascular: Foot color/temperature changes, numbness, tingling distal to the knee
- Neurologic: Weakness in dorsiflexion/eversion (peroneal nerve), sensation over dorsum of foot and lateral leg
- Musculoskeletal: Other extremity injuries, back pain, pelvic pain (polytrauma screening)
- Skin: Open wounds, skin tenting, dimple sign
- Constitutional: Mechanism-related symptoms (head injury, chest/abdominal pain in polytrauma)
6. Collateral History and Family History
- Witnesses to the mechanism (was the knee visibly deformed and then "popped back"?)
- Prehospital providers: any manipulation or spontaneous reduction in the field
- Prior knee injuries, surgeries, or ligamentous laxity
- Family history is generally not contributory, though connective tissue disorders (e.g., Ehlers-Danlos) may predispose to dislocation with lower-energy mechanisms
- Social context: Occupation, activity level, and sport participation are important for surgical planning and prognosis
7. Risk Factors
- High-energy trauma: MVC (most common), motorcycle accidents, falls from height [1][7]
- Sports: Contact sports (football, rugby, wrestling) [8]
- Morbid obesity: Ultra-low-velocity dislocations from ground-level falls are increasingly recognized; increased BMI is independently associated with vascular injury (OR 1.077 per unit BMI) [1][9]
- Open injuries: Associated with 3.4× greater risk of vascular injury [9]
- Posterolateral corner involvement increases risk of peroneal nerve injury [10]
- KD-IV pattern (bicruciate + both collateral ligaments) carries the highest vascular injury risk [11]
8. Differential Diagnosis
- Spontaneously reduced knee dislocation (the most commonly missed diagnosis — suspect in any grossly unstable, swollen knee after trauma) [4]
- Tibial plateau fracture (Schatzker IV–VI can be biomechanically equivalent to a knee dislocation) [12]
- Patellar dislocation (patellofemoral, not tibiofemoral — different entity entirely)
- Isolated multiligament knee injury without frank dislocation [13]
- Proximal tibiofibular joint dislocation
- Periarticular fracture (distal femur, proximal tibia) with subluxation
- Knee fracture-dislocation (Schenck KD-V) — dislocation with associated periarticular fracture [14]
9. Past Medical History
- Prior knee injuries, ligament reconstructions, or meniscal surgery
- Peripheral vascular disease (may confound ABI interpretation)
- Connective tissue disorders (Ehlers-Danlos, Marfan syndrome)
- Obesity (BMI)
- Anticoagulant/antiplatelet use
- Diabetes (affects wound healing and nerve recovery)
10. Physical Exam
- Vital signs: Tachycardia may indicate hemorrhage or pain; assess for polytrauma
- Inspection: Gross deformity (if unreduced), massive effusion, ecchymosis, skin tenting, open wounds, dimple sign
- Vascular exam (most critical):
- Palpate dorsalis pedis (DP) and posterior tibial (PT) pulses bilaterally
- Assess capillary refill, skin color, and temperature of the foot
- Ankle-brachial index (ABI): Perform on all suspected knee dislocations — ABI ≥ 0.9 combined with palpable pulses has 100% sensitivity for ruling out clinically significant vascular injury [9][15]
- Neurologic exam:
- Common peroneal nerve: Ankle dorsiflexion, great toe extension, foot eversion; sensation over dorsal foot and lateral leg
- Tibial nerve: Ankle plantarflexion, toe flexion; sensation over plantar foot
- Ligamentous exam (may be limited by pain/swelling; defer detailed exam to post-reduction or under anesthesia):
- Compartment assessment: Palpate all four leg compartments for tenseness and pain with passive stretch
11. Lab Studies
- Type and screen (anticipate possible vascular surgery)
- CBC, BMP, coagulation studies (PT/INR, PTT)
- Lactate (if concern for limb ischemia or polytrauma)
- Urinalysis (polytrauma screening)
- CK if prolonged ischemia or concern for rhabdomyolysis/compartment syndrome
- No specific lab is diagnostic for knee dislocation itself
12. Imaging
- AP and lateral knee radiographs: First-line; confirm dislocation (if still dislocated), identify associated fractures; obtain pre- and post-reduction films [4][16]
- CT angiography (CTA): Indicated when ABI < 0.9, asymmetric pulses, or any hard/soft signs of vascular injury; CTA has largely replaced conventional angiography as the preferred modality [16-18]
- MRI: Deferred to the inpatient setting; gold standard for characterizing ligamentous, meniscal, and chondral injuries for surgical planning [4][16]
- Stress radiographs: Useful for quantifying laxity and surgical planning (typically obtained later) [13]
- Imaging is unnecessary to delay reduction — reduce first, image after if the knee is still dislocated on presentation
13. Special Tests
- Ankle-Brachial Index (ABI): The cornerstone screening tool; ABI ≥ 0.9 with palpable pulses effectively rules out vascular injury; ABI < 0.9 warrants CTA [7][9][15]
- Schenck Classification (anatomic, based on ligament injury pattern): [19]
- KD-I: Single cruciate + collateral(s)
- KD-II: Bicruciate (ACL + PCL), collaterals intact
- KD-III: Bicruciate + one collateral (IIIM = medial; IIIL = lateral)
- KD-IV: Bicruciate + both collaterals (all four ligaments)
- KD-V: Fracture-dislocation
- Modifiers: C (vascular injury), N (nerve injury)
- Kennedy Positional Classification: Anterior, posterior, lateral, medial, rotatory — based on tibial displacement relative to femur [19]
- Compartment pressure monitoring if clinical suspicion for compartment syndrome
14. ECG
- Not routinely indicated for isolated knee dislocation
- Obtain ECG if:
- Polytrauma with hemodynamic instability
- Pre-procedural sedation assessment
- Elderly patients or those with cardiac comorbidities
- No specific ECG pattern associated with knee dislocation
15. Assessment
Knee dislocation is an orthopedic and vascular emergency. The primary threat is popliteal artery injury, which occurs in approximately 10.7% of cases per a meta-analysis of over 37,000 dislocations, with a 2.2% amputation rate. [2] Nerve injury (predominantly common peroneal) occurs in ~19.6%. [2] Up to 50% of dislocations spontaneously reduce before ED arrival, making a high index of suspicion essential in any patient with a grossly unstable, swollen knee after trauma. [4]
Severity stratification
- Limb-threatening: Absent pulses, hard signs of vascular injury, irreducible dislocation, open dislocation, compartment syndrome
- High-risk: ABI < 0.9, KD-IV pattern, posterolateral dislocation, morbid obesity, open injury
- Standard: Reduced dislocation with normal vascular exam and ABI ≥ 0.9 — still requires admission and serial monitoring
Complications include vascular injury with limb loss, compartment syndrome, arthrofibrosis, persistent nerve palsy (complete CPN palsy has only ~38% functional recovery), heterotopic ossification, and recurrent instability. [1][20]
16. Treatment Plan
Initial stabilization
- Immediate closed reduction under procedural sedation: Apply longitudinal traction to the tibia while correcting the translational deformity; for anterior dislocations, lift the distal femur while applying posterior force to the proximal tibia [4][7]
- Perform and document pre- and post-reduction neurovascular exams
- Post-reduction: Immobilize in a knee immobilizer or long-leg posterior splint at ~20° flexion [6]
- If reduction cannot be maintained → external fixator placement [1][6]
- Irreducible dislocations (often posterolateral with dimple sign) → emergent open reduction in the OR [1][5]
Vascular management algorithm: [7][18]
- Hard signs of vascular injury (absent pulses, active hemorrhage, expanding hematoma) → emergent vascular surgery exploration — do not delay for imaging
- Soft signs or ABI < 0.9 → CTA → vascular surgery consultation based on findings
- Normal pulses + ABI ≥ 0.9 → serial vascular exams q4–6h for 24–48 hours [6]
- Warm ischemia time > 6–8 hours significantly increases amputation risk
Definitive ligament management
- Operative reconstruction is generally favored over nonoperative management, with higher Lysholm scores (85 vs 67) and return-to-sport rates (41% vs 18%) [21]
- Early single-stage surgery (within ~3 weeks) is increasingly favored when feasible, with consensus supporting this approach [13][21]
- Repair vs. reconstruction: Reconstruction is preferred for cruciate ligaments; posterolateral corner repair has a higher failure rate (39% vs 8%) compared to reconstruction [21]
17. Disposition
- All knee dislocations require hospital admission for serial neurovascular monitoring (minimum 24–48 hours) [6]
- ICU/step-down: Polytrauma, active vascular injury requiring repair, hemodynamic instability
- Emergent OR indications: Irreducible dislocation, vascular injury requiring repair, open dislocation, compartment syndrome [1][7]
- Consults:
- Orthopedic surgery: All cases
- Vascular surgery: Any abnormal vascular exam, ABI < 0.9, or hard signs of vascular injury
- Trauma surgery: Polytrauma patients
- No knee dislocation should be discharged from the ED — even if reduced with a normal vascular exam, delayed vascular compromise and compartment syndrome can develop [6]
18. Follow Up / Return Precautions
- Inpatient: Serial neurovascular checks q4–6h for 24–48 hours post-reduction; monitor for compartment syndrome [6]
- Outpatient follow-up: Orthopedic surgery within 1–2 weeks of discharge for MRI planning and definitive surgical decision-making
- MRI should be obtained to fully characterize ligamentous, meniscal, and chondral injuries before definitive reconstruction [4]
- Return precautions (counsel patient):
- Return immediately for increasing pain, numbness/tingling in the foot, inability to move the toes, foot color changes (pale, blue), or increasing calf swelling/tightness
- Foot drop (inability to lift the foot) — needs urgent reassessment
- Expected recovery: Ligament reconstruction typically performed within 3 weeks if feasible; rehabilitation is prolonged (6–12+ months); many patients return to work and sport, though outcomes are worse with complete peroneal nerve palsy or vascular injury requiring repair [1][20-21]
- Peroneal nerve palsy: If no recovery by 12 months, posterior tibial tendon transfer may be considered for persistent foot drop [22]
References
1. Evaluation and Management of Knee Dislocations. — Wharton MG, Shultz CL, Schenck RC, Richter DL. The Journal of the American Academy of Orthopaedic Surgeons. 2025.
2. Vascular Injury After Knee Dislocation: A Meta-Analysis Update. — Constantinescu D, Luxenburg D, Syros A, et al. The Journal of the American Academy of Orthopaedic Surgeons. 2023.
3. Vascular and Nerve Injury After Knee Dislocation: A Systematic Review. — Medina O, Arom GA, Yeranosian MG, Petrigliano FA, McAllister DR. Clinical Orthopaedics and Related Research. 2014.
4. Evaluation and Management of Knee Dislocation in the Emergency Department. — Gottlieb M, Koyfman A, Long B. The Journal of Emergency Medicine. 2020.
5. A Systematic Review on Management and Outcome of Irreducible Knee Dislocations. — Malik SS, Osan JK, Aujla R, et al. Orthopaedics & Traumatology, Surgery & Research : OTSR. 2022.
6. Acute Management of Traumatic Knee Dislocations. — Jd Adams JD, Roward LG. The Orthopedic Clinics of North America. 2025.
7. Acute Management of Traumatic Knee Dislocations for the Generalist. — Boyce RH, Singh K, Obremskey WT. The Journal of the American Academy of Orthopaedic Surgeons. 2015.
8. Presentation and Surgical Management of Multiple Ligament Knee Injuries: A Multicenter Study From the Surgical Timing and Rehabilitation (STaR) Trial for MLKIs Network. — Poploski KM, Lynch AD, Burns TC, et al. The Journal of Bone and Joint Surgery. American Volume. 2023.
9. Can Vascular Injury Be Appropriately Assessed With Physical Examination After Knee Dislocation?. — Weinberg DS, Scarcella NR, Napora JK, Vallier HA. Clinical Orthopaedics and Related Research. 2016.
10. The Pathoanatomy of Posterolateral Corner Ligamentous Disruption in Multiligament Knee Injuries Is Predictive of Peroneal Nerve Injury. — Kahan JB, Li D, Schneble CA, et al. The American Journal of Sports Medicine. 2020.
11. Vascular Injuries in Knee Dislocations: The Role of Physical Examination in Determining the Need for Arteriography. — Stannard JP, Sheils TM, Lopez-Ben RR, et al. The Journal of Bone and Joint Surgery. American Volume. 2004.
12. Ankle-Brachial Index Is an Effective Screening Tool for Vascular Injury in Schatzker Type-4 to 6 Tibial Plateau Fractures With Symmetric Pulses. — Kantor AH, Thorne TJ, Dong W, et al. The Journal of Bone and Joint Surgery. American Volume. 2025.
13. Multiligament Knee Injury (MLKI): An Expert Consensus Statement on Nomenclature, Diagnosis, Treatment and Rehabilitation. — Murray IR, Makaram NS, Geeslin AG, et al. British Journal of Sports Medicine. 2024.
14. Establishing a Consensus Definition of a Knee Fracture-Dislocation (Schenck Knee Dislocation V) Using a Global Modified Delphi Method. — Medvecky MJ, Kahan JB, Richter DL, et al. The Journal of Bone and Joint Surgery. American Volume. 2023.
15. Single-Center Long-Term Results of Popliteal Artery Blunt Trauma Management Following Knee Dislocation - A Case Series Study. — Roditis K, Tzamtzidou S, Papas TT. Annals of Vascular Surgery. 2024.
16. ACR Appropriateness Criteria® Acute Trauma to the Knee. — Taljanovic MS, Chang EY, Ha AS, et al. Journal of the American College of Radiology : JACR. 2020.
17. Vascular Injuries Following Knee Dislocation. — Stannard JP, Schreiner AJ. The Journal of Knee Surgery. 2020.
18. Best Practices Guidelines In Imaging. — Gail T. Tominaga MD FACS, Mark Bernstein MD, Michael R. Aquino MD MHSc, et al American College of Surgeons (2018). 2018.
19. Knee Dislocation. — Bui K, Ilaslan H, Jones M, Sundaram M. Orthopedics. 2006.
20. A Systematic Review of Peroneal Nerve Palsy and Recovery Following Traumatic Knee Dislocation. — Woodmass JM, Romatowski NP, Esposito JG, Mohtadi NG, Longino PD. Knee Surgery, Sports Traumatology, Arthroscopy : Official Journal of the ESSKA. 2015.
21. Major Concern in the Multiligament-Injured Knee Treatment: A Systematic Review. — Vicenti G, Solarino G, Carrozzo M, et al. Injury. 2019.
22. Posterior Tibial Tendon Transfer Improves Function for Foot Drop After Knee Dislocation. — Molund M, Engebretsen L, Hvaal K, Hellesnes J, Ellingsen Husebye E. Clinical Orthopaedics and Related Research. 2014.