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Emergency And Acute Medicine – Knee Dislocation
Basics Description
Knee dislocation is defined by displacement of the tibia relative to the distal femur and represents a true orthopedic emergency because of the high risk of vascular and neurologic injury. Anterior dislocation is the most common type, accounting for approximately 60% of cases, and typically results from hyperextension. Rupture of the posterior capsule may occur at 30° of hyperextension, with disruption of the posterior cruciate ligament and potential popliteal artery injury at greater degrees. Posterior dislocation usually results from a direct blow to the anterior tibia with the knee flexed, such as a dashboard injury. Medial and lateral dislocations occur from varus or valgus stress, respectively, and are associated with multiligamentous injuries.
Popliteal artery injury occurs in up to 35% of knee dislocations and is the most limb-threatening complication. Anterior dislocations commonly cause traction-related intimal injury with delayed thrombosis, whereas posterior dislocations are more likely to cause direct arterial transection and immediate thrombosis. Peroneal nerve injury is less common but clinically significant and often accompanies arterial injury, particularly in medial or rotational dislocations.
Etiology
Knee dislocations typically result from high-energy mechanisms such as motor vehicle collisions, auto–pedestrian trauma, or athletic injuries, most commonly football.
Diagnosis Signs And Symptoms
Patients may present with a grossly deformed or unstable knee, though spontaneous reduction can mask deformity. Absence of distal pulses or signs of ischemia such as pallor, paresthesia, pain, paralysis, or poikilothermia raise immediate concern for popliteal artery injury. Neurologic deficits may include decreased sensation in the first web space or inability to dorsiflex the foot. A careful history of the mechanism of injury and repeated neurovascular examinations are essential.
Essential Workup
Evaluation requires a detailed history and thorough physical examination with emphasis on vascular and neurologic status. Distal pulses should be assessed by palpation and Doppler, capillary refill documented, and ankle–brachial index calculated. Neurologic examination should assess peroneal nerve function. Repeat examinations are mandatory, especially after reduction.
Diagnosis Tests And Interpretation
AP and lateral knee radiographs are required to confirm alignment and exclude associated fractures. MRI within one week is useful for defining ligamentous injury. An ABI ≥0.9 suggests low likelihood of major arterial injury, but abnormal findings warrant further evaluation. Vascular ultrasound or arteriography should be considered when pulses are diminished, ischemic symptoms persist, or peroneal nerve injury is present.
Differential Diagnosis
Conditions to consider include tibial plateau fracture, supracondylar femoral fracture, and ligamentous or tendinous avulsion injuries.
Treatment Pre Hospital
Initial management focuses on airway, breathing, and circulation. Distal pulses and motor function must be documented. The knee should be splinted in slight flexion to minimize popliteal artery tension.
Initial Stabilization Therapy
Address ABCs, particularly in polytrauma patients. Hypotension should be corrected, as it may obscure vascular compromise. Immediate closed reduction is indicated for any evidence of limb ischemia, with early orthopedic and vascular consultation.
Ed Treatment Procedures
Closed reduction is performed using longitudinal traction with gentle realignment, avoiding pressure in the popliteal fossa. The knee is immobilized in 15–20° of flexion. Neurovascular status must be reassessed immediately after reduction and monitored frequently. IV analgesia should be provided, and surgical consultation obtained for open injuries, vascular compromise, or irreducible dislocations.
Medication
IV narcotic analgesia is first-line. Oral medications should be avoided due to the high likelihood of operative intervention.
Follow-Up Disposition
All patients with knee dislocation require admission for observation and management of potential vascular injury. Discharge from the ED is not appropriate.
Follow-Up Recommendations
Orthopedic follow-up is required for staged ligamentous repair, typically delayed until swelling subsides. Vascular surgery follow-up is necessary if popliteal artery injury is identified.
Pearls And Pitfalls
Failure to restore popliteal artery flow within 6–8 hours carries an amputation risk approaching 90%. Peroneal nerve injury has a poor prognosis for recovery. Delayed compartment syndrome may occur and requires vigilant monitoring.
Basics Description
Knee dislocation is defined by displacement of the tibia relative to the distal femur and represents a true orthopedic emergency because of the high risk of vascular and neurologic injury. Anterior dislocation is the most common type, accounting for approximately 60% of cases, and typically results from hyperextension. Rupture of the posterior capsule may occur at 30° of hyperextension, with disruption of the posterior cruciate ligament and potential popliteal artery injury at greater degrees. Posterior dislocation usually results from a direct blow to the anterior tibia with the knee flexed, such as a dashboard injury. Medial and lateral dislocations occur from varus or valgus stress, respectively, and are associated with multiligamentous injuries.
Popliteal artery injury occurs in up to 35% of knee dislocations and is the most limb-threatening complication. Anterior dislocations commonly cause traction-related intimal injury with delayed thrombosis, whereas posterior dislocations are more likely to cause direct arterial transection and immediate thrombosis. Peroneal nerve injury is less common but clinically significant and often accompanies arterial injury, particularly in medial or rotational dislocations.
Etiology
Knee dislocations typically result from high-energy mechanisms such as motor vehicle collisions, auto–pedestrian trauma, or athletic injuries, most commonly football.
Diagnosis Signs And Symptoms
Patients may present with a grossly deformed or unstable knee, though spontaneous reduction can mask deformity. Absence of distal pulses or signs of ischemia such as pallor, paresthesia, pain, paralysis, or poikilothermia raise immediate concern for popliteal artery injury. Neurologic deficits may include decreased sensation in the first web space or inability to dorsiflex the foot. A careful history of the mechanism of injury and repeated neurovascular examinations are essential.
Essential Workup
Evaluation requires a detailed history and thorough physical examination with emphasis on vascular and neurologic status. Distal pulses should be assessed by palpation and Doppler, capillary refill documented, and ankle–brachial index calculated. Neurologic examination should assess peroneal nerve function. Repeat examinations are mandatory, especially after reduction.
Diagnosis Tests And Interpretation
AP and lateral knee radiographs are required to confirm alignment and exclude associated fractures. MRI within one week is useful for defining ligamentous injury. An ABI ≥0.9 suggests low likelihood of major arterial injury, but abnormal findings warrant further evaluation. Vascular ultrasound or arteriography should be considered when pulses are diminished, ischemic symptoms persist, or peroneal nerve injury is present.
Differential Diagnosis
Conditions to consider include tibial plateau fracture, supracondylar femoral fracture, and ligamentous or tendinous avulsion injuries.
Treatment Pre Hospital
Initial management focuses on airway, breathing, and circulation. Distal pulses and motor function must be documented. The knee should be splinted in slight flexion to minimize popliteal artery tension.
Initial Stabilization Therapy
Address ABCs, particularly in polytrauma patients. Hypotension should be corrected, as it may obscure vascular compromise. Immediate closed reduction is indicated for any evidence of limb ischemia, with early orthopedic and vascular consultation.
Ed Treatment Procedures
Closed reduction is performed using longitudinal traction with gentle realignment, avoiding pressure in the popliteal fossa. The knee is immobilized in 15–20° of flexion. Neurovascular status must be reassessed immediately after reduction and monitored frequently. IV analgesia should be provided, and surgical consultation obtained for open injuries, vascular compromise, or irreducible dislocations.
Medication
IV narcotic analgesia is first-line. Oral medications should be avoided due to the high likelihood of operative intervention.
Follow-Up Disposition
All patients with knee dislocation require admission for observation and management of potential vascular injury. Discharge from the ED is not appropriate.
Follow-Up Recommendations
Orthopedic follow-up is required for staged ligamentous repair, typically delayed until swelling subsides. Vascular surgery follow-up is necessary if popliteal artery injury is identified.
Pearls And Pitfalls
Failure to restore popliteal artery flow within 6–8 hours carries an amputation risk approaching 90%. Peroneal nerve injury has a poor prognosis for recovery. Delayed compartment syndrome may occur and requires vigilant monitoring.
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