Knee dislocation
Medical condition From Wikipedia, the free encyclopedia
A knee dislocation is an injury in which there is disruption of the knee joint between the tibia and the femur.[3][4] Symptoms include pain and instability of the knee.[2] Complications may include injury to an artery, most commonly the popliteal artery behind the knee, or compartment syndrome.[3][4][7]
| Knee dislocation | |
|---|---|
| |
| Plain lateral X-ray of the left knee showing a posterior knee dislocation[1] | |
| Specialty | Orthopedic surgery |
| Symptoms | Knee pain, knee deformity[2] |
| Complications | Injury to the artery behind the knee, compartment syndrome[3][4] |
| Types | Anterior, posterior, lateral, medial, rotatory[4] |
| Causes | Trauma[3] |
| Diagnostic method | Based on history of the injury and physical examination, supported by medical imaging[5][2] |
| Differential diagnosis | Femur fracture, tibial fracture, patellar dislocation, ACL tear[6] |
| Treatment | Reduction, splinting, surgery[4] |
| Prognosis | 10% risk of amputation[4] |
| Frequency | 1 per 100,000 per year[3] |
About half of cases are the result of major trauma and about half as a result of minor trauma.[3] About 50% of the time, the joint spontaneously reduces before arrival at hospital.[3] Typically there is a tear of the anterior cruciate ligament, posterior cruciate ligament, and either the medial collateral ligament or lateral collateral ligament.[3] If the ankle–brachial pressure index is less than 0.9, CT angiography is recommended to detect blood vessel injury.[3] Otherwise repeated physical exams may be sufficient.[2] More recently, the FAST-D protocol, assessing the posterior tibial and dorsalis pedis arteries for a ‘tri-phasic wave pattern’ with ultrasound, has been shown to be reliable in ruling out significant arterial injury.[8]
If the joint remains dislocated, reduction and splinting is indicated;[4] this is typically carried out under procedural sedation.[2] If signs of arterial injury are present, immediate surgery is generally recommended.[3] Multiple surgeries may be required.[4] In just over 10% of cases, an amputation of part of the leg is required.[4]
Knee dislocations are rare, occurring in about 1 per 100,000 people per year.[3] Males are more often affected than females.[2] Younger adults are most often affected.[2] Descriptions of this injury date back to at least 20 BC by Meges of Sidon.[9]
Signs and symptoms
Symptoms include knee pain.[2] The joint may also have lost its normal shape and contour.[2] A joint effusion may, or may not, be present.[2]
Complications
Complications may include injury to the artery behind the knee (popliteal artery) in about 20% of cases or compartment syndrome.[3][4] Damage to the common peroneal nerve or tibial nerve may also occur.[2] Nerve problems, if they occur, often persist to a variable degree.[11]
Cause
About half are the result of major trauma, the other half as a result of minor trauma.[3] Major trauma may include mechanisms such as falls from a significant height, motor vehicle collisions, or a pedestrian being hit by a motor vehicle.[2] Cases due to major trauma often have other injuries.[5]
Minor trauma may include tripping while walking or while playing sports.[2] Risk factors include obesity.[2]
The condition may also occur in a number of genetic disorders such as Ellis–van Creveld syndrome, Larsen syndrome, and Ehlers–Danlos syndrome.[12]
Diagnosis
Summarize
Perspective
As the injury may have self-reduced before arrival at hospital, the diagnosis may not be readily apparent.[2] Diagnosis may be suspected based on the history of the injury and physical examination[5] which may include anterior drawer test, valgus stress test, varus stress test, and posterior sag test.[5] An accurate physical exam can be difficult due to pain.[5]
Plain X-rays, CT scan, ultrasonography, or MRI may help with the diagnosis.[2][11] Findings on X-ray that may be useful among those who have already reduced include a variable joint space, subluxation of the joint, or a Segond fracture.[5]
If the ankle–brachial pressure index (ABI) is less than 0.9, CT angiography is recommended.[3] Standard angiography may also be used.[2] If the ABI is greater than 0.9 repeated physical exams over the next 24 hours to verify good blood flow may be sufficient.[2][11] The ABI is calculated by taking the systolic blood pressure at the ankle and dividing it by the systolic blood pressure in the arm.[2] More recently, the FAST-D protocol, using ultrasound to assess the posterior tibial and dorsalis pedis arteries for a ‘tri-phasic wave pattern’, has been shown to be reliable in ruling out significant arterial injury.[8]
Classification
They may be divided into five types: anterior, posterior, lateral, medial, and rotatory.[4] This classification is based on the movement of the tibia with respect to the femur.[11] Anterior dislocations, followed by posterior, are the most common.[2] They may also be classified on the basis of which ligaments are injured.[2]
Treatment
Initial management is often based on Advanced Trauma Life Support.[5] If the joint remains dislocated reduction and splinting is indicated.[4] Reduction can often be done with simple traction after the person has received procedural sedation.[11] If the joint cannot be reduced in the emergency department, then emergency surgery is recommended.[2]
In those with signs of arterial injury, immediate surgery is generally carried out.[3] If the joint does not stay reduced external fixation may be needed.[2] If the nerves and artery are intact the ligaments may be repaired after a few days.[11] Multiple surgeries may be required.[4] In just over 10% of cases an amputation of part of the leg is required.[4]
Epidemiology
Knee dislocations are rare: they represent about 1 in 5,000 orthopedic injuries,[5] and about 1 knee dislocation occurs annually per 100,000 people.[3] Males are more often affected than females, and young adults the most often.[2]
References
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