High Yield Topics

Knee Dislocation

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Ovid: 5-Minute Sports Medicine Consult, The


Knee Dislocation
Jane Kim
Basics
  • Knee dislocation is a rare but potentially devastating injury. It may lead to amputation or inability to return to full function.
  • The true incidence of knee dislocations is unknown owing to frequent spontaneous reduction. Missed spontaneous reductions may cause detrimental neurovascular damage. It is unnecessary to have complete dislocation for injury to the intimal wall of the popliteal artery (1,2,3).
  • High-velocity mechanism is a sudden violent force such as in a motor vehicle accident, falls from skiing, and injuries from gymnastics and extreme sports. They are usually associated with increased risk for neurovascular damage owing to more extensive disruption to the joint capsule.
  • Low-velocity injuries are usually due to sports such as football or rugby and usually have less soft tissue damage with better prognosis.
  • There are 6 structures within the knee that are at risk of injury with knee dislocation: Anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial cruciate ligament (MCL), lateral cruciate ligament (LCL), medial meniscus, and lateral meniscus.
  • The popliteal artery sits within the popliteal fossa with branches to the collateral artery supply. The geniculate collateral arteries cannot compensate for a ruptured popliteal artery.
  • The peroneal nerve wraps around the fibular head.
  • The definition of a knee dislocation is complete displacement of the tibia in regard to the femur with 3 or more stabilizing ligaments torn.
  • It is unnecessary to have complete dislocation for injury to the intimal wall of the popliteal artery.
  • Traditionally, 2 cruciate ligaments and 1 collateral ligament are torn; however, both cruciates do not have to be torn. Any 3 stabilizing ligaments torn is considered a dislocated knee.
  • The popliteal artery is damaged owing to the close proximity to the knee joint. It passes under the adductor canal cephalad and attaches to the soleus muscle caudad, which restricts its ability to stretch. Damage to the intimal wall of the popliteal artery may not be physically evident initially.
  • If vascular repair is not performed within 8 hr of injury, above-knee amputations are near 90% (1,3,4).
  • Cautions:
    • Documentation of pulses and motor response is essential.
    • Splint in slight flexion to prevent traction or compression of the popliteal artery.
Description
  • Defined by the position of the tibia in relationship to the distal femur
  • Anterior dislocation:
    • Most common dislocation; accounts for 60%
    • Hyperextension of the knee
    • Rupture of the posterior capsule at 30°
    • Rupture of the PCL and popliteal artery (PA)
  • Posterior dislocation:
    • Direct blow to the anterior tibia with the knee flexed at 90 degrees
    • ACL is usually spared.
  • Medial dislocation: Varus stress causing tear to ACL, PCL, and LCL
  • Lateral dislocation: Valgus stress causing tear to ACL, PCL, and MCL
  • Rotary dislocation:
    • Twisting mechanism (planted foot and body twis-ting in opposite direction) that can be further divided into anteromedial, anterolateral, posterolateral
    • Posterolateral dislocations are nearly impossible to be reduced by closed method.
  • Popliteal artery injury:
    • PA injury occurs in up to 30% of dislocations.
    • If vascular injury is not reversed within 6–8 hr, amputation rate approaches 90%.
    • Anterior dislocations place traction on the PA and cause contusion or intimal injury, which may result in delayed thrombosis.
    • Posterior dislocations cause direct intimal fracture or transection of the artery with immediate thrombosis.
  • Peroneal nerve injury:
    • Less common than arterial injury: If present, must rule out concomitant arterial insult.
    • Characterized by hypesthesia at 1st web space and lack of dorsiflexion of the foot
    • Poor prognosis for recovery
    • Medial dislocations cause injury by traction to the nerve.
    • Rotatory injuries have a high incidence of traction and transection.
Epidemiology
  • Up to 50% of knee dislocations reduce spontaneously; therefore, the actual incidence is unknown (2,3,4).
  • The most common mechanism of injury is a motor vehicle accident.
  • >50% of dislocations occur owing to anterior/posterior dislocation; most common cause for PA damage.
  • There is 10–40% PA injury rate with any knee dislocation
  • The peroneal nerve is injured close to 25% of the time; up to 50% of patients have permanent deficit (3,4).
Prevalence
  • Motor vehicle accidents (MVAs; 50–60%)
  • Falls (30%)
  • Industrial accidents (3–30%)
  • Sports (7–20%); on the rise owing to more extreme sports
Risk Factors
  • Morbid obesity is a potential risk factor for posterior dislocations.
  • Contact or high-velocity sports
Etiology
  • High-energy injuries such as MVAs, auto versus pedestrian accidents, and athletic injuries
  • Football is the most common source of athletic injuries.

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Diagnosis
  • Suspect a relocated knee dislocation if the patient had a high-impact injury with excessive knee laxity in full extension.
  • The initial physical exam may be difficult owing to excessive swelling and pain.
  • If peripheral pulses are normal initially, it is essential to do serial, frequent exams with documentation of pulses (1)[C].
  • Estimated 5–15% of knee dislocations may have a strong distal pulse initially with delayed expansion of intimal tear (1,5,6)[B].
  • Complete and careful physical exam, including:
    • Pulses: By palpation, Doppler, ankle-brachial pressure indexes, and distal perfusion (1)[C]
    • Neurologic: Sensation to the 1st web space and great toe, movement of the toes, dorsiflexion of the foot
  • Knee x-rays: Fractures common (periarticular, avulsion fracture, tibial plateau)
  • MRI
  • Repeat examination if any closed reduction is attempted.
  • Arterial imaging (“gold standard”) if any signs of limb ischemia (1,3)[A]
Pre Hospital
  • If covering a game or event with potential high-impact injuries, initially assess for life-threatening injuries.
  • Basic life support: ABCs; assess for head and neck injury.
  • If knee dislocation is suspected, immediate neurovascular assessment becomes the focus of the evaluation. Remove shoes and socks for better neurovascular exam only if safe. Compare posterior and dorsal pedal pulses bilaterally. Compare dermatomes, capillary refill, skin color, skin temperature, and motor strength (3,4)[C].
  • Splint in slight flexion (15–20 degrees) (1,3)[C].
  • Transfer to a facility capable of immediate reduction.
History
  • Patient will usually hear a pop at time of injury.
  • There is usually significant pain and swelling to knee immediately with decreased range of motion. However, there may be delayed swelling and effusion depending on the amount of capsular damage and fluid extravasation (4).
  • Have patient describe mechanism of injury, if possible.
Physical Exam
  • Subjective pain, instability, and swelling
  • Look at skin, palpate for pulses (DP/PT/popliteal)
  • Sensation, motor examination
  • Grossly deformed knee/asymmetry
  • Grossly unstable knee in anterior/posterior plane or on varus/valgus stress:
    • ACL and PCL, collateral ligament injuries
    • Suspect dislocation if having valgus/varus laxity with knee in extension or lack of distal pulses.
  • Popliteal thrill or expanding pulsatile hematoma
  • Signs of distal ischemia: Pallor, paresthesias (stocking glove or 1st web space), pain, paralysis
  • Unequal temperature of lower extremities
Diagnostic Tests & Interpretation
  • Patients with abnormal pulses who have symptoms or signs of ischemia should undergo immediate intraoperative arteriogram or surgical exploration (1,5,7)[C].
  • Patients with abnormal pulses but well-perfused limb should undergo arteriography (5)[C].
  • Those with normal pulses and well-perfused limb should undergo either arteriography or serial examinations depending on surgeon's preference (1,5)[C].
  • If no arteriogram is performed initially, observation for 24–48 hr is recommended for all cases of knee dislocation or multiligament injury (1)[C].
  • Frequent neurovascular checks should be performed, usually in the ICU.
  • A protocol that uses serial exams that include the dorsal medial pulse for 24–48 hr has been found to be highly sensitive and specific to detect vascular studies; however, it depends on the examiner and consistency (1,5)[C].
  • Currently there is a trend toward protocols that include serial physical exams and adjunctive studies (arterial-brachial index, duplex US) versus selective arteriography.
  • Adjunctive tests:
    • Duplex US may be able to detect injury that is non-flow-limiting (subclinical) and therefore may increase the sensitivity for a selective angiography protocol.
    • Arterial-brachial index (ABI): Systolic BP from all 4 extremities with Doppler probe and BP cuff. ABI = highest pressure from dorsal pedal pulse or posterior tibial pulse/highest brachial BP.
  • Prospective study: Mills and colleagues: 11/38 patients who required vascular surgery had an ABI <0.90.
    • No patients with an ABI >0.90 required vascular intervention surgery.
    • 1 patient had normal pulses and no hard signs of ischemia but had an ABI >0.90 and was found to have a positive arteriogram. This patient would have been missed without an ABI study.
    • 3 patients in this study would have undergone unnecessary arteriography.
    • Negative predictive value with an ABI >0.90 was 100%.
    • However, study is small and with no long-term follow-up.
    • Currently there is no conclusive evidence demonstrating any single selective angiography protocol to be superior. Therefore, any equivocal exam must have an arteriogram performed (1)[C].
  • Imaging/special tests:
    • Anteroposterior (AP) and lateral plain x-rays
    • Angiogram is indicated for any patient with poor distal perfusion, pulse return after reduction, abnormal pulses, signs of peroneal nerve injury, and ischemic symptoms despite normal pulse (1,3,4)[C].

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Lab
  • CBC
  • Basic metabolic protein with BUN/Cr
  • International normalization ratio (INR)/coagulation studies
Imaging
  • Radiographs
  • Duplex Doppler
  • ABI
  • MRI
Differential Diagnosis
  • Tibial plateau fracture
  • Supracondylar femoral fracture
Treatment
  • ABCs
  • Get history/mechanism of injury
  • Take off shoe/expose limb if stable (4)[C].
  • Assess distal pulses/popliteal pulses bilaterally, capillary refill, sensory, motor exam, range of motion (ROM), if able.
  • Splint knee in slight flexion or in position of comfort (1)[C].
  • Get pre- and postsplint distal pulses (1)[C].
  • Plan for reduction in ED.
ED Treatment
  • Closed reduction by longitudinal traction and lifting femur into normal alignment without placing pressure on the popliteal artery
  • Posterior leg splint in 15 degrees of flexion at knee (to avoid stretch of PA)
  • IV analgesia for patient comfort
  • Vascular and orthopedic surgical consultation for open injury, evidence of PA injury, or unable to reduce dislocation
  • If medial furrow on knee exam, suspect posterolateral dislocation, which cannot be reduced closed (3)[C].
Medication
  • Pain control with opiates
  • Avoid NSAIDs if possible need for surgery.
Additional Treatment
  • Physical therapy will be essential for conservative and postoperative treatment.
  • Rehabilitation depends on specific ligaments torn.
  • On average, 9 mos of arduous therapy (4)[C]
  • Knee dislocation complications: Chronic stiffness, pain, arthrosis, and instability (3,4)[C]
  • Unlikely to compete at same level
  • Peroneal nerve damage decreases likelihood of recovery to full activity (3,4)[C].
Surgery/Other Procedures
  • All vascular injuries will need a vascular surgeon consult.
  • Orthopedic consult
  • Ligamentous repair/reconstruction vs conservative treatment with splinting alone depends on activity level of patient.
  • Surgical treatment decreases stiffness.
  • Arthroscopic surgery is usually contraindicated until >2 wks after injury owing to capsular tears and extravasation of fluid. There is an increased risk for compartment syndrome (3).
  • Conservative treatment:
    • An option only for very sedentary patients, elderly, or if not able to undergo surgery
    • Knee immobilizer plus Jones compression dressing
    • Hinged knee brace locked in extension when good quadriceps strength
    • 6 wks average time of immobilization; if longer, complicated by stiffness (4)
In-Patient Considerations
Initial Stabilization
  • ABCs
  • Fluid resuscitation because hypotension may alter distal pulses and perfusion
  • Closed reduction must be performed as soon as possible in the ED.
  • Early surgical consultation in an open injury or a high suspicion of arterial injury
Admission Criteria
All patients with knee dislocation require admission for either arterial injury repair or observation of limb perfusion.

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Ongoing Care
Prognosis
  • Return to full competitive sport or activity is unlikely (3,4).
  • Prognosis depends on neurovascular damage, which depends on velocity of injury.
  • Peroneal nerve damage portends a worse prognosis.
  • Chronic stiffness, arthrosis, pain, and instability are common complaints (3,4).
Complications
  • Amputation
  • Compartment syndrome
  • Neurovascular deficit
  • Chronic pain
  • Stiffness
  • Instability
References
1. Nicandri GT, Chamberlain AM, Wahl CJ. Practical management of knee dislocations: a selective angiography protocol to detect limb-threatening vascular injuries. Clin J Sport Med. 2009;19:125–129.
2. Twaddle BC, Bidwell TA, Chapman JR. Knee dislocations: where are the lesions? A prospective evaluation of surgical findings in 63 cases. J Orthop Trauma. 2003;17:198–202.
3. Green J, Shahrdar C, Owens Brett. Knee dislocations. http://emedicine.medscape.com/article/1250829. updated 8/25/08. downloaded 7/12/09.
4. Henrichs A. A review of knee dislocations. J Athl Train. 2004;39:365–369.
5. Barnes CJ, Pietrobon R, Higgins LD. Does the pulse examination in patients with traumatic knee dislocation predict a surgical arterial injury? A meta-analysis. J Trauma. 2002;53:1109–1114.
6. Mills WJ, Barei DP, McNair P. The value of the ankle-brachial index for diagnosing arterial injury after knee dislocation: a prospective study. J Trauma. 2004;56:1261–1265.
7. Stannard JP, Sheils TM, Lopez-Ben RR, et al. Vascular injuries in knee dislocations: the role of physical examination in determining the need for arteriography. J Bone Joint Surg Am. 2004;86-A:910–915.
8. Ibrahim SA, Ahmad FH, Salah M, et al. Surgical management of traumatic knee dislocation. Arthroscopy. 2008;24:178–187.
Codes
ICD9
  • 836.0 Tear of medial cartilage or meniscus of knee, current
  • 836.1 Tear of lateral cartilage or meniscus of knee, current
  • 836.2 Other tear of cartilage or meniscus of knee, current
Clinical Pearls
  • Up to 50% knee dislocations reduce spontaneously.
  • If high-impact injury with knee deformity/gross swelling/laxity with valgus/varus stress testing, suspect knee dislocation.
  • Document pulses on serial exams prehospital, in ED, and as inpatient.
  • Normal pulse does not necessarily indicate normal PA.
  • Arteriogram is “gold standard” for diagnosis.
  • Duplex US and ABI are adjunctive studies to serial physical exams.
  • Neurologic deficit indicates worse injury and prognosis.
  • Address life-threatening conditions 1st.
  • When splinting, avoid full/hyperextension.
  • PA damage that is not surgically repaired within 8 hr is likely results in above-knee amputation (1,3,4).
  • Recovery to good function of the knee to perform daily activities of living is likely but to demanding sports is not predictable (8).
  • On average, extension loss is 0–2 degrees; flexion loss is 10–15 degrees (8).


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