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knee dislocation cover

Knee Dislocation

Case Introduction

A 65 year old male with COPD, HIV, Hypertension, coronary artery disease, peripheral vascular disease, and polysubstance abuse disorder presents via ambulance after getting struck by an automobile at an unknown speed. His vital signs are stable and the primary survey identifies an obvious left leg deformity which the patient characterizes as a 8 out of 10 pain. Sensation to light touch is intact in the superficial fibular, deep fibular and tibial nerve distributions. Motor exam is intact with extensor hallucis longus, flexor hallucis longus, tibialis anterior and gastrocsoleus. Radiographs are obtained which identify an anterior dislocation of the left knee.

Knee Dislocation

Knee dislocations are characterized by disruption of the normal articulation of the distal femur and proximal tibia. Note, a patella dislocation is a different clinical entity and should not be confused with a knee dislocation. The truce incidence of knee dislocation is likely underestimated as approximately 50% of them reduce spontaneously and are missed on initial evaluation. Studies have estimated knee dislocations to represent less than 0.02% of all orthopedic injuries and less than 0.5% of all joint dislocations.1Richter M, Lobenhoffer P, Tscherne H. Knee dislocation. Long term results after operative treatment. Chirurg. 1999;70:1294–301 One large database of knee dislocations identified that 83% were closed and 17% were open with a slightly increased risk in males and an average age of 35.2Arom, Gabriel A., et al. “The changing demographics of knee dislocation: a retrospective database review.” Clinical Orthopaedics and Related Research® 472.9 (2014): 2609-2614.
Knee XR - Dislocation AP, view 1 of 2
Anterior-posterior view of the knee dislocation
Knee XR - Dislocation Lateral, 2 of 2
Lateral view of initial knee dislocation
Knee dislocations can occur in any direction. Anterior is most common, representing about 40% of knee dislocations and occurs due to forced hyperextension.3Green NE, Allen BL. Vascular injuries associated with dislocation of the knee. J Bone Joint Surg Am 1977;59:236-9. Posterior occurs in 30% of cases and is commonly seen in motor vehicle crashes in which the knee impacts the dashboard. Medial (18%), lateral (4%) and rotational (<5%) are seen less commonly.
Knee Dislocation clinical
Presentation of our knee prior to reduction
The typical injury mechanism involves high energy trauma such as motor vehicle accidents, falls from height and industrial injuries. They can also be seen in lower energy mechanisms such as sports and sport-related activities. In morbidly obese patients, spontaneous dislocation can occur.
Associated injuries are implied by a knee dislocation as it is a catastrophic injury. The knee stabilizers are most commonly injured including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LC). Typically, 2 or more ligaments are injured. The biceps femoris, popliteus tendon and arcuate complex can also be injured. Also commonly seen are meniscus tears, chondral injuries, bone bruising, fractures and injuries to the extensor mechanism. Unfortunately, injuries to the popliteal artery (18 to 64%) and peroneal nerve can also be seen4Medina, Omar, et al. “Vascular and nerve injury after knee dislocation: a system

The differential diagnosis includes:

  • Knee Dislocation
  • Patella Dislocation
  • Distal Femur Fracture
  • Proximal Tibial Fracture
  • Proximal Fibular Fracture
  • Multiligament knee injury (consider a knee dislocation equivalent)
  • Extensor mechanism injury
  • Isolated ligament injury
knee dislocation dimple sign
The dimple sign1Harb, Ali, Denis Lincoln, and Jefferey Michaelson. "The MR dimple sign in irreducible posterolateral knee dislocations." Skeletal radiology 38 (2009): 1111-1114.
When obtaining a history, most patients should be able to describe a violent mechanism, although low energy mechanisms can occur. Deformity may or may not be present. The patient will be unable to ambulate and have instability if they tried to do so. On physical exam, about half of cases will have no deformity. The ‘dimple sign’ can be seen where there is buttonholing of the medial femoral condyle through the medial capsule. The most important part of the physical exam is performing a structural exam including drawer testing and varus and valgus testing. Additionally, a careful neurovascular exam should be performed. The popliteal, posterior tibial and dorsalis pedis arteries should be palpated. A nerve assessment should be performed on the tibial nerve and peroneal nerves
knee dislocation algorithim
Knee dislocation algorithm proposed by Ng et al2Ng, Jimmy Wui Guan, Yulanda Myint, and Fazal M. Ali. "Management of multiligament knee injuries." EFORT Open Reviews 5.3 (2020): 145-155.
Evaluation can be somewhat controversial depending on the clinical presentation. One algorithm has been proposed by Ng et al.5Ng, Jimmy Wui Guan, Yulanda Myint, and Fazal M. Ali. “Management of multiligament knee injuries.” EFORT Open Reviews 5.3 (2020): 145-155.In this algorithm, the first step is to reduce the knee if needed. If ischemia is noted on initial evaluation, the patient should go emergently to the operating room. If the limb is well perfused with present pulse and ankle-brachial index >0.9, the patient should be observed with serial examination. If a pulse is present but the ankle-brachial index is <0.9 OR if pulses are asymmetric, then CT angiography should be obtained. Much of the clinical decision making will be made based on physician preference and overall clinical picture. There may be a role for arterial ultrasound although this role is not yet well defined. Finally, MRI can typically be obtained as an outpatient and is much more useful to evaluate the extent of the soft tissue injuries.
In the acute setting, staff should follow the ATLS algorithm. The extent to which the patient requires a broader trauma workup will depend on the mechanism and clinical presentation. When focused on the knee, reduction should be performed only after radiographs are obtained to exclude fracture. Gentle traction distally is typically all that is required. The knee should be immobilized in extension. It is important to perform a thoughtful structural and neurovascular exam as discussed previously. If ischemia or a vascular injury is identified, then emergent surgical intervention for revascularization is indicated. Other indications for emergent surgery include an irreducible knee or an open dislocation.
knee dislocation popliteal artery injury
The popliteal artery is particularly susceptible to varying degrees of vascular injury as a result of a posterior knee dislocation. b DSA of the knee in this patient shows a lengthy non-opacified segment of the popliteal artery, which could be due to a partial transection or an occlusive intimal flap3Salloum, Elias, Sidhartha Tavri, and T. Gregory Walker. "Frostbite, Injury, and Trauma in the Extremities." Current Trauma Reports 3 (2017): 228-237.
Outside of the acute setting, most patients will need reconstruction of the major knee structures to have any chance of normal knee function. Rarely, nonoperative management will be considered in consultation with orthopedic surgery and that includes patients who are elderly, poor surgical candidates and/or unable to participate in the extensive rehabilitation process.
In terms of prognosis, patients with operative management have better functional outcomes compared to those with nonoperative management. One study found return to sport was 29% in the operative group and 10% in the nonoperative group.6Levy BA, Dajani KA, Whelan DB, Stannard JP, Fanelli GC, Stuart MJ, et al. Decision making in the multiligament-injured knee: An evidence-based systematic review. Arthroscopy. 2009;25:430–8. Patients who have surgery early are more likely to return to sport if performed within 3 weeks, however no functional differences were noted.7Levy BA, Dajani KA, Whelan DB, Stannard JP, Fanelli GC, Stuart MJ, et al. Decision making in the multiligament-injured knee: An evidence-based systematic review. Arthroscopy. 2009;25:430–8.
The most common complications are popliteal artery and peroneal nerve injuries. Amputation can occur and the rate is reported to be up to 85% if injuries are not corrected in the first 8 hours.8Green NE, Allen BL. Vascular injuries associated with dislocation of the knee. J Bone Joint Surg Am 1977;59:236-9. More chronically, patients will go on to develop some flavor of traumatic osteoarthritis, chronic pain, arthrofibrosis and knee stiffness. Some component of persistent knee instability is common and seen in nearly 50% of patients.

Case Conclusion

Consideration was made to obtain a CT angiography of the left lower extremity however, ultimately the patient was admitted for serial examination of distal pulses. MRI of the left knee was obtained the following day which showed: tearing of the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), fibular collateral ligament, medial collateral ligament (MCL), partial tear of the popliteus tendon, partial tear of the proximal head of the gastrocnemius, complex tear of the medial meniscus, bucket handle tear of the lateral meniscus, and a 8 mm osteochondral defect of the lateral femoral condyle. The popliteal artery was noted to be normal. The patient was subsequently discharged to subacute rehab and scheduled for staged reconstruction of the knee about one month later.

3 Key Points

  1. Knee dislocations are a catastrophic injury to the femoral-tibial joint
  2. They involve injury to multiple ligaments and internal structures of the knee that almost universally require surgical reconstruction
  3. The feared complication of popliteal artery injury is fairly common and requires emergent evaluation and surgical correction when present
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