knee dislocation cover

A Quick Update on Knee Dislocations

Knee dislocations are a catastrophic injury to the knee defined by loss of articulation between the femur and the tibia. (Note: They should not be confused with patellar dislocations, which are a separate entity). The incidence of knee dislocations is likely understated due to approximately half of them spontaneously reducing and being missed on initial evaluation. They represent less than 0.02% of all orthopedic injuries and less than 0.5% of all joint dislocations (Richter 1999). Among a larger cohort studied by Arom et al, approximately 17% were considered open (the rest were closed), the mean age was 35 and men were slightly higher risk than females (Arom 2014).

Case Introduction

You are called over to the examination table by the athletic trainer to evaluate a 19 year old soccer player with knee pain during a game. The player says he was cutting when he felt his knee buckle. On exam, he has an obvious effusion, has laxity with valgus stress at both 0 and 30 degrees as well as an equivocal lachmans. Given these findings, what is your most immediate concern in this player?

A) ACL Injury
B) MCL Injury
C) Vascular injury
D) Bone contusion

The etiology of knee dislocations is most commonly high energy trauma such as motor vehicle accidents or fall from height. They can also be seen in low energy mechanisms and sport-related activities. There are case reports of spontaneous dislocations during ambulation in morbidly obese patients (Marin 1990). The majority of dislocations are anterior due to forced hyperextension of the knee, representing about 40% of cases. Posterior dislocations are the second most common at 30%, often the result of the tibia impacting the dashboard of a car during a motor vehicle crash. Other directions including medial (18%), lateral (4%) and rotational (less than 5%) are less common.
In the setting of a high energy mechanism, patients may present with an obvious deformity. However many of these will spontaneously reduce in the field. Athletes and other low energy mechanisms are often more subtle and require a very careful physical exam. Physicians should very carefully document a neurovascular exam, especially the popliteal, dorsalis pedis (DP) and posterior tibial (PT) arteries. A structural exam of the knee is critical to assess the integrity of the ACL, PCL, MCL, LCL and posterolateral corner. It is important to mention that a multi-ligament knee injury should be considered the equivalent of a knee dislocation.
dislocation of knee arthroplasty xray

Image 1. Spontaneous posterior knee dislocation following total knee arthroplasty.

knee dislocation xray

Image 2. Posterior knee dislocation of native knee with significant pneumarthrosis

Standard radiographs may be normal but can show irregular or widened joint space, segund fracture or an osteochondral defect. MRI is indicated in all cases after reduction and prior to surgical intervention. CT can be useful to better evaluate fracture patterns. Vascular imaging is critical in these patients as palpable DP and PT pulses does not exclude a vascular injury. At the very minimum, these patients need to be admitted for serial vascular exams. Advanced vascular evaluation should include some combination of ankle-brachial index (ABI), duplex arterial sonography and CT arteriography is probably the gold standard. There is no consensus on the best workup for patients with known knee dislocation and no obvious vascular injury initially.
popliteal artery injury angiogram

Image 3. Angiography of politeal artery with occlusion of flow

knee mri popliteal artery hematoma

Image 4. Sagittal view of MRI following multiligament knee injury with popliteal artery hematoma

Acute management should include ATLS algorithm if the mechanism was high energy. If the knee is dislocated on evaluation in the emergency department, reduction should be performed after initial xrays under procedural sedation and immobilized. This is an orthopedic surgical emergency and potentially a vascular surgical emergency. Indications for emergent surgery include irreducible knee dislocation, open dislocation or vascular injury. If no emergent indication exists, then patients can have a delayed ligamentous reconstruction of their knee on an elective, outpatient basis. Operative management has resulted in better functional outcomes and return to sport when compared to nonoperative management (Levy 2009). Surgery performed within 3 weeks is associated with a higher likelihood of return to sport (Levy 2009).
Spontaneous knee dislocations are associated with numerous complications which can loosely be divided into acute and chronic. Acutely, popliteal artery injury is the most worrisome and seen in between 18 and 64% of knee dislocations (Medina 2014). The risk is lower in sports-related injuries than high-velocity injuries (Shelbourne 2000). Revascularization within 8 hours is associated with a lower risk of amputation than when delayed beyond that time with 11% vs 86% respectively (Green 1977). Peroneal nerve injuries occur in between 25 and 33% of knee dislocations (Meyers 1971) with complete palsies having a lower likelihood of functional recovery than incomplete palsies (Woodmass 2015). Additional acute injuries include ligamentous (ACL, PCL, MCL, LCL, posterior capsule, meniscus), chondral injuries, bone bruising (majority) or fractures (⅓ of cases), extensor mechanism, biceps tendon and popliteus tendon tears. Chronic complications include traumatic osteoarthritis, chronic pain (25-68%), arthrofibrosis (5-71%), knee stiffness and persistent knee instability (42%).
Transtrochanteric rotational osteotomy (TRO) has become one of the hip-preserving alternatives for AVNFH. The principle of TRO is to replace necrotic bone with healthy bone in weight-bearing area through anterior or posterior rotation after intertrochanteric osteotomy [25]. It is typically used only for small lesions with less than 15 percent involvement in which the lesion can be rotated away from a weight bearing surface. The clinical outcomes of TRO remain controversial because the promising results of several Japanese studies could not be confirmed by American and European studies [26-28]. One recent meta-analysis concluded hip survival was better in Asain populations [29].
More Knee Pain from Sports Medicine Review

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Case Answer

Case Conclusion. The answer is C. This athlete has an exam concerning for a multiligament knee injury which likely includes ACL and MCL. A multiligament knee injury should be considered the equivalent of a knee dislocation until proven otherwise. In this athletes case, it would be important to perform a thorough neurovascular exam. At the bare minimum, he will require serial exams over the next 24 hours. If there is any question or concern for a vascular injury, meaning popliteal artery, then he needs to be sent to the emergency department for advanced vascular workup.

Moatshe, Gilbert, et al. “Diagnosis and treatment of multiligament knee injury: state of the art.” Journal of ISAKOS: Joint Disorders & Orthopaedic Sports Medicine 2.3 (2017): 152-161.


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