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42. Multiligament Knee Injuries: The Knee Bone Is Connected to … Almost Nothing
Keywords
DislocationKneePoplitealMultiligamentCase
Knee Pain and Swelling Following Trauma
Pertinent History
The patient presented to the emergency department (ED) after crashing his mountain bike while out on a ride. His front tire got caught and he went over the handlebars coming down awkwardly on his right leg. He cannot recall the exact position of his leg when he landed, but he felt a pop and immediate pain in his knee. Since the accident he has been unable to ambulate due to the pain and swelling. He has never injured this knee before and has noticed some numbness in his right foot since the accident.
Pertinent Physical Exam
BP: 136/84, Pulse: 92, Temperature 98.4 °F (36.9 °C), RR 12, SpO2 99%.
Except as noted below, the findings of the complete physical exam are within normal limits.
Extremity:
2+ femoral pulses bilaterally, 2+ left DP/PT pulses, 1+ right DP/PT pulses, no ecchymosis or abrasions noted.
Musculoskeletal:
Negative log roll of the bilateral lower extremities. Right knee exam reveals an effusion and diffuse tenderness with limited range of motion. There is laxity and pain with varus and valgus stress at 0 and 30°, especially when compared with the left. Lachman testing reveals increased translation compared with the left with no firm endpoint appreciated.
PMH
None.
Pertinent Test Results
Right knee X-ray: Effusion with normal alignment and no signs of fracture.
ED Management
Knee immobilizer, crutches, pain control with urgent orthopedic referral.
Updates on Emergency Department Course
While waiting for his discharge, the patient reported increasing numbness to his right foot and lower leg. His knee pain was worsening despite pain medication. On re-examination, his right foot was dusky and cool and his distal pulses were no longer palpable. An ankle-brachial index (ABI) is obtained and a CT angiogram of his right lower extremity was ordered with emergent orthopedic surgery and vascular surgery consults. The CTA demonstrated an occlusion of the right popliteal artery. The patient was taken emergently to the OR for stabilization and revascularization.
Anthony Dean Godfrey, Fadi Hindi, Callum Ettles, Mark Pemberton, and Perbinder Grewal (https://commons.wikimedia.org/wiki/File:CTAngioOcclusionRtPop.jpg), https://creativecommons.org/licenses/by/4.0/legalcode
Learning Points
Priming Questions
- 1.
What injury mechanisms are most commonly associated with knee dislocations?
- 2.
How is this diagnosis made and what role does advanced imaging play in its immediate evaluation?
- 3.
What is the expected disposition for all patients with multiligament knee injuries?
Introduction/Background
- 1.
Although uncommon, multiligament knee injuries with dislocation/relocation, or identifiable knee dislocations, represent a limb-threatening emergency due to compromise of the vascular supply to the limb and, thus, must be recognized and acted upon urgently. Although the estimated incidence of knee dislocation is less than 0.02% of orthopedic injuries annually [1] or 2–29 orthopedic injuries per million annually, it is imperative to act swiftly and appropriately to avoid significant patient morbidity [2, 3]. In particular, it is important to maintain a high index of suspicion, as nearly 50% of knee dislocations spontaneously reduce prior to arrival in the emergency department (ED) and reduction does not preclude vascular injury [4].
Physiology/Pathophysiology
- 1.
Knee dislocations most commonly result from high-velocity mechanisms leading to blunt force against the knee and its many ligamentous attachments. Shearing of these stabilizing structures precedes translational movement of the tibia and fibula in reference to the femur and ultimately dislocation. Occasionally, low-energy mechanisms have resulted in dislocation injuries and typically involve an element of rotational force, particularly in obese patients. The translational displacement of the bones of the knee ultimately places significant stress on the limb’s vascular supply.
The knee joint is stabilized primarily by four collateral ligaments that are susceptible to rotational and shearing forces including the anterior and posterior cruciate ligaments as well as the medial and lateral collateral ligaments. In knee dislocations, typically three of the four stabilizing ligaments of the knee are disrupted, leaving the tibia and fibula vulnerable to translational displacement in reference to the femur resulting in dislocation [1].
The Kennedy system classifies knee dislocation based on displacement of the tibia in reference to the femur. Anterior dislocations are the most common, accounting for 30–50% of cases and generally occur with forced hyperextension of the knee [5]. Posterior dislocations are the second most common occurring in 25% of cases and are associated with the highest rate of complete tearing of the vascular supply of the lower leg [6]. Lateral dislocation occurs in approximately 13% of cases and result in the highest rate of peroneal nerve injury. Medial and rotational dislocation of the tibia occur infrequently [7].
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