Marc Aguilar Garcia MD1, Carla Carbonell Rosell MD2, and Joan Pijoan Bueno MD2 1 Vall d’Hebron University Hospital, Barcelona, Spain 2 Clínica Corachan, Barcelona, Catalonia, Spain The role of MRI in acute trauma has classically been controversial; this section aims to resolve these doubts by shedding light with the help of currently published literature. Knee injury secondary to sports is a common reason for presentation to the Emergency Department. The majority of injuries are often due to extra‐articular soft tissue injury. Despite this, sometimes we find severe knee effusion which suggests hemarthrosis, and may involve injury to intra‐articular structures. A large intra‐articular effusion after trauma often points directly to a diagnosis of hemarthrosis through physical examination. Physical examination has great sensitivity to detect knee injuries, although the specificity is very low because it is difficult to perform specific maneuvers given that the patient often has significant pain and guarding. This is accentuated more at an early age, due to fear, guarding, or difficulty in expressing current symptoms. Traditionally, a delayed MRI was the gold standard treatment due to concerns about missed intra‐articular injuries in an early MRI. However, new studies have demonstrated that perhaps there is a role for early MRI. There is a wide spectrum of articles that discuss timing of MRI following injury, though most are level III–IV studies. At the moment, no randomized clinical trials have been published. One of the characteristics that should matter most about a diagnostic test is the ability to detect injuries and the ability to distinguish between them, that is a test that minimizes false‐negatives and false‐positives. Munshi et al. published a prospective double‐blind study performing MRI on a 1.5 T magnet and comparing the results to knee arthroscopy.1 They reported sensitivity and specificity for early MRI of 90 and 67%, respectively, for detecting any anterior cruciate ligament (ACL) injury, 50 and 86% for detecting medial meniscal tears, and 88 and 73% for detecting lateral meniscal tears. The overall detection of injury requiring surgical intervention yielded a sensitivity of 100% and a specificity of 71%. As previously mentioned, there are injuries that can may go unnoticed in the Emergency Department. Askenberger et al. conducted a prospective study in a pediatric hospital with children aged between 9 and 14 years;2 they observed that, even though 77% of children who visited the Emergency Department with knee trauma had serious intra‐articular injuries, 56% of these patients had no apparent lesion on plain radiography. Therefore, if there is a suspicion of serious injury, an MRI is recommended even in the context of normal X‐rays. Phelan et al. published a systematic review of the articles that correlated the initial MRI findings with findings during knee arthroscopy.3 They found that a positive finding on MRI doubled the probability of an ACL tear from 35.7 to 85.8%. They found several confounding factors: (i) the magnetic field strength of the MRI, (ii) the year of publication of the article, since MRI techniques have evolved, (iii) the ability to differentiate between complete and partial ACL tear, (iv) the radiologist’s experience, and (v) the blinding of the arthroscopist. A similar study conducted by Monaco et al. compared MRI findings with intraoperative anterolateral exploration in the acute ACL‐injured knee.4 They concluded that MRI evaluation demonstrated high sensitivity, specificity, and accuracy for the detection of abnormalities of the anterolateral ligament complex. For other parameters, the sensitivity and specificity were not as high, such as whether there was a complete tear or not. Abbasi et al. conducted a prospective study that aimed to describe the MRI findings in adolescents with traumatic knee effusions and to compare injuries based on age, sex, and physeal maturity.5
133 Initial Management of the Sports Injured Knee
Clinical scenario
Top three questions
Question 1: In patients with an acutely injured knee, does magnetic resonance imaging (MRI) performed acutely provide greater diagnostic ability compared to delayed MRI?
Rationale
Clinical comment
Available literature and quality of the evidence
Findings
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