The posterolateral corner of the knee: the normal and the pathological Poster No.: P-0104 Congress: ESSR 2014 Type: Educational Poster Authors: M. Bartocci 1, C. Dell'atti 2, E. Federici 1, V. Martinelli 1, N. Magarelli 2, Keywords: DOI: L. Bonomo 2 ; 1 Roma/IT, 2 Rome/IT MR, Musculoskeletal joint, Extremities, Education, Education and training 10.1594/essr2014/P-0104 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.essr.org Page 1 of 11
Learning objectives To illustrate the MRI of the posterolateral corner of the knee in normal conditions and in case of injury. Background The anatomy of the posterolateral corner (PLC) is complex and it includes the following structures: the fibular collateral ligament, the biceps femoris tendon, the arcuate ligament, the popliteus musculotendinous unit, the popliteofibular ligament, and the variably present fabellofibular ligament, as well as the posterolateral portion of the joint capsule and the lateral gastrocnemius muscle (Fig. 1). PLC injuries are not as common as those involving the medial joint compartment and they are most often observed in severe extension and varus stress. Acute posterolateral instability is rarely an isolated event as it is often associated with concomitant injury to the cruciate ligaments, as such, the clinical picture may be dominated by a cruciate ligament or other ligamentous derangement. Neglecting an injury of the PLC can result in chronic posterolateral instability and/or failure of the anterior cruciate ligament and posterior cruciate ligament reconstruction. Moreover, diagnosis and subsequent surgical treatment of acute posterolateral injury should be performed in a timely fashion before scar tissue obscures identification of injured structures. Therefore, it is imperative that the musculoskeletal radiologist assist the referring physician in assessing injury to posterolateral structures to promote early and aggressive treatment. PLC injury is thus one of the few MRI emergencies in skeletal radiology. Images for this section: Page 2 of 11
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Fig. 1: Illustration of the structures of the PLC of the knee from a coronal plane perspective. From medially to laterally popliteus muscle, popliteofibular ligament, arcuate ligament with a medial limb spanning the popliteus muscle and a lateral limb that joins the lateral join capsule, fibular collateral ligament, biceps femoris tendon, lateral gastrocnemius muscle and posterolateral portion of the joint capsule. Page 4 of 11
Imaging findings OR Procedure Details The PLC structures are best identified using the coronal and axial MRI planes. Some investigators have found superior visualization of the ligaments by the use of a coronal oblique plane with the popliteus tendon as the key structure (Fig. 2). Specific components of the PLC that can be identified on MRI, albeit with some variability, are the fibular collateral ligament, the biceps femoris tendon, the popliteus musculotendinous unit, the popliteofibular ligament, the fabellofibular ligament and the arcuate ligament. The fibular collateral ligament originates from the lateral femoral condyle immediately below the lateral gastrocnemius muscle and insert as conjoined tendon with the biceps femoris tendon at the head of the fibula, laterally. The popliteus tendon arises from the lateral femoral condyle intra-articular below the lateral collateral ligament and attaches at the posteromedial surface of the proximal tibia. The popliteus tendon is connected to the fibula by the popliteofibular ligament, which inserts medially at the head of the fibula. The arcuate ligament is a thickening of the joint capsule, has an Y-shaped configuration and inserts at the head of the fibula immediately medially to the conjoined tendon of the fibular collateral ligament and biceps femoris. The fabellofibular ligament is an inconsistent ligament that arises from the fabella, an osseous or cartilaginous body adjacent to the gastrocnemius tendon, and inserts at the lateral base of the fibular head between the popliteofibular ligament and the arcuate ligament (Fig. 3). In general, these normally low-signal-intensity structures are defined as injured when there is thickening and intermediate signal intensity within the structure on T2-w images and as torn when the structure is discontinuous with a visible gap. Injuries to the posterolateral ligamentous structures are often classified as grade I, II, or III sprains, corresponding to minimal, partial, or complete tearing, respectively. Grade III injuries are usually associated with markedly abnormal joint motion and are the most clinically relevant from a surgical standpoint (Fig. 4). Injuries of the PLC structures are often associated with other ligamentous injuries, particularly the anterior cruciate ligament, the posterior cruciate ligament and the medial collateral ligament. Other imaging signs described to occur with posterolateral corner injuries include fractures of the fibular styloid process (arcuate fracture), avulsion fracture (Segond fracture) of the lateral tibia, fractures of the peripheral anteromedial tibial plateau and bone marrow contusion on the anteromedial femoral condyle (Fig. 5). Images for this section: Page 5 of 11
Fig. 2: a Coronal GRE MRI plane; b axial T1-w MRI plane; c coronal oblique T1-w MRI plane. Page 6 of 11
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Fig. 3: a, b, c Coronal GRE MRI; d, e axial T1-w MRI; f sagittal T1-w MRI. Specific components of the PLC that can be identified on MRI: fibular collateral ligament (white arrows), popliteus miotendinous unit (pink arrows), popliteofibular ligament (yellow arrow), fabellofibular ligament (orange arrow), biceps femoris tendon (green arrows), arcuate ligament (blue arrows). Fig. 4: a, b, d Coronal GRE MRI; c sagittal T1-w MRI. Partial injury of biceps femoris tendon (green arrow); high signal intensity consistent with oedema of the popliteus tendon (pink arrows); avulsion of the distal attachment to the fibular head of fibular collateral ligament (white arrow). Page 8 of 11
Fig. 5: a sagittal T1-w MRI; b coronal fatsuppressed FSE T2-w MRI; c XR of knee; d coronal GRE MRI. Acute lesion of anterior cruciate ligament (black arrow); arcuate fracture of the fibular styloid process (white arrow); avulsion fracture (Segond fracture) of the lateral tibia (yellow arrows). Page 9 of 11
Conclusion Because MRI is commonly performed in the setting of knee injury, radiologists familiar with the normal and abnormal appearances of the PLC structures on MRI can suggest the diagnosis of PLC injury when present, leading to improvements in treatment and functional outcomes for patients in whom the injury was not clinically suspected. References 1. S. Harisha et all, Imaging of the posterolateral corner of the knee, Clinical Radiology (2006) 61, 457-4662. 2. E. N. Vinson et all, The Posterolateral Corner of the Knee, AJR: 190 (2008)3. 3. Josephine Lee et all, Arcuate sign of posterolateral knee injuries: anatomic, radiographic, and MR imaging data related to patterns of injury, Skeletal Radiol (2003) 32:619-6274. 4. Nadja A. Farshad-Amacker et all, MRI of Knee Ligament Injury and Reconstruction, JOURNAL OF MAGNETIC RESONANCE IMAGING (2013) 38:757-7735. 5. David A. Pacholke et all, MRI of the Posterolateral Corner Injury: A Concise Review, JOURNAL OF MAGNETIC RESONANCE IMAGING (2007) 26:250-2556. 6. Ralph Gnannt et all, MR Imaging of the Postoperative Knee, JOURNAL OF MAGNETIC RESONANCE IMAGING (2011) 34:1007-10217. 7. A. A. Malone et all, Injuries of the posterior cruciate ligament and posterolateral corner of the Knee (2006) 37, 485-501 Personal Information M. Bartocci, E. Federici, V. Martinelli: radiology residents at Policlinico Agostino Gemelli, Largo Gemelli 8, 00168 Roma, Italy C. Dell'Atti, N. Magarelli: Radiologists at Policlinico Agostino Gemelli, Largo Gemelli 8, 00168 Roma, Italy L. Bonomo: Head of departement of Radiological Sciences at Policlinico Agostino Gemelli, Largo Gemelli 8, 00168 Roma, Italy Page 10 of 11
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