Clinical History: 20 year-old male injured playing soccer. Sagittal proton-density weighted fat-suppressed images are provided. What are the findings? What is your diagnosis?
Findings
Figure 3:
(3a, 3b) Inspection of the posterolateral corner demonstrates hemorrhage in the popliteus muscle (3a arrow) and soft tissue hemorrhage and edema adjacent to the styloid process of the fibular head (3b arrow), at the site of arcuate ligament attachment. Bone bruises are present at the posterolateral tibia and within the fibular head (3a and 3b arrowheads).
Diagnosis
Anterior cruciate ligament tear with associated posterolateral corner injury.
Discussion
Posterolateral stability of the knee is maintained by a complex and variable arrangement of ligaments and tendons known as the posterolateral corner. The arcuate complex, a component of the posterolateral corner, is composed of the arcuate ligament, the fibular collateral ligament, and the popliteus muscle. Additional elements of the posterolateral corner include the fabellofibular ligament, popliteofibular ligament, and the posterolateral capsule.
Figure 4:
(4a) Anatomy of the posterolateral corner. 3D rendering of the posterolateral corner with the biceps femoris muscle and tendon removed demonstrates the Y-shaped arcuate ligament composed of the medial (blue) and lateral (red) limbs and its attachment (green) to the fibular styloid process. The biceps femoris tendon (BF), fibular collateral ligament (FCL), fabellofibular ligament (FF), popliteofibular ligament (PF), and popliteus muscle (PM) are also demonstrated.
Figure 5:
(5a) A coronal fat-suppressed T2-weighted image demonstrates the "arcuate sign", caused by an avulsion fracture of the fibula at the site of the fibular collateral ligament and biceps femoris tendon attachment (arrow). Associated injuries of the arcuate complex are demonstrated by extensive hemorrhage and edema within and posterior to the popliteus muscle (p), as seen on (5b) a fat-suppressed proton- density weighted axial view.
Conclusion
Injuries to the posterolateral corner are important to recognize but may be difficult to assess clinically because of coexisting injuries at the knee. In such cases, MRI can provide vital information regarding the status of the posterolateral corner, thus enabling more effective treatment and surgical planning.
References
1 LaPrade RF, Resig S, Wentorf FA, et al. The effects of grade III posterolateral knee complex injuries on force in an anterior cruciate ligament reconstruction graft: a biomechanical analysis. Am J Sports Med 1999;27:469-475.
2 Cooley VJ, Larson RV, Harrington RM. Effect of lateral ligament reconstruction on intra-articular posterior cruciate ligament graft forces and knee motion. University of Washington Orthopaedic Research Report. 1996:37-41.
3 Larson RV, Metcalf MH.Surgical Treatment of Posterolateral Instability. In: Fanelli GC, ed. Posterior Cruciate Ligament Injuries: A Practical Guide to Management. New York: Springer-Verlag, 2001:237-247.
4 Juhng SK, Lee JK, Choi SS, Yoon KH, Roh BS, Won JJ. MR evaluation of the “arcuate” sign of posterolateral knee instability. AJR 2002 Mar;178(3):583-8.