RADIOLOGY CORNER

Military Medicine, Jun 2007 by Sanders, Timothy G, Folio, Les R

Answer to last month's radiology case and image: The Deep Lateral Femoral Notch: A Sign of Anterior Cruciate Ligament Disruption

Introduction

Internal derangement of the knee is a common sports related injury and the conventional radiograph is often the first imaging study performed following injury. Subtle osseous abnormalities can suggest the presence of a more serious underlying soft tissue injury and the "deep lateral femoral notch" sign is just such a finding and is usually associated with disruption of the anterior cruciate ligament (ACL). Identification of a deep lateral femoral sulcus on initial radiographs of the knee indicates the presence of anterolateral rotatory instability of the knee until proven otherwise. MR imaging of the knee will often demonstrate disruption of the ACL along with additional soft tissue injuries (1).

History

A 21-year-old man, twisted his knee while playing softball, and presented with pain and swelling of the knee. Radiographs of the knee (see lateral in Fig 1) were obtained.

Summary of Findings: Lateral radiograph of the knee demonstrates a deep, irregular appearing lateral femoral sulcus (arrow, Fig 1), and a small joint effusion, but is otherwise normal. MR demonstrates marrow edema in the lateral femoral condyle and in the posterior tibial plateau (small arrows, Fig 2). The lateral femoral sulcus appears deepened and irregular in contour (large arrow, Fig 2). MR T2 sagittal image through the region of the intercondylar notch demonstrates complete disruption of the anterior cruciate ligament (arrow, Fig 3).

Diagnosis

The Deep Lateral Femoral Notch: A Sign of Anterior Cruciate Ligament Disruption

Patient discussion: Several apparently minor osseous abnormalities of the knee have been described on conventional radiographs that are associated with more serious but radiographically occult soft tissue injuries. These include avulsion fracture of the anterior tibial spine and avulsion fracture of the lateral tibial plateau (Segond fracture), both associated with ACL disruption and avulsion fracture of the posterior intercondylar insertion of the posterior cruciate ligament (2-4). The deep femoral sulcus sign, however, is the most common radiographie sign associated with ligamentous injury of the knee. Because it is an impaction injury rather than an avulsion injury, it can be a subtle finding on radiographs, and one that is often overlooked.

A normal lateral radiograph of the knee demonstrates a normal shallow groove along the lateral femoral condyle that is formed by the junction of the tibiofemoral and patellofemoral curvatures. This notch is referred to as the lateral condylopatellar sulcus and it is normally smooth and symmetric in appearance measuring less than 1.5 mm in depth (5). During the pivot shift mechanism of injury, the knee while in slight flexion undergoes a twisting injury and valgus stress that leads to disruption of the ACL thus allowing anterior translation of the tibia relative to the femur. As the tibia and femur return to their normal position, the lateral femoral condyle impacts the posterolateral tibial plateau resulting in an osteochondral impaction fracture of the lateral femoral condyle.

The radiograph will demonstrate an irregular asymmetric appearing notch that is greater than 2 mm in depth. This is referred to as the "deep lateral femoral sulcus" sign. The depth of the notch is measured by drawing a line tangential to the sulcus (see figure 1 on the on-line full text version) along the articular surface of the lateral femoral condyle and then by measuring the distance from the line to the depth of the sulcus. The presence of a deep lateral femoral sulcus is nearly always associated with ACL disruption but lacks sensitivity; the absence of the sign therefore does not exclude the presence of an ACL tear (5).

References

1. Cobby MJ, Schweitzer ME, Resnick D: The deep lateral femoral sulcus notch: an indirect sign of a torn anterior cruciate ligament. Radiology 1992; 184(3): 855-8.

2. Eady JL, Cardenas CD, Sopa D. Avulsion of the femoral attachment of the anterior cruciate ligament m a seven-year-old child. J Bone Joint Surg [Am] 1982; 64-1376.

3. Woods GW, Stanely RF, Tullos HS. Lateral capsular sign: X-ray clue to a significant knee instability. Am J Sports Med 1979; 7:27.

4. Pauly T, VanEnde R. Avulsion fracture. Arch Orthop Trauma Surg 1989; 108:325.

5. Delzell PB, Schils JP, Recht MP. Subtle fractures about the knee: Innocuous-appearing yet indicative of significant internal derangement. AJR Am J Roentgenol 1996; 167(3): 699-703.

* Uniformed Services University, 4301 Jones Bridge Road, Bethesda, Maryland 20814

The full text version is available in a downloadable PDF file on the AMSUS page of the USUHS website at: http://rad.usuhs.mil/amsus.html

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Uniformed Services University of the Health Sciences or the Department of Defense. Reprint & Copyright euroby Association of Military Surgeons of U.S., 2006 .