uhrad.com - Musculoskeletal Imaging Teaching Files

Case Eight - Disruption of the Anterior Cruciate Mechanism

Click on Images for Enlarged View

Clinical History: A 42 year old woman presented after a twisting knee injury with associated fall.

Findings: AP and lateral radiographs of the knee (Fig. 1 a,b) were obtained. Three avulsion fractures are demonstrated:

A CT scan (Fig. 2) was performed 12 days later as the patient was not improving with conservative management. Coronal (2a), sagittal (2b,c), and 3D (2d) reconstruction were obtained. With CT, the fractures were more clearly delineated, additional fragments identified, and interval inversion of the intercondylar eminence fragment identified.

Due to failure of conservative management and the inversion of the eminence fracture fragment, the patient underwent arthroscopy. The eminence fracture was reduced, a coincident distal partial anterior cruciate ligament tear was identified and repaired, and partial meniscectomy was performed for a lateral meniscal tear.

Diagnosis: Disruption of the anterior cruciate mechanism with associated Segond fracture, avulsion fractures of the intercondylar eminence and fibular head, partial ACL tear, and lateral meniscus tear.

Discussion:In the MR era the roles of plain radiographs and computed tomography in the evaluation of knee trauma are often overlooked. In the setting of acute trauma where the physical examination can be difficult due to pain, swelling, and patient anxiety, x-ray studies can detect osseous injuries that can strongly impact on acute management, as well as signify significant internal derangement (1). In addition, these injuries, which are often small avulsions injuries, may be difficult to appreciate on MR.

The Segond fracture is an avulsion fracture at the insertion of the lateral capsular ligament in the directly lateral proximal tibia, right below the plateau. It has a characteristic radiographic appearance as a small (roughly 10 x 3mm) elliptical fragment with vertical fracture line separating it from the tibia (2). Optimal radiographic technique is essential in its identification as the fragment is often quite thin and difficult to see. The direct lateral position of the fracture is helpful in distinguishing it from the more uncommon avulsion fracture of the Gerdy tubercle at the insertion of the iliotibial band on the anterolateral proximal tibia (1). Radiographically, a donor site will be seen on the AP view with the Segond fracture; the more anterior donor site of avulsion of Gerdy's Tubercle will not be profiled.

The importance of the Segond fracture is its high association with internal derangement. Meniscal tears have been reported in more than 50% (3). Disruption of the anterior cruciate ligament mechanism occurs in 75-100% (2,3). Though most often taking the form of a midsubstance ligamentous tear, occasionally an avulsion fracture of intercondylar eminence of the tibia will be seen (2,3), as in this case. These fractures of the intercondylar eminence are classified into 4 types:

Management is generally conservative for isolated type I & II fractures and surgical for inverted fragments. Management of isolated complete fractures without inversion largely depends on the degree of displacement (4,5,6). Inversion can be difficult to ascertain on plain films, in part due to the thick subchondral sclerosis often seen at the proximal tibia. CT defines this much more readily, as in our case.

Our case demonstrated a third fracture, as well, a nondisplaced avulsion of the fibular head at the insertion of the conjoined tendon of the biceps femoris and the fibular collateral ligament. This injury has also been reported in a small percentage of participants with Segond fractures (2,3); We are not aware of other reports of all three avulsions occurring simultaneously.

References:
1.Capps GW, Hayes CW. Easily Missed Injuries Around the Knee. Radiographic 14:1191-1210, 1994

2.Dietz GW, Wilcox DM, Montgomery JB. Segond Tibial Condyle Fracture:
Lateral Capsular Ligament Avulsion. Radiology 159:467-469, 1986.

3.Goldman AB, Pavlow H, Rubenstein D. The Segond Fracture of the Proximal Tibia:
A Small Avulsion That Reflects Major Ligamentous Damage. AJR 151:1163-1167, 1988.

4.Hayes JM, Masear VR. Avulsion Fracture of the Tibial Eminence Associated
with Severe Medial Ligamentous Injury in an Adolescent: A Case Report
and Literature Review. Am J Sport Med 12:330-333, 1984.

5.Molander ML, Wallin G, Wikslad I. Fracture of the Intercondylar Eminence
of the Tibia: A Review of 35 Patients. JBJS(Br) 63-B:89-91, 1981.

6.Rogers LF. The Knee and Shafts of the tibia and Fibula, in Radiology
of Skeletal Trauma, Vol 2, 2 nd Ed. Churchill Livingstone, New York, pp. 1199-1317, 1992.

Return to Musculoskeletal Teaching File Page

Submitted by:
Stephen F. Hatem, M.D.
Cheryl A. Petersilge, M.D.