Knee pain and an abnormal radiograph in a skier

The patient is a 20-year-old male who fell while downhill skiing. He could not recall the exact mechanism of injury. The patient developed immediate pain and swelling in his left knee after the fall and was transported to the bottom of the run by the ski patrol. He was not able to ski for the remainder of the trip. After returning home, he presented to our orthopedic clinic with continued complaints of lateral knee pain, swelling, and a sense of weakness (because he was unable to fully bear weight). He believed he experienced a popping sensation around his left knee at the time of the fall.

Examination of the left knee demonstrated a 2+ effusion and tenderness directly over and superior to the fibular head. Active range of motion (ROM) was measured to be 0 to 40 degrees, passive ROM was 0 to 95 degrees, and both active and passive ROM were limited by pain laterally. Gross laxity was noted with the Lachman and anterior drawer maneuvers, but no clinical valgus or varus laxity, patellar apprehension, or posterior sag were present. The patient was neurologically intact with 2+ dorsalis pedis and posterior tibial pulses in both extremities. Radiographs of the left knee were performed in the clinic (see Figure 1). What does this image reveal?

DISCUSSION

Figure 1 is an anteroposterior (AP) view of the knee demonstrating an approximately 5-mm ovoid or elliptical fragment in an oblique orientation. The origin of the fragment is just inferior to the lateral tibial plateau. The differential diagnosis includes fibular head fracture, lateral tibial plateau fracture, or Segond fracture. The fragment in this patient's radiograph is consistent with a Segond fracture, which is visible only on the AP view in this case (see Figure 2). Note that in the absence of direct trauma, these fractures typically occur in association with anterior cruciate ligament (ACL) injuries.

The challenge for clinicians is in recognizing the importance of the fracture to the primary ACL injury. Segond fractures can easily be mistaken for other injuries, including a fracture of the fibular head or the lateral tibial plateau. A thorough physical examination and, possibly, additional imaging may be necessary to correctly diagnose the ACL injury.

Fibular head fractures may appear radiographically similar with pain in a similar location, and the patient may present with a similar history. However, in this case, a donor site can be identified on the proximal tibia, suggesting the fragment's origin. Fibular head fractures may also be accompanied by lateral laxity involving the lateral collateral ligament, which was not present in this patient. If no lateral laxity is found and clinical concern still exists for a fibular head fracture, then additional imaging, such as MRI or CT, would be helpful.

Lateral tibial plateau fractures can also be a consideration and are more commonly mistaken for the Segond fracture. A tibial plateau fracture would not necessarily demonstrate any lateral or anterior laxity on physical examination, eliminating or at least decreasing the likelihood of concomitant ligament injury. Some patients with lateral tibial plateau fractures may be in too much pain to examine. In this case, as with the fibular head fracture, additional imaging may be helpful.

The Segond fracture represents an avulsion of the lateral tibial cortex by the lateral capsular ligaments, specifically the meniscotibial arm (a thickening of the lateral joint capsule). The iliotibial band and anterior oblique band of the lateral collateral ligament may also have a role in the pathogenesis of this fracture fragment.1 This fracture was first recognized by Paul Segond in 1879 during cadaveric experiments where varus loads with internal rotation were applied to the knee joint.2 The fractures are typically small ovoid or elliptical fragments that are minimally displaced in a vertical or oblique orientation. Fracture fragments usually range between 2 and 10 mm in length and can be wafer thin to several millimeters thick. AP and notch radiographs are the best views for identifying these fragments.3 However, a full set of radiographs (AP, lateral, notch, sunrise, and merchant views, as well as oblique views, if necessary) is still needed for complete evaluation of an acute knee injury.

The primary injury in the case of a Segond fracture is a ligament injury and not the bony fracture itself. Segond fractures, when identified radiographically, are considered in clinical practice to be pathognomonic for ACL tears.4-6 Varus loads that include a rotational component and are significant enough to rupture the ACL may produce this bony finding. The ACL is a primary restraint to anterior tibial translation and also to internal rotation. As forces are accepted by the primary ligamentous structures (in this case the ACL), the loads are transferred to the secondary stabilizers and surrounding tissues.

ACL injuries are estimated to occur more than 250,000 times each year.4 Hess and colleagues reported a 9% incidence of Segond fractures in their series of 151 patients that, if extrapolated, could represent a significant number of Segond fractures seen each year.5 A complete history, physical examination, and a full set of knee radiographs are necessary to identify these injuries. In some cases the physical examination is limited by pain or mechanical sources inside the joint. MRI is helpful to identify associated soft tissue injuries and may also assist in identifying areas of bony injury or fractures. However, MRI or CT is not necessary to evaluate the Segond fracture itself. Plain radiographs should be obtained first when a bony injury or an ACL tear is suspected. Recognizing this injury radiographically is essential to identifying the ACL component, counseling patients, and initiating appropriate treatment.

Many of those injured will present to primary care settings for initial evaluation. We are challenged as medical practitioners to look beyond the radiographs and use our history-taking and physical examination skills to reach accurate conclusions. Thus, clinical awareness about radiographic findings and ACL injuries will assist in correctly diagnosing the primary injury and providing appropriate care for patients with ACL injuries. JAAPA

Brian Downie is a PA in the Department of Orthopaedic Surgery—MedSport, University of Michigan, Ann
Arbor. He has indicated no relationships to disclose relating to the content of this article.

REFERENCES

1. Campos JC, Chung CB, Lektrakul N, et al. Pathogenesis of the Segond fracture: anatomic and MR imaging evidence of an iliotibial tract or anterior oblique band avulsion. Radiology. 2001;219(2):381-386.

2. Davis DS, Post WR. Segond fracture: lateral capsular ligament avulsion. J Orthop Sports Phys Ther. 1997;25(2): 103-106.

3. Goldman AB, Pavlov H, Rubenstein D. The Segond fracture of the proximal tibia: a small avulsion fracture that reflects major ligamentous damage. AJR Am J Roentgenol. 1988;151(6):1163-1167.

4. Griffin LY, Albohm MJ, Arendt EA, et al. Understanding and preventing noncontact anterior cruciate ligament injuries: a review of the Hunt Valley II meeting, January 2005. Am J Sports Med. 2006;34(9):1512-1532.

5. Hess T, Rupp S, Hopf T, et al. Lateral tibial avulsion fractures and disruptions to the anterior cruciate ligament. A clinical study of their incidence and correlation. Clin Orthop Relat Res. 1994;(303):193-197.

6. Woods GW, Stanley RF, Tullos HS. Lateral capsular sign: x-ray clue to a significant knee instability. Am J Sports Med. 1979;7(1):27-33.