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10. Radiology Case 2
Keywords
The Segond fractureExternal varus stressTibiaLateral capsular disruption ACLMeniscal tearsAnterior obliqueFibular collateral ligament [3]Indication for the Exam
27 y/o m with left knee swelling, lateral tenderness, and pain with rotational movements after a motor vehicle accident.
Radiographic Findings
AP view of the left knee demonstrating an avulsion fracture of the lateral tibia.
Diagnosis
Segond fracture.
Learning Points
Priming Questions
What is the mechanism of injury?
What are additional injuries associated with this fracture?
What is the Reverse Segond fracture?
What is the arcuate sign?
Introduction/Background
Named after French surgeon Paul Segond in 1879, a Segond fracture is an avulsion fracture of the tibia at the insertion site of the lateral capsular ligament [1].
Pathophysiology/Mechanism
The Segond fracture occurs from internal rotation of the knee with an external varus stress. This motion increases tension upon the lateral capsular ligament, which then causes a cortical break at its insertion on the tibia. There is a high association of lateral capsular disruption with ACL and meniscal tears. Patients will complain of pain along the lateral aspect of the tibia with lateral rotational instability [1]. Other injuries associated with a Segond fracture can include trauma to the iliotibial band and anterior oblique band of the fibular collateral ligament [2].
Making the Diagnosis
On AP knee radiographs, an elliptical-shaped bone fragment is seen along the lateral aspect of the tibia just below/adjacent to the lateral tibial plateau. Radiologists will often refer to this as the lateral capsular sign [1].
Conspicuity of the small avulsed bone fragment is best appreciated on cross-sectional imaging; however, AP radiographs of the knee are the initial test of choice.
It is important to note that nonemergent MRI is indicated for all patients with a Segond fracture given the strong association with anterior cruciate ligament (>70%) (2–3) and meniscal tears [1, 3].
The Reverse Segond Fracture is described as an avulsion injury to the deep capsular medial collateral ligament. An elliptical bone fragment is located adjacent to the medial tibial plateau. This injury occurs with external rotation and valgus stress: the reverse mechanism of a Segond fracture [1].
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