A 17-year-old male baseball catcher presents with right knee pain after an opponent slid into home plate, striking the anteromedial aspect of the patient’s knee while it was in extension trying to block the plate. An x-ray of the tibia and fibula was obtained (courtesy of Dr. Haytham Bedier, Radiopaedia.org).
This is a proximal avulsion fracture of the styloid process of the fibula, indicating injury to the posterolateral corner (PLC) of the knee [1].
- Pearl: In most cases, the avulsed fragment is attached to the lateral collateral ligament and/or the biceps femoris [2].
This injury usually occurs from varus stress in a hyperextended knee- think a blow to the anteromedial tibia with the knee in extension [2].
The arcuate sign is a horizontal linear lucency through the head of the fibula that represents a fracture of the styloid process [3].
- Pearl: This injury may be confused with a Segond fracture, which is a small avulsion fracture fragment from the lateral tibial plateau associated with anterior cruciate ligament injury.
A proximal fibular avulsion fracture is commonly associated with injury to the posterior cruciate ligament, anterior cruciate ligament, popliteus, or meniscus. It is frequently seen with bone contusions and sometimes a tibial plateau fracture [2].
- Pearl: Injury to the common peroneal nerve may occur as well. Remember to perform a thorough neurovascular examination [1].
- Pearl: This fracture is a sign of posterolateral instability and likely internal derangement of the knee. Outpatient MRI can be used to evaluate the soft tissue components of the injury and diagnose associated injuries [2].
This injury indicates potential significant instability of the knee and requires outpatient follow-up with MRI. Operative management will be dictated on an individual basis, after evaluating MRI results. In the emergency department, place the patient in a knee immobilizer and recommend non-weight-bearing status until further imaging. Follow-up with orthopedics or sports medicine within 1 week.
- Pearl: As always, perform a thorough neurovascular examination and consult orthopedics immediately if there is evidence of compromise. If your exam demonstrates significant instability and you are concerned about a spontaneously-reduced knee dislocation, consider ankle-brachial indices and/or further vessel imaging.
If diagnosis of this injury is delayed, posterolateral instability may develop. If not recognized and managed appropriately, this may hinder the success of a cruciate ligament reconstruction [1].
References and Resources:
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- Shon OJ, Park JW, Kim BJ. Current concepts of posterolateral corner injuries of the knee. Knee Surg Relat Res. 2017;29(4):256-268. PMID: 29172386
- Juhng SK, Lee JK, Choi SS, Yoon KH, Roh BS, Won JJ. MR evaluation of the “arcuate” sign of posterolateral knee instability. Am J Roentgenol. 2002;178(3):583-588. PMID: 11856678
- Strub WM. The arcuate sign. Radiology. 2007; 244(2):620-621. PMID: 17641383
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