bone

Point-of-Care Ultrasonography for Bone Injury: A Boy With a Distal Fibula Fracture

Marsha Elkhunovich, MD; Dina Seif, MD, MBA, RDMS; Mikaela Chilstrom, MD, RDMS; Tarina Kang, MD, RDMS; and Thomas Mailhot, MD, RDMS 

An 11-year-old boy presented to the emergency department (ED) 24 hours after a fall down several stairs. He complained of left ankle pain and difficulty bearing weight after the injury. He was taken to an urgent care clinic where he was diagnosed with an ankle sprain, and he was discharged with crutches and pain medicine. The patient presented to the ED again the next day because of worsening swelling and inability to bear weight on his left ankle. 

The patient had no past medical or surgical history, did not take any medications, and had no prior trauma to his ankle. His physical examination results were significant for moderate swelling over the lateral aspect of the left ankle with point tenderness over the lateral malleolus. There was no crepitus. He had limited range of motion of his ankle and had difficulty bearing weight. There was a strong dorsalis pedis pulse on the affected side with brisk capillary refill and intact sensation.

Due to the degree of swelling, point-of-care ultrasonography (POCUS) to evaluate the distal tibia and fibula was performed while the patient was awaiting radiographic studies. The examination was performed using a 13-6 MHz linear transducer. The fibular shaft was visualized proximal to the lateral malleolus initially in transverse view and then in longitudinal view. The transducer was then moved distally until the joint space was visualized. The study was repeated on the nonaffected extremity for comparison. Cortical disruption was noted in the distal fibula on the affected side. There was also subperiosteal fluid at the level of the metaphysis (Figure 1A) compared with the unaffected side (Figure 1B). These findings were consistent with a diagnosis of Salter Harris II fracture of the distal fibula, which was subsequently confirmed with radiographs (Figure 2). 

A short leg splint was placed to immobilize the ankle. Orthopedics was notified and follow-up was arranged in 1 week. 

Discussion

In the United States, there are more than 3 million ED visits each year for ankle and foot injuries, and the largest percentage of self-reported musculoskeletal injuries (>10%) is to the ankle. More than 628,000 ankle injuries, including ankle sprains and fractures, per year are treated in US EDs, accounting for 20% of all injuries treated in emergency facilities.1 Among the pediatric population, ankle fractures account for 5% of all fractures.2 

The most frequent injuries of the ankle joint are sprains of the anterior aspect of the tibiofibular ligament, which occur most often by inversion of the ankle in pre-adolescents.3 However, when a fracture is diagnosed, physeal fractures of the distal fibula are the most common. Despite the low percentage of bony injuries in these patients, radiographs are ordered in 85% to 95% of patients, even though only 15% of those patients with isolated ankle injury have a fracture.4,5

In the early 1990s, Stiell and colleagues developed the Ottawa Ankle Rules in an effort to systematically evaluate patients with isolated ankle injuries by physical examination to determine the need for radiographs.6 Subsequent observational studies have shown that when the rules were followed, the sensitivity of detecting ankle fractures increased to almost 100%, and the number of ankle radiographs ordered decreased by 19% to 30%.7 Despite these impressive results, the decision of whether to order radiographic studies is made based on the Ottawa Ankle Rules in only 50% to 60% of cases.8

POCUS is a promising diagnostic imaging tool for the detection of extremity fractures in children. A recent meta-analysis concluded that POCUS is an accurate diagnostic test in the ED with sensitivity and specificity ranging from 90% to 96% and 83% to 100%, respectively, in pediatric upper and lower extremity fractures.9 Studies have also demonstrated that POCUS can be an effective tool in the hands of emergency physicians with limited ultrasonography training for the diagnosis of long bone fractures, especially diaphyseal fractures of the upper extremities.10-13 A recent study showed that orthopedic surgeons with a brief focused training were able to use ultrasonography to exclude significant fractures of the ankle.14 Furthermore, case reports have demonstrated that in children some radiographically silent fractures of the ankle can be identified with POCUS.15,16

In our case, a Salter Harris II fracture of the distal fibula was quickly and correctly identified using POCUS after a misdiagnosis the previous day at an urgent care clinic with no radiographic capabilities. POCUS may prove to be a useful diagnostic tool for identifying fractures in urgent care clinics, at sporting events, camps, and other remote settings where radiography is not immediately accessible. Compared with radiography, the potential benefits of POCUS may include reducing radiation exposure, saving time, and lowering cost. Further studies are necessary to evaluate the accuracy, cost, and time of POCUS vs radiography in pediatric ankle fractures.  

Marsha Elkhunovich, MD, is with the division of emergency medicine at Children’s Hospital Los Angeles in California, and an assistant professor with the Keck School of Medicine at the University of Southern California. 

Dina Seif, MD, MBA, RDMS; Mikaela Chilstrom, MD, RDMS; Tarina Kang, MD, RDMS; and Thomas Mailhot, MD, RDMS, are from the department of emergency medicine at Los Angeles County+University of Southern California Medical Center in Los Angeles, California, and are assistant professors with the Keck School of Medicine at the University of Southern California.

References

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