PEM Pearls: Ultrasound for Diagnosing Occult Supracondylar Fractures

Supracondylar humerus fractures are the most common type of elbow fracture in pediatric patients, most often seen in a fall on an outstretched hand (FOOSH) or a fall on a hyper-extended elbow.^​1,2​ If there is no obvious fracture on x-rays, the patient may have an occult fracture; look for secondary radiographic signs including a posterior fat pad sign, an enlarged anterior fat pad or ‘sail sign’, or malalignment. Occult supracondylar fractures (those with initial normal radiographs that are later diagnosed in follow up) make up 2-18% of all the fractures we see in kids.^​3​ When x-ray findings are nonspecific but the index of suspicion for fracture remains high, ultrasound may aid in your clinical decision making.

Technique

Probe: High resolution linear probe with frequencies ranging from 6-13 MHz

Maximum Depth:6 cm

Scanning Scheme: With the elbow bent at 90 degrees, scan along posterior edge of the distal humerus in longitudinal and transverse axes.

Findings on Elbow Ultrasound

Normal Elbow

Identify:

• Distal humerus without cortical irregularity
• Posterior fat pad

Abnormal Elbow

Identify signs of potential occult fracture:

• Bulging posterior fat pad
• lipohemarthrosis

Elbow Ultrasound vs Radiograph

Study 1: European Journal of Trauma and Emergency Surgery 2014

A German study investigated ultrasound accuracy (identifying cortical deformity or a posterior fat pad) compared to standard radiographs in diagnosing supracondylar fractures in 106 pediatric patients. The test characteristics were as follows:^​4​

• Sensitivity 100%
• Specificity 93.5%
• Negative predictive value 100%
• Positive predictive value 95.2%

Study 2: Orthopaedics & Traumatology: Surgery & Research 2016

A French study of 34 cases of pediatric elbow trauma with suspected occult fracture. Patients with bone deformity diagnosed on initial radiographs were excluded. Patients were splinted until they had an ultrasound performed within 6 days of the injury.^​3​

• 13 of the 34 cases had identified an occult fracture
  • Of the 21 cases who had normal ultrasounds, none were later diagnosed with a fracture.
• Posterior fat pad sign sensitivity 100% (13 cases)
• Lipohemarthrosis sensitivity 92% (11 cases)
• Cortical disruption (11 cases)

Study 3: Annals of Emergency Medicine 2013

130 pediatric patients with elbow injuries. Before obtaining radiographs, pediatric emergency physicians performed an ultrasound. 33% patients had a radiograph result positive for fracture.^​5​ The ultrasound demonstrated either an elevated posterior fat pad or lipohemarthrosis with the following test characteristics:

• Sensitivity 98%
• Specificity 70%
• Positive likelihood ratio 3.3
• Negative likelihood ratio 0.03

Study 4: Pediatric Radiology 2008

14 patients with x-rays showing elbow joint effusion but no fracture who underwent ultrasound and MRI.^​6​ The test characteristics for ultrasound in demonstrating lipohemarthrosis are as follows:

• Sensitivity 88%
• Specificity 100%
• Negative predictive value 86%
• Positive predictive value 100%

The Bottom Line

1. Elbow ultrasound can assist in ruling out a supracondylar fracture, which is particularly helpful in the case of an equivocal x-ray but high clinical suspicion.
2. Next time you encounter a pediatric elbow injury with negative x-rays in the ED, grab an ultrasound probe to evaluate for a fat pad sign and lipohemarthrosis.
3. Although not ready for prime time yet, this is an interesting technique that may result in decreased painful immobilization and improved overall morbidity. For now, continue to splint patients for whom you have high suspicion of an occult fracture.

Thumbnail Image: © Monkey Business, #14117524

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