349 The Physical Examination Is Unreliable in Determining the Location of the Ankle Physis in Healthy Children

Abstract

Pediatric ankle injuries are a common presentation to the emergency department (ED). The Salter-Harris classification defines a type 1 fracture of the distal fibula as tenderness overlying the physis of the distal fibula without radiographic evidence of a fracture. Our primary objective was to establish the reliability of physical examination performed by pediatric emergency physicians in determining the location of the physis of the distal fibula as compared to a criterion standard using ultrasound. This was a prospective, observational, single-site study of a convenience sample of pediatric patients aged 4 to 10 years old. It was performed at an urban academic pediatric ED between March 2019 and April 2020. Otherwise healthy children presenting to the ED for reasons other than lower extremity injury were eligible to participate. A pediatric emergency physician or fellow performed a physical examination of the patient’s distal fibula and marked the location of the physis based on his or her examination with a marker. After this, the study investigator (an ultrasound fellow) scanned the distal fibula, established the location of the physis on ultrasound, and used an invisible ink pen to mark the location of the physis. Using an ultraviolet light, the investigator measured the distance between the clinician’s estimated position and the actual sonographic position of the physis. Because the distal fibular physis measures only 3 mm on average, a clinically accurate position was defined a priori as a marked point located within a 5 mm distance of the sonographic marking. We compared the accuracy rate of physical examination to ultrasound landmarking using proportions as well as means with 95% confidence intervals (CI). Using a simulation assuming the participation of at least 15 physicians assessing multiple patients, we calculated a sample size of 90 patients to detect a difference in 70% versus 50% physician accuracy with at least 80% power. Enrolment was stopped early due to the novel coronavirus pandemic, so we were unable to recruit our target sample size of 90 participants. We enrolled 71 patients, of whom 52 (73%) were male. The mean age was 6.7 years and the mean weight was 25.5 kg. Participating pediatric emergency physicians included 18 staff physicians and 2 fellows. The assessments were performed by staff physicians in 60 (85%) patients and by fellows in 11 (15%) patients. Each physician examined a mean of 3.6 patients (range 1-15). The physis of the distal fibula was correctly identified in only 24 patients, yielding an accuracy rate of 34% (95% CI 23%-46%). The mean distance between the physician’s estimated position of the physis and the sonographic position was 7.4 mm (95% CI 6.4-8.4 mm). In a sensitivity analysis where the remaining 19 patient examinations would have all been accurate, the probability of accurate identification was 48% (95 CI 37%-59%). We found that pediatric emergency physicians were only 34% accurate with their physical examination in identifying the physis of the distal fibula. This calls into question the utility of the definition of a type 1 Salter-Harris fracture given that the physical examination is unreliable in identifying the location of the physis of the distal fibula.