The anterior tilt angle of the proximal tibia epiphyseal plate: A significant radiological finding in young children with trampoline fractures

Abstract

Objective

Evaluation of the anterior tilt angle of the proximal tibia epiphyseal plate in young children, which suffered a trampoline fracture in comparison with a normal population.

Materials and methods

62 children (31 females, 31 males) between 2 and 5 years of age (average 2 years 11 months, standard deviation 11 months) with radiographs in two views of the tibia were included in this retrospective study. 25 children with proximal tibia fractures were injured with a history of jumping on a trampoline. All other causes for tibia fractures were excluded. A normal age-mapped control cohort of 37 children was compared. These children had neither evidence of a trampoline related injury nor a fracture of the tibia. The anterior tilt angle of the epiphyseal plate of the tibia was defined as an angle between the proximal tibia physis and the distal tibia physis on a lateral view. Two radiologists evaluated all radiographs for fractures and measured the anterior tilt angle in consensus. An unpaired Student's t-test was used for statistical analysis (SPSS). Original reports were reviewed and compared with the radiological findings and follow-up radiographs.

Results

In the normal control group, the average anterior tilt angle measured −3.2°, SD ± 2.8°. The children with trampoline fractures showed an anterior tilt of +4.4°, SD ± 2.9°. The difference was statistically significant, P < 0.0001. In 6 patients (24% of all patients with confirmed fractures) the original report missed to diagnose the proximal tibial fracture.

Conclusion

Young children between 2 and 5 years of age are at risk for proximal tibia fractures while jumping on a trampoline. These fractures may be very subtle and difficult to detect on initial radiographs. Measurement of the anterior tilt angle of the proximal tibia epiphyseal plate on lateral radiographs is supportive for interpreting correctly trampoline fractures.

Introduction

Trampoline injuries in children are steadily increasing [1], [2], [3]. Boyer et al. observed in the 1980s over a period of 4 years 7 children with trampoline fractures in a tertiary care hospital [4]. In the last 5 years we observed 25 trampoline fractures. Children 2–5 years of age are particularly at risk for a “trampoline fracture” [5]. This fracture may occur by bouncing repeatedly on the trampoline, especially if the infant jumps together with older or heavier children. There is usually no specific traumatic event identified. The knee joint hyperextends and excessive axial compression to the proximal tibia occurs [1], [3], [4], [6], [7]. This mechanism leads to this classic trampoline fracture, since the bone of young infants and toddlers is relatively soft and less resistant to axial forces [2], [3], [4], [8]. Radiological signs of a trampoline fracture may be a buckle or torus fracture or a transverse hairline fracture of the proximal tibia metaphysis. A scooping of the notch for the tibial tubercle and subtle buckling of the anterior cortex of the upper tibia is typically noted [5]. An anterior tilting of the proximal tibia epiphyseal plate epiphysis is an important finding [3], [4], [6], [7], [9], [8], [10]. In clinical routine a trampoline fracture however may be subtle and difficult to depict. The aim of this study is to determine the anterior tilting of a normal population between 2 and 5 years of age and to compare this finding with young children which suffered a trampoline fracture.