An animal bone model study to predict spiral fracture strength of long bones in the young infant.

INTRODUCTION

The risk of fracture from a non-accidental injury is highest in the infant age group. A spiral fracture of the long bone can occur equally from accidental and non-accidental causes, meaning the clinical judgement of non-accidental injury in an infant is particularly challenging. This study aimed to assist in differentiating accidental, from non-accidental, injury in infants, by establishing whether correlation exists between geometry and torsional strength in the immature long bone.

METHODS

Immature porcine third and fourth metacarpals (n = 21) were imaged with a dual energy x-ray absorptiometry (DEXA) scanner to measure their linear bone mineral content (BMC), bone mineral density (BMD) and section modulus (Z). The specimens were then subjected to a torque of one degree per second until failure. The failure strength and the three DEXA measures were analyzed for a correlation.

RESULTS

The mean failure strength of 11 successful tests was 13.71Nm (+/-SD 2.42Nm), with correlation to BMC, BMD and Z described by r = 0.81, 0.283 and 0.75 respectively.

CONCLUSION

This study is a novel attempt at estimating torsional strength of long bones in a specific paediatric age group using a size-matched animal bone model. It found a strong correlation between bone and fracture strength parameters over the BMC range of 0.59-0.77 g/cm.