Determination of inter-spinous process distance in the lumbar spine - Evaluation of reference population to facilitate detection of severe trauma

Fracture of a spinal segment with minimal or no compression of the vertebra l body can be highly unstable. Screening for such an injury in the lumbar s pine is often obstructed in a multi-injured patient, because of difficulty in obtaining adequate sagittal radiographs. The position of the spinous pro cesses in relation to each other is the key for proper evaluation of the st atus of the posterior stabilising structures. The amount of separation or a xial rotation of the posterior part of the vertebra that can occur before f ailure of the posterior structures has not been unambiguously defined. Desp ite this, it can be assumed that severe separation of the spinous processes indicates a more or less pronounced loss of mechanical support. An analysi s of how the posterior spinous processes relate to each other on an anterop osterior (AP) radiograph could obviate this problem. A new, simple and repr oducible radiographic tool is presented for screening of an eventual ruptur e of posterior structures of the lumbar spine. This method is based on meas urements of the variation in interspinal process distance between adjacent levels in lumbar spine in a normal population. Two hundred normal AP radiog raphs of non-injured thoracolumbar spine were studied. The interspinal proc ess distance was measured as the distance between the cranial ends of the a djacent projections of spinous processes on AP radiographs. The mean values and 99% confidence limits for changes in the interspinal process distances between adjacent spinal levels were determined and analysed in relation to age, gender and spinal segment level. An upper limit of a normal differenc e in distance between the spinous processes at two adjacent levels was dete rmined to be 7-10 mm, depending on age and location in the lumbar spine. A difference in interspinal process distance exceeding 7 mm between two adjac ent lumbar levels should alert a surgeon to severe and unstable injury.