Variation in position of the L4/5 disc inter-space from the anatomical landmark: Review of 450 radiographs and clinical applications

The L4/5 disc inter-space is commonly believed to be represented by a line drawn between the two highest points of the iliac crests. This line is frequently used as a pre-operative guide for incision placement, in patients undergoing spinal surgery. We reviewed the antero-posterior and lateral lumbar spine films of 450 patients, ranging in age from 20 to 90 years, measuring the distance from the supracristal plane to the midpoint of the L4/5 disc interspace. The plane intersected the spine at the L4/5 interspace in only 31.9% of cases and was found to lie at the lower half of the body of L4 or above in 49.5% of cases. There was significant variation in the position of the supracristal plane between the different patient age groups studied (P≤0.05). The use of additional imaging, along with plain radiography is advised when attempting identification of this spinal level, as reliance on palpation of the iliac crests alone to identify this landmark may lead to unintentional cranial placement of a surgical incision during spinal procedures, or cannulation at a level above the intended interspace, during epidural and spinal anaesthesia. © Springer-Verlag 2006.