VARIATION IN POSITION OF THE L4/5 DISC INTER-SPACE FROM THE ANATOMICAL LANDMARK – REVIEW OF 450 RADIOGRAPHS.

Abstract

Introduction: The position of 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 used frequently as a pre-operative guide for incision placement, in patients undergoing spinal surgery.

Aim: To investigate whether a line drawn between the two highest points on the iliac crests corresponds to the L4/5 disc inter-space, in varying patient age groups.

Patients and Methods: We reviewed 450 AP and lateral lumbar spine radiographs in patients ranging in age from 20 – 90 years. Patients with an obvious deformity or previous spinal surgery were excluded from the study. In the AP films, a line was drawn between the two highest points on the iliac crests. From this line, the distance to the midpoint of the L4/5 disc was measured.

Results: In all age groups measured, the true L4/5 disc inter-space lay below the line between the iliac crests, at an average of 4.33mm below the supracristal plane. 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 L4 body or above in 49.3% of cases.

Conclusions: These results show that, using a line drawn between the two highest points on the iliac crests as a guide to the position of the L4/5 disc interspace may lead to unintentionally cranial positioning of an incision or cannulation in this area. Therefore, it is advisable to perform a pre-operative AP and lateral radiograph of the lumbar spine, to enable accurate incision placement when performing spinal surgery in this area.