Increasing attention has focused on the spinal muscles with respect to stability and low back pain (LBP) with suggestions of a de-conditioning syndrome. What is less clear is the extent of this degeneration and whether it is a long term of short term consequence of LBP. This study sought to explore the cross section area (CSA) and muscle quality of the spinal extensor group in a subset of LBP patients. MRI scans of 100 spinal clinic patients were retrospectively reviewed; sagittal and transverse (from levels L3-5) images were annoymised and archived along with details of age, gender and presenting symptoms. An image analysis package was used to determine CSA of the extensor muscle groups, and levels of fat infiltration were calculated using a pseudocolouring technique. 46 patients had spinal stenosis (28 males, 18 females, mean age 66±14.2 years) and 54 had a disc prolapse (28 males, 26 females, mean age 50±12.9 years). CSA was significantly smaller in the stenotics at both L3/4 and L4/5. Patients presenting with leg pain and a disc herniation had a significantly smaller CSA (p<
0.01) at L3/4 and L4/5 levels. A left right CSA asymmetry was noted but this was not specific to diagnosis, or presenting symptoms. Fat infiltration was present in both groups but was significantly greater in the stenotic group (p<
0.01) and was present at a similar degree at all spinal levels. Multiple regression analysis confirmed that reduced CSA was linked to leg pain (p<
0.01) and age was linked with fat infiltration (0<
0.01).
