Background context: It is frequently stated that referred pain does not travel below the knee. However, for many years studies provoking referred pain have demonstrated pain radiating below the knee.

Methods: Over a twelve month period, 643 patients with mechanical back pain and 185 patients with nerve root compressions were seen. For each patient two body map images (front and back) were obtained. Some patients attended for review, at a minimum of six weeks after their first visit. These images were also analysed.

Composite images were created by combining all images from patients in one diagnosis group. Colour based overlays were used to analyse the body map images, to locate the locations of pain. Colour density was scaled so that the site with the most hits had a pure colour, reducing down to zero colour for sites with no hits.

Results: There were 720 nerve root compression images. 216 (30%) showed no leg pain, 91 (12.6%) showed upper leg pain, 134 (18.6%) showed lower leg pain and 279 (38.8%) showed upper and lower leg pain.

There were 1964 mechanical back pain images. 674 (34.3%) showed no leg pain, 528 (26.9%) showed upper leg pain, 308 (15.7%) showed lower leg pain and 454 (23.1%) showed upper and lower leg pain.

Conclusion: A large proportion (39%) of the mechanical back pain images indicated that the patient experienced referred pain below the knee. This has significant implications in the diagnosis of nerve root compressions, potentially leading to inappropriate surgery.

Conflicts of Interest: None

Source of Funding: None