Is it possible that a full colon impinges on the sciatic nerve? Is there anything that physically separates the sciatic nerve from the colon?
Sciatic nerve pain cannot be caused by a full colon.
The sciatic nerve runs at the back of the pelvis down the the leg. The sciatic nerve exits the spine from the lumbar spine to S3 in the sacrum (Fig. 1).
Fig.1. Left: sciatic nerve overview. Right: Sacral plexus. Source: Manchester Bedford Clinic
Hence the sciatic nerve does not come into contact with the bowel and intestines located ventrally in the abdominal cavity (Fig. 2).
Fig.2. Left: sciatic nerve in detail showing dorsal location. Right: Intestines ventrally situated in abdominal cavity. Source: Manchester Bedford Clinic and University of Maryland
Pain in the sciatic nerve (sciatica) is often caused by compression or entrapment by muscles, tendons, and other soft tissues along the nerve path Manchester Bedford Clinic.
$\begingroup$ I appreciate the extensive answer with the nice diagrams. However, it doesn't actually answer my question: just how far is it between the sciatic nerve and the colon at the closest point? $\endgroup$ May 22, 2015 at 2:40
$\begingroup$ Alas, I cannot provide you with an absolute distance measure. $\endgroup$– AliceD ♦May 22, 2015 at 2:44
1$\begingroup$ And I appreciate it! Do you have a particular source that backs your statement that "Sciatic nerve pain cannot be caused by a full colon"? It appears to me that they might only be an inch or so apart, and if tight muscles in the area can cause sciatic pain, a full colon should be able to at least contribute. $\endgroup$ May 22, 2015 at 4:25
$\begingroup$ The figures showed me they (nerve and colon) were physically separated and across various websites sciatic nerve pain is not associated with the intestines: mbmyoskeletal.com/learning/sciatica $\endgroup$– AliceD ♦May 22, 2015 at 4:49