Spine
From Memory Alpha, the free Star Trek reference.
A spine is the column of a vertebrate skeletal system, it houses the spinal cord.
Some Klingon infants have a curvature of the spine, which may be corrected for by surgery. This "defect" tends to run in Klingon families, especially among females. Federation medicine has advanced beyond that, allowing an additional choice of treatment which involves genetic modification. (VOY: "Lineage")
One of the symptoms of the Urodelan flu is a stinging sensation in the lower spine. (TNG: "Genesis")
