--at the L4/L5 level could certainly cause sciatic symptoms, as that nerve root does contribute heavily to the make-up of the sciatic nerve.

An EMG/nerve conduction study would likely be able to determine if any disruption in nerve function is coming from the nerve root area, farther down the sciatic nerve, or both. The sciatic nerve has several common compression sites, not only at its "origins" in the nerve roots but in the back hip area even farther down behind the piriformis muscle in some cases.

See:

http://en.wikipedia.org/wiki/Sciatica

http://en.wikipedia.org/wiki/Piriformis_syndrome