Quadratus femoris injections are performed for ischiofemoral impingement, where there is quadratus femoris impingement.  Both CT and US are used, but US can be more difficult with those with a larger habitus. 

The sciatic nerve is the most important structure to avoid and should be identified regardless of imaging modality.   A lateral approach means the needle passes inferior to the sciatic nerve.  Using a short-acting and smaller amount of local anesthetic i.e. 1% lidocaine, reduces the risk of a long-lasting post-procedure sciatic nerve block.