the correct term used is nerve palasy.this is very important issue and needs correct training of health personnale regarding safe and proper injection technique.generally upper most quadrant of gluteal muscle is rendered safe for intramuscular injection,as no major vessel or nerve passes through this part,however over generalisation of this principle has led to severe nerve palasies,this is due to fact of anatomical variation .thus site angle of peneteration and depth of penetration needs to be assessed by a good physician and only he must be allowed to give injections.
anyhow any nerve palasy symptom should be treated seriously and reported to neurologist immidiately.