Billing codes, 20610, & j1040

In reviewing a bill from my doctors office, I received 1 injection to my right knee, thats code j1040, but I dont understand why there is also a code 20610-arthrocentesis asp? I received one injection and no fluid was extracted at any point. Please help me understand how this bill is correct, before I pay my part of the payments. Thank you.

re: BILLING CODES, 20610, & J1040

CPT® code 20610 defined as arthrocentesis, aspiration and/or injection; major joint or bursa (eg, shoulder, hip, knee joint, subacromial bursa) this is is for the injection. The J code of J1040 represents 80mg of methypenisolone which was the medicine in the needle. Hope this helps.