The procedure described, where a mix of steroid and pain medication is injected into the knee joint, is referred to as arthrography. However, it's important to note that "arthrography" typically refers to imaging of a joint after a contrast material is injected, while the injection itself might be commonly referred to as a "joint injection" or "intra-articular injection".
Since "arthrography" is the closest option related to joint procedures in the provided responses, that would be the most appropriate answer.
So the correct answer is:
arthrography.