You would look up Anthem's Bilateral Surgery policy. However, in your example, it would be One line, 20610-50, 1 unit, M17.0 for (B) knee injections. See the underlined part below, they automatically adjust the reimbursement.
Example:
https://files.providernews.anthem.com/2182/Multiple-and-Bilateral-Surgery.pdf
Bilateral surgical procedure reimbursement: A bilateral surgery that uses a unilateral code should be reported on a single line with modifier 50, using one (1) unit of service.
Reimbursement is 150% of the allowance for the procedure code. In the below instances,
the Health Plan will apply the applicable standard multiple surgical reimbursement or multiple arthroscopic and endoscopic surgical procedure reimbursement guidelines. When a surgical procedure code contains the terminology “bilateral” or “unilateral or bilateral” or the code is considered inherently bilateral, modifiers LT, RT, or 50 should not be appended since the description of the code defines it as a bilateral procedure. Such services should only be reported on one (1) line with one (1) unit. When a bilateral surgical procedure, that uses a unilateral code, is reported with multiple surgical procedures, the RVU will increase to 150%, and apply the standard or arthroscopic/endoscopic multiple surgical reduction if applicable.
Modifier 51 does not make sense in your example. Medicare doesn't want modifier 51 at all and many payers don't need it either because their systems automatically rank the CPT by RVU and pay the primary at 100% and do the multiple payment reduction on the additional. Plus, if you are only reporting two procedures of the same RVU and fee (e.g.; 20610) it wouldn't make sense either because they are the exact same fee/RVU.
Example from a MAC:
https://www.novitas-solutions.com/w...df.ctrl-state=86hvagjfk_33&contentId=00144532
I rarely to never use modifier 51 any longer even on big surgeries because most payers rank the codes automatically. You would want to check the payer policy 1st.