Answer: Coding for a sinus tarsi injection can be tricky because the sinus tarsi is neither a joint nor a ligament, but a space. The area is the soft indentation just in front of the lateral malleolus and contains nerve endings, fat, joint capsule, arterial anastomoses, and five ligaments.
Your coding will depend on whether the physician administers an injection into the surrounding soft tissue — in which case 20550 (Injection[s]; single tendon sheath, or ligament, aponeurosis [e.g., plantar “fascia”]) is appropriate — or, most often, into the actual sinus tarsi space, which provides the lateral access to the subtalar joint. If this is the case, you can more accurately describe your work using 20605 (Arthrocentesis, aspiration and/or injection; intermediate joint or bursa [e.g., temporomandibular, acromioclavicular, wrist, elbow or ankle, olecranon bursa]).
Your diagnosis will also need to support the appropriate injection code. Physicians often turn to ICD-9 code 726.79 (Other enthesopathy of ankle and tarsus) to report sinus tarsi syndrome.
Don’t forget to include a corresponding J code to gain reimbursement for the drug injected.