Synovial cyst of popliteal space [Baker], unspecified knee

This code signifies a fluid-filled sac, often a distended bursa, located in the popliteal fossa (behind the knee). Commonly known as a Baker's cyst, it results from the herniation of the synovial membrane through the joint capsule or enlargement of the gastrocnemius-semimembranosus bursa. This particular code indicates that the specific knee affected (left or right) is not documented.

Use this code when documentation confirms the presence of a synovial cyst or Baker's cyst in the popliteal space, but the medical record does not specify laterality. This typically occurs when the physician's notes or imaging reports simply state "Baker's cyst" or "popliteal cyst" without indicating which knee. Supporting documentation includes physician notes, imaging reports (e.g., ultrasound, MRI), and operative reports.

• Only use this code when laterality is truly unspecified; otherwise, select the more specific M71.21 (right knee) or M71.22 (left knee).
• Do not confuse this with other knee effusions or bursitis not specifically identified as a synovial cyst of the popliteal space.
• Always query the provider if laterality is missing from the documentation to allow for more specific coding.