Derang of ant horn of med mensc d/t old tear/inj, unsp knee

This code describes a chronic internal derangement of the medial meniscus, specifically involving the anterior horn, resulting from a prior injury or tear. The condition affects the knee joint's stability and function due to the long-standing meniscal damage. The "unspecified knee" indicates that laterality (left or right) is not documented.

Use this code when documentation indicates a chronic or old tear of the anterior horn of the medial meniscus, leading to symptoms of derangement such as locking, clicking, or instability. This code is appropriate when the physician explicitly states "old tear" or "chronic injury" and the specific knee (left or right) is not specified in the medical record.

• Ensure documentation clearly specifies "anterior horn" and "medial meniscus."
• Do not use this code for acute tears; look for codes indicating acute derangement.
• If laterality (left or right knee) is documented, select a more specific code from the M23.21- subcategory.