Derang of post horn of medial mensc d/t old tear/inj, l knee

This code signifies a chronic or pre-existing injury to the posterior horn of the medial meniscus in the left knee, resulting in its internal derangement. This derangement implies a disruption of the normal anatomical relationship and function of this specific meniscal segment, often leading to mechanical symptoms.

Apply this code when documentation clearly indicates a past tear or injury to the posterior horn of the left medial meniscus, leading to ongoing symptoms of derangement. This is typically supported by imaging reports (e.g., MRI) showing an old tear and clinical notes describing mechanical symptoms like locking, catching, or instability attributed to this chronic meniscal issue.

• Differentiate from acute tears; "old tear or injury" is key documentation.
• Ensure laterality (left knee) is explicitly stated in the medical record.
• Consider additional codes for associated conditions like osteoarthritis if present and documented.