Spontaneous rupture of other tendons, unspecified lower leg

This code describes the non-traumatic tearing or breaking of a tendon in the lower leg, excluding the Achilles tendon, that occurs without an external force or injury. It signifies a spontaneous event where the tendon fails due to underlying degeneration, overuse, or systemic conditions rather than an acute trauma. The specific tendon involved is not documented.

Apply this code when documentation clearly states a spontaneous rupture of an unspecified tendon in the lower leg, such as the tibialis posterior, tibialis anterior, or peroneal tendons, and the laterality is not specified. This code is appropriate when the physician explicitly rules out an acute traumatic event as the cause of the rupture. Documentation should support the spontaneous nature and the lower leg location.

• Ensure documentation specifies "spontaneous" and not "traumatic" rupture.
• Avoid using this code if the specific tendon (e.g., Achilles) is identified; use a more specific code from the M66.0-M66.5 series.
• If laterality (right or left) is documented, choose a more specific code from the M66.86 series (M66.861, M66.862).