Final answer:
The accessory peroneal anomaly occurs when the peroneal nerve innervates abnormal muscles, causing abnormal muscle contractions and movements.
Step-by-step explanation:
The accessory peroneal anomaly occurs when the peroneal nerve innervates abnormal muscles. It is characterized by abnormal muscle contractions and movements in the leg and foot due to the peroneal nerve supplying muscles it normally doesn't.
For example, in a normal anatomy, the peroneal nerve innervates the fibularis (peroneus) longus and fibularis (peroneus) brevis muscles in the lateral compartment of the leg. However, in an accessory peroneal anomaly, the peroneal nerve may also innervate other muscles outside its normal zone.
This anomaly can lead to issues with foot and ankle movement, muscle weakness, and improper gait patterns.