Paralysis of the common peroneal nerve, which may cause foot drop and difficulty lifting the foot.
Medical records that document the specific physical findings matter most here. For a 40% rating, exam findings would need to show foot drop, inability to dorsiflex the foot, loss of dorsal extension of the proximal toe phalanges, absent abduction of the foot, weakened adduction, and documented anesthesia covering the entire top of the foot and toes. Nerve conduction studies or electromyography (EMG) results that confirm complete loss of function along the common peroneal nerve support this level.
For incomplete ratings — severe, moderate, or mild — exam records showing partial loss of strength, limited range of motion, reduced or absent sensation in part of the foot, and abnormal nerve conduction values help establish the degree of impairment. Your own statements, and statements from people who know you, describing how foot weakness or numbness affects your ability to walk, work, or carry out daily activities can help show the functional impact. If the involvement is sensory only, records and statements should reflect that, since the regulation limits purely sensory involvement to no higher than the moderate level.
Conditions that are often caused or made worse by this one. If you have any of these, they may be claimable as secondary service connection.