Final answer:
Numbness and tingling on the top of the foot and big toe is the likely change in sensation in the L4 dermatome. This results from trauma affecting the nerve roots that supply this area. In more severe cases like spinal cord injuries, additional sensory deficits can be observed, depending on the pathways involved.
Step-by-step explanation:
The change in sensation in the L4 dermatome following trauma to the lower leg is likely to manifest as numbness and tingling on the top of the foot and big toe. This is due to the L4 nerve root which supplies sensation to this area. In a scenario like a motorcycle accident, a hemisection of the spinal cord can result in different sensory deficits. For example, on the paralyzed leg, the patient will acknowledge painful stimuli, but not fine touch or proprioceptive sensations. This occurs because the dorsal column pathway, responsible for fine touch and proprioception, ascends on the same side as the injured tract, whereas the spinothalamic pathway for pain and temperature sensations crosses over to the opposite side immediately upon entering the spinal cord and would therefore be unaffected on the side of the injury.