A lower motor neuron injury to C5 primarily affects which muscle group?

A lower motor neuron injury to the C5 level primarily impacts the deltoid and biceps brachii muscle groups because these muscles are directly innervated by the ventral spinal roots associated with the C5 spinal segment. The deltoid, responsible for shoulder abduction, and the biceps brachii, crucial for flexing the elbow and supinating the forearm, are both critical for upper limb mobility and function.

Injuries at this level can disrupt the signals from the spinal cord to these muscles, leading to weakness or paralysis in their function. As a result, the person may struggle with lifting their arm or bending their elbow. The strength and control over these movements are significant for many daily activities, such as reaching or holding objects, which underscores the importance of the deltoid and biceps in the context of a C5 lower motor neuron injury.