The size of injured metamere (IM) in tetraplegia exhibits a high variability that explains the different clinical presentations in patients who have the same neurologic level. Even when functional electrical stimulation is not planned, the lower motor neuron (LMN) integrity of paralyzed muscles must be evaluated, especially in patients with high-level tetraplegia. During the acute phase, detecting the size of the IM is important to prevent supination contracture and stiffness of the thumb and finger joints. When planning functional surgery, the LMN integrity of intrinsic muscles helps the surgeon adapt his surgical procedures. Assessing IM size must be integrated systematically into the evaluation of tetraplegic patients.