为啥会有逗号？

One should pay particular emphasis to the identification of“upper motor neuron signs” versus“lower motor neuron signs.” Distinguishing the two can be of critical importance in the practice of pain medicine. Upper motor neuron injury can masquerade as many of the common lumbar pain syndromes. As a general rule, spine injury thought to occur at a particular level, for example, pain involving the front of the thighs (L2 distribution), can be due to injury at any more cephalad level. One should pay particular attention to cervical spine injury mimicking pain thought to be due to a more caudal injury.

应特别强调需要区别“上运动神经元体征” 和“下运动神经元体征”，这在疼痛医学中至关重要。上运动神经元损伤可以类似成许多常见的腰椎疼痛综合征。一般认为脊柱损伤发生在特定的节段，例如，涉及大腿前部(L2分布)的疼痛，也可以是由于在颅脑水平上的病变所致。应该特别注意颈椎损伤，颈椎损伤造成的疼痛更多地误以为源于骶尾部的损伤。

pain involving the front of the thighs (L2 distribution), can be due to injury at any more cephalad level.

当中不应该有逗号的吧？