Final answer:
The correct sequence of structures encountered during a subarachnoid block using the midline technique is skin, subcutaneous tissue, supraspinous ligament, intraspinous ligament, ligamentum flavum, epidural space, dura, and arachnoid, with the correct option being B.
Step-by-step explanation:
When performing a subarachnoid block using the midline technique, the correct sequence of structures that the spinal needle would encounter, before reaching the cerebrospinal fluid (CSF), is as follows: skin, subcutaneous tissue, supraspinous ligament, intraspinous ligament, ligamentum flavum, epidural space, dura, and finally arachnoid. Hence, the most correct option from the ones provided is:
B. Skin, subcutaneous tissue, supraspinous ligament, intraspinous ligament, ligamentum flavum, epidural space, dura, pia.
After the dura mater, the needle then enters the subarachnoid space where CSF is located. The arachnoid mater is the middle layer of the meninges and does not have to be pierced to withdraw CSF because it is not a tissue layer that provides resistance to the advancing needle. The pia mater lies closest to the spinal cord and is not traversed in a lumbar puncture procedure.