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Figure A labels the neuroforamen of four vertebral motion segments. Groups A-E lists combinations of the nerve roots which exit the corresponding neuroforamen. Assuming normal vertebral anatomy with 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebra, which group is anatomically correct?
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Group D correctly matches the nerve roots with the correct vertebral neuroforamen.
Understanding the nerve root anatomy in relation to the anatomic structures of the vertebral motion segment is critical when evaluating patients with cervical and lumbar radiculopathy. One important concept to understand is that in the cervical spine the nerve roots exit above the corresponding pedicle. Therefore, the C7 nerve root exits above the C7 pedicle. This is different than in the lumbar spine where the nerve roots exit below the corresponding pedicle. Therefore, the L3 nerve root travels below the L3 pedicle. The difference can be explained by an extra nerve root (C8) in the cervical spine that does not have a corresponding pedicle (there is no C8 vertebral body). Therefore, C8 exits below the pedicle of C7. T1 is the first nerve root to exit below the corresponding pedicle (T1 travels below the T1 pedicle).
Devlin et al. discussed methods to monitor nerve root function during surgery. They report electromyograpy can be classified into two categories based on method of elicitation — mechanical and electrical. Mechanically elicited electromyography (EMG), also called spontaneous or free-running EMG, may be useful during the dynamic phases of surgery (eg, implant placement, nerve root manipulation). Electrically elicited EMG, also called stimulus-evoked EMG or triggered EMG, may be useful during static phases of surgery (eg, testing pedicle screws after placement). Together, these electromyographic techniques encourage early detection of excessive nerve root traction, mechanical injury, or cortical breach.
Illustration A shows a labeled version of Figure A. Illustration B illustrates the difference between the horizontal nature of the cervical nerve roots and the vertical nature of the lumbar nerve roots. The horizontal nature in the cervical spine explains why both a central and foraminal disc herniation affect the same nerve root. Additionally, because the spinal cord ends at L2, large central herniations can cause upper motor symptoms in the cervical spine, but similar large central discs can cause cauda equina syndrome below L2. Illustration V is a video showing how to read an MRI of the cervical spine and identify foraminal stenosis.
Group A,B,C and E: These groups have a least one nerve root which is incorrectly placed in the neuroforamen.
Devlin VJ, Schwartz DM
J Am Acad Orthop Surg. 2007 Sep;15(9):549-60. PMID: 17761611 (Link to Abstract)
Devlin, JAAOS 2007
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Which artery labeled in Figure A provides the predominant blood supply to the spinal cord?
None of the above
The anterior spinal artery (A) is the predominant blood supply to the spinal cord and supplies the anterior 2/3rds of the spinal cord. There is only one anterior spinal artery in comparison to the paired dorsal spinal arteries. The paired dorsal spinal arteries (B) supply the dorsal 1/3rd of the spinal cord, mainly to the dorsal columns.
Morishita et al performed a cadaveric study to evaluate the mechanisms of spinal cord injury after thoracoabdominal aneurysm repair. They found that while the anterior spinal artery provides the predominant blood supply to the spinal cord, after repair of a thoracoabdominal aneurysm, the spinal cord becomes progressively dependent on the arteria radicularis vasculature at a rate depending on the degree of anterior spinal artery narrowing.
In a historical manuscript, Dommisse defines the cranial/caudal thoracic arterial watershed zone of spinal cord vascularity and identifies the anterior spinal artery as the predominant blood supply to the spinal cord. The thoracic arterial watershead zone renders the spinal cord vulnerable to intraoperative ischemic damage.
Morishita K, Murakami G, Fujisawa Y, Kawaharada N, Fukada J, Saito T, Abe T
Ann. Thorac. Surg.. 2003 Dec;76(6):1967-71. PMID: 14667623 (Link to Abstract)
J Bone Joint Surg Br. 1974 May;56(2):225-35. PMID: 4854669 (Link to Abstract)
Dommisse, BJJ 1974
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ARTERIAL SUPPLY AND VENOUS DRAINAGE OF SPINAL CORD
3D anatomy tutorial on the blood supply to the spinal cord using the BioDigital...