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| Thoracic vertebrae have structural differences from the lumbar and cervical in that the transverse processes of thoracic vertebrae are elongated, angle approximately 40 degrees posterior from the coronal plane, and articulate with the ribs. The ribs generally pass just superiorly and anterior to the transverse process and attach to the transverse process through a transverse-costal facet. The radiographic image is often difficult to interpret both in AP and lateral positions due to the overlapping ribs and transverse processes in the AP and overlapping ribs and oblique transverse processes in the lateral view. Pathologies of the thoracic spine are rare compared to the lumbar or cervical spine. Disc prolapse is seen in the thoracic region only 1% of the total cases of disc prolapse with the lumbar spine containing 80% of the pathology. Other structures in the thoracic spine that may lead to pain are the zygapophyseal joints, however the thoracic spine does not have the single segment rotation, flexion, or extension capabilities of the lumbar or cervical spine. The zygapophyseal joints are only rarely injured in the thoracic spine due to the relative immobility of the segments of the thoracic spine, constrained by ligaments and the fixation provided by the ribs. The capsules usually do not have enough motion with which to tear the capsule. The joints are mostly non-weightbearing except for the very low thoracic facets. The T12 level is a unique transitional vertebral body with the upper zygapophyseal joints typical thoracic in the coronal plane while the lower articulation with the L1 vertebrae contains zygapophyseal joints in the sagittal plane. Because of the unique anatomy at this level, the T12 may be more predisposed to injury than the upper thoracic zygapophyseal joints. The surface innervation of the T11 and T12 posterior rami are also unique. Pain maps of the thoracic facets are from three sources: Dreyfuss, Fukui, and Maigne. A composite pain map is included on the left. The differential diagnosis of thoracic pain includes pain from the disc, costo-transverse facet capsule or arthritis, myofascial (esp. levator, rhomboids), scapulocostal syndrome, splenius cervicus enthesopathy, cutaneous nerve entrapment on exiting through the fascia or dorsal muscles, primary or secondary rib pain, costovertebral arthritis, thoracic spondylosis, intercostal neuralgia, post herpetic neuralgia, foraminal stenosis, pulmonary or cardiac disease, and compression fractures of the vertebral body. More rare causes include vertebral body subluxation and spinal canal or cord tumors. The anatomy of the thoracic medial is unique as compared to the lumbar or cervical spine where the medial branch lies in close approximation to the superior articular process. Only at T12L1 does the more typical relationship apply. The thoracic medial branches take off from the posterior primary ramus and course posteriolaterally from the neuroforamina, then pass over the superior border of the transverse process at the inflexion point, then loop back medially to the z-joint. The medial branch gives off a descending branch to the lower facet segment. The C8 medial branch leaves the C7T1 neuroforamen and courses over the T1 transverse process, giving innervation to the C7-T1 and the T1-T2 Z-joints. The T1 medial branch passes over the lateral transverse process of T2 and gives innervation to the T1-2 and T2-3 Z-joints. The T12 medial branch exits the neuroforamen of T12-L1 passes over the junction of the transverse process with the superior articular process of L1 and gives innervation to the T12-L1 and the L1-2 joints. Between T4 and T8 the medial branches do not lie in close approximation to the lateral transverse processes, instead coursing between the transverse processes above and below. Other structures using the medial branches to transmit pain are the skin near the thoracic midline, the supraspinous ligaments, and the intraspinous ligaments. Medial branch blocks may be performed at the T1-4 levels and T6-10 levels as a field block on the posterior superior lateral border of the transverse processes where the nerve crosses anteriorly. Transverse Processes are not always easy to see, however if the beam is rotated contralateral after squaring off the endplates, the transverse processes are viewed at a more orthogonal vector across the body of the transverse processes. If the transverse processes cannot be seen after this manuver, consider adjusting the contrast and brightness on the fluoroscopy videoscreen. If this does not permit TP visualization, then lateral window collimation of the fluoroscope beam may be employed. If this does not help with visualization, then one may elect to define the boundaries of the TP with additional needles. The TP always comes off the lateral border of the inferior part of the pedicle as seen on AP projection. The needles are walked laterally (and more superficially due to the posterior slant of the TP) until the lateral border of the TP is defined. The medial branches cross the TP superior border approximately 2/3 distance to the tip of the TP. Of course this doesnt apply to the T4-8 medial branches whose course is more variable and often lies between the transverse process above and that below. Therefore a different approach is necessary to block these nerves. The approach I have found most useful is to place a needle at the 2/3 point on the adjacent TP and insert a third needle into the space directly between the marker needles. Then under lateral fluoroscopy, the third needle is advanced to the same depth as the other two needles. A low volume field block or nerve block around the medial branch is then used to define the potential success of radiofrequency thermocoagulation. Thermocoagulation of the medial branches is performed at several locations on the superior-lateral border of the transverse process. Usually at least 3 lesions are performed at each medial branch. The lesioning parameters chosen are typically 80 degrees C. for 60 sec each lesion. Additionally lesion time of another 30 seconds will only increase the lesion size by another 6%. Therefore because of the number of lesions to be created, it is necessary to be time efficient. Stimulation is controversial due to the need to lesion multiple levels close together. If the patient has multiple needles placed simultaneously on one transverse process, then stimulation may be useful, but once local anesthetic has been injected at one location pre-lesioning, it is likely the entire medial branch will be anesthetized and therefore further stimulation will result in no meaningful information. As there are no significant motor nerves in the immediate vicinity, motor stimulation would at most stimulate the multifidus muscle. Therefore, motor stimulation is not helpful as a safety feature. |
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