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Cervicothoracic Junction: Fusion
• Imaging: Magnetic resonance imaging (MRI) of the cervical spine (Figures 15-1 and 15-2) revealed diffuse central stenosis from the second to the seventh cervical segments secondary to marked spondylosis with both anterior and posterior compression. The patient’s MRI scans also showed loss of the nor- mal lordotic curvature with straightening. Flexion and extension radiographs revealed no hypermobility or instability.
SURGICAL OPTIONS
Surgical options include the following: anterior decompression via multilevel dis- kectomies or corpectomies, laminoplasty, laminectomy without posterior fusion, or laminectomy with posterior fusion (and/or posterior-anterior fusions if there is sig- nificant athetoid motion).
FIGURE 15-1 Sagittal T2-weighted MRI scan of the cervical spine showing straight- ening of the spine with circumferential ste- nosis secondary to spondylosis. (Courtesy Barrow Neurological Institute.)
FIGURE 15-2 Axial T2-weighted MRI scan showing a representative axial view of the circumferential stenosis and spinal cord impingement and deformity. (Courtesy Barrow Neurological Institute.)
Given the patient’s loss of lordosis and circumferential compression, a multilevel cervical laminectomy with lateral mass fusion was recommended. Intraoperatively, his habitus prevented optimal intraoperative imaging. He ultimately underwent a decompressive laminectomy from C3 through C7. Given the disruption of his C7-T1 interspinous ligament, it was deemed that fusion would need to include T1. C7 was skipped to facilitate instrumentation.
Postoperatively, the patient’s myelopathic findings did not progress and his del- toid weakness improved modestly. He did well for several months until he fell from standing height. He noted immediate neck pain. Examination revealed no significant change in his baseline neurologic status. Radiographs (Figure 15-3) revealed bilat- eral fracture of the T1 screws at the interface between the pedicle and pars interar- ticularis. Flexion and extension radiographs showed persistent motion (see Figure 15-3) despite salvage attempts with a rigid cervical orthosis and strict adherence to treatments with an external bone growth stimulator. Ultimately, his fusion had to be extended to more caudal thoracic segments without anterior supplementation.
This case raises several questions that will be addressed using published evidence:
• Would standalone laminectomy have been appropriate in this patient?
• Was there a place for laminoplasty in this case?
• Should the initial fusion have been longer? If so, how far caudally should it have been extended? What type of instrumentation would have been optimal in this case?
• Would anterior stabilization have helped?
• Would intraoperative navigation (use of three-dimensional [3D] systems rather than two-dimensional [2D] fluoroscopy) have been helpful in this case?
FUNDAMENTAL TECHNIQUE
Laminectomy is performed using established techniques. Subsequent lateral mass fusion is facilitated by wide exposure of facets. An appropriate starting point can be determined by creating an imaginary X over the lateral mass (Figure 15-4). Superior and inferior boundaries are the facet joints, and medial and lateral boundaries of the lateral mass serve as the other boundaries. The ideal starting point is 1 mm medial to the middle of the imaginary X. A “matchstick” bur is used to penetrate the cortex and create a starting point (Figure 15-5). An up-and-out technique is used for the hand drill trajectory (Figure 15-6). A medial to lateral trajectory at 30 degrees avoids injury to the vertebral artery, and a cephalad to caudal trajectory at 20 degrees avoids injury to the nerve root. Before placement of screws, the facet joints of the segments
A B C
FIGURE 15-3 Lateral cervical spine radiographs in neutral position (A), flexion (B), and extension (C) show- ing the fractured T1 screws bilaterally. Note the persistent motion as evidenced by angulation and displace- ment of the screw fragments on the flexion and extension views. (Courtesy Barrow Neurological Institute.)
C7 C6 C5 Point of entry
Approximately equal distances beween guide holes C3
C2
Inferior facet Superior facet Lamina
FIGURE 15-4 An appropriate starting point can be determined by creating an imaginary X over the lateral mass. Superior and inferior boundaries are the facet joints, and medial and lateral boundaries of the lateral mass serve as the other boundaries. The ideal starting point is 1 mm medial to the middle of the imaginary X.
(From Chen MY, Duenas MJ, Jandial R: Procedure 62: Lateral mass fixation. In Jandial R, McCormick P, Black P, editors: Core techniques in operative neurosurgery, Philadelphia, 2011, Saunders, pp 440-444, Figure 62-3.)
included in the fusion are decorticated (Figure 15-7). The dorsal cortical surfaces are decorticated for onlay arthrodesis as well. Polyaxial screws are placed and can be measured before placement during the hand drill and feeler steps . A medial trajec- tory risks injury to the vertebral artery (Figure 15-8). Failing to aim cephalad places the nerve root at risk. Starting too far laterally risks fracture of the lateral mass.
When extension to the upper thoracic region is necessary, upper thoracic pedicle screws are placed using anatomic landmarks, because visualization with fluoroscopy at these levels can be difficult in the sagittal plane. T1 pedicle screw trajectory is described in Figure 15-9; a large lateral mass screw can be used to avoid the need for a transitional rod in the construct.
Tips from the Masters 15-1 • The caudal trajectory for thoracic pedicle screws decreases from 20 degrees to 5 degrees from T1 to T12.
Facet joints
“emptied”
Mini matchstick bur marks cortex
FIGURE 15-5 “Matchstick” bur is used to penetrate the cortex and create a starting point. (From Chen MY, Duenas MJ, Jan- dial R: Procedure 62: Lateral mass fixa- tion. In Jandial R, McCormick P, Black P, editors: Core techniques in operative neu- rosurgery, Philadelphia, 2011, Saunders, pp 440-444, Figure 62-4.)
A B
C
30°
20°
20°
FIGURE 15-6 Up-and-out technique is used for hand drill trajectory. A medial to lateral trajectory at 30 degrees avoids injury to the vertebral artery, and a cephalad to caudal trajectory at 20 degrees avoids injury to the nerve root. (From Chen MY, Duenas MJ, Jandial R: Procedure 62: Lateral mass fixation. In Jandial R, McCormick P, Black P, editors: Core techniques in operative neurosurgery, Philadelphia, 2011, Saunders, pp 440-444, Figure 62-5.) FIGURE 15-7 Before placement of screws,
the facet joints of the segments included in the fusion are decorticated. Dorsal cor- tical surfaces are decorticated for onlay arthrodesis as well. (From Chen MY, Duenas MJ, Jandial R: Procedure 62: Lateral mass fixation. In Jandial R, McCormick P, Black P, editors: Core techniques in opera- tive neurosurgery, Philadelphia, 2011, Saunders, pp 440-444, Figure 62-6.)
Too far lateral, drill breaks through pars
Lateral to medial puts the vertebral artery and nerve root at risk
FIGURE 15-8 Medial trajectory risks injury to the vertebral artery. Failing to aim ceph- alad places the nerve root at risk. Starting too far laterally risks fracture of the lateral mass. (From Chen MY, Duenas MJ, Jandial R: Procedure 62: Lateral mass fixation. In Jandial R, McCormick P, Black P, editors:
Core techniques in operative neurosur- gery, Philadelphia, 2011, Saunders, pp 440-444, Figure 62-8.)