Tips and Pearls
Pedicle screws are very commonly used for fixation of spine especially the thoracolumbar region because of their biomechanical advantage. Various techniques described are anatomic free-hand techniques or image-guided/navigation techniques with their respective pros and cons.
Pedicle screw entry point in thoracolumbar spine, and is commonly guided by superior articular facet, transverse process, and ridge of pars interarticularis. With respect to the cranial-caudal orientation, few texts describe targeting the opposite transverse process for keeping the screws parallel to upper end plate.1 Craniocaudal angulation varies from about 14 degrees cranial to 20 degrees caudal from T1 to S1.2,3
We present a simple technique for guiding this angulation. The patient is placed in prone position with bolsters without any excessive flexion or extension with spinous processes in midline. Standard dissection is performed to expose adjacent laminae, which should be cleared of soft tissues. A small size Langenbeck or 90-degree retractor (Fig. 1A) is placed with the blade flat on the bony surface of adjacent laminae. The pedicle screws are then placed by using pars interarticularis technique. The bone is removed from anticipated entry point using small bone nibbler until pedicle blush is seen and then candle K-wire is put in the direction guided by this technical pearl. The direction of the pedicle screw is usually oriented orthogonal to the retractor blade at various levels (Fig. 1B).
The craniocaudal angulation trick works well in both thoracic and lumbar spine and also in deformity cases where vertebral bodies are not anatomically deformed. It can be used in kyphotic deformities at vertebra above and below the deformity apex (Figs. 2A, B). We do not use this technique in coronal plane deformities and scoliosis. It is difficult to apply when the anatomy is disturbed due to degeneration and osteophyte formation and unilateral posterior element injuries like laminar fractures. Prior compression fractures if symmetrical will cause some degree of kyphosis and screws can be directed using this method above and below the fracture levels.
This relatively simple and novel surgical tip accelerates the screw placement and reduces frequent imaging during surgery. It is easy to use and does not require any special instrument. Hence, we suggest it may be used as a guide in craniocaudal pedicle screw angulation.
1. Vaccaro A, Kandziora F, Fehlings M, et al. AO Surgery Reference (www2.aofoundation.org
). 2015. Available at: srg/popup/additional_material/53/X100-PedicleScrewInsertion.jsp. Accessed October 2, 2015.
2. Defino HLA, Mauad Filho J. Estudo morfometrico do pediculo das vertebras toracicas e lombares [Morphometric study of the pedicle of thoracic and lumbar vertebrae]. Rev Bras Ortop. 1999;34:97–108; [in Portuguese].
3. Mattei TA, Meneses MS, Milano JB, et al. “Free-hand” technique for thoracolumbar pedicle screw instrumentation
: critical appraisal of current “State-of-Art”. Neurol India. 2009;57:715–721.