Percutaneous Pedicle Screw Placement for Spinal Instrumentation

37 Percutaneous Pedicle Screw Placement for Spinal Instrumentation


Steven H. Cook, Robert E. Isaacs, Hyun-Chul Shin, Jonathan B. Lesser, Moumita S.R. Choudhury, and Mick J. Perez-Cruet


Abstract


Percutaneous pedicle screw placement for spinal instrumentation is an important procedure for spine surgeons to treat a wide variety of spinal pathologies. The indications, necessary equipment, and procedure are explained in detail in this chapter. Modifications to include reduction of radiation exposure are discussed while stressing the importance of imaging for safe and efficient pedicle screw placement. Tips on complication avoidance and management are also presented.


Keywords: pedicle screw, percutaneous, fusion, internal fixation, minimally invasive


37.1 Introduction


There are multiple spinal pathologies in the thoracolumbar spine that require internal fixation ranging from deformity to traumatic injuries. Pedicle screws have historically been placed using a midline incision and further lateral dissection, resulting in extensive muscle retraction and concern for tissue disruption. More recently, the use of minimally invasive procedures allows for safe placement of pedicle screws through smaller bilateral incisions with less tissue damage.


Percutaneous pedicle screw placement was first described by Magerl in 19821 as part of an external fixation device first used in the thoracolumbar spine for treatment of traumatic injuries and osteomyelitis. In 2001, the Sextant (Medtronic) system was developed by Foley et al to safely pass a rod using percutaneous methods.2 In subsequent years, there has been further development of intraoperative imaging and spinal instrumentation as well as refinement of percutaneous techniques to allow for accurate and safe placement of pedicle screws in a minimally invasive manner.


Comparisons of percutaneous pedicle screws to open techniques have identified advantages of minimally invasive procedures, including reduced damage to paraspinal musculature,3,4 reduced blood loss,5 decreased operative time,6 and improved injury reduction in fractures.7 There has been a concern for increased risk of facet violation or medial misplacement in the percutaneous approach, which could lead to increased risk of adjacent segment disease or neurological injuries. Recent studies imply a concern that percutaneous pedicle screw placement increases the risk of superior facet violation compared to open procedures,8,9 but malposition of screws has been shown to be as low as 0.3% in the lumbar spine and 4.4% in the thoracic spine, which is comparable to open reported rates.10,11 Additionally, accurate placement of pedicle screws has been shown to be as high as 98% in traumatic injuries.12 The instrumentation for percutaneous placement can present a higher initial cost but combined with shorter hospital stay and decreased blood transfusions, the total cost can be lower than or comparable to open minimally invasive procedures.13


A current disadvantage for percutaneous placement is radiation exposure to the patient and surgeon with use of imaging during the procedure.14 With advancements in protective equipment and imaging techniques, and changes in pulse/dosing, these radiation risks can be lowered.15 Recent developments in percutaneous pedicle screw targeting techniques and instrumentation have resulted in minimal radiation exposure to the surgeon (image Fig. 37.1).



37.2 Indications and Contraindications


Indications for pedicle screw placement have been increasing. Degenerative disease, traumatic injuries, and infection have all been shown to have good results with percutaneous pedicle screw placement. Contraindications are not exclusive to this technique but are in line with other techniques of spine fusion, and patients who are poor candidates for fusion should be carefully reviewed. The only direct contraindication is inability to adequately arrange the screw within the confines of the pedicle. Patients with severe rotational scoliotic deformity have been a relative contraindication; however, improved techniques and experience has made this less so.16


37.3 Preoperative Planning


The preoperative evaluation of the patient should include a thorough physical examination. This includes a neurological evaluation for signs of myelopathy or nerve root compression, which may alter your surgical plan. A skin examination should note any prior incisions to assist in planning surgical approach and placement of incisions for percutaneous screws. Radiographic evaluation should be performed with lumber spine X-rays at a minimum but usually to include either CT or MRI for visualization of pedicles to accurately determine size of pedicle screws to be placed and any abnormal anatomy.


37.3.1 Instrumentation Notes


The surgical tools needed for percutaneous pedicle screws can be divided into imaging requirements and spinal instrumentation:


Fluoroscopy.


Lead drape including thyroid shield for surgeon and operative personnel.


Radiolucent table and frame that permits adequate anteroposterior (AP) and lateral fluoroscopic views of the spine.


Cannulated instruments for pedicle screw placement.


Kirschner’s wire (K-wire) and K-wire driver.


Rod instrumentation device.


37.4 Surgical Technique


This chapter briefly describes two different techniques that have been used safely and effectively for accurate percutaneous pedicle screw placement for spinal instrumentation using fluoroscopic guidance.


The patient is positioned prone on a radiolucent frame while maintaining a good sagittal balance (image Fig. 37.2a). Next, electrophysiologic monitoring can be applied (electromyography, somatosensory evoked potentials, or combination may be employed). The K-wires and pedicle screws are stimulated intraoperatively to assure placement is not impinging upon a nerve. Action potential of less than 8 mA warrants that the K-wire or pedicle screw be repositioned. The fluoroscope is brought into field to plan entry sites. AP images are taken at each vertebral level where pedicle screws will be placed to obtain a Ferguson angle, delineating the superior end plate of the body. Next, a true AP view is obtained so that the spinous process is centered between the pedicles. Heavyset individuals may require manipulation of the contrast mode of the fluoroscopic unit to adequately visualize these landmarks. This measurement is marked at each vertebral level with a transverse line that is parallel to the end plate and bisects bilateral pedicles using a radiopaque instrument and also recorded on fluoroscope for later use (image Fig. 37.2b). Next, 10 to 25 degrees off-angle oblique views are obtained through the pedicles (owl’s eye view) on each side and recorded on the fluoroscope. A craniocaudal line is marked on the skin that bisects all the pedicles on each side of levels receiving instrumentation (image Fig. 37.2c). Once adequately positioned, the two pedicles on the vertebral body should be clearly visible. It is especially important to view the medial border of the pedicle because violating this border by either a K-wire or Jamshidi needle can result in neural element injury. Looking at the pedicles on the vertebral bodies above and below helps delineate the anatomy of the targeted pedicle, particularly when targeting the sacrum (S1) where the pedicle can be hard to visualize.


The patient is then sterilely draped and the C-arm is likewise draped to provide AP and lateral images without contaminating the field when repositioning the fluoroscopic unit intraoperatively. Local anesthetic may be instilled along the planned incision, which incorporates the craniocaudal line that bisects the pedicles on either side of the spine. The skin is incised and the fascia may be opened sharply or with electrocautery with care taken not to disrupt underlying musculature.


Oct 17, 2019 | Posted by in NEUROSURGERY | Comments Off on Percutaneous Pedicle Screw Placement for Spinal Instrumentation
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