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Pedicle screw placement-current concepts
Prof. P S John*
* Prof & Head of Dept of Orthopaedics,
  Medical College, Kottayam.

Address for Correspondence

Prof. P S John,
Prof & Head of Dept of Orthopaedics, 
Medical College Hospital, Kottayam,
Kerala, India



In the last few decades pedicle screw placement has brought in a genuine scientific revolution in the surgical care of spinal disorders, although their introduction and widespread adoption by spinal surgeons all over the globe has created one of the most difficult regulatory problems ever witnessed in the history of orthopaedics. The technique has dramatically improved the outcomes of spinal reconstruction requiring spinal fusion. Short segment surgical treatments based on the use of pedicle screws for the treatment of neoplastic, developmental, congenital, traumatic and degenerative conditions have been proved to be practical, safe and effective. The funnel technique provides straightforward, direct and inexpensive way to very safely apply pedicle screws in the cervical (1), thoracic (2,3) or lumbar spines (4). 

Timeline of Pedicle screws 

In 1948 King introduced facet screws for the treatment of degenerative lumbar conditions. Boucher has been widely credited with the first use of pedicle screws in North America. His innovation was a longer facet screw that occasionally obtained oblique purchase across the pedicle. His screws were not aimed at long axis of the pedicle. It seems that Harrington & Tullos deserve credit for the first deliberate attempt to put pedicle screw through the isthmus of the pedicle. Pioneering the use of pedicle screws with clinical success Roy-Camille (5), popularized the technique in European countries. A strong stimulus to North American use of pedicle screws techniques was the presentation by Roy-Camille (5) at the 1979 American Academy of Orthopaedic Surgeons meeting at San Francisco. Subsequently a number of American surgeons began to use it in US. Arthur Steffee used them most creatively. Steffee et al developed variable screw placement (VSP) plate, which permitted pedicle screws to be placed according to individual patient anatomy. This device provided much more clinical latitude than the Roy-Camille plate which had fixed screw hole distances for  application of the screws. Since the introduction of pedicle screws, engineers, surgeons, radiologists, neurophysiologist, anatomists, epidemiologist and statisticians have made fundamental efforts to improve what was universally recoganised as a clinical liability in surgical spine care; the lack of a truly high quality spinal internal fixation similar to what was available for internal; fixation of long bones. What was introduced as an infant in 1970 for clinical use, is now well accepted all over the world as indicated in the “State of the Art treatment” statements by the North American spine society in 1993 and 1996. 

The long regulatory battle with the FDA started in 1992, when pedicle screw was enjoying class three clearance. Because of the litigation problems FDA was forced to down grade pedicle screws to class 2 in 1995 for use in lumbar spine. The legal battle still continues. It would seem that it is because of their unproven clinical value rather than their mechanical defects that the FDA has acted. In the treatment of spinal fractures and tumors, and perhaps in some types of spondylolisthesis, the usefulness of pedicle screws seem evident, but they are most widely utilized in the treatment of degenerative low back pain, in which their value has not been established, despite what most spinal surgeons seem to believe. Perhaps this confrontation will be of benefit by encouraging manufactures to support, and clinicians to organize prospective studies of the value of newly developed devices before they are widely marketed. If they do not, they may find themselves from 1995 onwards, confronting not only the FDA but an array of licensing authorities in the rest of the world.  


The anatomy of the human pedicle has been studied exhaustively in different races in children and in adults. Measurements of the outer and inner diameters of the pedicle have been performed extensively. The inner diameter of the pedicle – “the critical surgical dimension” has been shown to be more directly related to the height of the patient than to the gender. However, wide individual variations with in common pattern of anatomy are the rule. This forces the surgeons to understand the individual anatomy of the patient, in order to achieve clinical success.


The use of pedicle screws has resulted in dramatic clinical improvements in the surgical care of spinal diseases; Stabilization of spinal fractures, scoliosis, spondylolisthesis, spinabifida, pars-interarticularis defects, neoplasms , lesions of cervical spine and cervico-thoracic junction. Spino pelvic trauma, traumatic spino pelvic disruption and vertical fractures of sacrum have been successfully repaired with either iliac or iliosacral screws.  

In the correction of severe scoliosis, the use of pedicle screws, because of their firm whole in 3 columns of the spine, allows accurate correction at each segment in all the 3 planes. There is however, a greater risk of serious neuro injury when they are used in the thoracic spine and greater caution is necessary. The rigid  hold of the pedicle screws also simplifies the reduction of spondylolisthesis. The most contentious issue, however, is the use of pedicle screws in the treatment of degenerative lumbar disc disease.  

In 1986 Robert et al showed the fundamental importance of load transfer across the spinal column itself along with the implant in the treatment of spinal fractures – a concept known as load sharing, which was subsequently widely adopted by the spinal surgery community. The load sharing classification provides a simple way to differentiate spinal fractures according to comminution. It suggest that anterior vertebrectomy, strut-grafting, and instrumentation be performed in patients with severely comminuted injury to avoid the high screw –breakage rates that occur when short-segment posterior pedicle-screw-based instrumentation is used for highly comminuted injuries. The load-sharing classification permits quantification of comminution of spinal fracture sites so that the load-sharing capability of the injured vertebral body itself, along with the implant system, can be determined. This approach has allowed surgeons to perform short-segment fixation for most isolated spinal fractures in cooperative patients. Three parameters(A, B, C) are considered. A:1:- <30% comminution  2: 30 to 60% comminution. 3: >60% comminution on computed tomographic sagittal plane sections. B: Apposition of fragments 1: minimal displacement. 2: at leat 2 mm of displacement of less than 50% of the cross section of the body 3: at least 2 mm of displacement of more than 50% of the cross section of the body C: deformity 1: kyphosis of 3 degree of less 2: 4 to 9 degrees 3: 10 degrees or more on lateral plain radiograph.  

Methods of Pedicle screw placement 

Various methods have been described for identifying the pedicle and placing the pedicle screws, but basic steps include cleaning the soft issues, exposing the cancellous bone of the pedicle canal by decortication at the intersection of the base of the facet and the middle of the transverse process, probing the pedicle, verifying the 4 walls of the pedicle, tapping the pedicle and placing the screw (6).  

In the lumbar spine, pedicle screws are commonly inserted using anatomical land marks and conformatory roentgenogrames are obtained. Because of the deformed pedicles associated with scoliosis, many surgeons use fluoroscopic guidance (7). Although Suk et al, used anatomical land marks, and confirmed the position of the guide pins with plain roentgenograms, most surgeons believe that because of the tight confines of the pedicle in the thoracic spine, intra operative fluoroscopic is indicated. Frameless stereo tactic technology is available that allows 3 dimensional navigation, but requires time consuming segmental registration and pre-operative CT data. Investigations are currently underway using stereo tactic technology combined with fluoroscopic. This technology has the potential to greatly diminish radiation exposure to both the surgeon and the patient and to allow spontaneous viewing of instrument positions in as many projections as desired.  

Great care is taken to advance the instrument slowly and carefully. If resistance is encountered, the probe is re-positioned. An intra operative roentgenogram or C-arm image can be used to verify correct position. Instruments should pass relatively easily and should not be forced in to the pedicle. In addition to roentgenograms or image intensification, laminotomy and medial pedicle wall exposure helps to confirm the intra pedicular passage of the instrument. Once satisfactory entry into the pedicle has been achieved and palpation from within the pedicle demonstrates solid bone margins along the pedicle wall throughout 360 degrees, the screw can be inserted. If the screws are self tapping, the screw itself is inserted. If the screws require tapping, the tap is inserted first and then the screw.  

In the original technique described by Roy-Camille, the entrance point for screw insertion was situated in the inter section between a vertical line passing through the middle of the inferior facet and a transverse line passing through the middle of the transverse process. The direction of the screw was perpendicular to the posterior plane of the vertebra and straight forward. No information on pedicle wall violation was documented by Roy-Camille. Vaccaro et al were the first to evaluate the feasibility of Roy-Camille technique. They observe 41% penetration. A higher percentage of lateral (31.6%) and inferior (11.6%) wall perforation was observed. Anatomically the pedicle’s and anteromedial inclination in transverse plane varies from cephalad to caudal (2). In general, this angle decreases gradually from T1 to T12. In the lower thoracic levels, screw placement with a straight forward direction may be safe. However in the middle and upper thoracic levels, this techniques will have a higher incidents of lateral wall penetration (8) because of medial inclination of the pedicle. The high incidence of inferior wall violation is due to too low level of starting point. The incidence of pedicle wall violation was significantly reduced when screws were placed using open-lamina technique through a partial laminectomy. However, this technique is not widely used.  

Roy-Camille et al suggested that a pedicle screw should be introduced by drilling the path and then applying the screw. The danger of this approach is now realized and a blunt technique to identify the pedicle along with a 2 plane image intensification during screw placement is adopted now (7). The use of taps of gradually increasing diameter assess  the quality of cortical purchase through the isthmus of the pedicle, and use of image intensification to assess the length of the screw to obtain adequate purchase, result in strong fixation. This technique named as the funnel technique is now used widely. 

Irrigation with Saline solution down the pedicle and visualization of the pedicle by an endoscope, have both been used to assess proper screw placement. Routine monitoring of the somatosensory and dermatomal somatosensory evoked potentials as well as electromyography, also have been used for this purpose. Herthein et al described the application of the pedicle screw from the anterior approach. The use of robotics and computer assisted guidance technology also are getting popular.  


Routine use of pedicle screw has not been free of complications (9,10). The rate of screw misplacement has ranged from 10 – 25% and cortical violation upto 50% in some reports. A learning curve has been demonstrated for surgeons in general. A variable prevalence of nerve root and cauda equina injury has been reported. Computer based navigation techniques improve screw placement according to some authors. In one series dural injury was reported in 7 of 124 patients (11). Deep infections is reported to be 1.1%. The frequency of screw breakage has ranged from 2.6 to 9%. Screw pull out and screw connector disengagements has been reported both in vitro testing and in patients.  


1. Ebraheim NA, Rupp RE, Savolaine ER, Brown JA, Posterior plating of the cervical spine. J Spinal Disord 1995;2:111-15

2. Dickman CA, Yahiro MA, Lu HTC, Melkerson MN. Surgical treatment alternatives for fixation of unstable fractures of the thoracic and lumbar spine. Spine 1994;20(Suppl):S2266-73.

3. Vaccaro AR, Rizzolo SJ Allardyce TJ et al. Placement of pedicle screws in the thoracic spine Part 2 An anatomical and radiographic assessment. J.Bone Joint Surg (Am) 1995;5:951-5.

4. Farber GL. Place HM, Mazur RA, Jones CDE, Damiano TR. Accuracy of pedicle screw placement in lumbar fusions by plain radiographs and computed tomography. Spine 1995;13:1494-9.

5. Roy-Camille R. Osteosynthese du rachis dorsal, lombaire et lombo-sacre par plaques metalliques vissees dansles pedicules vertebraux et less apophyses articulaires. Presse Med 1970;78:1447.

6. Gertzbein SD, Robbins SE. Accuracy of pedicular screw placement in vivo. Spine 1990;1:11-14.

7. Weinstein JN, Spratt KF, Spengler D, Brick C, Reid S, Spinal pedicle fixation: reliability and validity of roentgenogram-based assessment and surgical factors on successful screw placement. Spine 1988;9:1012-8.

8. Esses SI, Sachs BL, Dreyzin V. Complications associated with the technique of pedicle screw fixation. Spine 1993;15:2231-9.

9. Castro WH, Halm H, Jerosch J, Malms J, Steinbeck J, Blasius S. Accuracy of pedicle screw placement in lumbar vertebra. Spine 1996:11:1320-4.

10. Merloz P, Tonetti J, Eid A, et al. Computer assisted spine surgery. Clin orthop 1997;337:86-96.

11. Amiot L-P, Lang K, ZAippel H, Labella H(1998) Comparative accuracy between conventional and computer assisted pedicle screw installation. Presented at the Annual Meeting of the International Society for the study of the lumbar spine, Brussels, Belgium, June 9-13.


 This is a peer reviewed paper 

Please cite as :
Prof. P S John: Pedicle screw placement-current concepts
J.Orthopaedics 2004;1(3)e5





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