|Year : 2022 | Volume
| Issue : 1 | Page : 106-111
Learning curve of thoracic pedicle screw fixation by freehand technique
Zahir Abbas, Sanjeev Asati, Vishal G Kundnani, Sanyam Jain, Ankit Patel, Saijyot Raut
Mumbai Institute of Spine Surgery, Bombay Hospital and Medical Research Centre, Mumbai, Maharashtra, India
|Date of Submission||22-Jan-2021|
|Date of Acceptance||12-Aug-2021|
|Date of Web Publication||02-Feb-2022|
Mumbai Institute of Spine Surgery, Room No. 128, First Floor, M.R.C. Wing, Bombay Hospital and Medical Research Centre, Marine Lines, Mumbai 400020, Maharashtra.
Source of Support: None, Conflict of Interest: None
Background: The freehand method of inserting thoracic pedicle screw has become one of the most popular techniques; however, data on its learning curve are scanty. The purpose of this study was to delineate the learning curve and to evaluate the safety of freehand technique of thoracic pedicle screw placement in nondeformed spine. Materials and Methods: A total of 92 consecutive patients who underwent thoracic posterior stabilization with pedicle screws using freehand technique between 2012 and 2017 in various pathologies of nondeformed spine from T1 to T10 at a single institution by a single surgeon were analyzed. Patients were divided into four quartiles (Q1, Q2, Q3, Q4, with 23 patients each) with each consecutive group serving as control for its prior. Demographics (age, sex, pathology involved) and complications were evaluated. Postoperative computed tomography (CT) scan was taken for evaluation of screws perforation including level, direction, grade, and severity of perforation. Results: Of total of 735 screws inserted in 92 patients, 72 screws were perforated with a perforation rate of 9.79%. Of the total perforations, more than half (63.88%) were of Grade 2 and maximum perforations were seen in the lateral direction (58.3%). Total three critical perforations were noted but none of them were symptomatic. The highest rate of perforation was evident at T4 vertebra (18.29%), whereas it was lowest at T9 (3.79%). The perforation rate showed a statistically significant (P < 0.05) decline in Q2 as compared to Q1 achieving asymptote in Q1 after approximately 80–100 screws. Conclusion: A steep learning curve is associated with the freehand technique of thoracic pedicle screws and asymptote can be achieved after approximately 80–100 screws. Novice surgeons can reduce the learning curve by doing practice on saw bone models and cadaveric dissection learning to avoid perforations and other complications with understanding the complex anatomy and variations encountered in the typical thoracic spine.
Keywords: Freehand technique, learning curve, perforation, thoracic pedicle screw
|How to cite this article:|
Abbas Z, Asati S, Kundnani VG, Jain S, Patel A, Raut S. Learning curve of thoracic pedicle screw fixation by freehand technique. Indian Spine J 2022;5:106-11
|How to cite this URL:|
Abbas Z, Asati S, Kundnani VG, Jain S, Patel A, Raut S. Learning curve of thoracic pedicle screw fixation by freehand technique. Indian Spine J [serial online] 2022 [cited 2022 May 25];5:106-11. Available from: https://www.isjonline.com/text.asp?2022/5/1/106/337136
| Introduction|| |
Pedicle screws have been used widely for spinal disorders since the 1960s when first reported by Roy-Camille. Thoracic pedicle screws are required for various pathologies and various techniques for insertion have already been described.,, Transpedicular instrumentation allows for three-column fixation with a more rigid construct, which is clinically and biomechanically superior to hook-rod construct.,, Insertion of thoracic screws is technically more difficult than lumbar screw insertion due to its complex anatomy and variations at different levels. Perforation rate of the pedicle screw in the thoracic spine ranges from 1.5% to 58% and these perforations can sometimes lead to disastrous complications because of the proximity to vital structures in the thoracic spine. Use of intraoperative fluoroscopy and image-guided techniques helps in appropriate screw placement.,,, The goal of the freehand technique is to avoid the harmful effects of radiation and to mimic as close as possible the technique of lumbar screw placement without the use of any intraoperative fluoroscopy, radiography, and/or image-guided technique. Roy-Camille advocated a point of entry for screw insertion at the intersection between the midline of the facet joint and the midline of the transverse process. The learning curve was mentioned in the health-care field in the 1970s and came into common usage with the development of laparoscopic surgery in the 1990s. Studying the learning curve of a surgical procedure will help not only in understanding the problems faced by novice surgeons in their initial few cases but also to find solutions to them, to set guidelines for training and educational purposes, to guide implant industry for any changes in the instruments. Understanding the learning curve is also crucial when comparing a new procedure with older interventions.
The purpose of this study was to delineate the learning curve and to evaluate the safety of freehand technique of thoracic pedicle screw placement in thoracic vertebrae in nondeformed spine.
| Materials and Methods|| |
After institutional board approval, this retrospective analysis was done on 92 consecutive patients who underwent posterior stabilization utilizing 735 transpedicular thoracic screws in various pathologies in nondeformed spine from T1 to T10 at a single institution by a single surgeon (2-year fellowship trained spine surgeon) from 2012 to 2017 (over a period of 5 years).
Patients were divided into four quartiles (Q1, Q2, Q3, Q4-23 patients each) as per the date of surgery with each consecutive group serving as control for prior.
All the patients who underwent thoracic pedicle screw insertion for stabilization due to any pathology (trauma, infection, degeneration, and tumor) in a nondeformed spine from T1 to T10 were included in the study and the patients in whom thoracic pedicles screws inserted in T11 and T12 vertebrae, those with revision surgery and deformed spine were excluded from the study.
Demographics (age, sex, pathology involved) and complications (neurological worsening, infection, dural leak, visceral/vessel injury) were evaluated. Postoperative computed tomography (CT) scan was done in all the cases for the evaluation of number of screws perforated, level of screw insertion, direction of perforation, grade of perforation (critical breach: ≥3 mm, noncritical breach: <3 mm). The Gertzbein criteria (Grade 0: no breach, Grade 1: < 2 mm breach, Grade 2: 2–4 mm breach, Grade 3: 4–6 mm breach and Grade 4: 6–8 mm breach) was used to evaluate the accuracy of TPS placement as following.
After making a midline incision, the spinal segment was exposed carefully to the tip of the transverse processes bilaterally. The author used the freehand technique described by Lenke for inserting pedicle screws.
Removal of the inferior facets with a 0.5-inch straight osteotome was done. Removal of the articular cartilage from the dorsal side of the superior facet of the inferior vertebra using a small curette was done.
The entry point was identified using posterior landmarks (transverse process and articular surface) and decorticated using a nibbler. Proper placement of the gearshift probe is critical. The probe should feel snug fit in the cancellous bone, and any sudden advance or persistent resistance indicates that the probe should be repositioned. Gear shift probing done which includes initially direct the gearshift laterally till the depth of 20 mm (approx. length of pedicle) to diminish the likelihood of medial pedicle wall perforation. Then, reverse the gearshift and redirect it medially for a proper medial trajectory. Once the tract was made, a flexible ball-tip probe was used to palpate all four walls of pedicle bony walls and floor to ensure intra-pedicular placement.
Then, after tapping with 0.5 mm less diameter tap then intended screw and re-palpating the distinct bony ridges confirming intraosseous position, the screws were placed slowly to maximize the expansion of pedicle tract. The same surgeon inserted screws on both sides by switching sides.
Anteroposterior and lateral C-arm imaging was performed in every case after insertion of all the screws and doubtful screws on X-ray were removed and again checked with ball tip probe for confirmation and reinserted.
Standard SPSS 20.0 software was used for statistical analysis. Chi-square test was used to compare each variable in different quartiles.
| Results|| |
The mean age of the patients was 43.46 years (range 22–79) with M:F ratio 52:40. Patients with varied pathologies like infection (n = 56), trauma (n = 15), degenerative (n = 11), and tumors (n = 10) were noted. Total 735 screws were inserted in 92 patients, of which 72 screws were perforated at various levels in different directions with a total perforation rate of 9.79%.
Maximum number of perforations were observed in lateral direction (58.3%) and minimum perforations were seen in superior direction (2.7%). The total number of medial, lateral, superior, and inferior perforations has shown a decline in Q2 as compared to Q1. There was no case of superior perforation after Q1 and inferior perforation after Q2. The perforation rate showed statistically significant (P < 0.05) decline in Q2 as compared to Q1 achieving asymptote in the first quartile [Table 1].
|Table 1: Perforation rate with direction of screw perforation in different quartile|
Click here to view
Of total perforations, more than half (63.88%) were of Grade 2, most of which were in Q1 (36.9%) and least in Q4 (17.3%). Grade 1 perforation was observed in 30.55% of perforated screws of which maximum belonged to Q1 (45.4%) and minimum to Q2 (13.6%). Grade 3 perforations (5.55%) were present only in Q1 and Q2 [Figure 1]. There was statistically significant difference (P < 0.05) between different grade of perforations between Q1 and Q2. There were three critical perforations in Q1 and one in Q2 with no critical perforation in further quartiles. However, none of the critical perforations were symptomatic [Table 2].
|Table 2: Different grades of perforations as per “Gertzbein criteria of pedicle perforation” among the different quartiles|
Click here to view
The overall highest rate of perforation of total screws inserted was seen in T4 vertebra (18.29%), whereas minimum perforations were seen in T9 (3.79%) [Table 3].
|Table 3: Rate of perforation of all the screws inserted at each thoracic vertebra (T1–T10) among different quartiles|
Click here to view
No significant difference was observed in the side (right or left) of screw perforated. In eight patients, sudden give away was felt during gear shift probing and a breach confirmed on palpation/probing and the screw was re-directed intraoperatively. All the perforated screws seen on CT scan were not symptomatic, and hence were not revised. There was no case of neurological worsening, infection, dural leak and visceral/vessel injury due to screw placement.
| Discussion|| |
Various instrumentation techniques have been attempted to treat pathologies of thoracic spine. These various techniques have evolved and surpassed from simple wire and hook construct to stronger pedicle screw construct. Thoracic pedicle screws have clear biomechanical advantages over standard hook or hybrid construct, with recent data suggesting improved radiographic and clinical outcomes.,, Numerous authors have elucidated the biomechanical, radiographic, and clinical benefits of using thoracic pedicle screws which includes improved pull-out and torsional strength, reduced revision rates, better fusion rates and lower pseudo-arthrosis rates.,,, Placement of thoracic pedicle screws is more challenging as the thoracic vertebrae tend to be more anatomically varied than lumbar vertebrae when considering pedicle angles and attachment to the vertebral body. The analysis of the learning curve is based on the assessment of the accuracy of each TPS placement. The perforation rate of TPS ranges from 1.5% to 58%, and is related to the evaluation methods used, which are typically radiograph and CT scans. Ferrick considered that the radiograph is inadequate to assess the pedicle position. A CT scan provides better accuracy to evaluate the breach of the pedicle wall, which is considered as the gold standard for evaluating the position of pedicle screws. It is difficult to measure the breach length less than 2 mm on the CT images, partly because the screws could generate scatter. We used CT scan with bone window and automatic exposure control to evaluate perforation and found overall perforation rate 9.79% which is comparable to other studies which used freehand technique like Schizas et al. (12%).Most of our perforation were grade 2 (63.88%). Of the total perforations author has seen 34.7% medial, 58.3% lateral, 2.7% superior and 4.16% inferior perforation rate as compared to Modi et al., (medial 32.8% and lateral 67.2%) and Karapinar et al. (medial 32.4% and lateral 48.6%). Parker et al. found that screws inserted into T4–T6 were most likely to breach, whereas Modi et al., found that screws inserted into the pedicles of T5–T8 had a greater incidence of breaches as these levels have the narrowest pedicles and have decreased space between the medial border of the pedicle and spinal cord. Similar trend had been found in our study with maximum breach at T4 level and minimum at T9. The perforation rate was significantly reduced in Q2 (8%) as compared to Q1 (16.66%) after achieving the asymptote at approximately 80–100 screws inserted as similar to previous studies., There was no case of neurological worsening, infection, dural leak and visceral/vessel injury and no perforation was revised postoperatively. Comparison between different studies has been shown in [Table 4]. Based on our analysis of learning curve, we realized that there are many pitfalls that beginners encounter in freehand pedicle screw insertion in thoracic spine and there are certain recommendations with some technical points during surgery to reduce them which are:
|Table 4: Comparative analysis between different studies on thoracic pedicle screw insertion by freehand technique|
Click here to view
- 1) Proper preoperatively planning with evaluation of pedicles (size and shape) in CT scan preoperatively and to plan pedicle screw placement (size and trajectory) accordingly.
- 2) Adequate exposure from transverse process to transverse process on both sides with visualization of all the anatomical landmarks.
- 3) In the initial cases, it is advisable to remove the inferior articular process of superior vertebrae with osteotome to visualize the exact entry point.
- 4) Choose the right entry point for screw insertion.
- 5) After decortication of the entry point for the first 20 mm the Lenke’s probe should be directed outward to prevent medial pedicle wall breach and then inward for proper medial trajectory.
- 6) Use of pedicle feeler at every step (after entry with Lenke probe and after tapping) as Lehman’s study indicated that the accumulation of experience increases the accuracy rate of detecting breach with a ball-tip probe.
- 7) If any breach felt, then making a new entry and repeat all the steps again.
- 8) Craniocaudal angulation should be kept in mind while inserting upper thoracic pedicle screws. Always check with one strict AP and lateral C-arm view intraoperatively at the end of the procedure.
First, nonmodifiable confounding factors are present, which include individual surgeons learning ability as some surgeons are slow, whereas some are quick learners. The number of operations carried out per month by surgeon has also an effect on the final outcome. Second, long term effects of the screws which perforated the pedicles are not analyzed in the present study.
| Conclusion|| |
To reduce the learning curve of inserting the pedicle screws in thoracic spine, novice surgeons should follow above recommendations and practice on cadavers and saw bone model with understanding the complex anatomy and variations encountered in typical thoracic spine.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Roy-Camille R, Saillant G, Mazel C Internal fixation of the lumbar spine with pedicle screw plating. Clin Orthop Relat Res 1986;203:7-17.
Vaccaro AR, Rizzolo SJ, Balderston RA, Allardyce TJ, Garfin SR, Dolinskas C, et al
. Placement of pedicle screws in the thoracic spine. Part II: An anatomical and radiographic assessment. J Bone Joint Surg Am 1995;77:1200-6.
Gertzbein SD, Robbins SE Accuracy of pedicular screw placement in vivo. Spine (Phila Pa 1976) 1990;15:11-4.
Magerl FP Stabilization of the lower thoracic and lumbar spine with external skeletal fixation. ClinOrthop 1984;189:125-41.
Suk SI, Lee CK, Min HJ, Cho KH, Oh JH Comparison of Cotrel-Dubousset pedicle screws and hooks in the treatment of idiopathic scoliosis. Int Orthop 1994;18:341-6.
Suk SI, Lee CK, Kim WJ, Chung YJ, Park YB Segmental pedicle screw fixation in the treatment of thoracic idiopathic scoliosis. Spine (Phila Pa 1976) 1995;20:1399-405.
Dobbs MB, Lenke LG, Kim YJ, Kamath G, Peelle MW, Bridwell KH Selective posterior thoracic fusions for adolescent idiopathic scoliosis: Comparison of hooks versus pedicle screws. Spine (Phila Pa 1976)2006;31:2400-4.
Gang C, Haibo L, Fancai L, et al
. Learning curve of thoracic pedicle screw placement using the freehand technique in scoliosis: How many screws needed for an apprentice? Chinese section Springerlink.com 2011.
Youkilis AS, Quint DJ, McGillicuddy JE, Papadopoulos SM Stereotactic navigation for placement of pedicle screws in the thoracic spine. Neurosurgery 2001;48:771-8; discussion 778-9.
Rampersaud YR, Simon DA, Foley KT Accuracy requirements for image-guided spinal pedicle screw placement. Spine (Phila Pa 1976) 2001;26:352-9.
Schwarzenbach O, Berlemann U, Jost B, Visarius H, Arm E, Langlotz F, et al
. Accuracy of computer-assisted pedicle screw placement. An in vivo computed tomography analysis. Spine (Phila Pa 1976) 1997;22:452-8.
Stauber MH, Bassett GS Pedicle screw placement with intraosseous endoscopy. Spine (Phila Pa 1976) 1994;19:57-61.
Kim YJ, Lenke LG, Bridwell KH, Cho YS, Riew KD Freehand pedicle screw placement in the thoracic spine: Is it safe? Spine (Phila Pa 1976) 2004;29:333-42; discussion 342.
Dhawan A, Klemme WR, Polly. DWJr Thoracic pedicle screws, comparison of start points and trajectories. Spine 2008;33:2675-81. Lippincott Williams & Wilkins.
Lekawa M, Shapiro SJ, Gordon LA, Rothbart J, Hiatt JR The laparoscopic learning curve. Surg Laparosc Endosc 1995;5: 455-8.
Nowitzke AM Assessment of the learning curve for lumbar microendoscopic discectomy. Neurosurgery 2005;56:755-62; discussion 755-62.
Chung KJ, Suh SW, Desai S, et al
. Ideal entry point for the thoracic pedicle screw during the freehand technique. International Orthopaedics [SICOT] 2008;32:657-62.
Liljenqvist U, Hackenberg L, Link T, Halm H Pullout strength of pedicle screws versus pedicle and laminar hooks in the thoracic spine. Acta Orthop Belg 2001;67:157-63.
Kuklo TR, Potter BK, Lenke LG, Polly DW Jr, Sides B, Bridwell KH Surgical revision rates of hooks versus hybrid versus screws versus combined anteroposterior spinal fusion for adolescent idiopathic scoliosis. Spine (Phila Pa 1976) 2007;32:2258-64.
Speelman C, Kirsner K Skill acquisition: History, questions and theories. In: Speelman C, Kirsner K, editors. Beyond the Learning Curve. Oxford: University Press; 2005. p. 27-65.
Ferrick MR, Kowalski JM, Simmons ED Jr. Reliability of roentgenogram evaluation of pedicle screw position. Spine (Phila Pa 1976) 1997;22:1249-52; discussion 1253.
Schizas C, Theumann N, Kosmopoulos V Inserting pedicle screws in the upper thoracic spine without the use of fluoroscopy or image guidance. Is it safe? Eur Spine J 2007;16:625-9.
Modi HN, Suh SW, Hong JY, Yang JH Accuracy of thoracic pedicle screw using ideal pedicle entry point in severe scoliosis. Clin Orthop Relat Res 2010;468:1830-7.
Modi H, Suh SW, Song HR, Yang JH Accuracy of thoracic pedicle screw placement in scoliosis using the ideal pedicle entry point during the freehand technique. Int Orthop 2009;33: 469-75.
Karapinar L, Erel N, Ozturk H, Altay T, Kaya A Pedicle screw placement with a freehand technique in thoracolumbar spine: Is it safe? J Spinal Disord Tech 2008;21:63-7.
Parker SL, McGirt MJ, Farber SH, Amin AG, Rick AM, Suk I, et al
. Accuracy of freehand pedicle screws in the thoracic and lumbar spine: Analysis of 6816 consecutive screws. Neurosurgery 2011;68:170-8; discussion 178.
Samdani AF, et al
. Accuracy of freehand placement of thoracic pedicle screws in adolescent idiopathic scoliosis: How much of a difference does surgeon experience make? Eur Spine J 2010;19: 91-5.
Gonzalvo A, Fitt G, Liew S, de la Harpe D, Turner P, Ton L, et al
. The learning curve of pedicle screw placement: How many screws are enough? Spine (Phila Pa 1976) 2009;34:E761-5.
Lehman RA, Potter BK, Kuklo TR, Chang AS, Polly DW, Shawen SB, et al
. Probing for thoracic pedicle screw tract violation(s): Is it valid? J Spinal Disord Tech 2004;17:277-83.
Laine T, Schlenzka D, Mäkitalo K, Tallroth K, Nolte LP, Visarius H Improved accuracy of pedicle screw insertion with computer-assisted surgery. A prospective clinical trial of 30 patients. Spine (Phila Pa 1976) 1997;22:1254-8.
Sim E Location of transpedicular screws for fixation of the lower thoracic and lumbar spine. Computed tomography of 45 fracture cases. Acta Orthop Scand 1993;64:28-32.
Fisher CG, Sahajpal V, Keynan O, Boyd M, Graeb D, Bailey C, et al
. Accuracy and safety of pedicle screw fixation in thoracic spine trauma. J Neurosurg Spine 2006;5: 520-6.
Yalniz E, Ciftdemir M, Eskin. D, Dulger H the safety of pedicle screw fixation in thoracic spine. Acta Orthop Traumatol Turc 2009;43:522-7.
Gelalis ID, Paschos NK, Pakos EE, Politis AN, Arnaoutoglou CM, Karageorgos AC, et al
. Accuracy of pedicle screw placement: A systematic review of prospective in vivo studies comparing freehand, fluoroscopy guidance and navigation techniques. Eur Spine J 2012;21:247-55.
Seo HY, Yim JH, Heo JP, Patil AS, Na SM, Kim SK, et al
. Accuracy and safety of freehand pedicle screw fixation in age less than 10 years. Indian J Ortho 2013;47:559-64.
Fennell VS, Palejwala S, Skoch J, Stidd DA, Baaj AA Freehand thoracic pedicle screw technique using a uniform entry point and sagittal trajectory for all levels: Preliminary clinical experience. J Neurosurg Spine 2014;21:778-84.
[Table 1], [Table 2], [Table 3], [Table 4]