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 Table of Contents  
ORIGINAL ARTICLES
Year : 2022  |  Volume : 5  |  Issue : 1  |  Page : 106-111

Learning curve of thoracic pedicle screw fixation by freehand technique


Mumbai Institute of Spine Surgery, Bombay Hospital and Medical Research Centre, Mumbai, Maharashtra, India

Date of Submission22-Jan-2021
Date of Acceptance12-Aug-2021
Date of Web Publication02-Feb-2022

Correspondence Address:
Sanjeev Asati
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.
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ISJ.ISJ_11_21

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  Abstract 

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 Top


Pedicle screws have been used widely for spinal disorders since the 1960s when first reported by Roy-Camille.[1] Thoracic pedicle screws are required for various pathologies and various techniques for insertion have already been described.[2],[3],[4] Transpedicular instrumentation allows for three-column fixation with a more rigid construct, which is clinically and biomechanically superior to hook-rod construct.[5],[6],[7] 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%[8] 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.[9],[10],[11],[12] 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.[13] 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.[14] 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.[15] 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 Top


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.[3]

Surgical technique

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.[13]

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.

Statistical analysis

Standard SPSS 20.0 software was used for statistical analysis. Chi-square test was used to compare each variable in different quartiles.


  Results Top


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

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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].
Figure 1: Different grades of perforations among the quartiles

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Table 2: Different grades of perforations as per “Gertzbein criteria of pedicle perforation” among the different quartiles

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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

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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 Top


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.[5],[6],[7] 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.[16],[17],[18],[19] 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.[20] 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.[8] Ferrick[21] 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.[22] (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.[23],[24] (medial 32.8% and lateral 67.2%) and Karapinar et al.[25] (medial 32.4% and lateral 48.6%). Parker et al.[26] found that screws inserted into T4–T6 were most likely to breach, whereas Modi et al.[23],[24] 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.[27],[28] 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

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  • 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.[29]


  • 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.


Limitations

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 Top


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.[36]

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

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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2.
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.  Back to cited text no. 2
    
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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.  Back to cited text no. 5
    
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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.  Back to cited text no. 13
    
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Lekawa M, Shapiro SJ, Gordon LA, Rothbart J, Hiatt JR The laparoscopic learning curve. Surg Laparosc Endosc 1995;5: 455-8.  Back to cited text no. 15
    
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