Predicting the Medial Angulation of the Jamshidi Needle Based on Trigonometric Calculation Using the Pedicle Width Measurement in Percutaneous Pedicle Screw Insertion Technique

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J Minim Invasive Spine Surg Tech. 2025;10(Suppl 2):S278-S287

Publication date (electronic) : 2025 July 31

doi : https://doi.org/10.21182/jmisst.2025.02306

Subramaniam Macherla Haribabu, Senguttuvan Pandian, Muralidharan Venkatesan

Department of Spine surgery, Apollo Specialty Hospital, Chennai, India

Corresponding Author: Subramaniam Macherla Haribabu Department of Spine surgery, Apollo Specialty Hospital, Rajiv Gandhi Salai, Perungudi, Chennai, India Email: chennaidrmhs@gmail.com, orthdrmhs@gmail.com

Received 2025 May 4; Revised 2025 June 30; Accepted 2025 July 1.

Abstract

INTRODUCTION

The use of Minimally invasive spine surgery techniques (MISSTs) by spine surgeons has been on the rise in the last decade [1]. An online survey, conducted globally in the year 2020 among practicing spine surgeons into the implementation of MISST revealed 43% of spine surgeons adopt it in their day-today practice. A significant 82.5% of the surgeons claimed - personal interest as the reason behind their adoption of MISST in their practice [2]. The innovations and technologies have increased the spectrum of indications of MISST not restricting only to degenerative spine but to include spine trauma, tumors, metastasis, revision surgeries as well as spinal deformity [3].The advantages of MISST include less soft tissue disruption with lesser paraspinal muscle denervation and/or devascularization; decreased postoperative site pain; reduced use of analgesics in the postoperative period; lesser inpatient hospital stay; minimal incidence of postoperative infection; preservation of spinal biomechanics and early return to recovery when compared to the conventional open spinal procedures [4-7].

The primary usage of MISST by spine surgeons is in the placement of percutaneous pedicle screw insertion [8,9]. Allied technologies such as robotics and spinal navigation have increased the accuracy and precision of inserting percutaneous pedicle screws in well developed countries. However, such a scenario does not apply for surgeons practicing in developing and underdeveloped low socioeconomic countries equipped with low resource settings. Spine surgeons in those countries still rely on a single conventional image intensifier(C-arm/fluoroscopy) in their surgical practice of using MISSTs.

Placement of percutaneous pedicle screw insertion with the use of a C-arm involves targeting the pedicle with the Jamshidi needle as the first step [9]. The Jamshidi needle has to be placed on the lateral pedicle wall border at 3-o’clock position for the right pedicle and 9-o’clock position for the left pedicle inclined sagittal and medial with its trajectory to be correlating to the ideal screw position within the pedicle and vertebral body without violating the medial dura and the lateral visceral or vascular critical structures [10]. The required sagittal angulation is as per the sagittal inclination of the C-arm providing the ideal anteroposterior (AP) view of the vertebral body with parallel superior, inferior vertebral body endplates, midline spinous process and both the pedicles at equal distance from the spinous process [9,10]. The medial angulation of the needle varies pertaining to each particular thoracic or lumbar vertebra. The optimal medial angulation should be such that the needle should not cross the medial pedicle border in the AP view before it crosses the posterior vertebral cortex of the vertebral body in the lateral view of C-arm [9-12]. One cannot deny the fact that the misplaced medial trajectory of the Jamshidi needle can lead to injury to the dural sheath with consequent nerve root injury and iatrogenic postoperative neurological deficit [10-12].

We hypothesized the medial angulation of the Jamshidi needle which varies to each particular thoracic and lumbar vertebra can be predicted based on their pedicle width measurement obtained intraoperatively with the help of ideal AP view of the concerned vertebral body (fluoroscopy providing the AP view) by using the trigonometric mathematical calculation at that particular vertebral segment level in the process of inserting percutaneous pedicle screws. Our aim is to estimate the optimal medial angulation of the Jamshidi needle in inserting percutaneous pedicle screws from the vertebral level D10 to L5 by using pedicle width measurement and to assess the correlation between pedicle width measurement and Jamshidi needle medial angulation value.

MATERIALS AND METHODS

Our hypothesis is based on the simple mathematical trigonometrical formula depicted in Figure 1. As per the trigonometry mathematical formula in Figure 1, tan θ = BC/AB. So θ = tan^-1 BC/AB. We know that the length of AB (length of pedicle) is constant 20 mm [13,14]. Hence, if we knew the corresponding value of BC (pedicle width) of each vertebral body one can estimate angle θ using logarithmic Clarke tables [15]. Figure 2 provides an assessment of the optimal medial angulation of the Jamshidi needle if the pedicle width distance is 5 mm.

Figure 1.

Schematic illustration depicting the estimation of angle θ. ABCD represents an idealized form of the vertebral pedicle. A: Entry point for the Jamshidi needle. AC: Required trajectory for optimal medial angulation of the Jamshidi needle. AB: Lateral pedicle wall. BC (or AD): Pedicle width. CD: Medial pedicle wall. ABC: Right-angled triangle, with AC as the hypotenuse, BC as the base, and AB as the altitude of the triangle.

Figure 2.

Assessment of optimal medial angulation of the Jamshidi needle. The medial and lateral borders of the pedicle are marked on the operative site using the anteroposterior view of the vertebral body, with measurements taken using a sterile ruler. Assuming an estimated pedicle width of 5 mm, in the right-angled triangle, BC equals 5 mm and AB (the constant) equals 20 mm. Thus, tan θ = BC/AB = 5/20 = 0.25, so θ = tan⁻¹ 0.25. As shown in the logarithmic Clarke’s table below, tan⁻¹ 0.25 corresponds to 14° (circled in green). Using the same method, for pedicle widths of 3 mm, 4 mm, 6 mm, 7 mm, and 8 mm, the corresponding optimal medial angulations of the Jamshidi needle are 8°, 11°, 16°, 18°, and 21°, respectively.

This is a retrospective study conducted in a tertiary care hospital in South Asia. A single fellowship-trained spine surgeon (MHS) has cannulated the pedicles of the thoracic and lumbar vertebral body (D10 to L5) using Jamshidi needle (Globus Medical 685.0225) for various surgical indications including spinal degeneration, trauma and infection. All patients who intend to undergo surgery will be evaluated preoperatively with AP and lateral radiographs. Patients whose radiographs reveal clear; distinct medial and lateral pedicle borders; superior and inferior pedicle boundaries in the preoperative AP and lateral radiographs of the spine at the levels to be instrumented were included in the study during the period from August 2023 to July 2024. Preoperative radiographs showing dysmorphic pedicles, sclerotic pedicles and vertebral bodies showing vertebral rotation more than or equal to grade 2 (Nash Moe grade [16]) were excluded from the study. Patients with age less than 18 years, more than 70 years and patients who were found to be osteoporotic with T score less than -2.5 were excluded from the study. The surgeon cannulated the pedicles under fluoroscopy control based on the degrees of medial angulation obtained using the formula (Table 1, Figure 3).

Table 1.

Estimation of optimal medial angulation of Jamshidi needle for pedicle width measurements using Trigonometric calculation

Figure 3.

Sequence of events in the insertion of a percutaneous pedicle screw using the described method. (A) Marking the medial and lateral borders of the pedicle on the vertebral body and measuring with a sterile ruler. (B) Insertion of the Jamshidi needle with the appropriate medial angulation based on the pedicle width, and with sagittal angulation as determined by the fluoroscopy tilt to achieve the ideal anteroposterior view. (C) Docking the Jamshidi needle at the lateral pedicle border. (D) Tapping the Jamshidi needle to a depth of 20 mm with the calculated medial and sagittal angulation. (E) Advancing the Jamshidi needle across the posterior vertebral cortex in the lateral fluoroscopic view, followed by guide wire insertion. (F) Final placement of pedicle screws.

All the patients who were included in the study underwent percutaneous pedicle screw fixation as per the hypothesis and were subjected to undergo a three-dimensional computerized axial tomography (CAT) scan (Toshiba Aquilion cxl) of the instrumented levels by the 12th postoperative day. The axial cut of the CAT scan is evaluated with the PACS (picture archiving and communication system) system (20/20 Opal rad imaging version 20.15.2). The axial cut is chosen in such a way that the entire profile of the screw is visualized with the medial and lateral pedicle borders (Figure 4) from D10 to L4 segmental levels. At L5 segmental level due to the sagittal tilt of the vertebral body it was difficult to visualize the full profile of the screw. Hence, the appropriate profile of the screw with its medial and lateral pedicle borders was chosen for evaluation. Pedicle screw violation of pedicles is to be graded as per Gertzbin-Robbins scale [17,18] (Table 2). The vertebral body level at which the pedicle screw breached and the degree of breach of the pedicles as per the grading of the Gertzbin-Robbins scale are to be recorded. Accuracy rate [19], significant error in pedicle cannulation (Gertzbin-Robbins scale D and E) and the complications encountered in the postoperative period as assessed by the Modified Clavien-Dindo-Sink classification system [20] are to be documented. Correlation between pedicle width measurement and the medial angulation of the Jamshidi needle used is to be evaluated. The accuracy rate [19] was calculated by using the formula, accuracy rate (%) = number of screws in grade A/number of screws in grade A+ grade B+ grade C +grade D + grade E.

Figure 4.

Computed tomography scan (axial view) showing the entire profile of the inserted screws.

Table 2.

Gertzbin-Robbins scale

Patients were included in the study as per the inclusion and exclusion criteria laid above by the first author (MHS). Pedicle screw violation at each level and the grading as per the Gertzbin-Robbins scale in the obtained CAT scan were evaluated by the second and third authors (SP, MV). The second author is an experienced senior consultant radiologist and the third author is a senior consultant spine surgeon. Being an observational study, we followed the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) checklist in conducting the study. Interrater reliability agreement – kappa coefficient [21] between the 2 observers has to be documented. The study was done with approval from the ethical committee of the institution (No. AOH-C-S-OOI/Ol-24) and was performed by following ethical standards laid down as per declaration of Helsinki 1975 and its amendments. Being retrospective nature, the institutional ethical committee board disregarded the informed consent of the patients.

Data entry was done in MS Excel sheets. All categorical variables were represented as proportions/percentages and continuous variables were represented as mean ± standard deviation. Comparison of categorical variables was done by chi-square test or Fisher exact test. Agreement between 2 observers was assessed by kappa value. Pearson correlation coefficient was used to assess the association between pedicle width measurement and Jamshidi needle medial angulation value. Data validation and analysis was carried out using IBM SPSS Statistics ver. 30.0 (IBM Co., USA). A p-value of less than 0.05 was considered statistically significant.

RESULTS

There were 22 patients included in the study with slight female preponderance (male:female=10:12). The mean age of the patients were 44.5 years. There were 56 vertebral levels (112 pedicles) cannulated in the study with predominant level cannulated being L4. The commonest need for surgery being L4–5 degenerative disc disease followed by traumatic fracture at the L1 level. The commonly done surgery was minimally invasive spine-transforaminal lumbar interbody fusion. Patient demographics have been tabulated in Table 3.

Table 3.

Patient demographics

There was a sum of 15 pedicle breaches as per the grading done by the third author (Figure 5). Eighty percent of the pedicle breaches were of ‘B’ grade and the remaining were of ‘C’ grade. There were no pedicle breaches of scale ‘D’ and ‘E.’ The commonest level of breach was found at L5 level—5 pedicle breaches, of which 3 were seen on the left side and 2 were seen on the right side. The pedicle breaches on the left side pedicle were 2 of ‘C’ grade and 1 of ‘B’ grade. The 2 pedicle breaches seen on the right side were of ‘B’ grade. It was followed by L4 vertebral level—4 pedicle breaches, 3 were found on the left side (C grade, 1; B grade, 2) and 1 on the right side (B grade). The remaining breaches were found at the L2 level (2 breaches) and at L3, L1, D12 levels (1 pedicle breach each). Of the 15 pedicle breaches, 6 were on the lateral side and 9 were on the medial side of the pedicle.

Figure 5.

Gertzbin-Robbins grading of the studied pedicle screw breaches (as assessed by author 3).

The accuracy rate was found to be 86.6%, indicating the pedicle perforation rate (PPR) to be 13.4% with the method. No pedicle breaches were found to be of grades D and E in the study. None of the patients with pedicle breaches developed significant postoperative complications as assessed by the Modified Clavien-Dindo-Sink classification system. Though, there were 3 ‘C’ grade pedicle breaches none of the patients developed significant neurological and vascular complications related to it.

There was concordance between the 2 observers in grading the pedicle breaches in 103 pedicles among the studied 112 pedicle screws (concordance rate 91.9%). The disparity between the 2 observers was less with grade A pedicle breaches (2%) when compared to grade B–E (46.6%) (Table 4). Interobserver agreement between the 2 observers was found to be moderate (kappa coefficient=0.597, p<0.001). (Table 5, Figure 6). On assessing the correlation between the pedicle width measurement and medial angulation of the Jamshidi needle there was a positive correlation between them and it was found to be statistically significant (r: +0.974, p<0.0.001) (Table 6, Figure 7).

Table 4.

The observer’s cross tabulation

Table 5.

Interrater reliability agreement between the 2 observers (112 pedicle screws)

Figure 6.

Gertzbin-Robbins grading by authors 2 and 3.

Table 6.

Correlation between pedicle width measurement (mm) and Jamshidi needle medial angle value in degrees (n=55)

Figure 7.

Relationship between pedicle width measurement and Jamshidi needle medial angulation.

DISCUSSION

The first generation of percutaneous pedicle screw system (PPS) was used by spine surgeons globally, during the year 2001. With further modification in the design and development of extended tabs for the screws, pathfinder for the insertion of rods underneath the muscle in the last 2 decades currently the third generation of PPS—the usage of Jamshidi needle, insertion of threaded k-wire and subsequent insertion of percutaneous pedicles screws with extended tabs is being used by spine surgeon’s worldwide [9]. The ease of technique and the modifications in the instrumentation of PPS have made it to be used in recent times in the upper thoracic spine too, apart from its routine usage in the lower thoracic spine, thoracolumbar spine and lumbar spine [22].

Though the advantages of the percutaneous pedicle screw insertion technique are many the distinct disadvantages claimed with the technique are the increased radiation exposure to the body; eyes and extremities to the surgical team; the possible neurological and vascular complications to the patient with misplaced pedicle screw [23,24]. Mroz et al. [25] in their in vitro-cadaveric study have recorded the radiation exposure to the extremities and eyes as 10.3 mREM and 2.3 mREM respectively per percutaneous pedicle screw placement using fluoroscopy. They further add, one can confidently do at least 4,854 percutaneous pedicle screws annually to exceed the occupation exposure limit for the year.

The possible encountered neurological and vascular complications with a misplaced percutaneous pedicle screw is the main reason behind our study. The PPR was 13.4% with our method. The spine literature quotes PPR in the thoracolumbar and lumbar spine with percutaneous pedicle screw insertion using fluoroscopy to be of range between 0.4% to 23% [26-28]. When compared to the maximal value quoted in the literature the PPR in our study was reduced by 41.8% which is an added advantage if one uses the above-described method in the insertion of percutaneous pedicle screws using fluoroscopy.

Many authors [29,30] have cited the transverse pedicle width measurement based on the CAT scan evaluation to be of range from 5.8±0.8 mm to 13±1.4 mm (D10 to L5 vertebral levels). However, under fluoroscopy the range of transverse pedicle width measurement in our study was found to be between 3- and 7-mm with the minimum value obtained at the D12 vertebral body level and maximum value obtained at the L5 vertebral body level. The reduction in values could be attributed to ‘radiological optical illusion’ [31]—a phenomenon occurring due to the disparity between physical reality and visual perception while using fluoroscopy. Nonetheless, we found a statistically significant strong positive correlation between the pedicle width measurement and the Jamshidi needle medial angulation value in our study (r: +0.974, p<0.001).

Chong et al. [32] postulates a medial breach of the pedicle is likely if the screw has transgressed less than 50% of the vertebral body in the lateral view and the screw tip has crossed the midline of the vertebral body in the AP view. A lateral pedicle breach is likely if the pedicle screw tip is overlapped by the screw head or minimally visualized in the AP view. Of the 15 pedicle breaches identified in our study, 9 were on the medial side and 6 were on the lateral side of the pedicle. Of the 9 medial pedicle breaches, 8 were of ‘B’ grade and one was of ‘C’ grade (11.1%) on the Gertzbin-Robbins scale. Few authors [17,33] have quoted that up to 4 mm (B and C of Gertzbin-Robbins scale) of medial pedicle breach is safer. The recent systematic review [34] (2024) on medial pedicle breaches following pedicle screw insertion portrays the risk of neurological deficit increases by 83% with ‘C’ grade on the Gertzbin-Robbins scale and none with ‘B’ grade medial pedicle breach. Out of the 6 lateral pedicle breaches in our study, 4 were of ‘B’ grade and 2 were of ‘C’ grade (33.3%). Librianto et al. [35] had specified that lateral pedicle breaches up to 4 to 6 mm are without any clinical consequences in the thoracic spine due to the presence of costovertebral joint. In the lumbar spine [36] injury to the psoas muscle and lumbar plexus seems to be uncommon with the lateral pedicle breach except for screw loosening and less improved quality of life/back pain at one-year follow-up. This effect seems to be more added with 2 or more lateral pedicle breached screws. Aoude et al. [37] in a survey among Canadian spine surgeons has emphasized more than 60% of the survey participated surgeons, would reoperate if the pedicle breach is medial or inferior in the postoperative CAT scan with less than or equal to 4 mm and associated with a new onset radicular pain or motor weakness in the lower limb. Lateral pedicle breaches are given much lesser importance by the participating surgeons in the survey when compared to the medial or inferior pedicle breaches both in the thoracic and lumbar spine in his study. We did not encounter any inferior pedicle breaches in our study and there were no serious neurological or vascular complications seen in the postoperative period due to medial or lateral pedicle breaches in our study group.

The disparity between the 2 observers in grading the pedicle breaches as per the Gertzbin-Robbins scale can be related to one being a radiologist and the other being a spine surgeon. However, the high concordance rate between them and the moderate kappa interrater reliability agreement between them delineates the reliability of the pedicle breach grading between the 2 observers.

The least PPR of 13.4%; high concordance rate of 91.9% between the 2 evaluators; statistically significant moderate interrater reliability agreement between the 2 evaluators (kappa coefficient=0.597, p<0.001); no serious neurological or vascular complications in the postoperative period provides the operating surgeon a distinct edge in the insertion of percutaneous pedicle screws from D10 to L5 vertebral body levels following the above method using fluoroscopy.

Twenty-two patients in the study group are relatively small, limits the strength and generalizability of the findings of the study. The study being retrospective in nature and carried out in a single center are some of its limitations. The reliability and validity of the method need to be assessed at multiple spinal centers.

CONCLUSION

The medial angulation of the Jamshidi needle used to insert percutaneous pedicle screws under fluoroscopy can be predicted based on the intraoperative pedicle width measurement in inserting the percutaneous pedicle screws. The medial angulation of the Jamshidi needle increases with the increase in intraoperative pedicle width measurement.

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