|Ahead of print
|Accuracy and safety of free-hand pedicle screw placement in cervical injury patients
Sanjeeb Rijal1, Sarvdeep Singh Dhatt2, Vishal Kumar2, Deepak Neradi2, Mahesh Prakash3
1 Department of Orthopaedics, Chitwan Medical College, Bharatpur, Nepal
2 Department of Orthopaedics, Postgraduate Institute of Medical Education and Research, Chandigarh, India
3 Department of Radio Diagnosis and Imaging, Postgraduate Institute of Medical Education and Research, Chandigarh, India
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|Date of Submission||18-Jul-2020|
|Date of Acceptance||09-Aug-2020|
|Date of Web Publication||14-Sep-2020|
Objectives: The purpose of this study was to describe the free hand method of pedicle screw placement without intraoperative imaging monitors and to evaluate the accuracy of the screw placement in quadriplegics patients.
Methods: A free hand screw was inserted in the eleven cervical injury patients with quadriplegia. We studied the preoperative pedicle dimension in all the patients and assessed the clinical and radiological outcome and accuracy of the screw placement.
Results: A total of 44 screws were inserted in the cervical pedicles of eleven patients. The postoperative images showed that 28 of the 44 screws had perforated the pedicles but none of them had breached the spinal canal. Among them 16 screws were grade 2 and 12 screws were grade 3. All the screws had penetrated the lateral wall. There were no neurovascular complications related to any malpositioned screw and there was no screw loosening or instrumentation failure in the patients.
Conclusion: The free hand screw placement without intraoperative image guidance seems to be safe and effective method of fixation. But this technique requires sound knowledge of the cervical anatomy and experience and is useful in the places where navigation system are not available.
Keywords: Accuracy, cervical, freehand, malposition, pedicle screws
|How to cite this URL:|
Rijal S, Dhatt SS, Kumar V, Neradi D, Prakash M. Accuracy and safety of free-hand pedicle screw placement in cervical injury patients. J Spinal Surg [Epub ahead of print] [cited 2020 Nov 27]. Available from: http://www.jossworld.org/preprintarticle.asp?id=295009
| Introduction|| |
Cervical spine fixation using the cervical pedicle screw was first reported by Abumi et al. and Jeanneret et al. in 1994. They first described the cervical pedicle screw in a cervical instability caused by the cervical trauma. The cervical pedicle screw is thought to be the most stable instrumentation for the reconstructive surgery of the cervical spine. The short-segment surgical treatment by the use of pedicle screw has been used safely and effectively in congenital, traumatic, and degenerative conditions. The pedicle screw system is the preferred method of stabilization of the spine in the presence of deformity. It has the advantage of three column fixation, improved coronal, sagittal, and rotational correction. The goal of fixation devices used in spine are to assist in correcting or preventing additional changes in spinal alignment, to enhance fusion rates, and to allow early mobilization of patient. The screw insertion is a technically demanding procedure as there is marked variation in the cervical pedicle anatomy, small pedicle diameter, and large transverse angles of the pedicle.,, The potential risk of injury to neurovascular structures is of great concern, thus an accurate and safe insertion is of paramount importance.
There are various methods of screw fixation described in the literature, but in this study, we used free-hand cervical pedicle screw fixation using anatomical landmarks. The pedicle wall perforation of the screw ranges from 3.7% to 21% with lateral perforation being common.,, The accuracy of the pedicle screw insertion can be increased by using intraoperative imaging, which is highly recommended, but for the surgeon with no access to navigation system, experience of free-hand technique can be useful. The purpose of the study was to study the accuracy of pedicle screw placement by free-hand technique using the postoperative computed tomography (CT) scan.
| Methods|| |
The present study included 11 patients of cervical injury with quadriplegia. The average age of the patients was 36.7 years in all the patients we studied the pedicle morphology using postoperative CT scan. The mean OPW (outer pedicle width), IPW (inner pedicle width), PTA (pedicle transverse angle), and PH (pedicle height) were calculated in every patient.
The patients were placed on the prone position with Crutchfield tongs attached. All the patients were operated under general anesthesia using fiber-optic intubation. The vertebrae to be exposed were identified and marked preoperatively using imaging. A long-straight posterior midline incision was made between the spinous process and retracting the soft tissue laterally made the necessary exposure. The vertebrae planned to insert screw were identified, and lateral mass was exposed until the lateral margin of the lateral mass.
The entry point in to the pedicle was made just lateral to the center point of the lateral mass and close to the inferior articular process of the superior vertebrae [Figure 1]. This entry point varied at every level. The cortex was penetrated, and the probe was inserted into the pedicle at the transverse angle, which was measured and calculated preoperatively on CT scans, which was almost 35°–45° [Figure 2]. The direction of the probe was guided by hand feeling of the soft area in the spongy bone. When obvious resistance was encountered, some adjustment was made to the direction to locate the spongy area [Figure 3]. The procedure was carefully and slowly performed to avoid injury of the neural and vascular structure. The feel of the surgeon's hand was very much important during the process. The palpation of the pedicle track with a small ball tip probe was performed to identify the floor and wall of the pedicle. After the confirmation of the pedicle integrity, a screw of 3.5 mm and screw length that was approximately preoperatively measured were inserted. Bending the rod created anatomical lordosis and construct was tightened. The decompression of the spinal cord was done in two cases. Postoperatively, X-rays are done [Figure 4].
Postoperative assessment of the screw placement
The accuracy of the placement of the screw into the medial and lateral pedicles wall was evaluated on the CT scan [Figure 5]. An independent radiologist did the position of the cervical pedicle screw. The grading of the screw was done.
|Figure 5: Postoperative computed tomography scan showing the pedicle screws|
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- Grade 1: Screw accurately inserted in the pedicle
- Grade 2: Less than 50% of the screw outside pedicle (screw exposure)
- Grade 3: More than 50% screw outside the pedicle (screw perforation).
| Results|| |
The mean operative time by free-hand pedicle screw placement was 101.36 min. There were a total of 44 pedicle screws inserted in 11 patients. Two levels of screw fixation were done in all patients. Most common fracture dislocation was C5 and C6 dislocation, so majority of the screw were inserted at C4 and C5 vertebrae [Table 1]. Out of the 44 screws inserted 36.36% of the screw were inserted accurately and were classified as Grade 1. The pedicle breach was classified as Grade 2 and Grade 3 and was 63.63% (grade 2%–36.36% and grade 3%–27.27%) [Table 2]. All the screws breached in the lateral direction, and there was no medial breach into the spinal canal in any of the patient [Table 3]. There was no complication directly attributable to pedicle screw insertion such as arterial bleeding from the vertebral artery or injury to the spinal cord as there was no intraoperative bleeding during pedicle screw insertion, and there was no medial breach of the pedicle screw in any of the cases [Table 4].
Our study showed minimum OPW at C4 vertebrae and gradual increasing value and maximum at C7 vertebrae. There was no statistical difference in the OPW dimension comparing left side and right side (P=0.45). IPW had minimum value at C3 vertebrae and maximum at C7 vertebrae with no statistically significant value between right side and left side (P=0.66). The mean value of the pedicle transverse angle also showed highest value at the level of C4 vertebrae and the lowest value at C7. There was no significant difference in the right side and the left side measurement (P =0.95). minimum height atC4 and maximum height at C7. In our study, we found majority of the screw perforated was on the right more than left but the difference is not statistically significant [Table 5].
|Table 5: Pedicle perforation (in our study we found majority of the screw perforated was on the right more than left but this was not statistically significant (P=0.13)|
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All the patients selected were quadriplegics, and there was no neurological improvement in any of the cases. Three patients expired postoperatively after 2 days of surgery probably due to high cord edema. In eight patients follow-up, there was no screw loosening or instrumentation failure. There was no surgical site infection in any of the patients. The patients were mobilized on wheel chair immediately postoperatively, so this improved the nursing care and genera status of the patients.
| Discussion|| |
The cervical pedicle screw system has become popular for treating the unstable cervical spine resulting from trauma, degenerative, inflammatory, and neoplastic condition. Cervical pedicle screw has superior biomechanical stability as the lateral mass or transarticular screw., The pedicle screw allows for shorter instrumentation with improved spinal alignment. However, pedicle screw insertion is technically demanding because of small pedicle diameter and large transverse angle of the cervical pedicle., The potential risk of injury to neurovascular structure such as vertebral artery, spinal cord, or nerve root remains a great concern. The appropriate determination of the entry point for the screw insertion as well proper trajectory angle of the screw on axial plane is important for the screw placement.
There was a similar study of free hand pedicle screw done by Xu et al. who carried out a study in 144 pedicle screws. The postoperative CT images 16 (11.1%) of the screw had penetrated the pedicle wall, which was low as compared to our study, which had perforation of 27.27%. There was no medial breach of the pedicle in both studies. The high pedicle perforation in our study could be due to narrow pedicle dimension in our study compared to the pedicle dimension of their study.
A study conducted Ishikawa et al. reported the prevalence of pedicle perforation was 18.7% in a three-dimension fluoroscopy-based navigation and 27% in conventional free hand group which was comparable to our study of perforation of 27.27%.
The cervical pedicle screw fixation has been considered a serious risk to the surrounding structures. Roy Camille stated that the placement of transpedicular screw into C3–C6 pedicle would increase the risk of injury to the neurovascular structure, spinal cord, or nerve root. However, there was no incidence of vertebral artery perforation and spinal cord injury in our study in our study. This finding was also similar to other study. In our study, where lateral Grade 3 perforation, we did not observe vertebral artery injury. This may be because vertebral artery does not occupy the whole area of foramen transversium which was similar to other study in which the lateral perforation occurred, but there was no incidence of vertebral artery injury.
In our study, we also observed that major perforation (Grade 3) occurred in C5 and C6 vertebrae despite it having larger pedicle dimension compared to C3 and C4 vertebrae, this result is because our majority of the screw were inserted in C5 and C6 level. Hence, we require more pedicle screw being inserted at multiple levels to compare the association of pedicle dimension and the screw perforation.
Abumi et al. have suggested that entry point should be lateral to the centre of the facet and close to the posterior margin of the superior articular surface. The angle of insertion of the screw can vary from 25° to 45° medial to midline in the horizontal plane. In the sagittal plane, the angle of insertion should be parallel to the upper end plate of the vertebral body. In our study, we found the characteristics trend of decreasing of trajectory angle with the maximum angle of 44.58 for C4 and minimum angle 37.83 for C7 vertebrae.
Our study also showed higher rate of perforation compared to other study, this is because pedicle dimension was smaller to other population that was statistically significant. Thus, we should be very careful in during pedicle screw insertion and select a smaller screw diameter to avoid pedicle breach.
There are several techniques of pedicle insertion technique being described. Abumi et al. described a technique in which cortex of insertion point is penetrated using high-speed burr resulting in direct observation of pedicle introits, they reported perforation of 6.7%. Karaikovic et al. described the funnel technique in which the entrance into pedicle and vertebral body was identified by removing the outer cortex. They reported perforation of 16.8%. Several authors have reported that computer-assisted navigation system ,,, to have lower pedicle perforation than the free hand technique.,, Kotani et al. reported that screw placement rate was significantly lower in computer-assisted group (1.2%) then in the free-hand group (6.7%). A computer-assisted surgical navigation system has been reported to improve the accuracy of the screw placement, but these are cumbersome and time-consuming, owing to their high cost, they are not installed in many hospitals.
| Conclusion|| |
The good bony purchase of the pedicle screw comparing to the lateral mass has favored pedicle screw in the fixation of unstable cervical injuries, correction of the cervical kyphosis, severe osteoporosis, and cervical instability attributable to degeneration. The free hand pedicle screw fixation is capable of obtaining clinical efficacy and safety in management of cervical instability, but there are other methods such as intraoperative fluoroscopy and computerized navigation system that has lower perforation rate. The CT navigation system is an innovative landmark in the modern era of spinal surgery, which has improved the accuracy of cervical pedicle screw system, but because of cost application of it in many hospitals is difficult. Thus, the detail knowledge of the cervical pedicle anatomy and the surgeon experience in the free hand screw can be important where there are no facilities of modern navigation system, but this requires further studies and long-term follow-up.
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Conflicts of interest
There are no conflicts of interest.
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Sarvdeep Singh Dhatt,
Department of Orthopaedics, Postgraduate Institute of Medical Education and Research, Chandigarh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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