A new technique for anterior cervical pedicle screw implantation

Abstract

Objective:  To introduce and evaluate a new technique, anterior pedicle screw implantation, for anterior cervical reconstruction.

Methods:  Seven patients (five men and two women) with an average age of 65 years were included in this group. After carefully preparation, anterior pedicle screws were implanted under fluoroscopy in all patients. The position of the anterior pedicle screws was evaluated three days postoperatively by X‐ray and CT imaging. The mean recovery rate as assessed by the Japanese Orthopaedic Association (JOA) score was recorded at final follow‐up.

Results:  A total of fourteen anterior pedicle screws were implanted in our group. The average follow up period was 8 months. The mean JOA score was 12.5 preoperatively and 14.8 postoperatively. The mean improvement in the JOA score was 50.5% at final follow‐up. The average local alignment improved from 4.0 of kyphosis preoperatively to 6.5 of lordosis at final follow‐up. Early bony union was observed in four cases that were followed up for more than 3 months. There were no serious complications. No “pedicle perforation” was observed in any of the fourteen anterior pedicle screws, whereas one screw exposure occurred.

Conclusion:  Anterior cervical pedicle screw implantation is a feasible method for selected cases. It provides another choice for strong anterior cervical reconstruction.

Introduction

Posterior cervical pedicle screws have been demonstrated to be effective for reconstruction of the cervical spine and to provide the greatest stability for an unstable cervical spine ¹ , ² , ³ . To date, most cervical pedicle screws have been implanted posteriorly. Theoretically, it is possible to insert cervical pedicle screws anteriorly; this would have the combined advantages of providing the strongest biomechanical characteristics and using a less invasive approach (anterior only) for patients who need to undergo anterior procedures. For example, in patients who have one‐level three‐column injuries or multilevel anterior compression, the biomechanical stability of the normal anterior cervical vertebral screw and plate system is limited. In addition, according to published reports the failure rate of anterior fixation alone is very high ⁴ , ⁵ . In such cases, supplemental posterior stabilization is often needed. To avoid additional posterior stabilization and the related complications, a stronger anterior fixation technique is needed for patients who are scheduled to undergo anterior reconstructive surgery. From September 2009, we have used a new technique for anterior pedicle screw implantation in selected cases. It was successful and we believed this new technique is feasible and useful in clinical application.

Materials and methods

Patient data

There were seven patients (five men and two women) in this group. The average age was 65 years. Four cases had one‐level three‐column traumatic injuries, two cervical spondylotic myelopathy, and one cervical spondylotic radiculopathy. All patients had associated osteopenia or osteoporosis as confirmed by bone densitometry.

Surgical preparation

The preparation for anterior pedicle screw fixation was the same as for normal cervical surgery. Skull traction was usually performed for reduction of fracture‐dislocations in traumatic cervical injuries. CT images were obtained before surgery to evaluate the feasibility of implantation of anterior cervical pedicle screws. “True cervical pedicle axial and sagittal views” were constructed, and the entry point and trajectory of the anterior cervical pedicle screws accurately marked out on them before surgery.

Surgical technique

After successful general anesthesia, the patient was placed on a surgical bed in a supine position, with the neck extended beyond the edge of the bed to facilitate handling of the fluoroscope. The patient's head was fixed with a special frame and tape, and the shoulder girdles pulled caudally and immobilized by tape (Fig. 1). The surgical level of the cervical spine was positioned as parallel to the floor as possible in order to evaluate the true angle of the screw trajectory during implantation. The “true cervical pedicle axial view”, which shows the approximate circular portion of the pedicle cortex where it attaches to the vertebral body, was clearly identified under fluoroscopy before surgery (Fig. 2). In addition, the “true cervical pedicle sagittal view”, in which the total length of the cervical pedicles and the intervertebral foramens can be clearly seen, was also acquired to evaluate the sites of superior and inferior perforation of the pedicle screw (Fig. 3).

Figure 1.

Position of patient for anterior cervical pedicle implantation.

Figure 2.

True cervical pedicle axial view.

Figure 3.

True cervical pedicle sagittal view.

An anterior surgical approach with a left oblique incision was performed. After corpectomy, decompression and strut grafting or titanic mesh insertion, anterior cervical pedicle screws were implanted with the assistance of the fluoroscopy imaging. Usually, the most important fluoroscope image was the “true cervical pedicle axial view” because the centre of the circular portion of the cortex in the “true cervical pedicle axial view” indicates the pedicle entry point.

An entry hole was created with a straight awl. Subsequently, a 1.5 mm guide wire of cannulate screw was inserted into the pedicle cavity using a drill. The trajectory angle conformed to the C‐arm beam angle of the fluoroscope which clearly depicted the “true cervical pedicle axial view”. Accurate placement of the guide wire was confirmed on the “true cervical pedicle axial and sagittal views” under fluoroscopy (4, 5). The “true cervical pedicle axis view” is normally inclined at 30° to 45° from the sagittal plane in the lower cervical spine (C3–C7). If the guide wire had migrated outside the cervical pedicle, insertion was reattempted to create a correct pathway. Once this had been achieved, tapping was performed and the required length of pedicle screw measured. After contouring an axis plate to a suitable length, the anterior cervical pedicle screws were inserted into the lower cervical spine (Fig. 6). The diameters of the anterior pedicle screws were mainly 3.5 mm, the length ranging from 30 to 34 mm.

Figure 4.

True cervical pedicle view showing the guide wire in the circle.

Figure 5.

True cervical pedicle sagittal view demonstrating the guide wire in the cervical pedicle.

Figure 6.

Implantation of anterior cervical pedicle screw and plate.

Postoperative management and evaluation

The drainage tube was removed 48 hours after operation and the patients permitted to ambulate the next day with a cervical collar. Cervical anteroposterior and lateral views and CT images were taken three days postoperatively to evaluate the accuracy of the anterior pedicle screw implantation. Screw mal‐position was classified as “screw exposure” (non‐critical breach) or “pedicle perforation” (risk of neurovascular injury) ⁶ . The mean improvement in the JOA score was recorded at final follow‐up.

Results

Fourteen anterior pedicle screws were implanted in this group. The mean operative time was 165 min (range, 95–240 min) and average blood loss 150 mL (range, 50–350 mL). All cases were followed up for more than one month, the mean follow‐up period being 8 months (range, 1–15 months). The mean JOA score was 12.5 preoperatively and 14.8 postoperatively. The mean improvement in JOA score was 50.5% at final follow‐up. The average local alignment improved from 4.0 of kyphosis preoperatively to 6.5 of lordosis at final follow‐up. Early bony union was observed in four cases that were followed up for more than 3 months. There were no serious complications. “Pedicle perforation” was not observed in any of the fourteen anterior pedicle screws, however one screw exposure occurred.

Images of a typical case are shown in Fig. 7.

Figure 7.

A 78‐years‐old patient who had a C5/6 fracture‐dislocation. (A) Preoperative X‐ray film (B) CT scan and (C) MRI showing C5/6 fracture‐dislocation. (D–F) Postoperative anteroposterior, lateral and oblique X‐ray films and (H, I) CT scan showing the C5 and C7 anterior cervical pedicle screws are in the correct position and the sagittal alignment has been reconstructed.

Discussion

To date, normal anterior vertebral body screws and limited or semi‐limited plates have been widely used in China. They are effective for most patients who require anterior construction and have normal bone quality. However, there is cause for concern if fixation is required in elderly patients with poor quality bone, or in patients with one‐level three‐column injuries or multilevel anterior compression. The reason for concern is that the biomechanical stability of the normal anterior cervical vertebral screw and plate system in these patients is limited. In addition, the failure rate of anterior fixation alone can be as high as 20%–50% ⁷ . Supplemental posterior stabilization seems to be reasonable in these situations. However, complications such as infection and neurovascular injury are more likely with the addition of posterior construction, and can be fatal in the elderly. To avoid additional posterior stabilization and the related complications in such patients, an anterior pedicle screw technique is necessary and promising.

According to published reports, the pull out strength of anterior pedicle screws is 2.5 times that of vertebral body screws ⁸ . Koller et al. designed a group of prototypes for cervical reconstruction after C5 and C6 corpectomy and compared their biomechanical characteristics ⁹ . They demonstrated that the anterior pedicle screw and plate prototype offered encouraging results comparing to posterior counterparts.

Several techniques for anterior pedicle screw implantation have been reported. Aramomi et al. used an “in‐out‐in” technique for anterior pedicle screw insertion ¹⁰ . After corpectomy, these authors inserted guide wires under oblique fluoroscopy from the inner wall of the excavated vertebral body until they were concealed within the pedicle. After a fibular autograft had been put in place, the graft was penetrated in the reverse direction by the guide wires. Cannulated screws were then inserted into the pedicles through the grafted fibular bone along the guide wires. Yukawa et al. reported a new cervical reconstruction technique for inserting anterior cervical pedicle screw and plate fixation using fluoroscopy‐assisted pedicle axis view imaging ⁶ . These authors used a screw trajectory angle of 45° from the sagittal plane for C3‐C6 and 40° for C7. Koller et al. introduced their technique for anterior cervical pedicle implantation in experiments ⁸ . The crucial points about this technique were achieving certain parameters before implantation and using a “fluoroscopic pedicle axis view” during the procedure. Our technique for anterior cervical pedicle screw insertion uses the cortical circular portion in the “true cervical pedicle axial view” as an important marker of entry point and trajectory, whereas the “true cervical pedicle sagittal view” is used to check the superior and inferior points of perforation of the anterior cervical pedicle screws. Using this new technique, anterior cervical pedicle screws can be implanted precisely and the complications of the implantation decreased significantly. This new technique provides another choice for strong cervical reconstruction. Its indications and contraindications have not yet been established. Although it can be performed with most cervical pedicles, at this stage we believe it should be used reserved for patients with poor bone quality, one‐lever three column injuries, or those who require multilevel anterior compression or anterior revision surgery, especially when they are elderly. Another advantage of this new technique is that segmental anterior pedicle screw insertion can be performed at each level, even via grafted bone in patients who have undergone reconstruction after long segmental corpectomy ¹⁰ .

Although this new technique has been demonstrated to be a feasible method for selected cases, it should be considered an adjunct procedure rather than a replacement for the usual techniques for routine cervical spine surgery. Although our results were satisfactory and no complications occurred in our group, it included only seven patients and fourteen anterior pedicle screws. Moreover, only four cases were followed up for more than three months. Another very important aspect we must point out is that this new technique demands a high level of surgical skill and has relatively higher risks. It demands that the surgeon has a clear understanding of cervical anatomy, as well as experience with posterior pedicle screw and special imaging techniques. In addition, a suitable plate should be designed and used in clinical practice. In depth study is necessary to improve the accuracy of screw placement.

Disclosure

The authors declare that they have no competing interests.