Paravertebral foramen screw fixation for posterior cervical spine surgery: clinical case series

Tomoaki Shimizu Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Masao Koda Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Tetsuya Abe Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Tomoyuki Asada Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Kosuke Sato Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Yosuke Shibao Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Mamoru Kono Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Fumihiko Eto Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Kousei Miura Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Kentaro Mataki Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Hiroshi Noguchi Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Hiroshi Takahashi Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Toru Funayama Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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Masashi Yamazaki Department of Orthopedic Surgery, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan

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OBJECTIVE

The goal of this study was to clarify the clinical utility of paravertebral foramen screws (PVFSs) and to determine intraoperative indicators for appropriate screw placement during posterior cervical fusion surgery to improve its safety.

METHODS

The authors included data from 46 patients (29 men and 17 women, mean age 61.7 years) who underwent posterior cervical spine surgery with 94 PVFSs. Of the 94 PVFSs, 77 were used in C6, 9 in C3, 5 in C4, and 3 in C5. According to the cervical lateral radiographic view, the authors divided the 94 PVFSs into 3 groups as follows: a longer group, in which the tip of PVFS was located anteriorly from the line of the posterior wall of the vertebral body (> +0 mm); an intermediate group, in which the screw tip was located up to 2 mm posteriorly to the posterior wall of the vertebral body (–2 to 0 mm); and a shorter group, in which the screw tip was located more than 2 mm posteriorly (< –2 mm). The accuracy of screw placement was assessed using CT imaging in the axial plane, and the proportion of screws penetrating a vertebral foramen or a transverse foramen was compared between the 3 groups. Screw loosening was defined as a lucent zone around the screw evaluated on cervical radiography at 1 year after surgery. Complications related to PVFS insertion and revision surgery related to PVFS were evaluated.

RESULTS

The authors classified 25 PVFSs into the longer group, 43 into the intermediate group, and 26 into the shorter group. The proportion of screws penetrating a vertebral foramen was largest in the shorter group, and the proportion penetrating a transverse foramen was largest in the longer group. Screw loosening was confirmed for 3 of 94 PVFSs. One PVFS inserted in C6 unilaterally within a long construct from C2 to C7 showed loosening, but it did not cause clinical symptoms. Revision surgery was required for 2 PVFSs inserted in C3 bilaterally as the lower instrumented vertebra in occiput–cervical fusion because they pulled out. There was no neurovascular complication related to PVFS insertion.

CONCLUSIONS

PVFSs are useful for posterior cervical fusion surgery as alternative anchor screws, and the line of the posterior wall of the cervical body on lateral fluoroscopic images is a potential intraoperative reference to indicate an appropriate trajectory for PVFSs.

ABBREVIATIONS

BMD = bone mineral density; CPS = cervical pedicle screw; LMS = lateral mass screw; OPLL = ossification of the posterior longitudinal ligament; PVFS = paravertebral foramen screw; VA = vertebral artery.

OBJECTIVE

The goal of this study was to clarify the clinical utility of paravertebral foramen screws (PVFSs) and to determine intraoperative indicators for appropriate screw placement during posterior cervical fusion surgery to improve its safety.

METHODS

The authors included data from 46 patients (29 men and 17 women, mean age 61.7 years) who underwent posterior cervical spine surgery with 94 PVFSs. Of the 94 PVFSs, 77 were used in C6, 9 in C3, 5 in C4, and 3 in C5. According to the cervical lateral radiographic view, the authors divided the 94 PVFSs into 3 groups as follows: a longer group, in which the tip of PVFS was located anteriorly from the line of the posterior wall of the vertebral body (> +0 mm); an intermediate group, in which the screw tip was located up to 2 mm posteriorly to the posterior wall of the vertebral body (–2 to 0 mm); and a shorter group, in which the screw tip was located more than 2 mm posteriorly (< –2 mm). The accuracy of screw placement was assessed using CT imaging in the axial plane, and the proportion of screws penetrating a vertebral foramen or a transverse foramen was compared between the 3 groups. Screw loosening was defined as a lucent zone around the screw evaluated on cervical radiography at 1 year after surgery. Complications related to PVFS insertion and revision surgery related to PVFS were evaluated.

RESULTS

The authors classified 25 PVFSs into the longer group, 43 into the intermediate group, and 26 into the shorter group. The proportion of screws penetrating a vertebral foramen was largest in the shorter group, and the proportion penetrating a transverse foramen was largest in the longer group. Screw loosening was confirmed for 3 of 94 PVFSs. One PVFS inserted in C6 unilaterally within a long construct from C2 to C7 showed loosening, but it did not cause clinical symptoms. Revision surgery was required for 2 PVFSs inserted in C3 bilaterally as the lower instrumented vertebra in occiput–cervical fusion because they pulled out. There was no neurovascular complication related to PVFS insertion.

CONCLUSIONS

PVFSs are useful for posterior cervical fusion surgery as alternative anchor screws, and the line of the posterior wall of the cervical body on lateral fluoroscopic images is a potential intraoperative reference to indicate an appropriate trajectory for PVFSs.

Cervical pedicle screws (CPSs) and lateral mass screws (LMSs) are mainly used in subaxial posterior cervical fusion surgery. CPSs have been recognized as the strongest instruments in posterior cervical fusion surgery,1 but they must be applied carefully because misplacement of a CPS could potentially result in tragic complications including injury to the vertebral artery (VA) and the spinal cord,2 especially in C3–6, for anatomical reasons. Thus, CPSs are usually used at C2 and C7, and adaptation of CPSs to C3–6 for routine use remains controversial. By contrast, LMSs are considered relatively safe compared with CPSs in terms of their potential to injure the VA and spinal cord. Thus, at C3–6, LMSs are mainly used routinely. However, the pullout force of LMSs is less than one-quarter that for CPSs.3 Yoshihara et al. reported that the rate of screw loosening of an LMS was significantly greater than that of a CPS.4

Aramomi et al. reported paravertebral foramen screws (PVFSs) as an alternative screw trajectory for posterior cervical fusion surgery.5 The entry point of PVFSs was similar to that for LMSs mediolaterally, and to that for CPSs craniocaudally, and the trajectory of a PVFS is similar to that of a short CPS or a pars screw. After their biomechanical study, Maki et al. reported that the pullout force for PVFSs tends to be greater than that for LMSs.6 Furthermore, the risk of VA injury by PVFSs would be lower than that by CPSs because the length of a PVFS is determined by the distance from the surface of the lateral mass to the transverse foramen, so as not to penetrate the foramen. Thus, it could be said that PVFSs are safer than CPSs in terms of their potential to injure the VA, and stronger than LMSs in terms of fixation.

Despite the expectations for PVFSs, reports about their use have been limited to date. Although there are several reports about PVFSs in cadaver- or morphometric-based studies,6–8 there has been no report to our knowledge about the utility of PVFSs in clinical practice. Moreover, indicators that could potentially be evaluated intraoperatively for appropriate screw placement remain to be elucidated. In the present study we sought to clarify the clinical utility of PVFSs and to determine intraoperative indicators for appropriate screw placement during posterior cervical fusion surgery.

Methods

Patient Population

The design of the present study was as a clinical case series. The present series included data from 46 consecutive patients who underwent posterior cervical fusion surgery with PVFSs between January 2016 and February 2020. We included data from 29 men and 17 women with a mean age at the time of surgery of 61.6 years (range 35–89 years). The mean follow-up period was 31.1 months (range 12–56 months). Pathologies requiring surgery were as follows: ossification of the posterior longitudinal ligament (OPLL) in 29 patients, cervical spondylosis in 6, rheumatoid arthritis in 5, cervical spine kyphosis in 4, cervical spinal tumor in 1, and cervical spine injury in 1. The level of spinal fusion was C2–T1 in 19 patients, C2–7 in 15, Oc–T1 in 3, C3–7 in 3, C3–T1 in 3, Oc–C3 in 1, Oc–C4 in 1, and Oc–C5 in 1 (Table 1).

TABLE 1.

Demographic data for all 46 patients in this case series

CharacteristicValue
Total pts46
Mean age in yrs (range)61.6 (35–89)
Sex, M/F29:17
BMI25.3
FU period in mos (range)31.1 (12–56)
Diagnosis
 OPLL29
 Cervical spondylosis6
 RA5
 Cervical spine kyphosis4
 Cervical spinal tumor1
 Cervical spine injury1
Level of fusion
 C2–T119
 C2–715
 Oc–T13
 C3–73
 C3–T13
 Oc–C31
 Oc–C41
 Oc–C51

BMI = body mass index; FU = follow-up; pts = patients; RA = rheumatoid arthritis.

In the present series, 94 PVFSs were used for 46 patients. Of the 94 PVFSs, 77 were used in C6, 9 in C3, 5 in C4, and 3 in C5. The length of 7 PVFSs was 8 mm, in 79 PVFSs it was 10 mm, and in 8 PVFSs it was 12 mm (Table 2). Of 77 PVFSs in C6, 74 were inserted between LMS and CPS and 3 between PVFS and CPS. Of 9 PVFSs in C3, 7 were inserted between CPS and PVFS and 2 in the lower instrumented vertebrae. Of 5 PVFSs in C4, 3 were inserted between PVFS and LMS and 2 between PVFSs. All 3 PVFSs in C5 were between PVFS and LMS.

TABLE 2.

Spinal level of insertion and length of PVFSs used in this case series

Screw LengthSpinal LevelTotal
C3C4C5C6
8 mm20057
10 mm7536479
12 mm00088
Total9537794

Of 94 PVFSs, 91 were applied during surgery according to the preoperative planning and 3 were applied in an improvised manner because of intraoperative lateral mass fractures that occurred when inserting LMSs.

Surgical Technique

The technique to insert a PVFS is shown in Fig. 1. In principle, we set the entry point of the PVFS on the intersection between the lateral notch of the lateral mass and midline of the mediolateral width of the lateral mass in the coronal plane. The length of the PVFS was selected from 8 to 12 mm based on preoperative CT imaging in the axial plane being shorter than the distance from the surface of the lateral mass to the transverse foramen. A drill with a planned screw length stopper was used under lateral fluoroscopic imaging guidance toward the entrance of the pedicle. The drill was directed approximately 20° medially toward the cortical bone around the vertebral foramen. After tapping a hole with the drill, screws were inserted. Screws 4.5 mm in diameter (Synapse; DePuy Synthes) were used in all of the patients in this study (Fig. 2).

FIG. 1.
FIG. 1.

Insertion technique of PVFS. A: Ideal insertion point for PVFS (red dot). It is the intersection between the lateral notch of the lateral mass and midline of the mediolateral width of the lateral mass. B: Preoperative measurements. It is most important to determine the screw length shorter than the shortest distance between the posterior surface of the lateral mass and posterior wall of the transverse foramen (measurement a). Ideal insertion angle of PVFS is inward at approximately 20° (angle b). C: First, a pilot hole is made with an air drill at the abovementioned insertion point. D: The hole is drilled with a stopper set to the planned length. E: After tapping the hole, the screw can be inserted. If the trajectory is correct, screw purchase will be firm. Figure is available in color online only.

FIG. 2.
FIG. 2.

Overview of PVFSs. A: Intraoperative photograph showing the lineup of PVFSs. The PVFSs were inserted to C6 bilaterally (arrowheads). Note the approximation between C6 PVFS and C5 LMS/C7 CPS and their natural lineup, possibly facilitating rod application. It is often difficult to insert a C6 LMS in a natural lineup as shown in this photo. B: A 4.5-mm-diameter screw in lengths from 8 mm to 12 mm (Synapse; DePuy Synthes). C: The ideal trajectory for a PVFS. The tip of the PVFS touches the cortical bone of a vertebral foramen. D: The trajectory of a PVFS on a cervical lateral radiographic view is similar to that of a CPS. The arrows show PVFSs inserted in C6. Figure is available in color online only.

Radiological Assessments

All 46 patients underwent cervical radiography and CT multiplanar reconstruction 1 week after surgery. According to the position of the tip of the PVFS on the cervical lateral radiographic view 1 week after surgery, we divided 94 PVFSs into 3 groups as follows: a longer group, in which the tip of the PVFS was located anteriorly from the line of the posterior wall of the vertebral body (> +0 mm); an intermediate group, in which the screw tip was located up to 2 mm posteriorly to the posterior wall of the vertebral body (–2 to 0 mm); and a shorter group, in which the screw tip did not reach the posterior wall of the vertebral body, which was located more than 2 mm posteriorly (< –2 mm) (Fig. 3).

FIG. 3.
FIG. 3.

Classification based on the position of the tip of the PVFS on cervical lateral radiographic views. A: Longer group: the tip of PVFS was located anteriorly from the line of the posterior wall of the cervical body (> +0 mm). B: Intermediate group: the tip of PVFS was located up to 2 mm posteriorly from the line of the posterior wall of the cervical body (–2 to 0 mm). C: Shorter group: the tip of PVFS was located more than 2 mm posteriorly from the line of the posterior wall of the cervical body (< –2 mm). The arrows show the position of the tip of PVFSs on the cervical lateral radiographic view.

The accuracy of screw placement was assessed using CT imaging in the axial plane 1 week after surgery. An appropriate screw position was defined as when the tip of the screw touched the cortical bone of a vertebral foramen, but did not penetrate it, or when the tip of the screw was located in the lateral mass. An inappropriate screw position was defined as when the tip of the screw penetrated a vertebral or a transverse foramen. Screw loosening was defined as a lucent zone more than 1 mm around the screw on cervical radiography at 1 year after surgery. Complications related to PVFS insertion including neurovascular injury and revision surgery related to PVFS were collected from medical records. All procedures used in this research were approved by the institutional review board of the University of Tsukuba Hospital, and written informed consent was obtained from all patients to participate in this study.

Results

Of the 94 PVFSs, 25 were classified as being in the longer group, 43 were classified as being in the intermediate group, and 26 were classified as being in the shorter group according to cervical lateral radiographic views.

Of the 94 PVFSs, 80 (85.1%) were classified as having an appropriate screw position, and 14 (14.9%) were classified as having an inappropriate screw position. Of 80 screws classified as having an appropriate position, 39 touched the cortical bone of a vertebral foramen, and 41 were located in a lateral mass. Of 14 screws classified as having an inappropriate position, 9 penetrated a vertebral foramen, and 5 penetrated a transverse foramen.

Of the 25 PVFSs in the longer group, 5 (20%) penetrated a transverse foramen, whereas no screw penetrated a vertebral foramen. Of the 43 PVFSs in the intermediate group, 3 (7.0%) penetrated a vertebral foramen, whereas no screw penetrated a transverse foramen. Of the 26 PVFSs in the shorter group, 6 (23.1%) penetrated a vertebral foramen, whereas no screw penetrated a transverse foramen.

The relationship between the location of the tip of the PVFS on cervical lateral radiographic views and penetration of a vertebral or transverse foramen is shown in Fig. 4. The proportion penetrating a vertebral foramen in the shorter group was largest (23.1%) and the penetrating screw length to a vertebral foramen of the intermediate group (n = 3, 1.16 ± 0.76 mm) was shorter than that of the shorter group (n = 6, 2.73 ± 1.86 mm), which indicated that the risk of neurological injury of the intermediate group could be lower than that of the shorter group. In contrast to vertebral foramina, the proportion penetrating the transverse foramina in the longer group was large (20%) and no screw in the intermediate or shorter groups penetrated a transverse foramen.

FIG. 4.
FIG. 4.

Correlation between the location of the tip of PVFS on the cervical lateral radiographic view and penetration of a vertebral or transverse foramen. The arrows show a PVFS penetrating a transverse foramen or vertebral foramen.

Of the 94 PVFSs, screw loosening was confirmed for 3. These 3 PVFSs were all applied according to the preoperative planning, and there was no screw loosening in PVFSs applied in an improvised manner because of intraoperative lateral mass fractures. One PVFS inserted in C6 unilaterally showed loosening, but it did not cause clinical symptoms or implant failure (Fig. 5). By contrast, 2 PVFSs inserted in C3 bilaterally to instrument lower vertebrae in occiput–cervical fusion pulled out in the early postoperative period and revision surgery was required (Fig. 6). However, this was the only case of revision surgery.

FIG. 5.
FIG. 5.

Case illustrating screw loosening. A 71-year-old woman underwent C2–7 posterior decompression and fusion surgery for OPLL. CPSs were used in C2 and C7, LMSs were used in C3–5, and a PVFS was used in C6 on the right side unilaterally. A: Postoperative cervical anteroposterior radiographic image obtained at 1 week after surgery. B: Postoperative cervical lateral radiographic image obtained at 1 week after surgery. C: Postoperative CT scan obtained at 1 week after surgery showing that the C6 PVFS on the right side was inserted in an appropriate position. D: Screw loosening was not confirmed on a postoperative CT scan obtained at 6 months after surgery. E: Screw loosening around the C6 PVFS was confirmed on cervical radiography at 1 year after surgery (arrow). There was no symptom related to this screw loosening.

FIG. 6.
FIG. 6.

Case illustrating implant failure. A 78-year-old woman underwent occiput (Oc)–C3 posterior decompression and fusion surgery for atlantoaxial subluxation as a result of rheumatoid arthritis. A plating system was used in the occiput, pars and laminar screws were used in C2 on each side, and PVFSs were used in C3 bilaterally as anchor screws for lower instrumented vertebrae. A: Postoperative cervical lateral radiographic image obtained at 1 day after surgery. B: Cervical radiography obtained at 1 week after surgery showing that PVFSs on both sides in C3 had pulled out (arrow) and the reduction at the atlantoaxial joint had been lost. C: Revision surgery was performed by removing C3 PVFSs and extending the caudal level of fusion to T1.

There was no neurovascular complication related to PVFS insertion in the present case series.

Discussion

Nagashima et al. reported that buttress screw insertion to C6 might reduce the implant failure when C7 was the lowest instrumented vertebra.9 However, because of the difference of entry points between C6 LMSs and C7 CPSs, applying a rod to their screw heads is often challenging and additional connecting rods are sometimes required. In addition, the extension of the skin incision and removal of the C7 spinous process are sometimes required when LMSs are inserted in C6, because cranial angulation is required with insertion of an LMS. By contrast, the entry point for PVFSs is near the midpoint of C5 LMSs and C7 CPSs; therefore, PVFSs are expected to connect them suitably. In the present study, 77 of 94 PVFSs were used in C6, and most of these (74 of 77) were inserted between C5 LMSs and C7 CPSs. In addition, of 77 PVFSs inserted in C6, just one showed screw loosening and the others did not. Adaptation of PVFSs to C6 is useful in terms of screw connection and mechanical strength in posterior cervical fusion surgery.

By contrast, 2 PVFSs used in lower instrumented vertebrae pulled out in the early postoperative period and revision surgery was required. There may be a considerable risk of failure when we adapt a PVFS to upper or lower instrumented vertebrae because the mechanical strength of a PVFS depends on only the tip of the screw touching the cortex of vertebral foramen. Thus, it would be better to avoid using a PVFS for upper or lower instrumented vertebrae as an anchor screw, and instead use it as an intermediate screw.

CPSs undoubtedly have the greatest biomechanical strength for instrumented posterior cervical fusion surgery. LMSs are inferior to CPSs in terms of the length of screw and rotational resistance,3 as are PVFSs. Although the biomechanical strength of PVFSs has not been directly compared with CPSs to our knowledge, it seems clear that PVFSs are not an alternative to CPSs. However, it remains unclear whether PVFSs could be alternative instruments to LMSs. In morphometric studies of screw length, the lengths of trajectories of PVFSs were 9.19–10.65 mm8 and those of LMSs were 13.51–15.44 mm8,10 in C3–6; the trajectories of LMSs were longer than those of PVFSs. By contrast, the diameter of LMSs is generally restricted up to 4.0 mm because of the risk of intraoperative lateral mass fractures, whereas the diameter of PVFSs is generally set to 4.5 mm. In addition, the bone mineral density (BMD) of the pedicles where the tip of the PVFSs is located is greater than that of the lateral mass and laminae.11 After biomechanical testing, Maki et al. reported that the pullout force for PVFSs tends to be greater than that for LMSs.6 Taking these matters into consideration, PVFSs could be alternative instruments to LMSs in terms of mechanical strength.

In our present series, 3 of the 94 PVFSs were applied intraoperatively as salvage instruments because of intraoperative lateral mass fractures caused by insertion of LMSs. Neither these PVFSs nor primary PVFSs induced screw loosening. Hostin et al. reported that increasing the diameter of LMSs offered no biomechanical advantage and that CPS fixation provided superior biomechanical strength in revision strategies for failed LMS fixation.12 However, conversion to CPS is technically demanding and there is a risk of VA injury. Maki et al. reported that PVFSs as a salvage instrument for LMS placement failure had a stability as strong as that of the primary LMS.6 PVFSs may have sufficient biomechanical strength for a fractured lateral mass because their trajectories differ from those of LMSs and the bone surrounding the pedicle is usually preserved even when the lateral mass fracture occurs. Furthermore, the BMD where the tip of the screw is located is relatively high. Although the number of salvage PVFSs in our series is insufficient for statistical analysis, it is possible that PVFSs are useful in clinical practice as salvage screws, as suggested by their trajectory in a study using cadavers.

Despite the fact that we carefully selected the length of PVFSs based on the preoperative CT imaging in the axial plane so as not to breach the transverse foramen, 5 of the 94 PVFSs (5.3%) used actually penetrated the transverse foramen. Penetration of a transverse foramen is unacceptable because it may result in injury to the VA, which could develop into serious complications, such as cerebellar infarction or brainstem infarction. The proportion of LMSs penetrating the transverse foramen has been reported as 1.9%,13 lower than that of PVFSs in the present study. We consider that PVFSs are inferior to LMSs in terms of safety unless we recognize the appropriate trajectory of the PVFS. Theoretically, a PVFS whose length is shorter than the distance from the surface of the lateral mass to the transverse foramen could not possibly penetrate a transverse foramen. However, this occurs in practice because it is difficult to match with complete accuracy the entry point and trajectory of the PVFS intraoperatively with the ideal trajectory determined by preoperative planning using CT imaging, and to recognize the posterior edge of a transverse foramen on fluoroscopic images intraoperatively. Thus, we need a method to determine the appropriate trajectory of a PVFS intraoperatively.

Kim et al. reported that PVFSs can be safe at C3–6 if they are inserted up to 1–2 mm anteriorly from the line of the posterior wall of the cervical body on lateral fluoroscopic images based on their anatomical measurements.7 Despite this, they also reported that the prevalence of vertebrae in which the posterior edge of a transverse foramen was located dorsally to the line of the posterior wall of the cervical body was highest for C6 (C3, 3.8%; C4, 0.6%; C5, 6.4%; C6, 9.7%). Therefore, attention must be paid to the distance from the line of the posterior wall of the cervical body to the transverse foramen preoperatively, especially at C6, because there is a risk of penetration of a transverse foramen in such cases, even if the tip of the PVFS is located 1–2 mm anteriorly from the line of the posterior wall of the cervical body on lateral fluoroscopic images.

In the present study, 5 of 25 PVFSs penetrated a transverse foramen in the longer group, and this proportion was greater than the 0 of 43 penetrating PVFSs in the intermediate group. By contrast, 6 of 26 screws penetrating a vertebral foramen in the shorter group was greater than the 3 of 43 screws penetrating a vertebral foramen in the intermediate group. From these findings, the more anteriorly the tip of the PVFS was located on a lateral fluoroscopic image, the higher the risk of penetrating a transverse foramen, and the more posteriorly the tip of the PVFS was located on a lateral fluoroscopic image, the higher the risk of penetrating a vertebral foramen. Therefore, we consider that the line of the posterior wall of the cervical body on lateral fluoroscopic images could potentially be an indicator for appropriate PVFS trajectory intraoperatively.

There are several limitations to the present study. First, we could not evaluate the entry point of PVFS and the correlation between the entry point and misplacement. Of course, the accuracy of screw placement is stipulated by several factors, such as the entry point, the length of the screw, the surgical technique, and the insertion angle. For example, when the entry point is too medial, the screw could potentially penetrate a vertebral foramen even if the tip of the PVFS is located on the line of the posterior wall of the cervical body on lateral fluoroscopic images. Therefore, the line of the posterior wall of the cervical body is simply an indicator for an appropriate depth for the PVFS that can be evaluated intraoperatively, and does not certify the accuracy of screw placement. Second, the screw loosening was not defined on CT imaging, but on cervical radiographic images, and radiographic imaging may not be sufficient to evaluate screw loosening. Third, we could not determine factors associated with screw loosening such as BMD, the length of the screw, or screw placement, because the incidence of screw loosening was too small. To address these limitations, accumulation of further cases using PVFSs in posterior cervical fusion surgery is warranted.

Despite these limitations, to our knowledge, this is the first study to indicate the utility of PVFSs in posterior cervical fusion surgery as anchor screws in C6 in terms of screw connection and mechanical strength. Although it is true that the proportion of inappropriate screw positions in this initial case series for PVFS was higher than for conventional screw trajectory such as LMS, we could detect that the line of the posterior wall of the cervical body on lateral fluoroscopic images is potentially an intraoperative reference by which to indicate the appropriate trajectory for a PVFS, so as not to penetrate a transverse foramen. Based on this intraoperative reference, we can possibly improve the accuracy of PVFS placement.

Conclusions

PVFSs are useful for posterior cervical fusion surgery as alternative anchor screws, but there was a potential risk associated with the relatively high breach rate in this initial case series. To improve the accuracy of screw placement of PVFS and avoid potential complications, the line of the posterior wall of the cervical body on lateral fluoroscopic images could be used as a potential intraoperative reference to indicate an appropriate trajectory for PVFSs.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Shimizu, Abe. Acquisition of data: Shimizu, Abe, Asada, Sato, Shibao, Kono, Eto, Miura, Mataki, Noguchi. Analysis and interpretation of data: Shimizu, Abe. Drafting the article: Shimizu. Critically revising the article: Koda, Yamazaki. Reviewed submitted version of manuscript: Koda, Abe, Asada, Sato, Shibao, Kono, Eto, Miura, Mataki, Noguchi, Takahashi, Funayama, Yamazaki. Study supervision: Koda, Yamazaki.

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    Kim MK, Cho HJ, Kwak DS. A new anatomical approach of cervical lateral mass for cervical pedicle screw and paravertebral foramen screw insertion. PLoS One. 2019;14(7):e0219119.

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  • 8

    Chen X, Yang Q, Kalisi KUMM, Yuan S, Tian Y, Liu X. Comparison of morphometric measurements of traditional posterior cervical screw and paravertebral foramen screw in Chinese population. Spine (Phila Pa 1976). 2021;46(7):E443E449.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Nagashima K, Koda M, Abe T, Kumagai H, Miura K, Fujii K, et al. Implant failure of pedicle screws in long-segment posterior cervical fusion is likely to occur at C7 and is avoidable by concomitant C6 or T1 buttress pedicle screws. J Clin Neurosci. 2019;63:106109.

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  • 10

    Mohamed E, Ihab Z, Moaz A, Ayman N, Haitham AE. Lateral mass fixation in subaxial cervical spine: anatomic review. Global Spine J. 2012;2(1):3946.

  • 11

    Anderst WJ, Thorhauer ED, Lee JY, Donaldson WF, Kang JD. Cervical spine bone mineral density as a function of vertebral level and anatomic location. Spine J. 2011;11(7):659667.

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    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Hostin RA, Wu C, Perra JH, Polly DW, Akesen B, Wroblewski JM. A biomechanical evaluation of three revision screw strategies for failed lateral mass fixation. Spine (Phila Pa 1976). 2008;33(22):24152421.

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    • Search Google Scholar
    • Export Citation
  • 13

    Coe JD, Vaccaro AR, Dailey AT, Skolasky RL Jr, Sasso RC, Ludwig SC, et al. Lateral mass screw fixation in the cervical spine: a systematic literature review. J Bone Joint Surg Am. 2013;95(23):21362143.

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Illustration from Dibble et al. (pp 498–508). Copyright Neurosurgery, Washington University School of Medicine. Published with permission.

  • FIG. 1.

    Insertion technique of PVFS. A: Ideal insertion point for PVFS (red dot). It is the intersection between the lateral notch of the lateral mass and midline of the mediolateral width of the lateral mass. B: Preoperative measurements. It is most important to determine the screw length shorter than the shortest distance between the posterior surface of the lateral mass and posterior wall of the transverse foramen (measurement a). Ideal insertion angle of PVFS is inward at approximately 20° (angle b). C: First, a pilot hole is made with an air drill at the abovementioned insertion point. D: The hole is drilled with a stopper set to the planned length. E: After tapping the hole, the screw can be inserted. If the trajectory is correct, screw purchase will be firm. Figure is available in color online only.

  • FIG. 2.

    Overview of PVFSs. A: Intraoperative photograph showing the lineup of PVFSs. The PVFSs were inserted to C6 bilaterally (arrowheads). Note the approximation between C6 PVFS and C5 LMS/C7 CPS and their natural lineup, possibly facilitating rod application. It is often difficult to insert a C6 LMS in a natural lineup as shown in this photo. B: A 4.5-mm-diameter screw in lengths from 8 mm to 12 mm (Synapse; DePuy Synthes). C: The ideal trajectory for a PVFS. The tip of the PVFS touches the cortical bone of a vertebral foramen. D: The trajectory of a PVFS on a cervical lateral radiographic view is similar to that of a CPS. The arrows show PVFSs inserted in C6. Figure is available in color online only.

  • FIG. 3.

    Classification based on the position of the tip of the PVFS on cervical lateral radiographic views. A: Longer group: the tip of PVFS was located anteriorly from the line of the posterior wall of the cervical body (> +0 mm). B: Intermediate group: the tip of PVFS was located up to 2 mm posteriorly from the line of the posterior wall of the cervical body (–2 to 0 mm). C: Shorter group: the tip of PVFS was located more than 2 mm posteriorly from the line of the posterior wall of the cervical body (< –2 mm). The arrows show the position of the tip of PVFSs on the cervical lateral radiographic view.

  • FIG. 4.

    Correlation between the location of the tip of PVFS on the cervical lateral radiographic view and penetration of a vertebral or transverse foramen. The arrows show a PVFS penetrating a transverse foramen or vertebral foramen.

  • FIG. 5.

    Case illustrating screw loosening. A 71-year-old woman underwent C2–7 posterior decompression and fusion surgery for OPLL. CPSs were used in C2 and C7, LMSs were used in C3–5, and a PVFS was used in C6 on the right side unilaterally. A: Postoperative cervical anteroposterior radiographic image obtained at 1 week after surgery. B: Postoperative cervical lateral radiographic image obtained at 1 week after surgery. C: Postoperative CT scan obtained at 1 week after surgery showing that the C6 PVFS on the right side was inserted in an appropriate position. D: Screw loosening was not confirmed on a postoperative CT scan obtained at 6 months after surgery. E: Screw loosening around the C6 PVFS was confirmed on cervical radiography at 1 year after surgery (arrow). There was no symptom related to this screw loosening.

  • FIG. 6.

    Case illustrating implant failure. A 78-year-old woman underwent occiput (Oc)–C3 posterior decompression and fusion surgery for atlantoaxial subluxation as a result of rheumatoid arthritis. A plating system was used in the occiput, pars and laminar screws were used in C2 on each side, and PVFSs were used in C3 bilaterally as anchor screws for lower instrumented vertebrae. A: Postoperative cervical lateral radiographic image obtained at 1 day after surgery. B: Cervical radiography obtained at 1 week after surgery showing that PVFSs on both sides in C3 had pulled out (arrow) and the reduction at the atlantoaxial joint had been lost. C: Revision surgery was performed by removing C3 PVFSs and extending the caudal level of fusion to T1.

  • 1

    Abumi K, Itoh H, Taneichi H, Kaneda K. Transpedicular screw fixation for traumatic lesions of the middle and lower cervical spine: description of the techniques and preliminary report. J Spinal Disord. 1994;7(1):1928.

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  • 2

    Wright NM, Lauryssen C. Vertebral artery injury in C1–2 transarticular screw fixation: results of a survey of the AANS/CNS section on disorders of the spine and peripheral nerves. J Neurosurg. 1998;88(4):634640.

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  • 3

    Johnston TL, Karaikovic EE, Lautenschlager EP, Marcu D. Cervical pedicle screws vs. lateral mass screws: uniplanar fatigue analysis and residual pullout strengths. Spine J. 2006;6(6):667672.

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  • 4

    Yoshihara H, Passias PG, Errico TJ. Screw-related complications in the subaxial cervical spine with the use of lateral mass versus cervical pedicle screws: a systematic review. J Neurosurg Spine. 2013;19(5):614623.

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  • 5

    Aramomi M, Ishikawa T, Maki S. Paravertebral foramen screw fixation for posterior cervical spine surgery. Conference abstract. Article in Japanese. J Spine Res. 2014;5:549.

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  • 6

    Maki S, Aramomi M, Matsuura Y, Furuya T, Ota M, Iijima Y, et al. Paravertebral foramen screw fixation for posterior cervical spine fusion: biomechanical study and description of a novel technique. J Neurosurg Spine. 2017;27(4):415420.

    • Crossref
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    • Export Citation
  • 7

    Kim MK, Cho HJ, Kwak DS. A new anatomical approach of cervical lateral mass for cervical pedicle screw and paravertebral foramen screw insertion. PLoS One. 2019;14(7):e0219119.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8

    Chen X, Yang Q, Kalisi KUMM, Yuan S, Tian Y, Liu X. Comparison of morphometric measurements of traditional posterior cervical screw and paravertebral foramen screw in Chinese population. Spine (Phila Pa 1976). 2021;46(7):E443E449.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9

    Nagashima K, Koda M, Abe T, Kumagai H, Miura K, Fujii K, et al. Implant failure of pedicle screws in long-segment posterior cervical fusion is likely to occur at C7 and is avoidable by concomitant C6 or T1 buttress pedicle screws. J Clin Neurosci. 2019;63:106109.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10

    Mohamed E, Ihab Z, Moaz A, Ayman N, Haitham AE. Lateral mass fixation in subaxial cervical spine: anatomic review. Global Spine J. 2012;2(1):3946.

  • 11

    Anderst WJ, Thorhauer ED, Lee JY, Donaldson WF, Kang JD. Cervical spine bone mineral density as a function of vertebral level and anatomic location. Spine J. 2011;11(7):659667.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12

    Hostin RA, Wu C, Perra JH, Polly DW, Akesen B, Wroblewski JM. A biomechanical evaluation of three revision screw strategies for failed lateral mass fixation. Spine (Phila Pa 1976). 2008;33(22):24152421.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13

    Coe JD, Vaccaro AR, Dailey AT, Skolasky RL Jr, Sasso RC, Ludwig SC, et al. Lateral mass screw fixation in the cervical spine: a systematic literature review. J Bone Joint Surg Am. 2013;95(23):21362143.

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

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