Halo vest fixation effectively maintains cervical alignment through intraoperative repositioning in patients with cervical spine instability

Abstract

Introduction

The objective of this study was to examine if halo vest fixation provides sufficient stabilization of cervical spine alignment to endorse its use through intraoperative positional changes in patients with cervical spine instability.

Methods

The subjects of this study were 14 patients with cervical spine instability who were immobilized in halo vests until they underwent subsequent internal fixation surgery. After induction of anesthesia, the patients in halo vests were repositioned from the supine position to the prone position. The halo ring was fixed to the surgical table and the dorsal struts and vest were removed for surgery. Radiographs obtained in the preoperative sitting position and intraoperative prone position were compared for the following measures of cervical alignment: O–C2 angle, C2–C6 angle, pharyngeal inlet angle (PIA), atlantodental interval (ADI), Redlund-Johnell (R–J) value as a measure of O–C2 length, O–C6 length, and O–C2 length/O–C6 length (%).

Results

There were no significant differences in O–C2 angle, C2–C6 angle, PIA, ADI, or O–C2 length/O–C6 length (%). However, the R–J value and O–C6 length were significantly higher in the intraoperative prone position than in the preoperative sitting position. None of the patients presented with any complications, including dysphagia or neurological deterioration.

Conclusions

Our results suggest that when patients are repositioned to the prone position while immobilized in halo vests, the cervical spine is distracted in the cephalocaudal direction across all cervical segments but the cervical alignment is sufficiently maintained. Halo vests are a highly effective external fixation method for patients with cervical spine instability, allowing for a safe repositioning to the prone position for surgery while preserving cervical alignment and preventing neurological deterioration.

Graphical abstract

Highlights

• •Halo vest (HV) is an external fixation device for treating cervical instability.
• •We examined cervical alignment with HV in sitting and prone positions.
• •HV effectively maintains cervical stability, with minimal stretching effects.

1. Introduction

Cervical spine disease, including traumatic cervical spinal cord injury and cervical degenerative myelopathy, can cause neurological disturbance and severe neck pain and can significantly impair the patient's quality of life [1]. Both surgical approaches and conservative treatment with cervical orthoses are important options for restoring the stability of the injured cervical spine [2,3]. The halo vest is a representative external fixation device that is often used in cases of upper cervical spine instability prior to or following surgery or as a definitive treatment [4,5]. The halo vest consists of a ring that is placed around the patient's head and attached to a vest worn over the chest, enabling definitive external stability from the skull to the mid-lower cervical spine. It helps prevent further insult to the cervical cord and allows for improved healing of cervical instability [6,7].

Patients with cervical spinal cord injury can present with progressive cervical kyphosis in the chronic phase after conservative treatment [8], which can lead to persistent neck pain and stiffness due to cervical spine malalignment [9]. Therefore, it is important for these patients to obtain optimal cervical alignment as soon as possible after their injuries. In addition to providing a rigid external fixation force, the halo vest enables the adjustment of cervical spine alignment without the need for general anesthesia or surgical intervention [10]. However, overcorrection of the cervical spine leads to the over-enhancement of cervical lordosis or traction and may cause dysphasia and neurological deterioration [11]. Therefore, it is important to obtain proper cervical alignment while asking the patient not to complain during the fitting of the halo vest.

Intraoperative corrective maneuvers can be performed by manipulating the fixation part of the head connected to the skull clamp (e.g., the Mayfield skull clamp), but its maneuvers are not very reliable, and it is technically difficult to obtain proper cervical alignment. Positional changes during surgery for internal fixation while the patient is wearing a halo vest could be useful for facilitating the correction of cervical deformity and maintaining preoperatively obtained cervical alignment [12]. Theoretically, cervical alignment should be maintained by moving patients from the supine position to the prone position while wearing a halo vest. However, very few studies have reported on whether cervical alignment is precisely maintained after a positional change while the halo vest is worn. In the present study, we evaluated cervical spine alignment in preoperative sitting and intraoperative prone positions using radiographic findings after attaching halo vests to patients with cervical spine instability. The objective of this study was to determine whether the halo vest stabilizes cervical spine alignment and is neurologically safe to use during intraoperative positional changes.

2. Materials and methods

This study sample comprised 14 patients (5 males and 9 females) with upper cervical spine disease who were admitted to the Spinal Injuries Center at Fukuoka Prefecture in Japan and treated with halo vest immobilization and subsequent internal fixation between 2014 and 2022. We retrospectively reviewed the patients’ electronic medical records and extracted radiographic data. Table 1 lists the demographics of the patients. The mean age was 66 ± 5 years (median: 69.5 years; range: 20–90 years). Six patients had atlantoaxial subluxation, three had odontoid fractures, and one patient had subaxial subluxation, atlas dislocation, cervical facet fracture, dropped head syndrome, and Charcot joint. Four patients had rheumatoid arthritis (RA), and seven presented with traumatic injuries as underlying diseases.

Table 1.

Patient demographics in this study.

Case	Age (Year)	Sex	BH (cm)	BW (kg)	BMI (kg/m2)	RA	Trauma	Diagnosis
1	72	F	138.0	35.5	18.6	+	–	Atlantoaxial subluxation
2	20	F	140.5	42.4	21.5	–	–	Atlantoaxial subluxation
3	93	F	141.0	53.0	26.7	–	+	Atlantoaxial subluxation
4	46	M	146.0	29.6	13.9	+	–	Subaxial subluxation
5	54	F	163.1	50.1	18.8	–	+	Odontoid fracture
6	84	F	155.0	70.5	29.3	–	+	Odontoid fracture nonunion
7	67	M	155.0	49.9	20.8	–	–	Charcot joint
8	81	M	163.0	48.6	18.3	–	+	Odontoid fracture
9	80	M	162.0	53.9	20.5	–	+	Cervical facet fracture
10	74	M	168.0	50.6	17.9	–	+	Atlas dislocation
11	67	F	152.0	37.0	16.0	+	–	Atlantoaxial subluxation
12	56	F	152.0	66.9	29.0	–	–	Dropped head syndrome
13	58	F	151.0	44.0	19.3	–	+	Odontoid fracture, Atlantoaxial subluxation
14	76	F	145.5	37.5	17.7	+	–	Atlantoaxial subluxation

BH: body height, BW: body weight, BMI: body mass index, RA: rheumatoid arthritis.

Preoperatively, the patients were placed in a supine position and fitted with a halo vest while they were awake. Subsequently, radiographs were taken in a sitting position to explore cervical alignment (Fig. 1a). External fixation with the halo vest was loosened and tightened as corrective maneuvers when necessary. We confirmed that corrective maneuvers did not cause any symptoms of dysphasia or neurological deterioration in the patients. The pins in the halo vest were tightened two days after the initial fixation and then retightened twice a week until surgery.

Fig. 1.

Preoperative and intraoperative photographs of a patient with halo vest immobilization (a) The patient was placed in a sitting position and fitted with a halo vest before the operation. The halo vest is attached by a halo ring (arrow) on the head and four struts (arrow) connected to the vest on the trunk. (b) General anesthesia was inducted through nasal intubation while the patient was in the supine position wearing a halo vest. The halo ring is connected to a device that secures the skull to the operating table (arrow). (c) The patient underwent a positional change from supine to prone after the induction of general anesthesia. The patient was repositioned to the prone position while being held at the connection between the struts and the halo ring (arrow). (d) The halo vest is connected to both the operating table and the reference for 3D navigation (arrow). Following the connection of the ring portion to the operating table, the dorsal struts and vest were removed.

For surgical preparations, general anesthesia induction was performed by nasal intubation in a supine position in all patients while wearing a halo vest. Intraoperatively, the patients were moved from the supine position to the prone position after anesthesia induction. Subsequently, the dorsal struts and vest were removed after connecting the ring portion of the device to the operating table (Fig. 1b–d). All patients were treated in the prone position during the intraoperative period. Radiographs were taken in prone and sitting positions to confirm cervical alignment, and we compared the cervical alignment in these positions. It was important to determine whether cervical alignment was maintained in the sitting position because this position is more common than the supine position in daily living.

The cervical alignment measurements included the O–C2 angle between the McGregor line and the lower endplate of C2, the C2–C6 angle between the lower endplate of C2 and the lower endplate of C6, the pharyngeal inlet angle (PIA) between the McGregor line and a line drawn tangentially from the center of the anterior arch of the atlas to the ventral cervical spine, and the atlantodental interval (ADI) between the posterior margin of the anterior arch of the atlas and axial odontoid, O–C2 length represented by Redlund-Johnell (R–J) value, O–C6 length between the McGregor line and the center of C6 lower endplate, and O–C2 length/O–C6 length (%) (Fig. 2a and b). The PIA reflects three factors of cervical alignment below the occiput, atlas, and axial vertebrae, and it has been shown to be an indicator of dysphagia in previous studies [13,14]. In addition, for each patient, changes from the preoperative sitting position to the prone position under general anesthesia were measured in the form of ΔO–C2 angle, ΔC2–C6 angle, ΔPIA, ΔADI, and ΔR–J values, ΔO–C6 length, and O–C2 length/O–C6 length (%). Observers reviewed the images and measured the parameters using computer software (Synapse; Fujifilm, Tokyo, Japan).

Fig. 2.

Radiographic measurements for the evaluation of cervical spine alignment (a) The O–C2 angle indicates the angle between the McGregor line and the lower endplate of C2. The C2–C6 angle indicates the angle between the lower endplate of C2 and the lower endplate of C6. The pharyngeal inlet angle (PIA) indicates the angle between the McGregor line and the line drawn tangentially from the center of the anterior arch of the atlas to the ventral cervical spine. (b) The Redlund-Johnell (R–J) value indicates the O–C2 length, and the O–C6 length indicates the distance between the McGregor line and the center of the C6 lower endplate.

3. Statistical analysis

A paired t-test was conducted to determine differences in the O–C2 angle, C2–C6 angle, PIA, ADI, R–J values, O–C6 length, and O–C2 length/O–C6 length (%) between the preoperative sitting position and prone position under general anesthesia. The Wilcoxon rank sum test was used to assess the differences in ΔO–C2 angle, ΔC2-C6 angle, ΔPIA, ΔADI, ΔR–J values, ΔO–C6 length, and O–C2 length/O–C6 length (%) between the RA and non-RA groups, as well as between the trauma and non-trauma groups. For all statistical analyses, the significance level was defined as P < 0.05. The values for all groups are presented as the average ± standard error of the mean (SEM). All statistical analyses were conducted using the JMP software program (version 13; SAS Institute).

4. Results

The comparison of radiographic findings between the preoperative sitting position and the prone position under general anesthesia revealed no significant differences in the O–C2 angle (sitting: 17.64° ± 4.85° vs prone: 16.07° ± 3.84°, P = 0.4949), C2–C6 angle (sitting: −2.08° ± 5.08° vs prone: 0.08° ± 4.54°, P = 0.2116), PIA (sitting: 100.00° ± 4.65° vs prone: 97.00° ± 4.12°, P = 0.1457), ADI (sitting: 4.91 mm ± 1.06 mm vs prone: 4.49 mm ± 0.95 mm, P = 0.2074), or O–C2 length/O–C6 length (%) (sitting: 33.28% ± 1.53% vs prone: 34.17% ± 1.14%, P = 0.1898). However, the R–J value (sitting: 38.10 mm ± 2.42 mm vs prone: 40.46 mm ± 1.93 mm, P = 0.0398) and O–C6 length (sitting: 108.18 mm ± 4.03 mm vs prone: 115.18 mm ± 3.69 mm, P = 0.0045) showed significant differences between the two groups (Fig. 3a–g and Table 2). In terms of changes in these parameters, no consistent trend was observed in ΔO–C2 angle, ΔC2–C6 angle, ΔPIA, ΔADI, or O–C2 length/O–C6 length (%). However, increasing trends were observed for ΔR–J values and ΔO–C6 lengths (Fig. 4a–g). Our results suggest that the prone position, even with halo vest immobilization, induces cervical traction, as evidenced by the greater R–J value and O–C6 length compared to the sitting position.

Fig. 3.

Comparison of radiographic findings between the preoperative sitting position and the prone position under general anesthesia (a–g) the results indicate that there were no significant differences observed in the O–C2 angle (a), C2–C6 angle (b), PIA (c), atlantodental interval (ADI) (d), or O–C2 length/O–C6 length (g) between the two groups. However, significant differences were found in the R–J value (e) and O–C6 length (f) between the two groups.

Table 2.

Comparison of radiographic measurements.

	Sitting position	Prone position	p value
O–C2 Angle (degree)	17.64 ± 4.85	16.07 ± 3.84	0.4949
	(−13 to 52)	(1–43)
C2–C6 Angle (degree)	−2.08 ± 5.08	0.08 ± 4.54	0.2116
	(−44 to 30)	(−40 to 20)
PIA (degree)	100.00 ± 4.65	97.00 ± 4.12	0.1457
	(75–125)	(72–114)
ADI (mm)	4.91 ± 1.06	4.49 ± 0.95	0.2074
	(0.6–10.5)	(0.9–8.9)
Redlund-Johnell value (mm)	38.10 ± 2.42	40.46 ± 1.93	0.0398*
	(20.7–50.3)	(25.2–51.0)
O–C6 Length (mm)	108.18 ± 4.03	115.18 ± 3.69	0.0045*
	(77.5–125.3)	(93.2–130.0)
O–C2 Length/O–C6 Length (%)	33.28 ± 1.53	34.17 ± 1.14	0.1898
	(22.77–41.45)	(24.46–40.02)

PIA: pharyngeal inlet angle, ADI: atlantodental interval.

*p < 0.05.

Variables are given as the mean and standard error of the mean with the range in parenthesis.

Fig. 4.

Comparison of the number of radiographic changes between the preoperative sitting position and the prone position under general anesthesia (a–g) while a consistent trend was not observed in the ΔO–C2 angle (a), ΔC2-C6 angle (b), ΔPIA (c), ΔADI (d), and O–C2 length/O–C6 length (g), increasing trends were noted for ΔR–J value (e) and ΔO–C6 length (f).

The results of the comparison between the RA and non-RA groups revealed no significant differences in ΔO–C2 angle (RA: −2.75° ± 2.78° vs non-RA: −1.10° ± 3.00°, P = 1.0000), ΔC2–C6 angle (RA: +2.25° ± 0.85° vs non-RA: +2.21° ± 2.38°, P = 0.6411), ΔPIA (RA: −0.50° ± 0.96° vs non-RA: −4.11° ± 2.72°, P = 0.8765), ΔADI (RA: −0.70 mm ± 0.45 mm vs non-RA: −0.29 ± 0.39, P = 0.4941), ΔR–J value (RA: +3.03 mm ± 1.67 mm vs non-RA: +2.23 ± 1.75, P = 0.7237), ΔO–C6 length (RA: 6.43 mm ± 3.68 mm vs non-RA: +7.15 mm ± 2.42 mm, P = 0.9323), or ΔO–C2 length/O–C6 length (%) (RA: 104.73% ± 3.88% vs non-RA: 102.91% ± 2.80%, P = 0.9323) (Fig. 5a–g and Table 3). Similarly, there were no significant differences found in the comparison between the trauma and non-trauma groups for ΔO–C2 angle (trauma: +0.29° ± 3.73° vs non-trauma: −3.43° ± 2.57°, P = 0.6544), ΔC2–C6 angle (trauma: +1.57° ± 3.07° vs non-trauma: +2.83° ± 0.70°, P = 1.0000), ΔPIA (trauma: −7.00° ± 3.48° vs non-trauma: +0.43° ± 0.95°, P = 0.2214), ΔADI (trauma: −0.85 mm ± 0.53 mm vs non-trauma: −0.12 mm ± 0.34 mm, P = 0.1658), ΔR–J value (trauma: +2.81 mm ± 2.47 mm vs non-trauma: +2.10 mm ± 1.12 mm, P = 1.0000), ΔO–C6 length (trauma: +8.10 mm ± 3.04 mm vs non-trauma: +5.72 mm ± 2.56 mm, P = 0.6889), or ΔO–C2 length/O–C6 length (%) (trauma: 104.35% ± 3.57% vs non-trauma: 102.68% ± 2.82%, P = 0.6889) (Fig. 6a–g and Table 3). These results suggest that the external fixation force of the halo vest is maintained, even in patients with complications of RA or cervical spine disease with underlying trauma.

Fig. 5.

Comparison of the number of radiographic changes between the rheumatoid arthritis group and the non-rheumatoid arthritis group (a–g) The results indicate that there were no significant differences in the O–C2 angle (a), C2–C6 angle (b), PIA (c), atlantodental interval (ADI) (d), R–J value (e), O–C6 length (f), or O–C2 length/O–C6 length (g) between the two groups.

Table 3.

Comparison of radiographic measurements between the RA and non-RA groups and between the trauma and non-trauma groups.

	RA	Non-RA	p value	Trauma	Non-Trauma	p value
ΔO–C2 Angle (degree)	−2.75 ± 2.78	−1.10 ± 3.00	1.0000	+0.29 ± 3.73	−3.43 ± 2.57	0.6544
	(−11 – +1)	(−14 – +15)		(−14 – +15)	(−14 – +5)
ΔC2-C6 Angle (degree)	+2.25 ± 0.85	+2.11 ± 2.38	0.6411	+1.57 ± 3.07	+2.83 ± 0.70	1.0000
	(+0 – +4)	(−13 – +11)		(−13 – +11)	(+0 – +5)
ΔPIA (degree)	−0.50 ± 0.96	−4.11 ± 2.72	0.8765	−7.00 ± 3.48	+0.43 ± 0.95	0.2214
	(−3 – +1)	(−16 – +5)		(−16 – +4)	(−3 – +5)
ΔADI (mm)	−0.70 ± 0.45	−0.29 ± 0.39	0.4941	−0.85 ± 0.53	−0.12 ± 0.34	0.1658
	(−1.6 to −0.2)	(−2.4 – +0.8)		(−2.4 – +0)	(−1.6 – +0.8)
ΔRedlund-Johnell value (mm)	+3.03 ± 1.67	+2.23 ± 1.75	0.7237	+2.81 ± 2.47	+2.10 ± 1.12	1.0000
	(+0.2 – +7.8)	(−6.4 – +13.5)		(−6.4 – +13.5)	(−1.4 – +7.8)
ΔO–C6 Length (mm)	+6.43 ± 3.68	+7.15 ± 2.42	0.9323	+8.10 ± 3.04	+5.72 ± 2.56	0.6889
	(−0.9 – +15.7)	(−0.4 – +16.5)		(−0.4 – +16.5)	(−0.9 – +15.7)
ΔO–C2 Length/O–C6 Length (%)	104.73 ± 3.88	102.91 ± 2.80	0.9323	104.35 ± 3.57	102.68 ± 2.82	0.6889
	(98.5–114.5)	(95.6–120.2)		(95.6–120.2)	(96.5–114.5)

RA: rheumatoid Arthritis, PIA: pharyngeal inlet angle, ADI: atlantodental interval.

Variables are given as the mean and standard error of the mean with the range in parenthesis.

Fig. 6.

Comparison of the number of radiographic changes between the trauma group and non-trauma group (a–g) The results indicate that there were no significant differences in the O–C2 angle (a), C2–C6 angle (b), PIA (c), atlantodental interval (ADI) (d), R–J value (e), O–C6 length (f), and O–C2 length/O–C6 length (g) between the two groups.

5. Discussion

In this study, we conducted a retrospective review of the radiographic findings of cervical alignment in patients with cervical spine instability who were wearing the halo vest in the preoperative sitting position and intraoperative prone position under general anesthesia. We observed that the R–J value and O–C6 length increased after placement of the patients in the prone position, suggesting stretching of the cervical spine in a craniocaudal direction. However, the O–C2 angle, C2–C6 angle, PIA, ADI, and O–C2 length/O–C6 length (%) showed no significant differences between the sitting and prone positions. Our findings indicate that the external fixation force provided by the halo vest immobilizer was effective in maintaining stability, with minimal stretching effects resulting from the positional change.

The increased trend of traction in the prone position can be attributed to various factors, including muscle relaxation caused by general anesthesia, alternations in the effects of gravity on the cervical spine due to postural changes, and a reduction in head weight in the prone position [15]. Previous biomechanical research using dummy dolls wearing halo vests has demonstrated increased O–C1 and O–C2 angles and extension in the mid-lower cervical spine following placement in the prone position [16]. In our study, no significant change was observed in the O–C2 angle. However, we observed increases in the R–J value and the O–C6 length. It is important to note that the patients in our study had underlying conditions, such as RA, which could affect stability in the upper cervical spine, potentially accounting for the differences in our results from those of past research [5]. Considering the inclusion of anesthesia effects and underlying diseases, we believe that our study provides a more representative understanding of clinical practice.

Cervical malalignment after the attachment of the halo vest or cervical fusion surgery may cause dysphasia [17]. Dysphasia can also be caused by neurological disorders, muscular disorders, and structural abnormalities. Because the halo vest can put pressure on the muscles and nerves involved in swallowing, there is a relationship between halo vest immobilization and dysphasia [18]. The halo vest can also cause discomfort and decrease the range of motion in the cervical spine, which can further affect the ability to swallow [19]. However, halo vest immobilization prior to internal fixation could be a useful option to safely correct cervical deformity. Moreover, if surgical treatment is applied after halo vest immobilization, the duration of wearing the vest can be reduced. A decrease of more than 10° in the O–C2 angle [20], an increase of more than 5° in the C2–C7 angle [21], and a decrease of less than 90° in the PIA [22] are associated with the occurrence of dysphagia. The O–C2 angle, C2–C7 angle, and PIA in all patients in this study did not indicate the aforementioned risks, and none of the patients presented difficulty swallowing during treatment. The use of the halo vest preoperatively and intraoperatively could reduce the incidence of iatrogenic complications, such as dysphasia, by preventing substantial changes in cervical alignment prior to and following surgical treatment.

Both the R–J value and O–C6 length tended to increase after placement in the prone position, but there were no significant changes in O–C2 length/O–C6 length (%), suggesting that the cervical spine was not stretched selectively in the upper cervical spine but rather in all cervical segments from occiput to C6. Excessive cervical traction may cause serious neurological insults [23], but none of the patients in this study presented with neurological deterioration after surgery. Surgeons should be cautious to avoid overtraction of the cervical spine, which may increase the risk of neurological complications.

In this study, we observed no significant differences in the C2–C7 length between the RA and non-RA groups or between the trauma and non-trauma groups. The halo vest is generally used to treat upper cervical spine disorders [6]. In this study, 12 patients (85.7%) with underlying RA or traumatic injury insults to the upper cervical spine showed dynamic instability of the upper cervical spine. Only two patients showed dynamic instability of the mid-lower cervical spine due to underlying subaxial subluxation or Down's syndrome, which possibly resulted in smaller dynamic instability of the upper cervical spine. Therefore, changes in cervical alignment in cases with instability of the mid-lower cervical spine should be selectively investigated in future studies. It is important to note that the total number of cases was only 14, and there were variations in underlying cervical diseases, which could be a potential limitation of this study.

Another potential limitation is that we compared radiographic findings in the preoperative sitting position and the intraoperative supine position but did not compare the preoperative sitting position with the preoperative supine position. There are two reasons for this. First, the halo vest is typically used in the sitting or prone position during the recovery period if employed as conservative therapy. Patients are not placed in the prone position while wearing the halo vest as part of conservative therapy. Second, the primary objective of the current study was to confirm the neurological safety and stability of cervical spine alignment during the transition from a sitting position to a prone position during surgery for a patient wearing a halo vest. Comparing preoperative radiographic findings in the sitting and prone positions could offer additional valuable insights, considering the intraoperative effects of muscle relaxants used during general anesthesia.

Recent studies have shown that malalignment of the cervical spine significantly impacts patients' activities of daily living (ADLs) [24,25]. Importantly, the development of decreased cervical lordosis has been associated with exacerbation of the Neck Disability Index (NDI) and Visual Analogue Scale (VAS) for neck pain [26]. However, a previous study of spinal alignment in asymptomatic volunteers has reported that optimal cervical spine alignment varies with age [27]. For example, the normal range of cervical lordosis is 16 ± 16° for women in their 30s and 25 ± 16° for those in their 60s [28]. There are also many variations in the shape of the cervical spine, described as kyphotic, sigmoid, straight, and lordotic [29]. In the results of this study, cervical sagittal alignment did not change significantly between the sitting and prone positions. However, the small number of cases and the variation in age groups made it difficult to accurately assess whether cervical spine alignment was appropriate for the patients included in this study. Additionally, not only malalignment of the cervical spine but also malalignment of global balance, including the thoracic and lumbar spine, is reported to be involved in disc degeneration, neck pain, or back pain [24]. Previous reports have shown a spontaneous increase in compensatory cervical lordosis following an increase in lumbar lordosis and thoracic kyphosis [30,31]. This adjustment helps maintain overall cervical sagittal balance and global spinal balance. Evaluation from the viewpoint of global spinal balance and clinical outcomes in patients undergoing spinal surgery via halo vest fitting was also considered an important issue to be addressed in the future.

Although the use of a halo vest immobilizer to stabilize the cervical spine has significant advantages, it also has some risks. First, surgeons must be aware of the risk of infection at the pin insertion site of the ring portion. Previous studies have shown that pins have perforated the skull, reaching intracranial space, and the fixation torque may need to be adjusted according to the patient's bone fragility [32]. Second, psychological distress following halo vest immobilization may be another issue when the device needs to be worn for long periods. In a previous study, 58% of patients reported discomfort when wearing a halo vest, describing it as intolerable [33]. Despite these disadvantages, we believe that the halo vest is a useful method for maintaining better cervical alignment perioperatively; however, it must be used with caution to avoid complications.

6. Conclusions

Throughout the treatment with halo vest immobilization in the prone position under general anesthesia, the cervical spine exhibited a tendency to stretch in a cephalocaudal direction across all cervical segments. However, complications such as dysphasia and neurological deterioration were not observed. The use of the halo vest effectively maintained cervical alignment, even during the transition from a sitting position to a prone position under general anesthesia. Our findings demonstrate that the halo vest is a valuable method for external cervical fixation.

Ethical statement

This study was approved by the Ethical Review Board of the institution (Approval code: 16-7). We confirm that this research was conducted in accordance with relevant guidelines and regulations, and it adhered to the principles outlined in the Declaration of Helsinki. We obtained all necessary consent from the patients and/or their legal guardians who participated in the study, including consent to participate in the study. Written informed consent for the publication of their clinical details was obtained for the patients. This study includes images of human subjects and informed consent for the release of the images has been obtained from the patients themselves.

Funding information

KAZUYA YOKOTA reports financial support was provided by JSPS KAKENHI Grant Number JP21K16671. KAZUYA YOKOTA reports financial support was provided by Kobayashi Magobe Memorial Medical Foundation. KAZUYA YOKOTA reports financial support was provided by ZENKYOREN (National Mutual Insurance Federation of Agricultural Cooperatives). KAZUYA YOKOTA reports financial support was provided by Ogata Memorial Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability statement

All the data necessary to support the conclusions of the paper are contained within the published article itself, and there is no need for additional data to be deposited in a publicly available repository. Additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

Consent for publication

Written informed consent for publication of their clinical details was obtained for the patients.

CRediT authorship contribution statement

Takafumi Arita: Writing – original draft, Investigation, Data curation. Osamu Kawano: Formal analysis, Data curation. Hiroaki Sakai: Formal analysis, Data curation. Yuichiro Morishita: Formal analysis, Data curation. Muneaki Masuda: Formal analysis, Data curation. Tetsuo Hayashi: Formal analysis, Data curation. Kensuke Kubota: Formal analysis, Data curation. Takeshi Maeda: Resources, Project administration. Yasuharu Nakashima: Resources, Project administration. Kazuya Yokota: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Declaration of competing interest

The authors declare that they have no conflict of interest.

Abbreviations

ADI

atlantodental interval

PIA

pharyngeal inlet angle

RA

rheumatoid arthritis

R–J

Redlund-Johnell