Clinical and Radiographic Outcomes of Modified Posterior Atlantoaxial Temporary Fixation with Preservation of Semispinalis Cervicis: A Comparative Study

Abstract

Study Design:

Retrospective study.

Objective:

Current studies suggested that the posterior cervical deep muscles should be preserved during the atlantoaxial posterior approach. This study aimed to modify the conventional temporary posterior fixation by preserving the semispinalis cervicis and to evaluate the radiographic and clinical outcomes compared with the conventional technique.

Methods:

Applied anatomical and imaging study were assessed prior to the clinical studies. Thirty patients with odontoid fracture were enrolled. 12 patients underwent modified operation with preservation of semispinalis cervicis (Group P-SSC), and 18 patients underwent conventional approach with detachment of the semispinalis cervicis (Group D-SSC) as controls. Clinical and radiological assessments were evaluated postoperatively, including activities of daily living (ADL), axial symptom scoring system (Ass), cervical range of motion (ROM), and the average atrophy rate of muscles.

Results:

All patients experienced fracture healed within 10 months after temporary fixation. At early follow-up, ADL accompanying extension and flexion were significantly different between the two groups. The Ass scores in the Group P-SSC were constantly higher than that in Group D-SSC. Flexion-Extension ROM in Group P-SSC was significantly larger than that of Group D-SSC. The average atrophy rate at the C3 and C5 level in Group P-SSC was 7.62±3.38% and 7.55±3.89%, repectivcly, while 15.67±5.97% and 8.56±4.76% in Group D-SSC, respectively. Significant differences in the atrophy rate were found between groups at C3 level.

Conclusions:

Compared with the conventional technique, the modified surgical technique with preservation of semispinalis cervicis was effective in improving axial symptoms, decreasing the atrophy rate of muscles, and increasing the cervical ROM.

Keywords

semispinalis cervicis odontoid fracture temporary fixation atlantoaxial cross-sectional areas

Introduction

Anderson-D’Alonzo type Ⅱ and Ⅲ odontoid fractures are the most common odontoid fractures, and there is a lack of consensus on how to treat them.^1-3 Anterior screw fixation is regarded as the treatment of choice for fractures with intact transverse ligament because this approach can preserve the motion of the atlantoaxial joint. Although posterior screw-rod fixation possesses a unique three-dimensional fixation, posterior C1-C2 fusion has to be conducted in cases with contraindications to anterior fixation, sacrificing atlantoaxial joint motion and posterior cervical muscles. Since Harms and Melcher have introduced a posterior temporary-fixation technique, it has been progressively employed to treat odontoid fractures with intact transverse ligament.⁴ This non-fusion technique has also shown the ability to retain the motion of the atlantoaxial joint and has achieved satisfactory clinical outcomes.⁵ However, in order to completely expose the C2 lamina and pedicle during C2 screws fixation, it is generally necessary to detach the deep extensor muscles attached to the C2 spinous process that have a principal role in stabilizing and mobilizing the neck with five bilateral muscular attachments.

Over recent years, axial symptoms have received a lot of attention as postoperative complications which adversely affect patients’ quality of life after posterior cervical fixation.⁶ Although the causes of axial symptoms remain uncertain, many studies have shown that when C-2 and C-7 spinous processes are preserved, the frequency of persistent postoperative axial neck pain is reduced.^6-9 The semispinalis cervicis (SSC) is attached to the spinous process of the C2–C5 vertebra and distally to the transverse process of the T1–T6 vertebra, acting as the primary power source for cervical spine extension.¹⁰ Surgeons often ignores the function of the SSC. Accordingly, for complete preservation of the function of SSC after the operation, we modified the conventional temporary posterior fixation by preserving the SSC inserted into the C2 process. To evaluate the role of SSC in the atlantoaxial posterior approach, this study compared the preservation of the SSC during temporary posterior fixation with conventional fixation process of muscle detached from the C2 spinous.

Methods

Applied Anatomy and Imaging Study

To safely perform this modified surgery, the approach was assessed by applied anatomy prior to clinical studies. Anatomical observations were performed in 6 fresh cadavers (3 females and 3 males) aged between 55 to 75 years at the time of death, with no evidence of spinal pathology. The cadaveric dissections were performed with the cadavers in the prone position. The skin and the nuchal fascia were opened. The lateral edge of the trapezius muscle was seen and retracted medially. The fibers of the splenius capitis muscle run cranial and lateral below the nuchal fascia. This muscle was split, and down below we found the fibers of the semispinalis capitis muscle. To observe the axial lamina, this muscle was also detached and retracted. The obliquus capitis inferior muscle was found running across the surgical field. The obliquus capitis inferior muscle and semispinalis cervicis muscle could be mobilized and retracted without damaging the attachments to the C2 spinous process. The entry points for the C1 lateral mass screws and C2 pedicle screws were identified (Figure 1).

Figure 1.

Anatomical observation in cadavers: (A). Cadaveric dissections (B). Anatomic locations of C2 in the cadaver. SSCa: semispinalis capitis; Trap: trapezius; OCi: Obliques capitis inferior; RCpm: Rectus capitis posticus major. The black circle indicates the insertion points for the C2 screw; the black star indicates the C2 spinous process.

To ensure that the operation was performed according to preoperative plans, the cervical posterior muscles were assessed using Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) images. The main planned parameters of screws insertion points, direction of screws trajectories, and intermuscular space were studied on preoperative cross-sectional images (C1-C2 level) of patients (Figure 2).

Figure 2.

The cross-sectional images on C2 level. Picture (A) shows the MRI image; Picture (B) shows the CT image. SSCe: semispinalis cervicis; M: multifidus; SSCa: semispinalis capitis; SpCa: splenius capitis; Trap: trapezius; LgCa: longissimus capitis; LgCe: longissimus cervicis; The black circle indicates the insertion points for C2 screw; the arrows indicate the screw trajectory for C2 screw.

Patient Population

From June 2015 to January 2017, we conducted the conventional fixation with detachment of the SSC (Group D-SSC), and from February 2017 to December 2018, we conducted the temporary posterior fixation by modified fixation with preserving the SSC (Group P-SSC). Therefore, 35 consecutive patients diagnosed with odontoid fractures who met the inclusion criteria were divided into two groups. All procedures were performed by the same surgical team, with the same operator and assistant. The study has been approved by the Ethical Committee of our hospital. Every patient gave informed consent.

The inclusion criteria were: (1) Grauer typeⅡA fractures with fragmentation but displacement less than 1 mm, which could not be reduced by external fixation; (2) Grauer type ⅡB fractures with displaced transverse fractures that could not be fixed by the anterior approach; (3) Grauer typeⅡC fractures that manifested with anterior inferior to posterior superior or comminuted fractures; (4) Patients with Grauer type Ⅲ fractures could not tolerate long-term external fixation; (5) Postoperative follow-up was at least 2 years. The exclusion criteria were: (1) Aged 65 or older or with severe osteoporosis or tumor; (2) Poor physical status, unable to tolerate the second surgery; (3) Grauer type Ⅰ and Ⅲ fractures that was expected to have predictabley good results with external immobilization; (4) Odontoid fractures with atlantoaxial instability or disruption of the transverse atlantal ligament, or atlantoaxial subluxation with atlantodens interval more than 3 mm, for whom posterior C1-C2 fusion has to be conducted. (5) History of anterior or posterior cervical fusion surgery.

Operative Technique

All patients underwent nasotracheal or fiberoptic endotracheal intubation. After induction of general anesthesia, the patients were placed in prone position with a Mayfield head clamp with a slight degree of cervical hyperextension. A gauze roll was placed in the mouth to permit an unobstructed anteroposterior view of the odontoid process.

The surgical procedure for Group P-SSC included the SSC insertion that was completely preserved in C2. After a midline incision, the nuchal fascia and trapezius muscle were dissected. Off the midline, splenius capitis and semispinalis capitis were dissected to expose the deep cervical muscles. The C2 lamina and pedicle were exposed by blunt dissection through the intermuscular plane between the SSC muscle and the obliquus capitis inferior muscle without damaging the attachments to the C2 spinous process. Then, the suboccipital muscles and obliquus capitis inferior muscles were detached and the entry points for the C1 lateral mass screw were identified (Figure 3). The insertion points for the C1 and C2 screws were located at the position described by Harms and Melcher.⁴ The surgical procedure in Group D-SSC included the conventional temporary fixation technique previously described, in which the SSC was detached from the C2 spinous process.⁵

Figure 3.

Picture A and B shows the operative field in Group D-SSC and Group P-SSC respectively. (A) The conventional surgery detaching SSC attaching to the C2 spinous process; (B) The modified surgery preserving SSC.

The postoperative collar period was 6-8 weeks. Cervical CT scan and image reconstruction were performed at 3-6 months postoperatively or later to evaluate fracture healing which was defined as evident bridging bone across the odontoid fracture site. Once fracture healing was observed, the removal of instrumentation was performed as described in previous studies.⁴ The routine of the second surgery was to reuse the previous incision and remove the hardware via a posterior approach. The SSC and its attachment were carefully retained in Group P-SSC.

Radiological and Clinical Assessment

Plain radiographs were taken before surgery, and at 3, 6, and 12 months after the first surgery and after instrumentation removal. Clinical and radiological assessments after the first surgery and removal of instrumentation were listed below.

Measurements of flexion to extension ROM (F-E ROM) and rotation ROM (R-ROM)

The postoperative O–C7 angles on cervical flexion and extension position were measured using the McGregor line and the posterior tangents of the C7 vertebral body on lateral cervical extension and flexion radiographs, respectively. Then the F-E ROM was calculated as the difference between the two angles (Figure 4). The postoperative R- ROM of the patients were photographed in the cranial view using a digital camera ,with spectacles as the measurement lines (Figure 4).¹¹

Figure 4.

Measurements of rotation ROM (A & B) and O–C7 angle at F-E ROM (C & D). (A&B) The lines for measurements were obtained using the glasses and the pattern of clothes. The total of the left and right rotation angles was calculated as rotation ROM (α + β). (C&D) The lines for measurements were obtained using McGregor line and posterior tangents of the C7 vertebral body on lateral extension or flexion radiographs. The F-E ROM was calculated as (β - α ).

Measurements of Cross-Sectional Areas (CSA) of the Cervical Posterior Muscles

The cervical spine was examined by CT before surgery and 3 months postoperatively. The CSA at the C3-4 and C5-6 levels was measured for evaluation. The preoperative and postoperative CSA of the posterior cervical muscles, including the trapezius, splenius capitis, semispinalis capitis, SSC, and multifidus muscles were measured on axial CT scanning with soft-tissue window at C5, while SSC and multifidus muscles were measured at C3 level (Figure 5). The rate of muscle atrophy was calculated at each level using the following formula^7,12: Atrophy rate (%) = (1 - postoperative area/preoperative area) * 100%. The measurement was performed using ImageJ imaging software (version 1.43, National Institutes of Health, Bethesda, Maryland).

Figure 5.

Outline of the cervical extensor muscles. (A) Posterior extensor muscles visualized on axial CT images at the C5–C6 level. a multifidus, b semispinalis cervicis, c semispinalis capitis, d splenius capitis. (B) Outline of the semispinalis cervicis and multifidus at the C3-C4 level.

All measurements were performed independently by two researchers who were blinded to the operative method. Analysis performed using the average values of the two observations at each level.

Evaluation of ADL

The frequencies of postoperative limitations of activities of daily living (ADL) associated with each of the following neck movements were investigated: (1) ADL (E): extension, (2) ADL (F): flexion, and (3) ADL (R): rotation. The severity of the limitations of each ADL was assessed by a questionnaire using the method described in previous studies¹¹ (Tables 1 and 2). The postoperative limitations of ADL were compared between the two groups.

Table 1.

Activities of Daily Living Index for Neck Mobility in Daily Living.

Movement	ADL
Extension	Gargling
Flexion	Watching one’s step when climbing down the stairs or tie one’s shoes
Rotation	Looking right and left when driving car or crossing the street

Abbreviations: ADL, activities of daily living.

Table 2.

The Severity of the Limitation of ADL.

Grade	Severity
1	Easy (no limitation)
2	Mild difficulty (mild limitation)
3	Difficult (limitation)
4	Impossible (severe limitation)

Abbreviations: ADL, activities of daily living.

Evaluation of axial symptoms

Axial symptoms were evaluated using the Axial Symptom Scoring System (Ass) reported in previous studies.¹³ In this scoring system, there were four parameters (including posterior neck pain, posterior neck stiffness, shoulder pain, and shoulder stiffness), and each parameter was classified into four grades (none: 3, occasional mild: 2, continuous mild or occasionally severe: 1, continuously severe: 0). The total of the axial symptom system score was calculated as the sum score of each parameter.

Statistical Analysis

The SPSS statistical software (Version 25; IBM Corp., NY, USA) was used to complete the statistical analyses. Continuous variables were presented as mean with standard deviation, and categorical variables as total number and percentage. Continuous variables were compared using Student's t-tests including patients’ age, healing time, CSA, ROM, and atrophy rate. ADL scores and Ass scores were compared using Spearman’s rank correlation test, and Mann-Whitney U tests. Comparisons of categorical variables were performed with the Chi-square test or Fisher test, including gender, fracture classification. A P < .05 was considered statistically significant.

Results

In total, from June 2015 to December 2018, 35 consecutive patients diagnosed as Anderson-D’ Alonzo type ⅡB and ⅡC, and type Ⅲ odontoid fractures received modified fixation with SSC preservation and conventional fixation with SSC detachment. Five patients were excluded because of the unwillingness to re-operation to remove the instrumentation or incomplete radiographic or clinical data. Thirty patients with odontoid fracture were enrolled in this study. The general information of the patients was listed in Table 3. Twelve patients received P-SSC (Figure 6), and 18 patients received D-SSC served as controls. There were no significant differences between the general data. No infections, cerebrospinal fluid leakage, neurological injuries, vascular injuries, or any other serious complications were identified during or after operations. All patients experienced fracture healing within 10 months after temporary fixation.

Table 3.

Patients’ General Information.

Variable	Group P-SSC (n = 12)	Group D-SSC (n = 18)	P-value
Age (year)^a	44.3 ± 9.9	47.3 ± 12.0	.472
Sex (number)^b
Male	8	13	1.000
Female	4	5	1.000
Cause of fracture^b
Fall from a considerable height	4	6	1.000
Motor vehicle accident	8	12	1.000
Fracture classification^c
TypeⅡ B	3	7	.750
TypeⅡ C	8	9
Type Ⅲ	1	2
Time for fracture healing (months)^a	6.1 ± 2.0	6.2 ± 1.7	.840
Time to removal (months)^a	11.3 ± 2.5	12.6 ± 3.3	.288
Average follow-up time (months)^a	27.0 ± 4.6	28.4 ± 5.1	.436

Data expressed as mean standard deviation unless otherwise indicated.

^at test.

^bChi-square test.

^cFisher test.

Figure 6.

A type II C odontoid fracture managed with temporary posterior fixation (A) Preoperative CT scan; (B) postoperative sagittal view of CT scan; (C) axial view of CT at the C1 level; (D) axial view of CT at the C2 level; (E) preserved SSC attached to the C2 spinous process; (F) postoperative CT scan and reconstruction; (G) postoperative Magnetic Resonance Imaging; (H) postoperative coronal view of CT showing the intact signal of SSC.

Limitations of Activities of Daily Living

The frequency and severity of limitations of ADL in both groups at each point through the follow-up were shown in Table 4 and Figure 7. The higher the ADL score, the more limited the activities of daily living. The ADL(R)-time curve showed a downward trend. The mean ADL(R) in the Group P-SSC and D-SSC gradually decreased from 3.8 to 2.7 postoperatively. No significant difference was observed in this parameter between the two groups (P > .05; Figure 7A), but the values of Group P-SSC were always lower than that of Group D-SSC. The mean ADL(E) in Group P-SSC was significantly lower than that in Group D-SSC at the 6-, 12-month follow-up after the first surgery, and 3-month follow-up after the second operation (Mann-Whitney U test, Z = 3.049, 2.795, and 2.792, respectively; P = .010, .017, and .015, respectively), but there was no significantly difference in the ADL(E) between the two groups at 6 months and last follow-up (P > .05; Figure 7B). The mean ADL(F) in the Group P-SSC was significantly lower than that in Group D-SSC at 12-month follow-up after the first surgery and 3-month follow-up after the second operation (Mann-Whitney U test, Z = 2.387 and 2.952, respectively; P = .043 and .039, respectively), and the difference gradually narrowed over time (Figure 7C).

Table 4.

Postoperative ADL, Axial Symptom Score, and ROM in Two Groups.

Parameter	6-month follow-up after the first surgery			Before the remove of instrumentation			3-month follow-up after the second surgery			6-month follow-up after the second surgery			Final follow-up
Group	P-SSC	D-SSC	p	P-SSC	D-SSC	p	P-SSC	D-SSC	p	P-SSC	D-SSC	p	P-SSC	D-SSC	p
ADL(R)	3.8 ± 0.5	3.8 ± 0.4	.917	3.3 ± 0.7	3.4 ± 0.5	.917	3.2 ± 0.4	3.6 ± 0.5	.079	2.8 ± 0.5	2.9 ± 0.2	.391	2.7 ± 0.5	2.7 ± 0.5	.819
ADL(E)	2.7 ± 0.5	3.3 ± 0.5	.010*	2.4 ± 0.5	3.0 ± 0.5	.017*	2.6 ± 0.5	3.2 ± 0.5	.015*	2.3 ± 0.6	2.5 ± 0.5	.346	2.0 ± 0.6	2.3 ± 0.5	.215
ADL(F)	2.8 ± 0.5	3.1 ± 0.3	.134	2.4 ± 0.5	2.9 ± 0.5	.043*	2.6 ± 0.5	3.0 ± 0.2	.039*	2.0 ± 0.6	2.4 ± 0.5	.095	1.9 ± 0.5	2.1 ± 0.6	.465
Ass	7.7 ± 0.5	7.1 ± 0.7	.035*	8.3 ± 0.7	7.5 ± 0.9	.019*	7.4 ± 0.7	6.8 ± 0.7	.048*	9.9 ± 0.9	8.8 ± 0.9	.006*	10.2 ± 0.7	9.3 ± 0.9	.015*
R- ROM	35.6 ± 1.1	34.2 ± 2.2	.067	39.2 ± 1.9	38.6 ± 2.3	.458	41.9 ± 3.7	40.3 ± 2.8	.194	47.3 ± 2.1	45.2 ± 3.5	.073	48.4 ± 3.6	46.9 ± 3.2	.226
F-E ROM	44.9 ± 2.9	41.0 ± 3.0	.002*	50.7 ± 3.2	47.9 ± 3.6	.037*	50.1 ± 3.0	46.7 ± 4.2	.015*	54.8 ± 2.7	51.2 ± 3.0	.002*	57.1 ± 3.2	52.9 ± 3.7	.003*

Notes: The Between-group comparisons of ADL and Ass were tested by the Mann-Whitney U test.

R- ROM and F-E ROM were compared using independent samples t-tests.

The symbol * indicates a significant difference between groups.

Abbreviations: ADL, activities of daily living; R, rotation; E, extension; F, flexion; Ass, Axial Symptom Score; ROM, range of motion; F-E ROM, range of motion from flexion to extension.

Figure 7.

Changes in the ADL, Axial symptom score, and ROM evaluated postoperatively. (A∼C) The changes of limitations of activities of daily living (ADL) accompanying extension, flexion, and rotation movements; (D) The changes of axial symptom scoring system; (E,F) The changes of the flexion to extension ROM (F-E ROM) and rotation ROM; The bars indicate standard deviations, *P < .05 significant differences between two groups by the independent samples t-test or Mann-Whitney U tests; 6/12m, 6/12 months after the first operation; 3/6/12m^′, 3/6/12 months after the second operation.

Axial Symptom Scores

Axial symptom scores in Group P-SSC and Group D-SSC were listed in Table 4. The Ass scores in the Group P-SSC were constantly higher than that of Group D-SSC. The incidence and severity of axial symptoms were constantly lower in the Group P-SSC and significantly differed between the two groups in each postoperative follow-up (Mann-Whitney U test, Z = −2.315, −2.463, −2.123, −2.839, and −2.553, respectively; P = .035, .019, .048, .006, and .015, respectively; Figure 7D).

Cervical Range of Motion

The Rotation ROM and F-E ROM exhibited a trend of gradual increase, and the clinical assessment outcomes were listed in Table 4. The mean rotation ROM of C1-C2 in Group P-SSC increased gradually from 35.6°±1.1° to 48.4°±3.6°. As for Group D-SSC, the mean ROM increased gradually from 34.2°±2.2° to 46.9°±3.2°. The mean value of Group P-SSC was higher than that of Group D-SSC but there was no statistical difference between the two groups at each follow-up (P > .05; Figure 7E). During each follow-up, the F-E ROM in Group P-SSC was 44.9°±2.9°, 50.7°±3.2°, 50.1°±3.0°, 54.8°±2.7°, and 57.1°±3.2° respectively, which was significantly higher than that of Group D-SSC (41.0°±3.0°, 47.9°±3.6°, 46.7°±4.2°, 51.2°±3.0°, and 52.9°±3.7°). Significant differences remained until the end of the 12-month follow‐up (t-tests, F = .422, .064, 2.007, .240, and .122, respectively; P = .002, .037, .015, .002, and .003, respectively; Figure 7F).

Cross-Sectional Areas

A CT scan of the cervical spine was taken before surgery and 3 months after the first surgery. The average preoperative of CSA at the level C3 was 4.59±.82 cm² in Group P-SSC, and 4.46±.56 cm² in Group D-SSC. The average preoperative CSA at the level C5 was 20.70±2.27 cm² in Group P-SSC, and 19.89±2.67 cm² in Group D-SSC. No significant difference was observed preoperatively between the two groups. The average 3-month postoperative CSA at level C3 was 4.25±.83 in Group P-SSC and 3.75±.47 in Group D-SSC. CSA at level C5 was 19.17±2.50 cm² in Group P-SSC and 18.11±1.98 cm² in Group D-SSC. According to the atrophy rate formula mentioned before, the average atrophy rate at the level C3 was 7.62±3.38% in Group P-SSC, and 15.67±5.97% in Group D-SSC. There was a significant difference between the two groups in the atrophy rate at the level C3 (t-tests, F = 2.682, P < .01). The average atrophy rate at the level C5 was 7.55±3.89% in Group P-SSC, and 8.56±4.76% in Group D-SSC, no significant difference was observed between the two groups in terms of atrophy rate. (P > .05; Table 5)

Table 5.

Atrophy Rate of Cervical Posterior Muscles between P-SSC and D-SSC.

Parameter	C3-level			C5-level
	Group P	Group D	P-value	Group P	Group D	P-value
Pre-operation CSA (cm²)	4.59 ± .82	4.46 ± .56	.611	20.70 ± 2.27	19.89 ± 2.67	.396
Final follow-up CSA (cm²)	4.25 ± .83	3.75 ± .47	.045	19.17 ± 2.50	18.11 ± 1.98	.205
Atrophy rate (%)	7.62 ± 3.38	15.67 ± 5.97	<.01	7.55 ± 3.89	8.56 ± 4.76	.547

Abbreviations: CSA, Cross-Sectional Areas.

Discussion

Based on fracture line obliquity, displacement, and comminution to guide treatment options, Grauer et al have classified Anderson-D’Alonzo type II of odontoid fractures into three subtypes.¹⁴ The type IIC fracture, which has an oblique fracture line from posterosuperior to anteroinferior that parallels screw trajectory, is a contraindication to anterior screw fixation since interfragmentary compression cannot be achieved using the odontoid screw.¹⁵ Recently, temporary posterior fixation has been reported as a new cervical posterior surgery for treatment of Anderson-D’Alonzo type II odontoid fractures, which does not include the fusion of the atlantoaxial joint thus preserving the cervical movement. By comparing clinical outcomes and the range of motion (ROM) in rotation of these two non-fusion techniques, Guo et al have reported that temporary posterior fixation could spare the motion of the C1-C2 complex and achieve similar clinical outcomes to anterior screw fixation in the treatment of Anderson-D’Alonzo type II odontoid fracture.^15,16

Unlike the posterior atlantoaxial fixation and fusion surgery, it is unnecessary to place autologous iliac crest graft between the posterior C1/2 articulation after grinding the cortical bone in temporary posterior fixation, thus avoiding the detachment of the deep extensor musculature.¹⁰

The SSC, which are mostly inserted into the C2 spinous process, act as the primary dynamic stabilizers and as extensors of the cervical spine. According to existing research, the SSC and multifidus muscle pair show significant relative activation during head extension. They also have an essential postural role, which is likely to be affected by atrophy and loss of strength during exposure to microgravity or long-term bed rest.¹⁷ Current research suggests that the posterior cervical deep muscles should be preserved without detachment from the C2 spinous process during the atlantoaxial posterior approach.^8,18,19 Therefore, it is crucial to preserve SSC, especially in upper cervical spine surgery. Kazunari and colleagues have reported that the posterior cervical approach preserving the SSC insertion into C2 could reduce the postoperative axial symptoms compared to the conventional approach, which implies reattaching the muscle to the C2 spinous process.²⁰ Besides, some authors have verified that the preservation of neck extensor could benefit patients by restoring the lordotic angle of the cervical spine and reducing pain in patients with loss of cervical lordosis.^20-22

In the current study, we evaluated and compared outcomes of ADL, ROM, axial symptoms, and CSA of cervical muscles of two non-fusion techniques in the treatment of fresh Anderson-D’Alonzo type II odontoid fractures. To our knowledge, there is no previous detailed clinical study on the effect of preserving the SSC inserted in the C2 spinous process in the atlantoaxial posterior approach. Clinical data demonstrated that the frequency of limitations of ADL accompanying extension or rotation in the Group P-SSC was lower than Group D-SSC. Moreover, objective data showed that the postoperative ranges of motion from flexion to extension (F-E ROM) in the Group P-SSC were significantly larger than those in the Group D-SSC. As the SSC inserted into the C2 spinous process acts as an essential extensor of the cervical spine, preserving the SSC in surgeries might allow a larger angle at extension and a reduction of limitations of ADL accompanying extension during follow-up.^17,21 Nevertheless, Yukawa et al have compared a laminoplasty that preserved the SSC with skip laminectomy, observing no significant differences in the extension ROM.²³ In our study, we found that the atlantoaxial posterior approach with preservation of the SSC inserted into C2 did not influence the postoperative neck rotation ROM and limitations of ADL accompanying rotation.

As reported, the CSA of the posterior cervical muscles has a strong relationship with the movement strength during flexion and rotation.^7,22 Decrease in the CSA of posterior extensor muscles was significantly associated with the development of shoulder stiffness, which has been related to dysfunctions or spasms in the posterior extensor muscles of the cervical spine.²⁴ Takeuchi et al have evaluated the CSA of the posterior cervical muscles prospectively after laminoplasty by preserving or reattaching the SSC inserted into C2. They reported that only the preservation of the SSC inserted into C2 could maintain the whole cervical posterior muscular volume.⁷ Some studies have also reported that posterior surgeries may lead to atrophy and cause damage to these muscles, leading to instability or malalignment of the cervical spine.^24,25 In our study, the average atrophy rate in the group preserving the SSC was significantly lower in the atrophy rate at the level C3. The difference was not significant at level C5, this might be due to the limited motion of the upper cervical fixation and increased compensatory activity of the lower cervical muscles, which in turn lead to the less obvious atrophy at lower levels.

In order to minimize muscle substance destruction and to maximally preserve both the mobility and stability of the cervical spine, various modified minimally invasive atlantoaxial fixation such as intramuscular and intermuscular exposure techniques have been used for preserving the posterior elements.^19,26 They all achieved satisfactory clinical outcomes, verifying the importance of the deep extensor muscles of the neck. However, due to increased surgery risks and a steeper learning curve, this approach should only be taken by surgeons with rich experience.

Even though the C1–C2 temporary fixation with preservation of SSC technique leads to good outcomes, it cannot be used as the treatment of choice for all types of odontoid fracture. This technique has been indicated in Grauer type II fractures with good reduction. For irreducible fractures and elderly patients with severe osteoporosis, posterior C1–C2 fixation and fusion are more suitable approaches. The posterior approach is also not considered for fractures with Anderson-D’Alonzo type Ⅰand III fractures which have predictably good results by the external immobilization.

There are some limitations to our study. The sample size is relatively small. Further studies with larger sample size should be conducted to verify the current result. Moreover, we did not evaluate the role of function exercise, rehabilitation, and the individual variation between two groups, which may lead to variability in the results of this study.

Conclusions

Compared with the conventional technique, this modified surgical technique with preservation of semispinalis cervicis was effective in improving the axial symptoms, decreasing the atrophy rate of posterior cervical muscles, and increasing the cervical ROM accompanying neck extension and flexion.

Footnotes

Authors’ contributions

JL, EZJ; study design, analyses, and interpretation of data, draft of manuscript with tables and figures. JL, SL, EZJ, GHX; substantial contributions to conception and critical revision for important intellectual content. ZCS, GHX; substantial contributions to study design and data acquisition, JL, SL; data acquisition. All authors read and approved the final manuscript.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

This work was funded by the clinical management optimization project of Shanghai Shenkang Hospital Development Center (SHDC22020211).

Abbreviations

SSC: semispinalis cervicis; P-SSC: preserving SSC; D-SSC: detaching the SSC; ROM: range of motion; CT: Computed tomography; ADL: activities of daily living; Ass: axial symptom scoring system.

Ethics approval and consent to participate

The study was approved by the ethical committee of Changzheng Hospital. All the patients gave written consent for research applications of their clinical data. The patient data were anonymized in this study.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding authors upon reasonable request.

ORCID iD

Guohua Xu

References

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