Abstract
Background
The impact of cervical sagittal parameters on patient-reported outcomes (PRO) after posterior cervical fusion (PCF) remains inconclusive. We sought to evaluate whether normative sagittal cervical alignment was independently associated with improved PRO.
Methods
Retrospective review of consecutive patients who underwent PCF for degenerative conditions from January 2016 to December 2020 at a single institution with multiple surgeons. Cervical sagittal vertical axis (cSVA), McGregor’s slope (McGS), and T1 slope minus C2-7 lordosis (T1S-CL) were measured using standing neutral lateral radiographs at preoperative and 1 year postoperatively. Normative parameters were defined as cSVA ≤4 cm, −5° ≤ McGS ≤ 15°, and T1S-CL < 20°. The primary outcome was the minimum clinically important difference (MCID) among validated PRO (12-item Short Form Mental and Physical Component Summaries, Neck Disability Index, neck and arm numeric rating scale, and modified Japanese Orthopaedic Association scale) collected prospectively preoperatively, 6 months, and 1 year postoperatively. Univariate analysis was used to compare demographics, operative characteristics, and proportions achieving MCID between parameter groups. Multiple logistic regression models were used to adjust for confounders. Radiographic parameters were included as the predictor. P < 0.05 was considered significant.
Results
One hundred and four patients (54 men and 50 women with a mean age of 61.8 ± 10.6 years), were included. Operative levels ranged from C2 to T3, with 4 to 8 operative levels. Normative cSVA patients were younger (59.4 vs 67.5 years, P < 0.001) and had more prior anterior surgery (63% vs 38.7%, P = 0.019). All PRO showed significant improvement at 1-year follow-up, with proportions achieving MCID ranging from 51.9% (visual analog scale neck) to 31.7% (modified Japanese Orthopaedic Association). There was no significant PRO difference between normative and non-normative groups. Change of McGS, cSVA, or T1S-CL from non-normative to normative parameter was not independently associated with increased odds of achieving MCID for PRO.
Conclusion
In this retrospective cohort study of patients undergoing multi-level PCF, achievement of MCID in PRO was comparable between patients with normative and non-normative postoperative cervical sagittal alignment.
Clinical Relevance
Normative cervical cSVA, McGS, or T1S-CL following PCF surgery is not independently associated with improvement in PRO.
Level of Evidence
3.
Keywords: posterior cervical fusion, cervical sagittal parameters, cervical alignment, spine osteoarthritis, patient-reported outcomes
Introduction
The role of optimal cervical sagittal alignment in patient satisfaction following posterior cervical fusion (PCF) remains imprecise, with mixed results found in previous studies.1,2 The importance of sagittal cervical balance in relation to multilevel cervical fusion has been shown, as increased cervical sagittal malalignment is generally correlated with poor patient-reported outcomes (PRO).2 Hyun et al demonstrated that T1 slope minus cervical lordosis (T1S-CL) mismatch after PCF can cause severe cervical misalignment, leading to greater postsurgical patient-reported disability.3 It is well established that increased sagittal imbalance in the thoracolumbar region is associated with greater disability and poorer health status.4 However, investigation remains incomplete concerning the degree to which cervical sagittal malalignment affects PRO and, if postoperative sagittal cervical measurement goals are met after surgery, how well they correlate to decreased pain and functional disability per PRO.1,5,6
The primary objective of this study was to determine if there was a meaningful relationship between normative sagittal alignment of the cervical spine and PRO following multilevel PCF. The secondary objective was to determine which radiographically measured cervical sagittal parameters, if any, have the most significant impact on PRO.
Methods
This study was written following the Strengthening of the Reporting of Observational Studies in Epidemiology (STROBE) guidelines.7
This study was approved by the hospital’s institutional review board (approval no. 1583435-1). A retrospective review of prospectively collected data was conducted. Inclusion criteria consisted of consecutive adult patients who underwent PCF for cervical degenerative indications, including cervical myelopathy, cervical radiculopathy, pseudoarthrosis, and adjacent segment degeneration from prior surgery. Surgeries were performed at a single institution from January 2016 to December 2020. Patients older than 18 years were included. Exclusion criteria consisted of (1) fewer than 4 instrumented segments; (2) instrumentation not including the cervicothoracic junction (C7–T1); (3) prior long-segment thoracic instrumentation (greater than 7 segments). All patients underwent posterior cervical fixation with cervical lateral mass screw, thoracic pedicle screw, C2 pedicle screw if C2 included, and rod instrumentation. The procedures were performed either by 1 orthopedic spine surgeon or 1 of 5 neurosurgeons at our institution. Patients were in a standard prone position with slight neck flexion with either a Mayfield head holder (Integra LifeSciences, Plainsboro, NJ, USA) or Sugita head holder (Mizuho, Union City, CA, USA). Laminectomy and/or foraminotomy were performed at the surgeon’s discretion based upon clinical and radiographic diagnosis and preoperative symptomatology. No facetectomies or osteotomies were performed in the included patients. Prior to rod insertion, each surgeon readjusts the head holder, with an assistant’s help, to slightly posteriorly translate and extend the head to induce cervical lordosis and a neutral line of sight.
Standing radiographs of the cervical spine in a neutral position were obtained preoperatively and at 12 months postoperatively. C2 to C7 plumbline (cervical sagittal vertical axis [cSVA]), McGregor’s slope (McGS), and T1S-CL were measured using validated imaging software (Surgimap, Nemaris, New York City, NY, USA) at each time point.8–11 The cSVA normative value was defined as less than 4 cm of positive sagittal balance; the McGS normative range was defined as −5° to 15°; and T1S-CL was defined as less than 20° (Figure 1). Measurements were made by fourth- and fifth-year neurosurgical residents and a fourth-year medical student.
Figure 1.
Sample patient from this cohort with prior anterior instrumentation. Sagittal parameters using validated imaging software (Surgimap, Nemaris, New York City, NY, USA) are shown. cSVA, cervical sagittal vertical axis; McGS, McGregor’s slope.
PROs were collected by telephone or in person in a standardized fashion at baseline, 6 months, and 1 year postoperatively. The 12-item Short Form Mental and Physical Component Summaries (SF-12 MCS and PCS) general health questionnaires were used.12 Neck Disability Index (NDI) and neck and arm visual analog scale (VAS) were used to assess disability and pain.13,14 Myelopathy severity was analyzed using the modified Japanese Orthopaedic Association (mJOA) scale.15 PROs were collected prospectively using the BACS (Stryker, Kalamazoo, MI, USA) data collection system.
Patient and operative characteristics were examined using independent-samples t tests for continuous variables and χ 2 tests for nominal variables. Demographics and operative characteristics were compared across normative and non-normative groups for cSVA, McGS, and T1S-CL. Changes in PROs from baseline to 1 year follow-up were analyzed using paired-samples t tests. Patient achievement of minimum clinically important difference (MCID) was assessed using independent-samples proportion tests. MCID thresholds were defined as ≥2 for VAS, ≥7.5 for NDI, ≥3.3 for SF-12 PCS, ≥3.8 for SF-12 MCS, and ≥2 for mJOA.15–17 MCID PRO achievement was compared between normative and non-normative groups for cSVA, McGS, and T1S-CL using independent-samples proportions tests. Cervical sagittal parameters, when changing from non-normative to normative, were assessed for MCID achievement for each PRO using binary logistic regression with preoperative baseline PRO, age, and smoking status as covariates.
Results were considered statistically significant at P < 0.05. Bonferroni correction was used for the multivariable regression analysis, and significance was set at P < 0.013. All analyses were performed using SPSS version 31.0.0.0 (117, IBM Corp, Armonk, NY, USA).
Results
A total of 237 patients were identified who initially met the inclusion criteria. Patients whose pre- and postoperative cervical parameters could not be accurately measured due to inability to visualize T1 on radiograph or missing imaging, and those without PRO data at all 3 time points (preoperatively, 6 months, or 1 year), were removed, as shown in the Strengthening of the Reporting of Observational Studies in Epidemiology diagram (Figure 2). Thus, 104 patients (54 men and 50 women with a mean age of 61.8 ± 10.6 years) were included.
Figure 2.
Strengthening of the Reporting of Observational Studies in Epidemiology diagram. PRO, patient-reported outcome; XR = x-ray imaging.
The average number of levels fused was 5.1. The highest cervical level included was C2, and the lowest thoracic level was T3. The total number of included levels per construct ranged from 4 to 8 (median 5). The most common fusion levels were C3 to T1 (66 patients). A total of 55.8% of patients had a prior single- or multilevel anterior cervical fusion surgery, and 52.9% of patients had preoperative cervical myelopathy. Only 1 patient, who underwent surgery during the study period, required revision surgery (T1 screw malposition causing radiculopathy) at the time of variable extraction in May 2023. A complete summary of baseline and perioperative characteristics of patients included in this study is detailed in Table 1.
Table 1.
Patient and operative characteristics.
| Characteristic | N = 104 |
| Age, y | 61.8 ± 10.6 |
| Sex | |
| Men | 54 (51.9) |
| Women | 50 (48.1) |
| BMI | 28.9 ± 5.9 |
| Osteoporosis | 2 (1.9) |
| Current smoker | 19 (18.3) |
| Diabetes mellitus | 27 (26.0) |
| Length of stay, d | 3.1 ± 1.5 |
| Prior anterior instrumentation | 58 (55.8) |
| Preoperative CDDD | 26 (25.0) |
| Preoperative stenosis | 69 (66.3) |
| Preoperative myelopathy | 55 (52.9) |
| Revision surgery within study period | 1 (1) |
| No. of operative levels | |
| 4 | 17 (16.3) |
| 5 | 67 (64.4) |
| 6 | 14 (13.5) |
| 7 | 4 (3.8) |
| 8 | 2 (1.9) |
Abbreviations: BM, body mass index; CDDD, cervical degenerative disc disease.
Note: Quantitative variables are represented as mean ± SD; categorical variables are represented as n (%).
Baseline (preoperative), 6 months, and 1 year postoperative PRO were available for all patients. Univariate analysis comparing pre- and postoperative PRO demonstrated a significant overall improvement at 1 year, compared with baseline, with proportions achieving MCID ranging from 51.9% (VAS neck) to 31.7% (mJOA; Table 2).
Table 2.
Changes in PRO and MCID at 1 y, univariate analysis (N = 104).
| Outcome Measure | Preoperative | Postoperative | Δ | 95% CI | P | MCID |
| NDI | 41.3 ± 21.4 | 31.1 ± 22.9 | 10.2 | 4.7–15.7 | <0.001 | 35 (33.7) |
| VAS neck | 6.8 ± 3.1 | 4.3 ± 3.6 | 2.5 | 1.6–3.4 | <0.001 | 54 (51.9) |
| VAS arm | 5.2 ± 3.9 | 2.9 ± 3.5 | 2.3 | 1.3–3.2 | <0.001 | 38 (36.5) |
| mJOA | 12.9 ± 2.8 | 13.5 ± 2.4 | −0.62 | −1.3 to −0.1 | 0.045 | 33 (31.7) |
| SF-12 MCS | 45.6 ± 10.8 | 48.6 ± 11.9 | −3.2 | −5.6 to −0.7 | 0.006 | 38 (36.5) |
| SF-12 PCS | 30.5 ± 8.5 | 34.2 ± 10.8 | −3.7 | −5.6 to −1.9 | <0.001 | 40 (38.8) |
Abbreviations: MCID, minimal clinically important difference; MCS, Mental Component Summary; mJOA, modified Japanese Orthopaedic Association Score; NDI, Neck Disability Index; PCS, Physical Component Summary; PRO, patient-reported outcome; SF-12, 12-item Short-Form; VAS, visual analog scale.
Note: Quantitative variables are represented as mean ± SD; categorical variables are represented as n (%); P < 0.05 was considered statistically significant.
One-year postoperative cervical sagittal parameters were dichotomized into normative and non-normative categories. There was a higher proportion of patients with prior anterior instrumentation in the normative cSVA group (63.0% vs 38.7%, P = 0.019). Patients within the normative cSVA range were also found to be significantly younger compared to non-normative cSVA patients (59.4 vs 67.5 years, P < 0.001, Table 3). There was a higher proportion of male sex in the normative McGS (57.3% vs 20%, P = 0.007, Table 3). There were no significant differences identified in baseline patient characteristics with respect to normative vs non-normative T1S-CL (Table 3). Differences in the number of patients achieving MCID at any postoperative time point (either 6 months or 1 year) were compared. No statistical difference in any MCID for PRO, comparing normative vs non-normative sagittal parameters, was identified (Table 4). Subgroup analysis of patients without prior anterior instrumentation also yielded no statistical difference in any MCID for PRO.
Table 3.
Patient and operative characteristics by 1 y cervical parameters, univariate analysis (N = 104).
| Characteristic | Normative | Non-normative | P |
| cSVA ≤4 cm ( n = 73) | cSVA > 4 cm ( n = 31) | ||
| Age, y | 59.4 ± 10.8 | 67.5 ± 8.4 | <0.001 |
| Male sex | 37 (50.7) | 17 (54.8) | 0.432 |
| Current smoker | 16 (21.9) | 3 (9.7) | 0.112 |
| Diabetes mellitus | 16 (21.9) | 11 (35.5) | 0.116 |
| Prior anterior instrumentation | 46 (63.0) | 12 (38.7) | 0.019 |
| Preoperative CDDD | 16 (21.9) | 10 (32.3) | 0.192 |
| Preoperative myelopathy | 35 (47.9) | 20 (64.5) | 0.091 |
| Length of stay, d | 3.0 ± 1.6 | 3.2 ± 1.0 | 0.271 |
| 4 levels | 13 (17.8) | 4 (12.9) | 0.827 |
| 5 levels | 47 (64.4) | 20 (64.5) | |
| 6 levels | 10 (13.7) | 4 (12.9) | |
| −5° ≤ McGS ≤ 15° (n = 89) | 5° > McGS > 15° (n = 15) | ||
| Age, y | 61.7 ± 8.4 | 61.8 ± 11.1 | 0.357 |
| Male sex | 51 (57.3) | 3 (20.0) | 0.007 |
| Current smoker | 16 (18) | 3 (20.0) | 0.546 |
| Diabetes mellitus | 23 (25.8) | 4 (26.7) | 0.585 |
| Prior anterior instrumentation | 48 (53.9) | 10 (66.7) | 0.264 |
| Preoperative CDDD | 22 (24.7) | 4 (26.7) | 0.548 |
| Preoperative myelopathy | 48 (53.9) | 7 (46.7) | 0.403 |
| Length of stay, d | 3.1±1.5 | 3.3 ± 1.3 | 0.281 |
| 4 levels | 12 (13.5) | 5 (33.3) | |
| 5 levels | 60 (67.4) | 7 (46.7) | 0.238 |
| 6 levels | 11 (12.4) | 3 (20.0) | |
| T1S-CL < 20° (n = 36) | T1S-CL > 20° (n = 68) | ||
| Age, y | 59.6 ± 11.3 | 63.0 ± 10.4 | 0.065 |
| Male sex | 20 (55.6) | 34 (50.0) | 0.370 |
| Current smoker | 5 (13.9) | 14 (20.6) | 0.288 |
| Diabetes mellitus | 8 (27.9) | 19 (22.2) | 0.349 |
| Prior anterior instrumentation | 22 (61.1) | 36 (52.9) | 0.278 |
| Preoperative CDDD | 9 (25.0) | 17 (25.0) | 0.598 |
| Preoperative myelopathy | 21 (58.3) | 34 (50.0) | 0.274 |
| Length of stay, d | 2.8 ± 1.3 | 3.3 ± 1.5 | 0.061 |
| 4 levels | 7 (19.4) | 10 (14.7) | |
| 5 levels | 23 (63.9) | 44 (64.7) | 0.921 |
| 6 levels | 4 (11.1) | 10 (14.7) |
Abbreviations: CDDD, cervical degenerative disc disease; cSVA, cervical sagittal vertical axis; McGS, McGregor's slope; T1S-CL, T1 slope minus C2–C7 cervical lordosis.
Note: Quantitative variables are represented as mean ± SD; categorical variables are represented as n (%); P < 0.05 was considered statistically significant.
Table 4.
MCID PRO by cervical parameters, univariate analysis (N = 104).
| Outcome Measure | Normative | Non-normative | Δ | 95% CI | P |
| cSVA ≤ 4 cm (n = 73) | cSVA > 4 cm (n = 31) | ||||
| NDI | 35 (47.9) | 13 (41.9) | 6.0 | −14.5 to 25.2 | 0.574 |
| VAS neck | 58 (79.5) | 21 (67.7) | 11.7 | −5.6 to 30.9 | 0.201 |
| VAS arm | 19 (59.4) | 20 (64.5) | −5.1 | −27.5 to 18.0 | 0.674 |
| mJOA | 42 (57.5) | 20 (64.5) | −7.0 | −25.3 to 13.6 | 0.507 |
| SF-12 MCS | 42 (57.5) | 17 (54.8) | 2.7 | −17.0 to 22.8 | 0.800 |
| SF-12 PCS | 37 (50.7) | 19 (61.3) | −10.6 | −29.3 to 10.1 | 0.321 |
| −5° ≤ McGS ≤ 15° (n = 89) | 5° > McGS > 15° (n = 15) | ||||
| NDI | 40 (44.9) | 8 (53.3) | −8.4 | −32.4 to 17.0 | 0.547 |
| VAS neck | 68 (76.4) | 11 (73.3) | 3.1 | −15.5 to 29.5 | 0.797 |
| VAS arm | 34 (59.6) | 5 (83.3) | −23.7 | −42.5 to 17.7 | 0.256 |
| mJOA | 50 (56.2) | 12 (80.0) | −23.8 | −40.4 to 3.2 | 0.082 |
| SF-12 MCS | 50 (56.2) | 9 (60.0) | −3.8 | −26.5 to 22.4 | 0.782 |
| SF-12 PCS | 46 (51.7) | 10 (66.7) | −15.0 | −35.8 to 11.9 | 0.282 |
| T1S-CL < 20° (n = 36) | T1S-CL > 20° (n = 68) | ||||
| NDI | 16 (44.4) | 32 (47.1) | −2.6 | −21.6 to 17.0 | 0.799 |
| VAS neck | 30 (83.3) | 49 (72.1) | 11.3 | −6.5 to 25.9 | 0.201 |
| VAS arm | 11 (57.9) | 28 (63.6) | −5.7 | −30.8 to 18.3 | 0.667 |
| mJOA | 19 (52.8) | 43 (63.2) | −10.5 | −29.4 to 8.9 | 0.301 |
| SF-12 MCS | 21 (58.3) | 38 (55.9) | 2.5 | −17.2 to 21.2 | 0.810 |
| SF-12 PCS | 18 (50.0) | 38 (55.9) | −5.9 | −25.0 to 13.6 | 0.567 |
Abbreviations: cSVA, cervical sagittal vertical axis; McGS, McGregor's slope; MCID, minimal clinically important difference; MCS, Mental Component Summary; mJOA, modified Japanese Orthopaedic Association; NDI, Neck Disability Index; PCS, Physical Component Summary; PRO, patient-reported outcome; SF-12, 12-item Short-Form; T1S-CL, T1 slope minus C2–C7 cervical lordosis; VAS, visual analog scale.
Note: P < 0.05 was considered statistically significant.
A multivariable regression model was performed to assess if any sagittal parameter was independently associated with significant odds of achieving anytime MCID among PRO. Covariates used in the model included age, smoking, baseline PRO, and normative radiographic parameters. Lower baseline PRO was independently associated with significantly increased odds of achieving anytime MCID for NDI, SF-12 MCS, and SF-12 PCS (Table 5). Transition from non-normative to normative alignment for cSVA or McGS did not independently increase the odds of achieving anytime MCID for PRO (Table 5).
Table 5.
Anytime MCID PRO difference when changing from non-normative to normative cervical parameters, multivariable regression (N = 104).
| Variable | OR | 95% CI | P | Variable | OR | 95% CI | P | Variable | OR | 95% CI | P |
| NDI | |||||||||||
| cSVA | 1.32 | 0.49–3.51 | 0.583 | McGS | 0.68 | 0.21–2.19 | 0.518 | T1S-CL | 0.85 | 0.35–2.08 | 0.719 |
| Baseline NDI | 1.04 | 1.02–1.06 | <0.001 | Baseline NDI | 1.04 | 1.02–1.06 | <0.001 | Baseline NDI | 1.04 | 1.01–1.06 | <0.001 |
| VAS neck | |||||||||||
| cSVA | 2.12 | 0.73–6.19 | 0.168 | McGS | 1.06 | 0.29–3.89 | 0.934 | T1S-CL | 2.22 | 0.75–6.55 | 0.151 |
| Baseline VAS neck | 1.21 | 1.04–1.41 | 0.015 | Baseline VAS neck | 1.21 | 1.04–1.40 | 0.014 | Baseline VAS neck | 1.21 | 1.04–1.41 | 0.015 |
| VAS arm | |||||||||||
| cSVA | 1.05 | 0.41–2.66 | 0.921 | McGS | 1.01 | 0.36–3.43 | 0.863 | T1S-CL | 0.88 | 0.37–2.09 | 0.769 |
| Baseline VAS arm | 0.93 | 0.83–1.03 | 0.175 | Baseline VAS arm | 0.93 | 0.83–1.03 | 0.176 | Baseline VAS arm | 0.93 | 0.83–1.04 | 0.178 |
| mJOA | |||||||||||
| cSVA | 0.98 | 0.38–2.54 | 0.960 | McGS | 0.28 | 0.07–1.08 | 0.065 | T1S-CL | 0.68 | 0.29–1.62 | 0.384 |
| Baseline mJOA | 0.98 | 0.85–1.14 | 0.836 | Baseline mJOA | 0.99 | 0.85–1.15 | 0.862 | Baseline mJOA | 0.98 | 0.84–1.14 | 0.791 |
| SF-12 MCS | |||||||||||
| cSVA | 1.73 | 0.59–5.04 | 0.319 | McGS | 1.05 | 0.31–3.54 | 0.936 | T1S-CL | 1.55 | 0.59–4.13 | 0.376 |
| Baseline SF-12 MCS | 0.89 | 0.84–0.94 | <0.001 | Baseline SF-12 MCS | 0.89 | 0.85–0.94 | <0.001 | Baseline SF-12 MCS | 0.89 | 0.85–0.95 | <0.001 |
| SF-12 PCS | |||||||||||
| cSVA | 0.97 | 0.37–2.57 | 0.954 | McGS | 0.65 | 0.20–2.14 | 0.474 | T1S-CL | 0.85 | 0.35–2.05 | 0.715 |
| Baseline SF-12 PCS | 0.93 | 0.89–0.98 | 0.006 | Baseline SF-12 PCS | 0.94 | 0.89–0.98 | 0.007 | Baseline SF-12 PCS | 0.93 | 0.89–0.98 | 0.005 |
Abbreviations: cSVA, cervical sagittal vertical axis; McGS, McGregor’s slope; MCID, minimal clinically important difference; MCS, Mental Component Summary; mJOA, modified Japanese Orthopaedic Association; NDI, Neck Disability Index; PCS, Physical Component Summary; PRO, patient-reported outcome; SF-12, 12-item Short-Form; T1S-CL, T1 slope minus C2–C7 cervical lordosis; VAS, visual analog scale.
Note: P < 0.05 was considered statistically significant. Covariates used in the model: age, smoker, baseline PRO, and normative radiographic parameter. Anytime MCID PRO is based on the difference between 1 y and baseline PRO; normative cervical parameters are based on 1 y cervical parameters.
Discussion
We conducted a retrospective comparative cohort study of patients who underwent multilevel PCF to evaluate whether normative vs non-normative cervical sagittal alignment was associated with achieving MCID. Overall, patient characteristics between normative and non-normative cervical parameter groups were largely similar, apart from younger age (59.4 vs 67.5 years, P < 0.001) and higher prior anterior surgery (63.0% vs 38.7%, P = 0.019) in the normative cSVA group. Though age remains a confounder, it may be that anterior surgery restores alignment to some degree, which is then augmented during PCF, allowing for better improvement of cSVA. No significant PRO differences were observed among parameter groups, and neither cSVA, McGS, nor T1S-CL, when normative, emerged as an independent predictor of achieving MCID in multivariable models. Patients who transitioned from non-normative to normative cSVA or McGS postoperatively did not have significantly higher odds of achieving MCID in any PRO, even after adjusting for baseline factors.
The impact of maintaining horizontal gaze and the role of cervical sagittal alignment have been increasingly recognized as playing a crucial role in patient outcome and satisfaction following multilevel cervical fusion and spinal deformity surgery.2,5,18–22 The natural head position is based upon a balance between minimal energy expenditure and a horizontal gaze, as described by Lafage et al.19 The degree of disability correlates with the balance of these 2 components.19 A key biomechanical study by Patwardhan et al proposed forward head posture (cSVA > 4 cm) as a possible compensatory adoption to alleviate cervical radiculopathy, particularly in patients with increased upper thoracic kyphosis. Consequently, the lower cervical spine (C2–C7) flexes and the suboccipital spine (C0–C2) hyperextends in compensation to maintain a horizontal gaze.9 This increases the burden on the posterior cervical muscles and produces higher moment arm forces on the cervicothoracic junction, which may hasten adjacent segment disease and contribute to adverse PRO. The chin-brow vertical angle (CBVA) is also an important cervical parameter that has been described to characterize horizontal gaze.19,23,24 In the present study, McGS was used to characterize horizontal gaze as a surrogate for CBVA, consistent with the description by Moses et al, given that anatomical landmarks needed for CBVA measurement are not typically imaged in standing cervical radiographs.8,10
Prior studies have shown mixed results for PRO among patients with normative cervical sagittal parameters following cervical laminectomy and fusion.1,2,11,18,19,21,25–27 Hyun et al demonstrated that T1S-CL mismatch after PCF can cause severe cervical misalignment, leading to greater postsurgical patient-reported disability.3 Pinter et al showed that patients with preoperative cSVA < 4 cm undergoing C2-T2 PCF had more improvement in VAS neck pain and NDI scores at 3 months and 1 year, respectively.6 Interestingly, patients in whom both cSVA and C2 to C7 lordosis improved after surgery had superior NDI and VAS neck at 3 months, but not at 1 year postoperatively.6 Evaniew et al found that while increased cSVA was associated with inferior PRO at presentation, there were no significant associations between alignment parameters or change in alignment after surgery and health-related quality of life or function.21 The present study similarly found that transitioning from non-normative to normative alignment postoperatively did not significantly impact the likelihood of achieving MCID at any time point for any PRO. Thus, it may be that the overall degree of improvement of cervical sagittal parameters after surgery, regardless of normative vs non-normative correction, correlates more strongly with improved PRO.
This study has several limitations. First, the study was retrospective in nature, which renders our findings susceptible to inherent methodological biases, including selection bias and unmeasured confounding. A relatively small sample size may also limit the statistical power and generalizability of our findings. Other perioperative factors may inherently positively or adversely impact PRO that are not directly attributable to cervical sagittal alignment alone. Furthermore, symptom duration has been reported in other studies to better characterize the preoperative baseline of patients and assist with the standardization and comparison of outcomes in groups. In the present study, this metric was not readily available; thus, we relied on baseline PRO scores, which are generally measured within 1 month prior to surgery. Patients in this study underwent varying degrees of decompression with laminectomy and/or foraminotomy at the discretion of the surgeon, which was unaccounted for in the present analysis. Additionally, the extent of posterior paraspinal muscle dissection, including potential detachment of the semispinalis capitis at C2, is a recognized factor that can influence postoperative cervical alignment and functional recovery. Although not directly quantified in this study, differences in surgical technique and muscle preservation may have contributed to the observed radiographic and clinical outcomes. Similarly, preoperative paraspinal muscle quantity and quality were not assessed, and given that the non-normative cSVA group was significantly older, age-related sarcopenia may have influenced alignment and PRO. Moreover, over half of patients (55.8%) had prior anterior cervical instrumentation; pseudoarthrosis for PCF may have introduced patients who were more likely to have adverse PRO from multiple surgeries or pre-existing pathology. Variation in surgical levels also contributes to individual patient recovery, perhaps based on the need for increased surgical exposure, decompression, and resultant postoperative alignment, depending on the surgery at hand.28 Although we employed methodology to standardize metrics and account for multilevel surgeries—such as including only patients undergoing 4 to 8 levels and those that spanned the cervicothoracic junction—we recognize this as a possible limitation. Finally, the use of MCID has inherent limitations, as its determination often depends on changes in PRO scores, which are strongly influenced by baseline status.29,30 Consequently, a validated MCID for one population may not be universally applicable, as has been described in prior studies.31
Conclusions
In this retrospective cohort study of patients undergoing multilevel PCF, achievement of MCID in PRO was comparable between patients with normative and those with non-normative postoperative cervical sagittal alignment. Normative cervical cSVA, McGS, or T1S-CL following PCF surgery was not independently associated with improved PRO. While cervical sagittal alignment remains an important biomechanical factor in surgical planning, further studies are needed to better define its clinical significance in relation to patient quality of life outcomes.
Acknowledgments
We thank Heather Heitkotter, PhD, for her key role in the acquisition of essential software tools and for providing invaluable project support throughout the research. Her expertise and assistance greatly contributed to the success of this project. We also thank Heather Lucke, MS, who also assisted with the statistical analysis and project support.
References
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