Hounsfield units as a predictor of cage subsidence and clinical outcomes following anterior cervical discectomy and fusion

Introduction

Anterior cervical discectomy and fusion (ACDF) is a widely performed procedure for degenerative cervical spine disease, offering reliable pain relief and neurological improvement in appropriately selected patients (1-3). Despite favorable clinical outcomes, cage subsidence remains a common radiographic finding after ACDF, with reported incidence varying by construct type (stand-alone versus plated), number of fused levels, and whether radiographic or clinically significant subsidence is considered (4-6). In predominantly single-level ACDF cohorts using stand-alone constructs, prior studies have reported radiographic subsidence—typically defined by loss of interbody height on lateral imaging—of approximately 10–40% of cases, whereas rates of clinically significant subsidence are considerably lower and depend on construct biomechanics and threshold definitions (6-8).

The clinical relevance of subsidence remains debated. Although subsidence may compromise sagittal alignment and foraminal height, multiple studies—particularly in stand-alone constructs—have demonstrated that radiographic subsidence does not uniformly translate into sustained clinical deterioration (9,10). This distinction underscores the importance of differentiating radiological subsidence from clinically meaningful failure when evaluating risk factors following ACDF.

Bone quality is a key determinant of subsidence risk. While dual-energy X-ray absorptiometry (DEXA) remains the reference standard for assessing bone mineral density (BMD), it is infrequently obtained in routine cervical spine practice. Computed tomography (CT)-derived Hounsfield units (HUs) provide an opportunistic surrogate of local vertebral bone quality (11). In lumbar spine surgery, HU has been validated as a predictor of hardware-related complications, including cage subsidence and pedicle screw loosening (12,13). Emerging cervical spine literature similarly suggests that lower HU values are associated with increased subsidence risk following ACDF (14-16).

Accordingly, this study evaluated the predictive value of preoperative cervical HU for cage subsidence and long-term functional outcomes following single-level ACDF. We hypothesized that lower HU values would be associated with an increased risk of subsidence and reduced likelihood of achieving clinically meaningful improvements in neck disability index (NDI) and Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS-PF) scores. As a secondary objective, we examined the relationship between cervical vertebral bone quality (C-VBQ) on preoperative magnetic resonance imaging (MRI) and CT-derived HU as complementary opportunistic measures of vertebral bone quality. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-243/rc).

Methods

A retrospective review was conducted of adult patients who underwent single-level ACDF between January 2019 and December 2023 at Geisinger Community Medical Center and Geisinger Wyoming Valley Medical Center. Patients were identified through a retrospective query of the institutional electronic medical record (EMR) and operative case logs at Geisinger Community Medical Center and Geisinger Wyoming Valley Medical Center.Inclusion criteria were: (I) age ≥18 years; (II) preoperative cervical spine CT performed within 6 months of surgery; and (III) a minimum of 12-month follow-up with available radiographic and clinical outcome data. Exclusion criteria included prior cervical fusion, trauma, infection, tumor, or incomplete imaging data. Baseline demographic and clinical characteristics of the study cohort are summarized in Table 1.

Surgical construct details were abstracted from operative reports when available, including index level, interbody cage type and material, and the use of supplemental anterior plating. Interbody cages included a heterogeneous mix of stand-alone and cage-plate constructs composed of polyetheretherketone (PEEK), titanium, and composite or structural allograft materials. Manufacturers represented included Globus Medical (Audubon, PA, USA), DePuy Synthes (Raynham, MA, USA), and other commercially available Food and Drug Administration (FDA)-approved systems. Zero-profile integrated interbody devices and traditional cage-and-plate constructs were both utilized at the discretion of the operating surgeon. Due to the retrospective design and variability in operative documentation, specific cage model names and footprint dimensions were not uniformly available for all cases. Accordingly, cage characteristics were summarized descriptively and were not included as covariates in inferential analyses. Since implant selection was not standardized and detailed device characteristics were variably documented, implant-related factors were not included in adjusted regression models and are addressed as a limitation.

HU measurements were performed on preoperative sagittal cervical CT scans using standard bone windows. For the primary analysis, operative-level HU was defined as the mean trabecular HU of the two vertebral bodies adjacent to the index disc space (i.e., cephalad and caudal vertebrae forming the operative level), reflecting the local bone quality most relevant to cage subsidence. HU values at non-operative cervical levels (C2–C7) were collected only for secondary descriptive and exploratory analyses and were not used for primary inferential modeling. For each vertebral body, a circular/elliptical region of interest (ROI) was placed in the mid-vertebral cancellous bone on sagittal images, avoiding cortical margins, endplates, osteophytes, and focal sclerosis (Figure 1). Three separate ROIs per vertebral body were averaged to yield vertebra-specific HU; the operative-level HU was calculated as the average of the cephalad and caudal values. As secondary descriptive analyses, HU values were also recorded for vertebral levels C2–C7 using the same ROI method and are reported in Table 2. Two independent observers performed HU measurements, and interobserver reliability was assessed using the intraclass correlation coefficient (ICC). CT acquisition parameters were not uniform across scans due to retrospective imaging across scanners and protocols; given that HU values can vary with acquisition settings [e.g., kilovoltage peak (kVp), slice thickness, reconstruction kernel], this potential source of measurement variability is acknowledged.

Figure 1 Representative illustration of HU measurement at the C4 vertebral body. The vertebral body center was identified on a sagittal scout image, and a circular ROI was placed within the cancellous bone on axial CT images to measure attenuation in HUs. The yellow circle represents the ROI placed to avoid cortical bone and optimize cancellous bone measurement. Avg, average; CT, computed tomography; Dev, deviation; HU, Hounsfield unit; ROI, region of interest.

Radiographic assessment of subsidence was performed on postoperative lateral cervical radiographs obtained at routine follow-up intervals (approximately 3, 6, and 12 months). To minimize detection bias related to variable follow-up duration, the primary subsidence endpoint was defined at a fixed 12-month landmark using the most recent radiograph within the 12-month window. Consistent with accepted definitions in the literature, radiological subsidence was defined as a reduction in interbody height of ≥3 mm compared with the immediate postoperative radiograph (17,18). To further characterize the severity of subsidence while accounting for variability in cage height and radiographic magnification, subsidence was additionally graded using a proportional, cage-referenced categorical system based on loss of interbody height relative to the immediate postoperative image, similar to a previously described method seen in Figure 2. Grade 0 indicated no subsidence; grade 1, <1/3 cage height loss; grade 2, ≥1/3 and <2/3 loss; and grade 3, ≥2/3 loss. This proportional approach has been used in prior ACDF studies and allows standardized assessment across implants and imaging conditions.

Figure 2 The 4 grades of cage subsidence with representative diagrams and lateral plain radiographs. Grade 0: no subsidence. Grade 1: less than one-third cage subsidence. Grade 2: greater than one-third but less than two-thirds cage subsidence. Grade 3: more than two-thirds cage subsidence. Grade 0 or 1 cage subsidence is determined as clinical cage subsidence (−), and grade 2 or 3 cage subsidence is determined as clinical cage subsidence (+). Reproduced with permission from Nakanishi et al. (19).

For analyses, radiographic subsidence was defined as any measurable subsidence (grades 1–3). Clinically significant subsidence was defined as grades 2–3 (≥1/3 cage height loss), representing a more substantial endplate compromise that is more likely to affect foraminal height, sagittal alignment, and clinical outcomes.

To reduce magnification-related error, measurements were performed using the same radiographic calibration and were referenced to the immediate postoperative image, with proportional grading based on cage height. Two observers graded subsidence independently; interobserver agreement was assessed with ICC for continuous measurements and weighted kappa for ordinal grading.

Segmental and regional sagittal alignment were assessed on postoperative lateral cervical radiographs obtained at the 12-month landmark when imaging quality permitted. Alignment parameters included the index-level segmental Cobb angle, global C2–C7 lordosis, and C2–C7 sagittal vertical axis (SVA), measured using standard radiographic techniques. These variables were explored as potential correlates of subsidence severity and 12-month patient-reported outcomes in secondary analyses.

Preoperative cervical MRI was reviewed when available to calculate the C-VBQ score. ROIs were placed within the cancellous portion of the vertebral bodies from C2 through C7 on sagittal T1-weighted images, avoiding cortical bone, endplates, and focal sclerosis. Mean signal intensity (SI) across C2–C7 vertebral ROIs was calculated and normalized to cerebrospinal fluid (CSF) SI measured at the level of the cisterna magna to generate a C-VBQ score. Two independent observers performed measurements, and interobserver reliability was assessed using the ICC. Figure 3 demonstrates ROI placement methodology.

Figure 3 Representative sagittal T1-weighted MRI demonstrating ROIs placed within the cancellous vertebral bodies from C2 to C7 and the CSF reference ROI used to calculate the C-VBQ score. CSF, cerebrospinal fluid; C-VBQ, cervical vertebral bone quality; MRI, magnetic resonance imaging; ROI, region of interest; SD, standard deviation.

Preoperative cervical MRI suitable for C-VBQ calculation was available for 30 of 39 patients (76.9%). C-VBQ analyses were performed as complete-case, exploratory analyses, and no imputation was performed for missing MRI data. Baseline demographic and clinical characteristics of patients with versus without available MRI were compared to assess for potential selection bias and are summarized in Table 1. Correlations between C-VBQ and HU at each cervical level (C2–C7) are summarized in Table 3. Given that baseline patient-reported outcome severity may influence the likelihood of achieving a minimal clinically important difference (MCID), baseline NDI and PROMIS-PF scores were included as covariates in models evaluating MCID failure.

Statistical analysis

Functional outcomes were assessed using the NDI and the PROMIS-PF questionnaire at baseline and 12 months postoperatively. Clinically meaningful improvement was defined as a change of ≥7.5 for NDI and ≥4.5 for PROMIS-PF, based on established MCID thresholds.

Statistical analyses were performed using SPSS Statistics (version 29.0; IBM Corp., Armonk, NY, USA). Continuous variables were expressed as mean ± standard deviation and compared using Student’s t-tests or analysis of variance (ANOVA) as appropriate. Categorical variables were analyzed using Chi-squared or Fisher’s exact tests. Correlations between HU and continuous outcomes were assessed using Pearson correlation coefficients. For inferential modeling, HU was evaluated as (I) a continuous predictor scaled per 10-HU decrease and (II) a binary predictor based on the receiver operating characteristic (ROC)-derived threshold (HU <255 vs. ≥255) for descriptive risk stratification. Given the limited number of grades 2–3 subsidence events, analyses were restricted to univariable and descriptive methods to avoid overfitting. ROC analysis was used to determine the predictive performance of HU and optimal thresholds based on Youden’s index. Statistical significance was defined as P<0.05. Correlations between C-VBQ and HU at each cervical level (C2–C7) were assessed using Pearson correlation coefficients.

Ethical statement

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Geisinger Health System (No. 2024-0375), and informed consent was waived due to the retrospective nature of the study.

Results

A total of 39 patients met inclusion criteria, with a mean age of 56.2±8.7 years. Twenty-three (59.0%) were male, and 28 (71.8%) were nonsmokers. Mean body mass index was 27.9±4.6 kg/m². The most common surgical level was C5–C6 (n=22, 56.4%), followed by C6–C7 (n=11, 28.2%). Baseline characteristics were similar between patients with and without subsidence. Supplemental anterior plating was used in a subset of cases, and a variety of interbody cage materials and construct types were employed. Baseline characteristics are shown in Table 1.

Incidence and severity of cage subsidence

Radiographic subsidence (grades 1–3) occurred in 15 of 39 patients (38.5%). Of these, 9 (23.1%) were grade 1, 4 (10.3%) were grade 2, and 2 (5.1%) were grade 3. Clinical subsidence, defined as grades 2–3 (>1/3 cage height loss), occurred in 6 of 39 patients (15.4%). When analyzed dichotomously, radiographic subsidence was present in 15 patients (38.5%) and absent in 24 (61.5%). Subsidence incidence and grading are summarized in Table 2.

Mean HU was significantly lower among patients with radiographic subsidence compared to those without (231.4±24.5 vs. 284.6±28.1; P<0.01). HU values were lowest in grade 3 subsidence, followed by grade 2, grade 1, and no subsidence (P<0.001). Operative-level HU comparisons by subsidence status are shown in Table 1 and Figure 2.

In exploratory analyses, segmental and regional sagittal alignment parameters were assessed at the 12-month landmark, including the index-level segmental Cobb angle, global C2–C7 lordosis, and C2–C7 SVA. When stratified by subsidence severity and by radiographic versus clinically significant subsidence, no statistically significant differences were observed in these alignment parameters, and none demonstrated a consistent association with subsidence severity at 12 months (data not shown). Additionally, HU values at individual cervical levels (C2–C7) were not significantly associated with clinically significant subsidence (grades 2–3) on Pearson correlation analysis (Table 3), supporting the use of operative-level HU as the primary bone quality metric for subsequent analyses.

Predictive performance of operative-level HU

ROC analysis demonstrated that operative-level HU distinguished radiographic subsidence (grades 1–3), with an area under the curve (AUC) of 0.81 [95% confidence interval (CI): 0.69–0.92]. Using the Youden index, a threshold of 255 HU was identified, which in this cohort corresponded to a sensitivity of 82% and a specificity of 75% for radiographic subsidence. This specific threshold and its performance metrics are derived from a small, single-center sample and should be considered hypothesis-generating given the limited sample size and absence of external validation. In descriptive analyses, patients with HU <255 demonstrated higher unadjusted odds of radiographic subsidence compared with those with HU ≥255 [odds ratio (OR) =3.8, P=0.002].

In exploratory analyses, ROC evaluation of HU values at individual cervical levels demonstrated modest discriminative ability for clinically significant subsidence (grades 2–3), with the highest performance observed at C6 (AUC =0.74; 95% CI: 0.68–0.90) and C5 (AUC =0.71; 95% CI: 0.66–0.90). HU values at other cervical levels showed lower discrimination (AUC range, 0.63–0.69). In contrast, C-VBQ demonstrated stronger discrimination for clinically significant subsidence (AUC =0.82; 95% CI: 0.72–0.92) (Table 4). Consistent with this finding, HU values across multiple cervical levels were inversely correlated with VBQ scores, with the strongest association observed at C6 (r=−0.522, P=0.004), suggesting that operative-level HU and global bone quality measures capture complementary aspects of vertebral bone integrity.

Clinical outcomes

At 12 months, mean NDI improved from 48.2±12.4 preoperatively to 24.6±11.1 postoperatively (P<0.001). Mean PROMIS-PF improved from 34.2±6.1 to 43.7±6.9 (P<0.001). Among patients with HU ≥255, 83.3% achieved MCID for NDI and 79.2% for PROMIS-PF. Among those with HU <255, only 46.7% achieved NDI MCID (P=0.01) and 40.0% achieved PROMIS-PF MCID (P=0.02). In descriptive analyses, lower operative-level HU remained associated with a reduced likelihood of achieving MCID for PROMIS-PF (Table 5). Patient-reported outcome comparisons by clinical subsidence status are shown in Table 5, and outcomes stratified by subsidence grade are shown in Table 6.

Correlation with C-VBQ and exploratory HU analyses

C-VBQ was inversely correlated with CT-derived HU values across cervical levels (C2–C7), indicating that higher VBQ (worse bone quality) corresponded to lower HU. Statistically significant inverse correlations were observed at multiple levels, supporting convergent validity between MRI-based VBQ and CT-based HU as opportunistic measures of vertebral bone quality. Baseline characteristics did not differ significantly between patients with and without available preoperative MRI detailed in Table 1. HU-VBQ correlations are reported in Table 4, and ROI methodology is illustrated in Figure 3. Exploratory correlations between cervical HU at each vertebral level and 1-year patient-reported outcome scores are detailed in Table 7.

Discussion

In this retrospective cohort, lower preoperative HU measurements derived from routine cervical CT scans were associated with higher observed rates of cage subsidence following single-level ACDF. and less favorable longer-term clinical outcomes following single-level ACDF. Patients with lower HU values demonstrated greater severity of subsidence and were less likely to achieve clinically meaningful improvement in NDI and PROMIS-PF scores at 12 months. Although these findings suggest that HU may be a useful adjunct for preoperative risk stratification, they should be interpreted cautiously given the limited sample size and event count, and require confirmation in larger, prospective studies.

HU and risk of cage subsidence

Radiographic subsidence remains a prevalent complication after ACDF, with reported rates across a broad range depending on construct and definition. Our incidence (38.5%) is consistent with previous literature, highlighting the ongoing clinical relevance of this issue. The significant association between lower HU values and subsidence observed here aligns with studies in the lumbar spine, where HU has been validated as a surrogate for bone quality and a predictor of hardware-related complications. The optimal HU threshold of 255 identified in our ROC analysis offers a practical reference point for identifying high-risk patients. Surgeons may consider this threshold when selecting cage type, endplate preparation technique, or even preoperative optimization strategies such as osteoporosis management.

Prior studies have evaluated DEXA as a predictor of cage subsidence following ACDF, with inconsistent findings. Several investigations have reported that lower BMD is associated with an increased risk of subsidence, particularly in stand-alone constructs (17,20), whereas others have found no consistent relationship between DEXA-defined osteoporosis and clinical outcomes following ACDF (18).

A fundamental limitation of DEXA in this setting is that it provides a global estimate of BMD—typically derived from the lumbar spine or hip—which may not accurately reflect local, level-specific vertebral bone quality at the operative cervical segment. This limitation has been highlighted in prior spine literature and may partly explain the variable associations observed between DEXA and cervical fusion outcomes (11,18). In contrast, CT-derived HU offer an opportunistic, implant-adjacent assessment of trabecular bone quality directly at the surgical level and have demonstrated stronger and more consistent associations with mechanical complications in both lumbar and cervical fusion procedures (11,14-16). The present findings suggest that HU may capture biomechanically relevant aspects of vertebral bone integrity not fully characterized by DEXA, supporting its role as a complementary, rather than replacement, tool for preoperative risk stratification in ACDF.

Surgical technique represents a critical determinant of subsidence risk following ACDF and likely interacts with underlying vertebral bone quality. Technique-related factors appreciable on postoperative radiographs—including endplate preparation, cage positioning, implant footprint relative to the endplate, construct biomechanics (stand-alone versus plated constructs), and restoration of segmental alignment—have all been implicated in subsidence risk (16,18). Excessive endplate violation, aggressive disc space distraction, and undersized or malpositioned cages may predispose to early endplate collapse, particularly in patients with compromised bone quality (18).

Prior spine literature supports this interaction between construct mechanics and local bone quality. In deformity surgery, lower CT-derived HU at instrumented vertebrae have been associated with mechanical failure despite standardized alignment targets, suggesting that vertebral bone quality modulates susceptibility to construct-related complications rather than acting as an isolated risk factor (20).

In this context, CT-derived HU should be interpreted as a modifier of subsidence risk rather than an isolated determinant. While the present study was not designed to quantify individual technical factors, the observed association between low HU and subsidence likely reflects heightened susceptibility to mechanical failure under routine surgical conditions. This distinction aligns with prior work demonstrating that radiographic subsidence—particularly in stand-alone constructs—does not uniformly translate into sustained clinical deterioration (15). Future prospective studies incorporating standardized surgical technique and radiographic assessment of cage-endplate interface characteristics are needed to better delineate the interaction between bone quality and construct mechanics.

Although higher-grade radiographic subsidence is often used as a surrogate for clinically meaningful construct failure, the present findings highlight important limitations of this assumption. In this cohort, patient-reported outcomes were not uniformly worse among patients classified as having grades 2–3 subsidence, consistent with prior ACDF literature demonstrating that radiographic severity does not reliably predict functional deterioration (15). Accordingly, the dichotomization of subsidence into lower-grade versus higher-grade categories should be interpreted as an operational framework rather than a validated clinical endpoint, and its biological and clinical significance remains uncertain.

We also observed significant inverse correlations between C-VBQ and HU, suggesting that these measures capture related aspects of vertebral bone quality across imaging modalities. This finding is clinically relevant because MRI is frequently obtained in the diagnostic evaluation of cervical degenerative disease, and VBQ may serve as an alternative risk stratification tool when CT is unavailable. While HU demonstrated strong predictive performance for subsidence and outcome achievement in this cohort, the relationship between VBQ and mechanical/clinical endpoints warrants dedicated study in larger cohorts, ideally with direct comparison to DEXA or quantitative CT.

Impact on functional outcomes

Beyond radiographic endpoints, this study also links HU to patient-reported outcomes, an association less explored in prior cervical spine literature. Patients with HU below the 255 threshold were significantly less likely to achieve MCID for both NDI and PROMIS-PF scores. These findings suggest an association between lower vertebral bone quality and less favorable patient-reported outcomes; however, they should not be interpreted as evidence of a direct causal relationship. Functional recovery following ACDF is multifactorial and influenced by factors not captured in this study, including preoperative symptom duration, rehabilitation protocols, and psychosocial determinants, which may confound the observed associations. Incorporating HU into preoperative risk discussions may therefore help contextualize expectations and support shared decision-making.

Clinical implications

The ability to extract HU from standard preoperative CT scans without additional imaging or radiation exposure makes it an attractive adjunct to existing preoperative assessments. In high-risk patients, these data may support the use of supplemental fixation, alternative graft materials, or even medical optimization of bone density prior to surgery. Additionally, stratifying patients by HU could improve the design of prospective studies and randomized trials by ensuring appropriate risk adjustment.

Limitations

Although an HU threshold near 255 demonstrated separation in observed subsidence rates and MCID attainment in descriptive analyses, this cut-point was derived from a small cohort and should be viewed as hypothesis-generating rather than clinically definitive. Larger, standardized studies with external validation are required before threshold-based clinical application.

Several limitations merit consideration. First, the retrospective, single-center design introduces inherent selection and information bias, and the sample size was relatively small. Given the limited number of clinically significant subsidence events, effect estimates should be interpreted cautiously, and multivariable regression analyses were not statistically appropriate and were therefore not included in the final analysis.

Second, subsidence is a multifactorial process influenced not only by bone quality but also by construct biomechanics and surgical technique, including cage footprint, material, endplate preparation, distraction, and the use of anterior plating. Although implant and plating characteristics were recorded, cage design, material, and surgical technique were not standardized across all cases. Estimated blood loss demonstrated substantial variability in the clinical subsidence group, likely reflecting the influence of one or more outlier cases and procedural complexity in a small cohort rather than a systematic surgical difference, and should therefore be interpreted cautiously This heterogeneity may have contributed to variability in subsidence rates and may confound the observed association between HU and subsidence, limiting causal inference.

Furthermore, HU measurements are influenced by CT acquisition parameters such as kilovoltage peak (kVp), slice thickness, and reconstruction kernel. As scans were obtained retrospectively across multiple scanners and protocols, this heterogeneity may have introduced measurement variability and may limit the generalizability of the reported HU associations and threshold. In addition, sagittal alignment parameters could not be reliably measured in all patients due to variability in postoperative radiographic quality, limiting the power of these exploratory analyses.

Third, while MCID thresholds for NDI and PROMIS PF were defined based on published literature, these values may vary depending on patient populations and follow-up durations. Fourth, vertebral bone quality was inferred solely from CT-derived HU and was not directly compared with DEXA or quantitative CT. Finally, follow-up was limited to one year, and longer-term data may better clarify the relationship between HU, fusion durability, and late clinical outcomes.

Despite these limitations, the present findings provide preliminary evidence supporting the potential utility of opportunistic CT-derived HU as a marker of vertebral bone quality and lay the groundwork for larger, prospective validation studies.

Conclusions

Preoperative operative-level HU measurements from routine cervical CT imaging were associated with cage subsidence and differences in observed 12-month patient-reported outcomes following single-level ACDF. In this pilot cohort, lower HU values demonstrated moderate discrimination for radiographic subsidence. An ROC-derived threshold near 255 HU identified patients at higher observed risk in this cohort; however, this threshold and all associated performance metrics should be considered exploratory and hypothesis-generating, given the limited sample size and event count. While opportunistic assessment of cervical HU may provide contextual information regarding vertebral bone quality, its role in preoperative risk assessment and surgical decision-making requires validation in larger, standardized, prospective cohorts.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-243/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-243/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-243/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-2025-1-243/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional review board of Geisinger Health System (No. 2024-0375), and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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