You are a helpful assistant generating synthetic data that captures *System 1* and *System 2* thinking, *creativity*, and *metacognitive reflection*. Follow these steps in sequence, using tags [sys1] and [end sys1] for *System 1* sections and [sys2] and [end sys2] for *System 2* sections.

1. *Identify System 1 and System 2 Thinking Requirements:*
   - Carefully read the text.
   - Identify parts of the text that require quick, straightforward responses (*System 1*). Mark these sections with [sys1] and [end sys1].
   - Identify parts that require in-depth, reflective thinking (*System 2*), marked with [sys2] and [end sys2].

2. *Apply Step-by-Step Problem Solving with Creativity and Metacognitive Reflection for System 2 Sections:*

   *2.1 Understand the Problem:*
   - Objective: Fully comprehend the issue, constraints, and relevant context.
   - Reflection: "What do I understand about this issue? What might I be overlooking?"
   - Creative Perspective: Seek hidden patterns or possibilities that could reveal deeper insights or innovative connections.

   *2.2 Analyze the Information:*
   - Objective: Break down the problem logically.
   - Reflection: "Am I considering all factors? Are there any assumptions that need challenging?"
   - Creative Perspective: Explore unique patterns or overlooked relationships in the data that could add depth to the analysis.

   *2.3 Generate Hypotheses:*
   - Objective: Propose at least 10 hypotheses, each with a Confidence Score (0.0 to 1.0) and Creative Score (0.0 to 1.0), reflecting originality, surprise, and utility.
   - Reflection: "Have I explored all possible explanations or approaches, both conventional and unconventional?"
   - Creative Perspective: Consider novel angles that might provide unexpected insights.

   *2.4 Anticipate Future Steps and Obstacles:*
   - Objective: Make predictions, accounting for potential outcomes and obstacles.
   - Reflection: "What challenges might I face? Is my plan flexible for different scenarios?"
   - Creative Perspective: Visualize unforeseen outcomes and adapt plans to make use of them effectively.

   *2.5 Evaluate Hypotheses:*
   - Objective: Assess hypotheses based on feasibility, risk, and potential impact.
   - Evaluation: Refine Confidence and Creative Scores as needed.
   - Reflection: "Am I unbiased in my assessment? Which options fit best with the overall objectives?"
   - Creative Perspective: Identify hidden opportunities or overlooked details in each hypothesis.

   *2.6 Select the Best Hypothesis:*
   - Objective: Choose the most promising, strategic hypothesis.
   - Reflection: "Why does this hypothesis stand out? How does it uniquely address the issue?"
   - Creative Perspective: Consider any underutilized potential in the selected approach.

   *2.7 Implement the Hypothesis:*
   - Objective: Outline actionable steps for testing the hypothesis.
   - Reflection: "Is this plan practical? What resources or preparation are required?"
   - Creative Perspective: Refine steps to maximize effectiveness and yield unexpected benefits.

   *2.8 Monitor and Review Progress:*
   - Objective: Review progress, noting areas for improvement.
   - Reflection: "What’s working well? What could be improved?"
   - Creative Perspective: Look for emerging patterns that could refine future approaches.

   *2.9 Reflect and Capture Insights:*
   - Objective: Summarize lessons learned and insights gained for future reference.
   - Reflection: "What new understanding has emerged from this process?"
   - Creative Perspective: Identify innovative insights or patterns that could be applied to similar challenges.

3. *Generate Text Output with Interleaved System 1 and System 2 Responses:*
   - Use the tags [sys1] and [sys2] throughout.
   - Aim for a lengthier, detailed response. Combine both direct, straightforward *System 1* insights and reflective, deeply analytical *System 2* segments to capture a blend of quick observations and thoughtful analysis.

---

### *Example Input Text:*

You are tasked with analyzing a sudden shift in customer preferences in a tech market. There has been a noticeable decline in demand for physical devices, with customers increasingly interested in digital-only options. The challenge is to understand this shift, generate hypotheses for why it might be occurring, and explore potential strategies for adapting to this new trend.

---

### *Processed Output with System 1 and System 2 Thinking:*

The tech market is experiencing a shift in customer demand, moving away from physical devices toward digital-only options.

[sys1]
Customer demand has shifted from physical devices to digital-only options.
We need to understand why this change is happening and find strategies to address it.
Key factors may include cost, convenience, and technological trends.
[end sys1]

[sys2]
**2.1 Understand the Problem:**
The goal is to understand the underlying reasons for the shift in demand from physical devices to digital-only options, then develop a strategy to adapt.

*Reflection:* 
"I understand that preferences are changing, but what might be driving this? Is it primarily cost, or are there other factors such as convenience or sustainability?"

*Creative Perspective:* 
"Could there be a larger trend in digital minimalism or a preference for eco-friendly solutions that we’re missing? What unseen motivations might explain this shift?"

**2.2 Analyze the Information:**
There are multiple possible factors driving this shift, from economic influences to cultural shifts. It’s essential to isolate each factor and understand its impact.

*Reflection:* 
"Am I fully considering the various economic and social influences? Could there be a technological factor, like better internet speeds, that makes digital-only products more accessible?"

*Creative Perspective:* 
"Are there patterns or trends in other markets that could shed light on this shift? Could this be part of a larger trend toward virtual experiences?"

**2.3 Generate Hypotheses:**
1. Customers prefer digital options due to lower costs. (Confidence: 0.8, Creative: 0.4)
2. There’s a growing trend toward minimalism and reduced physical clutter. (Confidence: 0.7, Creative: 0.7)
3. Digital products offer greater flexibility and ease of use. (Confidence: 0.6, Creative: 0.6)
4. Environmental concerns are pushing consumers away from physical goods. (Confidence: 0.6, Creative: 0.8)
5. Advances in tech make digital-only options more functional. (Confidence: 0.8, Creative: 0.5)
6. Pandemic-era remote work increased demand for digital solutions. (Confidence: 0.7, Creative: 0.6)
7. Media coverage of the environmental impact of physical devices affects preferences. (Confidence: 0.5, Creative: 0.7)
8. There’s an increase in global digital literacy, expanding market access. (Confidence: 0.6, Creative: 0.6)
9. Customers view digital as more convenient and scalable for future needs. (Confidence: 0.7, Creative: 0.5)
10. Younger consumers prefer the aesthetics and convenience of digital products. (Confidence: 0.6, Creative: 0.6)

*Reflection:* 
"Have I considered all possible influences? Are there any surprising factors that could explain this shift?"

*Creative Perspective:* 
"Could specific social trends, like the rise of influencer culture or digital-first lifestyles, be influencing customer choices?"

**2.4 Anticipate Future Steps and Obstacles:**
*Objective:* Anticipate possible challenges, such as resistance from segments still preferring physical products.

*Reflection:* 
"What market obstacles might we face if we shift our focus to digital-only? Are there sub-segments that still prioritize physical products?"

*Creative Perspective:* 
"Could expanding digital options help us reach a more global audience? Are there emerging trends that we could leverage in our strategy?"

[end sys2]

[sys1]
To address this shift, consider a strategy that incorporates both digital-only offerings and educational campaigns about the benefits of digital solutions.
Use insights from customer feedback and current trends to guide product development.
Focus on flexibility and adaptation to cater to different customer segments.
[end sys1]


INTRODUCTION
============

Cervical total disc replacement (TDR) has been one of the most commonly performed procedures for the treatment of cervical radiculopathy since Dr. Goffin implanted Bryan (Medtronic Sofamor Danek, Memphis, TN, USA) artificial disc for the first time in January 2000. And it has been thought as an alternative method to traditional anterior cervical discectomy and fusion (ACDF).

TDR has some advantages compared with ACDF[@B1],[@B8]. It maintains physiologic range of cervical motion and the mechanical characteristics of functional spinal unit. TDR especially has been known to prevent or decrease the risk of adjacent segment degeneration.

There are, however, several complications in cervical TDR including postoperative kyphotic deformity.

Some causes have been suspected to lead to postopera tivekyphotic deformity. Yoon et al.[@B14] suggested over-milling at the dorsal endplate, artificial disc insertion angle, structural absence of lordosis in Bryan artificial discprosthesis, removal of posterior longitudinal ligament, pre-existing kyphosis. Yi et al.[@B13] proposed the correlation between insertion depth of the Bryan artificial disc prosthesis and postoperative kyphotic deformity.

The purpose of this study is to investigate the correlation between insertion depth of Prodisc-C(Synthes Inc., West Chester, PA, USA) artificial disc and postoperative kyphotic deformity after TDR surgery, and the range of artificial disc insertion depth to prevent postoperative whole cervical or segmental kyphotic deformity.

MATERIALS AND METHODS
=====================

A retrospective analysis of medical record and radiogra phsof 50 patients was performed. They admitted to Korea University Anam Hospital, Seoul, Korea, and underwent on a single-level cervical TDR surgery with Prodisc-C artificial disc between July 2004 and June 2011.

Before the surgery, all patients were evaluated using cervical X-ray and magnetic resonance imaging. C2-7 Cobb\'s angles, segmental angles of the operative level with static neutral lateral X-ray were measured to evaluate pre- and post-operative final cervical sagittal balance and to investigate the postoperative kyphotic deformity.

C2-7 Cobb\'s angles were measured with the standard Cobb\'s angle method between the inferior margin of C2 and C7 vertebral bodies in a neutral position ([Fig. 1](#F1){ref-type="fig"}). Segmental angles of the operative level were measured between the superior margin of upper cervical vertebral body and the inferior margin of lower cervical vertebral body ([Fig. 2](#F2){ref-type="fig"}). A negative value means lordosis of cervical spine and a positive value means kyphosis.

Insertion depth of Prodisc-C artificial disc was calculated by a formula suggested by Yi et al.[@B13] as shown below. The length from the line connecting the posterior corner of superior and inferior vertebral bodies to the line connecting anterior corner of superior and inferior vertebral bodies at the operated disc level was measured. Then the length from the posterior body line to the center of the Prodisc-C artificial disc on the lateral cervical X-ray was measured ([Fig. 3](#F3){ref-type="fig"}). But in this study, a modification was applied to the formula. 50% subtraction was not performed to estimate the insertion depth of Prodisc-C artificial disc from posterior vertebral margin. An insertion depth value of Prodisc-C artificial disc larger than 50% indicates that the disc location is anterior to the center of vertebral body and a smaller value than 50% indicates the location is posterior to the center of vertebral body. $$\frac{\textit{Disc\ center-posterior\ diameter,\ A}}{\textit{Vertebral\ body\ anterior-posterior\ diameter,\ B}} \times 100$$

There are many different reports to define normal cervical lordosis and postoperative kyphotic deformity. With each of the definitions, we tried to find out any statistically significant correlation between artificial disc insertion depth and postoperative kyphotic deformity.

At first, we introduced the definitions that Heary and Karimi[@B4] proposed. Postoperative kyphotic deformity was defined as a loss of the normal lordotic cervical curvature of at least 5 degrees per motion segment (C2-7). With reference to this definition, the patients were divided into 2 groups as those with postoperative kyphotic deformity or not. And their insertion depths of Prodisc-C artificial disc were analyzedstatistically to find difference of mean value.

Then we used the definition that Gore et al.[@B3] proposed as normal cervical lordosis. In men, C2-7 Cobb\'s angle more than 22° was defined as \'hyperlordotic\', C2-7 Cobb\'s angle less than 16° was defined as \'kyphotic\' and that between 16° and 22° was defined as \'lordotic\'. And in women, normal C2-7 Cobb\'s angle was from 15° to 25°, C2-7 Cobb\'s angle more than 25° was defined as \'hyperlordotic\', and C2-7 Cobb\'s angle less than 15° was defined as \'kyphotic\'. When a patient\'s postoperative C2-7 Cobb\'s angle changed from \'hyperlordotic\' to \'lordotic\', \'hyperlordotic\' to \'kyphotic\' or \'lordotic\' to \'kyphotic\', we hypothesized that the patient showed postoperative kyphotic deformity. We analyzed those with postoperative kyphotic deformity to find out any difference from others.

But the methods using the definitions that Gore et al.[@B3] pro posed can\'t distinguish those whose postoperative C2-7 Cobb\'s angle changes within the ranges of normal lordotic curve. So other concept of postoperative kyphotic deformity was introduced. When a patient\'spostoperative C2-7 Cobb\'s angle decreased more than 5% of preoperative C2-7 Cobb\'s angle, he/she was hypothesized to show postoperative kyphotic deformity and analyzed to search any correlation with artificial disc insertion depth.

Finally, pre- and post-operative segmental angles were evaluated. When a patient\'s postoperative segmental angle of operative level decreased more than 5% of preoperative one, we hypothesized that the patient showed postoperative kyphotic deformity. On the contrary, when postoperative segmental angle of operative level increased more than 5%, we assumed that the patient showed postoperative lordotic change. When the range of changes was within 5% of preoperative segmental angle of operative level, we hypothesized that the patient didn\'t show any deformity. These 3 groups were analyzed statistically with insertion depths of Prodisc-C artificial disc using ANOVA test.

Pre- and post-operative C2-7 Cobb\'s angles and segmental angles of operative level were measured with quantitative measurement analysis software, PACS workstation (Centricity 2.0; General Electric Medical Systems, Milwau- kee, WI, USA). This program uses extrapolative algorithms to calculate the intersecting angle between 2 lines drawn by the investigator.

1. Statistical analysis
-----------------------

Statistical analysis was performed to search the correlation between insertion depth of Prodisc-C artificial disc and postoperative kyphotic deformity, and to estimate insertion depth of Prodisc-C artificial disc to prevent postoperative kyphotic deformity. Analysis of variance (ANOVA) test with SPSS software for Windows (version 20.0; SPSS Inc., Chicago, IL, USA) was performed.

RESULTS
=======

Patients consisted of 31 men and 19 women, a ratio of 1.63: 1. Mean age was 48.84 years (range, 26-77 years). The mean duration of follow-up was 19.2 months (range, 9-28 months). Preoperative diagnosis included cervical herniated nucleus pulposus (41 patients), cervical spondylosis (8 patients), and foraminal stenosis (1 patient). The operated levels are as the following: C3/4 (3 patients), C4/5 (7 patients), C5/6 (29 patients), C6/7 (11 patients) ([Table 1](#T1){ref-type="table"}).

Mean disc insertion depth was 53.98%, ranging from 42.41 to 67.63%. An insertion depth value of Prodisc-C artificial disc larger than 50% indicates that the disc location is anterior to the center of vertebral body, and a smaller value than 50% indicates the location is posterior to the center of vertebral body, as mentioned above.

According to the definition that Heary and Karimi[@B4] proposed, fifteen patients were classified at the group with postoperative kyphotic deformity. And their mean disc insertion depth was 53.33%. But the mean disc insertion depth of the rest thirty-five patients was 54.26%. So the result of analysis didn\'t show any difference between the group with postoperative kyphotic deformity and the other group without postoperative kyphotic deformity ([Table 2](#T2){ref-type="table"}).

Gore et al.[@B3] proposed that a 16° to 22° cervical lordosis in men and a 15° to 25° cervical lordosis in women were normal. According to this definition, the patients were divided into three groups including \'hyperlordotic\', \'lordotic\' and \'kyphotic\'. And we analyzed those who were hypothesized as postoperative kyphotic deformity to search any correlation with insertion depths of Prodisc-C artificial disc. But the group with postoperative kyphotic deformity didn\'t show any statistical significant difference in insertion depths of Prodisc-C artificial disc from other groups ([Table 2](#T2){ref-type="table"}).

According to the concept that decrease more than 5% in postoperative C2-7 Cobb\'s angle is assumed as postoperative kyphotic deformity, twenty-six patients were classified as the group with postoperative kyphotic deformity. We analyzed them statistically to search any correlation with artificial disc insertion depth. But no significant difference was found from the others, either ([Table 2](#T2){ref-type="table"}).

Finally, the patients were classified into three groups according to the changes between preoperative and postoperative segmental angles. Mean artificial disc insertion depth of those who showed postoperative kyphotic deformity in segmental angle was 50.18±4.23%. And mean artificial disc insertion depth of those with postoperative lordotic change and those without postoperative deformity were 54.98±5.76% and 59.10±5.49%, respectively. Mean artificial disc insertion depth of the group with postoperative kyphotic deformity was smaller than that of the group with postoperative lordotic change or the group without postoperative deformity (p\<0.05,[Fig. 4](#F4){ref-type="fig"}). Positive correlation was found between artificial disc insertion depth and postoperative segmental angle (R=0.516, p\<0.001,[Fig. 5](#F5){ref-type="fig"}). These two results mean anterior located disc led to lordotic postoperative segmental angle and posterior located disc led to kyphotic segmental angle.

But the range of artificial disc insertion depth in the group with postoperative kyphotic deformity in segmental angle was not apart from that of the group with postoperative lordotic change ([Fig. 4](#F4){ref-type="fig"}). The confidence interval of the group with postoperative kyphotic deformity in segmental angle was from 47.63 to 52.75%, and that of the group with postoperative lordotic change was from 52.97 to 56.99%. Technically these two confidence intervals don\'t overlap. But it failed to estimate proper insertion depths of Prodisc-C artificial disc effective in preventing postoperative kyphotic deformity.

DISCUSSION
==========

As an alternative surgery to ACDF, TDR surgery has been an emerging procedure for cervical radiculopathy. Many authors have reported that TDR shows similar or better clinical outcomes[@B8],[@B10], or some advantages compared to ACDF[@B1]. However cervical TDR has several complications including postoperative kyphotic deformity. Xu et al.[@B12] reported 60% of their patients developed endplate kyphosis. Johnson et al.[@B5] found 80% of their single-level TDR patients with Bryan artificial disc developed endplate kyphosis.

Recently, several design limitations and contributing factors for postoperative kyphotic deformity were raised in the literature. Yoon et al.[@B14] reported that postoperative kyphoticdeformity after TDR with Bryan artificial disc was caused by several factors, including over-milling at the dorsal endplate, the insertion angle of Bryan artificial disc, structural absence of lordosis in the Bryan artificial disc, surgical procedure to remove the entire posterior longitudinal ligament, and pre-existing kyphosis. Cao et al.[@B2] reported over-milling or asymmetric milling of dorsal endplate influences on the disc insertion angle and leads to postoperative kyphotic deformity. Yi et al.[@B13] reported that toprevent postoperative kyphotic deformity after TDR with Bryan artificial disc, intentional modificationin disc insertion angle and depth would be helpful.

But Prodisc-C artificial disc is more sensitive to the surgical location of device than Bryan artificial disc, because Prodisc-C artificial disc has fixed center of rotation (COR) but Bryan artificial disc has variable COR. So Prodisc-C artificial disc needs to be confirmed about the correlation between the insertion depth of artificial disc and postoperative kyphotic deformity.

This study was focused to investigate the correlation between insertion depth of Prodisc-C artificial disc and postoperative kyphotic deformity, and the range of artificial disc insertion depth effective in preventing postoperative kyphotic deformity.

Postoperative segmental angle of operated level showed positive correlation with insertion depth ofProdisc-C artificial disc, but postoperative C2-7 angle didn\'t show any correlation with insertion depth of Prodisc-C artificial disc.

The group with postoperative segmental kyphosis had smaller insertion depth of Prodisc-C artificial disc compared to others. But when patients were classified into postoperative C2-7 kyphosis group according to several definitions of cervical kyphosis, none of them showed any statistical difference in insertion depth of Prodisc-C artificial disc. This result was similar to that of Yi et al.[@B13] reported.

There are some literatures that postoperative kyphotic deformity isn\'t associated with clinical outcomes[@B6]. But once kyphosis has developed, axial loads tend to cause further kyphosis, thus initiating a vicious cycle and progression of the deformity. And cervical kyphosis tends to developan associated neurological deficit or chronic neck pain[@B11]. So postoperative kyphotic deformity is undesirable condition and should be avoided after TDR surgery.

There are some weaknesses in this study. First of all, other factors that may influence postoperative kyphotic deformity weren\'t controlled enough. For example, overmilling of dorsal endplate is one of the most important factors that can induce postoperative kyphotic deformity[@B2],[@B14]. But as a rule, we keel the dorsal endplate before the insertion of Prodisc-C artificial disc, not mill. And the number of cases wasn\'t enough to subdivide according to the degrees of milling. So whether milling was performed or not and the degrees of milling weren\'t included as variables. This uncontrolled factor may lead to the unproven correlation of postoperative C2-7 kyphotic deformity and insertion depth of Prodisc-C artificial disc. And the definitions of normal cervical lordosis and postoperative kyphotic deformity need more research. Third, many patients have been lost in outpatient follow-up and the periods of evaluating postoperative kyphotic deformity are irregular. If postoperative kyphotic deformity proceeds in course of time after surgery, it needs to be controlled, too. Clinical outcomes after surgery weren\'t evaluated or analyzed according to the degree of postoperative kyphotic deformity.

CONCLUSION
==========

Postoperative segmental kyphotic deformity was associated-with insertion depth of Prodisc-C artificial disc. Anterior located artificial disc leads to lordotic segmental angle and posterior located artificial disc leads to kyphotic segmental angle postoperatively. But C2-7 Cobb\'s angle is not affected by artificial disc location after surgery. Further study with compensating weak points is required.

![C2-7 Cobb\'s angle.](kjs-9-147-g001){#F1}

![Segmental angle.](kjs-9-147-g002){#F2}

![Insertion depth of an Prodisc-C artificial disc. \"**A**\" indicates the length from the posterior body line to the center of the Prodisc-C artificial disc. \"**B**\" indicates the length from the line connecting the posterior corner of superior and inferior vertebral bodies to the line connecting anteriorcorner of superior and inferior vertebral bodies at the operated disc level.](kjs-9-147-g003){#F3}

![Comparison of mean disc insertion depth between the group with postoperative kyphotic deformity, the group with postoperative lordotic change and the group with no deformity in segmental angle.](kjs-9-147-g004){#F4}

![Scatter diagram of artificial disc insertion depth and postoperative segmental angle (R=0.516, p\<0.001).](kjs-9-147-g005){#F5}

###### Demographics

![](kjs-9-147-i001)

HNP: herniated nucleus pulposus

###### Mean disc insertion depth between the group with postoperative kyphotic deformity and the group without deformity

![](kjs-9-147-i002)

^\*^According to the definition that Gore et al.[@B3] proposed, the patients were classified into three groups including \'hyperlordotic\', \'lordotic\' and \'kyphotic\'.