Lumbar Degenerative spondylolisthesis (LDS) is a common spinal disease in middle age and older adults with a prevalence of 4% in the general population (1). Most of the cases with LDS are asymptomatic and fortunately, and most of the symptomatic patients respond favorably to routine conservative treatment including drugs, physiotherapy, and lifestyle modification (2). In few cases, clinical complaints remain refractory or neurologic deficit appears and these peculiar cases finally need surgery (3, 4).
Meyerding classification is an old, popular, and still, practical classification proposed to categorize lumbar spondylolisthesis based on the severity of vertebral slippage (5). This classification has 5 types; every 25% of vertebral slippage over the adjacent below vertebra gets one type and in type 5, vertebral spondyloptosis occurs. The major disadvantage of this classification in LDS is its inability to classify the disease into different groups and most cases are placed in type 1 or rarely 2. Another limitation is that other radiologic parameters (such as kyphosis and disc height) as well as clinical characteristics are not considered (6). In 2015, a new classification called Clinical and Radiographic Degenerative Spondylolisthesis (CARD classification) was introduced to address these limitations (7). If different types of LDS in CARD classification could show different clinical features and responses to treatment, then CARD classification can be more effective and helpful in clinical practice. This study aims to investigate the clinical significance of CARD classification based on clinical outcomes of the disease using valid questionnaires and assessment methods.
 

At the beginning of the study, 60 patients met the study criteria, but during the study, nine patients could not be followed-up and two died during this period. Finally, 49 patients were fully evaluated, 11 patients (22.4%) male and 38 female (77.6%). The mean age of the patients was 56.8 ± 9.8 (range: 33 to 76 years old). Body mass index (BMI) was normal only in 26.2% of the patients. The mean follow-up period was 40.5±6.8 months (range: 26 -72 months). Demographic characteristics are summarized in Table 1.

Table 1. Demographic variables in the study

Table 2 shows the age and BMI in different types; the age distribution between the types was not statistically significant, although the oldest patients were more commonly placed in type A. Table 2 shows the severity of pain (in both leg and back) and disability in preoperative, postoperative, and the amount of improvement with surgery. Although based on the paired t-test, surgery in all types of LDS could dramatically improve both pain and disability, no significant difference was observed between the types.
The mean BMI had a significant difference across types; patients in type C had a significantly higher BMI than those in types D and A. Gender distribution was similar across the four types (Figure 1).

Table 2. variables in each type

^aKruskal-Wallis test.

  Figure 1. Body Mass Index (BMI) in different types of LDS

To investigate the effect of kyphotic alignment on clinical behavior, we also placed our patients into two groups; kyphotic (type D) and non-kyphotic (types A, B, and C) and compared them with each other (Table 3). Again, we could find no difference.
 

Discussion

One of the issues complicating research on LDS is the lack of a standard to classify the patients into subgroups. There are currently several classification systems for LDS that need further evaluation (5, 7, 11-13). CARDS classification system has been favored due to its ease of use and accuracy. In this study, we tried to examine the outcome of the patients after surgery based on CARDS classification. Generally speaking, this disease is more common in women (2-3:1, female: male) which is related more to hormonal issues and ligamentous laxity (14). Most of the patients in Kung's, Sobol's, and ours were women, but it was only in Chen's study that the number of men was higher (6, 15, 16).
LDS is a disease of old age. Its incidence increases in both sexes with age (1, 14, 17). More than 70% of the patients in our study were middle-aged and older, and type A group had the oldest patients. The mean age of Kung et al.'s study was 62 years old, and type D was the oldest (15).
In the study we carried out, BMI was significantly different across the types and BMI in type C was significantly higher than that in type A and D. The highest BMI in our study was present in type C. The highest BMI in Kung et al.'s and Sobol et al.'s studies were observed in type B and type D, respectively (6, 15), which did not show any significant difference with other types in these two studies. Rihn et al.'s study sought to answer the question of whether obesity affects the outcome of treatment for spondylolisthesis and spinal stenosis (18). They concluded that BMI had no significant effect on the clinical outcome following surgery for lumbar stenosis. Obese patients undergoing surgery experience a higher rate of wound infection, and their reoperation rate is twice higher than non-obese patients in a 4-year follow-up study. Obese patients who did not undergo surgery and were just treated conservatively had worse clinical outcomes than non-obese patients.
In our study, type B had the highest prevalence across different types of LDS and type A had the lowest, while in both Kung et al.'s and Sobol et al.'s studies, type C had the highest and type A had the lowest (6, 15).
Although it was shown that CARDS type D has more segmental instability relative to other types, its relationship with clinical behavior is not clear. It was proposed that in the kyphotic group, the turgor pressure of the disc is reduced due to insufficient support of the anterior column, thereby impairing the disc's ability to withstand anterior shear forces, resulting in a much larger instability (19). In our study, the pain in the leg and back was reduced significantly after surgery, and disability improved significantly by the operation but this improvement in pain and disability did not differ across types of LDS; also, kyphotic alignment had no clinical effect. Contrary to our study, Sobol et al. and Kong et al. in two separate retrospective studies on their operated patients with L4-L5 LDS found that the patients with kyphotic alignment (type D) had worse preoperative back pain and a more favorable response to the surgical treatment in compared with a non-kyphotic group (6, 15). Similar to these two studies, Chen et al. reviewed their patients with LDS operated with transforaminal lumbar interbody fusion and placed them into two groups: kyphotic and non-kyphotic (20). They also found that the patients with kyphotic alignment not only have more dynamic instability and worse preoperative disability and pain but also achieve more clinical improvement with surgical treatment. 
This study had several limitations. With a retrospective design and a small sample size, the statistical significance of this study may not guarantee the clinical consequence. The minimum clinically important difference (MCID) is the smallest improvement that is valued by the patient, but this improvement may not be statistically significant in this study. The results of this study were reported using VAS, ODI and no other external criteria were used as dependent variables. We could not obtain a valid MCID due to the lack of a suitable dependent variable. We did not take account of the sagittal balance, which might alter the surgical outcome, although this is not proven for low-grade spondylolisthesis. All of these factors may be biased in this study. Also, our results do not fully represent all patients with spondylolisthesis because only patients referred to one hospital were evaluated. Due to the discrepancy found in our study with similar studies, more research is needed in this area with larger sample size.

 

Conclusion

In conclusion, surgical treatment of LDS could significantly improve both pain and disability in all different types of the disease, but this improvement was not significantly different across radiographic types. It seems that here, like other areas of the spine, no significant relationship exists between the clinical and radiological characteristics.

 

Acknowledgements

This study was supported by Students Research Center of Mashhad University of Medical Sciences, Mashhad, Iran. All authors have nothing to declare.

 

Funding

This work was supported by Students Research Center of Mashhad University of Medical Sciences, Mashhad, Iran [grant NO. 980443].

 

Conflicts of Interest

The authors declared no potential conflict of interests relevant to this article.