COMPARISON OF THE RESULTS OF MIS-TLIF AND OPEN TLIF TECHNIQUES IN LABORERS

Objective: To compare clinical outcomes in laborers who have undergone open transforaminal interbody fusion (TLIF) and minimally invasive transforaminal interbody fusion (MIS TLIF). Methods: 78 patients were submitted to lumbar arthrodesis by the same two spine surgeons partners from January 2008 to December 2012. Forty-one were submitted to traditional open arthrodesis and 37 to the minimally invasive procedure. Three patients were not included because they had already retired from work. The analyzed variables were length of hospitalization, length of follow-up, type of access (TILF or MIS TLIF), need for blood transfusion, percentage of improvement or worsening after surgery, pre- and postoperative VAS scale, time off work, pre-and postoperative Oswestry disability index, and general aspects of the laborers such as age, education, profession, working time, amount of daily weight carried at work, and use or not of personal protective equipment. Results: Time off work was longer in the TLIF group (average of 9.84 months) compared with the MIS TLIF group (average of 3.20 months). Significant improvement in postoperative VAS and Oswestry was achieved in both groups. Average length of hospitalization was 5.73 days for the TLIF group and 2.76 days for the MIS TLIF group. Conclusions: Minimally invasive transforaminal lumbar interbody fusion presents similar results when compared to open TLIF, but has the benefits of less postoperative morbidity, shorter hospitalization times, and faster rehabilitation in laborer patients. hospitalaria Conclusiones: La fusión transforaminal mínimamente invasiva muestra resultados a la hospitalaria y retrospective, descriptive study with 78 patients submitted to transforaminal lumbar arthrodesis by the same pair of spine da Serra de Horizonte, in in the period from January 2008 to December 2012. This approval from the Ethics Committee of our Institution. The inclusion criteria were laborers submitted to lumbar arthrodesis by the TLIF technique, whether traditional open or minimally invasive. (We define minimally invasive arthrodesis as a procedure performed using a tubular retractor followed by percutaneous pedicle screw fixation). The inclusion criteria for laborers were: those engaged in pro-fessional activities that mainly use the upper and/or lower limbs, with a total daily weight lifted of more than 35 kg. were divided into two groups: kg lifted/day, and more than 50 kg lifted/day. the keywords: TLIF, laborer, invasive surgery, open


INtrODUctION
Spinal diseases correspond to approximately 30 cases of retirement out of every 100 thousand people receiving social welfare benefits, as well as being among the main causes of medical leave.¹ The way to lift objects and the laborer's mass related to the mass of the object should be observed to prevent damage to the spine. The International Labour Organization (ILO-1988) recommends that in activities that involve lifting a total weight of more than 55 kg, steps must be taken to reduce it. It is observed that back problems among Brazilian laborers who handle heavy loads represent approximately 70% of cases.¹ According to the specialized literature, incorrect handling and manual movement of loads are the most frequent cause of occupational accidents involving individuals.¹ Brazil is a country that invests very little in the prevention of accidents at work. According to Silva et al. 2 the majority of accidents are due to poor working conditions, where the laborer's own body is the work tool.
Lumbar arthrodesis has been widely used for different pathological conditions of the spine resulting from degeneration, trauma or neoplasm. Reports from the beginning of the last century have described lumbar arthrodesis, whether by the anterior (ALIF, by Capener 3 in 1932) or posterior (PLIF, by Cloward 4 in 1953) routes. Following on from those ideas, transforaminal lumbar interbody fusion (TLIF), which uses a less invasive approach by the posterior unilateral route, was perfected and popularized by Harms and Jeszensky. 5 Since 1991, when Obenchain 6 described the first laparoscopic lumbar discectomy, the field of minimally invasive surgery of the spine has continued to evolve. Surgeons and patients have been attracted by the advantages of minimally invasive surgery, such as the fact that it causes less tissue trauma during the surgical approach, less postoperative pain, shorter hospitalization times, and a faster return to daily activities. [7][8][9][10] There are no comparative studies in the literature on the results of minimally invasive arthrodesis and open arthrodesis in the Brazilian population of laborers. This study therefore compares these techniques in this specific population.

MAtErIALs AND MEtHODs
This is a retrospective, descriptive study with 78 patients submitted to transforaminal lumbar arthrodesis by the same pair of spine surgeons at Hospital Lifecenter, Hospital Santa Rita and Hospital Vila da Serra de Belo Horizonte, in Minas Gerais, in the period from January 2008 to December 2012. This study gained approval from the Ethics Committee of our Institution.
The inclusion criteria were laborers submitted to lumbar arthrodesis by the TLIF technique, whether traditional open or minimally invasive. (We define minimally invasive arthrodesis as a procedure performed using a tubular retractor followed by percutaneous pedicle screw fixation).
The inclusion criteria for laborers were: those engaged in professional activities that mainly use the upper and/or lower limbs, associated with a total daily weight lifted of more than 35 kg. The patients were divided into two groups: 35 to 50 kg lifted/day, and more than 50 kg lifted/day. Patients who had already retired were not included in the research.
Searches were carried out in the Pubmed, Bireme, and Scielo databases, using the keywords: TLIF, laborer, minimally invasive surgery, open transforaminal versus minimally invasive arthrodesis.
Questionnaires were applied to all the patients, laborers who had undergone minimally invasive or open TLIF. All the patients signed an informed consent form and were in agreement with the research.
To compare the variables raised in the research for the groups "Open surgery" (OS) and "Minimally invasive surgery" (MIS), the Mann-Whitney test was used for the quantitative variables, and the Chi-square test (replaced by Fisher's exact test where necessary) for the qualitative variables.
To determine the difference in the VAS and Oswestry scores be-tween preoperative and postoperative values, the Wilcoxon signed--rank test was used.
To determine the correlation of the VAS and Oswestry scores with follow-up time, Spearman's correlation coefficient (measure of correlation limited between 1 and -1) was used. The closer the coefficient is to -1, the greater the negative correlation. The closer the coefficient is to 1, the greater the positive correlation. A level of significance of 5% was used. The software used in the analysis was R version 2.15.2.

rEsULts
The patients in this study were mostly industrial workers (18 patients) -an industrial assembler and industrial cooks. The remaining patients were: mechanics (16), electricians (12), truck drivers (7), fire fighters (6) and police officers (6), among other professions, including: personal trainer, textile factory worker, and drinks deliverer.
The average age of the workers who underwent OS was 48.29 years, while the average age of those who underwent MIS was 42.27 years. (Table 1) To compare the groups that underwent the different types of surgery through the quantitative variables, the Mann-Whitney test was used. (Table 1 and Figure 1) Thus, it can be seen that there was a significant difference in hospitalization times of patients between the types of surgery; the OS group tended to present longer hospitalization times than the MIS group. In the OS group, at least 50% of the patients had a hospitalization time of five days or less, while in the MIS group, at least 50% of the patients had a hospitalization time of three days or less.
There was significant difference in return to work time of patients between the surgery types; the OS patients tended to present longer times than the MIS patients. In the MIS group, at least 50% of the patients returned to work in 2.5 months or less, while in the OS group, at least 50% of the patients returned to work in 7 months or less. To compare groups by type of surgery through the qualitative variables, the Chi-square test was used, and where necessary, Fisher's exact test. Thus, it can be seen in Table 2 and Figure 2 that: there was a significant association between the variable blood transfusion and the type of surgery performed. Only patients in the OS group received blood transfusions (39.5%).  Variable use of personal protective equipment (PPE): it was found that of the total number of patients, 56.4% had used PPE while 43.6% had not. In the OS group, 56.1% of patients had used PPE, while 43.9% had not. In the MIS group, 70.3% of the patients had used PPE, while 29.7% had not.
The Wilcoxon test was used to determine whether there was any significant difference between the pain scales before and after surgery. (Table 3 and Figure 3) It was observed that the postoperative VAS score was significantly lower than the preoperative VAS score (less than 50% of individuals had a decrease of up to seven points in the VAS score).
The postoperative Oswestry score was significantly lower than the preoperative Oswestry score (less than 50% of individuals decreased by up to 30 points).
To determine whether there was any significant difference between the pain scales before and after surgical intervention, stratified by type of surgery, the Wilcoxon test was used again (Table 4 and Figure 4), with no statistical difference being observed between the improvement in preoperative and postoperative VAS scores for the two types of surgery.
In terms of Oswestry score, the MIS group showed a greater decrease in the postoperative period than the OS group (p-value < 0.001). In the OS group, at least 50% of the patients showed a decrease of 14 points in the postoperative period, while in the MIS group, at least 50% of the patients showed a decrease of 52 points.
Spearman's correlation test was used to determine whether there were any correlations between the preoperative and postoperative Oswestry scores for each type of surgery with the variable follow-up time. (Table 5) We also found a significant negative correlation between postoperative Oswestry score and follow-up time in the patients who underwent minimally invasive surgery. In other words, in these patients, the longer the follow-up time, the lower the postoperative Oswestry score.

DIscUssION
Lumbar arthrodesis surgery is associated with extensive dissection of the soft tissues, and several authors have reported the negative consequences of this procedure, with a significant increase in morbidity. 11 Because MIS-TLIF involves parasagittal access between the multifidus and the longissi mus (erector spinae), it preserves the natural posterior tension band created by the inter-and supraespinous ligaments, as well as the insertion, vascularization and innervation of the paravertebral musculature. [12][13][14] Transforaminal access, whether open or minimally invasive, promotes complete exposure of the posterolateral aspect of the intervertebral disc, requiring minimal retraction of nerve roots and dural sac in order to perform the intersomatic arthrodesis, and the insertion of an intersomatic spacer. [15][16][17] The retractors are used merely as protectors during the proper preparation of the intersomatic space and insertion of the bone graft and spacer. The separation of tissues is therefore unilateral and minimal, significantly reducing the risk of neural injury caused by traction and manipulation. 18 The percutaneous screws also ensure that the soft parts of the layers adjacent to the operated layer remain intact, preventing the occurrence of a proximal iatrogenic instability. 19 In this study, another clear advantage of MIS-TLIF was the reduction of intraoperative bleeding when compared to open TLIF. Substantial blood loss is frequently reported in the literature in association with open arthrodesis. This reduction in bleeding observed in MIS virtually does away with the need for blood transfusion and its associated risks. Both groups achieved an improvement in VAS and Oswestry scores. It was expected that the groups would maintain this relationship of equivalence, demonstrating the benefits of transforaminal arthrodesis, whether by the open or minimally invasive route. 20 However, as already described by several authors, the immediate benefits of a significant reduction in surgical morbidity justify the use of the minimally invasive technique, which proved       showed similar results to those of the present study, with two years of follow-up. However, the author also noted that with four years of follow-up, the patients of the MIS group tended to continue to show lower scores, while the OS group tended to show an increase in VAS and Oswestry scores. The average time to return to work was 9.84 months for the OS group and 3.20 months for the MIS group.
A longer learning curve and adequate training are essential for the safe development of this technique. Unlike traditional open access routes, minimally invasive surgeries are limited to the area of surgical interest, exposing only the anatomical points of interest, in a guided field of vision. [22][23][24][25][26] Familiarity with the procedure enables the surgeon to perform the surgery safely, without having to expose anatomical structures not involved in the procedure. 27 cONcLUsIONs There are major benefits of MIS-TLIF when compared to open TLIF in laborers. The patients who underwent open TLIF tended to present longer hospitalization times than those who underwent MIS-TLIF, and needed longer time to return to work. In addition, they were more likely to require a blood transfusion, which was not observed in the patients who underwent MIS-TLIF.
Both groups showed an improvement in pre-and postoperative scores, with a tendency to better results in the MIS group.
Prospective studies with long follow-up times are still needed to better establish the comparison between the techniques.