Low back pain is most often defined as pain between the rib cage and the lower fold of the buttocks, which can (but does not have to) spread to the legs (1). If this pain is caused by a specific pathophysiological mechanism, we speak of specific low back pain. However, in cases where we are talking about pain without a clear nociceptive-specific cause and no indication for further interventions (apart from the conservative treatment method) (2), that is the case of non-specific low back pain (3). If low back pain lasts up to 12 weeks, it falls into the category of chronic low back pain. (1)

The greatest non-pharmacologically proven effect on non-specific chronic low back pain, according to several studies, is shown with the use of kinesiotherapy (4, 5) such as the McKenzie method (6) or dynamic neuromuscular stabilization (7) and hydrotherapy (8). Mineral mud (MM), a peloid used as a form of balneotherapy, was mainly used in previously conducted research to show the effect of mud on specific joints, e.g. the knee (9) or small joints of the hands (10) as well as to show its effect on specific conditions such as fibromyalgia (11, 12) or seronegative spondyloarthritis (13).

The term balneotherapy originates from the Latin words “balneum” and “logos” (literally translated, the science of bathing), and is most often defined as the science of natural thermal mineral waters (14). Balneotherapy also includes treatment using natural water sources, thermal/mineral springs, as well as the methods of using said waters, which also includes mineral mud (MM) (14). Thermal mineral waters are natural waters that contain over 1 g of mineral substances and/or gases in one liter of water, which are not regularly found (or are significantly less present) in “normal” water and that have a temperature above 20°C at the source (15). The effects of thermal mineral waters are divided into mechanical, chemical and thermal, all of which lead to changes in the physiological reactions of the body (16). The thermal mineral waters at “Daruvarske toplice” show excellent balneological properties (17) and have been used since Roman times as a form of hydrotherapy, but also as peloid therapy, or mud enriched with thermal mineral water. The analysis showed that, according to their composition, the above-mentioned springs in Daruvar contain a mixed type of geothermal waters: CaMgNa-HCO3 (calcium, magnesium, sodium-hydrogen carbonate type of water). The measured water temperature ranges from 24.6°C to 47.1°C. The above mentioned values show that these are geothermal waters, due to the fact that their temperature is significantly higher than the average annual temperature of the area used for the replenishment of springs, wells and shafts. In addition to that, it is possible to analyze and classify these waters as mineral waters because their total dissolved solids range is in concentrations between 0.92 and 1.9 g/l (17). Even though each thermal mineral water is specific and it is difficult to objectively compare the effects of individual peloid therapies used in other regions, several studies have shown the positive effect of treating patients suffering from non-specific low back pain with peloid therapy (18, 19), and they also proved that peloid therapy has a better effect on the patients’ condition in comparison to kinesiotherapy and/or hydrotherapy (20, 21). Several review articles have highlighted the need for further research to be conducted on this topic, given that some studies have not shown a significant effect of balneotherapy (22, 23). Chronic non-specific low back pain is a major public health issue (1) and its pharmacological treatment is based primarily on the use of nonsteroidal anti-inflammatory drugs (NSAIDs) (24) combined with numerous non-pharmacological modalities such as the use of pain relief creams (25) and massages (26) with the ultimate result of pain reduction and mobility improvement.

One of the forms of non-pharmacological treatment is certainly the mineral mud (MM) treatment, which is still considered controversial and insufficiently researched.

This prospective randomized study included 64 subjects (40 women and 24 men) who were divided into two treatment groups.

The first group, which consisted of thirty-one patients, received kinesiotherapy treatment five times a week, hydrotherapy twice a week, and mineral mud from Daruvar was applied to the patients’ lumbar spine three times a week. The control group, which consisted of 33 patients, received kinesiotherapy treatment and hydrotherapy five times a week. All treatments were carried out in accordance with the previously established criteria (hydrotherapy and kinesiotherapy treatment in the duration of 20 minutes with standardized trunk stretching and stabilization exercises and the application of peloid wraps in the duration of 30 minutes) during the course of three weeks. Out of the total number of patients, 37 of them were 55 years old or older, and 27 of them were younger than 55.

The study was conducted at the Special Hospital for Medical Rehabilitation “Daruvarske toplice” in accordance with the 1967 Helsinki Convention and its subsequent amendments, as well as the principles of good clinical practice. All subjects have signed an informed consent before participating in the study, and were previously informed in detail about the study itself, its objectives and risks. The approval for this study was granted by the Ethics Committee of Daruvarske toplice at a meeting held on March 9th, 2021. The inclusion criterion was chronic non-specific/mechanical low back pain (27). Patients with febrile conditions of any type of cause, patients with previous lumbar spine or hip surgery, patients with neurological diseases and conditions that could interfere with the study and consequently affect its results, as well as those who could not follow the study protocol for any somatic or psychosocial reason were excluded from the study.

During the course of the treatment, only paracetamol (1 to 2 tablets of 500 mg, for a maximum of 2 days) could be used as an analgesic. It was not allowed to use this drug on the first day and one day after the last treatment, as evaluation was being conducted at that time.

On the first day of treatment and one day after the last intervention, the patients completed the EQ-5D-5L, a validated questionnaire for assessing the quality of life with domains of mobility, self-care, usual activities, pain and anxiety/depression (28); the Rolland-Morris Questionnaire (RMDQ) as a standardized instrument of functional capacity in patients with low back pain (29) and the ClinFit questionnaire for classifying patient functioning, disability and health in daily activities using a set of 30 questions, ranked on a scale of 1 – 10 (30).

As measures of spinal mobility, we used the Thomayer’s fingertip-to-floor distance test at maximum inclination of the trunk and arms extended towards the floor (31), the modified Schober’s test as a standard measure of sagittal mobility for the lumbar spine (32), and the measure of spinal lateroflexion, expressed in centimeters (with one decimal place for millimeters). A tailor’s tape measure was used for performing all length measurements. When testing lateroflexion, the subject stands upright with his legs together, flexes the trunk to one side and then to the other, sliding the outstretched palm along the body (leg), and then the distance is measured between the tip of the middle finger and the floor (33).

All measurements were performed by two physical medicine and rehabilitation specialists (DK and AK) who took turns at performing each measurement, and the data for each individual measure were recorded in separate sections of the questionnaire, without any insight into previous measurements. The measurements were always performed in the same room and at the same time of day. The first measurement was performed immediately before the first treatment and the final measurement was performed one day after the last treatment.

The exploratory data analysis included standard measures of central tendency and variability for numerical data. The Shapiro-Wilk test was used to test for normal distribution of data. In accordance with that, the dependent Student’s t-test was used to test the differences in pre- and post-treatment scores for normally distributed data and the dependent Wilcoxon signed-rank test was used for non-normally distributed data. Univariate and multivariate ANOVA methods were then performed to examine whether delta score changes were significantly related to age (patients < 55 years of age and patients ≥ 55 years of age), sex (male and female), and type of treatment (additional MM treatment). Correlations between variables were analyzed using Spearman’s correlation tests with Bonferroni correction of p-values for multiple cross-comparisons. All tests had a significance level set at < 0.05. The R Statistical Software (v4.1.2; R Core Team 2021) was used for exploratory and statistical data analysis (34).

All subjects had significantly different results after the intervention in all monitored parameters (variables) and the results have significantly improved (Table 1). The largest difference was observed in the values of EQ-5D-5L variables VAS scores, ClinFit questionnaire and Thomayer’s test (Table 1). Univariate analysis showed that the MM treatment was significantly associated with left lateroflexion (p = 0.046), the age of patients was associated with VAS pain (p = 0.01) and gender was associated with Schober’s test (p < 0.05). After including the variables of age and sex in the multivariate analysis, the type of treatment (MM) was still significantly associated with delta changes in left lateroflexion measures (p < 0.01), but also with significant differences in Thomayer’s test (p < 0.01) and RMDQ questionnaire (p = 0.01) (Table 2).

When sex and treatment type were included in the analysis as constant variables, multivariate analysis found an association between age and delta changes in VAS pain scores (p = 0.03), with better results in individuals under 55 years of age (Table 2). When age and treatment type were included in the analysis as constant variables, sex was found to be associated with left (p < 0.01) and right lateroflexion (p < 0.01) and Schober’s test (p = 0.049), with better results in the male population (Table 2). All correlations were mild to moderate in strength (Figure 1).

Significant negative correlations were observed between EQ-5D-5L VAS health with ClinFit (p < 0.0001), DASS 21 (p < 0.0001), EQ-5D-5L activity (p < 0.0024), VAS pain (p < 0.0001), and EQ-5D-5L pain (p < 0.0001), while there were 14 significant positive correlations (Figure 1). Age, Schober’s, and Thomayer’s test were the only variables that did not correlate with any other variable (Figure 1).

Due to the significantly better statistical results of the left lateroflexion variables, Thomayer’s test, and RMDQ questionnaire in the group treated with MM, this study demonstrated greater effectiveness in the treatment of chronic non-specific low back pain with the application of peloid wraps in comparison to hydrotherapy and kinesiotherapy treatments. Through the use of univariate analysis of variance, the only significant difference found was increased left lateroflexion in the group treated with MM therapy, which could be explained by the predominantly unilateral mechanical low back pain which was present in the majority of subjects. However, we did not examine the specific side on which the lumbar pain was present (predominantly present on the left or right side). In addition to the lateroflexion, multivariate analysis confirmed a significant difference in the RMDQ questionnaire and Thomayer’s test results (Table 2), indicating that patients treated with MM therapy also experienced more ease in the performance of their daily activities as well as greater mobility due to increased range of motion in the lumbar spine.

Multivariate analysis also revealed interesting data: the results have shown a significant reduction of pain in the younger population, as well as an increased range of motion in the male population (Table 2). We were not able to find these data in literature to date, but we can associate them with a better recovery of the younger patients and potentially more persistent exercise in the male population.

Although there are numerous studies that question the superiority of hydrotherapy over kinesiotherapy (22, 23, 35), the use of mineral waters as a form of conservative treatment for patients with chronic low back pain has been confirmed in several studies (8, 21). The advantage of their use over kinesiotherapy has also been confirmed, whether it be the case of additional hydrotherapy (36, 37) or the use of MM peloid treatment (18, 38). In addition to improved mobility and pain reduction, studies on the effectiveness of hydrotherapy and MM therapy have also looked at other variables such as maximal oxygen uptake (VO₂ max) and percentage of body fat (39, 40).

In some studies, variables such as VAS pain, RMDQ questionnaire and Schober’s test (41, 42) are used as indicators of effectiveness, but so far, we have not found any studies that include all the variables used in our study, which relate to lumbar spine mobility, functional status and patients’ daily activities. By comparing our research with research performed in previously conducted studies, we can conclude that most studies (18, 40-42) confirm facilitated lumbar spine mobility after therapy.

We were able to confirm the expected results of the study with correlation analysis. Negative correlations were in line with the assumptions: in cases where there is a higher level of health (observed in the VAS pain and EQ-5D-5L questionnaire scores) there is a decrease in pain (monitored through the use of the VAS pain and EQ-5D-5L pain methods) (Figure 1). Positive correlations indicated that a better level of health leads to greater activity (EQ-5D-5L questionnaire) and better daily functioning (RMDQ questionnaire) (Figure 1). Interestingly enough, lumbar spine mobility tests (Thomayer’s and Schober’s test) and age did not correlate with any other variable (Figure 1), although we expected a correlation with the VAS pain variable, for example.

The causes of non-specific low back pain are mainly mechanical in nature (43, 44), which was one of the reasons why we expected that an increase in mobility would significantly affect other variables. Working and socioeconomic conditions, whose influence on low back pain symptoms is possible but still debatable (1), were not the subject of this study. A shortcoming of this study is the inability to compare these treatment methods with a peloid of the same composition, as each thermal mineral water is unique, making it difficult to compare its chemical effects. Another limitation of this study could also be the small number of subjects (n=64), as well as the lack of the patients’ health status follow-up after treatment (e.g. after 6 months), which would allow for an assessment of the long-term effectiveness of the treatment to be performed.

In this study, measures of lumbar spine mobility (lateroflexion, Thomayer’s test) and functional abilities (RMDQ) showed significant improvement after three weeks of therapy (in comparison to baseline values) in the group of patients additionally treated with peloids in comparison to the control group that only received standard hydrotherapy and kinesiotherapy treatments. Additional studies with a larger number of subjects and long-term follow-up are needed in order to assess the long-term effectiveness of the treatment. Based on new findings, it is possible to give recommendations for physical therapy treatments in patients with chronic non-specific low back pain.

Author Contributions: Responsible for the concept: all authors; responsible for the methodology: D.K., A.K.; responsible for the formal analysis: D.K., V.M.R., E.R., D.S.; responsible for conducting research: D.K., A.K.; responsible for the preparation of the original text: D.K., A.K., D.S.; responsible for writing the first version of the text (draft): D.K.; responsible for the editing and revision: all authors.