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- Eur Spine J
- v.14(6); 2005 Aug
- PMC3489231
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Eur Spine J. 2005 Aug; 14(6): 546–550.
Published online 2005 Jan 25. doi:10.1007/s00586-004-0824-z
PMCID: PMC3489231
PMID: 15668775
S. Shabat,
1,3,3 T. Gefen,1 M. Nyska,1 Y. Folman,2 and R. Gepstein1
Author information Article notes Copyright and License information PMC Disclaimer
Abstract
The prevalence and incidence of low back pain in general society is high. Workers whose job involves walking long distances have an even higher tendency to suffer from low back pain. A positive effect of insoles in reducing low back pain was found in professional sports players. This was not examined on people whose job involves walking long distances. In this double blind prospective study we examined the effectiveness of insoles constructed in a computerized method to placebo insoles in 58 employees whose work entailed extensive walking and who suffered from low back pain. The evaluation was performed by the MILLION questionnaire, which is considered as a valid questionnaire for evaluation of low back pain. We calculated the differences of the pain intensity before and after the intervention, in the employees using the insoles manufactured by computer in comparison to the users of the placebo insoles. In each group, the analysis was performed in comparison to the baseline. A total of 81% of the employees preferred the real insoles as effective and comfortable in comparison to 19% of the users of the placebo insoles (P<0.05). The results of this study indicate a substantial improvement in the low back pain after the use of the true insoles. The average pain intensity according to the MILLION questionnaire before the use of the insoles was 5.46. However, after the use of the real insoles and the placebo insoles, the average pain intensity decreased to 3.96 and 5.11, respectively. The difference of the average pain intensity at the start of the study and after the use of the real insoles was significant: −1.49 (P=0.0001), whereas this difference after the use of the placebo insoles was not significant: −0.31 (P=0.1189). The reported severity of pain also decreased significantly: a level 5 pain and above was reported by 77% of the subjects at the start of the study. After the use of the real insoles only 37.9% of the subjects reported a similar degree of pain severity, and 50% of the subjects did so after the use of the placebo insoles (P< 0.05). We did not find a link between low back pain and other variables such as gender, age, number of offspring, work seniority, smoking, previous use of insoles and previous medication. This study demonstrates that the low back pain decreased significantly after the use of real insoles compared to placebo ones.
Keywords: Low back pain, Workers, Insoles, Long distance walking
Introduction
The prevalence of low back pain in the general population is estimated to be between 60 and 80% [28]. Low back pain is considered to be the second complaint of patients arriving to their primary care physician, only following upper respiratory tract infection [7], and is one of the most common causes that every occupational physician faces each day in his/her daily practice [8]. The prevalence of low back pain is 25 times higher in the industrial countries [11], and it is common during the second and fifth decades, which means it creates a heavy financial burden on society [28].
One of the common causes for low back pain is walking long distances [5, 18]. This is common in some professional workers such as post-office deliverers, nurses, etc. It is assumed that there is a connection between the anatomical shape of the foot and foot pain or low back pain during walking. There is a physiological connection between the feet and the back muscles. The thoracolumbar fascia is a very important link between these two structures, and it transmits the loads from the upper extremities, to the back, and from the back to the lower extremities and the ground [29]. Therefore, the assumption is that unbalanced pressure over the feet will cause low back pain due to a compensatory spasm on the quadratus lumborum muscles. This assumption was not validated so far.
Insoles have been used for many years. They make the person feel more comfortable [2]. This phenomenon is achieved by decrease in the point pressure by 30–50% (depends on the material the insole is made of) [16]. It was also proven by electromyographic studies that insoles decrease the fatigability in the back muscles [14, 19, 27].
Not many studies have looked into the agronomic physiological aspects of insoles [4, 9, 12, 13, 20, 24]. Brown and co-workers concluded that more research is needed to explain the clinical success in using insoles [20].
The Foot Support Anterior Posterior (FSAP) (TekScan, Inc., Boston, Mass., USA) is one of the methods to make insoles. This is a computerized method, which shows an individual map of the foot with the various pressure points, and therefore enables to make insoles with maximal support to the foot. This method was used for searching pressure points in diabetic patients in order to prevent chronic ulcers [22]. After a comprehensive search in Medline, we found only one study that examined the relation between the use of insoles to low back pain during long distance walking in military recruits [15]. The purpose of this work was to examine if such a connection exists.
Materials and methods
A total of 105 postmen whose job includes walking long distances (walking for many hours a day) were asked if they suffered from low back pain. Of these 105 persons, 75 (71.4%) answered that they did. Out of these 75 (80%), 60 persons agreed to participate in this prospective double-blind study. The feet of these 60 subjects were fitted before the beginning of this study for the insoles, and after randomization they received, either a true FSAP insole or a placebo insole for 5 weeks, and then it was switched to the other insole for the next 5 weeks. Either the true or the placebo insoles were made from a commercially available and widely used viscoelastic polymeric material for shoe inserts (Sorbothane, Sorbothane Inc., Kent, Ohio, USA). Both the caregiver and the subjects were blinded and both shoe insoles looked the same when used. The participants were permitted to put the insoles during work time, or non-work time (including home use).
Demographical parameters which included age, sex, marital status, smoking habits, height and weight, number of years at work and number of children were recorded. Each patient filled a MILLION questionnaire [21] to assess his/her back pain intensity before receiving insoles and after each period of using either the true or placebo insoles. The questionnaire was distributed and collected by another person not connected with this study. This questionnaire is widely used in the spine literature for assessing the changes in the back pain after a certain procedure or treatment and is considered as valid [3, 21]. In addition, each patient filled a questionnaire after each period with questions regarding the use of insoles, timing of pain in relation to walking distance, feeling of being tired after work and if at all so and preference for one of the insoles.
Statistical analysis was done using the SAS statistical program. Due to a normal distribution we used the Student’s t-test. A P value of less than 0.05 was considered as statistically significant.
Results
A total of 60 patients (25 men and 35 women) agreed to participate in this study. In the first round, 41 patients received the true insoles (FSAP) and 19 received the placebo. After the first period of 5 weeks, two patients (one from each group) dropped from the study. One patient from the true insoles group was hospitalized for a non-related reason, and another patient from the placebo group refused to continue in the study because the insoles were inconvenient for him. Therefore, in the second round 40 patients received placebo insoles and 18 patients received true insoles. A comparison between the groups in terms of the demographical parameters did not reveal statistical difference in any of the examined parameters (P>0.05) (Table1).
Table1
Demographic data of the 60 patients
| Parameters | Mean±SDa | Mean±SDb, placebo first use | Mean±SDc, true first use | P-value |
|---|---|---|---|---|
| Age (years) | 39.14 | 37.8±9.07 | 39.7±7.67 | 0.415 |
| Weight (Kg) | 69.74 | 69.2±10.6 | 70.0±12.1 | 0.494 |
| Height (cm) | 167.98 | 166.8±7.7 | 168.5±8.9 | 0.821 |
| BMI (kg/cm2) | 24.67 | 24.8±2.8 | 24.6±3.6 | 0.857 |
| No. of children | 2.21 | 1.66±1.8 | 2.45±1.8 | 0.123 |
| No. of years at work | 8.59 | 8.3±6.7 | 8.7±6.6 | 0.847 |
| Shoe size | 40.71 | 40.5±2.3 | 40.8±2.6 | 0.675 |
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aTotal—58.
bEighteen subjects, 9 females, 9 males
cForty subjects, 24 females, 16 males
A constant use with the insoles was reported by 49 patients (84.5%) from the true insole group and by 45 (77.6%) of the placebo group. Of these patients, four (6.9%) and six (10.3%), respectively, reported that they used it often, while five patients from each group (8.6%) reported only part-time use. Two patients from the placebo group (3.5%) did not use it at all.
The frequency of low back pain that was found in relation to the type of insole is presented in Table2. This frequency was found to be lower after the use of true insoles relative to placebo (P<0.05). A total of 54 patients (93.1%) from the true insoles group and 46 (79.3%) from the placebo group would have liked to continue with the use of the insole (P>0.05). However, 47 patients out of the 58 (81%) would have preferred the true insole (P<0.05). This shows that the patients were satisfied with both insoles including the placebo (placebo effect), but were much satisfied with the true insoles.
Table2
Frequency of low back pain according to type of insole (MILLION questionnaire). M0 “Basic” Million questionnaire (before enrollment), M1 million questionnaire after use of true insoles, M2 million questionnaire after use of placebo insoles
| Frequency of LBP | M0 | M1 | M2 |
|---|---|---|---|
| Never | 0 (0%) | 6 (10.3%) | 2 (3.4%) |
| Seldom | 15 (25.9%) | 34 (58.6%) | 26 (44.8%) |
| Often | 37 (63.8%) | 15 (25.9%) | 24 (41.4%) |
| Every day | 6 (10.3%) | 3 (5.2%) | 6 (10.3%) |
| Total | 58 (100%) | 58 (100%) | 58 (100%) |
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The average back pain according to MILLION was 5.46±1.8 before the study, 3.96±1.74 after the use of the FSAP insoles and 5.11±1.85 after use with the placebo insoles (P<0.05). This led us to examine if there is an influence on the results according to the first insole that was used by the patients. Such an influence was not found (Table3).
Table3
The efficiency of the insoles (according to MILLION questionnaire). P–T placebo insoles were used prior to the true, T–P true insoles were used prior to the placebo
| Questionnaire | Delta D | P–T (18 patients) | P value | T–P (40 patients) | P value |
|---|---|---|---|---|---|
| M1–M2 | Between true insoles and placebo | −1.30 | 0.0008 | −1.16 | 0.0001 |
| M1–M0 | Between use of true insoles to “basic” MILLION | −1.91 | 0.0001 | −1.31 | 0.0001 |
| M2–M0 | Between use of placebo insoles to “basic” MILLION | 0.61 | 0.146 | −0.17 | 0.4443 |
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Discussion
The relation between insoles, feet pain and low back pain was examined mainly on professional sports players [4, 9, 12, 16, 20] and on people whose their job involves a lot of standing [2, 19, 27]. In the latter, it was found that 74% of the examinees found the insoles to be comfortable and reported decrease in their feet and lower back pain [2]. However, none of these papers examined the relation between insoles and low back pain in patients whose job includes walking long distances. Only one study examined the relation between insoles and low back pain in military conscripts who are supposed to walk relatively long distances and found a positive relation between the use of insoles to reduction of low back pain [15].
There is evidence that the frequency and severity of low back pain is related to heavy loading of the spine [1, 25, 26]. It was also shown that walking, a regular daily activity produces heavier loads on the lumbar spine [6]. This increase in the loads is transferred from the foot during heel strike to the lower extremity and then to the spine.
The most crucial factor for the development of shock wave related injuries is not the absolute value of the force at heel strike but the loading rate [23]. Our study group consisted of postmen who used to walk regularly for long distances each day, which means a high loading rate. In this group of examinees, we could have anticipated a high rate of low back pain. The fact that the insoles reduced the low back pain rate proves its potential to absorb some of the force, which is generated by repetitive walking. Windle and co-workers have shown that the insoles placed in shoes would attenuate the peak pressure at heel strike during running and marching compared to a “no insole” condition [30]. A decrease in the shock-wave amplitude transferred to the tibia in subjects who had insoles was reported by Light et al. [17]. This decreased load, which in turn transfers less energy towards the upper part of the lower extremity and the lumbar spine, is probably the cause for the decrease in low back pain.
This study was designed as a double blind study. To our knowledge, this is the only study reported in this subject which utilizes a double-blind technique. This is superior to other methodologies which do not use double blind techniques.
In this study, it was shown that the patients reported a greater reduction in their low pain when used the true insoles, in comparison to the period that they used the placebo insoles. It was found that the contribution of the true insoles to the improvement in the low back pain, after reducing the placebo effect, is 79.2%. We did not find any correlation between improvement of low back pain to other measured criteria such as age, sex and marital status.
Evaluation of back pain is a subjective evaluation. For this evaluation we used the MILLION questionnaire that was proven to be valid in this subject [3, 21]. This work also contributes to the validity of this questionnaire as there was a good correlation between the different times that the subjects filled out this questionnaire, in terms of their low back pain.
Reduction in pain intensity by about 2 points in a 10-point scale, or more than 30%, has been reported to represent a clinically important difference in pain between treatments [10]. In our study we found this reduction in the patients when they used the true insoles and not when they used the placebo.
In conclusion, it was proven that insoles causes improvement of low back pain for subjects with repetitive loading such as walking long distances every day.
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