Deep heating therapy via MF radiowaves versus superficial heating therapy in the treatment of nonspecific chronic low back pain: A double blind randomized trial

1. Background

Nonspecific low back pain (LBP) is one of the most diffused pathologies of the spine [1, 2]. Possible noninvasive treatments have been widely studied [3, 4] without any conclusive evidence on their efficacy. As far as chronic nonspecific low back pain (CLBP) is concerned, which refers to LBP lasting more than twelve weeks [5, 6], it is commonly believed that the best therapeutic approach should be multidisciplinary [3] due to a most probable mixed etiopathology of this condition [7, 8, 9]. Physical modalities have always been largely used for the treatment of CLBP, despite the low quality evidence of studies supporting them [3, 10]. Among these, ultrasound therapy seems to be beneficial in the short term, but not for CLBP [11, 12]. TENS is also not indicated in the management of CLBP [13] and so is LASER therapy [4, 15], while acupuncture has proven to be effective in combination with other therapies [16].

The use of heat is probably the oldest form of physiotherapy. Heat therapy can be delivered superficially (Superficial Heating Therapies, or SHT) with low direct penetration. There is some evidence that superficial heat therapy reduce pain and disability in the short term, in a mixed population of patients with acute and sub-acute LBP and that the combination with physical exercise can improve its efficacy [17]. In addition, heat can be dispensed deeply, employing instruments able to transfer it in depth, such as ultrasound and, particularly, radio waves (Deep Heating Therapies, or DHT). Radio waves diathermy is largely used in the treatment of CLBP [18], although with very different modalities [19, 20, 21, 22]. Discovered at the beginning of the 1900s, in the last fifty years radio waves diathermy was mostly performed with High Frequency (HF) waves (27 MHz); then, with Ultra High Frequency (UHF) waves (2.45 GHz, 433–920 MHz) and more recently, with Medium Frequency (MF) waves (450–1000 KHz). This latter has the advantage of a greater tissue-penetration and a better localization of energy in the target area [23].

Despite the rapid and wide diffusion of the new MF waves therapy, in our knowledge no studies are available, in particular on spine pathologies, where it is one of the most used therapies. A few studies on different radio waves diathermy (UHF and HF) can be found in literature [19, 20, 21, 22] without agreement on findings.

The aim of the present study was to evaluate the efficacy of a diathermy treatment with MF radio waves for nonspecific CLBP. For this purpose, this treatment has been compared with a superficial heat delivered by an electric resistance. Already in the past phantom models demonstrated that the thermal gradient induced by a thermal applicator, like the one used as control in the present study, is very steep and limited to few millimeter in depth and that the temperature rise is negligible [24, 25].

In the present trial the two sources of heat have been emitted separately and alternately by the same instrument, with the use of a software able to automatically generate either type of heat treatment (blind and random) and, consequently, create the-two well distinct groups.

The hypothesis is that the greater penetration of MF radio waves in the tissues would be more effective in the treatment of nonspecific CLBP compared to superficial heat.

2. Methods

This Phase IV study has been approved by the local Ethics Committee (Protocol n. 0.005.787-13/02/2014).

The two groups were homogeneous at baseline (T0) for age, BMI and sex, although a slight prevalence of female patients was present in the DHT Group. Both NRS and ODI values were not statistically different at baseline (Table 1).

Forty nine patients completed the study; tolerance to therapy was very good in both groups: adherence was 100% and none of the patients missed a treatment session; all patients were subjected to the scheduled tests up to 45 days. None of the patients took the rescue therapy during the study.

4. Discussion

In the present study both DHT and SHT demonstrated to be effective in reducing nonspecific CLBP. DHT, with MF radio waves, allowed better result than SHT in improving disability. The best result obtained with MF radio waves heat therapy (DHT) confirms the hypothesis of the present work that the greater penetration of MF radio waves in the tissues is more effective compared to superficial heat.

Actually, all superficial heating therapies are essentially based on the release of infrared radiations that can reach deep tissues only indirectly, by conduction from surrounding tissues or by convection via blood circulation [24]. It can be deduced that treating a biological target (in this case the lumbar spine and deep soft tissues) with a direct form of energy, can have some therapeutic advantage. This seems to support the role of mechanical causes (inter-vertebral disk, articular facets, sacral-iliac articulations pathologies and muscle diseases) compared to neurological and psycho-social causes in nonspecific chronic LBP [8, 29, 30, 31, 32].

These considerations are confirmed by the Oswestry Disability Index, demonstrating a constant and notable decrease of disability in the DHT group from one follow-up to the next, approaching in time to minimal levels of disability, corresponding to a value below 20% [26]. It is very likely that the reduced disability obtained by DHT group is a direct consequence of the effect of diathermy on extensibility of deep tissue, as already demonstrated by other authors, in different body districts as shoulder, ankle and knee [33, 34, 35], although using other types of radio waves (HF and UHF).

Among previous studies on the use of radio waves diathermy, we found conflicting results. Shakoor et al. [22] performed a study on CLBP comparing a therapy based on the combination of short waves (HF) and NSAIDs to a therapy based on the combination of sham short waves and NSAIDs. The frequency used in their study (27.12 MHz) was relatively close to the MF band of our trial (450 KHz). The authors found a statistically significant difference in favor of the treatment with HF waves compared to the sham treatment at 3 weeks after the end of the trial. Unfortunately, despite leading to results very similar to ours, this study was not a true double blind because the sham instrument did not produce heat.

Durmus et al. [20] carried out a trial in CLBP using tests very similar to those used in the present study (VAS and ODI) and a protocol based on a combination of microwaves (UHF: 2.45 GHz) and exercises, compared to a group performing only exercises. The study, which was randomized but not a double blind, did not show significant differences between the groups.

Akyol et al. [36] used the radio waves (HF: 27.12 MHz) and physical exercise in a group of knee osteoarthritis (OA) patients, compared to a sham diathermic treatment and physical exercise, without a significant improvement in pain and disability. The authors used a very complex double blind design: in order to confuse the heat sensation of diathermic and sham treatment, both groups of patients were pre-treated with hot pack.

A similar double blind method was used by Leung and Cheing [33] in the treatment of frozen shoulder, with a better result in the diathermic group.

Rabini et al. [35] carried out a clinical double blind study on knee OA, comparing a DHT treatment to a SHT treatment. The authors, in the group DHT, used a diathermic device delivering microwaves (UHF: 434 MHz); in the SHT group he used the same hyperthermia device, kept warm at 38 ∘ without switching on the microwaves generator. The clinical results showed an improvement in pain and disability only in the DHT group.

One of the strongest points of the present study with respect to previous literature is the double blind design, achieved by a computerized system applied to the device to provide both DHT and SHT. We believe this has been an important step toward a real randomization. It is in fact well known that is quite difficult to have a real double blind setting in physiotherapy clinical studies. Furthermore, the reported studies never used MF radio waves. For these reasons our trial is unique and not comparable to other studies performed in the past.

Another important aspect is the absence of a considerable drop-out rate from the study (one patient declined to participate to the study for family problems), demonstrating that heat is a form a physiotherapy well tolerated by patients with CLBP and chronic disability.

Given the widespread diffusion of CLBP in the population, the main limitation of the study was the small number of patients ( n = 49 pts.). Although the sample ( n = 50 pts.) was calculated by a power analysis, and it was similar to previous studies (Akyol n = 40 pts. and Rabini n = 54 pts.), results should be reproduced in a wider sample. Furthermore, since CLBP has a marked tendency to relapse, another limitation was the relatively short observation period (45 days): as patients suffered from chronic lower back pain, we do not know if the benefits of heat therapy have lasted in the longer term. In the future, studies with a greater number of cases and longer follow ups (at least one year) are desirable.

In conclusion, with the numbers of the present study, the Deep Heating Therapy, based on targeted MF waves diathermy, seems to be effective in the treatment of nonspecific CLBP, and could be considered for the multidisciplinary management of this complex pathology.