Trial design
The trial design was a single-blinded, longitudinal randomised controlled, non-inferiority trial.
Ethical approval was given by the Milton Keynes Local Research Ethics Committee (05/Q1603/34) and all patients were approached and gave informed consent to participate in the study.
Sample size
A power calculation for a non-inferiority trial was made [10]. The non-inferiority limit (-d) was set at 20 on a 100 mm Visual Analogue Scale back pain scale as the primary outcome measure. A minimal clinical difference change of 20 mm was set [11]. From a pilot sample of 50 current patients the standard deviation (σ) of the VAS back was 2.07. δ = d/σ, δ = 0.966. This required 25 patients in each arm of the trial, allowing for 10% attrition/non-compliance rate, 55 subjects were required. This gave a 90% power and a Type 1 error rate of 2.5%.
Participants
Patients referred to a Physiotherapy Department with a diagnosis of chronic low back pain were recruited to the study.
Inclusion criteria were patients aged over 18 years with a diagnosis of chronic low back pain lasting a minimum of 3 months.
Exclusion criteria were patients with leg pain, those who were current TENS users or patients where either of the treatment modalities might harm them. This was based on the warnings and precautions for the use of TENS namely, patients with pacemakers, damaged or broken skin, malignancy, poorly enervated areas and spinal infection.
Randomisation
Randomisation was performed using a random numbers table. Randomisation was restricted to permuted blocks to ensure equal numbers being allocated to each group. Four blocks of patient assignment were used; two blocks of 0–9 and two of 0–19. Each random permuted block was transferred to a sequence of consecutively numbered, sealed, opaque envelopes and these were stored in a locked drawer until required. As each participant formally entered the trial, the researcher opened the next envelope in the sequence in the presence of the patient.
Blinding
We attempted to ensure integrity of blind assessment by maintaining separation between the therapists providing the treatment and those assessing We followed practical tips to try and reduce 'unblinding' accepted within the field [12], such as participants being reminded before each assessment not to reveal details of their allocation group.
Interventions
Patients were randomly allocated to use either TENS or the FairMed device. For the TENS group a dual channel portable TENS TPN 200 PLUS unit was used. Stimulation was based upon best available evidence from the literature. For conventional TENS, parameters between 80–100 Hz and 100–200 μs are considered to be effective in the treatment of chronic pain [6, 9, 13]. In studies specifically on chronic low back pain populations [7, 9], parameters of 80 Hz/140 μs and 100 Hz/125 μs resulted in pain reduction. It is suggested that patients use TENS as much and as often as required [13]. Our protocol used stimulation given in continuous trains at high frequency (80 Hz, using square-wave 100 μs pulses). Two surface electrodes (5 cm × 5 cm2 TPN 40 each) were placed in or adjacent to the painful area at a distance of 5 cm–20 cm apart. The intensity of TENS was adjusted to produce a tingling sensation that was approximately 2–3 times the sensory threshold.
The FairMed group received the device (Figure 1) which includes 2 components: a hand held controller as subject interface and an array of 16 vibrators closely applied to the lumbar spine. One or more stimulator is activated randomly and the subject responds by indicating which stimulator(s) are active. The device display indicates if the response is correct or not via a visual and auditory display. The cycle is then repeated until the test session is complete. This requires a high level of attention. Subjects were asked to use the device for 30 minute sessions. The FairMed is specifically not a device to deliver either painful stimuli or massage. The stimulus is as localised as possible; it is brief and probably insufficient to impair position sense. The device was designed to teach localised discrimination of stimuli to the lumbar spine. The device was conceived by JF, developed in conjunction with KB, and prototype models were produced by a product design and development consultancy, which completed pre-trial laboratory testing.
Outcome measures
The outcome measures used in this trial were collected in accordance with recommendations from the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials [IMMPACT]. These 6 core outcome domains are i) pain, ii) physical functioning, iii) emotional functioning, iv) participant ratings of improvement and satisfaction with treatment, v) symptoms and adverse events, and vi) participant disposition [14].
Pain was recorded using a 100 mm VAS recording patient's present pain intensity level, their average and worst pain intensity levels recorded over a week and averaged [15].
Physical functioning was recorded using the Oswestry Disability Index v 2.1 [16]. Functional physical tests – 5 minute walking distance, 1 minute stair climb and 1 minute standing up and sitting down from a chair were used to assess those aspects of physical performance most relevant to everyday activities [17].
Emotional functioning was assessed using a battery of questionnaires, the Health Anxiety and Depression Scale used to assess emotional functioning [18]; the Tampa Scale for Kinesiophobia (TSK) to assess pain-related fear of movement [19]; the Pain Coping Scale (PCS) to assess the three components of catastrophising: rumination, magnification and helplessness [20] and the Pain Self Efficacy Questionnaire to assess people's self-efficacy beliefs [21].
A global rating of patient reported improvement and satisfaction, the Patient Global Impression of Change scale [22], was assessed, having been widely used in chronic pain clinical trials e.g. Farrar, Young et al.[23], the PGIC has been demonstrated to have validity and it provides a responsive and readily interpretable measure. Participants were asked how they felt after their treatment, firstly, with regards to their ability to cope with their pain and, secondly, to their ability to perform everyday activities.
Participants completed outcome questionnaires at baseline, 3 weeks, 6 weeks and 12 weeks. They underwent functional testing at baseline and 3 weeks with a masked assessor. Over the 3 weeks that participants used their devices, they were asked to keep a daily pain diary.
Patients were explicitly asked about any adverse events they experienced using the devices, and to record these in their pain diary and by telephone report. An adverse event is considered any unwanted effect detected in participants of a clinical trial regardless of whether the effect can be attributed to the intervention under evaluation [24].
Finally, information on participant disposition was collected to document the recruitment of participants and their progression through the trial, numbers receiving intended treatment, those completing the study protocol and analysed for the primary outcome [14, 24].
Data analysis
Data were analysed using intention-to-treat analysis and the statistical package SPSS 12.0.1 for Windows.
Non-parametric statistics were used to compare outcome measures between groups (One way ANOVA). Statistical significance was set at the p < 0.05 level.
