Comparison of 3 devices on clinical outcomes in plantar fasciitis
wed that baseline pain intensity, age, washout length,
and discontinuation due to adverse events accounted
for approximately 10% of placebo response variability,
and patients’ perception of treatment allocation and
expectations toward treatment efficacy was strongly
predictive of RCT outcomes (34). Nevertheless, most
of the placebo effect is due to individual factors that
are not yet well identified; hence, there is a growing
interest in determining the individual factors that can
predict the placebo response (35).
Patient expectations have been identified as one of
the major components contributing to placebo respon-
ses. Patients requiring therapeutic interventions are
exposed to stimuli in the clinical setting that trigger
specific expectations about treatment and outcomes.
These stimuli include the nature of the treatment it-
self, such as surgery, drugs, injections or therapeutic
devices. They also include the characteristics of the
clinician and the relationship formed with the patient,
as well as the clinician’s confidence in the therapy
and explanation of the treatment. The wider treatment
context, such as the reputation of the facility and status
of the clinic, may also affect treatment outcome ex-
pectations. These factors all operate psychologically
and can enhance or diminish treatment efficacy (36).
The design of the current RCT allowed us to isolate
and analyse the external appearance of the device as a
contextual element of the placebo and nocebo respon-
ses. The strict inclusion and exclusion criteria allowed
appropriate selection of patients with chronic plantar
fasciitis, excluding patients with heel pain caused by
other pathologies. The main clinical outcome, foot
functionality, was assessed through the FFI, which has
been proven as a validated and reliable instrument, and
is one of the most-used tools in clinical trials on the
effectiveness of plantar fasciitis treatment interventions
(25, 26); the quality of this evidence has been rated
as high (grade A recommendation by the American
Physical Therapy Association) (37). A strong statistical
power was reported; thus we can reasonably dismiss
a type II error (or beta type error). In contrast to other
studies, this study was carried out in a real healthcare
setting, with patients rather than healthy volunteers.
Other similar studies have used small samples and short
follow-up periods (18, 36, 38), and were therefore less
reflective of real clinical practice.
Limitation
One limitation was the wording of the study. It was
decided not to use the words “placebo effect” with the
participants and this was not included in the informed
consent form, because it could have confused the par-
ticipants and made them mistakenly believe that there
207
was a group without treatment. Another limitation of
this study was the presence of the 3 devices in the same
room, since in a real healthcare setting only a single
device would be available. This could increase patients’
expectations and thus generate placebo or nocebo re-
sponses. This aspect might have been relevant for the
external validity of the study, if differences had been
found between the groups.
The current study may have some practical conse-
quences. The results could encourage the industry to
manufacture rESW devices with a more austere design,
which would allow lower production costs. Therefore,
equipment and treatment sessions would be cheaper,
potentially increasing the number of patients who could
access this therapy.
Creative experimental efforts are needed to rigo-
rously assess the clinical significance of placebo and
nocebo effects and investigate the individual elements
that may contribute to a therapeutic benefit. Future
research should place more emphasis on patient–thera-
pist interactions rather than the diagnostic and thera-
peutic tools used. The placebo effect must be isolated
from other phenomena present in clinical trials, such as
the Hawthorne effect, natural fluctuations in diseases,
and regression to the mean (20–22). These phenomena
can cause confusion and lead to clinical improvements
being wrongly attributed to a placebo effect.
Conclusion
In patients with chronic plantar fasciitis treated with
rESW therapy, the appearance of the device did not
influence clinical outcomes: function, pain with the
first weight-bearing step in the morning, pain during
the day, fascia thickness, and adverse effects. As device
appearance did not affect treatment outcomes, it should
not currently be considered as one of the contextual
elements that generate placebo and nocebo responses.
Further research is needed to identify the contextual va-
riables, including patient-therapist interactions, which
influence such responses.
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