INTRODUCTION
Diabetic foot is considered to be one of the most serious complications for patients
suffering from Diabetes Mellitus (DM). Approximately 20–25% of all diabetic patients
will present with lower extremity ulceration at some time in their lives. Diabetic
foot is the leading cause of non-traumatic lower limb amputations in the world, resulting
in an amputation risk for diabetic patients that is approximately 40 times greater
than that of the general population. Post-amputation mortality is extremely high,
with a three-year survival rate of 65% and a five-year survival rate of 41%. It is
a health issue affecting several countries and represents a significant socioeconomic
problem.1-4 In Brazil, amputation, admission, ulceration, and cost data are similar
to other Western countries.5-7 Recognition of individuals at risk for ulceration,
followed by adequate intervention, may reduce the chance of unfavorable results up
to 80%.8
Peripheral sensory-motor neuropathy, which is responsible for the progressive loss
of protective and proprioceptive sensations, is considered the main agent of the clinical
abnormalities found in diabetic foot patients. It is important to consider that in
the final phases of the disease the patient may present with a completely insensitive
foot.9,10 One of the first studies looking to improve touch sensitivity screening
dates back to 1898 and used a horsehair attached to a thorn.11 This method was refined
and currently a 10g nylon monofilament, developed by Semmes and Weinstein, is accepted
as the gold standard for detecting ulcer risk.12 Its reproducibility and predictive
value lead the World Health Organization (WHO) and the International Diabetes Federation
(IDF) to recommend its use in clinical practice.1,2
In 2006, Bourcier et al. showed the effectiveness of the “house made” monofilament,
constructed from a fishing line, for screening for diabetic foot. The main characteristic
of this line is that it exerts a 10 g pressure when bent (4 cm length by 500 µm diameter
N° M-1425, South Bend Inc. North Brook, EUA).13 In Brazil, the 10 g monofilament is
produced locally, but is not always available for purchase.
The objective of this study was to identify a similar nylon line and compare it to
the commercially available one.
METHODOLOGY
This was a prospective, investigative, non-interventionist study with minimal risk
to the participants. It was approved by the Local Ethics in Research Committee (CAPPesq
n° 1184/09) and informed consent was obtained from all subjects who agreed to participate.
The study consisted of three phases. Initially, we assessed the fishing lines available
in the national market that presented bending characteristics similar to the 10 g
monofilament. If possible, we identified lines that did not require any other device
for clinical use, i.e. the only holding structures could be the thumb and index finger
of the examiner. This step was done inside the laboratory using a precision digital
scale (OHAUS Max model – capacity = 210 g/d = 1 mg).
In the second phase, we evaluated the chosen line, referred to here as the “white-line”,
in relation to the commercially available (SORRI-BAURU), referred to here as the “yellow-line”.
We proceeded with the clinical evaluation of this filament in 100 healthy (56 male
and 44 female), non-diabetic medical students and physicians from the State University
of Sao Paulo who volunteered for the study. The diabetes criteria used to select this
group followed the ADA (American Diabetes Association) diabetes diagnosis criteria.
To exclude the presence of abnormalities in lower limb sensations in this group, all
individuals submitted to a clinical evaluation using vibration perception (128 Hz
tuning fork) at two sites (hallux pulp and malleolus) and point pressure (Semmes-Weinstein
10 g monofilament) at five sites (halux, 3rd toe, 1st, 3rd, and 5th metatarsal heads).
No individuals presented with any kind of insensitivity.
Evaluation with the new monofilament was compared to the commercially available monofilament.
Subjects were evaluated in the sitting position. Each filament was initially applied
to the back of the hand so that it could be identified and then randomly applied to
the foot sole at the following sites (3 times each): halux, 3rd toe, 1st, 3rd, and
5th metatarsal heads. Individuals were asked to close their eyes and identify which
filament was being used at each time.
The third phase was carried out in two distinct diabetic foot reference units (Diabetic
Foot Unit, Endocrinology and Metabolism Division at the State University of São Paulo
and the Medical Specialties Centre of Aracaju-CEMAR). We invited 190 diabetic subjects
(80 male and 110 female) with a history of at least 5 years of disease (according
to the ADA diabetes diagnosis criteria) to participate in this study. One hundred
of the subjects had a previous diagnosis of clinical diabetic neuropathy and 90 did
not. One patient declined to participate. All patients were re-examined to confirm
their diagnosis and no discordance with the cited criteria was found.
The neuropathy criteria used in both diabetic foot units were the absence of vibration
perception (128 Hz tuning fork) in at least one site (hallux pulp and/or malleolus),
insensitivity to plantar point pressure (Semmes-Weinstein 10 g monofilament in at
least one of seven sites), ankle reflex reduction, and/or absent answer.2 We again
evaluated both filaments, as described above. Answers were recorded as present/absent.
Data from phases 2 and 3 was organized into tables of contingency and analyzed by
the Chi-Square method after Pearson's correction. Significance value was fixed at
5%. The kappa coefficient was used as a measure of inter-annotator agreement for qualitative
(categorical) items. Kappa coefficient was expected to be equal to 1 if the 2 evaluation
methods were in complete agreement.
RESULTS
Phase 1: We initially investigated the physical characteristics of lines with diameters
and raw materials that allowed compression in “grams”. There were 6 lines that fulfilled
such criteria. We obtained a 10 g bend in the Nylon 6 (homopolymer) line, which had
a diameter of 0.50 mm cut at a length of 4 cm (Table 1). This result was confirmed
in 100 consecutive tests by 2 different examiners (50 tests per examiner), who used
the thumb and index finger to hold the line. This line used in the fabrication of
fishing nets and rod sport fishing (TREVO brand, Equipesca, SP-Brazil) and is available
in 250 g reels.
Phase 2: Chi-Square analysis of the 5 sites studied showed that the individuals were
incapable of differentiating between the touch of the 2 filaments (p<0.05, Figure
1).
Phase 3: The patient analysis showed a satisfactory concordance between answers for
both monofilaments. There was no difference in results at any site evaluated. Correlation
coefficients (k) confirmed the equivalence of both nylon filaments with a variation
of 0.96 to 1.00. This value was 0.96±0.02 (p<0.05) and 0.98±0.01 (p<0.05) for the
right and left foot, respectively (Table 2).
DISCUSSION
The present study shows that it is possible to reduce the cost of detecting ulcer
risk of the foot in diabetic patients. In the initial phase of the research we sought
to find a fishing line available in the nation market that had characteristics similar
to the 10 g internationally standardized monofilament in terms of composition and
bending. We subjected these lines to evaluation of their physical and tonometric characteristics.
Non-diabetic individuals were not capable of differentiating one monofilament from
the other. A previous study found similar results with a different line that also
reproduced the necessary characteristics.12,20 When we tested, in a patient-blind
way, both monofilaments in diabetic patients with and without neuropathy, we found
similar results. The kappa values revealed the strong concordance of the lines. It
is worth noting that the population studied was multicentric, representative, and
homogeneous, with no demographic differences from other local populations previously
described.21,22
Bourcier et al.13 developed their fishing line instrument to foment patient auto-examination.
We had a very distinct socioeconomic goal for addressing this public health concern.
Our study was conducted in a country with a developing economy that has huge inter-regional,
social, and economic differences. Performing routine foot screening in the various
health units in Brazil faces a lack of capacitation and adequate material. Thus, with
the exception of a few reference centers, the great majority of health services across
the country, particularly primary care units, do not perform screening for the risk
of diabetic foot. Therefore, we are justified to repeat a study already done in another
country but with a line that is easy to obtain locally.
The present cost of the commercially available monofilament is R$7.00 (USD 3.68) per
unit (two lines in a kit). The studied line is produced commercially on large scale
for exportation and is also sold all over the country. Its unit cost is only R$0.00053
(USD 0.00029). The cost savings this line may generate are significant, potentially
allowing access to this instrument at locations with few resources as well as supporting
its day-to-day use. Indirectly, it can also reduce the costs of diabetic foot complications
through early detection.
The line was developed to not need any support instruments. The examiner's fingers
act as the necessary pincer. Any attempt to modify this technique, such as fixation
to paper or plastic, will alter the line's physical properties and, in so doing, will
necessitate new studies. It is also noteworthy that lines from other brands could
also be used, but similar studies are necessary to validate their equivalence.
This study has its limitations. We used the same materials to fabricate the monofilaments
and all were made by the same person. For large-scale use, caution should be taken
in regards to the line's fabrication in order to avoid use of lines of different brands
and measures, preventing inadequate accuracy. We also realize that in the present
study there were no new findings: a 10 g monofilament derived from a fishing line
performs as a 10-gram nylon monofilament. However, at the public health policy level,
this confirmation was critical. The encouraging results of Bourcier et al. can be
expanded to include locally available materials.
CONCLUSION
We have demonstrated that a low cost instrument developed from a fishing line is equivalent
to instrument used internationally to evaluate ulcer risk of the foot in diabetic
patients. It can be used as the standard line to screening for diabetic neuropathy.
ACKNOWLEDGMENTS
The authors would like to thank the engineer Mr. Milton Xavier, who helped us in the
first phase of this work, related to the search of fishing line suitable for this
study, Dr. Karla Melo for her continuous encouragement and stimulus to this paper
realization and Dr. Arnaldo Moura Neto who revised the last version.