Download Plantar sensitivity, foot loading and walking pain

Rheumatology 2006;45:212–214
Advance Access publication 4 October 2005
doi:10.1093/rheumatology/kei137
Concise Report
Plantar sensitivity, foot loading and walking pain in
rheumatoid arthritis
D. Rosenbaum, A. Schmiegel, M. Meermeier and M. Gaubitz1
Objective. The aim of the present study was to investigate the tactile sensitivity of the plantar surface in rheumatoid feet and
its relationship to walking pain and plantar foot loading characteristics.
Methods. In 25 patients with rheumatoid arthritis (RA) and 21 healthy controls, Semmes-Weinstein monofilaments were
used to assess tactile sensitivity in six foot regions. Walking pain was examined clinically. Pedography was used to analyse
foot loading parameters during barefoot walking.
Results. In RA patients, plantar sensitivity was significantly decreased under all foot regions examined compared with
the control group (P_0.05). A loss of protective sensation was found in a total of 10 regions in seven patients but not in the
control group. In the RA patients, foot loading was reduced in the hindfoot (P_0.05) but was slightly increased in the forefoot
(not significant). Average walking pain was 3.8 2.1 on a scale from 0 to 10 but did not correlate with the sensitivity levels.
Conclusion. In patients with RA, no direct relationship between pain intensity and plantar foot loading was found. The
decreased tactile sensitivity may be indicative of a disturbed sensation for high plantar pressures. Therefore, pedography can
be useful as an additional tool in the detection of excessive forefoot loading before complications are manifested.
KEY WORDS: Rheumatoid arthritis, Foot pain, Plantar sensitivity, Pedography.
RA is one of the most frequent reasons for limited functional
capacity [1] and limited mobility is often due to the burden of
foot problems [2]. Pedography is an established tool for measuring dynamic foot loading characteristics and is therefore able
to reveal foot deformities of rheumatoid feet [3; A. Schmiegel,
M. Gaubitz, A. Schorat, A. Hilker and D. Rosenbaum, manuscript in preparation]. Until now, the relationship between foot
loading and walking pain has not been fully clarified [4].
There is still a lack of understanding of the aetiology of pain
in rheumatoid feet [5]. RA patients with longer disease durations
are known to suffer from greater foot pain in inflamed joints but
pain sensitivity is increased in non-inflamed tissues as well [6, 7].
High pain intensity may decrease the tactile sensitivity due to
an inhibitory effect of nociceptive input [7–9]. Neuropathy can
affect somatosensory functions of RA patients, leading to
reduced or decelerated sensory conduction [10, 11]. Reports
concerning the prevalence of compression neuropathies are
inconsistent and vary between 32% [12] and 42% [10], but it
appears that neuropathies increase with higher age [13].
The only report on the relationship between neurological
abnormalities and foot pressure investigated vibration perception
in RA patients compared with diabetic patients [3]. To date, no
study has examined the impairment of tactile sensitivity on the
plantar surface of patients with RA compared with controls.
Tactile sensation is mediated by mechanoreceptors that conduct
action potentials via A-fibres [14] and can be detected with monofilaments, which are easy to use and reliable for quantifying
plantar sensitivity [15, 16].
Therefore, the primary aim of this study was to examine
the tactile sensitivity in rheumatoid feet compared with healthy
control feet. A secondary aim was to investigate the relationship
between tactile sensitivity, self-assessed walking pain and plantar
foot loading characteristics.
Methods
Twenty-five patients (23 females, 2 males) with RA who met
the 1987 American College of Rheumatology criteria for
RA were examined. The average age of the patients was
55.0 9.9 yr and their body mass index was 26.8 6.6 kg/m2.
Further inclusion criteria were: (i) independent walking ability;
(ii) bilateral foot pain during walking; (iii) no other joint
diseases; (iv) no other systemic disease with relevant effects
on walking ability and pain sensation; and (v) no previous
foot and ankle surgery. All patients continued their long-term
anti-rheumatic medication but were off medications that might
have altered their mental state. Average duration of disease
was 9.6 7.0 yr and the HAQ score averaged 1.4 0.7 (on a
scale of 0–3).
Furthermore, 21 subjects (20 females, 1 male) with an average
age of 50.8 9.3 yr and a body mass index of 24.1 3.5 kg/m2
served as a control group. These subjects were free of foot
problems and any other orthopaedic impairment or systemic
disease that could have affected their gait patterns.
Walking pain of the right foot of every patient was evaluated
with multiple-item scales that represent the degree of pain in
Movement Analysis Laboratory, Orthopaedic Department, University Hospital Münster and 1Department of Rheumatology, University Hospital Münster,
Münster, Germany.
Received 31 May 2005; revised version accepted 19 August 2005.
Correspondence to: D. Rosenbaum, Funktionsbereich Bewegungsanalytik Klinik und Poliklinik für Allgemeine Orthopädie, Universitätsklinikum
Münster, Domagkstr. 3D-48129 Münster, Germany. E-mail: [email protected]
212
ß The Author 2005. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: [email protected]
Plantar sensitivity, foot loading and walking pain in RA
Results
The RA patients did not differ from controls with respect to
age or body mass index. Average walking pain was 3.8 2.1 on
a scale from 0 to 10.
Sensitivity was significantly reduced in the RA patients under
all foot regions investigated (P50.05; Table 1). In seven RA
patients (27%) loss of protective sensation was found in a total
of 10 regions located under the heel (one patient), midfoot (one),
first metatarsal head (one), third metatarsal head (three), fifth
metatarsal head (three) and hallux (one).
Dynamic pedographic measurements revealed several differences between groups. The significantly longer total contact time
in the RA patients (797 146 ms) indicated that the gait velocity
was lower than in control group (716 66 ms, P50.03).
TABLE 1. Results of the sensitivity assessment (because of the discrete
nature of the data, the median and first and third quartiles are reported)
Sensitivity threshold
Heel
Midfoot
First metatarsal
Third metatarsal
Fifth metatarsal
Hallux
RA patients
4.56
4.17
4.17
4.31
4.31
4.17
(4.17,
(3.61,
(4.17,
(4.17,
(4.17,
(4.17,
Controls
4.74)
4.17)
4.56)
4.61)
4.56)
4.56)
Controls
Average Pressure [kPa]
4.24
3.84
4.08
4.17
4.17
4.17
(4.13,
(3.42,
(4.08,
(4.17,
(4.17,
(3.84,
P-value
4.31)
3.90)
4.17)
4.31)
4.31)
4.17)
0.027
0.018
0.032
0.032
0.015
0.035
RA patients
600
500
400
300
*
*
200
100
45
T3
T2
H
45
M3
M2
M1
LM
MM
LH
0
MH
chronic diseases [17]. We did not include both feet to avoid falsepositive statistical findings [18]. The RA patients were asked
to fill in the Health-Assessment Questionnaire (HAQ) [19].
Furthermore, a foot function index was used to assess the footspecific impairment [20].
Tactile sensitivity under the plantar aspect of the right foot
was assessed by measuring the perception threshold to light
touch [7] with Semmes–Weinstein monofilaments (North Coast
Medical, Morgan Hill, CA, USA). A set of these filaments
consists of 20 pens with different force levels. The detection of
sensory thresholds was conducted in a random order in six
plantar regions: heel, midfoot, first, third and fifth metatarsal
head, and hallux. For each filament, a total of 10 stimuli were
applied: seven real stimuli and three null stimuli were randomly
included. If three failures were observed the level was classified
as failed. We used a modified 4–2–1 step algorithm that has
been described before [15, 21]. Beginning with the filament at
an intermediate level (4.56), the stimulus was increased (if the
first level was not felt) or decreased (if felt) by four steps. After
the first turnaround (felt at the higher level when not felt at
lower levels or vice versa) stepping was changed to steps of two.
After the second turnaround the final stepping was reduced to
a single level step. The last level that was correctly felt was used
as the tactile threshold. For the present study, a filament index
above 5.07 was considered as an indication of loss of protective
sensation [22]. Therefore, we noted every region under the foot
with reduced sensitivity and registered every subject with at least
one region above this threshold.
For pedographic measurements, patients and controls were
asked to walk barefoot over a capacitive platform (EMED ST4;
Novel, München, Germany) embedded flush in the floor. The
platform consisted of 2736 sensors with a spatial resolution of
four sensors per cm2 and a measurement frequency of 50 Hz. The
subjects were asked to walk barefoot across the platform with
normal step length and self-selected walking speed. Measurements were repeated until five steps of the right foot had been
recorded.
Pedographic pressure patterns were subdivided into 10
regions: medial (MH) and lateral heel (LH), medial (MM) and
lateral midfoot (LM), first metatarsal (M1), second metatarsal
(M2), lateral metatarsals (M345), hallux (H), second toe (T2)
and lateral toes (T345) (Database Pro-M 11.26; Novel). The
average pressure was calculated for each foot region [8]. The
contact time during the roll-over process was measured as an
indication of the patient’s gait velocity
[23].
Õ
Data were analysed using StatView 5.0 (SAS Institute, Cary,
NJ, USA). The Kruskal–Wallis test for non-parametric data was
used to reveal the significance of differences between subject
groups ( level 0.05). Correlation analysis was performed with
Spearman’s correlation coefficient.
Informed consent was obtained from all patients and subjects.
This study was approved by the local ethics committee.
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FIG. 1. Pedographic results for average pressure. *P50.05.
The average pressure was reduced under the medial and lateral
hindfoot (P50.05; Fig. 1) and the lesser toes (not significant)
but slightly increased under the midfoot, forefoot and hallux
(not significant).
Only one significant correlation coefficient was found between
sensitivity level (i.e. filament indices) and average pressure in the
same foot region, i.e. under the third metatarsal head (r ¼ 0.564).
This indicated that patients tended to produce higher pressures
under less sensitive areas. No significant correlation was found
between walking pain and sensitivity level.
Discussion
The present study revealed that plantar sensitivity may be
impaired in patients with rheumatoid feet. While not all patients
showed a loss of protective sensation in at least one of the foot
regions investigated, the patients were on the average significantly less sensitive in all regions compared with the control
group. This result may help to explain previous findings that
revealed significantly increased pressures under the central and
lateral forefoot in less severely affected patients with lower
walking pain, as opposed to lower pressures in more severely
affected patients with higher walking pain [A. Schmiegel,
M. Gaubitz, A. Schorat, A. Hilker and D. Rosenbaum, manuscript in preparation]. However, we found only one significant
correlation coefficient between sensitivity and pressure under
the central forefoot (r ¼ 0.564), which explains only 32% of the
variance of the pressure changes. Furthermore, no correlation
was found between sensitivity level and pain, which indicates
that other factors in addition to the local sensitivity may play
a role in the relationship between pain and pressure. Plantar
pressures may be affected by insufficient ligaments in the
forefoot [24, 25], rearfoot pronation [26], and pain-induced gait
modifications [27–30].
In conclusion, plantar sensitivity is decreased in RA patients
compared with healthy controls. Decreased tactile sensitivity
may indicate disturbed sensation for high peak pressures that
may ultimately cause mechanical damage in the foot. Therefore,
in RA patients—especially in those with impaired sensation—
pedography may be a useful tool in the detection of excessive
214
D. Rosenbaum et al.
forefoot loading before complications are manifested. However,
walking pain in RA patients is caused by multiple factors
and depends on inflammation and deformity of the foot joints
and impairment of pain sensation as well as pain-induced
changes in gait patterns.
Acknowledgements
Financial support from the German Ministry of Economy
is gratefully acknowledged (BMWA, PROINNO Project KF
0497301KWM3). The authors have declared no conflicts of
interest.
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