novel Award First Prize PaperOrthotic management of plantar pressure and pain in rheumatoid arthritis☆
Introduction
Rheumatoid arthritis (RA) has been associated with a range of foot deformities and distinctive patterns of plantar pressure distribution [1], [2], [3], [4], [5]. More importantly, the rheumatoid foot can be painful on weight bearing to the extent that ambulation is severely restricted, greatly limiting the person's ability to perform even basic tasks of daily living [5]. Investigation of deformity and pressure distribution in RA highlight the metatarsal heads as particularly problematic and this observation is supported by reports of maximum pain in the metatarsal head region [2], [3], [4], [6].
It is presumed that metatarsalgia associated with RA is caused by excessive pressure being applied to the metatarsal heads [2], [7]. This is thought to be a result of bone deformity and soft tissue atrophy which alter the normal plantar pressure distribution, subjecting normally unloaded foot regions to pressure [2]. In addition, normally pressure tolerant regions may become overloaded or abnormally sensitive to pressure [8]. To date, however, there have been no investigations of the relationship between pressure and pain in the rheumatoid foot. One investigation of the effects of orthoses in relieving metatarsalgia in a non-RA group found custom made orthoses more effective than ready made orthoses, but did not find a relationship between peak pressure and pain [9].
Clinicians aim to reduce pressure to the metatarsal heads by distributing forces more equally over the plantar surface [10], [11]. Foot orthoses incorporating a variety of design features are used to reduce metatarsal head pressure [7], [12], [13], [14], [15]. Selection and refinement of orthosis design commonly involves a ‘trial and error’ approach in which the orthosis is adjusted repeatedly until the patient reports some relief from pain. While addressing the functional needs of the patient (pain reduction), the technique is inefficient and relies on the experience of the orthotist. There are no general guidelines regarding the most effective design features for management of pain in the RA foot.
Recently, there have been attempts to utilise foot shape or pressure distribution as inputs for computer aided design and manufacture (CAD/CAM) of foot orthoses (eg. Amfit, Footmaxx). It seems plausible that a CAD/CAM system for foot orthoses could be developed if the relationship between pressure and pain in the rheumatoid foot was better understood.
One aim of this project was to evaluate the relative effectiveness of four different orthosis designs in managing pressure and pain in the rheumatoid foot. A second aim was to investigate the relationship between second metatarsal head plantar pressure and pain in the rheumatoid foot.
Section snippets
Subjects
Twelve people with a history of RA with forefoot pain on shod weightbearing volunteered for the study. Subjects were excluded on the basis of prior excision of one or more metatarsal heads, the presence of foot deformity that prevented application of testing apparatus, or the presence of other signs and symptoms that prevented the subject making a judgment of foot pain severity. Of the 12 subjects and 24 feet tested, one foot was excluded from all analysis because foot deformity prevented the
Cadence
Cadence data was analysed to assess whether cadence (and, by implication, the closely associated walking velocity) varied with orthosis condition since these variables have been demonstrated to affect plantar pressure [22], [23]. Mean and standard deviation cadence scores are listed in Table 2. A one way ANOVA for repeated measures indicated no significant differences in cadence between orthosis conditions (F=0.11, P=0.980). As a result, it was not considered necessary to include cadence as a
Discussion
This investigation demonstrated that foot orthoses can be effective in management of pain in rheumatoid feet. Custom moulded orthoses with a metatarsal dome significantly reduced both walking and standing pain and were the orthoses preferred by the majority of subjects.
A highly significant relationship was found between walking pain and standing pain. The relationship suggests that the increased movements required during gait and the increased forces produced during walking did not magnify or
Conclusion
Overall, the custom made foot orthosis with a metatarsal dome performed best in terms of simultaneous pressure reduction and pain relief. A custom made foot orthosis with a metatarsal bar and a prefabricated foot orthosis were equally effective in metatarsal head pressure reduction but had no effect on pain levels. The standard custom made foot orthosis was effective in relieving metatarsalgia in walking but had less effect on plantar pressure.
A relationship was demonstrated between average
Acknowledgements
The authors wish to acknowledge Dr Ken Greenwood from the Department of Psychological Science, La Trobe University, for his assistance with statistical analysis and also the Orthotic and Prosthetic Department at the Royal Perth Rehabilitation Hospital for supporting the Project.
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This paper was awarded 1st prize for the novel award 1998 at the VI EMED User Meeting, Brisbane, Australia, 8–12 August, 1998.