Caliper test reliable for feet

By Lynda Williams, Senior medwireNews Reporter

Two-point discrimination (TPD) using mechanical calipers is a reliable assessment for testing tactile acuity of the foot, demonstrates research published in Rheumatology.

TPD - the ability to determine whether one or two objects close together are touching the skin - was found to have good intra- and inter-rater reliability in 28 healthy volunteers who underwent measurement by 28 clinicians given 30 minutes of mechanical caliper training.

TPD was performed distally along the lateral margin of the sole, at the base of the fifth metatarsal.

Although TPD measurements at the neck were also found to have good reliability for both intra- and inter-rater assessments, only intra-rater measurements taken at the back and the hand were accurate, add G Lorimer Moseley (University of South Australia, Adelaide) and co-authors.

"This is important because tactile acuity is recognized as a clinical signature of cortical reorganization and TPD threshold is considered the key clinical assessment of cortical reorganization in rheumatology and musculoskeletal medicine," the team explains.

However, the researchers note that pooling or comparing TPD thresholds becomes less effective even at the foot or neck when taken by more than one physician which commonly happens among patients visiting more than one specialist.

Further analysis showed a large variability in measurements "suggesting that TPD assessment is reliable but not precise," Moseley et al write. Factors such as skin thickness or temperature, pressure, patient cooperation, and clinician technique have all previously been shown to affect TPD results.

But they note that clinician experience appeared to have no impact on the reliability of TPD measurement, despite some participants having no caliper experience and others reporting extensive TPD use in clinical practice.

"This is encouraging insofar as the utility of any measure depends on how much the equipment costs and how time consuming and difficult it is to perform. The callipers used here cost about AU$15 [US$ 15, € 12] each, the assessment took about 3 min and proficiency was obtained with minimal training," the researchers conclude.

"On the other hand, the lack of effect of experience is discouraging insofar as we can expect no improvement in reliability or precision with practice."

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