1. The Reliability of Pressurestat for Measuring Plantar Foot Pressures in Rheumatoid Arthritis Jill Firth1, Philip Helliwell2, Debbie Turner3, Wendy Smith3 and James Woodburn4 1Academic Unit of Musculoskeletal Nursing, University of Leeds, 2Academic Unit of Musculoskeletal Disease, University of Leeds, 3Department of Podiatry, University of Huddersfield,4 HealthQWest, Glasgow Caledonian University , UK
1 Background
Plantar pressure measurements have been used to measure foot function and as a screening tool to establish risk for tissue injury in the 'at risk' foot.
One disadvantage of plantar pressure measurements is that they are often dependent on costly specialist equipment and therefore data collection is often limited to specific sites.
PressurestatTM is a semi-quantitative foot pressure measurement system that is relatively cheap and easy to use and therefore has the potential to be used in routine clinical practice.
Some reliability work has been undertaken in the area of the identification of high plantar pressures in the diabetic foot, but the reliability of this pressure measurement system in the rheumatoid foot has not been established.
3 Methods
10 RA patients were recruited. Simultaneous barefoot plantar pressure measurements were recorded from the PressurestatTM footprint mat (Footlogic, Inc, New York, USA) and the EMED-ST (Novel, GmbH, Munich, Germany) systems using a first-step approach.
The foot was divided into six regions for analysis: distal medial and lateral, middle medial and lateral and proximal medial and lateral.
Four independent examiners quantified the peak pressure in each of the regions on the PressurestatTM using the calibration card provided on two separate occasions at least one week apart.
The absolute peak pressure values in each mask region were determined from the EMED-ST platform by masking in the same manner using a real size plantar pressure printout.
Table 1 Inter-observer kappa values at 1st and 2nd reading
Observer 2
Observer 3
Observer 4
Observer 1
0.45 / 0.59
0.26 / 0.38
0.37 / 0.49
0.27 / 0.30
0.43 / 0.47
0.38 / 0.21
Figure 2 – Background Noise
2 Aims
To establish the inter and intra–rater reliability of PressurestatTM to measure plantar foot pressures in patients with rheumatoid arthritis (RA).
4 Results
The raw PressurestatTM readings consistently exceeded those obtained by the EMED-ST system, whether the average (the mean of the range given by PressurestatTM) or maximum values were used (median differences 266kPa and 370 kPa for mean and maximum readings).
Correcting the PressurestatTM scores for 'background noise' (not suggested by manufacturer) inverted and improved these figures (median differences: -100kPa and -55kPa for mean and maximum).
Inter-observer kappa values are given in the Table (first and second readings). This represents fair to moderate agreement, with the level of improvement improving with the second readings.
Intra-observer kappa values were 0.57, 0.51, 0.33 and 0.43 for observers 1-4 respectively. This represents fair to moderate intra-observer agreement.
Agreement varied by region assessed. For the forefoot observers had 62% complete agreement, for the mid-foot 45%, and the rearfoot 51%.
Figure 1 – PressurestatTM
5 Conclusions
Pressure data obtained with the Pressurestat TM system in patients with rheumatoid arthritis is imprecise.
This study has shown fair to moderate intra- and inter- observer agreement when reading the PressurestatTM prints, with some evidence of a learning effect.
Acknowledgements
Jill Firth is funded by a Smith & Nephew Foundation Doctoral Scholarship