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Improving footwear to prevent ulcer recurrence in diabetes: Analysis of
adherence and pressure reduction
Waaijman, R.
Publication date
2013
Document Version
Final published version
Link to publication
Citation for published version (APA):
Waaijman, R. (2013). Improving footwear to prevent ulcer recurrence in diabetes: Analysis of
adherence and pressure reduction.
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Improving footwear to prevent
ulcer recurrence in diabetes
Analysis of adherence and pressure reduction
IMPROVING FOOTWEAR TO PREVENT ULCER
RECURRENCE IN DIABETES
ANALYSIS OF ADHERENCE AND PRESSURE REDUCTION
Waaijman, R.
Improving footwear to prevent ulcer recurrence in diabetes. Analysis of adherence and pressure reduction.
Academisch proefschrift, Universiteit van Amsterdam. ISBN/EAN 978-94-6108-470-5
Cover design and lay-out by Roelof Waaijman. Printed by Gildeprint Drukkerijen, Enschede.
© 2013, Roelof Waaijman, The Netherlands.
No parts of this thesis may be reproduced or transmitted in any form or by any means, electronically or mechanically, including photocopying, recording or any information storage and retrieval system, without prior permission from the author.
IMPROVING FOOTWEAR TO PREVENT ULCER
RECURRENCE IN DIABETES
ANALYSIS OF ADHERENCE AND PRESSURE REDUCTION
ACADEMISCH PROEFSCHRIFT
ter verkrijging van de graad van doctor
aan de Universiteit van Amsterdam
op gezag van de Rector Magnificus
prof. dr. D.C. van den Boom
ten overstaan van een door het college voor promoties ingestelde
commissie, in het openbaar te verdedigen in de Aula der Universiteit
op vrijdag 5 juli 2013, te 13:00 uur
door
Roelof Waaijman
Promotiecommissie:
Promotor:
prof. dr. F. Nollet
Co-promotores:
dr. S.A. Bus
dr. M. de Haart
Overige leden:
prof. dr. P.M.M. Bossuyt
prof. dr. R.W.M. van Deursen
prof. dr. C.N. van Dijk
prof. dr. K. Postema
prof. dr. N.C. Schaper
dr. J.G. van Baal
Faculteit der Geneeskunde
The DIAbetic Foot Orthopedic Shoe (DIAFOS) trial was financially supported by:
The Dutch Diabetes Research Foundation (Diabetes Fonds)
The Dutch Foundation for the Development of Orthopedic Footwear Technology (OFOM) The Dutch Organization for Health Research and Development (ZonMW)
Department of Rehabilitation, Academic Medical Center Amsterdam
Printing of this thesis was financially supported by:
Academic Medical Center Amsterdam | www.amc.nl Roessingh Revalidatie Techniek | www.rrt.nl Anna Fonds | www.annafonds.nl
George In der Maur orthopedische schoentechniek | www.indermaur.nl Penders Voetzorg | www.pendersvoetzorg.nl
Biometrics | www.biometrics.nl Buchrnhornen | www.buchrnhornen.nl
Tomorrow Options | www.tomorrow-options.com OIM Orthopedie | www.oim.nl
Livit Orthopedie | www.livit.nl Novo Nordisk | www.novonordisk.nl Hanssen footcare | www.footcare.nl
Chapter 1 General introduction 9
Chapter 2 The interdependency of peak pressure and pressure-time 23
integral in pressure studies on diabetic footwear: no need to report both parameters.
Gait and Posture 2012; 35: 1-5
Chapter 3 New monitoring technology to objectively assess 35
adherence to prescribed footwear and assistive devices during ambulatory activity.
Archives of Physical Medicine and Rehabilitation 2012;
93: 2075-2079
Chapter 4 Adherence to wearing prescription custom-made footwear 47
in patients with diabetes at high risk for plantar
foot ulceration.
Diabetes Care 2013; 36: 1613-1618
Chapter 5 Pressure-reduction and preservation in custom-made 63
footwear of patients with diabetes and a history of
plantar ulceration.
Diabetic Medicine 2012; 29: 1542–1549
Chapter 6 Effect of custom-made footwear on foot ulcer recurrence 79
in diabetes: a multicenter randomized controlled trial. Submitted
Chapter 7 Prognostic factors of plantar foot ulcer recurrence in 97
neuropathic diabetic patients. In preparation
Chapter 8 General discussion 115
Summary / Nederlandse samenvatting 129
Dankwoord 137
List of Publications 143
1
Chapter 1
Diabetes mellitus affects more than 366 million people worldwide and its prevalence is expected to rise substantially in the next decade1. The lifetime incidence of developing
an ulcer is as high as 25% in patients with diabetes2. Ulcers can cause infections,
ampu-tations and emotional and physical loss2, 3. It is believed that every 30 seconds a lower
limb is lost somewhere in the world4 due to diabetes of which 85% is preceded by a foot
ulcer5. Ulcers are a costly complication of diabetes, accounting for approximately one
third of the direct healthcare costs associated with diabetes6. Therefore, diabetic foot
ulcers are a major problem in patients with diabetes and the prevention of foot ulcers has a great potential in the individual well-being and public health gain.
Patients with a previous plantar foot ulcer often develop a recurrent ulcer7-12. It is
sug-gested that the development of a foot ulcer reflects the presence of underlying patho-logic conditions, such as micro- and macro-vascular dysfunction, and peripheral nerve damage. Therefore patients with previous ulcers are at high risk for ulcer recur-rence7, 9. One of the strategies used to prevent ulcer recurrence is providing
custom-made footwear. There are many studies on the effectiveness of custom-custom-made footwear to prevent ulcer recurrence, but the evidence to support this approach is still meagre13.
Since ulcer recurrence is found to be multi-factorial14, the effectiveness of custom-made
footwear needs to be studied in a broader perspective of factors to determine prognos-tic factors of plantar foot ulcer recurrence. In this introduction, the causes of ulceration are described, followed by a description of the existing evidence on the effectiveness of custom-made footwear and a description of a broad range of possible risk factors for plantar foot ulcer recurrence. Thereafter the approach we took to study the effective-ness of custom-made footwear and prognostic factors of plantar foot ulcer recurrence is described and this chapter will be finalized with the aims and outline of this thesis.
CAUSES OF ULCER RECURRENCE
The current theory of foot ulcer pathogenesis is that ulcers are caused by a combina-tion of interacting risk factors, the three most relevant being: 1) a previous ulcer; 2) peripheral neuropathy; and 3) increased plantar foot pressures15. Several studies found
an association between having previous ulcers and ulcer recurrence with relative risks between 1.6 and 5.3 in patients with diabetes7-9, 11. Especially a previous ulcer on the
plantar side of the foot increases the risk for ulcer recurrence12. Peripheral neuropathy
is also associated with ulcer occurrence. Odds ratio’s of 18 were found in diabetic pa-tients with the inability to sense a 10-gram SWF monofilament11, 16. Peripheral
neuropa-thy results in loss of protective sensation and is present in half of the diabetic patients with an age above 60 years17. Due to this inability to sense pressure and pain, high
pres-sures may not be detected and patients continue to walk, which could lead to damage of the skin18. Also, a more than twofold risk on ulcer recurrence was found in patients
with high plantar pressures11, 19, which could account for the fact that half of the ulcers
occur on the plantar side of the foot20. Thus, high plantar pressures to a neuropathic
foot play an important contributing role in ulcer recurrence11, 19-24. Furthermore, foot
deformities, limited joint mobility and reduced plantar soft tissue thickness result in higher plantar peak pressures25, 26. Since patients with diabetes and neuropathy often
have these abnormalities, their feet often show high peak pressures and are therefore at high risk for ulcer recurrence.
Introduction
1
PRESSURE, CUSTOM-MADE FOOTWEAR AND ULCER OCCURRENCE
Elevated plantar peak pressures are associated with ulcer recurrence11, 19, 24, 27. To date,
the association between plantar peak pressure and ulcer recurrence has only been as-sessed in barefoot studies. These peak pressures do not fully reflect the biomechani-cal stress that the patient experiences during the day, because patients do not walk barefoot all day but use footwear most of the time. Therefore, in-shoe peak pressures are also necessary to determine the biomechanical stress on the foot. For that reason, footwear that reduces biomechanical stress on the foot might prevent ulcer recurrence. Custom-made footwear aims to reduce in-shoe plantar peak pressures as compared to confection footwear. Based on this assumption, diabetic foot care-providers currently prescribe patients at high risk for ulceration with custom-made footwear to prevent foot ulceration15, 28-30. Despite custom-made footwear, a recent study showed that still
40% of the patients with neuropathy and a previous ulcer developed a recurrent ulcer, in a median 126 days31. This high recurrence rate indicates that besides foot care,
foot-wear might not (sufficiently) target the relevant risk factors. Possible explanations for this high recurrence rate might be that relieving pressure (offloading) in custom-made footwear is variable32 or that the prescribed footwear is not worn sufficiently33. In this
regard the quality of the custom-made footwear and patient’s adherence to wearing the prescribed footwear are thought to be important prognostic factors.
The offloading effect of custom-made footwear is achieved by accommodating the insoles to the foot and the use of special materials and corrective elements in such a way that load from high pressure locations is redistributed to low pressure locations34.
Cross-sectional studies found that in-shoe plantar peak pressures is reduced in custom-made footwear and a longitudinal study demonstrated that the initial pressure reduc-tion can be maintained in the first 6 months, but these studies did not follow-up the patients to evaluate ulcer outcome35-40. Prospective studies show conflicting results
re-garding the effectiveness of custom-made footwear to prevent ulcer recurrence. Several non-randomized longitudinal studies have found that ulcer recurrence rates were much lower in patients wearing custom-made footwear compared to patients wearing their own shoes33, 41-43. However, a randomized controlled trial found no beneficial effect of
specialized footwear on foot ulcer recurrence rate44. In none of these longitudinal
stud-ies on ulcer recurrence the in-shoe plantar pressures were measured, and therefore, the effectiveness of footwear in pressure relief is unknown. Therefore, it remains unclear if the conflicting results of these studies can be explained by differences in pressure-relieving quality of the different footwear used or by other factors. Furthermore, these longitudinal studies had several other limitations: 1) patients were not always repre-sentative of the appropriate high risk population: not all patients had neuropathy and often patients with amputations and major foot deformities were excluded; 2) not all studies randomized the patients to an intervention group, or there was cross-over be-tween study groups; 3) the definition of the primary ulcer outcome was often unclear, unreliable or very conservative and only one study assessed adherence to wearing the studied footwear subjectively. In view of this, two systematic reviews concluded that there is still no compelling evidence on the effectiveness of therapeutic footwear in pre-venting ulcer recurrence13, 45.
PROGNOSTIC RISK FACTORS OF ULCER RECURRENCE
Elevated dynamic barefoot plantar pressure during walking is, in the presence of neu-ropathy, an important predictor of diabetic foot ulceration. One biomechanical study found the most optimal barefoot peak pressure cut-off level, 700kPa, to be 70% sensi-tive and 65% specific for ulceration46, while another study found a barefoot peak
pres-sure of 875kPa to be 64% sensitive and 46% specific27. These findings indicate that a
significant number of patients develop a recurrent ulcer despite lower pressure than threshold and patients do not develop an ulcer despite higher pressures than threshold. These results suggest that ulcer recurrence can not be predicted solely based on bare-foot pressure and predictions may be improved by taking other prognostic factors into account. Possible prognostic factors can be divided biomechanical, behavioural, and disease-related factors14. The main factors of interest in this thesis are discussed below.
Biomechanical factors
Biomechanical stress parameter
One of the risk factors of ulcer recurrence is biomechanical stress on the plantar side of the foot. Often used indicators of biomechanical stress are plantar pressure and peak pressure-time integral. Maximum peak pressure represents the maximum measured pressure of a defined region during one step cycle. Peak pressure-time integral inte-grates the peak pressure to the time duration of one step cycle. Although both param-eters are often reported, specific conclusions per parameter are not usually reported, suggesting that these parameters may be interchangeable47. A study that explores the
association between maximum peak pressure and pressure-time integral in the diabetic foot is needed to further explore whether or not these parameters are interchangeable.
Barefoot pressure
Foot deformities, minor amputation, limited joint mobility, major callus and reduced plantar soft tissue thickness frequently occur in diabetic patients and all result in in-creased plantar foot pressures25, 26, 48-50. Several studies assessed the association
be-tween barefoot plantar peak pressure and ulcer occurrence and found that elevated barefoot plantar peak pressure is predictive for ulcer occurrence in diabetic patients with neuropathy11, 19, 24, 27. As mentioned before, the defined pressure thresholds in these
studies showed a low sensitivity and specificity. It is unlikely that these patients walk barefoot all day. Adherence determines the amount of steps the patient wears (pro-tective) footwear. Furthermore, these patients show variation in the level of ambulant activity51. Therefore, an approximation of the true biomechanical stress on the plantar
side of the foot might be improved when in-shoe pressures, adherence and ambulant activity are taken into account in combination with barefoot pressures. This suggests that the prediction of plantar foot ulceration can be more precise when more factors are included to estimate the biomechanical stress.
In-shoe plantar pressure in custom-made footwear
Inappropriate footwear has been reported to be the root cause of 21-76% of diabetic foot ulcers and/or amputations52. It is said, for example, that inappropriate footwear
Introduction
1
in clinical practise prescribe custom-made footwear in the belief that such footwear reduces plantar peak pressures and thereby reduce the incidence of foot ulceration. However, the evidence base for such a view is unclear. Currently, prescription of cus-tom-made footwear is primarily based on clinical expertise and the effectiveness of this footwear is most often evaluated on whether the patient remains free of ulceration. Regular objective evaluation of peak pressures in custom-made footwear is not being done. Due to the presence of peripheral neuropathy, the patient’s feedback on pressure, pain and comfort is limited. Therefore, variability exists in the offloading properties of this footwear32, 34. This variability in offloading may explain the high recurrence rates
of ulceration31. Offloading may be improved by modifying footwear after it has been
delivered to the patient, using objective measurement tools. In-shoe plantar pressure analysis is such a tool that can efficiently guide footwear modification to create better offloading properties, although studied in a relatively small and heterogeneous group of patients53. Furthermore, wear and tear of footwear or progress of foot deformities
may alter the pressure offloading over time, requiring repeated footwear modifications over time. Therefore a study that explores the effect of improving offloading guided by in-shoe pressure analyses and the course of peak pressure over time in a large homog-enous group of high-risk patients and footwear conditions is needed.
Behavioural factors
Adherence to footwear use
To effectively contribute to the prevention of ulcer recurrence, custom-made footwear should be worn by the patient, in particular when being ambulant54. An observational
study reported that half of the ulcer recurrence can be prevented when therapeutic footwear was worn more than 60% of the daytime33. But, studies in which footwear use
was self-reported have shown that only 22-36% of patients with diabetes wear their prescribed footwear regularly (>80% of the day)55, 56. This indicates that many patients
do not wear their therapeutic footwear as intended, elevating the risk of ulcer recur-rence. Furthermore, to date, footwear adherence has been measured subjectively and might therefore be less accurate and reliable than objective methods. Therefore, data on footwear adherence in patients who have diabetes and are at high risk for ulceration should be measured objectively, but these methods have until recently been unavail-able. Having these data and knowing what determines footwear use is valuable in ad-dressing issues of footwear effectiveness.
Ambulant activity
Apart from plantar foot pressure and adherence, other factors such as the type and intensity of daily ambulant activity might determine clinical outcome, since the amount of weight-bearing activity is likely to influence the amount of mechanical stress accu-mulated by plantar tissues57. So far, evidence for the relation between ambulant activity
and ulcer recurrence is unclear. Several studies assessed daily weight-bearing activity, but none found that increased activity was associated with ulcer occurrence51, 58-60.
How-ever, increased intra-individual day to day variability in activity was associated with ulcer recurrence51. Furthermore, weight-bearing activity in combination with plantar
pressures is suggested to predict ulcer recurrence60. The number of steps taken during
accumu-lated stress on the foot. This accumuaccumu-lated stress was surprisingly lower in patients who had previous ulcers60, 61. In these previous studies on accumulated stress, adherence to
wearing footwear was not taken into account and accumulated stress was calculated as if the patients wore the footwear in each step, which seems unlikely. Therefore, as mentioned before, information on ambulant activity in relation to footwear adherence, barefoot peak pressures, and in-shoe peak pressures might result in an improved esti-mate of the accumulated stress, with improved prediction of ulcer recurrence.
Patient and disease-related factors
Besides the above mentioned biomechanical and behavioural factors, several studies have identified many significant patient and disease-related risk factors for diabetic foot ulceration7-12, 62, 63. These factors include age, gender, BMI, degree of peripheral
neu-ropathy, peripheral arterial disease, diabetes type and duration, history of ulceration, Hb1Ac, deformities and minor lesions (callus, hematoma, blisters). These patient and disease-related factors might mediate or moderate the relation between biomechanical and behavioural factors and ulcer outcome, and therefore they are important to exam-ine. For that reason these parameters should be integrated in a broader perspective to study their influence on ulcer recurrence in relation to other risk factors.
THE DIABETIC FOOT ORTHOPAEDIC SHOE TRIAL
To increase knowledge on the effect of plantar foot pressure and custom-made footwear on plantar foot ulcer recurrence, the DIAFOS trial was conducted. DIAFOS (the DIAbetic Foot Orthopaedic Shoe trial; Dutch trial register NTR1091) is a multicenter randomized controlled trial, in which the effectiveness of offloading-improved custom-made foot-wear in comparison with non-improved custom-made footfoot-wear on plantar foot ulcer recurrence in diabetic patients with neuropathy and a previous ulcer was studied. In this study, the Academic Medical Centre in Amsterdam collaborated with 9 other mul-tidisciplinary diabetic foot centres and 9 orthopaedic footwear companies in the Neth-erlands. Patients in the intervention group were provided with custom-made footwear that was improved in its offloading capacity using in-shoe plantar pressure measure-ments as guidance tool for footwear modifications. Since the offloading properties of this footwear might be affected over time due to wear and tear or an altered foot shape, each 3 months a follow-up visit was scheduled so that adjustments could be made to ensure improved offloading. In the control group, patients received custom-made foot-wear that was prescribed following normal clinical practice, in which in-shoe pressure measurements were not used to improve offloading of the footwear. This footwear was also monitored for pressure each 3 months. Additionally, we measured many other pa-rameters in addition to foot pressure to gain further insight in prognostic risk factors of ulcer recurrence. These data provided us with more insight in the biomechanical stress applied to the foot in combination with adherence to wearing prescribed footwear use and ambulatory weight-bearing activity (e.g. walking)14.
In summary, the review of the literature shows that ulcer recurrence is a major problem in patients with a diabetic foot. Several studies have explored causal pathways and elab-orated on prognostic factors of ulcer recurrence. These studies led to screening tools to identify patients at risk and interventions with the goal to prevent ulcer recurrence. One of the interventions that is often used is prescription of custom-made footwear,
Introduction
1
because there is an almost universal clinical opinion that this intervention is effective52.
However, intervention studies show conflicting results in this matter. None of the pro-spective studies on ulcer recurrence measured the offloading properties of prescribed footwear and none of the studies measured adherence to wearing this footwear objec-tively. With the use of in-shoe pressure analysis we can evaluate, improve, and preserve pressure offloading of prescribed footwear. Furthermore, by applying new quantitative technologies, adherence to footwear use and ambulant activity can be measured in an objective way. With these technologies, a wide range of biomechanical, behavioural, and patient- and disease-related prognostic factors of ulcer recurrence can be assessed which so far have remained underexposed. Therefore, the goal of the DIAFOS project was to study the effectiveness of offloading-improved custom-made footwear in a lon-gitudinal multicenter randomized controlled trial that includes objectively measured peak pressures, adherence to wearing custom-made footwear and ambulant activity.
AIMS OF THIS THESIS
The aims of this thesis were to select the most appropriate biomechanical stress para-meter to use in pressure studies on the diabetic foot, to evaluate the use of foot pressure analysis to modify footwear, to develop a method to measure adherence and to assess adherence to wearing custom-made footwear objectively in these patients. These stu-dies will form the basis of the main aims of this thesis, which are: assessing the effecti-veness of pressure-improved custom-made footwear on plantar foot ulcer recurrence and to expand the body of knowledge on the predictive value of a broad range of bio-mechanical, behavioural, and patient and disease-related factors on plantar foot ulcer recurrence in diabetic patients with neuropathy and a previously healed plantar foot ulcer.
More specifically, the objectives of this thesis are:
1. To explore the interdependency of maximal peak pressure and pressure-time inte-gral in diabetic patients wearing different types of footwear.
2. To assess the validity and feasibility of a new temperature-based adherence moni-tor to measure adherence of wearing different types of footwear.
3. To assess objectively measured adherence to wearing prescribed custom-made foo-twear during ambulant activity.
4. To assess the value of using in-shoe plantar pressure analysis for evaluating, impro-ving and maintaining the offloading properties of newly prescribed custom-made footwear.
5. To assess if offloading-improved custom-made footwear reduces recurrence of plantar ulcers.
6. To assess the prognostic value of biomechanical, behavioural, and patient and di-sease-related factors on plantar foot ulcer recurrence.
OUTLINE OF THIS THESIS
Chapter 2 presents a study that explores the association between maximum peak pres-sure and prespres-sure time integral. The results of this study guided us to select the most appropriate parameter to be used for the subsequent studies.
In chapter 3 a study in which the validity and feasibility of a new sensor that measures adherence to wearing footwear in an objective way, was tested. With this technology we assessed adherence to wearing prescribed custom-made footwear in diabetic patients with neuropathy and a previous ulcer. The study results are described in chapter 4. Chapter 5 assesses the value of using in-shoe plantar pressure analysis to evaluate, improve and preserve the offloading properties of newly prescribed custom-made foo-twear. Whether this approach was effective in preventing plantar foot ulcer recurrence in diabetic patients was studied in a multicenter randomized controlled trail of which the results are described in chapter 6.
In chapter 7 a study is described in which the prognostic value of a broad range of bio-mechanical, behavioural, and patient- and disease-related factors on plantar diabetic foot ulcer recurrence was assessed in order to explore risk factors for ulcer recurrence. Finally, in chapter 8 the main findings of this thesis are presented and some metho-dological considerations are discussed. Additionally, the clinical implications of these studies and some recommendations for further research together with an overall con-clusion is described.
Introduction
1
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Introduction
1
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35. Guldemond NA, Leffers P, Schaper NC, Sanders AP, Nieman F, Willems P, Walenkamp GH. The effects of insole configurations on forefoot plantar pressure and walking convenience in diabetic patients with neuropathic feet. Clin Biomech 2007; 22: 81-87.
36. Mueller MJ, Lott DJ, Hastings MK, Commean PK, Smith KE, Pilgram TK. Efficacy and mecha-nism of orthotic devices to unload metatarsal heads in people with diabetes and a history of plantar ulcers. Phys Ther 2006; 86: 833-842.
37. Praet SF, Louwerens JW. The influence of shoe design on plantar pressures in neuropathic feet. Diabetes Care 2003; 26: 441-445.
38. Tsung BY, Zhang M, Mak AF, Wong MW. Effectiveness of insoles on plantar pressure redistri-bution. J Rehabil Res Dev 2004; 41: 767-774.
39. Bus SA, Valk GD, van Deursen RW, Armstrong DG, Caravaggi C, Hlavacek P, Bakker K, Cava-nagh PR. The effectiveness of footwear and offloading interventions to prevent and heal foot ulcers and reduce plantar pressure in diabetes: a systematic review. Diabetes Metab Res Rev 2008; 24 Suppl 1: S162-S180.
40. Lobmann R, Kayser R, Kasten G, Kasten U, Kluge K, Neumann W, Lehnert H. Effects of pre-ventative footwear on foot pressure as determined by pedobarography in diabetic patients: a prospective study. Diabet Med 2001; 18: 314-319.
41. Busch K, Chantelau E. Effectiveness of a new brand of stock ‘diabetic’ shoes to protect against diabetic foot ulcer relapse. A prospective cohort study. Diabet Med 2003; 20: 665-669. 42. Uccioli L, Faglia E, Monticone G, Favales F, Durola L, Aldeghi A, Quarantiello A, Calia P,
Men-zinger G. Manufactured shoes in the prevention of diabetic foot ulcers. Diabetes Care 1995; 18: 1376-1378.
43. Dargis V, Pantelejeva O, Jonushaite A, Vileikyte L, Boulton AJ. Benefits of a multidisciplinary approach in the management of recurrent diabetic foot ulceration in Lithuania: a prospec-tive study. Diabetes Care 1999; 22: 1428-1431.
44. Reiber GE, Smith DG, Wallace C, Sullivan K, Hayes S, Vath C, Maciejewski ML, Yu O, Heagerty PJ, Lemaster J. Effect of therapeutic footwear on foot reulceration in patients with diabetes: a randomized controlled trial. JAMA 2002; 287: 2552-2558.
45. Spencer S. Pressure relieving interventions for preventing and treating diabetic foot ulcers. Cochrane Database Syst Rev 2000: CD002302.
46. Armstrong DG, Peters EJ, Athanasiou KA, Lavery LA. Is there a critical level of plantar foot pressure to identify patients at risk for neuropathic foot ulceration? J Foot Ankle Surg 1998; 37: 303-307.
47. Bus SA, Waaijman R. The value of reporting pressure-time integral data in addition to peak pressure data in studies on the diabetic foot: A systematic review. Clin Biomech 2013; 28: 117-121.
48. Mueller MJ, Hastings M, Commean PK, Smith KE, Pilgram TK, Robertson D, Johnson J. Fore-foot structural predictors of plantar pressures during walking in people with diabetes and peripheral neuropathy. J Biomech 2003; 36: 1009-1017.
49. Payne C, Turner D, Miller K. Determinants of plantar pressures in the diabetic foot. J Diabetes Complications 2002; 16: 277-283.
50. Pataky Z, Golay A, Faravel L, Da SJ, Makoundou V, Peter-Riesch B, Assal JP. The impact of cal-losities on the magnitude and duration of plantar pressure in patients with diabetes melli-tus. A callus may cause 18,600 kilograms of excess plantar pressure per day. Diabetes Metab 2002; 28: 356-361.
51. Armstrong DG, Lavery LA, Holtz-Neiderer K, Mohler MJ, Wendel CS, Nixon BP, Boulton AJ. Va-riability in activity may precede diabetic foot ulceration. Diabetes Care 2004; 27: 1980-1984 52. Cavanagh PR. Therapeutic footwear for people with diabetes. Diabetes Metab Res Rev 2004;
20 Suppl 1: S51-S55.
53. Bus SA, Haspels R, Busch-Westbroek TE. Evaluation and optimization of therapeutic foot-wear for neuropathic diabetic foot patients using in-shoe plantar pressure analysis. Diabe-tes Care 2011; 34: 1595-1600.
54. Connor H, Mahdi OZ. Repetitive ulceration in neuropathic patients. Diabetes Metab Res Rev 2004; 20 Suppl 1: S23-S28.
55. Knowles EA, Boulton AJ. Do people with diabetes wear their prescribed footwear? Diabet Med 1996; 13: 1064-1068.
56. McCabe CJ, Stevenson RC, Dolan AM. Evaluation of a diabetic foot screening and protection programme. Diabet Med 1998; 15: 80-84.
57. Cavanagh PR, Ulbrecht JS, Caputo GM. Biomechanical aspects of diabetic foot disease: aetio-logy, treatment, and prevention. Diabet Med 1996; 13 Suppl 1: S17-S22.
58. Lemaster JW, Reiber GE, Smith DG, Heagerty PJ, Wallace C. Daily weight-bearing activity does not increase the risk of diabetic foot ulcers. Med Sci Sports Exerc 2003; 35: 1093-1099. 59. Lemaster JW, Mueller MJ, Reiber GE, Mehr DR, Madsen RW, Conn VS. Effect of weight-bearing
activity on foot ulcer incidence in people with diabetic peripheral neuropathy: feet first ran-domized controlled trial. Phys Ther 2008; 88: 1385-1398.
60. Maluf KS, Mueller MJ. Novel Award 2002. Comparison of physical activity and cumulative plantar tissue stress among subjects with and without diabetes mellitus and a history of recurrent plantar ulcers. Clin Biomech 2003; 18: 567-575.
61. Lott DJ, Maluf KS, Sinacore DR, Mueller MJ. Relationship between changes in activity and plantar ulcer recurrence in a patient with diabetes mellitus. Phys Ther 2005; 85: 579-588. 62. Apelqvist J, Larsson J, Agardh CD. Long-term prognosis for diabetic patients with foot ulcers.
J Intern Med 1993; 233: 485-491.
63. Monteiro-Soares M, Boyko E, Ribeiro J, Ribeiro I, Dinis-Ribeiro M. Predictive factors for dia-betic foot ulceration: a systematic review. Diabetes Metab Res Rev 2012.
Chapter 2
Gait and Posture 2012; 35: 1-5
© Reprinted with permission from Elsevier
Roelof Waaijman
Sicco A. Bus
THE INTERDEPENDENCY OF PEAK PRESSURE AND
PRES-SURE-TIME INTEGRAL IN PRESSURE STUDIES ON
DIABE-TIC FOOTWEAR: NO NEED TO REPORT BOTH PARAMETERS
ABSTRACT
Background: In plantar pressure studies on diabetic footwear, both the maximum peak pressure (MPP) and peak pressure-time integral (PTI) are often reported. However, specific conclusions for each parameter are not commonly reported, suggesting these parameters may be interchangeable. The aim was to explore the interdependency of MPP and PTI in diabetic patients wearing different types of footwear.
Methods: In-shoe plantar pressure was measured in 69 neuropathic diabetic patients who walked in custom made footwear, forefoot offloading shoes, cast shoes, and/or standard footwear. For each of six anatomical foot regions, correlation coefficients were calculated between MPP and PTI. To assess parameter congruency, the percentage of patients showing correlation coefficients > 0.7 or coefficients of variation for both MPP and PTI < 10%, was calculated.
Results: Across all footwear conditions, MPP and PTI were highly correlated in the fo-refoot and midfoot (r > 0.78 in all but one foot region in one footwear condition). Lo-wer correlations coefficients Lo-were found in the rearfoot (r = 0.43-0.45). Across regions, between 46% and 87% of patients (mean 72%) showed parameter congruency in the forefoot and midfoot.
Conclusions: The results showed that the MPP and PTI are highly interdependent in those foot regions most at risk for plantar ulceration in patients wearing commonly prescribed footwear. Since MPP has been shown to date to be the clinically more rele-vant parameter of the two, these results suggest that the value of reporting PTI in ad-dition to MPP in the same diabetic footwear study is small.
2
INTRODUCTION
In-shoe plantar pressure assessment is becoming increasingly popular in both research and clinical practice to evaluate the effects of prescribed footwear in diabetic patients who have a foot ulcer or who are at risk for ulceration. Foot ulcers are a serious pro-blem, with a life-time prevalence of 15-25% in the diabetic population1. These ulcers
can lead to infection and lower limb amputation, with 85% of all non-traumatic ampu-tations in diabetes being preceded by a foot ulcer2. In the presence of loss of protective
sensation due to peripheral neuropathy, the majority of plantar foot ulcers develop as a result of the repetitive action of increased mechanical stress (i.e. pressure) on the foot during ambulation3. The goal of prescribed footwear is to lower these pressures in
or-der to heal a plantar foot ulcer or to prevent it from (re)occurring.
In pressure studies on diabetic footwear, often multiple pressure parameters are repor-ted. The maximum peak pressure (MPP) is almost always reported, likely because both in retrospective and prospective studies, diabetic foot ulceration has been associated with the presence of elevated MPP3-6. A significant odds ratio of 3.2 has been found7.
The peak pressure-time integral (PTI) is also often reported. The PTI has also been as-sociated with foot ulceration, but this association has not yet been demonstrated in a prospective analysis8-10. Recently, a systematic review of the diabetic foot literature
from our group showed that in the majority of studies collecting both MPP and PTI data, differences in outcomes between these two parameters were generally small and con-clusion were non-specific11. Also recently, Keijsers et al.12 found that MPP and PTI were
highly interdependent in healthy subjects walking barefoot across a pressure platform. The findings in these studies suggest that these parameters may be interchangeable and the value of reporting both parameters in the same study may be limited.
Because of their suggested relevance in diabetic foot ulceration and their suggested in-terdependency in previous studies, we chose to further explore the association between MPP and PTI in the diabetic foot. The aim of this study was to assess the degree of inter-dependency of MPP and PTI in foot pressure analyses of neuropathic diabetic patients wearing different types of offloading footwear. We hypothesized that a strong associ-ation between these two pressure parameters would suggest that there is no need to report both parameters in the same footwear study.
METHODS
Subjects
A total 69 diabetic patients at risk for foot ulceration were included in this study (60 males, mean (SD) age 60.7 (8.9) years, mean (SD) diabetes duration 17.7 (14.4) years). All patients had loss of protective sensation due to peripheral neuropathy. This was confirmed by the inability to sense the pressure of a 10g monofilament on the plan-tar hallux, first or fifth metaplan-tarsal head or a 25V vibration on the dorsal hallux from a Bio-thesiometer (Bio-Medical Instrument Company, New-bury, OH, USA)7. Patients had
one or more foot deformities, including claw/hammer toes, hallux valgus or rigidus, prominent metatarsal heads, pes cavus, pes planus or Charcot osteoarthropathy, or had
experienced a partial foot amputation. Patients were excluded if they had a current foot ulcer, lower-leg amputation, or if they were unable to walk repeatedly unaided over a distance of 12 m. All patients gave their written informed consent for participation in the study, which was approved by the Local Research Ethics Committee.
Footwear conditions
Patients were measured in four different types of footwear, all ankle-high modalities commonly prescribed for treatment or prevention of plantar foot ulcers in diabetes. The footwear included custom made therapeutic footwear, a cast shoe (Mabal, Almelo, Netherlands), a forefoot offloading shoe (FOS, Rattenhuber Talus, http://www.ratten-huber.de), and a standard shoe (Pulman, http://www.fld.fr) with flexible outsole and flat insert (Figure 1). Patients wore their therapeutic footwear on both feet. The other footwear conditions were tested on the right foot only (patients wore their own shoe on the left). Not all patients were tested in each footwear condition. A total of 30 patients were tested in the custom made footwear, 24 in the cast shoe, 38 in the forefoot offloa-ding shoe, and 39 in the standard shoe.
Figure 1. The four different types of footwear tested in this study: (A) custom made therapeutic footwear, (B) a cast shoe, (C) a forefoot offloading shoe, and (D) a standard shoe.
Procedures
After a baseline assessment, in which data on health history, neuropathy, and foot de-formities was collected, patients were tested in one or more footwear conditions in a laboratory setting. Patients were asked to walk at their comfortable speed along a 12 m long walkway. For each footwear condition, several practice trials were used for the patient to familiarize with the procedures and the footwear tested. The walking speed
2
was measured using a photocell system and was standardized between walking trials within a footwear condition (maximum variation 10%). In-shoe dynamic plantar pres-sures were measured at 50 Hz sampling rate using the Pedar-X system (Novel, Munich, Germany). This system comprised a matrix of 99 sensors in 2-mm thick capacitance based flexible insoles which were placed between the foot and the insole of the shoe. Six pairs of wide Pedar insoles were available to accommodate each foot size. All insoles were calibrated following guidelines from the manufacturer. A minimum of 20 midgait steps per foot in multiple walking trials were collected in each footwear condition.
Figure 2. Peak pressure-time curves shown in the left panes and scatter plots of maximum peak pressure (MPP) versus peak pressure-time integral (PTI) shown in the right panes for two foot regions in one subject: the mid-foot and metatarsals 2-5. These figures clarify the two different criteria of congruence used for the individual analysis. The midfoot region shows a high correlation coefficient between MPP and PTI (r > 0.7). The metatarsals 2-5 region shows a low correlation coefficient (r < 0.7), but small coefficients of variation (CV < 10%) for both parameters, indicating a high congruence of peak pressure-time curves from subsequent foot steps.
Data analysis
In-shoe pressure data was analyzed using Novel software. The first and last step of each trial was automatically excluded by the software to eliminate acceleration and decele-ration effects. Only the right foot was analyzed. The foot was divided into six anatomical regions using an automated masking procedure: the rearfoot, midfoot, metatarsal 1, metatarsals 2-5, hallux, and lesser toes. For each foot region the maximum peak pres-sure (MPP) and the peak prespres-sure-time integral (PTI) were calculated. The MPP is the highest measured pressure in any sensor within a region in one foot step. This is the highest value in the peak pressure-time curve of a particular region. The PTI is the time integral of the peak pressure measured in any sensor within the region during one foot
step. This is the area under the peak pressure-time curve of a particular region.
Statistical analysis
All statistical analyses were performed using SPSS, version 18.0 and Matlab, version R2010b. Data was analyzed at a patient group level and at an individual patient level. For group level analysis, correlation coefficients were calculated between mean MPP and mean PTI. For normally distributed data, Pearson correlations coefficients were computed. For skewed data, Spearman correlations coefficients were calculated. At the individual patient level, correlation coefficients between MPP and PTI were obtained using the values of each single foot step in a pressure measurement. Higher coefficients reflect more interdependency between parameters. However, low correlation coeffi-cients may incorrectly imply that MPP and PTI are not interdependent (i.e. congruent). This may be the case when the MPP versus PTI scatter plot is concentrated within a small value range, something that is expected from in-shoe pressure measurements in which multiple footsteps are taken by a patient and between-step variability is known to be small (Figure 2)13. To take this into account, the coefficient of variation (= SD /
Mean * 100%) over all footsteps was calculated for both the MPP and PTI. If the coef-ficient of variation was < 10% in both MPP and PTI, these parameters were considered congruent. If the correlation coefficient between MPP and PTI was > 0.7 the parameters were considered interdependent. These two criteria were named the “criteria of con-gruence”.
Table 1. Mean ± SD results for MPP and PTI expressed for each of the six foot regions and four footwear condi-tions.
Rearfoot Midfoot
Metatar-sal 1 Metatar-sals 2-5 Hallux Lesser toes
MPP Therapeutic footwear 193 ± 44 155 ± 44 243 ± 107 264 ± 85 169 ± 104 178 ± 76 Cast shoe 168 ± 41 111 ± 45 201 ± 65 162 ± 59 172 ± 92 130 ± 71 Forefoot offloa-ding shoe 248 ± 68 111 ± 30 152 ± 34 134 ± 38 179 ± 122 131 ± 54 Standard shoe 275 ± 47 99 ± 40 348 ± 95 300 ± 92 244 ± 112 232 ± 90 PTI Therapeutic footwear 76 ± 22 79 ± 18 79 ± 27 99 ± 28 44 ± 24 55 ± 23 Cast shoe 40 ± 8 39 ± 18 54 ± 22 46 ± 19 40 ± 23 33 ± 15 Forefoot offloa-ding shoe 61 ± 16 45 ± 20 52 ± 16 52 ± 20 26 ± 20 32 ± 17 Standard shoe 66 ± 17 33 ± 20 99 ± 38 92 ± 39 50 ± 29 63 ± 32
MPP, maximum peak pressure; PTI, peak pressure-time integral.
RESULTS
2
coefficient between MPP and PTI across all regions and footwear conditions was r = 0.78 (P < 0.01). For each region and condition, significant correlation coefficients were found (Table 2). The highest coefficients were found in the forefoot and midfoot (r = 0.64 - 0.93), the lowest in the rearfoot (r = 0.43 - 0.45). Between footwear conditions, the variation in correlation coefficients was small.
Table 2. Correlation coefficients between MPP and PTI for each of the six foot regions and four footwear condi-tions.
Rearfoot Midfoot
Metatar-sal 1 Metatar-sals 2-5 Hallux Lesser toes
Therapeutic footwear 0.44* 0.80** 0.85** 0.92** 0.86** 0.82**
Cast shoe 0.43* 0.93** 0.82** 0.92** 0.90** 0.92**
Forefoot offloading shoe 0.45** 0.82** 0.64** 0.80** 0.81** 0.78**
Standard shoe 0.44** 0.90** 0.78** 0.85** 0.81** 0.92**
MPP, maximum peak pressure; PTI, peak pressure-time integral. * Significantly correlated at P<0.05.
** Significantly correlated at P<0.01.
Table 3. Percentage of patients that reached the criteria of congruence for MPP and PTI expressed in each of the six foot regions and four footwear conditions.
Rearfoot Midfoot
Metatar-sal 1 Metatar-sals 2-5 Hallux Lesser toes
Criterion 1*
Therapeutic footwear 63% 13% 17% 30% 3% 30%
Cast shoe 29% 4% 0% 0% 0% 4%
Forefoot offloading shoe 37% 32% 16% 42% 3% 8%
Standard shoe 28% 5% 21% 41% 5% 21%
Criterion 2**
Therapeutic footwear 20% 77% 73% 47% 67% 43%
Cast shoe 8% 71% 79% 46% 75% 54%
Forefoot offloading shoe 21% 58% 74% 29% 84% 74%
Standard shoe 18% 62% 54% 31% 67% 44%
Criterion 1 or 2
Therapeutic footwear 83% 83% 87% 70% 67% 63%
Cast shoe 38% 75% 79% 46% 75% 58%
Forefoot offloading shoe 55% 79% 84% 66% 87% 76%
Standard shoe 44% 67% 69% 69% 69% 62%
MPP, maximum peak pressure; PTI, peak pressure-time integral. * Criterion 1: coefficients of variation in both MPP and PTI < 10%. ** Criterion 2: correlation coefficient between MPP and PTI > 0.7.
patients fulfilling the ‘criteria of congruence’ ranged from 38% to 87% across regions and conditions. Higher percentages were found in the forefoot and midfoot than in the rearfoot. For the forefoot and midfoot, most patients fulfilled the criteria of congru-ence based on a calculated correlation coefficient between MPP and PTI of >0.7. For the rearfoot, more patients fulfilled the criteria based on small coefficients of variation (<10%) found in both parameters.
DISCUSSION
The in-shoe pressure results show that the MPP and PTI are highly interdependent in the four different types of footwear tested in these high-risk diabetic patients. Strong interdependency was found, both at the group and individual patient level, in those regions that are most at risk for plantar ulceration (forefoot and midfoot). At group le-vel, correlation coefficients between MPP and PTI ranged from 0.64 to 0.93 across foot regions and conditions (from 0.78 to 0.93 if the metatarsal 1 region in the forefoot of-floading shoe was left out). At the individual patient level, parameter congruency varied across the same regions and conditions between 46% and 83% (mean 72%). Between subjects, these data suggest a high degree of similarity in the shape of the peak pressu-re-time curves, which may differ only in amplitude and time of contact. Within subjects, the results suggest a high reproducibility of the peak pressure-time curves. These fin-dings suggest that the MPP and PTI are interchangeable parameters and therefore do not seem to have a mutual additional value in the same footwear study.
The interdependency of MPP and PTI found in this study is in agreement with findings from recent reports. Our own systematic review of the diabetic foot literature showed that the majority of studies found no or only minimal differences in the pattern and significance of outcomes between reported MPP and PTI data11. Specific conclusions for
each parameter were drawn in a minority of papers. A recent study on dynamic bare-foot pressures measured in healthy subjects also showed a strong interdependency bet-ween measured MPP and PTI (r = 0.78; same value as in current study)12. The findings in
these previous studies add to the conclusion that the value of reporting one parameter in addition to the other is small.
The lowest correlation coefficients were found in the rearfoot. Also the percentage of subjects showing high parameter congruence was lowest in the rearfoot. Similar fin-dings were reported by Keijsers et al. for measured barefoot pressure in healthy sub-jects12. Lower correlation coefficients in the rearfoot may be explained by a smaller
va-riability in measured MPP and PTI found between subjects in the rearfoot than in other regions (Table 1). Less scattered data generally leads to lower correlation coefficients. Also, differences in the shape of the normalized peak pressure-time curves may explain these results. Visual inspection of these curves showed more variability in shape for the rearfoot than for the other regions, particularly during mid stance and terminal stance, suggesting that the rollover dynamics of the foot may play a role. Nevertheless, the clinical relevance of finding lower correlation coefficients in the rearfoot is not very high, because pressure related plantar ulcers are rare in this region2. In cases where the
measurement of rearfoot pressures is important, calculating both the MPP and PTI may give a more valuable description.
2
Four different types of footwear were tested in this study to be representative of the range of footwear conditions commonly prescribed to diabetic patients. Two types of custom made and two types of prefabricated shoes were included. Small differences for calculated correlation coefficients and percentages of parameter congruency were found between footwear conditions. This suggests that the interdependency of MPP and PTI is not affected by the type of footwear. Based on these results, we may further speculate that the different design principles incorporated in the tested footwear, such as custom molding, total contact, rocker bottom, and negative heel outsole, do not in-fluence MPP or PTI in such a different way that specific conclusions would be expected. Future pressure studies on the effects of footwear modifications are needed to confirm or refute these hypotheses.
Based on the current and previous findings, it seems difficult to determine in which way the PTI may be mediated differently than the MPP. Some factors such as the size of a masked foot region or the speed of walking may play a role. Within one masked region, more than one anatomical structure (e.g. multiple metatarsal heads) can be loaded. This could affect PTI more than MPP, because only for the calculation of PTI multiple sensors within one mask may contribute. With smaller masks, the interdependency between MPP and PTI has been shown to be stronger12. Speed of walking affects MPP and PTI
dif-ferently, in particular at low speeds14, 15. With decreased walking speed, the MPP
decre-ases in a linear fashion, whereas the PTI incredecre-ases in a non-linear fashion15. This is not
an issue when walking speed is controlled or standardized between tested conditions. However, it may be important when treatment methods enforce a significant decrease in walking speed, such as with the use of a total contact cast for treating plantar foot ulcers in diabetes. In such cases, different conclusions may be drawn based on the PTI data than on the MPP data. More research is needed to determine how these parame-ters may be influenced differently and how such a difference should be interpreted. The MPP has been shown in both retrospective and prospective studies to be predictive of foot ulceration in diabetes3-6. Although the PTI has been suggested by several authors
to be associated with diabetic foot ulceration, its clinical value has not been proven in prospective analyses. Therefore, we may consider the PTI as the redundant parameter of the two. More practical reasons for preferring the MPP instead of the PTI is that the MPP is more comprehensible, and it is directly interpretable on-screen during measu-rement. Therefore, until studies demonstrate that the PTI is similarly or more predic-tive of ulceration than the MPP, it seems sufficient to report only MPP data in diabetic footwear studies.
A limitation of the study was that the cut-off levels to define a high correlation coef-ficient or a good congruency between MPP and PTI were arbitrarily chosen. We consi-dered a correlation coefficient above 0.7 as high because ~50% or more of the variance in one parameter would be explained by the other. The cut-off level of 10% to define small coefficients of variations was based on common sense rather than scientific de-duction. Such a percentage indicates a concentrated cloud of dots in the MPP versus PTI scatter plot that may illustrate the congruency between parameters. With a different cut-off level chosen, outcomes may have been different, but conclusions likely would have been similar. Another limitation of the study may be that the results are specific
for the calculation method for PTI as defined by the measurement system used in this study (i.e. area under the peak pressure-time curve). Different calculation methods may lead to different results and potentially to different conclusions on the added value of using the PTI. Also as part of a composite parameter, such as in the calculation of daily cumulative tissue stress16, the value of PTI may be interpreted differently. Additionally,
the shape of the peak pressure-time curve that determines the PTI has been shown to distinguish patients with different levels of foot impairment17. Despite the presence of
these different calculation methods and uses of the PTI, the way it is used and analyzed in the current study is the most commonly reported and, therefore, the most represen-tative method to include.
CONCLUSION
This foot pressure study showed a high interdependency and congruency between the two most reported pressure parameters, the MPP and the PTI, when measured in neu-ropathic diabetic patients wearing commonly prescribed diabetic footwear. This inter-dependency was strongest in the foot regions most prone to pressure-related ulcers and was independent of type of footwear tested. These results suggest that the MPP and PTI are interchangeable and that outcomes on each parameter will likely lead to similar conclusions. Until the moment that prospective studies show that the PTI is a better or equally good predictor of diabetic foot ulceration as the MPP, the value of reporting the PTI in addition to the MPP in the same diabetic footwear study seems small.
2
REFERENCES
1. Singh N, Armstrong DG, Lipsky BA. Preventing foot ulcers in patients with diabetes. JAMA 2005; 293: 217-228.
2. Reiber GE, Vileikyte L, Boyko EJ, del AM, Smith DG, Lavery LA, Boulton AJ. Causal pathways for incident lower-extremity ulcers in patients with diabetes from two settings. Diabetes Care 1999; 22: 157-162.
3. Veves A, Murray HJ, Young MJ, Boulton AJ. The risk of foot ulceration in diabetic patients with high foot pressure: a prospective study. Diabetologia 1992; 35: 660-663.
4. Boulton AJ, Hardisty CA, Betts RP, Franks CI, Worth RC, Ward JD, Duckworth T. Dynamic foot pressure and other studies as diagnostic and management aids in diabetic neuropathy. Dia-betes Care 1983; 6: 26-33.
5. Frykberg RG, Lavery LA, Pham H, Harvey C, Harkless L, Veves A. Role of neuropathy and high foot pressures in diabetic foot ulceration. Diabetes Care 1998; 21: 1714-1719.
6. Kastenbauer T, Sauseng S, Sokol G, Auinger M, Irsigler K. A prospective study of predictors for foot ulceration in type 2 diabetes. J Am Podiatr Med Assoc 2001; 91: 343-350.
7. Pham H, Armstrong DG, Harvey C, Harkless LB, Giurini JM, Veves A. Screening techniques to identify people at high risk for diabetic foot ulceration: a prospective multicenter trial. Diabetes Care 2000; 23: 606-611.
8. Sauseng S, Kastenbauer T, Sokol G, Irsigler K. Estimation of risk for plantar foot ulceration in diabetic patients with neuropathy. Diabetes Nutr Metab 1999; 12: 189-193.
9. Shaw JE, Boulton AJM. Pressure time integrals may be more important than peak pressures in diabetic foot ulceration (Abstract). Diabet Med 1996; 13: S77.
10. Stess RM, Jensen SR, Mirmiran R. The role of dynamic plantar pressures in diabetic foot ul-cers. Diabetes Care 1997; 20: 855-858.
11. Bus SA, Waaijman R. The additional value of reporting pressure-time integral results in foot pressure studies on the diabetic foot. In: Proceedings of the EMED Scientific Meeting 2008, 28-31 July 2008, Dundee, Scotland, UK; 2008. p. 36 [Abstract].
12. Keijsers NL, Stolwijk NM, Pataky TC. Linear dependence of peak, mean, and pressure-time integral values in plantar pressure images. Gait Posture 2010; 31: 140-142.
13. Arts ML, Bus SA. Twelve steps per foot are recommended for valid and reliable in-shoe plan-tar pressure data in neuropathic diabetic patients wearing custom made footwear. Clin Bio-mech 2011; 26: 880-884.
14. Hsi WL, Chai HM, Lai JS. Comparison of pressure and time parameters in evaluating diabetic footwear. Am J Phys Med Rehabil 2002; 81: 822-829.
15. Melai T, Lange de T. Foot loading during different walking speeds: is there a balance
bet-ween peak pressures and pressure-time integrals? In: Proceedings of the 17th IVO World
Congress for Orthopedic Shoe Technicians, 13-14 November 2009, The Hague, The Nether-lands; 2009. p. 67 [Abstract].
16. Maluf KS, Mueller MJ. Novel Award 2002. Comparison of physical activity and cumulative plantar tissue stress among subjects with and without diabetes mellitus and a history of recurrent plantar ulcers. Clin Biomech 2003; 18: 567-575.
17. Giacomozzi C, Martelli F. Peak pressure curve: an effective parameter for early detection of foot functional impairments in diabetic patients. Gait Posture 2006; 23: 464-470.
Chapter 3
Archives of Physical Medicine and Rehabilitation 2012; 93: 2075-2079
© Reprinted with permission from Elsevier
Sicco A. Bus
Roelof Waaijman
Frans Nollet
NEW MONITORING TECHNOLOGY TO OBJECTIVELY ASSESS
ADHERENCE TO PRESCRIBED FOOTWEAR AND ASSISTIVE
ABSTRACT
Objective: To assess the validity and feasibility of a new temperature-based adherence monitor to measure footwear use.
Design: Observational study.
Setting: University medical center and participants’ homes.
Participants: Convenience sample of healthy subjects (n = 11) and neuropathic dia-betic patients at high risk for foot ulceration (n = 14).
Interventions: In healthy subjects, the validity of the in-shoe attached adherence moni-tor was investigated by comparing its registrations of donning and doffing of footwear during 7 days to an accurately kept log registration. In diabetic patients, the feasibility of using the adherence monitor for seven days in conjunction with a time-synchronized ankle-worn step activity monitor to register prescribed footwear use during walking was assessed. Furthermore, a usability questionnaire was completed.
Main Outcome Measures: For validity, the mean time difference and 95% confidence interval (CI) between moments of donning/doffing footwear recorded with the adher-ence monitor and in the log were calculated. For feasibility, technical performance, us-ability, and the percentage of steps that the footwear was worn (adherence) were as-sessed.
Results: The mean time difference between the adherence monitor and log recordings was 0.4 minutes (95% CI, 0.2 - 0.6 min). One erroneous and 2 incomplete recordings were obtained in diabetic patients. Three patients reported discomfort with the step activity monitor, and 4 patients would not favor repeated testing. Patients used their footwear for between 9% and 99% of their walking steps.
Conclusions: The adherence monitor shows good validity in measuring when footwear is used or not, and is, together with instrumented monitoring of walking activity, a fea-sible and objective method to assess treatment adherence. This method can have wide application in clinical practice and research regarding prescribed footwear and other body-worn assistive devices.
