ReviewAssociation between ankle equinus and plantar pressures in people with diabetes. A systematic review and meta-analysis
Introduction
Diabetes is one of the most common chronic diseases in the world, affecting 9% of the population in 2014 (World Health Organization, 2015), and is associated with a life-time risk of foot ulcer of 12–25% (Cavanagh et al., 2005). Diabetic foot ulcers lead to high morbidity, increased associated healthcare costs and are estimated to precede lower extremity amputations in 75–85% of cases (Boulton et al., 2005). Foot ulcer development has been associated both prospectively and retrospectively with elevated plantar pressures in people with diabetes (Boulton et al., 1983, Veves et al., 1992). It is well established that factors such as peripheral neuropathy (Caselli et al., 2002), foot deformity (Mueller et al., 2003a) and limited joint mobility in the foot (Fernando et al., 1991) contribute to elevated plantar pressures.
Ankle equinus has emerged as a possible contributory factor to increased plantar pressures (Amemiya et al., 2014, Lavery et al., 2002), and may play a significant role in the development of pressure related foot ulcers (Boffeli et al., 2002, Francia et al., 2013). Limited ankle joint dorsiflexion, or equinus, acts to restrict the forward progression of the tibia over the foot during stance phase. This is proposed to result in gait compensations such as an early heel lift, excessive subtalar joint pronation and associated midtarsal joint pronation (Michaud, 2011). It is hypothesised that these changes lead to prolonged weight bearing at the forefoot and increased plantar pressures which subsequently contribute to the development of pressure ulceration (Aronow et al., 2006, Mueller et al., 1989).
Prevalence of equinus in the general population is not well documented, with most reports being observational or anecdotal (Charles et al., 2010, DiGiovanni et al., 2002). Prevalence of equinus in an urban population with diabetes is variable, ranging from 10.3% to 37.2%, a threefold increase in risk compared to a group without diabetes (Frykberg et al., 2012, Lavery et al., 2002). The higher prevalence of equinus in people with diabetes is thought to be, in part, due to the non-enzymatic glycosylation of soft tissues resulting in structural abnormalities and thickening of the Achilles tendon leading to increased tendon stiffness and reduced joint mobility (Giacomozzi et al., 2005, Grant et al., 1997).
Given the increasing burden of diabetic foot complications, it is important that risk factors for foot ulcer development and subsequent amputation are identified and managed. If ankle equinus is found to contribute to high plantar pressures then it could present an opportunity for earlier clinical detection of patients at risk of pressure-related foot ulcer and, may also provide additional preventative treatment options for these patients (Francia et al., 2013). Therefore, the aim of this review is to systematically evaluate the current literature to determine if, for people with diabetes, there is an association between equinus and high plantar pressures, and to evaluate study findings by meta-analysis where possible.
Section snippets
Methods
An electronic database search of EBSCO Megafile Premier (containing MEDLINE, CINAHL, SPORTSDiscus and Academic Search Complete), EMBASE, and The Cochrane Library was conducted from their inception to 23rd November 2016. The search strategy used for the EBSCO database used the following terms:
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#1 Diabet* and ((Pressure or loading or function) and (plantar or foot or forefoot or peak))
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#2 Ankle or dorsiflex* or DF
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#3 Equinus or contracture or LJM or “joint mobility” or “joint motion” or “joint
Results
The initial database search resulted in a total of 386 citations of which 47 were appropriate for full review (Fig. 1). After review, 15 studies were included (Table 1) and 32 were rejected on the basis of exclusion criteria (Supplementary Table 1). The 15 studies, with sample sizes from 10 to 1666 people, included a total of 2544 participants with an age range of 45 to 80 years of age and duration of diabetes of between 1 and 31 years. Twelve of these studies measured ankle joint dorsiflexion
Discussion
We found fifteen studies that allowed comparison of ankle joint dorsiflexion and plantar pressures. The three studies that were included in the meta-analysis showed a significant but small effect size of equinus on increased plantar pressures, although this is predominantly due to the findings of the large Lavery et al. (2002) study. Of the remaining twelve studies, eight studies reported evidence of an association between limited ankle dorsiflexion and increased plantar pressures while four
Conclusion
Our findings support the possibility that limited ankle joint dorsiflexion may be an important factor in elevating plantar pressures in people with diabetes. This relationship appears to be independent of neuropathy and it may also be related to whether people with diabetic neuropathy go on to develop a foot ulcer. All the included studies where the population had a history of neuropathic foot ulceration found a relationship between limited ankle dorsiflexion and increased plantar pressures.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Acknowledgements
We would like to thank Associate Professor James S. Wrobel (University of Michigan), Dr. Michael S. Orendurff (Orthocare Innovations, Seattle) and Professor Lale Cerrahoglu (Celal Bayer University, Turkey) for providing access to data.
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