Prevalence of ankle equinus and correlation with foot plantar pressures in people with diabetes

Highlights

• We found a high prevalence of ankle equinus in a low risk cohort of adults with diabetes.

• Adults with an equinus were more than twice as likely to have at risk in-shoe peak plantar pressures.

• Significantly more males and people with neuropathy or elevated HbA1c levels displayed an equinus.

• Ankle equinus diagnosis may help identify adults at increased risk of diabetic foot complications.

Abstract

Background

An association between equinus and plantar pressure may be important for people with diabetes, as elevated plantar pressure has been linked with foot ulcer development. To determine the prevalence of equinus in community dwelling people with diabetes and to examine any association between presence of equinus and forefoot plantar pressures.

Methods

Barefoot (Tekscan HR Mat™) and in-shoe (Novel Pedar-X®) plantar pressure variables, non-weight bearing ankle range of motion and neuropathy status were assessed in 136 adults with diabetes (52.2% male; 47.8% with neuropathy; mean (standard deviation) age and diabetes duration: 68.4 (11.5) and 14.6 (11.1) years respectively).

Findings

Equinus, when measured as ≤5° dorsiflexion, was present in 66.9% of the cohort. There was a significant correlation between an equinus and barefoot (r = 0.247, p = 0.004) and in-shoe forefoot pressure time integrals (r = 0.214, p = 0.012) and in-shoe forefoot alternate pressure time integrals (r = 0.246, p = 0.004). Significantly more males (p < 0.01) and people with neuropathy (p = 0.02) or higher glycated haemoglobin levels (p < 0.01) presented with an equinus.

Interpretation

Community dwelling adults with diabetes have a high rate of ankle equinus which is associated with increased forefoot pressure time integrals and a two-fold increased risk of high in-shoe peak pressures. Clinical assessment of an ankle equinus may be a useful screening tool to identify adults at increased risk of diabetic foot complications.

Introduction

An ankle equinus has been described as reduced sagittal plane range of motion at the ankle joint, such that the minimum of 10° of dorsiflexion of the foot required for normal gait cannot be achieved (Root et al., 1977). However there is no definitive definition of equinus in the literature. In addition to <10°, authors have also used ≤5° (DiGiovanni et al., 2002; Orendurff et al., 2006; Van Gils and Roeder, 2002) or ≤0° (Frykberg et al., 2012; Lavery et al., 2002; Lin et al., 1996) of dorsiflexion to indicate equinus. This lack of consensus may partly explain why the reported prevalence of equinus in populations with diabetes is so varied, ranging from 10.3% to 37.2% in urban populations (Frykberg et al., 2012; Lavery et al., 2002), and from 72.4% to 91% in populations with a history of ulcer, amputation or neuropathy (Boffeli et al., 2002; Van Gils and Roeder, 2002).

An equinus may result from diabetes, aging, bony block, neurological abnormalities such as cerebral palsy and stroke, soft tissue contracture as a result of prolonged inactivity or wearing high heel shoes (DiGiovanni et al., 2002). An equinus is more common in people with diabetes than in the general population and this may be due to the underlying metabolic changes occurring with the disease (Frykberg et al., 2012). It is believed that chronic hyperglycaemia promotes non-enzymatic glycosylation of proteins, resulting in excessive advanced glycation end product (AGE) formation and abnormal collagen cross links (Somai and Vogelgesang, 2011). These changes lead to structural abnormalities, resulting in thickening and decreased elasticity in periarticular structures such as joint capsules, ligaments and tendons, including the Achilles tendon (Grant et al., 1997). The higher prevalence of equinus reported in populations with a history of neuropathy and foot complications could be expected as hyperglycaemia and AGE formation have been implicated in the development of both conditions (Singh et al., 2014).

An equinus has been reported to contribute to conditions such as metatarsalgia, chronic heel pain, forefoot nerve entrapment, toe deformity and diabetes related foot ulcers (Barrett and Jarvis, 2005; Cheuy et al., 2016; DiGiovanni et al., 2002; Irving et al., 2006; Lin et al., 1996). Elevated plantar pressures, particularly forefoot pressures, resulting from an equinus are proposed as one of the underlying mechanisms for development of foot ulcer. However, studies investigating the link between equinus and elevated plantar pressures have had variable outcomes (Christensen and Albert, 1994; Guldemond et al., 2008; Lavery et al., 2002; Orendurff et al., 2006; Payne et al., 2002). The potential contribution of ankle equinus to high plantar pressure may be of particular importance in people with diabetes. Elevated plantar pressures have been associated both prospectively and retrospectively with increased risk of foot ulcer (Frykberg et al., 1998; Lavery et al., 1998; Veves et al., 1992). While assessment of plantar pressure has been suggested as a tool for earlier identification of increased ulcer risk, the equipment is expensive and not readily available in clinical practice (Patry et al., 2013).

Ankle dorsiflexion range of motion testing is easy to perform in a clinical situation, and, if associated with increased plantar pressure, may be a simple screening tool to identify people at increased risk of foot ulcer in diabetes cohorts. However, the majority of previous studies investigating a link between equinus and plantar pressures have tested ankle dorsiflexion using a goniometer and manual force applied by an examiner. Serious concerns have been raised about the reliability and validity of this method, and it is recommended that patient and foot position, and direction and magnitude of force should be standardised (Gatt and Chockalingam, 2011; Van Gheluwe et al., 2002). Only two studies investigating ankle dorsiflexion and plantar pressures (n = 27 and n = 10) have measured ankle dorsiflexion using a method meeting these requirements (Orendurff et al., 2006; Rao et al., 2006). Therefore, the primary aims of this study were 1) to determine the prevalence of equinus in community dwelling people with diabetes using a standardised measurement method, and, 2) to examine any association between presence of equinus and forefoot plantar pressures in this population.