Elsevier

Clinical Biomechanics

Volume 27, Issue 7, August 2012, Pages 725-730
Clinical Biomechanics

Impact of strut height on offloading capacity of removable cast walkers

https://doi.org/10.1016/j.clinbiomech.2012.03.001Get rights and content

Abstract

Background

Reducing weight-bearing stress to diabetic foot ulcers is critical to healing and commonly called offloading. Removable cast walkers are frequently used for offloading; however, patient compliance is often poor. Walkers commonly extend to the knee. Patients complain about walkers' weight and diminished balance with their use. This study compared the offloading capacity of walkers that varied by height. Heights included: knee, ankle, and shoe levels. To ensure a fair comparison the outsole and insole were standardized across the devices.

Methods

Eleven diabetic subjects with moderate to high risk of ulceration were recruited. Subjects completed four 20 m walking trials. Subjects performed one trial with each walker and one trial with an athletic shoe. Primary outcomes focused on plantar loading and were measured by pressure insoles. Secondary outcomes were associated with gait kinematics as collected by body worn sensors.

Findings

Significant differences were found for the peak pressure and pressure time integrals of the different footwear. All walkers performed better than the athletic shoe. The ankle and knee-high devices performed best. Center of mass rotation data showed a trend of the ankle walker yielding a smaller range of motion (18% medial/lateral and 22% anterior/posterior) than the knee level.

Interpretation

The ankle-high walker was able to provide similar offloading capacities as the knee-high walker. The diminished weight, along with potentially improved stability, may result in improved compliance with ankle-high walkers. A study comparing the use of the two devices for treating ulcers is now suggested.

Introduction

Roughly 25% of all hospital days for persons with diabetes are due to foot complications (Block, 1981, Gibbons and Eliopoulos, 1984, Smith et al., 1987). A large number of these days are attributable to diabetic foot ulcers (DFU). Individuals with diabetes run a 12–25% lifetime risk of developing a DFU (Abbott et al., 2005, Singh et al., 2005). Foot ulcers are among the most serious complications associated with diabetes. Stockl et al. found that the average cost to treat a DFU during the years 2000–2001 was $13,179 and the mean cost for the most severe wounds was $27,721 (Stockl et al., 2004). Besides the sizable economic burden, these ulcers induce extensive emotional, physical, and productivity losses (Boulton et al., 2004, Meijer et al., 2001, Vileikyte, 2001, Vileikyte and Boulton, 2000). In addition to the immediate negative impact of ulcers on persons with diabetes, ulcers often lead to even more dire consequences. Persons with diabetes are 15 to 46 times more likely to have lower extremity amputations than persons without diabetes, (Armstrong et al., 1997, Lavery et al., 1999, Most and Sinnock, 1983, Reiber, 1996) and ulcerations are “the most important factor for lower-extremity amputation” (p 1725) (Cavanagh et al., 2005).

DFUs commonly occur on the plantar aspect of the foot in response to the repetitive trauma induced by the pressures generated by weight-bearing activities (Lavery et al., 1996, Wu et al., 2005). Thus one of the most critical components to the paradigm of preventing and healing these ulcers is pressure reduction at the wound site or “offloading” (Cavanagh et al., 2005, Wu et al., 2005). Knowing that offloading is critical, practitioners are still faced with the challenge of selecting the appropriate offloading modality for their patient. To date the total contact cast (TCC) and removable cast walkers — particularly the DH Pressure Relief Walker (Royce Medical, Camarillo, CA), have the most data to support their use in healing ulcers (Cavanagh and Bus, 2010). However, TCC are not commonly used in practice in the US, with only 1.7% of foot clinics using them as their standard offloading modality (Wu et al., 2008). Although RCW are used more commonly, they have been shown to provide poorer healing outcomes (Armstrong et al., 2001, Gutekunst et al., 2011). This is despite the fact that the two modalities provide nearly equivalent offloading (Baumhauer et al., 1997, Gutekunst et al., 2011, Lavery et al., 1996).

The specific mechanism by which RCW offload is not fully understood. RCW typically have rigid struts (or circumferential lattice encasements) that run up the majority of the shank. The struts are believed to limit isolated pockets of high pressure on the foot by immobilizing the ankle. With the ankle immobilized the foot is not free to progress through its typical heel strike to toe offloading pattern. Instead with the ankle locked and a rocker bottom sole on the RCW, a large portion of the foot maintains contact and subsequently loads throughout the step. Shaw et al. previously found that approximately 1/3 of a subject's load was transferred as shear stress to the walls of the TCC, which act as rigid conical receptacles to support the inverted cone shaped legs (Shaw et al., 1997). It is unlikely that RCW provide offloading by a similar means as they do not provide rigid direct contact with the entire surface of the leg, nor are they custom fit to legs. Whether any load might be transferred to the struts, which are circumferentially fixed to the leg, is unknown.

The decreased healing associated with RCW has been attributed to patient behavior as opposed to the device itself. When RCW are not securely fixed to a patient by casting tape or other means, many patients do not compliantly use them (Armstrong et al., 2003). Impeded balance (van Deursen, 2008) and the weight of the device likely contribute to this lack of adherence. While weight concerns may be argued to be more of an inconvenience than a serious problem, decreased stability poses a serious risk of fall related injuries to these patients. In 2009 59.9% of all US adults with diabetes reported some type of mobility limitation Centers for Disease Control and Prevention (2011). Furthermore, the same severe neuropathy that allows DFUs to form also puts individuals at risk of falls (Richardson, 2002) and individuals with DFU have been shown to have an even greater deterioration in balance than individuals with diabetic neuropathy alone (Kanade et al., 2008). Should a fall occur, it has been shown that diabetes is associated with longer hospital stays following falls (Kennedy et al., 2001). If lower (or no) struts that weighed less with a lesser impact on balance could provide similar offloading capabilities, the incorporation of them into RCW may improve compliance. Additionally, as peripheral edema is more common in individuals with type 2 diabetes than non-diabetic individuals (Brodovicz et al., 2009), patients with DFUs may present with large amounts of edema in the leg. When a RCW is used with these patients there may be tissue that hangs over the top of the rigid struts. Consequently, this poses the risk of the development of new wounds at the interface of this tissue and the strut.

The purpose of this study was to compare the offloading capacity of RCW of varied height. A comparison was made between RCW's that extended proximally: up the majority of the shank (knee-high), just past the ankle (ankle-high), or only encompassed the foot (shoe-offloader). To ensure a fair comparison, the rocker outsole and insole were standardized across the three devices. Should RCW with lowered strut height still provide adequate offloading, patients that use them may have better healing outcomes due to increased adherence.

Section snippets

Subjects

Subjects were eligible to participate if they were an adult with type 1 or 2 diabetes mellitus at moderate/high risk for DFU (risk grade 1 or higher: Diabetic Foot Risk Classification System of the International Working Group on the Diabetic Foot (Peters and Lavery, 2001)). Exclusion criteria included inability to walk without an assistive device such as a walker or crutches, and the presence of an active DFU. All subjects read and signed an institutional review board approved consent form

Offloading

The peak pressure data revealed a significant interaction between footwear and foot region. Therefore, the Least Significant Difference post hoc was used to compare each footwear condition within each foot region. Fig. 3 displays the results of the post hoc analyses for four masks (5, 6, 7 and 8) corresponding to commonly ulcerated regions of the foot: the hallux and metatarsal heads. The pressure time integral data also yielded a significant difference for the interaction between footwear and

Discussion

The primary outcomes pressure data are in line with previous work. For example a previous study found the mean peak pressure at the hallux ranged from 64 to 122 kPa for four RCW in patients with a history of DFU (Lavery et al., 1996). In the present study the peak pressure at the hallux was 76 kPa in the knee-high, 90 kPa in the ankle-high, and 145 kPa in the shoe level RCW. As a gauge of cumulative stress, the pressure time integral indicated the ankle-high and knee-high RCW provided equivalent

Conclusion

Considering the ankle-high RCW was a nearly equivalent offloader to the knee-high RCW, while weighing less and potentially providing better stability, it may prove to provide better outcomes in treating DFU. It may also be a good choice for individuals with significant edema at the proximal end of the leg, as it would likely conform better to edematous legs.

Acknowledgement

The project described was supported by Award Number T35DK074390 from the National Institute of Diabetes and Digestive and Kidney Diseases. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Diabetes and Digestive and Kidney Diseases or the National Institutes of Health. Removable cast walkers were provided at no cost by Össur, however, representatives from Össur had no role in the study design, data

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