Efficacy and Mechanism of Orthotic Devices to Unload Metatarsal Heads in People With Diabetes and a History of Plantar Ulcers

Abstract

Background and Purpose. Total-contact inserts (TCIs) and metatarsal pads (MPs) frequently are prescribed to reduce excessive plantar stresses to help prevent skin breakdown in people with diabetes mellitus (DM) and peripheral neuropathy. The first purpose of this study was to determine the effect of a TCI and an MP on metatarsal head peak plantar pressures (PPP) and pressure-time integrals (PTI). The second purpose of this study was to determine a possible mechanism of pressure reduction by measuring contact area and loaded soft-tissue thickness (STT) under the metatarsal heads and second metatarsal shaft. Subjects. Twenty subjects (12 men and 8 women; age [mean±SD]=57±9 years) with DM (duration [mean±SD]=16±11 years), peripheral neuropathy, and a history of plantar ulcers participated. Methods. A repeated-measures research design was used, and outcome measures are reported for 3 footwear conditions: shoe, shoe with TCI, and shoe with TCI and MP. In-shoe plantar pressures were collected during walking and during spiral x-ray computed tomography (SXCT). The STT and identification of the pressure sensor and location of the MP in relationship to the metatarsal heads were determined by use of SXCT. Results. The PPP and the PTI were 16% to 24% lower at the metatarsal heads in the TCI condition than in the shoe condition. The PPP and the PTI decreased an additional 15% to 28% (for a total reduction of 29% to 47%) with the addition of the MP. The contact area increased 27% with the TCI but not with the MP. The STT did not increase under the metatarsal heads in the TCI condition (compared with the shoe condition) but did increase 8% to 22% at metatarsal heads 2 to 5 with the addition of the MP. The PPP increased substantially (308%) and the STT decreased 14% under the shaft of the second metatarsal with the addition of the MP to the TCI-plus-shoe condition. Discussion and Conclusion. The TCI and the MP caused substantial and additive reductions of pressures under the metatarsal heads. The TCI reduces excessive pressures at the metatarsal heads by increasing the contact area of weight-bearing forces. Conversely, the MP acts by compressing the soft tissues proximal to the metatarsal heads and relieving compression at the metatarsal heads. These findings can assist in the design of effective orthotic devices to relieve excessive plantar stresses that contribute to skin breakdown and subsequent amputation in people with DM and peripheral neuropathy. [Mueller MJ, Lott DJ, Hastings MK, et al. Efficacy and mechanism of orthotic devices to unload metatarsal heads in people with diabetes and a history of plantar ulcers. Phys Ther. 2006;86:833–842.]

Treatment of modifiable risk factors for foot ulceration in persons with diabetes: a systematic review

“…49 A series of studies show that custom-moulded insoles or orthoses more effectively offload the foot than prefabricated insoles. [50][51][52][53][54][55][56][57][58][59][60][61] Shoes with flat insoles showed to be less effective than shoes with custom-made insoles, 58,62 even though the use of polyurethane foam sheets inside the patients' own shoes can improve offloading compared with wearing standard shoes. 63 Custom-made insoles designed on the basis of foot shape and plantar pressure profile of the patient provide significantly more offloading than custom insoles that are designed on the basis of foot shape alone.…”

“…65 Metatarsal pads, used either alone or in combination with a medial longitudinal arch support, provide a significant pressure relief compared with not using these elements, but this is critically dependent upon placement; pads may actually increase plantar pressure if placed incorrectly. 61,66,67 Two studies have examined long-term pressure relief provided by insoles. 68,69 Peak pressures with these insoles were found to be higher compared with baseline after the subject took 50 000 steps.…”

Footwear and offloading interventions to prevent and heal foot ulcers and reduce plantar pressure in patients with diabetes: a systematic review

“…A series of studies show that custom-moulded insoles or orthoses more effectively offload the foot than noncustom-made insoles [151,[166][167][168][169][170][171][172][173][174][175][176]. Shoes with flat insoles showed to be less effective than shoes with custom-made insoles [173,177], even though the use of polyurethane foam sheets inside the patients' own shoes can improve offloading compared with wearing standard shoes [178].…”

State of the art design protocol for custom made footwear for people with diabetes and peripheral neuropathy

“…The base of the insole in a fully custom-made shoe should be of 5-mm-thick micro cork (shore 55) with on top 5-mm-thick Ethylene Vinyl Acetate (EVA) (shore [35][36][37][38][39][40]. With prefabricated shoes the base should consist of 6-mm-thick EVA (shore [35][36][37][38][39][40]. The use of materials with proven similar properties in mainly compressibility and durability is also possible.…”

“…A metatarsal support significantly improves peak pressure reduction at the metatarsal heads. 10,19,[27][28][29][30][31][32][33][34][35][36][37][38] • Use a transmetatarsal bar that covers all metatarsal heads as support. 30 A metatarsal pad or dome can be used if only one metatarsal region shows (signs of) high pressure, or is a previous ulcer site.…”