Efficacy and mechanism of orthotic devices to unload metatarsal heads in people

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Phys Ther. 2006 Jun;86(6):833-42.

Efficacy and mechanism of orthotic devices to unload metatarsal heads

in people with diabetes and a history of plantar ulcers.

Mueller MJ, Lott DJ, Hastings MK, Commean PK, KE, Pilgram TK.

Program in Physical Therapy, Washington University School of

Medicine, 4444 Forest Park Blvd, Box 8502, St Louis, MO 63110, USA.

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.