The purpose of this research study is to determine the relationships between foot muscle, foot motion, and toe deformity. Results from this investigation will help the investigators to understand what contributes to foot deformities and the role of the foot muscles in the development of foot deformities. This could potentially guide treatment options focusing on strengthening the foot muscles to prevent or reduce the risk of developing a foot deformity.

The long term goal of this research is to reduce the incidence of lower extremity amputation in people with diabetes mellitus and peripheral neuropathy. It is hypothesized that muscle, joint, and movement deterioration associated with diabetes and peripheral neuropathy contribute to metatarsophalangeal joint (MTPJ) hyperextension deformity. MTPJ deformity results in excessive plantar stress on the insensitive forefoot, leading to ulceration and amputation. However, the specific cause of MTPJ deformity is not clear. The overall goal of this proposal is to identify the causes of MTPJ deformity and examine the ability of a targeted foot specific intervention to de-couple diabetes related mechanisms from MTPJ deformity and progression, following participants for 3 years. The investigators hypothesize that the cause of MTPJ deformity is an interaction of the accumulation of advanced glycation end products, muscle deterioration, limited joint mobility and compensatory movement strategies.

The specific aims are to determine:

1. relationships between advanced glycation end products, intrinsic foot muscle volume, limited ankle dorsiflexion joint mobility, MTPJ hyperextension movement pattern, and MTPJ alignment;
2. estimate the effect of a foot specific intervention on the MTPJ extension alignment and
3. determine progression of MTPJ deformity and the predictors of progression over three years.

The following will be collected on participants with diabetes mellitus and peripheral neuropathy and monitored over three years to understand the causes and progression of MTPJ deformity:

1. Skin intrinsic florescence to measure advanced glycation end product accumulation which increases collagen cross-linking and is associated with peripheral neuropathy, limited joint mobility, and muscle deterioration.
2. Magnetic resonance images to measure intrinsic foot muscle deterioration that precedes extrinsic foot muscle deterioration as a result of distal to proximal peripheral neuropathy. The muscle imbalance of weak intrinsic foot muscles, the only muscles able to flex the MTPJ, in the presence of relatively stronger extrinsic toe extensors, results in a force couple that hyperextends the MTPJ.
3. Kinematic and computed tomography measurement of foot and ankle joint positions to examine mobility and movement patterns that contribute to repeated and extreme MTPJ hyperextension during daily activities.

The investigators believe advanced glycation end products lead to limited ankle joint dorsiflexion. As a result, there is increased reliance on the extensor digitorum longus to assist in dorsiflexing the stiff ankle joint during activities like sit to stand. This study will have profound implications for reducing risk for skin breakdown and amputation by helping to understand and treat the causes of acquired neuropathic foot deformities. A successful foot specific intervention that improves MTPJ alignment will provide a non-invasive option to halt or slow the cascade of events leading to major lower extremity amputation, while improving function and minimizing disability.

Inclusion Criteria:

• Type 2 Diabetes Mellitus (DM)
• Diabetic peripheral neuropathy

Exclusion Criteria:

• active plantar ulcers, unable to ambulate or complete required testing, anyone who have amputations of their lower extremity (>1 toe), weigh more than 400 lbs, pregnant, have metal implants or pace makers (incompatible with MRI), greater than 75 years old, Subjects with other causes of PN (lumbar radiculopathy, microvascular disease, alcoholic/HIV/chemotaxic neuropathy), on dialysis, with peripheral arterial disease (ABI<0.9 or >1.3), with fixed MTPJ deformity (excursion <30 degrees active/passive), acute shoulder pain or disability that would prevent participation in shoulder specific intervention (i.e. severe shoulder pain >6/10, rotator cuff tear, upper extremity surgery, thoracic outlet syndrome);

Other researchers may contact us to get access to the data but we will not be placing the data in a repository

Through study completion, on average 3.6 years

Adverse event were collected systematically through standardized questions answered during 3 month follow up phone calls or during study visits (e.g. falls, skin breakdown, foot pain, shoulder pain, changes in medical conditions, or new medical conditions). Unexpected adverse events were recorded when information was volunteered or discovered (e.g. failure to answer follow up phone calls resulted in a search of the social security web site to identify of participants were deceased).

We excluded individuals with more severe foot deformity limiting generalizability of the study findings.

There were some delays in final time point assessment and participant attrition due to Covid-19 related restrictions on human subjects research around the final time point