Metatarsal Phalangeal Joint Deformity Progression - R01

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: relationships between advanced glycation end products, intrinsic foot muscle volume, limited ankle dorsiflexion joint mobility, MTPJ hyperextension movement pattern, and MTPJ alignment; estimate the effect of a foot specific intervention on the MTPJ extension alignment and 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: 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. 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. 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.

The intervention is a progressive, home based exercise program aimed to increase ankle and foot plantarflexion muscle strength, increase ankle dorsiflexion and toe flexion range of motion, and to retrain individuals to dorsiflex the ankle while keeping the toes in a neutral position. A trained physical therapist with experience working with older adults with diabetes and foot specific complications will monitor and progress the exercise program assuring participant safety and maximizing exercise benefit.

Participants will be trained in a progressive home exercise program that includes passive stretching of end range shoulder flexion and external rotation and a tailored dose of active shoulder motion.

Change in metatarsal phalangeal joint angle (degrees) in people with diabetes from baseline and at a 3-year period

The investigators will measure baseline metatarsal phalangeal joint angle and again at the 3-year time point

Inclusion Criteria: Type 2 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);

Bohnert KL, Zellers JA, Jeong HJ, Chen L, York A, Hastings MK. Remote Research: Resources, Intervention Needs, and Methods in People with Diabetes and Peripheral Neuropathy. J Diabetes Sci Technol. 2023 Jan;17(1):52-58. doi: 10.1177/19322968221103610. Epub 2022 Jun 30.

Jeong HJ, Mueller MJ, Zellers JA, Yan Y, Hastings MK. Heel Rise and Non-Weight-Bearing Ankle Plantar Flexion Tasks to Assess Foot and Ankle Function in People With Diabetes Mellitus and Peripheral Neuropathy. Phys Ther. 2021 Jul 1;101(7):pzab096. doi: 10.1093/ptj/pzab096.