title: Plantar pressure relief under the metatarsal heads: therapeutic insole design using three-dimensional finite element model of the foot.
abstract: Therapeutic footwear with specially-made insoles is often used in people with diabetes and rheumatoid arthritis to relieve ulcer risks and pain due to high pressures from areas beneath bony prominences of the foot, in particular to the metatarsal heads (MTHs). In a three-dimensional finite element study of the foot and footwear with sensitivity analysis, effects of geometrical variations of a therapeutic insole, in terms of insole thicknesses and metatarsal pad (MP) placements, on local peak plantar pressure under MTHs and stress/strain states within various forefoot tissues, were determined. A validated musculoskeletal finite element model of the human foot was employed. Analyses were performed in a simulated muscle-demanding instant in gait. For many design combinations, increasing insole thicknesses consistently reduce peak pressures and internal tissue strain under MTHs, but the effects reach a plateau when insole becomes very thick (e.g., a value of 12.7mm or greater). Altering MP placements, however, showed a proximally- and a distally-placed MP could result in reverse effects on MTH pressure-relief. The unsuccessful outcome due to a distally-placed MP may attribute to the way it interacts with plantar tissue (e.g., plantar fascia) adjacent to the MTH. A uniform pattern of tissue compression under metatarsal shaft is necessary for a most favorable pressure-relief under MTHs. The designated functions of an insole design can best be achieved when the insole is very thick, and when the MP can achieve a uniform tissue compression pattern adjacent to the MTH.
authors.affiliation: Department of Mechanical Engineering, Melbourne School of Engineering, University of Melbourne, Victoria, Australia. Electronic address: wenming.chen@unimelb.edu.au.
authors.forename: Wen-Ming
authors.initials: WM
authors.lastname: Chen
authors.affiliation: Department of Biomedical Engineering, College of Biomedical Science & Engineering, Inje University, Gyongnam, Republic of Korea.
authors.forename: Sung-Jae
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, Melbourne School of Engineering, University of Melbourne, Victoria, Australia. Electronic address: pvlee@unimelb.edu.au.
authors.forename: Peter Vee Sin
authors.initials: PVS
authors.lastname: Lee
mesh_terms: D001696:Biomechanical Phenomena / Q000502:physiology; D003198:Computer Simulation; D004867:Equipment Design; D020342:Finite Element Analysis; D005528:Foot / Q000033:anatomy & histology / Q000502:physiology*; D061826:Foot Orthoses; D006801:Humans; D008682:Metatarsal Bones / Q000033:anatomy & histology / Q000502:physiology*; D008954:Models, Biological; D011312:Pressure / Q000009:adverse effects*; D016474:Weight-Bearing / Q000502:physiology
keywords: Biomechanical model; Finite element method; Plantar pressure; Therapeutic footwear; Tissue strain