Foot biomechanics. Stephan F.E. Praet, MD PhD

MOVEFIT Foot biomechanics from an evolutionary perspective Stephan F.E. Praet, MD PhD Sports & exercise physician MoveFIT-Sports Medicine Dept. Rehabilitation Medicine Erasmus University Medical Centre, Rotterdam, the Netherlands

Overview and Acknowledgements Evolution of the Foot in a Split Second Foot biomechanics and pedobarography Effect of Habitual Shoe use on Foot function

Overview and Acknowledgements Evolution of the Foot in a Split Second Foot biomechanics and pedobarography Effect of Habitual Shoe use on Foot function Dr Kristiaan D'Août Department of Musculoskeletal Biology Institute of Ageing and Chronic Disease University of Liverpool

The complexity of the human foot Why this complexity? Why is the foot not a simple hinged plate? Some complexity can be functionally understood: adaptation to substrate is needed (flexible foot) efficient push-off is also needed (rigid foot) balance

The complexity of the human foot The human foot is a very complex structure: 26 bones (+ sesamoids) numerous ligaments numerous intrinsic muscles numerous extrinsic muscles Why this complexity? Why is the foot not a simple hinged plate? Some complexity can be functionally understood: adaptation to substrate is needed (flexible foot) efficient push-off is also needed (rigid foot) balance

Complexity of the Foot In order to understand foot anatomy, we have to account for two aspects: 1. Function: foot anatomy reflects functional requirements BUT! The foot has not been «engineered» de novo 2. Evolution: foot anatomy reflects its historical background and may show vestigeal remains 1. A structure (in the broad sense) can change (over generations) if there is an adaptive benefit. If there is a cost, or if there is no benefit, they are unlikely to change. Courtesy of dr. K. Août, University of Liverpool

«early» feet Primitive amphibians Eustenopteron shape fin-like rayed Tarsus Ichtyostega (363 MYA) 5-rayed wading crawling ecological function terrestrial locomotion locomotion manipulation Courtesy of dr. K. Août, University of Liverpool

Primate feet Courtesy of dr. K. Août, University of Antwerp Plesiadapis - ancestral primate arboreal lifestyle - claws

Primate feet Courtesy of dr. K. Août, University of Antwerp Proconsul ancestor of the apes approx. 20 MYA nails instead of claws grasping foot

Anthropoid relationships African apes (Homininae) Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

Anthropoid relationships Gibbons (Hylobatidae) African apes (Homininae) Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

Anthropoid relationships Gibbons (Hylobatidae) Orang-utans (Ponginae) African apes (Homininae) Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

Anthropoid relationships Gibbons (Hylobatidae) Orang-utans (Ponginae) Gorilla African apes (Homininae) Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

Anthropoid relationships Gibbons (Hylobatidae) Orang-utans (Ponginae) Gorilla Chimpanzee Bonobo African apes (Homininae) Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

Anthropoid relationships Gibbons (Hylobatidae) Orang-utans (Ponginae) Gorilla Chimpanzee Bonobo Hominini African apes (Homininae) Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

Anthropoid relationships Gibbons (Hylobatidae) Orang-utans (Ponginae) Gorilla Chimpanzee Bonobo Hominini African apes (Homininae) 6-7 MYA Great Apes (Hominidae) Hominoidea Courtesy of dr. K. Août, University of Liverpool

The human lineage (hominins) - bipedalism Courtesy of dr. K. Août, University of Liverpool

The human lineage - documented foot bones Anatomically modern feet (exc. details) Courtesy of dr. K. Août, University of Liverpool

Early hominin feet to the modern human foot So far the known fossils. Is it a mess? Not really, there are general patterns! All related to bipedalism! (and the same selective pressures) - and to running? What are these patterns/features? Ankle morphology Hallux as propulsive structure (adducted & robust) Toes that can dorsiflex Elaborate foot arch support Disappearance of mid-tarsal break Big calcaneal tuberosity Change in proportions (short toes) Courtesy of dr. K. Août, University of Liverpool

Morton s view on the Human Foot

Insights from Modern Apes Bonobo: upright tree climbing Bonobo: upright tree walking Bonobo: upright terrestial walking Macaque: Acute upright terrestial walking (After narcosis?????)

Terrestial changes: Reduced Metatarsal Torsion: Chimpansee Gorilla Man Improved Leverage Axis in Movement Direction

Terrestial changes: Reduced Obliquity of Sustentaculum Tali: Body weight distribution towards lateral side Less Abduction of Hallux / Metatarsal I Gorilla Neanderthal man Modern Man Development of Lateral Longitudinal Arch Deepening of Transverse Tarsal Arch

Functional Role of Sustentaculum Tali: 4 Inter- and Intra Racial Patterns of Articular Facets Subtalar Joint Egyptians N=300 (L/R) Africans N>500 Indians N=401 Caucasians N>500 Veddah (Ceylon) 63% 30% 4.7% 2% 60-63% 30-36% 10% <1% 67% 26% 5% 2% 33-40% 67% 12% <1%??? >50%

Design of the Longitudinal Arch : 1 st ray supports Sustentaculum Tali

Structural Design of the Normal Foot 5 Arcs Different Leverage Lengths Static Plane of Balance

Mechanics of the Foot during Walking and Running: Transfer of Stress from Static Dynamic Plane of Balance Heel off

Structure and Function Coupling foot mechanics to morphology Healthy foot Division of weight stress during Running: M1:M2:M3:M4:M5= 4 : 1 : 1 : 1 : 1

Structure and Function Coupling foot mechanics to morphology Healthy foot Division of weight stress during Running: M1:M2:M3:M4:M5= 4 : 1 : 1 : 1 : 1 Relative Shaft Diameter: M1:M2:M3:M4:M5= 2 : 1 : 1 : 1 : 1 Relative Shaft Strength = (Diameter) 2 M1:M2:M3:M4:M5= 4 : 1 : 1 : 1 : 1

Loading mechanics of MT-I MT-I support MT-I support

Foot disorders Biomechanically weak or disbalanced feet Short Hallux Hyperlaxity first ray /TarsoMetaTarsal Joint Posterior located sesmoids From D.J. Morton (1954)

Neutral & First degree Pronation

Advanced degree of Hypermobility

Hallux valgus deformity: Caused by Stiffening of Hallux to compensate Functional Short or Hypermobile 1 st Ray or Steep Subtalar joint configuraton? Late MT-I support MT-I support

Navicular drop : Insufficient support Sustentaculum Tali from 1 st Ray: Hypermobility TarsoMetaTarsal Junction Less Oblique Sustentaculum (Intra and Inter-Racial differences)

The «normal» human foot Shod South Indians wear less constricting footwear than Western populations. They remove their shoes often. BI < SI < W Picture by dr. K. Août, University of Antwerp D Aout et al, Footwear Science Vol. 1, No. 2, June 2009, 81 94

The «normal» human foot 137 subjects «SI» 70 subjects «BI» 48 subjects «W» - static plantar pressure - dynamic plantar pressure (3 x each foot) - mass, age, length, leg length, BMI, footwear use D Aout et al, Footwear Science Vol. 1, No. 2, June 2009, 81 94

The «normal» human foot #009 #014 #022 South-Indians, habitually wearing footwear (group «SI») #141 #150 #156 Pictures by dr. K. Août, University of Antwerp South-Indians, habitually walking barefoot (group «BI») D Aout et al, Footwear Science Vol. 1, No. 2, June 2009, 81 94

Effect of Habitual Footwear Use D Aout et al, Footwear Science Vol. 1, No. 2, June 2009, 81 94

Conclusion Foot Nature (evolution/genetics/ethnicity) Foot Biomechanics Foot Nurture (growth/habitual shoe wear)

The «normal» human foot Three examples out of 207 South Indian subjects #141 #156 #022 Indian, barefoot Indian, barefoot Indian, «shod» D Aout et al, Footwear Science Vol. 1, No. 2, June 2009, 81 94

The «normal» human foot Three examples out of 48 Western subjects D Aout et al, Footwear Science Vol. 1, No. 2, June 2009, 81 94