functional anatomy and biomechanics of the foot · evolution of the equine digit order...
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Functional anatomy and biomechanics of the foot
Andrew van EpsAssociate Professor of Musculoskeletal Research
New Bolton Centre
Evolution of the equine digit
Order Perissodactyla
Odd‐toed ungulates
• Brontotheridae
• Chalicotheridae
• Paleotheridae
• Hyracodontidae
• Amynodontidae
• Equidae
• Tapiridae
• Rhinocerotidae
The Rise of Horses: 55 Million Years of Evolution, by J.L. Franzen, 2010 (Baltimore: JHU Press)
Living Perissodactyls
• Odd‐toed• Hindgut fermenters• Molarized premolars/transverse ridges on grinding surface
Perissodactyls: Odd‐toe
Photos taken by Sasha Kopf at the Woodland Park Zoo, Seattle, WA, downloaded from https://commons.wikimedia.org/wiki/File:Tapir_hooves.jpg
Remaining images: Laminitis Discovery Database
From Davies & Philip and Floyd, in Equine Podiatry, 2007
Image: Danielle Byerly, University of Florida
Bones of upper limbs fused
The Rise of Horses: 55 Million Years of Evolution, by J.L. Franzen, 2010 (Baltimore: JHU Press)
Equine adaptations for speed
Digit Loss, tip‐toe, & Joint Mobility
Fetlock Joint/Distal MC III
Mac Fadden, 1992 Franzen, 2010
Pads to Tip‐toe
The hoof lamellae
44.9 ml
• SA ~ 1m2
Epidermal basal
cells
What holds it together?
• Maintenance ofcytoskeleton andcellular adhesions isa dynamic, energyconsuming process
Courtesy of Chris Pollitt
Vascular supply to the foot: Arteries
Veins
Lamellar arteriovenousanastomoses
500/cm2
40
0
-10
-20
10
20
TempoC
Time (hours)6 12 18 24 30 36 42 48 54
CoreLeft fore
Right fore
Ambient
FOOT TEMPS: SUB ARCTIC CONDITIONS
30
Courtesy C.C. Pollitt
Blood perfusion and load
C.C. Pollitt
Unloaded
Square standing
Unilateral weight bearing
Maximal load
Venous return
Digital cushion and ungual cartilages: hoof expansion, energy absorption, venous return
Parks 2006
Energy metabolism in the lamellae
• Highly metabolically active
– High glucose consumption
– Rich in mitochondria
• Functionally anaerobic?
– Aerobic glycolysis
Pawlak et al 2013
Studying energy metabolism in vivo: Tissue Microdialysis
Glucose
Lactate
Pyruvate
Lac:Pyr ratio
Lac:Gluc ratio
Tissue Microdialysis
• Energy metabolism
Glucose
Lactate
Lac:Pyr ratio
Lamellar Microdialysis
Measuring perfusion with microdialysis
• Urea clearance
LAM
SUB
Glucose
Pyruvate
Lactate
Lac:Pyr ratio
Urea Clearance
Ischaemiamean +/‐ s.e. % change (n=9)
Medina‐Torres et al 2014
Lactate dehydrogenase
↓O2
↑L:P = ISCHEMIA ORMITOCHONDRIAL DYSFUNCTION
Lamellar energy balance is highly dependent on limb load cycling
Walkingmean +/‐ s.e. % change
Medina‐Torres et al 2014
Glucose
Pyruvate
Lactate
Lac:Pyr ratio
Urea Clearance
Enhanced static limb cycling activitymedian [IQR] % change
Enhanced static limb cycling activitymedian [IQR] % change
What about vasodilating agents?
Acepromazinemedian [IQR] % change
ACP affects load cycling frequency median [IQR] % change
Innervation of the foot
• Palmar digitalnervesinnervate thelamellae
(Paz et al 2016)
• Lamellatedcorpuscles soleardermis ‐proprioception
Palmar nerve
Dorsal branch palmar digital n
Palmar digital nerve
Palmar metacarpal n
Artwork: John McDougall
The hoof wall: anatomy and growth
Coronary groove
Periople
Lamellar hoof
Hoof wall
Coronary papillae
Chris Pollitt
Hoof wall
• Viscoelastic– Stiffer with increasing strain rate
• Highly resistant to fracture
• Less stiffness inner hoofwall– Gentle transfer of load
Proliferation of coronaryhoof - BrDU immunostaining
Hoof growth
Proliferation in the lamellar epidermis ?
Level 1
Proliferation in the lamellar epidermis ?
Level 4
% Hoof basal cells proliferating
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
COR L1 L2 L3 L4 L5 L6 L7 L8 L9 L10
Hoof level
%
n = 6 ponies
Hoof wall growth zone= proximal tubular and lamellar hoof
Lamellar basal cells
specialized for attachment
The wall grows down past the stationary dermis/bone – but where does the
“sliding” take place?
Lamellar response to injury
2d
3d 4d
Pollitt & Daradka, (2004)
Terminal papillae
Biomechanics of the foot
• GRF 1‐2 x bwt atfaster gaits
Biomechanics of the foot
