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Biomechanics of the Diabetic Foot
Robert G. Frykberg, DPM, MPHRobert G. Frykberg, DPM, MPHChief, Podiatry SectionChief, Podiatry Section
Carl T. Hayden VA Medical CenterCarl T. Hayden VA Medical CenterPhoenix, AZ USAPhoenix, AZ USA
Diabetes Mellitus
Neuropathy Vascular Disease
Trauma
MOTOR SENSORY AUTONOMIC MICROVASCULAR MACROVASCULAR
Weakness Loss of Protective Anhidrosis Structural: AtherosclerosisAtrophy sensation Dry skin, Fissures Capillary BM Decreased Sympathetic thickening Deformity tone Functional: Ischemia (Altered blood flow A-V shuntingAbnormal stress regulation) Increased blood flow Neuropathic edema High plantar pressure
Callus formation
Reduced nutrient capillary blood flow Osteoarthropathy
AmputationAmputation DIABETIC FOOT ULCERATION
Impaired Response to Infection
RGF
Causal Pathways to Foot UlcersCausal Pathways to Foot Ulcers
63%
77% 78%
Neuropathy
Deformity
Trauma
From: Reiber et al: Diabetes Care 22:157-162, 1999
Critical Triad in >63% of causal pathways
High Plantar Foot Pressures
Altered Biomechanics in Diabetes
• Biomechanical abnormalities / structural deformities are most frequently a consequence of Neuropathy
• Altered gait patterns can result in unsteady gait with increased plantar foot pressures for longer durations (pressure-time integrals)
• Combination of foot deformity and neuropathy increases the risk of ulcer
• Limited Joint Mobility (ankle, STJ, great toe) will also lead to higher plantar pressures and ulcers
Van Schie 2005Cavanagh 1996
Contributing Factors to the Abnormal Mechanics of the Diabetic Foot
Diabetes Mellitus
Neuropathy Structural Deformity Gait Abnormalities LJM Mononeuropathy Primary (idiopathic) Foot drop Collagen glycosylation Polyneuropathy Secondary Equinus reduced mobility Sensory Muscle atrophy Intrinsic muscle reduced shock absorption Motor Equinus atrophy increased pressures Autonomic Amputations Clawtoes Charcot Amputations
Abnormal BiomechanicsAbnormal BiomechanicsHigh Plantar PressuresHigh Plantar PressuresNeuropathic UlcerationNeuropathic Ulceration
Van Schie 2005Zimny 2004Frykberg 1995
Classification of Diabetic Neuropathy
Generalized Symmetric Polyneuropathies– Acute Sensory– Chronic Sensorimotor– Autonomic
Focal and multifocal neuropathies– Cranial – Truncal– Focal limb– Proximal motor (amyotrophy– Coexisting CIDP
Boulton, Malik et al: Diabetes Care, 2004Boulton, Vinik, et al: Diabetes Care, 2005
Andersen et al: 2004Andersen et al: 2004
Intrinsic Muscle Atrophy
Bus et al: Diabetes Care, 2002Bus et al: Diabetes Care, 2002
Intrinsic Muscle Atrophy
Common Foot Deformities in Diabetes
• Hammertoes (Clawtoes)• Bunions (hallux valgus)• Prominent metatarsal heads
(pes cavus)• Charcot arthropathy• Partial foot amputations• Equinus (Achilles contracture)• Foot drop
STRUCTURAL DEFORMITY
•Primary (idiopathic) Pes cavus, pes planus, hallux valgus, hammertoes, forefoot deformities Deformities, pressure points, calluses precede neuropathy.
•Secondary "intrinsic minus foot"- clawtoes, pes cavus, depressed metatarsals. Loss of intrinsic muscle stability with long flexor over-dominance. Anterior crural atrophy (Ant. Tib.,EHL) - weakness, foot drop Equinus deformity- triceps surae dominance, post. tibial, long flexors Charcot deformity - rocker bottom, Lisfranc subluxation, MTP subluxation
•Iatrogenic
Post amputation: digital, ray, TMA, Lisfrancs, Choparts, Symes
Frykberg 1995
AMPUTATIONS IN THE FOOTCONSEQUENCES
Structural alterations
Reduced contact areas
Increased plantar pressures
Altered function
Altered gait
STRUCTURAL DEFORMITY
Frykberg et al: J Foot Ankle Surg 2006
Any deformity can lead to high plantar Pressures and subsequent ulceration in the Neuropathic Foot
The Role of High Plantar Pressures in Diabetic Foot Ulceration
• High plantar foot pressures are consistently detected in diabetic pts with neuropathy
• Boulton 1987, Veves 1992, Stess 1997, Shaw 1998
• correlated with Limited Joint Mobility, plantar tissue thickness, and plantar fascia thickness
• Zimny 2004, Abouaesha 2001, D’Ambrogi 2003
• risk factor for foot ulceration• Fernando 1991 Lavery 1998 Frykberg 1998 Lavery 2003
• Racial variations are evident• Veves 1995 Frykberg 1998
Predictive Value of Foot Pressure Assessment
• 24 month study of 1666 DM patients
• Mean age 69 yrs 50% male• Mean Duration DM 11.1 yrs• Mean Peak Plantar Pressure
86.6 N/cm2• VPT 22.5 volts• 263 (15.8%) had or developed
ulcer• Ulcer group had higher
pressures
95.5
85.1
75
80
85
90
95
100
N/c
m2
Ulcer No Ulcer
Lavery LA, Armstrong, DG, et al, Diabetes Care 2003
Pressure is a factor
Lavery LA, Armstrong, DG, et al, Diabetes Care 2003
Deformities IWGDF Foot Risk Categories
Progressive Risk of Ulceration
5.114.3
18.8
55.8
0
10
20
30
40
50
60
Group 0 Group 1 Group 2 Group 3
No Neuropathy Neuropathy Neuropathy, PVD,And/ or Deformity
Hx Ulcer / Amp
Peters 2001IWGDF Foot Risk Classification
GAIT DISTURBANCES
Function of neuropathy, deformity, & LJM
Abnormal loading patterns - earlier and longer
Altered cadence - instability and limp
Altered weight bearing sites –
Partial foot amputations - smaller area
Increased plantar pressures
Susceptible to ulceration
• Proximal muscle atrophy - thigh weakness• Anterior crural atrophy - dorsiflexor weakness• Intrinsic muscle atrophy - clawtoes; reduced toe loading• Foot drop - Anterior tibial, Extensor hallucis longus paresis• Equinus - Posterior group dominance; triceps surae• Structural deformities - Charcot, post amputations
GAIT ABNORMALITIESContributing Factors
• A product of Nonenzymatic glycosylation of collagen – Also associated with retinopathy
• Decreased ankle and hallux motion
• Restricted subtalar range of motion– reduced shock absorption;
– Increased vertical and shear forces
– Increased peak plantar pressures
• Alone does not cause ulceration
• With neuropathy, contributes to plantar ulceration
Limited Joint Mobility
Delbridge 1988Fernando 1991Zimny 2004
0
10
20
30
40
50
60
70
VPT Ankle ROM 1st MTPROM
PTI
At-Risk DM
Control DM
Non-DM
The Role of Limited Joint Mobility in Diabetic Patients with an At-Risk Foot
Zimny, Schatz, Pfohl: Diabetes Care 27:942-946, 2004
Zimny: Diabetes Care, 2004
There is a strong inverse correlation between joint mobility and PTI in diabetic patients
At-Risk Neuropathic patients have less joint mobility and higher PTI’s than control DM (non-neuropathic) patients
Equinus Deformity
• Achilles tendon contracture• Increases plantar forefoot
pressure• May increase risk for
ulceration• Present in ~ 40% of high-risk
patients• At 3x greater risk for
presenting with high plantar pressures
Barry DC et al, JAPMA, 1993Grant WP et al, JFAS, 1997Lavery, et al, Arch Intern Med, 1998Lavery, Armstrong, Boulton, JAPMA, 2002
Equinus Deformity
• Diabetic population study San Antonio, TX n=1666
• 50% male Age ~ 69 yrs• Duration DM 11.1 yrs• VPT ~ 22.5• Equinus Prevalence 10.3%• Peak plantar pressure 86.6
N/cm2
Lavery, Armstrong, Boulton, JAPMA, 2002
SUMMARYSUMMARY
Biomechanics of The Diabetic Foot
Biomechanical alterations are a composite function of neuropathy, structural deformity, LJM, and associated gait disturbances
Neuropathy is a primary determinant
Early recognition, intervention, and prevention of deformity with high plantar pressures are crucial to the avoidance of ulceration
You can observe a lot just by watching
Yogi BerraAmerican Baseball Player and Philosopher
