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Biomechanics of the Diabetic Foot

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1 Biomechanics of the Diabetic Foot
Robert G. Frykberg, DPM, MPH Chief, Podiatry Section Carl T. Hayden VA Medical Center Phoenix, AZ USA

2 Amputation Impaired Response to Infection DIABETIC FOOT ULCERATION RGF
Diabetes Mellitus Neuropathy Vascular Disease Trauma MOTOR SENSORY AUTONOMIC MICROVASCULAR MACROVASCULAR Weakness Loss of Protective Anhidrosis Structural: Atherosclerosis Atrophy sensation Dry skin, Fissures Capillary BM Decreased Sympathetic thickening Deformity tone Functional: Ischemia (Altered blood flow A-V shunting Abnormal stress regulation) Increased blood flow Neuropathic edema High plantar pressure Callus formation Reduced nutrient capillary blood flow Osteoarthropathy Amputation DIABETIC FOOT ULCERATION Impaired Response to Infection RGF

3 Causal Pathways to Foot Ulcers
High Plantar Foot Pressures Critical Triad in >63% of causal pathways From: Reiber et al: Diabetes Care 22: , 1999

4 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 2005 Cavanagh 1996

5 Abnormal Biomechanics High Plantar Pressures Neuropathic Ulceration
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 Biomechanics High Plantar Pressures Neuropathic Ulceration Van Schie 2005 Zimny 2004 Frykberg 1995

6 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, 2004 Boulton, Vinik, et al: Diabetes Care, 2005

7 Intrinsic Muscle Atrophy
Andersen et al: 2004

8 Intrinsic Muscle Atrophy
Bus et al: Diabetes Care, 2002

9 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

10 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

Structural alterations Reduced contact areas Increased plantar pressures Altered function Altered gait

12 STRUCTURAL DEFORMITY Any deformity can lead to high plantar
Pressures and subsequent ulceration in the Neuropathic Foot Frykberg et al: J Foot Ankle Surg 2006

13 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 Lavery Frykberg Lavery 2003 Racial variations are evident Veves 1995 Frykberg 1998

14 Predictive Value of Foot Pressure Assessment
24 month study of 1666 DM patients Mean age 69 yrs % male Mean Duration DM 11.1 yrs Mean Peak Plantar Pressure 86.6 N/cm2 VPT volts 263 (15.8%) had or developed ulcer Ulcer group had higher pressures Lavery LA, Armstrong, DG, et al, Diabetes Care 2003

15 Pressure is a factor Deformities IWGDF Foot Risk Categories
Lavery LA, Armstrong, DG, et al, Diabetes Care 2003

16 Progressive Risk of Ulceration
Neuropathy, PVD, And/ or Deformity No Neuropathy Neuropathy Hx Ulcer / Amp IWGDF Foot Risk Classification Peters 2001

17 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

18 GAIT ABNORMALITIES Contributing Factors
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

19 Limited Joint Mobility
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 Delbridge 1988 Fernando 1991 Zimny 2004

20 The Role of Limited Joint Mobility in Diabetic Patients with an At-Risk Foot Zimny, Schatz, Pfohl: Diabetes Care 27: , 2004

21 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 Zimny: Diabetes Care, 2004

22 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, 1993 Grant WP et al, JFAS, 1997 Lavery, et al, Arch Intern Med, 1998 Lavery, Armstrong, Boulton, JAPMA, 2002

23 Equinus Deformity Diabetic population study San Antonio, TX n=1666
50% male Age ~ 69 yrs Duration DM yrs VPT ~ 22.5 Equinus Prevalence 10.3% Peak plantar pressure 86.6 N/cm2 Lavery, Armstrong, Boulton, JAPMA, 2002


25 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

26 You can observe a lot just by watching
Yogi Berra American Baseball Player and Philosopher

27 Robert G. Frykberg, DPM, MPH
THANK YOU! Robert G. Frykberg, DPM, MPH


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