Transcript Biomechanics of the Diabetic Foot Robert G. Frykberg, DPM, MPH Chief, Podiatry Section Carl T.

Biomechanics of the
Diabetic Foot
Robert G. Frykberg, DPM, MPH
Chief, Podiatry Section
Carl T. Hayden VA Medical Center
Phoenix, AZ USA
Diabetes Mellitus
Trauma
Neuropathy
MOTOR
MACROVASCULAR
Weakness
Atherosclerosis
Atrophy
SENSORY
Loss of Protective
sensation
Deformity
Ischemia
Abnormal stress
Vascular Disease
AUTONOMIC
MICROVASCULAR
Anhidrosis
Dry skin, Fissures
Decreased Sympathetic
tone
Structural:
Capillary BM
thickening
Functional:
(Altered blood flow
regulation)
A-V shunting
Increased blood flow
Neuropathic edema
High plantar pressure
Callus formation
Osteoarthropathy
Amputation
Impaired Response to Infection
DIABETIC FOOT ULCERATION
Reduced nutrient
capillary blood flow
Amputation
RGF
Causal Pathways to Foot Ulcers
High Plantar Foot Pressures
Deformity 63%
Trauma
77%
Neuropathy
78%
Critical Triad in >63% of causal pathways
From: Reiber et al: Diabetes Care 22:157-162, 1999
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
Contributing Factors to the Abnormal Mechanics of the Diabetic Foot
Diabetes Mellitus
Neuropathy
Mononeuropathy
Polyneuropathy
Sensory
Motor
Autonomic
Structural Deformity
Primary (idiopathic)
Secondary
Muscle atrophy
Equinus
Amputations
Charcot
Gait Abnormalities
LJM
Foot drop
Collagen glycosylation
Equinus
reduced mobility
Intrinsic muscle
reduced shock absorption
atrophy
increased pressures
Clawtoes
Amputations
Abnormal Biomechanics
High Plantar Pressures
Neuropathic Ulceration
Van Schie 2005
Zimny 2004
Frykberg 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, 2004
Boulton, Vinik, et al: Diabetes Care, 2005
Intrinsic Muscle Atrophy
Andersen et al: 2004
Intrinsic Muscle Atrophy
Bus et al: Diabetes Care, 2002
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 FOOT
CONSEQUENCES
 Structural alterations
 Reduced contact areas
 Increased plantar pressures
 Altered function
 Altered gait
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
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
• Racial variations are evident
• Veves 1995
Frykberg 1998
Frykberg 1998 Lavery 2003
Predictive Value of Foot
Pressure Assessment
100
95
N/cm2
• 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
90
85.1
85
80
75
Ulcer
No Ulcer
Lavery LA, Armstrong, DG, et al, Diabetes Care 2003
Pressure is a factor
Deformities
IWGDF Foot Risk Categories
Lavery LA, Armstrong, DG, et al, Diabetes Care 2003
Progressive Risk of
Ulceration
60
55.8
50
40
30
20
18.8
10
5.1
14.3
0
Group 0
No Neuropathy
Group 1
Neuropathy
Group 2
Group 3
Neuropathy, PVD,
And/ or Deformity
Hx Ulcer / Amp
IWGDF Foot Risk Classification
Peters 2001
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
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
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
The Role of Limited Joint Mobility in
Diabetic Patients with an At-Risk Foot
Zimny, Schatz, Pfohl: Diabetes Care 27:942-946, 2004
70
60
50
40
At-Risk DM
Control DM
Non-DM
30
20
10
0
VPT
Ankle ROM
1st MTP
ROM
PTI
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
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
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
SUMMARY
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 Berra
American Baseball Player
and Philosopher
THANK YOU!
Robert G. Frykberg, DPM, MPH
[email protected]