Role of Forces Rather than Motion and Posture in Foot Orthotic

Role of Forces Rather than
Motion and Posture in Foot
Orthotic Prescribing
Craig Payne
Running
§  Principles applied elsewhere
§  Fascination with social media fanaticism –
voyeuristic!
§  Fallacies: cherry picking; confirmation biases;
appeal to authority; etc
§  Evidence vs anonymous bloggers
§  ‘Turmoil’ in the ‘industry’
§  Trends away from foot orthotics
Overuse Injuries
§  Affect 30-70% of runners in any one
year
Why:
§  Cumulative stress in the tissues
beyond what the tissues can tolerate
Factors:
running footwear used and issues with them
the training routine
overtraining
the particular running technique or form used by the
runner
§  muscle strength imbalances and flexibility issues;
§  issues with foot and lower limb biomechanics or alignment
§  issues with the proximal control of lower limb
biomechanics
§ 
§ 
§ 
§ 
Traditionally:
§  Role of foot orthotics was to change
alignment or posture of the foot
Principle
What is the evidence that foot prona1on is even a problem? — Cross sec1onal studies: — Bunions and ‘flat feet’ (Kalen & Brechner; 1988; Inman, 1976; Goldner & Gaines, 1976) — MTSS (‘shin splints’) and pronated feet (ViLasalo and Kvist, 1983; Messier and PiLala, 1988)
— No correla1on (Rome et al, 2001; Hogan et al 2002) — Pronated foot protec1ve (Cain et al, 2006) What is the evidence that foot prona1on is even a problem? — Prospec1ve studies: — No rela1onship between foot prona1on and overuse injuries (Cowan et al, 1992; Cowan et al, 1996; Brusseuil et al, 1998; Wen et al, 1998; Twellaar et al, 1997; Kaufmann, Brodine & Shaffer, 1999; Michelson, Durant & McFarland, 2002; Giladi et al, 1985; Burns et al, 2005; Hetrsroni et al, 2006) — Weak rela1onship between foot prona1on and overuse injuries (White & Yates, 2002; Reinking 2006, Willems et al, 2007) Do foot orthoses change even change rearfoot motion?
§  They don’t change rearfoot kinematics (eg Rodgers &
Leveau, 1982; Blake & Ferguson, 1993; Brown et al,
1995; Nawoczenski et al, 1995; Nigg et al, 1997; Butler
et al, 2003; Stackhouse et al, 2003; Williams et al
2003…)
§  They change rearfoot kinematics (eg Bates et al, 1979;
Smith et al, 1986; Novick & Kelly, 1990; McCulloch et
al, 1993; Stell & Buckley, 1998; Leung et al, 1998;
Genova & Gross, 2000; Nester et al, 2001; Woodburn
et al, 2003…)
§  and when they do change rearfoot kinematics, its small
à biological significance?
Rearfoot mo1on changes and clinical outcomes •  Zammit GV & Payne CB: Rela1onship Between Posi1ve Clinical Outcomes of Foot Ortho1c Treatment and Changes in Rearfoot Kinema1cs. J Am Podiatr Med Assoc 2007 97: 207-­‐212 RCT’s; outcomes studies; patient satisfaction studies; eg
§  Blake & Denton (1985); Survey; Orthoses definitely
helped 70%; 78% felt that their devices improved their
posture
§  Donatelli et al (1988); 81 subjects; retrospective
survey; 91% satisfied with their foot orthoses; 94% still
wearing the foot orthoses; 52% would “not leave home
without them”
§  Mororas & Hodge (1993); prospective survey of 523;
83% satisfied with their orthoses; at 14 weeks post
issue 63% had their symptoms completely resolved and
95% completely or partially resolved.
§  Etc; etc; etc; etc; etc; etc; etc; etc; etc; etc; etc
Measuring force needed to supinate the foot
§  If alterations in the forces are important
clinically, how can that be applied?
§  Rather than focus on magnitude of
excessive foot pronation, may need to focus
on measuring the force needed to supinate
the foot (‘supination resistance’)
§  ‘Supination resistance’ is an example of one
of the forces that can be clinically estimated
(windlass forces are another).
Supina1on Resistance Test •  Supina)on resistance tes)ng: •  60-­‐350N range 60-350N
Unilateral pathology
(Payne et al, 2002)
§  Subjects – unilateral lower limb pathology that
could be to what is assumed as being due to
excessive pronation of the foot
§  n=28
§  FPI > on symptomatic side 15/24 (= in 4)
§  Supination resistance > on symptomatic side
25/28
§  p=0.012
§  Conclusion: Pronatory force more predictive of
symptomatic side that pronated position
Force needed to supinate the foot •  Posterior 1bial dysfunc1on group: –  328 (+21) Newtons (n=14) •  Reference group: –  138 (+46) Newtons (n=142) Peroneal tendonitis
Peroneal tendonitis
§  n=13
§  Mean FPI = 5.6 (+2.7)
§  Mean supination resistance 91 (+21)N
§  (reference population 138 (+46) N)
Conclusion:
§  Foot is pronated, but force needed to supinate the foot is
low (peroneals may have to work harder)
Implications:
§  May need to increase pronatory force on lateral side of
rearfoot (despite pronated position)
Peroneal tendonitis
Hypothesis?
§  The foot orthoses (~running shoe) need
design parameters that match the
supination resistance force
§  rigidity and/or inverted position of
orthotic
supination resistance
§  ‘motion control’ features in running
shoes
supination resistance
§  How test this? How to apply this
clinically?
Traditional Foot Orthotic Prescribing
§  Based on:
• decision making to change alignment or func1on of the foot • various clinical tests or observa1ons were used to derive the prescrip1on variables • design features were incorporated into the foot ortho1c to move the foot closer to what was theore1cally considered a normal or ideal structural alignment or func1on Pathology Specific Prescribing
§  Tissue stress model
§  based on the concept of the decision
making is based on the pathology present
and not necessarily on the structural
alignment or function of the foot.
§  Design features are used in the foot
orthoses to alter the forces through the
pathologic tissues to reduce the load to
below a level that the tissues can tolerate.
Summary
§  Clinical tests à prescription variables
à How best to deliver those prescription
variables (the design features)
Concept
§  Clinical test / Pathology Specific
Prescribing
§  Prescription variable
§  Design Feature
Orthotic Prescribing:
— Supination resistance (Clinical test)
— If high, need forces to match it (Prescription
Variable)
— Medial wedging designs; more rigid orthotics
(Design features)
Types of foot orthoses
— Arch cookies, medial wedges
— Triplane wedges
— LSR prefab’s (eg Formthotics, Vasyli)
— Direct molded devices
— FFO’s (Root & modified Root type
devices)
— HSR prefabs (eg Prothotic, Interpod)
— Kirby medial skive, MOSI, Blake inverted,
DC wedge
— (Surgical)
More control, force or aggressive
Unilateral plantar fascii1s and the force to establish the windlass •  n=12 •  Windlass tension: Degrees of
hallux
dorsiflexion
Asymptomatic
side (newtons)
Symptomatic
side (newtons)
0
4
8
12
20
30
4.6
10.4
19.7
34.7
56.5
75.1
7.9
19.2
37.5
59.3
86.0
119.8
Why is low-dye strapping so effective?
Orthotic Prescribing:
— Plantar fasciitis (Pathology specific prescribing)
— Lower the forces in the plantar
fascisa(Prescription Variable)
— Invert rearfoot; forefoot valgus post; 2-5 bar; met
dome; reverse Mortons; cuboid elevation; first ray
cut out (Design features)
Plantar fasciitis prescription
variables:
— Need to lower the forces through the
plantar fascia:
1.  Low dye strapping
2.  Invert rearfoot and evert the forefoot
Think Intuitively
§  Motion does not damage tissues
§  Foot posture/alignment does not
damage tissues
§  Forces/loads damage tissues
§  Kinetics hurt; kinematics doesn’t
Clinically
§  Clinical tests to determine the loadsà
are there prescription variables that
can be designed into a foot orthoses to
reduce that load?
Overuse Injuries
Why:
§  Cumulative load in the tissues beyond
what the tissues can tolerate
Role of Foot Orthotics:
§  Reduce that load
Turmoil in the running ‘industry’
§  Barefoot running (minimalism)
§  “Foot orthotics are evil and should be
banned”
§  “Foot orthotics weaken muscles”
§  “Running shoes weaken muscles”
§  Proximal control
§  Running ‘form’
§  Social media debates
What have we learnt
§  “Cumulative load in the tissues beyond
what the tissues can tolerate”
§  à increase the ability of the tissues to
take the load
§  à other strategies to reduce the load
§  à short vs long term use of foot
orthotics
Clinical tests to derive prescription
variables:
§  Supination resistance
§  Windlass mechanism forces
§  Lunge test
§  Navicular drop and drift
Delivery of the design features
§  There is no one best orthotic,
material, manufacturing process etc
§  The best one is the one that has the
design features that deliver the
variables that are needed for that
patient
§  Does it matter how you deliver them?
Design Features
§  Resist the pronatory forces (ie medial
wedging; material rigidity)
§  Facilitate the windlass (ie lateral
column elevation; Cluffy wedge)
§  etc
Specific Pathologies
§  Plantar fasciitis
§  Peroneal tendonitis
§  Medial tibial stress syndrome
§  Anterior compartment syndrome
§  Patellofemoral pain syndrome
§  Posterior tibial tendonitis
§  “Top of foot pain”
Conclusion
§  Think re forces in the tissues rather than foot
posture and alignment
§  Think re clinical tests to derive prescription
variables
§  Think re what design features are needed to
deliver those variables
§  Think re increase the ability of the tissue to take
the load
§  Think re other strategies to decrease the load
§  http://www.runresearchjunkie.com/
§  http://www.podiatry-arena.com
§ 
@CraigBPayne
§ 
/craig.payne.3958
§  [email protected]