Pathology Specific Orthoses:

Posterior Tibialis Dysfunction

(Adult Acquired Flatfoot)

Adult Acquired Flatfoot Pathology

Steroid use

Steroid injection

Rheumatoid arthritis

Chronic synovitis

Obesity

Avulsion

Adult Acquired Flatfoot

Focus of Intervention

Primary need is to address the abnormal

STJ axis position and resultant deformity

Stages of adult acquired flatfoot need to be

addressed with more aggressive

biomechanical intervention

Address with components related to

moment arms and axis location

Foot Orthoses

UCBL in-shoe device provided superior

restoration of both arch and hind foot

kinematics.

Imhauser, Foot Ankle Intl, 1999

Joint Physics

Subtalar Joint and it’s Axis

Concepts of Controlling the Hyper-pronated

STJ with Functional Foot Orthoses

Determination of STJ Axis Position

Orthotic Prescriptions for Controlling the

Hyper-pronated STJ

Linear Forces are Converted to

Rotational Forces

Moment of Force

M = F x D

M = Moment

F = Magnitude of Force

D = Distance (lever arm)

Physics

Lever Arm (Moment Arm)

The perpendicular distance from the line

of application of force to the joint axis

To Increase Moment

Increase Magnitude of Force

Increase Lever Arm

Joint Physics

Subtalar Joint and it’s Axis

Concepts of Controlling the Hyper-pronated

STJ with Functional Foot Orthoses

Determination of STJ Axis Position

Orthotic Prescriptions for Controlling the

Hyper-pronated STJ

STJA Position Manter, Root, et. al.

16 degrees from sagittal

42 degrees from transverse

STJA Position Exits Through Talar Head

Represents an

Average Only

STJA Deviation

Lateral Deviation

Medial Deviation

Subtalar Joint Axis Neutral STJ

Pronated STJ STJA Adducts with the Talus

“Medially Deviated Subtalar Joint

Axis”

Forces (Torques) Act Around

the Subtalar Joint Axis

Internal Torques

Muscle

External Torques Ground Reactive Forces

Orthotic Reactive Forces

STJA Deviation Changes the Length of the Lever Arm

Kirby, K. Rotational Equilibrium around the STJ axis.

JAPMA, 1987

To control STJ pronation, a FFO must act to

convert the GRF into an Orthotic Reactive Force

(ORF) which acts farther medial to the STJA

Standard Functional Foot Orthosis Effect On:

Normal STJA

Slight Supination Moment

Medially Deviated STJA

Large Pronation Moment

To control the Pes Planus type foot, you

must increase the ORF on the limited area

available medial to the subtalar joint axis

The Orthotic Prescription

Material

Size - Width and Heel Cup Depth

Positive Castwork

Posts

Top Cover

Forefoot Extensions

Special Additions

Material Selection: Enough Rigidity to Resist Deformation

Polypropylene: Vacuum Formed

Graphite / Fiberglass

EVA / Cork and Leather

Increased Width / Heel Cup Depth

Increased Surface Area Medial to STJA Longer Supination Lever Arm

Increased Supination Moment / Decreased Pronation Moment

x 22

x

Varus Wedge Effects: Change Position of Orthotic Force on Heel

Varus Wedge Effect

Increase Lever Arm Medial

to STJA

Increase Supination Moment

Medial Heel Skive (Kirby)

Inverted Techniques

Mildly Inverted

Highly Inverted (Blake)

Medial Heel Skive Technique Positive Cast Modification

Allows Varus Wedge Effect Without Jamming of

Medial Column

Increases Supination Moment Across STJA

Kirby, K. The Medial Heel Skive Technique. JAPMA, April 1991,

Shifts Center of

ORF Medial

Adds Varus

Wedge to Heelcup

Medial Heel Skive Prescription

Intrinsic Accommodations Sweet Spot to Accommodate Navicular

Mark Prominence with Lipstick

Vacuum Formed Accommodation Filled with Poron

Topcover - Glue Heel Only

x x

Rearfoot Post

Stabilizes Orthosis in Shoe

Not Necessarily Corrective

x x

x

Topcover

x

PTD Prescription Sample Material: 1/4” Polypropylene

Width: Medial Flange

Heel Cup Height: 22mm

Positive Cast : Medial Heel Skive

Positive Cast : Navicular Sweet Spot

Posting: 0/0 (flat) Rearfoot Post

Covers: EVA to Sulcus.

Glued Heel Only