Adult Acquired Flat Foot

Stabilisers of Medial Arch

Static

• Plantar Fascia
• Spring Ligament
• Interosseous Talocalcaneal ligament
• Superficial Deltoid

Dynamic

• Tibialis Posterior tendon

Aetiology of Flat Foot

• Tibialis Posterior Tendinopathy or rupture is the most common cause
  • Alone does not cause flat foot
  • Its deficiency places the arch at risk for developing flat foot
  • Flat foot deformity occurs when static restraints also fail

Other Causes

• Inflammatory arthritis
• Tarsal coalition
• Neurologic imbalance
• Trauma
• Mid and hindfoot arthritis

Biomechanics of Arch Stability

Function of the Medial Longitudinal Arch

• Provides a supple foot in early stance for shock absorption
• Acts as a rigid stiff lever for propulsion in terminal stance and pre-swing
• Not a rigid arch and lacks a keystone
• Allows functional variation throughout the gait cycle

Arch Mechanics During Gait

First Contact

• TA holds ankle dorsiflexed
• Subtalar joint inverted (supinated)
• Midtarsal joints locked (divergent) and adducted
• Arch stable

Loading

• Tibia internally rotates
• Subtalar joint everts (pronates)
• Midtarsal joints unlock and become abducted (convergent)
• Talus plantar flexes
• TNJ dorsiflexes and adducts
• Metatarsals dorsiflex
• Arch apex moves downward and medially
• Plantar fascia, spring ligament, and intraosseous TC ligament prevent further collapse

Midstance

• Static stabilisers support the arch
• Tibialis Posterior is inactive

Midstance to Preswing

• Tibia externally rotates
• Subtalar joint inverts (supinates)
• Arch stiffens for propulsion
• Tibialis Posterior fires for power

Summary of Gait Cycle

• TP insufficiency alone does not cause flat foot in midstance
• TP insufficiency weakens propulsion

Pathology of TP Insufficiency

• Loss of collagen alignment, myxoid degeneration, hypercellularity, neovascularisation
• Most common in avascular zone (14mm between medial malleolus and navicular)

Risk Factors

• Pre-existing flat foot deformity
• Female gender

Classification (Johnson & Hattrup + Myerson)

• Stage 0 – MRI changes, no symptoms
• Stage 1 – Painful but intact TP
• Stage 2 – Incompetent TP with flexible planovalgus foot
• Stage 3 – Incompetent TP with fixed planovalgus foot
• Stage 4 – Fixed planovalgus with talar tilt in ankle mortise
• Key Factor: Whether the deformities are fixed or flexible, and whether the ankle is affected

Clinical Assessment

History

• Pain
  • Posteromedial – TP tendinopathy
  • Anteromedial – Deltoid ligament involvement
  • Lateral (Sinus Tarsi) – Impingement
• Neurologic symptoms (Tarsal tunnel syndrome)
• Foot shape – New or pre-existing flat foot?
• Functional deficit
• Orthotic use
• Other medical problems

Examination

Look & Feel

• Too many toes sign
• Hindfoot valgus
• Pain along TP tendon
• Pain or osteophytes over TNJ
• Lateral impingement pain

Move

• Heel valgus correction to varus on tiptoeing
• Single foot heel lift test
  • Not useful in advanced stiff planovalgus
• Resisted foot inversion
  • Test in plantarflexion to eliminate TA
• Subtalar motion – flexible or stiff?
• Ankle ROM – Achilles contracture?
• Other foot problems (e.g., Hallux Valgus)

Investigations

X-Ray (AP & Lateral Standing)

• Meary’s angle
• Kite’s angle
• Joint arthritis
• Talar tilt in mortise (Severe disease)

MRI

• Useful in mild cases without deformity
• Differentiate between TP degeneration vs. inflammation
• Guides between debridement vs. FDL transfer

Management

Non-Operative

• Depends on patient’s main complaint (Pain, function, skin compromise)
• Initial approach for most patients
• Orthotics helpful in all cases

UCBL Insoles

• As effective as calcaneal osteotomy in flexible feet
• Medial arch support + medial hindfoot posting

For Stiff Deformities

• Accommodative orthoses for pain relief
• Custom shoes
• Braces/AFOs

Severe Skin Compromise

• Padded total contact casting

Surgical Treatment

Debridement of TP Tendon

• Only for pain, no deformity
• Not advisable in deformity cases
• Usually combined with FDL (or FHL) transfer

FDL Transfer

• FDL crosses FHL at Knot of Henry
• Harvesting proximal to Knot prevents loss of toe flexion
• Diseased TP removed
• FDL fixed into navicular with interference screw
• Proximal TP sutured to FDL for power
• Distal FDL sutured to FHL if needed

Cobb Procedure (Alternative Transfer)

• Split TA passed through medial cuneiform & sutured to TP stump
• Less popular than FDL transfer (not as synergistic)

Medial Displacement Calcaneal Osteotomy (MDCO)

• Usually combined with tendon transfer
• Realigns Achilles pull to varus
• Reduces ankle joint contact pressures
• Technique:
  • Chevron osteotomy
  • Medial shift by ~1cm
  • Fixed with cannulated screws

Lateral Column Lengthening (Evans Procedure)

• For severe planovalgus deformity
• Either:
  • Distraction osteotomy of calcaneus proximal to CCJ
  • Intra-articular CCJ distraction
• Fixed with tricortical graft & plate
• Combined with FDL transfer

Fusions

• For fixed deformities & obese patients
• Depends on which joint is stiff
  • Subtalar Fusion – Lateral impingement pain
  • Talonavicular Fusion – Corrects arch deformity
  • Double Fusion – Midtarsal joints
  • Triple Fusion – Severe stiff painful deformity (alters gait)
  • Pantalar Fusion or Ankle Replacement – If combined with ankle arthritis

Achilles or Gastrocnemius Lengthening

• Indicated if contracture present
• Common in established planovalgus

Management Algorithm

1. Pain, No Deformity, Mild MRI Changes → Debridement
2. Pain, No Deformity, Severe MRI Changes → Debridement + FDL Transfer
3. Pain, Fully Flexible Mild-Moderate Deformity → Debridement + FDL Transfer + MDCO
4. Pain, Fully Flexible Severe Deformity → Debridement + FDL Transfer + Lateral Column Lengthening
5. Stiff Subtalar, Everything Else Flexible → Debridement + FDL Transfer + STJ Fusion
6. Stiff Midtarsal, Everything Else Flexible → Debridement + FDL Transfer + MDCO + TNJ/Double Fusion
7. Completely Stiff Deformity → Corrective Triple Fusion
8. With Ankle Arthritis → Pantalar Fusion or Triple Fusion + Ankle Replacement