Adult Acquired Flatfoot Deformity (AAFD)
Adult Acquired Flatfoot Deformity (AAFD) is a progressive condition characterized by the collapse of the medial arch of the foot. It can lead to significant pain, deformity, and difficulty walking. Unlike congenital flatfoot, which is present from birth, AAFD develops over time, most often in middle-aged and older adults, particularly women.
What Causes AAFD?
The most common cause of AAFD is degeneration of the posterior tibial tendon (PTT)—a major tendon that helps maintain the arch of the foot and supports proper alignment during walking. Over time, this tendon can stretch, weaken, or rupture. When that happens, the foot loses its normal structure and begins to collapse inward and downward.
However, AAFD isn’t only about the PTT. As the condition progresses, other critical stabilizers—like the spring ligament, deltoid ligament, plantar fascia, and talocalcaneal ligaments—may also fail. When multiple structures are compromised, the deformity becomes more rigid and difficult to treat.
Factors that contribute to the development of AAFD include:
- Obesity
- Diabetes
- Hypertension
- Rheumatoid arthritis and other inflammatory conditions
- Use of steroids
- Pre-existing flexible flatfoot or foot abnormalities
In some cases, AAFD can occur without PTT damage—especially in individuals with spring ligament failure
Understanding the Foot’s Structure
The human foot contains 26 bones, more than 30 joints, and a complex network of tendons and ligaments that form three arches: the medial longitudinal arch, lateral longitudinal arch, and transverse arch. These arches distribute body weight and adapt to changes in terrain during walking or running.
The posterior tibial tendon runs behind the ankle bone and attaches primarily to the navicular bone. Its job is to lift the arch and lock the midfoot during the push-off phase of walking. When it fails, the arch collapses, the heel rolls outward (hindfoot valgus), and the front of the foot turns outward (forefoot abduction)
Symptoms of Adult Flatfoot
Symptoms vary depending on the stage of the condition:
- Pain and swelling along the inside of the ankle (especially early on)
- Flattening of the arch
- Difficulty standing on tiptoe
- Outward drifting of the foot
- Pain along the outer ankle or foot in later stages
- Ankle instability and difficulty with balance
One physical sign is the “too many toes” sign—when viewed from behind, more than two toes are visible on the outside of the foot due to the forefoot drifting outward
Staging the Condition
AAFD is classified into four stages, which guide treatment:
- Stage I: Mild PTT inflammation or degeneration without foot deformity. The foot remains flexible and patients can still perform a single-limb heel raise.
- Stage II: The foot begins to deform but remains flexible. Patients often lose the ability to invert the heel during a heel raise. This stage is divided into:
- Stage IIA: <30% talonavicular joint uncoverage Stage IIB: >30% uncoverage, indicating more severe deformity
- Stage III: The deformity becomes rigid. The foot cannot be manually corrected, and arthritis may begin to set in.
- Stage IV: The deformity extends to the ankle, often with deltoid ligament failure. This may lead to ankle arthritis and significant instability
Diagnosing AAFD
Diagnosis involves a combination of physical examination and imaging:
Clinical Examination
- Assessment of arch height
- “Too many toes” sign
- Single-limb heel raise test
- Flexibility testing (can the deformity be corrected with manual pressure?)
Imaging
- X-rays: Show alignment and joint uncoverage
- MRI: Best for assessing tendon and ligament integrity
- CT scans (weight-bearing): Helpful in surgical planning and for evaluating subtalar joint subluxation
Non-Surgical Treatment
In the early stages, nonoperative care can relieve symptoms and slow progression:
- Custom orthotics or braces (e.g., UCBL insert, Arizona brace)
- Anti-inflammatory medications
- Immobilization (boot or cast for acute pain)
- Physical therapy focused on strengthening, stretching, and proprioception
Structured physical therapy programs, combined with orthotics, have shown high success rates in improving pain and function for Stage I and early Stage II patients
Surgical Treatment
When conservative treatments fail (typically after 6 months), surgery may be recommended. Surgical options vary depending on the deformity’s stage and flexibility.
Common Procedures by Deformity Type
1. Hindfoot Valgus
- Medializing calcaneal osteotomy (MCO): Repositions the heel bone to correct heel alignment
- Gastrocnemius recession or Achilles lengthening: Reduces tightness contributing to deformity
2. Forefoot Abduction
- Lateral column lengthening (LCL): Lengthens the outer side of the foot to restore alignment
- Spring ligament reconstruction: Rebuilds critical support for the medial arch
3. Forefoot Supination
- Cotton osteotomy (opening wedge of medial cuneiform): Corrects forefoot alignment when the arch has collapsed unevenly
4. PTT Repair or Replacement
- Tendon transfer: Typically the flexor digitorum longus (FDL) is transferred to replace the damaged PTT
5. Rigid Flatfoot (Stage III)
- Triple arthrodesis: Fuses the subtalar, talonavicular, and calcaneocuboid joints to create a stable, plantigrade foot
6. Ankle Involvement (Stage IV)
- Deltoid ligament reconstruction
- Total ankle replacement or ankle fusion may be considered in cases of ankle arthritis
A Word on Accessory Navicular Bone
Some patients with flatfoot may have a type II accessory navicular bone, which alters the pull of the posterior tibial tendon and increases the risk of dysfunction. This condition often presents earlier than typical AAFD and may also require surgical management
Final Thoughts
Adult Acquired Flatfoot Deformity is more than just a fallen arch—it’s a progressive condition involving complex changes to tendons, ligaments, and bone alignment. Early recognition and intervention can make a significant difference. Whether managed conservatively or surgically, treatment should be tailored to the individual based on their symptoms, activity level, and degree of deformity.
If you are experiencing persistent foot pain, arch collapse, or instability, it’s important to consult a foot and ankle specialist for an accurate diagnosis and personalized treatment plan.
Dr. Mo Athar
