Posterior Tibial Tendon Dysfunction (PTTD)

Clinical Scenario

A 55-year-old woman presents with a 6-month history of progressively worsening right foot deformity and pain along the medial ankle. She has been unable to keep up with her walking group due to fatigue and pain. She has noticed her arch "collapsing" and difficulty fitting into her regular shoes.

History:

• 6-month progressive medial ankle pain
• Gradual collapse of medial arch
• Difficulty walking long distances
• Pain worse after activity
• Previous corticosteroid injection to medial ankle 2 years ago
• No history of trauma

Medical History:

• Type 2 Diabetes Mellitus (well controlled, HbA1c 6.8%)
• Hypertension (on ACE inhibitor)
• Obesity (BMI 34)
• Previous gestational diabetes

Examination Findings:

Standing (from behind):

• Right hindfoot valgus compared to left
• "Too many toes" sign positive on right (4 toes visible lateral to heel vs 2 on left)
• Loss of medial longitudinal arch on right
• No "peek-a-boo" heel on right (visible on left)

Single Heel Raise Test:

• LEFT: Able to perform, hindfoot inverts with heel raise
• RIGHT: UNABLE to perform single heel raise (cannot lift heel off ground)

Seated Examination:

• Tenderness along PTT from medial malleolus to navicular insertion
• Swelling along PTT sheath
• Weakness of inversion against resistance (MRC 3/5)
• Silfverskiöld test: Positive (tight gastrocnemius - 5° dorsiflexion with knee extended, 15° with knee flexed)
• Hindfoot valgus: Passively CORRECTABLE to neutral (FLEXIBLE)
• No forefoot supination when hindfoot corrected
• No arthritis at talonavicular joint on stress examination
• Normal neurovascular examination

Investigations

Laboratory Results

Imaging

Weight-Bearing Foot X-rays (AP and Lateral):

• Talonavicular uncoverage (AP view) - talar head uncovered medially
• Increased talus-first metatarsal angle (Meary's angle) - apex plantar (sag at talonavicular joint)
• Decreased calcaneal pitch angle (15°, normal 20-25°)
• Talonavicular subluxation
• No significant arthritis at subtalar, talonavicular, or calcaneocuboid joints

Hindfoot Alignment View:

• Hindfoot valgus alignment (heel lateral to tibial axis)

MRI Right Ankle:

• Complete rupture of posterior tibial tendon with gap at navicular insertion
• Tendon shows mucoid degeneration and longitudinal split proximally
• Spring ligament attenuation
• No significant subtalar or talonavicular joint effusion
• No bone marrow oedema suggesting arthritis

Questions & Model Answers

Key Teaching Points

Common Examiner Follow-up Questions

1. "Why do you use FDL rather than FHL for the transfer?"

   • FDL has a more similar line of pull to PTT
   • FDL is expendable (FHL can compensate for toe flexion)
   • FDL is easier to harvest and has sufficient excursion
   • FHL is stronger - preserved for push-off

2. "What is the spring ligament and why is it important?"

   • Calcaneonavicular ligament on plantar aspect
   • Primary static restraint of talar head
   • Supports medial longitudinal arch
   • Fails secondarily after PTT dysfunction
   • Should be repaired/augmented during reconstruction

3. "What is a Cotton osteotomy?"

   • Dorsal opening wedge osteotomy of medial cuneiform
   • Corrects forefoot supination (when forefoot varus is fixed)
   • Plantarflexes the first ray
   • Used in Stage IIB with residual forefoot varus after MCO

Related Topics

• Adult Acquired Flatfoot Deformity
• Tendon Transfers - Lower Limb
• Calcaneal Osteotomies
• Triple Arthrodesis
• Foot & Ankle Biomechanics