Posterior Tibial Tendon Dysfunction

Posterior tibial tendon dysfunction is degeneration and failure of the main dynamic stabilizer of the medial arch, producing the adult acquired flatfoot. It is most common in women over 40, with obesity, hypertension, diabetes, previous steroid exposure and inflammatory arthritis as risk factors. A hypovascular zone behind the medial malleolus predisposes to tearing.

Stages:

• I: tendinopathy or tenosynovitis with no deformity
• II: flexible flatfoot, with IIa (under 30% talonavicular uncoverage) and IIb (over 30% uncoverage with forefoot abduction)
• III: rigid hindfoot deformity with arthritis
• IV: ankle valgus from deltoid ligament failure

Untreated disease progresses through collapse of the arch, heel valgus, subtalar and talonavicular arthritis, and valgus tilt of the talus.

• Medial ankle and arch pain and swelling behind the medial malleolus
• A flattened arch, heel valgus and forefoot abduction, with too many toes visible from behind
• Inability to perform a single heel rise, or heel inversion that fails to occur on the rise
• Tenderness along the tendon
• Subfibular pain in later stages from calcaneofibular impingement
• Red flags: acute pop with medial collapse, inflammatory arthritis, neuropathy, and a rigid foot

• Clinical examination: observe from behind, assess the single heel raise, test flexibility of the hindfoot (passive correction of heel valgus).
• Weight bearing radiographs of the foot and ankle: talonavicular uncoverage, a lateral talo first metatarsal angle over 4 degrees (lost arch), calcaneal pitch below 15 degrees, talar tilt in the ankle view.
• Ultrasound or MRI for the grade of tendon degeneration, tears, spring ligament injury and the deltoid.
• Inflammatory markers when disease is bilateral or in a young patient.

Differentials: tarsal coalition, inflammatory arthropathy, midfoot arthritis, neuropathic arthropathy, tibialis posterior tendon avulsion fracture, lateral ankle impingement.

Stage I: a walking boot or cast for 6 to 8 weeks, then a custom orthosis with a medial heel post and arch support, eccentric tibialis posterior strengthening, and ibuprofen 400 mg orally every 8 hours with food for up to 7 days. Avoid corticosteroid injection (rupture).

Stage II: a custom orthosis with an ankle foot orthosis or lace up brace and physiotherapy. Surgery after 3 to 6 months of failed bracing:

• Flexor digitorum longus transfer to the navicular
• Medializing calcaneal osteotomy (10 mm)
• Lateral column lengthening with an Evans osteotomy or calcaneocuboid distraction for forefoot abduction (IIb)
• Spring ligament repair and gastrocnemius recession for equinus

Stage III: a triple arthrodesis (talonavicular, subtalar and calcaneocuboid) with correction of the deformity.

Stage IV: a hindfoot fusion with deltoid reconstruction, or a tibiotalocalcaneal fusion, in a patient with ankle arthritis.

Cefazolin 2 g IV before incision. Postoperative non-weight-bearing in a cast for 6 weeks, then a boot for 4 to 6 weeks, and enoxaparin 40 mg SC daily for 10 to 14 days in high risk patients.

Complications: wound breakdown (higher in smokers and diabetes), nonunion (arthrodesis), sural nerve injury, residual deformity and adjacent joint arthritis.

Follow up at 2 and 6 weeks, then every 3 months. Counsel on weight loss, supportive footwear and smoking cessation.