Posterior Tibial Tendon Dysfunction - Surgical Reconstruction

Indication. Symptomatic posterior tibial tendon dysfunction (PTTD) — progressive medial ankle pain, a collapsing medial longitudinal arch, heel valgus and loss of the single heel raise — that has failed at least six months of non-operative care (a University of California Biomechanics Laboratory — UCBL — orthosis, physiotherapy with eccentric strengthening, and NSAIDs). The operation is chosen by stage and, above all, by whether the deformity is flexible or rigid.

The one decision that matters — flexible versus rigid. Stand behind the patient and passively correct the heel valgus and arch collapse:

Clinical assessment. Take a focused history (progressive medial ankle pain and swelling, difficulty on uneven ground and stairs, noticed flatfoot and shoe-wear changes, duration and response to orthoses) and examine from behind:

Imaging for surgical planning. Obtain weight-bearing AP and lateral foot, and a hindfoot alignment view. Non-weight-bearing films underestimate the deformity. Key measurements: lateral talus-first metatarsal angle (normal 0-4 degrees, Stage II often 15-30 degrees), calcaneal pitch (normal 20-30 degrees, Stage II often under 15 degrees), and AP talus-first metatarsal angle (forefoot abduction when over 30 degrees). Add an ankle mortise view for Stage IV (medial clear space, talar tilt). MRI is not mandatory when the clinical and weight-bearing radiographic picture is clear, but confirms PTT pathology and spring ligament integrity when needed. Stress views confirm flexibility when the stage is uncertain.

Algorithm

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The stage-based surgical algorithm translates the clinical and radiographic assessment into the operation:

Consent specifically for 6 weeks of strict non-weight-bearing (the patient must have support at home), recurrent deformity in 10-15%, sural nerve injury from the lateral MDCO incision, wound problems, MDCO nonunion, and CRPS. Counsel that a long-term orthosis is usually recommended. Optimise risk factors first — weight, diabetes control, and smoking — since obesity (BMI over 35), diabetes and smoking predict failure.

The goal of Stage II reconstruction is to replace the failed posterior tibial tendon with the FDL (active arch support) and correct the bony deformity with an MDCO (passive realignment that offloads the new tendon), adding lateral column lengthening for forefoot abduction and a Cotton osteotomy for residual forefoot varus. The medial exposure is laid out in full below (and in depth on the medial approach to the talus and navicular page).

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Rehabilitation after FDL transfer plus MDCO. The 6-week non-weight-bearing period protects the FDL fixation (tendon-to-bone healing takes 6-8 weeks) while the MDCO unites.

Rehabilitation after triple arthrodesis (Stage III). Non-weight-bearing in a short leg cast for 6 weeks, then progressive weight-bearing in a boot as bridging trabeculae appear (expect 80-90% union by 12 weeks), advancing to a supportive shoe by 12-16 weeks with return to activity at 6-9 months. Triple arthrodesis carries a 10-15% nonunion rate, most often at the talonavicular joint — revise a painful nonunion with iliac-crest autograft, rigid fixation and BMP augmentation. Complications — recognition, prevention, management

Outcomes. FDL plus MDCO gives 85-90% good or excellent results with preservation of about 81% of subtalar motion and restoration of the single-leg heel rise; adding lateral column lengthening yields 80-85%. Triple arthrodesis gives 80-85% pain relief but sacrifices hindfoot motion, with adjacent-joint arthritis in 20-30% at 10 years. TTC fusion (Stage IV) is a salvage with 75-80% fusion and significant functional limitation. Long term, 80-85% of FDL-plus-MDCO patients maintain correction at 5 years.

Epidemiology. PTTD is the most common cause of acquired adult flatfoot deformity. It typically presents in active adults aged 40-60 years with a strong female predominance (about 9 to 1). Risk factors include obesity (BMI over 30), diabetes, hypertension and steroid use, and 10-20% have contralateral involvement. Without treatment, roughly half of Stage I feet progress to Stage II within 2-5 years, and 30-40% of Stage II feet develop rigidity. Classification. Johnson and Strom described Stages I to III in 1989; Myerson added Stage IV (ankle valgus from deltoid failure) in 1997, and examiners worldwide still expect this four-stage framework. A 2020 international consensus renamed the condition Progressive Collapsing Foot Deformity (PCFD) and replaced staging with a flexible-or-rigid classification (Classes 1 to 5 by deformity component A to E). State that you are aware of both and lead with Johnson and Strom unless asked for the current consensus; all systems hinge on the flexible-versus-rigid distinction that decides joint-sparing reconstruction versus arthrodesis.

Pathophysiology and biomechanics. The posterior tibial tendon inverts the heel during stance, locks the transverse tarsal (Chopart) joint to form a rigid lever, and maintains the medial longitudinal arch. When it fails, the heel drifts into valgus (ground reaction force falls lateral to the ankle), the transverse tarsal joint unlocks, the arch collapses and the forefoot abducts (the too many toes sign). The FDL is the ideal transfer because it runs deep to the PTT in the tarsal tunnel on a similar vector with minimal donor morbidity; the MDCO complements it by shifting the ground reaction force medial to the ankle axis, converting the Achilles moment from eversion to inversion and offloading the reconstructed tendon.