Adult Acquired Flatfoot — Posterior Tibial Tendon Dysfunction (PTTD)

Adult acquired flatfoot deformity (AAFD) is a progressive condition characterised by collapse of the medial longitudinal arch, hindfoot valgus, and forefoot abduction. The most common cause is posterior tibial tendon dysfunction (PTTD), where progressive insufficiency of the posterior tibial tendon (PTT) — the primary dynamic stabiliser of the medial arch — leads to a cascade of ligamentous failure, joint deformity, and ultimately arthritic change. Understanding the stages of progression is essential for directing the appropriate non-operative or surgical intervention.

• PTT function: primary dynamic stabiliser of the medial longitudinal arch; inverts the subtalar joint (locks the transverse tarsal joints) during terminal stance and toe-off, allowing efficient push-off
• Mechanism of failure: PTT insufficiency → spring ligament complex failure → subtalar and talonavicular joint subluxation → forefoot abduction and hindfoot valgus → peroneal tendons gain mechanical advantage → deformity self-perpetuates → eventually ligamentous tethers on the lateral side (calcaneofibular, sinus tarsi) fail → rigid flatfoot
• Risk factors for PTTD: female sex (4:1), obesity, diabetes, hypertension, seronegative arthropathies (particularly psoriatic arthritis), steroid use, age 40–60 years, previous trauma to the PTT
• Epidemiology: predominantly affects middle-aged women; prevalence approximately 3–5% in adults over 40; bilateral in 30% of cases

• History: medial ankle and arch pain; progressive deformity (shoes wearing out medially, inability to wear normal shoes); difficulty with stairs and uneven ground; lateral ankle pain in advanced disease (fibular impingement)
• "Too many toes" sign: from posterior, more than 2 toes visible on the lateral side — indicates forefoot abduction from spring ligament and talonavicular joint failure; highly sensitive clinical sign for AAFD when combined with heel valgus
• Single leg heel rise test: ask patient to stand on one leg and rise onto tiptoe; failure to invert heel (or inability to complete the test) = PTT insufficiency; normal = heel inverts during heel rise as subtalar joint locks through PTT action; perform bilaterally for comparison
• Double leg heel rise: ask patient to rise onto tiptoe on both legs — if they can only achieve this bilaterally but not unilaterally, PTT insufficiency is confirmed; some patients cannot perform single-leg heel rise due to pain even with intact PTT
• Palpation: tenderness along PTT course (posterior to medial malleolus, along medial midfoot to navicular insertion); swelling in PTT groove; hindfoot alignment assessment in standing and from behind
• Flexibility assessment: talonavicular and subtalar joint flexibility to distinguish Stage II (flexible) from Stage III (rigid) — passive correction of hindfoot valgus and forefoot abduction indicates surgical candidacy for joint-sparing procedures

• Weight-bearing foot and ankle radiographs: AP foot (talonavicular uncoverage, talar head-first metatarsal angle), lateral foot (loss of medial arch, talo-first metatarsal angle — Meary angle), hindfoot alignment view (hindfoot valgus angle)
• Meary angle (talo-first metatarsal angle on lateral WB X-ray): normal 0°; in flatfoot deformity, apex-plantar angulation develops (break in Meary line); angle >4° below horizontal indicates significant arch collapse; useful for pre-operative planning and quantifying deformity
• Talonavicular uncoverage: on AP foot X-ray, normally <10% of talar head uncovered; >40% = significant forefoot abduction (Stage IIB threshold)
• MRI ankle and foot: evaluates PTT integrity (tendinosis, partial or complete tear), spring ligament complex (superomedial and inferoplantar ligaments), subtalar and talonavicular cartilage; guides surgical planning; essential before surgery in Stage II–III
• USS: dynamic assessment of PTT; useful for guided injection; less comprehensive than MRI

• Stage I: RICE, NSAIDs, physiotherapy; medial arch orthosis; UCBL (University of California Biomechanics Lab) insole; short-leg walking cast or CAM boot for acute tenosynovitis; ultrasound-guided corticosteroid injection around (NOT into) the tendon — intratendinous injection risks rupture
• Stage II flexible: articulated AFO (ankle-foot orthosis) or UCBL with extended heel posting; 6 months of conservative management before considering surgery; physiotherapy focusing on intrinsic foot strengthening and eccentric calf strengthening; weight loss counselling
• Corticosteroid injection into the PTT sheath: acceptable for tenosynovitis (Stage I); AVOID direct injection INTO the tendon substance — risk of tendon weakening and rupture; peritendinous injection only
• Stage III–IV non-surgical candidates: custom-made AFO or CROW (Charcot Restraint Orthotic Walker) for rigid deformity; palliative management of arthritis

• FDL (flexor digitorum longus) transfer: FDL harvested at its knot of Henry; transferred to the navicular (or through a drill hole in the navicular) to replace PTT function; provides dynamic medial arch support; performed with calcaneal osteotomy in Stage II; FDL is preferred over FHL because FHL is more powerful but causes hallux weakness
• Medialising calcaneal osteotomy (MCO — Evans/Gleich osteotomy): shifts the calcaneal tuberosity medially by 8–10 mm; corrects hindfoot valgus; changes the mechanical line of Achilles tendon pull from valgus to neutral; standard procedure for Stage IIA combined with FDL transfer; alone insufficient for Stage IIB forefoot abduction
• Lateral column lengthening (Evans osteotomy): opening wedge osteotomy at the anterior calcaneus (calcaneocuboid junction); lengthens lateral column; corrects forefoot abduction and talonavicular uncoverage; used in Stage IIB; combined with MCO and FDL transfer for complete deformity correction
• Subtalar arthrodesis: Stage III rigid hindfoot valgus; corrects subtalar deformity and addresses arthritis; preserves ankle and transverse tarsal joints; combined with spring ligament repair and FDL transfer if tendon still has some function
• Triple arthrodesis (subtalar + talonavicular + calcaneocuboid): Stage III–IV; corrects all hindfoot joints; provides definitive correction of rigid flatfoot; significant functional loss of hindfoot motion; excellent pain relief; reserved for significant arthritis or severe deformity not correctable by isolated subtalar fusion
• Spring ligament reconstruction: the spring ligament (calcaneonavicular ligament complex) is the primary static stabiliser of the talar head; failure essential in AAFD pathogenesis; direct repair or reconstruction with allograft or autograft tendon increasingly performed at time of calcaneal osteotomy in Stage IIB to address the underlying ligamentous pathology

• Equinus contracture in AAFD: tight Achilles tendon or gastrocnemius complex contributes to flatfoot deformity by increasing forefoot and midfoot loads; Silverskiöld test differentiates gastrocnemius tightness (equinus resolves with knee flexion) from combined gastrocnemius-soleus tightness (equinus persists with knee flexed); gastrocnemius recession (Strayer procedure) or Achilles lengthening should be performed concurrently if equinus is present — failure to address equinus increases recurrence risk after bony correction
• Stage IV with ankle valgus: deltoid ligament insufficiency allows tibia to tilt into valgus on the talus (plafond obliquity); this requires addressing at the ankle level — supramalleolar osteotomy (SMOT) to correct tibial plafond obliquity, or deltoid reconstruction; some cases require combined SMOT + hindfoot fusion; total ankle arthroplasty (TAA) can be considered if ankle arthritis is present but technically challenging in significant valgus
• Cotton (medial cuneiform dorsal opening wedge) osteotomy: for persistent forefoot supination (forefoot varus) after calcaneal osteotomy and talonavicular correction; opens a wedge in the dorsal medial cuneiform to plantar-flex the first ray; addresses the residual forefoot component of deformity in Stage II patients
• Inflammatory arthropathy-associated AAFD: rheumatoid, psoriatic, and other inflammatory arthropathies cause AAFD through tenosynovitis and direct synovial joint destruction; management includes disease-modifying therapy, orthotics, and surgical fusion when conservative management fails; triple arthrodesis or pan-talar fusion for severe cases

• Johnson & Strom stages: I = tendinitis, no deformity; II = flexible flatfoot; III = rigid subtalar; IV = rigid + ankle valgus
• Single leg heel rise failure = PTT insufficiency; heel should invert during rise — failure to invert or inability to rise = PTT incompetent
• "Too many toes" sign = forefoot abduction = spring ligament/talonavicular failure; indicator of advanced Stage II or beyond
• Stage II surgical treatment: FDL transfer + medialising calcaneal osteotomy (IIA); add lateral column lengthening (Evans) for IIB (>40% talonavicular uncoverage)
• Meary angle: talo-first metatarsal angle on lateral WB X-ray; normal 0°; plantar break = significant arch collapse
• Corticosteroid injection: peritendinous ONLY; NOT into PTT — risk of rupture
• Equinus must be addressed: Silverskiöld test; gastrocnemius recession (Strayer) if positive; failure to correct equinus = deformity recurrence
• Triple arthrodesis: Stage III–IV; definitive correction; significant hindfoot motion loss; excellent pain relief
• Stage IV ankle valgus: deltoid insufficiency; SMOT or deltoid reconstruction at ankle level required
• FDL transfer: preferred over FHL (FHL more powerful but hallux weakness); inserted into navicular through drill hole