Adult Acquired Flatfoot Deformity

The stages. Each stage carries its own treatment.

The Stage II split (Myerson modification). Both IIA and IIB are flexible at the hindfoot; what separates them is the forefoot. In IIA the hindfoot corrects when the forefoot is unloaded and the Cotton test is negative, so hindfoot procedures alone will do. In IIB there is a fixed forefoot varus with the first ray dorsiflexed: the hindfoot valgus persists when the first ray is elevated (Cotton test positive) because the forefoot varus is driving the hindfoot valgus as a compensation. That foot needs its forefoot corrected as well as its hindfoot, and a reconstruction that leaves the forefoot alone fails.

Grading the tendon on MRI. Bluman grades the integrity of the tendon itself; the table gives the clinical correlation of each grade.

Why it matters. The grade helps predict which Stage I patients will progress and so guides the timing of surgery: a Grade 3 tear in a Stage I foot may benefit from early FDL transfer rather than prolonged conservative treatment.

Progressive Collapsing Foot Deformity. In 2020 an international consensus group (Myerson et al) renamed AAFD/PTTD to PCFD and replaced the linear Johnson and Strom stages with a system that records the condition as a three-dimensional, multi-component collapse rather than a single tendon disease. Each foot is given a flexibility stage and then whichever of five components it shows.

The flexibility stage comes first:

• Stage 1 - flexible deformity (passively correctable)
• Stage 2 - rigid deformity (fixed; arthritic or contracted)

Then the five deformity classes, or components, recorded for each foot:

How it reads. A foot is described as, for example, Stage 1ABC: a flexible deformity with hindfoot valgus, forefoot abduction and forefoot varus, rather than a single number. Most feet collapse in several planes at once and isolated single-component deformity is uncommon. Both PCFD and the older systems remain Level V expert opinion, and the interobserver reliability of PCFD is only moderate.

Who. Stage I (tenosynovitis without deformity); mild Stage IIA with minimal symptoms; patients unfit for surgery because of comorbidity; and the patient who, having understood the options, prefers not to have an operation.

When conservative treatment fails. Surgery is indicated in a Stage I foot for persistent pain despite 6 months of appropriate conservative treatment, for progressive deformity (transition to Stage II), for a failed single heel rise, and for a Grade 3 tear on MRI, because a complete rupture will not heal. Not every Stage I patient progresses: approximately 50% respond to conservative treatment with orthotics. Those with a Grade 3 tear should be offered early FDL transfer, before the deformity develops.

The goal is to correct the flexible deformity, restore PTT function and stop the foot progressing to a rigid Stage III.

IIA or IIB first. A Stage IIA reconstruction (hindfoot only) on a Stage IIB foot fails, because the uncorrected fixed forefoot varus drives the hindfoot back into valgus after surgery. Perform the Cotton test on every Stage II foot; if it is positive, add the medial cuneiform plantar flexion osteotomy. Missing the distinction is a common viva trap.

A menu assembled to fit the deformity. Stage IIA reconstruction is assembled to fit the foot in front of you rather than run as a fixed sequence. The calcaneal osteotomy and the FDL transfer are performed together in almost every case; lateral column lengthening and gastrocnemius recession are added only when their specific indication is present. Selecting components the foot does not need is how an over-corrected, painful lateral column is created.

Calcaneal osteotomy corrects the hindfoot valgus. Medialising the calcaneus under the tibia shifts the ground reaction force medial to the subtalar axis, converting a deforming valgus moment into a corrective inversion moment. The osteotomy changes the lever, which is why it protects the tendon transfer from stretching out. There are two options:

• Medialising calcaneal osteotomy (MCO) - simple medial translation of the posterior fragment; easy, reproducible, and the most common choice
• Koutsogiannis osteotomy - medial slide plus a lateral closing wedge; greater correction power, useful for severe valgus

FDL transfer restores dynamic support. The flexor digitorum longus is transferred to the navicular to replace the failed PTT and provide an active inversion force during gait. A tendon transfer alone fails if the bony malalignment is left uncorrected, because the transferred tendon is asked to resist a deforming moment it cannot overcome, which is precisely why the osteotomy accompanies it. FDL is preferred over FHL because it has:

• Better excursion (a longer muscle belly and arc of contraction, hence more active inversion force)
• Less donor morbidity (FHL is the stronger hallux flexor, and patients notice its loss more)
• An easier harvest through the medial approach, rather than the deep posterior approach for FHL
• Sufficient strength: biomechanical studies show FDL provides adequate force for arch support, and clinical outcomes are equivalent or better

FHL may be used if the FDL is unavailable after previous surgery, if a simultaneous hallux valgus correction is planned (harvest FHL and transfer FDL to the hallux for lesser toe balance, the "flexor swap"), or by surgeon preference. Both are acceptable; know the rationale for the choice.

Lateral column lengthening (Evans) only for forefoot abduction. The indication is significant forefoot abduction: talonavicular uncovering greater than 30%, an AP talo-first metatarsal angle greater than 20 degrees, a too many toes sign. Lengthening the anterior calcaneus corrects the abduction, reduces the uncovering and raises the arch through the windlass effect. Overcorrection produces a rigid, overloaded lateral column and calcaneocuboid arthritis, so lengthening is limited to 10-12 mm. This is the component most often added unnecessarily, and the resulting lateral pain is difficult to revise.

Gastrocnemius recession only if the Silfverskiöld test is positive. The indication is an isolated gastrocnemius contracture: ankle dorsiflexion short of neutral with the knee extended, improving with the knee flexed. A tight gastrocnemius blocks ankle dorsiflexion, so the foot obtains the dorsiflexion it needs by collapsing through the midfoot and everting the hindfoot. Leave the equinus uncorrected and that deforming force continues to act on the reconstruction, which is why an unrecognised contracture is a recognised cause of recurrence. The Strayer procedure (proximal gastrocnemius recession) or the Baumann procedure (distal recession at the musculotendinous junction) release it.

Stage IIB: add the forefoot. Confirm the Cotton test in clinic and again under anaesthesia: the hindfoot valgus persists when the first ray is elevated, so the forefoot varus is the driver. The medial cuneiform plantar flexion osteotomy (Cotton osteotomy) removes it by plantarflexing the first ray:

• Dorsal opening wedge osteotomy of the medial cuneiform
• Structural bone graft, typically 5-8 mm in height
• Fixation with a plate or screws

The alternative is a Lapidus fusion, fusing the medial cuneiform to the first metatarsal in a plantarflexed position: a more rigid correction, useful if the tarsometatarsal joint is arthritic. Either way this addresses the cause of the deformity in IIB, and without it the hindfoot correction will fail.

Stage III: Rigid Deformity

The concept. The hindfoot does not correct passively because the subtalar or talonavicular joint, or both, are stiff, from arthritis or from longstanding deformity with capsular contracture. Osteotomies alone will not work; a rigid deformity is corrected through an arthrodesis.

Subtalar or triple: alternatives chosen by the talonavicular joint. The single question that separates them is whether the talonavicular joint is mobile and non-arthritic. If it is, the deformity can be corrected through the subtalar joint alone and the midfoot motion is worth preserving. If it is not, fusing the subtalar joint alone will neither correct the deformity nor relieve the pain.

Subtalar arthrodesis, when the talonavicular joint is spared. The indications are isolated subtalar arthritis and rigid hindfoot valgus with a mobile, non-arthritic talonavicular joint. Through a medial or lateral approach the articular cartilage is resected from the posterior facet, the valgus corrected and the joint fixed with screws, typically two or three large lag screws, cannulated or solid. It preserves the talonavicular and calcaneocuboid joints, so some midfoot motion is retained and rehabilitation is faster than after a triple fusion. It may not fully correct the deformity if there is talonavicular instability, and it carries a long-term risk of adjacent-joint arthritis at the talonavicular joint and the ankle.

Triple arthrodesis, the powerful but costly option. The indications are rigid hindfoot valgus with talonavicular arthritis or instability, a need for greater correction power, and Stage III with severe deformity. The subtalar, talonavicular and calcaneocuboid joints are all fused, each fixed with screws or plates, correcting the valgus, restoring the arch and addressing the forefoot abduction. It is the most powerful correction, addresses every component of the deformity and recurs less often than an isolated subtalar fusion. The price is the loss of all hindfoot motion, accelerated ankle arthritis from the increased load, a longer rehabilitation and a higher nonunion risk with three joints to heal.

The modified triple. The modern trend is to preserve a non-arthritic calcaneocuboid joint and retain some motion. The reasoning is the reasoning that governs the whole choice: every joint you fuse transfers load to the joints you did not, and in this foot the joint waiting to receive that load is the ankle.

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Adjuncts. An FDL transfer can be considered in Stage IIIA (flexible forefoot, minimal talonavicular arthritis) and provides some dynamic support even after fusion. Lateral column lengthening may still be needed if severe forefoot abduction and a rigid calcaneocuboid joint prevent fusion.

Watch the ankle. Stage III patients remain at risk of progressing to Stage IV, where the deltoid attenuates and the talus tilts into valgus within the mortise. A hindfoot fusion does not prevent this and may hasten it, so counsel the patient at the outset rather than presenting the fusion as an endpoint.

Stage IV: Ankle Valgus

How it arises. Chronic hindfoot valgus attenuates the deltoid ligament until it fails, the talus tilts into valgus within the mortise, the tibiotalar joint becomes incongruent and the ankle becomes arthritic.

TTC fusion is a salvage. It costs the patient every degree of ankle and hindfoot motion in exchange for a stiff, plantigrade foot that is useful for standing and walking in adaptive shoes. Counsel extensively beforehand about what that means:

• Cannot walk on uneven ground
• Difficulty with stairs, ramps and kerbs
• Rocker-bottom shoes for life
• Compensatory hip, knee and back pain
• Difficulty driving, especially with the right foot

It is a quality of life decision, pain-free stability against functional motion, and some patients prefer amputation, which is controversial but documented.

Position. Supine on a radiolucent table (a Jackson table or a standard table with a radiolucent foot extension). Head neutral with airway access; arms on boards or across the chest according to the anaesthetist; pelvis centred and neutral. The operative hip is in neutral or slight external rotation with the knee extended or slightly flexed over a bump; the other leg is abducted and supported on a leg holder or pillow, out of the C-arm's path.

Padding. Sacrum, the non-operative heel and the elbows are padded; the ulnar nerve at the elbow and the peroneal nerve at the fibular head are at risk, the latter if the leg is externally rotated or in a leg holder. The operative heel must be off the table, the ankle hanging free or on a bolster.

Tourniquet. A thigh tourniquet over cast padding, the limb exsanguinated by Esmarch or elevation, inflated to 250-300 mmHg adjusted for the patient's size and blood pressure. Expect 90-120 minutes for multiple osteotomies and a transfer; if the time exceeds 2 hours, deflate and re-exsanguinate. A bloodless field helps the dissection, the tendon identification and the precision of the osteotomies; the costs are tourniquet pain, limited by the anaesthetic, and the time limit.

Prep and drape. Circumferential prep of the foot and ankle to mid-calf, and higher if a gastrocnemius recession is anticipated. Stockinette over the foot, then a U-drape or split sheet isolating the foot and ankle, exposing the medial malleolus to the toes (for the FDL and the medial cuneiform) and the lateral calcaneus (for the calcaneal osteotomy through a lateral or oblique approach, and the Evans if needed).

Test the C-arm before you prep. Confirm that AP, lateral and oblique views of the foot and a hindfoot alignment view are all obtainable without repositioning the patient. The Saltzman view is how intraoperative correction is judged after the osteotomy; if you cannot obtain it, you are operating blind on alignment.

The approach. A lateral oblique incision of 4-5 cm, centred over the lateral wall of the calcaneus and 1 cm inferior to the peroneal tendons, starting at the posterior tuberosity and running anteriorly parallel to the plantar surface. The lateral wall is palpable subcutaneously; stay inferior to the peroneals. Through skin and subcutaneous tissue, identify the sural nerve, which runs posterior to the lateral malleolus and may send branches across the field, and retract or protect it. Incise the periosteum longitudinally and elevate it superiorly and inferiorly, staying subperiosteal to protect the soft tissues.

Planning the cut. The osteotomy lies 1-1.5 cm distal to the posterior facet of the subtalar joint, to keep it out of the joint, and runs obliquely from posterosuperior to anteroinferior at about 45 degrees to the plantar surface. Confirm the level on a lateral fluoroscopic view and mark the line on bone with cautery or a pen. The oblique orientation increases the surface area for healing and allows translation without shortening.

The cut. An oscillating saw with a wide blade for the thick calcaneal cortex, starting posteriorly and cutting anteroinferiorly along the oblique line, irrigating continuously to prevent thermal necrosis, with retractors guarding the plantar nerves and the Achilles medially. The osteotomy is complete when gentle manipulation moves the posterior fragment; confirm on the lateral view that it is complete and does not enter the joint.

Translation and fixation. Grasp the posterior fragment with a bone clamp or a Schanz pin and translate it medially, typically 8-12 mm according to the preoperative deformity and the intraoperative assessment. On the Saltzman view the hindfoot should sit neutral to slight varus; translation greater than 12 mm risks varus overcorrection. Hold the reduction with a large K-wire or guidewire, then fix:

• Two 6.5 mm or 7.0 mm cannulated screws, the most common construct, passed from the posterior fragment into the anterior, either by lag technique (glide hole posteriorly, thread hole anteriorly) or as position screws, aiming for bicortical purchase anteriorly
• Plate fixation if the osteotomy is comminuted or the bone osteoporotic; a locking plate provides better fixation

Finish with AP and lateral fluoroscopy to confirm screw position, adequate translation and no intra-articular screw.

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The sural nerve. Injury during the lateral approach causes lateral foot numbness in a variable distribution. Always identify and protect it; if it is tethered across the osteotomy site, mobilise it gently or move the incision slightly anteriorly.

The approach. A curvilinear incision of 6-8 cm centred over the navicular tuberosity and extending posteriorly along the medial ankle, long enough to reach both the navicular insertion site and the FDL behind the medial malleolus, and extendable along the PTT if the diseased tendon is to be debrided or excised. Protect the saphenous vein and nerve, which run anterior to the incision, then incise the flexor retinaculum over the PTT and FDL. The PTT is the larger, more anterior tendon; the FHL lies posterior and deeper; the FDL sits between them.

Harvest. Open the FDL sheath longitudinally and confirm the tendon by pulling on it: the lesser toes flex, which is pathognomonic. Mobilise it proximally and distally by blunt dissection and divide it at the level of the navicular, or more distally if extra length is wanted. For maximal length, harvest through a small plantar midfoot incision over the master knot of Henry, where the FDL and FHL cross: identify the FDL as it splits into its four slips, divide it at or distal to the knot and draw the proximal end up into the ankle wound with a tendon passer or a blunt clamp.

The navicular tunnel. Expose the tuberosity and remove any diseased PTT remnants. The entry point is on the plantar aspect of the tuberosity, slightly inferior and medial to the normal PTT insertion. Drill a 7-8 mm tunnel from anterior to posterior, exiting the dorsal cortex (or drill anterior-posterior and tap out dorsally with a small curette), and pass a tendon passer through to confirm it is smooth. Check on a lateral view that the tunnel does not violate the talonavicular joint.

Tensioning and fixation. Pass the FDL through the tunnel from plantar to dorsal with a tendon passer or suture. Hold the foot with the hindfoot neutral to slight varus and the ankle in neutral dorsiflexion, and tension the tendon so that it is firm rather than slack but not overtightened, aiming for a slight inversion force. Fix with one of:

• Interference screw, bioabsorbable or metal, 6-7 mm, inserted into the tunnel alongside the tendon to compress it against bone: the gold standard, with strong immediate fixation
• Suture anchor in the dorsal cortex at the exit point, the alternative if the tunnel is too large or the tendon quality poor
• Tenodesis screw and spiked washer on the dorsal cortex, the tendon passed, folded back and secured beneath the washer: the traditional technique

Then check: on fluoroscopy that the screw or anchor sits within bone and not in the joint; clinically that the foot rests in slight inversion; and through a range of ankle and hindfoot motion that the transfer is not so tight as to cause equinus or restrict movement.

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The diseased PTT. Debride the degenerate portions if the tear is partial and some fibres are intact, or excise the tendon completely if it is ruptured or macerated; send tissue to pathology if an inflammatory cause such as a seronegative arthropathy is suspected. A diseased tendon left behind may go on hurting, and removing the source improves outcomes.

The approach. An oblique incision of 4-5 cm over the anterior process of the calcaneus, just posterior to the calcaneocuboid joint, mindful of sural nerve branches. Identify extensor digitorum brevis, which arises from the anterior calcaneus, and split or elevate it superiorly; expose the lateral wall of the anterior calcaneus subperiosteally and identify the calcaneocuboid joint, on a lateral fluoroscopic view if uncertain.

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Planning the cut. The osteotomy lies 1-1.5 cm posterior to the calcaneocuboid joint, keeping the cut out of the joint and preserving it, and runs obliquely from dorsal-lateral to plantar-medial, parallel to the joint surface. Mark the site with a K-wire or cautery and confirm it on the lateral view.

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The cut and the distraction. Cut with the oscillating saw through the lateral cortex and into the medial cortex, but do not complete it medially: the medial hinge gives stability. Open the osteotomy progressively with a lamina spreader or osteotomes to a target of 8-12 mm, measured with a ruler or calibrated osteotomes, and never beyond 12 mm, because over-distraction overloads the calcaneocuboid joint and leads to arthritis. Fluoroscopy confirms the width and that the distraction is parallel rather than hinged open dorsally or plantarly.

Graft and fixation. Three graft options:

• Allograft tricortical iliac crest, the most common: pre-shaped, sterile, no donor site, supplied in heights of 8, 10 and 12 mm to match the distraction
• Autograft iliac crest, from the ipsilateral anterior crest, if allograft is unavailable or by preference; it adds operative time and donor site pain
• Femoral head allograft, morselised or shaped into a wedge

Impact the graft gently with a mallet until flush with the lateral cortex, the medial hinge intact. The wedge shape usually holds it; add a small two- or three-hole plate on the dorsal surface if the graft is unstable or may displace. Confirm on AP and lateral views that the graft is in position, the distraction maintained and the joint not entered.

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Assess the correction. Clinically the forefoot should now sit aligned on the hindfoot. On the AP fluoroscopic view the navicular should be more congruent with the talar head and the uncovering angle reduced. Apply a varus stress to the hindfoot and watch the arch rise, which confirms the lengthening is doing its job.

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Overcorrection. The Evans is powerful and unforgiving. Lengthening beyond 12 mm produces a rigid lateral column with calcaneocuboid overload and pain, calcaneocuboid arthritis from the raised joint contact pressure, and an overcorrected, supinated, painful foot. Accept slight undercorrection rather than overcorrection, and if the talonavicular uncovering is extreme, greater than 40%, consider medial column procedures (medial cuneiform osteotomy, naviculocuneiform fusion) instead of excessive lengthening.

Haemostasis and irrigation. Deflate the tourniquet and secure haemostasis with cautery or ties, irrigate copiously (at least 3 L of normal saline across all incisions) and inspect each wound for bleeding vessels or haematoma.

Drains are generally not used for a routine Stage II reconstruction: the incisions are small and haemostasis good. Consider one after a large dissection (extensive PTT excision, several osteotomies with significant dead space), for ongoing ooze despite adequate haemostasis, or in a high-risk patient on anticoagulation or with a bleeding disorder. Use a small suction drain (10 Fr Blake or Hemovac) and remove it on day 1-2 once output is under 30 mL in 24 hours.

Layered closure. A deep absorbable layer (2-0 or 3-0 Vicryl) for periosteum or deep fascia is seldom needed for these incisions; close the subcutaneous layer with 3-0 or 4-0 absorbable (Vicryl or Monocryl) to obliterate dead space and approximate the dermis. For skin, choose by tension and skin quality:

• Subcuticular 3-0 or 4-0 Monocryl - best cosmesis and least scarring, for low tension and good skin
• Interrupted nylon 3-0 or 4-0 - simple and reliable; remove at day 10-14
• Staples - fast, for larger incisions or obese patients; remove at day 10-14

Dressing and splint. A sterile non-adherent dressing (Xeroform or Adaptic) over each incision, fluffed gauze, then a circumferential but non-constrictive soft roll. Over that a well-padded below-knee plaster or fibreglass backslab, from toes to below the knee, with the ankle in neutral dorsiflexion and the hindfoot neutral to slight varus to protect the osteotomy and the tension in the transfer, particularly padded over the malleoli, heel and dorsum, and secured with an overwrap rather than a circumferential cast so that it can accommodate swelling.

Why a backslab. The first 48 hours carry the highest risk of swelling and of compartment syndrome, rare in the foot but possible. A circumferential cast is constrictive and can compromise the circulation or cause pressure necrosis if the limb swells; a backslab with an overwrap immobilises adequately and leaves room. It protects the osteotomies and the transfer for the first 2 weeks, until the sutures are out and the foot moves into a cast or boot.

The shape of it. The osteotomies and the transfer are protected for the first 6 weeks without any load, weight is introduced in a boot only once the 6-week radiographs show healing, and the foot is fully loaded in the boot by 10-12 weeks. Some surgeons keep the foot non-weight-bearing for the full 12 weeks after a complex reconstruction (Stage IIB with multiple osteotomies) or in high-risk patients (diabetic, osteoporotic). Early loading risks nonunion or malunion of the osteotomies, especially the translated calcaneus, hardware failure (screw pull-out, plate breakage), failure of the transfer (anchor pull-out, or elongation with loss of tension) and a hindfoot that settles back into valgus.

Slower than an osteotomy. A fusion site has had its cartilage removed and presents a larger surface to heal, so it is loaded later than an osteotomy and only once the radiographs show it is fusing.

Nonunion after arthrodesis. Subtalar fusion fails to unite in 5-10%, triple fusion in 10-15%, higher because there are three joints to heal. Smoking is the biggest modifiable risk, so nicotine cessation before surgery is treated as mandatory; the others are diabetes, NSAID use during the healing period (use paracetamol and opioids instead), inadequate fixation and avascular bone. An asymptomatic fibrous union with stable alignment is observed. A painful or unstable nonunion is revised with bone graft, autograft iliac crest preferred and BMP considered if available, and more rigid fixation, larger screws or plate augmentation.