Tibialis Anterior Tendon Transfer (Whole / Split)

The indication. A dynamic forefoot supination deformity — the foot rolls into supination during the swing phase of gait but is plantigrade and passively correctable at rest — that has failed non-operative management (an AFO or brace adjustment, and botulinum toxin to the tibialis anterior). Three populations dominate: - Relapsed idiopathic clubfoot after Ponseti correction — dynamic supination develops in roughly 10 to 30 percent of treated feet; SPLATT is indicated when repeat casting and bracing fail. Most authors operate at age 3 to 8 years, before adaptive bony change sets in.

• Cerebral palsy (hemiplegia or diplegia, GMFCS levels I to III) — a dynamic equinovarus or supination pattern from swing-phase overactivity of the TA, often with a stance-phase equinus from the gastrocnemius-soleus.
• Stroke-related equinovarus — an acquired upper-motor-neuron spastic pattern in an adult; the equinus component is usually dominant, so an isolated TA transfer without TAL is rarely sufficient. Relative indications include mild-to-moderate dynamic supination in an ambulatory CP patient with a Silfverskiöld-negative ankle, a whole transfer for severe recurrence after failed SPLATT, dynamic supination in myelomeningocoele at a lower lumbar level with a supple foot, and a combined procedure with a calcaneal osteotomy once the fixed component of a rigid cavovarus foot has been corrected. Contraindications. Absolute: any fixed bony deformity — a rigid hindfoot varus, fixed cavus, or fixed equinus that does not correct passively (address it with a Dwyer calcaneal osteotomy, lateral column lengthening, or first metatarsal dorsiflexion osteotomy first); active infection in the field; and non-functioning peroneals (MRC grade less than 3) without a plan for augmentation (the transfer produces a stiff foot with no active eversion). Relative: severe spasticity uncontrolled by botulinum toxin or baclofen; a non-ambulatory patient without a functional goal the transfer can address (an AFO is simpler); age under 2 years (small tendon, small lateral cuneiform ossific nucleus, physis at risk); and previous anterior-compartment surgery with scarred planes. The one decision — split or whole. Every technique fixes the tendon into a bony tunnel at the lateral cuneiform or cuboid; the only real choice is whether the medial half of the TA is preserved:

Consent specifically for nerve injury (deep and superficial peroneal nerves, less than 2 percent), wound problems (5 to 8 percent), over-correction into valgus (5 to 10 percent, higher in whole transfer), under-correction (3 to 8 percent), growth-plate injury in children (less than 1 percent with fluoroscopy), and the planned period of cast immobilisation and non-weight-bearing. Setup. Supine with a sandbag under the ipsilateral hip to bring the foot to neutral or slight internal rotation (the foot tends to externally rotate in supine); the foot projects beyond the table end so the assistant can hold the ankle. A thigh tourniquet for cases over 60 minutes, or a calf tourniquet at 300 mmHg for shorter ones; exsanguinate with an Esmarch before inflation. General anaesthesia, with a popliteal sciatic block for analgesia (discuss with the anaesthetist — motor blockade of the peroneals can delay the early assessment of active eversion). A single dose of a first-generation cephalosporin at induction for clean bony surgery with hardware.

The goal is to harvest the lateral half (or whole) of the tibialis anterior tendon, re-route it subcutaneously across the dorsum of the foot superficial to the extensor retinaculum, and fix it under tension into a bony tunnel in the lateral cuneiform so it acts as a dorsiflexor-evertor. The exposure — an anterior incision kept medial to the TA with the deep peroneal nerve and dorsalis pedis artery identified and protected between EHL and TA — is the heart of the operation.

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Concurrent procedures are the rule rather than the exception and are performed BEFORE the TA transfer so the plantigrade position the transfer is tensioned against is defined: - Tendo-Achilles lengthening (TAL) — the commonest combined procedure, performed in an estimated 50 to 70 percent of transfers, for a Silfverskiöld-positive equinus. Either a percutaneous Hoke triple hemisection or an open sagittal Z-lengthening; performed first, with the foot then cast in 15 to 20 degrees of equinus for 3 to 4 weeks before gradual dorsiflexion to neutral.

• Posterior tibial tendon (PTT) lengthening — intramuscular coronal-split lengthening (the Barnes and Herring technique) when there is a mixed swing-phase TA supination AND a stance-phase PTT-driven varus.
• Calcaneal osteotomy — a lateral closing-wedge (Dwyer) or sliding osteotomy for the rigid cavovarus foot; performed and fixed first, then the transfer tensioned against the corrected hindfoot.

Rehabilitation | Phase | Timing | Immobilisation | Activity | |-------|--------|----------------|----------| | 1 | 0–4 weeks | Below-knee cast, non-weight-bearing (plantigrade; equinus if concurrent TAL) | Toe-touch weight-bearing with crutches only | | 2 | 4–6 weeks | Cast change — remove the plantar button and pull-out suture; re-cast plantigrade | Weight-bearing as tolerated in the cast | | 3 | 6–8 weeks | Walking boot or solid AFO | Active dorsiflexion and eversion; gentle passive stretching of any residual equinus | | 4 | 8–12 weeks | Stiff-soled shoe or UCBL insert for residual mild deformity | Physiotherapy — gait training, proprioception, strengthening of dorsiflexors and evertors | | 5 | Beyond 12 weeks | Normal footwear | Sport at 4 to 6 months; annual review in children until skeletal maturity | If a TAL was performed, its protocol dictates the first 3 to 4 weeks: the foot is cast in 15 to 20 degrees of equinus to protect the lengthened tendon, then progressively dorsiflexed with serial cast changes to neutral. The TA transfer benefits from early plantigrade positioning but must not compromise the TAL repair. Complications

Critical danger structures and exam traps

Epidemiology. Dynamic forefoot supination develops in roughly 10 to 30 percent of feet after successful Ponseti correction of an idiopathic clubfoot — the foot is plantigrade at rest but rolls into supination during the swing phase of gait. In cerebral palsy it is the characteristic swing-phase deformity of hemiplegic and diplegic gait, and in adults it follows an upper-motor-neuron stroke as an acquired spastic equinovarus. It must be distinguished from residual or recurrent bony deformity (a stiff, uncorrected clubfoot, or fixed cavovarus), which is not a dynamic problem and is not corrected by a tendon transfer. Pathoanatomy. The tibialis anterior is the primary ankle dorsiflexor but also inverts the foot in dorsiflexion. Dynamic supination is a relative imbalance: overactivity of the TA in swing, often compounded by weakness of the peroneals (peroneus brevis and longus), produces swing-phase supination. Equinus frequently coexists — the TA is recruited as a secondary dorsiflexor, and once it is transferred its equinus contribution is removed, unmasking a fixed equinus contracture. This is why a Silfverskiöld-positive equinus is addressed first. Surgical anatomy of the transfer. The TA originates from the lateral tibial condyle, the proximal half of the lateral tibial shaft, the interosseous membrane and the deep fascia; its tendon becomes tendinous about 5 to 6 cm proximal to the ankle, passes under the extensor retinacula lying medial to EHL, and inserts into the medial cuneiform and the base of the first metatarsal. At the ankle the tendon is 8 to 12 mm wide (enough for a longitudinal split into two 4 to 6 mm slips) with an excursion of 15 to 25 mm. The split follows the natural cleavage between the medially and laterally derived fibre bundles. The deep peroneal nerve (L4, L5, S1) and dorsalis pedis artery run between EHL and the TA, just deep to the retinaculum — the structures at risk throughout the operation; the superficial peroneal nerve emerges distally between peroneus longus and EDL and is at risk at the lateral incision. The lateral cuneiform is the preferred landing zone because it lies in the line of pull of the TA, has adequate bone stock in children over 3 years, and is dorsal to the subtalar joint axis so the transfer restores eversion; the cuboid is more lateral (more eversion moment) but needs a longer tunnel and has thinner stock. Key evidence. Hoffer et al. (1974) described the split transfer in 26 patients with spastic hemiplegia and established the SPLATT as the definitive procedure for dynamic supination in CP. Barnes and Herring (1991) reported 82 percent good-to-excellent results in 28 patients who had SPLATT combined with intramuscular PTT lengthening, with a concurrent TAL in 54 percent — establishing that the equinus must be addressed at the same sitting. For relapsed clubfoot, Mubarak and Van Valin (2009) reported complete correction in 91 percent of 32 feet at a mean 3.5-year follow-up, and Thompson et al. (2009) a 96 percent satisfactory outcome in 23 children at 5 years. Biomechanically, Knutsen et al. (2015) showed the split gives the most balanced correction of forefoot supination while preserving hindfoot motion, whereas the whole transfer over-everts. Mindler et al. (2020) confirmed with instrumented gait analysis that the transfer normalises forefoot supination (12.4 down to 5.2 degrees relative to the tibia), approaching the kinematics of healthy children. Patient selection is the key determinant of success: Limpaphayom et al. (2015) reported an 84 percent success rate in 73 CP feet, with failure predicted by fixed contracture, poor selective motor control and severe spasticity.