Anterior Tibial Tendon Rupture

Anterior tibial tendon (ATT) rupture is an uncommon but significant injury to the primary dorsiflexor of the foot. It may be acute (traumatic) or chronic (degenerative), and the two present differently and are managed differently. It is often misdiagnosed at first: up to 25% of diagnoses are delayed, because the long extensors compensate for the lost dorsiflexion.

How common. Rare, at an estimated 1% of lower-limb tendon ruptures, yet still the third most common lower-limb tendon rupture after the Achilles and patellar tendons. Men predominate about 3:1, with no significant difference between sides.

Who. The age distribution is bimodal. Degenerative ruptures typically affect older men with degenerative tendinopathy, over 45 years; acute traumatic ruptures occur in younger, active patients.

Origin and course. Tibialis anterior arises from the lateral tibial condyle, the proximal two-thirds of the lateral tibial shaft, the interosseous membrane and the deep fascia. Its belly is the largest and most medial of the anterior compartment, and the myotendinous junction lies 5-7 cm proximal to the ankle joint. The tendon, the most medial in the anterior compartment, crosses the front of the ankle beneath the superior extensor retinaculum and then the Y-shaped inferior extensor retinaculum.

Insertion. The medial and plantar surfaces of the medial cuneiform and the base of the first metatarsal, through a wide footprint of about 10-15 mm. It is the thickest of the ankle tendons.

Relations. Lateral to the tendon lie EHL, the deep peroneal nerve and the anterior tibial artery. Medially, and more proximally, run the saphenous vein and nerve.

The retinaculum. Superior, inferior and stem components of the extensor retinaculum constrain the ankle tendons, with separate compartments for TA, EHL, EDL and the peroneals. TA occupies the most medial tunnel, where it is susceptible to stenosis.

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Blood supply. Proximally the musculotendinous junction is well vascularised, with branches of the anterior tibial artery supplying the muscle belly, and longitudinal vessels run within the tendon substance. Distally the insertion has an osseous supply and branches from the dorsalis pedis. Between the two, beneath the extensor retinaculum and 2-3 cm proximal to the insertion, lies a watershed zone of reduced perfusion.

Why it matters. The hypovascular zone corresponds to the most common rupture site, much like the Achilles watershed, and it explains the pattern of degenerative tendinosis. The commonest site lies 0-3 cm from the insertion, a point of mechanical stress concentration, and the zone matters when planning repair versus reconstruction.

Function. Tibialis anterior is the most powerful dorsiflexor, providing 80% of ankle dorsiflexion strength. It is also a secondary hindfoot invertor (a synergist of tibialis posterior) and supports the medial longitudinal arch in stance. It can generate forces up to 3-4 times body weight, with about 25-30 mm of excursion through full ankle motion.

In the gait cycle. At heel strike it controls plantarflexion eccentrically, and in the loading response it decelerates the dropping foot. In swing it dorsiflexes concentrically so the toes clear the ground. Rupture therefore costs:

• A slap foot at heel strike, from the loss of eccentric control
• High steppage in swing to clear the toes, and an increased trip hazard
• Compensatory hip and knee flexion
• Loss of first-ray stability

Degenerative rupture, the common type. Age-related tendinosis (collagen degeneration with mucoid change) fails by attrition at the hypovascular zone. The onset is often insidious with minimal trauma, and the rupture may follow a minor stumble or a missed step. Intrinsic and extrinsic factors combine:

• Intrinsic - tendon degeneration, age over 45 years, the hypovascular zone
• Mechanical - a tight extensor retinaculum causing stenosis and friction, repetitive friction against the superior extensor retinaculum, osteophytes on the inferior anterior tibial lip causing attrition, tight footwear, and repetitive microtrauma from chronic overload in athletes or workers
• Corticosteroids - a previous local injection may predispose to rupture; systemic use is also a risk
• Inflammatory arthropathy - rheumatoid arthritis, seronegative spondyloarthropathy, psoriatic arthritis, gout
• Metabolic and vascular - diabetes mellitus (impaired tendon healing), chronic renal disease or failure, hypercholesterolaemia, obesity, peripheral vascular disease
• Drugs - fluoroquinolone antibiotics

Traumatic rupture. The younger, active patient, or the high-energy injury:

• Forced plantarflexion against resisted dorsiflexion, or eccentric loading during a fall or stumble
• Avulsion from sudden forceful dorsiflexion against resistance
• Laceration from a direct penetrating injury to the anterior ankle
• Sport, particularly skiing, basketball and dancing
• Iatrogenic injury during ankle arthroscopy or other anterior ankle procedures
• Ankle fracture-dislocation, with tendon disruption from high-energy trauma

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By chronicity. Time from injury sorts ruptures into three groups.

By location. Distal ruptures are the commonest, and the retinaculum complicates the middle zone: a Zone 2 rupture may need retinacular release for access, and the tendon can bowstring if the retinaculum is not reconstructed.

By severity and by cause. Severity is graded on imaging; the cause tells you the quality of tendon to expect.

Acute rupture. Sudden, sharp anterior ankle pain during a specific event, often plantarflexion against resistance, with an audible or palpable snap. Weakness is immediate: the patient cannot dorsiflex the ankle or walk on the heels. A visible anterior ankle swelling is the rolled-up proximal stump.

Chronic rupture. Weakness comes on gradually, and the complaints are of stairs, inclines and tripping. The foot slaps down after heel strike because eccentric control has gone, and the toes catch on uneven ground because clearance is reduced. Overuse of EDL brings anterior shin fatigue and discomfort, and the presentation is often delayed after a misdiagnosis of sprain or neuropathy.

What the patient cannot do.

• Walk on the heels
• Climb stairs without compensating at the hip and knee
• Walk without a steppage gait or circumduction to clear the foot
• Run, having lost push-off control
• Put shoes on easily, because dorsiflexion is weak

Look. The anterior ankle mass is the retracted proximal stump, with a gap distal to the extensor retinaculum. Watch the gait for a slap foot or steppage pattern, and the toes for clawing, the hyperextension of compensatory EDL overactivity. Wasting of the TA muscle in chronic cases is rare, because of the intramuscular tear pattern.

Feel. The gap is typically palpable 2-4 cm above the insertion, with the proximal stump a firm rolled mass above it and a thin or absent tendon below. An acute rupture is tender at the rupture site.

Power and special tests. With a complete rupture, dorsiflexion power is typically grade 0-1 despite EDL compensation, while a partial tear or a chronic compensated rupture may show grade 2-3 from EDL. Toe extension is normal or increased.

• Resisted dorsiflexion - severe weakness or absent function
• Heel walking - impossible
• Toe dorsiflexion - preserved or enhanced
• Passive plantarflexion - may reproduce pain at an acute rupture site
• Reverse Thompson test - squeezing the TA belly produces no dorsiflexion

Tendon or nerve. The single most examinable concept is separating a mechanical cause of foot drop from a neurological one. Isolated TA rupture is the only common cause with weak dorsiflexion but preserved toe extension and a palpable anterior mass. Check EHL power (the L5 sentinel), eversion, first web space sensation and the compartment for firmness and pain on passive stretch; in an isolated rupture all are normal.

Radiographs. Weight-bearing AP, lateral and oblique views of the foot and ankle. They are usually normal in an acute rupture. A chronic case may show:

• Anterior distal tibial osteophytes, the site of mechanical attrition
• Soft-tissue swelling or calcification in front of the ankle
• First-ray elevation from loss of plantarflexion force
• Arthritic change if the cause is inflammatory
• Rarely, an avulsion fracture at the cuneiform or first metatarsal base

Ultrasound. Dynamic, real-time and cost-effective. Use a high-frequency linear probe (10-15 MHz) in long and short axis along the whole tendon, compare with the other side, and scan dynamically with active dorsiflexion. A complete rupture shows a hypoechoic or anechoic gap with haematoma or fluid in it, and a retracted, thickened proximal tendon; a partial tear shows incomplete fibre disruption. Measure the gap, because it is critical to surgical planning.

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MRI. An ankle-foot protocol with T1, T2 and STIR sequences in axial, sagittal and coronal planes. It confirms the rupture location and assesses gap size, tendon quality and muscle status. It is indicated for:

• An uncertain diagnosis
• Pre-operative planning
• Assessment of a chronic rupture and of tendon quality
• Associated pathology

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Other tests. CT is rarely needed but may help identify bony pathology. Nerve conduction studies are for a suspected neurological cause of foot drop, and EMG distinguishes denervation from tendon rupture in unclear cases.

The decision. Surgery is the preferred treatment for most complete ruptures and is generally recommended for active patients. Four things decide what is done:

1. Gap size - under 3 cm, repair; over 3 cm, reconstruction
2. Tendon quality - good, repair; poor or degenerative, augment or reconstruct
3. Muscle status - minimal atrophy, repair; severe atrophy, consider conservative care
4. Patient goals - high function, surgery; minimal demands, conservative care

Timing. Emergency surgery is not required unless the injury is open and contaminated.

Which reconstruction. EHL transfer has long been taught as the workhorse, the most common and most reliable reconstruction for a chronic rupture. The largest pooled analysis disagrees: it ranked EHL autograft worst and the turn-down graft, semitendinosus autograft and direct repair best. On that evidence the preferred reconstructions for a chronic rupture are a turn-down flap, semitendinosus or allograft, and EHL transfer becomes a fallback for very large gaps, done with a hallux IP tenodesis to prevent a cock-up hallux.

At operation. The superficial peroneal nerve is injured in 2-3%; the anterior tibial artery rarely. The deep peroneal nerve is at risk in deep dissection and its injury numbs the first web space. A gap closed under excessive tension fails early, and tension set wrongly either way costs function: too tight gives an equinus contracture, too loose a weak dorsiflexor. Harvest can lacerate EHL or, rarely, devascularise the hallux.

Early complications (0-6 weeks). Wound complications run at 5-8% and are higher in diabetics, in patients with peripheral vascular disease and in chronic ruptures with poor tissue; careful tissue handling is essential. They present as delayed healing, dehiscence or superficial infection, and are managed with local wound care, oral antibiotics and revision closure if severe.

Late complications (beyond 6 weeks).

Stiffness follows prolonged immobilisation or adhesions, and adhesions are scarring to the retinaculum that limits gliding. An equinus contracture comes from excessive plantarflexion during immobilisation. A slap foot or steppage gait can persist despite an intact repair, and chronic anterior ankle pain comes from adhesions, nerve injury or arthrofibrosis.

Re-rupture. The most significant complication, commoner after primary repair of a chronic rupture. It usually occurs within the first 3 months and presents with acute pain, loss of dorsiflexion and a recurrent palpable gap; confirm it with ultrasound or MRI. The risks are a chronic rupture repaired under tension, poor tendon quality, early weight-bearing, inadequate immobilisation, non-compliance and premature return to activity. Revision is a reconstruction, with EHL transfer or allograft.

Persistent weakness. More common after reconstruction; measure it against the other ankle. Acceptable recovery is 70-80% after EHL transfer and 90% or more after primary repair. The causes are muscle atrophy, incomplete healing, adhesions and inadequate rehabilitation; treat with prolonged physiotherapy for 6-12 months and an AFO if severe, and consider revision if strength is under 50% with daily impairment.

Nerve injury. Superficial peroneal nerve injury numbs the dorsum of the foot and usually resolves in 3-6 months. Deep peroneal nerve injury leaves first web space numbness that persists but does not limit function. A painful neuroma is rare and may need excision or nerve decompression.

Prevention. Handle the tissues carefully, protect the nerve branches throughout, use adequate suture strength, set the tension correctly and augment poor tissue. Afterwards, immobilise strictly for 6-8 weeks, progress weight-bearing gradually under supervised physiotherapy and educate the patient about compliance. Start protected motion once healed to limit adhesions, and physiotherapy from week 8 against stiffness. The cock-up hallux is prevented by IP fusion or tenodesis at the time of EHL transfer.

Aftercare. The ankle is immobilised in plantarflexion and brought gradually to neutral, non-weight-bearing progressing to partial weight-bearing. Weight-bearing then progresses with active motion, gait normalisation and gentle strengthening, followed by progressive resistance, proprioception and functional work with a return to low-impact activity, and finally sport-specific training.

Return to work. Sedentary work at 6-8 weeks with protected weight-bearing, light duties at 12-16 weeks with a gradual transition, and heavy labour at 6-9 months at the earliest, which may need job modification. Driving with a right foot repair takes 3-4 months, once off immobilisation with adequate strength.

Surgery against an orthosis. Surgery gives significantly better function in active patients: near-normal strength, a normal gait, no orthosis, a normal fall risk and a return to sport. The non-operative patient keeps a slap foot or steppage gait, a permanent AFO, an increased fall risk and a reduced quality of life, with sport limited; non-operative care is appropriate only for the elderly, sedentary or high-risk.

Other reconstructions. EDL transfer restores 60-70% of the other side's strength, which may limit high-level sport, and allograft 70-85% once fully incorporated at 12-18 months. Satisfaction after revision surgery is lower, at 70-80%, because of complications and reoperations.

Prognosis.

• Favourable - acute rupture (under 4 weeks) treated by primary repair; good tendon and muscle quality with minimal atrophy; a young, healthy patient who complies with rehabilitation; non-smoker, non-diabetic, healthy weight; appropriate technique and aftercare
• Unfavourable - chronic rupture (over 3 months; over 6 months with muscle atrophy); severe tendon degeneration; significant atrophy or fatty infiltration; elderly with comorbidities; smoking, diabetes, obesity; inflammatory arthropathy; poor compliance with immobilisation or rehabilitation; failed prior surgery

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The rarity of this injury means much teaching rests on small case series and tradition rather than high-level evidence. Examiners reward candidates who can articulate where the genuine uncertainty lies.