Meary Angle (Talo-First Metatarsal Angle)

The film. A true lateral radiograph of the foot taken weight-bearing: the patient standing, the beam perpendicular to the foot and centred on the midfoot. The foot must be loaded, because a supine film underestimates flatfoot and overestimates cavus.

Rotation. Check it before drawing anything: on a true lateral the medial and lateral cortices of the talar dome overlap, and a malrotated film distorts the talar axis.

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The lines. Two axes, and the angle where they meet:

1. The longitudinal axis of the talus: a line through the midpoint of the talar head and the midpoint of the talar neck-body junction, or a best-fit line along the talar body.
2. The longitudinal axis of the first metatarsal: a line through the midpoints of the proximal and distal metaphyseal-diaphyseal junctions of the first metatarsal.
3. The Meary angle is the intersection of these two lines at the midtarsal region.

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The commonest error. The talar axis is drawn through the dome. The dome is a curved surface and a line across it does not represent the bone's long axis; the landmarks are the midpoints of the talar head and the neck-body junction, as above. The first-metatarsal axis should use the shaft midpoints, not the head or base alone.

On exam day. State exactly which landmarks you are using as you draw, and say that the film is weight-bearing.

Reading the angle. In a neutrally aligned foot the two axes are collinear and the angle is approximately 0°, with roughly 4° either way accepted as normal.

The apex. Beyond that, the direction of the apex names the deformity, and a number quoted without it is clinically meaningless: an apex directed plantarward means pes planus and an apex directed dorsalward means pes cavus. Plantar with planus, dorsal with cavus; the apex is the arrow pointing at the problem.

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Pes planus (flatfoot). When the apex points plantarward the talus is plantarflexed relative to the first metatarsal, indicating loss of the medial longitudinal arch. The angle does not tell you the cause; whether the foot is flexible or rigid, and the findings in the table, do.

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Pes cavus (cavovarus foot). When the apex points dorsalward the talus is dorsiflexed relative to the first metatarsal and the arch is excessively high. The aetiologies in the table share the radiograph and differ in what must be looked for clinically.

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Flatfoot and cavovarus are three-dimensional deformities, and the Meary angle describes one plane. It is read with the other sagittal angles on the same lateral film, with the transverse-plane angles on the weight-bearing AP film, with the hindfoot alignment view for the coronal plane, and with the clinical examination. It is never used in isolation.

Reading the lateral film. When shown a lateral foot radiograph, draw the Meary angle first, as the highest-yield measure, then the calcaneal pitch, and state the values and the interpretation out loud. Meary, calcaneal pitch and the Costa-Bartani angle are all read off the one weight-bearing lateral film, and together they are the sagittal-plane profile of the foot.

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The transverse plane. Meary is a sagittal measure; its companions are read on the weight-bearing AP (dorsoplantar) film:

• AP talonavicular coverage angle: the lateral uncoverage of the navicular on the talar head; increased (over about 7°) in planovalgus (forefoot abduction / peritalar subluxation), the radiographic correlate of the too-many-toes sign.
• AP talo-first-metatarsal angle (the AP Meary): the talar axis versus the first-metatarsal axis on the AP view; normal near 0°, with the forefoot abducted (talus medial to the first metatarsal) in planovalgus and adducted in cavovarus and metatarsus adductus.
• AP talocalcaneal (Kite) angle: the talar versus calcaneal axis on the AP view; normal about 15 to 30° (higher in young children); increased in planovalgus (the talar head adducts and plantarflexes, the bones diverge) and decreased or parallel in cavovarus and clubfoot (hindfoot varus).

The coronal plane. Inspect the heel from behind: in planovalgus it is in valgus, everted, with the too-many-toes sign; in cavovarus it is in varus, inverted, with the "peek-a-boo heel" sign.

The hindfoot alignment view. The radiograph is the hindfoot alignment view (the Saltzman & el-Khoury long-axial, or Cobey, view), a weight-bearing posteroanterior film angled about 20° that profiles the heel beneath the tibia. The hindfoot moment arm is the perpendicular distance from the long axis of the tibia to the lowest point of the calcaneus; lateral (valgus) is positive, medial (varus) is negative, and normal is small, a few millimetres.

It drives the choice of calcaneal osteotomy: a medialising osteotomy for hindfoot valgus in planovalgus, a lateralising or lateral closing-wedge osteotomy for hindfoot varus in cavovarus, complementing the sagittal correction the Meary angle quantifies.

The Meary angle directly informs operative planning for flatfoot and cavovarus reconstruction.

Flatfoot. The pattern and its flexibility choose the operation:

• Flexible flatfoot with a large plantar-apex Meary angle: medialising calcaneal osteotomy, flexor digitorum longus transfer and spring ligament repair; add a lateral column lengthening if the AP talonavicular coverage angle is also abnormal.
• Rigid flatfoot (tarsal coalition): if the angle does not correct on forced dorsiflexion or tiptoe views, resection of a calcaneonavicular coalition may restore flexibility; a large or degenerate talocalcaneal coalition may need subtalar or triple arthrodesis.
• Stage III–IV tibialis posterior dysfunction with degenerative change: triple arthrodesis regardless of flexibility, with the angle quantifying the correction achieved.

Cavovarus. Before any bone is cut, establish whether the hindfoot varus is flexible with the Coleman block test. Put the lateral border of the foot on a block so the first ray drops: if the heel comes out of varus the deformity is forefoot-driven, and if the heel stays inverted the hindfoot is rigid.

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The bony procedure then depends on flexibility and on whether degenerative change is present:

• Dorsal-apex deformity, flexible: a dorsiflexion (closing-wedge) osteotomy of the first metatarsal corrects the forefoot-driven hindfoot varus; a lateralising or closing-wedge calcaneal osteotomy addresses the hindfoot.
• Rigid cavovarus with degenerative change: triple arthrodesis correcting the Meary angle to neutral, restoring a plantigrade foot.
• Charcot-Marie-Tooth: tendon transfers (e.g. tibialis posterior to the lateral cuneiform, peroneus longus to brevis, Jones procedure for the great toe) supplement the bony correction; the Meary angle quantifies the bony correction needed.

• No single international guideline mandates the Meary angle as the sole criterion for surgery — it is one radiographic parameter used alongside clinical assessment and other angles (calcaneal pitch, talonavicular coverage, hindfoot moment arm).
• Global consensus recognises the Meary angle as a standard sagittal-plane measurement for pes planus and pes cavus; it features in foot-and-ankle textbook chapters and teaching curricula worldwide, with ~4° as the widely accepted abnormality threshold.
• AAOS (US), BOA/BOAST (UK), AO Foundation, EFORT and AOFAS educational materials include the lateral weight-bearing Meary angle in the standard set of foot radiographic parameters for flatfoot and cavovarus assessment and for pre-/post-operative comparison.
• Practice variation exists in whether surgeons routinely report the Meary angle versus relying on calcaneal pitch alone; fellowship-trained foot-and-ankle surgeons more commonly report multiple sagittal parameters.
• No joint registry tracks the Meary angle as an outcome measure (unlike alignment parameters in knee arthroplasty); it is used in research and surgeon databases for pre- and post-operative comparison.