Metatarsus Adductus

Original Editor - Shaniel Walters Top Contributors - Nupur Smit Shah, Lauren Heydenrych, Shaniel Walters, Kim Jackson and Naomi O'Reilly

Introduction

Metatarsus adductus (MA), also known as metatarsus varus, is a deformity occurring only in the transverse plane of the foot. It is an adduction deformity or medial deviation of the forefoot at the tarsometatarsal joints (Lisfranc joint) with respect to the hindfoot. . This occurs in association with soft tissue contractures. A convex lateral border of the foot and prominent styloid process. is observedThe foot therefore is observed as 'C' shape.

MA may also be known as metatarsus varus, metatarsus adductovarus, pes adductus, metatarsus supinatus, forefoot adductus and hooked forefoot.

Clinical Presentation

MA presents at birth with adduction of the metatarsals at the Lisfranc joint. The forefoot is medially deviated to the hindfoot, and thus appears as a concavity along the medial border of the foot and convexity on the lateral aspect. There is no deformity along the frontal or sagittal planes. The base of the 5th metatarsal appears prominent with no dorsolateral bump present (more indicative of skewfoot).

Radiologically the first metatarsal is medially deviated with an increased angle between the 1st and 2nd metatarsal.

Differential diagnosis

• Skewfoot
• Talipes equinovarus (clubfoot)

Clinically Relevant Anatomy

See: Basic Structure of the Foot and Ankle

Forefoot is comprised of: Tarsometatarsal Joints, Intermaetatarsal Joint, Metatarsophalangeal Joints and Interphalangeal Joints.

Hindfoot is comprised of : Tibiofibular joint , Talocular joint and the Subtalar (Talocalcanean) joint.

Midfoot (Midtarsal Joints) is comprised of: Talocalcaneonavicular Joint, Cuneonavicular Joint, Cuboideonavicular Joint, Intercuneuform Joints, Cuneocuboid joint and the Calcaneocuboid Joint.

Metatarsals

• These are the 5 long bones found in the foot.
• The metatarsals and tarsal bones help form the main arches of the foot - essential for weight-bearing and ambulation.

Lisfranc joint

The Lisfranc joints are tarsometatarsal articulations. Most of the joint is the articulation between the:

The orange bar in this image highlights the articular region of the tarsometatarsal joints

1. Medical surface of the 2nd metatarsal base
2. Lateral surface of the medial cuniform.

• The Lisfranc ligament spans this joint and is crucial for stability of the entire tarsometatarsal joint.
• Musculotendinous structures around the joint provide indirect stability to the joint.

It is caused by in-utero position and constriction of the fetus.It is also called as pigeon toes.

The child having this deformity walks with an in-toe gait during early infancy.

In many cases it is self-limiting too.

Types

Metatarsus Adductus can be divided into either flexible or rigid:

1. Flexible: Presents with adduction of the 5 metatarsal bones at the tarsometatarsal joint.
2. Rigid: Presents with medial subluxation of the tarsometatarsal joints. There is valgus of the hindfoot and the navicular is later to the head of the talus.

Classification and Diagnostic procedure

The most common classification of MA is by the Bleck manual assessment or 'heel bisector method'. This system comments on both the severity (mild, moderate or severe) and the reducibility/ flexibility (fully flexible, partially flexible or severe).

Heel bisector line (HBL)

The HBL was introduced by Bleck in 1983.

This is a simple measure that assesses the flexibility and severity of the metatarsus adductus. It is a manual assessment and no types of equipment is needed.

Procedure:

1. Making a mould of the weight-bearing foot so as to obtain an elipse at the heel. Today, modifications include the use of footprints or photocopying the weight-bearing foot.
2. A longitudinal line (the longitudinal axis) is then drawn from the elipse independent of the forefoot using a straight edge e.g. a ruler.

The norm for HBL would be passing through the 2nd interdigital web space (IWS).

Advantages of HBL

• Method that requires minimal time for both clinician and patient
• Cost effective

Disadvantages HBL

• Drawbacks to this classification is that it has no prognostic value.
• There has been little research into the measurement properties of the tool.
• A recent paper in the International Journal of Foot and Ankle (2020) highlights the geometrical inaccuracy of the HBL and proposes the Transmalleolar axis bisctor (TMAB).

Transmalleolar Axis Bisector procedure:

1. Patient in prone, knee in 90° flexion.
2. Assesesor maintains plantigrade at the ankle joint (thereby approximating the weight bearing posture).
3. With a pair of Vernier callipers, a line (AB) is drawn on the heel. A being the medial malleolus and B being the lateral malleolus.
4. The midpoint is marked on this line - C.
5. Using a goniometer: Axis on point C, the stationary arm aligned with AB and the movable arm 90° to the stationary arm.
6. The assessor checks the point at which the line made by the movable arm crosses the metatarsal heads. Records as follows:

• 2nd interdidital web space(2nd IWS)
• 3rddigit (3rd D)
• 3rd interdigital web space (3rd IWS) etc.

In this procedure no normative values have been established.

Other assessment methods

To grade severity:

• Multiple radigraphic angles - There is a disadvantage in this technique as it does not comment on the ridged vs flexible aspect of the MA. Furthermore, in the paediatric population, the lack of tarsal bone ossification makes angle measurements difficult. The studies with the highest rate of reliability are usually performed after the age of 5.
• Photocopies of the child's foot
• V- finger test
• Ultrasound - This assessment allows for the imaging of cartilaginous structures. allows for differentiation between MA and skewfoot. In MA the medial cuniform is displaced laterally over the navicular.

Epidemiology

MA is cited as being the most common congenital foot deformity in newborns. In a 2019 article by Rampal and Giuliano, it was stated as occurring in 0.2% of births.In an article published in June 2022, MA prevalence was cited as an estimated 1/1000 births.

Etiology

Metatarsus adductus is a foot deformity. Deformities are congenital pathologies that often occur during the fetal period to certain structures - in this case the foot - which has developed normally. This is in contrast to malformations, which occur during the embryonic period of development, causing anatomical defects.

The cause of metatarsus adductus remains unknown. It is however, thought to be related to intrauterine compression, osseous abnormality and abnormal muscle attachments - including abnormal tendon insertion of tibialis anterior, tibialis posterior and abductor hallucis muscles. Family history may also be a causative factor .

Management / Interventions

Self correction of MA only occurs in moderate forms. If it does not resolve in the first weeks of life, non-operative treatments are initiated. These include:

• Casting
• Curved hypercorrection pads
• Orthotics
• Strapping

With these treatments, the goal is to correct the deformity before ambulation is started.

Operative treatment is undertaken if conservative treatment fails or the child is > 4 years old at time of diagnosis.

Cahuzac procedure: Opening the cuneometatarsal joint capsule at the 1st ray and abduction oseotomy of metatarsals 2, 3 and 4.

Preferred technique: Opening-wedge osteotomy at the base of metatarsals 2 - 5.

A note on procedures noted in Rampal & Giuliano (2019) pg. s116 para 8 . : "Osteotomies performed on the 1st cuniform can impact the hind-foot (elevation of foot’s medial arch, without lengthening of medial column due to excessively tight plantar fascia"

This condition mostly doesn't require any form of treatment and resolves on its own. The conditions like cerebral palsy, spina bifida, Slipped capital femoral epiphysis, congenital displacement of the hip, and metabolic disorders like rickets, osteogenesis imperfecta needs to be ruled out.

Specific treatment for metatarsus adductus is often determined by the following factors:

• Child's Age
• Medical History
• The extent of the condition
• Tolerance for the specific procedure

• Expectations for the condition

Interventions include:

• Passive Stretching
• Passive Manipulation exercises
• Stretching
• Serial Casting
• Footwear
• Surgery to release the joints
  

Helpful resources

Webpage: https://www.orthobullets.com/pediatrics/4061/metatarsus-adductus