Introduction

Metatarsus adductus (MTA) is a condition in which an individual presents with congenital intoeing of the foot, commonly seen in infants. It can affect either one foot or both. It involves the medial deviation of the forefoot at the tarsometatarsal joint, while the hind foot remains in its natural position.¹ It can either be flexible or rigid. The prevalence of this condition is approximately one to two cases per one thousand live births, making it very common among infants. 

In the majority of cases - around 95% - the deformity improves spontaneously without the need for treatment as the foot grows.² For instance, stretching exercises can help. 

Although natural correction may not require medical intervention, it is still important to follow recommended guidance to ensure the deformity resolves. In about, 4-5% of cases, spontaneous improvement does not occur. This can affect them as they get older. For example, they may not be able to carry out functions that others their age can due to abnormal gait patterns, and they may have difficulty in wearing a range of different footwear.³ 

Therefore, early identification is essential, so that the required treatment can be carried out before detecting whether the foot presents with a flexible or rigid form of MTA. Thereby, appropriate management can be provided.

Anatomy and pathophysiology

When the foot develops in the uterus, it undergoes a complex process of formation. This process involves the bones, joints and soft tissues to be formed and differentiated from one another while growing so that they can work together to function properly once the structure is complete.⁴ During embryological development, it is natural for the foot to rotate into the correct orientation by the final stage. However, if there is a disturbance during this process, deformities can occur and lead to congenital conditions. 

MTA presents characteristics which typically show the forefoot at the tarsometatarsal joint is affected, while the hind foot remains in the natural or valgus position.⁵ 

The primary cause of this condition during embryonic developement is not fully understood, however a few contributing factors have been identified, such as intrauterine positioning (the baby’s position inside the uterus). This position is also known as ‘packaging disorder’. This is when the area of the womb restricts movement and lets mechanical forces to act on the growing foot.⁶

Other factors that can contribute to the development of this deformity can include family predispositions such as genetic influences.  

Epidemiology and risk factors

MTA is estimated to affect one to two individuals per one thousand live births. It is more common in firstborn children, likely due to the mother having a smaller uterus. Other risk factors may include breech presentation and oligohydramnios (a low amount of amniotic fluid). They can cause mobility to be limited, which can contribute to the development of the deformity.⁷  

Investigating family history, can ensure that the family is aware that the newborn has a higher risk of being born with this deformity. That way, appropriate treatments and management can be carried out in advance. 

Furthermore, MTA has been found to be associated with other musculoskeletal conditions, such as developmental dysplasia of the hip and clubfoot. This emphasises the importance of carrying out neonatal screening.⁸ Early screening allows clinicians to investigate further in case of any additional abnormalities that they may be present alongside MTA.

Early identification also allows a better understanding of potential risk factors the individual may have and allows further analysis to decide the most appropriate treatment. For instance, differentiating the MTA as either flexible or rigid is important as they have different characteristics, therefore, require different interventions.

Clinical examination 

Clinical examinations are the most useful practices in helping to differentiate the abnormality as flexible or rigid. Therefore, an accurate diagnosis can be made via thorough assessments. This includes investigating family history, breech delivery, restricted intrauterine environment, or oligohydramnios.⁹  Hereditary factors may predispose an individual to congenital foot conditions. Other associated conditions that are important to look out for include hip dysplasia or clubfoot, which may coexist with MTA.

Furthermore, individuals may present with a C-shaped lateral border due to medial deviation of the forefoot, which is typically only found in milder cases where the deformity is not that visible. However, in severe deformities, it is more recognisable.¹⁰ 

Further examination includes palpation and manipulation techniques such as the heel bisector line method. This is a method where an imaginary line is drawn through the heel to allow a physical examination where the severity of the deformity can be determined.¹¹  

Flexible MTA can be corrected with minimal or no resistance via stretching exercises. Whereas, rigid MTA cannot be corrected completely and is less responsive to conservative treatment. It can worsen into later childhood and may require interventions such as serial casting or, in severe cases, surgery.¹²

Imaging and diagnostic adjuncts 

Image scanning is useful to visually assess the deformity and its severity however, it is not the primary diagnostic too. This is because the condition is mostly assessed through clinical examinations, which tend to be more reliable and accurate.¹³ However, in certain cases, especially with individuals who present with flexible MTA, it is not necessary to have image scanning to obtain the diagnosis as the condition at this stage is mild and can be corrected and fixed via physical manipulation.¹⁴ These examinations are vital in proper diagnosis properly, as the information collected can help with the management and treatment of cases.  

One example of image scanning is radiography. It can help with diagnosing the condition when rigidity of the foot is suspected.¹³ Other scans may include X-rays, which allow the assessment of joints, such as the tarsometatarsal joint. By examining the direction of the bone structure and joint, the severity of deformities can be assessed. However, this method is not useful in infants as the bones in their foot are not fully developed. Therefore, ultrasound is an alternative method which allows doctors to see the softer cartilage and to understand the alignment of the foot.¹⁵ More advanced imaging techniques, for instance, computed tomography (CT) or magnetic resonance imaging (MRI) are rarely used. They are typically used in more complex cases and are required during the investigation of anatomical information. By using this technique, surgical planning can be conducted by differentiating the structure and position of the deformity.¹⁶ 

Importance of early identification 

Early diagnosis is essential for MTA diagnosis to prevent further complications from arising as the child grows up. Strain can worsen the condition therefore, it is important to carry out correct management techniques after accurate diagnosis. It is also important to differentiate between flexible and rigid forms of MTA. For instance, gentle stretching exercises are effective for flexible cases, which are the most common. This also prevents unnecessary treatment from being  offered due to flexible cases improving naturally.¹⁷ 

Conversely, rigid cases are far less likely to self-correct and frequently persist if left untreated. Early detection can help with preventing progression of the deformity which causes gait abnormalities, difficulties with shoe wear, and, in some cases, long-term pain or functional impairment. If diagnosed late, opportunities for initiating preventative methods of progression such as structured stretching programmes, physiotherapy, or serial casting, may be missed.¹⁸ Early diagnosis can help with improving clinical outcomes and reduces the likelihood of costly surgical interventions and the long-term burden of disability. It can also help the parents by reducing anxiety about their child’s condition.

Management strategies based on identification

The management of this condition depends on whether it is benign or not. Whether MTA presents as flexible, semi-rigid, or rigid, accurate early identification is crucial for timely treatment planning. Most treatments are usually successful when diagnosed earlier, and multidisclipinary approaches can help. For instance, paediatricians, physiotherapists, and orthopaedic surgeons can all play a vital role in treatment.¹⁹ 

Challenges and future directions 

Research for MTA management has been sought however, several challenges remain, especially when it comes to early diagnosis. One major factor includes the lack of consistency in clinical examinations, which can lead to misdiagnosis. Although emerging technologies may offer solutions to these challenges, and artificial intelligence–based diagnostic tools are promising as they can reduce inter-clinician variability.¹ 

Conclusion 

Metatarsus adductus is common foot deformity amongst infants, caused by the limited space in the womb. It can either present as flexible or rigid, which determines the treatment and management of the condition. While flexible MTA can self-improve through simple and gentle exercises, rigid MTA cannot be improved. Therefore, early diagnosis helps prevent rigid MTA from worsening and affecting an individual's daily life.¹ 

Clinical examinations are the most effective treatment method for diagnosis. Image scanning can help with the diagnosis by supporting consistent, evidence-based care for all affected children.