Metatarsus adductus (MA) is a congenital foot deformity that is characterized by the inward deviation or adduction of the forefoot in relation to the hindfoot. This condition is the most common congenital foot deformity seen in newborns, with an incidence rate of 1 to 2 cases per 1,000 live births. MA can often be distinguished from other foot deformities by its specific pattern, involving the forefoot only, while the hindfoot remains in a normal position. The deformity presents with a convex lateral border of the foot and inward slanting of the forefoot, which is typically visible at birth.
Understanding Metatarsus Adductus
The primary cause of metatarsus adductus has been debated, but it is generally believed to be associated with increased intrauterine pressure. The foot may be compressed in the womb, leading to an abnormal position of the forefoot. In some cases, this pressure might cause the foot to become deformed as the fetus grows. Other possible causes include osseous abnormalities or abnormal muscle attachments, but these factors are still unclear. It is important to differentiate MA from other conditions, such as talipes equinovarus and skewfoot, both of which also involve the hindfoot.
Classifying Metatarsus Adductus
Metatarsus adductus is typically classified based on the flexibility of the foot. The three main classifications are:
- Flexible MA: The forefoot can be corrected to the midline by manual manipulation.
- Semi-flexible MA: The forefoot can be partially corrected but not completely realigned with the hindfoot.
- Rigid MA: The deformity cannot be corrected by manual manipulation.
This classification helps clinicians determine the appropriate treatment options, which vary based on the severity and flexibility of the condition. Additionally, the severity of the deformity can be assessed using radiographic evaluations, where angles like the Metatarsus Adductus Angle (MAA) are measured to determine the degree of the deformity.
Treatment Options for Metatarsus Adductus
Conservative Treatment The majority of cases of metatarsus adductus, particularly flexible MA, resolve spontaneously over time. Therefore, conservative treatment is often recommended. For flexible MA, the most common approach is to do nothing and allow the condition to self-correct. This method has a strong evidence base, with studies indicating that 95% of children with flexible MA will experience natural resolution by the age of 16. However, it is essential to monitor the child’s progress and reassure parents about the benign nature of the condition.
For semi-flexible cases, parents may be instructed to perform stretching exercises, manually abducting the forefoot while maintaining the neutral position of the hindfoot. This approach can help encourage proper foot alignment. Additionally, adjustments in sitting and sleeping positions to avoid prolonged adduction of the foot can also be beneficial.
Footwear modifications, such as straight last shoes, may be recommended to help realign the forefoot with the hindfoot. These shoes provide support to maintain proper foot positioning and prevent further complications. In cases where the child is older, serial casting might be considered, though this treatment is generally reserved for infants over the age of 8 months with semi-flexible MA.
Surgical Treatment In rare cases where conservative methods do not resolve the deformity or if the child experiences significant functional impairments, surgical intervention may be necessary. Surgery typically involves the release of tight soft tissues or the use of osteotomies to correct the bony deformities. However, surgery is generally avoided in cases where the deformity is flexible or semi-flexible, as non-surgical methods tend to be sufficient.
Associated Complications
Although many cases of metatarsus adductus self-correct, some individuals may develop long-term complications if the condition is left untreated or if the deformity is severe. A common issue associated with MA is hallux valgus (HV), a condition in which the big toe deviates outward. Studies have shown that individuals with MA are at an increased risk of developing HV, as the adduction of the forefoot may lead to abnormal pressure on the big toe. In severe cases, HV can cause significant discomfort and require surgical intervention.
Metatarsalgia, or pain in the ball of the foot, is another common complication of MA, particularly in older children or adults who have persistent deformities. The misalignment of the metatarsals can lead to abnormal weight distribution during walking, causing pain in the forefoot and leading to calluses and corns. Lesser toe deformities, such as hammertoes, may also develop as a result of the altered foot position.
Conclusion
Metatarsus adductus is a common congenital foot deformity that, in many cases, resolves naturally without the need for intervention. However, when treatment is necessary, a conservative approach involving stretching, footwear modifications, and careful monitoring is typically sufficient for flexible and semi-flexible cases. Severe or rigid deformities may require more intensive treatments, such as serial casting or even surgery, particularly when associated with hallux valgus or metatarsalgia. It is important for clinicians to assess each case individually, considering the degree of deformity and the child’s age, and to guide parents through the various treatment options available. The long-term prognosis for most children with MA is positive, with many experiencing full resolution of the deformity as they grow.
