Bone and Muscle Defects
Birth defects can occur in any bone or muscle, although the bones and muscles of the skull, face, spine, hips, legs, and feet are affected most often. Bones and muscles may develop incompletely. Also, structures that normally align together may be separated or misaligned. Usually bone and muscle defects result in abnormal appearance and function of the affected part of the body. Most of these defects are repaired surgically if symptoms are troublesome. Often, the surgery is complex and involves reconstructing deformed or absent body parts.
Facial Defects
The most common defects of the skull and face are cleft lip and cleft palate. Cleft lip is a separation of the upper lip, usually just below the nose. Cleft palate is a split in the roof of the mouth resulting in a passageway into the nose. Cleft lip and cleft palate often occur together.
 See the figure Cleft Lip and Cleft Palate: Defects of the Face.
Cleft lip is disfiguring and prevents the infant from closing his lips around a nipple. A cleft palate interferes with eating and speech. A dental device can temporarily seal the roof of the mouth so the infant can suckle better. Cleft lip and cleft palate can be permanently corrected with surgery. The likelihood of cleft lip and cleft palate can be reduced if a woman takes folic acid before pregnancy and through the 1st trimester of pregnancy.
Another type of facial defect is a small lower jaw (mandible). Pierre Robin and Treacher Collins syndromes, which are characterized by several defects in the head and face, are among the causes of a small lower jaw. If the lower jaw is too small, the infant may have difficulty eating or breathing. Surgery may correct or diminish the problem.
Limb and Joint Defects
Limbs or joints can be missing, deformed, or incompletely developed at birth. A child with one limb or joint abnormality is more likely to have another related abnormality. Limbs and joints may form abnormally; for example, bones in the hand and forearm may be missing because of a genetic defect. Normal development of a limb can also become disrupted in the womb; for example, a finger can stop growing because the finger gets constricted by fibers. Another cause for limb and joint abnormalities is mechanical force; for example, pressure may cause the hip to dislocate. Chromosomal abnormalities can cause limb and joint abnormalities. Sometimes the cause is unknown. The drug thalidomide, which was taken by some pregnant women in the late 1950s and early 1960s for morning sickness, caused a variety of limb defects--usually short, poorly functioning appendages developed in place of arms and legs.
Abnormalities of the arms and legs may occur in a horizontal fashion (for example, if the arm is shorter than normal) or in a lengthwise fashion (for example, the arm is abnormal on the thumb side [from the elbow to the thumb] but normal on the little finger side). Children often become very adept at using a malformed limb, and an artificial limb (prosthesis) can often be constructed to make the limb easier to use.
Hand defects are common. Sometimes a hand does not form completely; part or all of the hand may be missing. For example, the person may have too few fingers. Sometimes a hand does not develop; for example, the fingers may not separate, producing a weblike hand. Some hand defects involve extra fingers; the little fingers or thumbs are most commonly duplicated. Overgrowth may occur, in which the hands or individual fingers are too large. Surgery is usually carried out to correct the hand defect and provide as much function as possible.
In congenital dislocation of the hip, also called developmental dysplasia of the hip, the newborn's hip socket and the thighbone (femoral head), which normally form a joint, become separated, often because the hip has a socket that is not deep enough to hold the head of the femur. Dislocation of the hip is a disorder more common in girls, in newborns born in a breech (buttocks-first) position, and in newborns who have close relatives with the disorder. The right and left legs or hips often look different from each other in newborns with the defect.
The doctor can detect the defect when examining the newborn. In infants younger than 4 months, an ultrasound of the hips can confirm the diagnosis; in infants older than 4 months, an x-ray can be used. The use of triple diapers (an older treatment) is not recommended. The best treatment is use of the Pavlik harness. The Pavlik harness is a soft brace that holds the infant's knees spread outward and up toward the chest. However, if the defect persists past the age of 6 months, surgery to fix the hip in the normal position is usually needed.
Clubfoot (talipes equinovarus) is a defect in which the foot and ankle are twisted out of shape or position. The usual clubfoot is a down and inward turning of the hind foot and ankle, with twisting inward of the forefoot. Sometimes the foot only appears abnormal because it was held in an unusual position in the uterus (positional clubfoot). In contrast, true clubfoot is a structurally abnormal foot. With true clubfoot, the bones of the leg or foot or the muscles of the calf are often underdeveloped.
 See the figure Common Types of Clubfoot.
Positional clubfoot can be corrected by immobilizing the joints in a cast and by using physical therapy to stretch the foot and ankle. Early treatment with immobilization is beneficial for true clubfoot, but surgery, often complex, is also generally needed.
In metatarsus adductus, the foot appears turned inward. Mobility of the joints of the foot and ankle may be limited. Treatment depends on the severity of the deformity and immobility of the foot. Most mild cases resolve spontaneously. Corrective shoes or splints may be needed in more severe cases. Surgery is required only in exceptional instances.
In arthrogryposis multiplex congenita, some joints become "frozen" and consequently cannot bend. Many children with this defect have weakened muscles. It is likely that decreased movement of the muscles and joints before birth causes the decreased movement of the joints after birth. The cause is unknown. Sometimes the nerves that would normally move the bones in the affected joints are also impaired. Infants with the defect may also have dislocated hips, knees, or elbows. Placing the limbs in a cast and performing physical therapy, in which the stiff joints are carefully manipulated, may improve joint movements. Surgically freeing the bones from attached tissue sometimes results in more normal joint movement.
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