Amyoplasia is a condition characterized by a generalized lack in the newborn of muscular development and growth, with

contracture In pathology, a contracture is a permanent shortening of a muscle or joint. It is usually in response to prolonged hypertonic spasticity in a concentrated muscle area, such as is seen in the tightest muscles of people with conditions like spasti ...

and deformity at most joints. It is the most common form of

arthrogryposis Arthrogryposis (AMC) describes congenital joint contracture in two or more areas of the body. It derives its name from Greek, literally meaning "curving of joints" (', "joint"; ', late Latin form of late Greek ', "hooking"). Children born with one ...

. It is characterized by the four limbs being involved, and by the replacement of

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

by dense fibrous and adipose tissue. Studies involving amyoplasia have revealed similar findings of the muscle tissue due to various causes including that seen in

sacral agenesis Sacral may refer to: *Sacred Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual respect or devotion; or inspires awe or reverence among believers. The property ...

and

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

. So amyoplasia may also include an intermediate common pathway, rather than the primary cause of the contractors.

Signs and symptoms

Amyoplasia results when a fetus is unable to move sufficiently in the womb. Mothers of children with the disorder often report that their baby was abnormally still during the pregnancy. The lack of movement in utero (also known as fetal akinesia) allows extra connective tissue to form around the joints and, therefore, the joints become fixed. This extra

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

replaces muscle tissue, leading to weakness and giving a wasting appearance to the muscles. Additionally, due to the lack of fetal movement, the tendons that connect the muscles to bone are not able to stretch to their normal length and this contributes to the lack of joint mobility as well.

Causes

There is no single factor that is consistently found in the prenatal history of individuals affected with amyoplasia and, in some cases, there is no known cause of the disorder. Amyoplasia is a sporadic condition that occurs due to lack of

fetal movement Fetal movement refers to motion of a fetus caused by its own muscle activity. Locomotor activity begins during the late embryological stage and changes in nature throughout development. Muscles begin to move as soon as they are innervated. These fi ...

in the womb. There is no specific gene that is known to cause the disorder. It is thought to be multifactorial, meaning that numerous genes and

environmental factor An environmental factor, ecological factor or eco factor is any factor, abiotic or biotic, that influences living organisms. Abiotic factors include ambient temperature, amount of sunlight, and pH of the water soil in which an organism lives. Bi ...

s play a role in its development. The recurrence risk is minimal for siblings or children of affected individuals. There have been no reports of recurrent cases of amyoplasia in a family. The fetal

akinesia Hypokinesia is one of the classifications of movement disorders, and refers to decreased bodily movement. Hypokinesia is characterized by a partial or complete loss of muscle movement due to a disruption in the basal ganglia. Hypokinesia is a sym ...

in amyoplasia is thought to be caused by various maternal and fetal abnormalities. In some cases, the mother's

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

does not allow for adequate fetal movement because of a lack of

amniotic fluid The amniotic fluid is the protective liquid contained by the amniotic sac of a gravid amniote. This fluid serves as a cushion for the growing fetus, but also serves to facilitate the exchange of nutrients, water, and biochemical products betwee ...

, known as

oligohydramnios Oligohydramnios is a medical condition in pregnancy characterized by a deficiency of amniotic fluid, the fluid that surrounds the fetus in the abdomen, in the amniotic sac. It is typically diagnosed by ultrasound when the amniotic fluid index (A ...

, or an abnormal shape to the uterus, called a

bicornuate uterus A bicornuate uterus or bicornate uterus (from the Latin ''cornū'', meaning "horn"), is a type of mullerian anomaly in the human uterus, where there is a deep indentation at the fundus (top) of the uterus. Pathophysiology A bicornuate uterus ...

. There may also be a

myogenic The myogenic mechanism is how arteries and arterioles react to an increase or decrease of blood pressure to keep the blood flow constant within the blood vessel. Myogenic response refers to a contraction initiated by the myocyte itself instead of ...

cause to the fetal akinesia, meaning that fetal muscles do not develop properly due to a muscle disease (for example, a congenital

muscular dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...

). Similarly, connective tissue tendon and skeletal defects may contribute to the fetal akinesia and be the primary cause of amyoplasia. Additionally, malformations may occur in the central nervous system and/or spinal cord that can lead to a lack of fetal movement in utero. This

neurogenic In Biology, biology, the nervous system is the Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals to and from different parts of its ...

cause is often accompanied by a wide range of other conditions. Other causes of fetal akinesia may include a maternal fever during pregnancy or a virus.

Diagnosis

It is the most common form of arthrogryposis multiplex congenita (AMC), where multiple joint contractures are present at birth. Arthrogryposis is derived from the Greek word meaning "with crooking of joints." It occurs in about one out of every 3,000 live births. There are more than 150 types of AMC. Amyoplasia accounts for 40% of AMC cases.

Characteristic appearance

Children with amyoplasia often suffer from internally rotated shoulders, extended elbows, ulnar flexed wrists. The type of displacement of the hips and knees is more variable, and they often have

club feet Club may refer to: Arts, entertainment, and media * Club (magazine), ''Club'' (magazine) * Club, a ''Yie Ar Kung-Fu'' character * Clubs (suit), a suit of playing cards * Club music * "Club", by Kelsea Ballerini from the album ''kelsea'' Brands a ...

. About 10% of children with amyoplasia have evidence of vascular compromise including Intestinal atresia,

abdominal wall defect Abdominal wall defects are a type of congenital defect that allows the stomach, the intestines, or other organs to protrude through an unusual opening that forms on the abdomen. During the development of the fetus, many unexpected changes occur i ...

s, and

gastroschisis Gastroschisis is a birth defect in which the baby's intestines extend outside of the abdomen through a hole next to the belly button. The size of the hole is variable, and other organs including the stomach and liver may also occur outside the ba ...

Treatment

Surgery may be necessary to address the congenital deformities frequently occurring in conjunction with arthrogryposis. Surgery on feet, knees, hips, elbows and wrists may also be useful if more range of motion is needed after therapy has achieved maximum results. In some cases,

tendon transfer A tendon transfer is a surgical process in which the insertion of a tendon is moved, but the origin remains in the same location. Tendon transfer involves redistribution of muscle power, not recreation. Tendons are transferred at the distal attac ...

s can improve function. Congenital deformities of the feet, hips and spine may require surgical correction at or about one year of age.

Prognosis

Overall prognosis for children with amyoplasia is good. Intensive therapies throughout developing years include

physical therapy Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patient ...

occupational therapy Occupational therapy (OT) is a global healthcare profession. It involves the use of assessment and intervention to develop, recover, or maintain the meaningful activities, or ''occupations'', of individuals, groups, or communities. The field of ...

and multiple orthopedic procedures. Most children require therapy for years, but almost 2/3 are eventually able to walk, with or without braces, and attend school.

References

{{reflist Arthrogryposis Congenital disorders