Arthrogryposis or arthrogryposis multiplex congenita (AMC) is a generic term used in connection with a very heterogeneous group of disorders with a common feature which includes multiple congenital joint contractures. The word arthrogryposis (arthro-joint, gryp-curved), literally means curved joint (implying that it is fixed or stuck in the curved position).
The etiology is variable and not entirely understood but it is presumed to be multi-factorial. In most cases, arthrogryposis multiplex congenita is not a genetic condition. However, in approximately 30% of cases, a genetic cause can be identified.
The major cause of arthrogryposis is fetal akinesia which can be due to fetal or maternal conditions.
Fetal causes of arthrogryposis:
They may include malformations or malfunctions of the central and peripheral nervous systems. Abnormalities include meningomyelocele, anencephaly, hydranencephaly, holoprosencephaly, spinal muscular atrophy, cerebrooculofacial-skeletal syndrome, and Marden-Walker syndrome
Muscular malformations or malfunctions
These are relatively rare causes of arthrogryposis. Some associated diseases include congenital muscular dystrophies, congenital myopathies, intrauterine myositis, and mitochondrial disorders.
Examples include synostosis, lack of joint development, aberrant fixation of joints (diastrophic dysplasia and metatropic dwarfism), aberrant laxity of joints with dislocations (Larsen syndrome), and aberrant soft tissue fixations (popliteal pterygium syndrome).
Mechanical limitations to movement
Oligohydramnios or chronic amniotic fluid leakage, multiple pregnancies, uterine abnormalities such as bicornuate uterus with a septum or uterine fibroid may cause fetal constraint and secondary contractures.
Maternal causes of arthrogryposis:
- Infections: rubella, rubeola, coxsackievirus, enterovirus, Akabane
- Fever more than 39° Celsius
- Teratogens: drugs, alcohol, curare, methocarbamol, and phenytoin,
- Neuromuscular diseases such as myotonic dystrophy, myasthenia gravis, or multiple sclerosis.
Generalized fetal akinesia can also lead to polyhydramnios, pulmonary hypoplasia, micrognathia, ocular hypertelorism, and short umbilical cord.
During early embryogenesis, joint development is almost always normal. Motion is essential for the normal development of joints and their contiguous structures. Lack of fetal movement causes development of the extra connective tissue around the joint. This results in fixation of the joint, limited range of motion and development of the joint contractures.
Prenatal ultrasound diagnosis is usually based on the detection of abnormal limb position, restrictive fetal movement with reduced or absent response to acoustic stimulation, growth restriction, polyhydramnios, and pulmonary hypoplasia. Low-set malformed ears, hypertelorism, short neck, cleft palate, scalp edema, thoracic deformities, camptodactyly, and micrognathia may also be found. There are also reports of early diagnosis of arthrogryposis in the first and early second trimester by detection of subcutaneous oedema.