Arthrogryposis multiplex congenita (AMC) is a condition present at birth in which two or more joints are permanently bent or locked in fixed positions, called contractures. It affects roughly 1 in 3,000 live births. AMC is not a single disease but rather a description of a physical finding that can result from many different underlying causes, all of which share one thing in common: reduced fetal movement during pregnancy.
Why Fetal Movement Matters
Joints need movement to develop normally. When a fetus doesn’t move enough in the womb, the connective tissue around the joints thickens and tightens, locking them into fixed positions. The earlier in pregnancy movement stops and the longer it stays reduced, the more severe the contractures tend to be.
Many different factors can restrict fetal movement. Some are structural, like a uterus with an unusual shape, very low amniotic fluid, or carrying multiples where there simply isn’t enough room. Maternal illnesses, including certain autoimmune conditions like myasthenia gravis and multiple sclerosis, can also play a role. Infections during pregnancy (rubella, Zika, Coxsackievirus), drug exposure, and physical trauma have all been linked to AMC. Neurological and muscular problems in the developing fetus are among the most common causes, though connective tissue disorders and limited uterine space account for many cases as well.
Genetics can be involved. More than 350 gene variants have been identified across different forms of arthrogryposis, with inheritance patterns that include autosomal dominant, autosomal recessive, and X-linked. Chromosomal abnormalities account for some cases too. But in many children, no genetic cause is found, and the condition appears to result from environmental or mechanical factors alone.
The Three Main Forms
Clinicians generally recognize three broad categories of AMC, each with different characteristics and implications.
Amyoplasia is the most common and most recognizable form. It involves a significant absence of muscle tissue from birth, likely caused by disrupted blood supply to the developing limbs rather than a heritable gene mutation. Children with amyoplasia typically have internally rotated shoulders, extended elbows, flexed wrists, and stiff fingers, along with clubfeet. Because it is not genetic in origin, it does not typically run in families.
Distal arthrogryposis primarily affects the hands and feet rather than the larger joints. Unlike amyoplasia, it has a clear genetic component and can be passed from parent to child. There are multiple subtypes, each linked to specific gene mutations affecting muscle proteins.
Syndromic arthrogryposis describes cases where joint contractures appear alongside a broader syndrome or neuromuscular disease. In these situations, arthrogryposis is one feature among many, and the underlying condition drives the overall prognosis.
How AMC Is Detected
AMC can sometimes be identified before birth through ultrasound. Characteristic findings include abnormal bending of both large and small joints, along with decreased or absent movement in the affected limbs. In the first trimester, increased fluid at the back of the neck (nuchal translucency) or fluid-filled sacs called cystic hygromas may raise suspicion. Three-dimensional ultrasound can provide more detailed views of affected limbs, and fetal MRI may be recommended if brain abnormalities are suspected.
When arthrogryposis is detected prenatally, genetic testing through amniocentesis or chorionic villus sampling is typically offered. A chromosomal microarray can identify deletions or duplications, but it won’t catch single-gene disorders. For that, gene panel testing or exome sequencing is more useful. Genetic variants, duplications, deletions, or chromosomal abnormalities are found in roughly 30% of arthrogryposis cases, meaning the majority remain without a clear genetic explanation. Testing for spinal muscular atrophy and congenital myotonic dystrophy is often considered, since these are treatable conditions that can present with joint contractures.
After birth, diagnosis is primarily clinical. A physician examines the pattern and severity of joint involvement, assesses muscle bulk, and evaluates neurological function to narrow down the underlying cause.
Treatment Starts Early
Therapeutic intervention should begin as soon as possible after birth, once the baby is medically stable. Connective tissue is most pliable in the newborn period, and early stretching offers the best window for improving joint position before the tissues become more resistant.
Physical and occupational therapy form the foundation of AMC management. Early goals include increasing the range of motion in all affected joints through gentle, careful stretching, encouraging any active muscle movement (even small amounts of antigravity strength), and correcting fixed positions that would interfere with daily activities like feeding. Therapists use developmental positions to build strength naturally. Placing an infant on their stomach, for example, promotes head control while simultaneously encouraging elbow bending for hand-to-mouth activities. Techniques like taping, sensory stimulation, and guided movement help activate the wrists and fingers.
Custom-molded splints, casts, and taping provide sustained or dynamic stretch to muscles and joints between therapy sessions. Nighttime splints are often necessary to maintain gains made during the day. For clubfeet, conservative management with casting should start as early as possible to prepare for standing and walking. A modified version of the Ponseti method, where the Achilles tendon is released before casting begins, has shown success in reducing the need for more extensive surgery.
When Surgery Is Needed
Surgery is not the first step for most children with AMC, but it becomes an option when stretching, splinting, and casting cannot achieve functional joint positions.
For elbows that cannot bend past 90 degrees despite conservative treatment, surgeons can lengthen the triceps tendon and release the tight tissue behind the joint. The goal is to allow a child to bring their hand to their mouth for eating and self-care.
Clubfoot correction often starts with casting, but rigid or recurring deformities may require a formal surgical release of the tight structures on the inner and back sides of the foot. The Achilles tendon is lengthened, and in some cases a bone procedure is added to correct persistent inward curvature.
Hip treatment follows a different logic than in other childhood hip conditions. Dislocated hips in AMC are a different type of dislocation than typical developmental hip dysplasia, and closed reduction (pushing the hip back in without surgery) has poor results. If a child’s hips have very limited range of motion or the child is unlikely to walk, surgeons generally leave dislocated hips alone. A flexible, dislocated hip often functions better than a stiff, surgically corrected one.
Living With AMC as an Adult
Most people with AMC have a normal life expectancy, though the condition creates lasting challenges. A study published in the journal Neurology examined adults with AMC and found that 88% could walk independently, but only 37% could get around without any assistive device or modification. Stairs posed the biggest mobility challenge: just 19% could climb them without help, while 58% needed a device like a railing or cane and 23% needed another person’s assistance.
Reaching and grasping are commonly affected. Reaching ability tends to be more limited than grip strength, which is relatively preserved. Between 15% and 30% of adults needed help from another person for daily tasks, with those who had amyoplasia generally needing more assistance than those with other forms, particularly for eating and bathing.
Pain is nearly universal. In the Neurology study, 91% of adult participants reported pain, often chronic and present since childhood. It was primarily muscular and joint-related, worsened by physical activity, and concentrated in the spine and lower limbs. Half of those with pain said it had psychological consequences. Anxiety affected 43% of participants, and 34% reported significant fatigue.
Work life is substantially affected. About a quarter of adults with AMC could not find suitable employment because of their disabilities. Among those who did work, 60% needed workplace modifications or adjusted hours. Only 23% were able to work without any accommodations. Roughly a third could not drive, with the rate climbing to 46% among those with amyoplasia.
Respiratory problems appeared in 23% of adults, caused by a combination of weak breathing muscles and spinal curvature (scoliosis). Urinary issues, most commonly incontinence, affected 16%. These secondary health problems tend to emerge or worsen over time and benefit from ongoing monitoring throughout adulthood.