AMC stands for arthrogryposis multiplex congenita, a condition where a baby is born with permanent joint stiffness (called contractures) in two or more areas of the body. It affects roughly 1 in every 3,000 live births. AMC isn’t a single disease but rather a physical finding that can result from many different underlying causes, all of which share one thing in common: reduced movement in the womb during development.
What Happens in the Body
A contracture means a joint is locked in a bent or straightened position. It can’t move through its normal range. Over time, the muscles around that joint may shrink and weaken because they were never used properly during fetal development. In AMC, these contractures show up in multiple joints, often affecting both the arms and legs symmetrically.
The root cause is decreased fetal movement during pregnancy. A developing baby needs to move its limbs for the joints and muscles to form correctly. When something prevents that movement, extra connective tissue builds up around the joints, locking them in place. What blocks that movement varies widely: it can be a problem with the baby’s brain or spinal cord, a genetic condition affecting the muscles, limited space in the uterus, or maternal illness during pregnancy. Neurological abnormalities account for an estimated 70 to 80 percent of cases.
The Most Common Types
Amyoplasia is the most frequently seen form, occurring in about 1 in 10,000 births. Babies with amyoplasia have underdeveloped muscles and a characteristic posture: shoulders rotated inward, elbows locked straight, wrists and fingers curled, and hips flexed outward. The pattern is usually symmetrical across all four limbs. Amyoplasia occurs randomly and is not inherited.
Distal arthrogryposis is a different category where the stiffness mainly affects the hands and feet. Unlike amyoplasia, distal forms are often hereditary. The most common subtypes are DA1, where babies are born with clenched fists and clubfeet, and DA2B (Sheldon-Hall syndrome), which also involves distinctive facial features like a small mouth, a triangular face, and a prominent chin. Researchers have traced these distal forms to mutations in genes that build the contractile machinery of muscle fibers, including TNNI2, TNNT3, TPM2, and MYH3. In some families, the exact same mutation causes DA1, while in others it causes DA2B, which makes genetic counseling complex.
How AMC Is Diagnosed
Many cases are first suspected during a routine prenatal ultrasound, typically in the second or third trimester, when a doctor notices joints in abnormal positions or the mother reports reduced fetal movement. However, a specific prenatal diagnosis of arthrogryposis is only accurate about 50 percent of the time. MRI can sometimes reveal underlying brain abnormalities that explain the lack of movement.
After birth, the diagnosis is more straightforward. A physical exam reveals the characteristic joint stiffness and positioning. Genetic testing can identify an underlying cause in some cases, though not all. Because so many different conditions can lead to AMC, finding the exact cause often requires a combination of imaging, genetic analysis, and neurological evaluation.
Associated Complications
Joint contractures are the defining feature, but AMC can come with additional challenges depending on the underlying cause. Some newborns with AMC experience respiratory distress at birth, sometimes severe enough to require breathing support. Feeding difficulties and aspiration (where food enters the airway) are also common, and some children need tube feeding early in life. Scoliosis can develop as a child grows, particularly when the spine is involved. The severity of these complications varies enormously from one person to the next.
Treatment and Rehabilitation
There is no cure for AMC, but treatment can significantly improve joint mobility and independence. Management typically starts in infancy and combines several approaches.
Physical therapy is the cornerstone. It includes gentle, progressive stretching of stiff joints, strengthening exercises for weak muscles, massage, and hydrotherapy. Therapists also work on motor development milestones like sitting, standing, and walking. For clubfoot, a common feature of AMC, a casting method called the Ponseti technique is widely used. Splints, braces, and functional orthoses help maintain the range of motion gained through therapy and reduce the need for surgery. There is no single standardized protocol; treatment plans are tailored to each child’s specific joints and level of involvement.
Surgery becomes an option when contractures are too severe for therapy alone. Common procedures focus on releasing tight tendons, correcting bone alignment, and improving elbow, wrist, and thumb positioning in the upper limbs. In the lower limbs, the goals are correcting hip and knee contractures to improve walking ability and prevent pain later in life. Surgical techniques specific to arthrogryposis have improved considerably, and outcomes research continues to shape which procedures offer the most long-term benefit.
Long-Term Outlook
One of the most important things to know about AMC is that it is non-progressive. The contractures present at birth do not get worse over time on their own, and a long-term study following patients up to age 68 found no significant loss of function beyond adolescence. The gains made through childhood treatment tend to hold.
Functional outcomes vary widely. In that same long-term study of 65 adults, 35 were completely independent in daily life, 20 needed some help with tasks like washing and dressing, and 10 were fully dependent on a caregiver. For mobility, 29 walked freely without any aids, 8 walked with crutches, 9 could walk indoors but used a wheelchair outside, and 18 used a wheelchair full time. Notably, 36 of the 65 were able to drive a car.
These numbers reflect the full spectrum of AMC severity. Many people with milder involvement live independently, work, and are physically active. Those with more extensive joint involvement or underlying neurological conditions face greater challenges but still benefit from early, consistent rehabilitation. The key factor in long-term outcomes is how many joints are affected, how severely, and whether an underlying neurological condition is present.