Hypermobility (joints)


Hypermobility, also known as double-jointedness, describes joints that stretch farther than normal. For example, some hypermobile people can bend their thumbs backwards to their wrists, bend their knee joints backwards, put their leg behind the head, or perform other contortionist "tricks". It can affect one or more joints throughout the body.
Hypermobile joints are common and occur in about 10 to 25% of the population. Most have no other issues. In a minority of people, pain and other symptoms are present. This may be a sign of hypermobility spectrum disorder. In some cases, hypermobile joints are a feature of connective tissue disorders. One of these, Ehlers-Danlos Syndrome, was classified into several types which have been found to be genetic. Hypermobile Ehlers–Danlos syndrome, formerly called EDS Type 3, remains the only EDS variant without a diagnostic DNA test.
In 2016 the diagnostic criteria for hEDS were re-written to be more restrictive, with the intent of narrowing the pool of hEDS patients, in the hope of making it easier to identify a common genetic mutation and create a diagnostic DNA test.
At the same time, joint hypermobility syndrome was renamed as hypermobility spectrum disorder, and redefined as a hypermobility disorder that does not meet the diagnostic criteria for any heritable Connective Tissue Disorder. Sometimes called "non-genetic EDS," hypermobility spectrum disorder can have the same signs as hEDS, but be caused not by a heritable genetic mutation but by problems in fetal development, such as pre-natal exposure to toxins like agricultural chemicals, drugs, or alcohol. Fetal Alcohol Spectrum Disorders affect at least 1 in 20 people in the U.S., and joint hypermobility with other symptoms is common.

Signs and symptoms

People with joint hypermobility syndromes may develop conditions caused by their unstable joints. These conditions include:
Joint hypermobility may be associated with other conditions. These include ADHD, autism, dyspraxia, fibromyalgia, hereditary connective tissue disorders, mitral valve prolapse, and anxiety disorders such as panic disorder. Joint hypermobility does not cause these other conditions. Most people with joint hypermobility do not have them. In people who do, the underlying cause can be a general syndrome that affects the whole body and brain, or a genetic condition or disease that affects certain tissues.
Medical conditions that can cause joint hypermobility include FASDs, Stickler syndrome, Ehlers–Danlos syndrome, Marfan syndrome, Loeys–Dietz syndrome, rheumatoid arthritis, osteogenesis imperfecta, lupus, polio, Fragile X syndrome, Down syndrome, Morquio syndrome, cleidocranial dysostosis and myotonia congenita. All have other diagnostic criteria as well.

Causes

Hypermobility generally results from one or more of the following:
  • Unusually-shaped ends of one or more bones where they form a joint, or an increased angle of the bone, such as in coxa valga.
  • A mutation in collagen or collagen-related genes or other connective tissue resulting in weakened ligaments/ligamentous laxity. Ligaments hold bones together at the joints.
  • Abnormal joint proprioception
Any of these causes can increase the level of mechanical stress on a joint. Chronically stressed joints may experience higher or faster than usual levels of wear, leading to osteoarthritis.
Hypermobility tends to run in families, suggesting a genetic basis for at least some forms. The term double jointed is often used to describe hypermobility; however, the name is a misnomer and should not be taken literally, as people with hypermobile joints do not have any extra joints, or any extra bones or parts in the joint.
Most people with hypermobile joints do not have a hypermobility spectrum disorder. Approximately 5% of the healthy population has one or more hypermobile joints. However, people with symptomatic hypermobility are subject to many difficulties. For example, their joints may be easily injured, be more prone to complete or partial dislocation due to the weakly stabilized joint, and they may develop problems from muscle fatigue. Hypermobility syndromes can lead to chronic pain or even disability in severe cases.
Hypermobility has been associated with myalgic encephalomyelitis and fibromyalgia. Hypermobility syndromes can cause physical trauma, pain, and stress, and chronic stress from repeated trauma is a possible trigger for chronic conditions such as fibromyalgia.
Symptoms are often exacerbated during pregnancy. During pregnancy, the body releases relaxin and certain hormones that alter ligament physiology, easing the stretching needed to accommodate fetal growth as well as the birthing process. The combination of hypermobility and pregnancy-related pelvic girdle during pregnancy can be debilitating. The pregnant person with hypermobile joints may be in significant pain as muscles and joints adapt to the pregnancy. Pain makes standing or walking difficult during pregnancy, so some women who have one of these disorders find they need to use a wheelchair during pregnancy. They are also at risk for excessive bleeding during and after childbirth, and the baby is at risk of dislocated joints, especially of the clavicle, hip, and neck.

Syndromes

Hypermobility syndrome is generally considered to comprise hypermobility together with other symptoms, such as myalgia and arthralgia. It is relatively common among children and reported more often in females than males.
Current thinking suggests four causative factors:
  • The shape of the ends of the bones—Some joints normally have a large range of movement, such as the shoulder and hip. Both are ball-and-socket joints. The joint ends of bones finish their growth last, so children tend to have more flexible joints than adults; children may "grow out of" hypermobility as their bone ends fully develop. But if a shallow rather than a deep socket is genetically inherited, or results from a problem in development, then a relatively large range of movement will be possible even as an adult. If the socket is particularly shallow, then the joint may dislocate easily.
  • Ligament problems—The ligaments that hold bones together are made of several types of protein fiber. These proteins include elastin, which gives elasticity. Gymnasts and athletes can voluntarially acquire functional hypermobility in some joints by stretching healthy ligaments over time. However, weak or abnormally long ligaments can cause unstable hypermobile joints. Protein deficiencies may weaken ligaments. Some hormones alter the structure of collagen proteins. For example, in late pregnancy, relaxin allows the ligaments of the pelvis to lengthen so the head of the baby can pass. Hormone imbalances may contribute to hypermobility.
  • Muscle tone—Opposing sets of muscles are attached to bones to move joints in various directions. The tone of muscles—a mild basic level of contraction that protects joints and organs—is controlled by the nervous system. Neuromuscular problems can cause loss of muscle tone, increasing the range of movement possible and removing the muscles' protection of the joint. Lack of exercise also weakens the muscles that support and anchor highly flexible joints such as the shoulder, hip, wrist, and ankle.
  • Proprioception—Disorders such as dyspraxia affect the brain's communication with the sensors that detect the motion and position of the body in space. A person with poor proprioception or kinesthetic awareness may habitually hyperextend joints during normal activities such as walking and sitting, because they can't internally sense where the joint is. If stress/pain perception is also affected, they may not experience hyperextension as uncomfortable until an injury occurs.
Hypermobility can also be caused by genetic or developmental disorders that reduce the strength of the connective tissue the body can make. Commonly, hypermobility is dismissed by medical professionals as nonsignificant, though it may be a sign of a systemic problem.

Ehlers–Danlos syndrome hypermobility type

Joint hypermobility is often correlated with hypermobile Ehlers–Danlos syndrome. Ehlers–Danlos syndrome is a genetic disorder caused by mutations or hereditary genes, but the genetic defect that produced hEDS is largely unknown. In conjunction with joint hypermobility, a common symptom for hEDS is smooth, velvety, and stretchy skin. When diagnosing hEDS, the Beighton Criteria are used, but are not always able to distinguish between joint hypermobility syndrome and hEDS.
Ehlers–Danlos hypermobility type can have severe musculoskeletal effects, including:
  • Jaw laxity that may make an individual's jaw open and close like a hinge, as well as open further than the average.
  • Neck pain that can lead to chronic headaches and is usually associated with a crackling or grinding sensation.
  • The spine may end up in a "round back" or inversely may extend too much into hyperlordosis. Individuals may also experience scoliosis.
  • Joints commonly associated with hypermobility may be at more severe risk to dislocate or strain.