The common phrase “double jointed” is a misnomer for the condition known scientifically as Joint Hypermobility. Individuals who appear to have extra joints actually possess a greater range of motion within their existing joints, allowing for unusual flexibility. This increased joint laxity is a biological reality resulting from the structure of the body’s connective tissues, affecting a significant portion of the population.
Understanding Joint Hypermobility
Joint hypermobility is defined as the ability of a joint to move beyond the typical limits of its normal range of motion. A hypermobile person can extend or bend their joints further than average because the supporting structures are unusually pliable. This increased flexibility is due to the inherent characteristics of the surrounding ligaments and joint capsules, not to having a “double” joint. These tissues normally act as natural restraints to prevent overextension, but in hypermobile individuals, they are looser or more elastic than usual, granting the joint greater movement.
How Hypermobility is Demonstrated
The physical manifestations that lead people to believe they are “double jointed” involve several distinct movements. Common examples include the ability to bend the little finger backward past 90 degrees or to touch the thumb to the forearm. Many hypermobile individuals can also hyperextend their elbows or knees past the straight neutral position, causing them to appear slightly bent backward. These observable signs are quantified by healthcare professionals using the Beighton Score, a standardized nine-point system for assessing generalized joint hypermobility.
The Beighton Score involves five specific maneuvers, four of which are performed bilaterally, with one point awarded for each successful demonstration. A score of five or more out of nine in adults, or six in children, typically indicates generalized hypermobility. While this tool is quick and effective for screening, it focuses only on a few specific joints, such as the pinkies, thumbs, elbows, knees, and the spine’s ability to flex forward. This standardized method allows doctors to consistently measure the extent of joint laxity during a clinical assessment.
The Role of Connective Tissue
The biological foundation for increased joint flexibility lies within the structure of connective tissue, which includes ligaments, tendons, and joint capsules. These tissues are primarily composed of collagen, a protein that provides both strength and elasticity to the body’s scaffolding. In hypermobile individuals, this collagen often has a genetically determined variation in its structure or organization. This variation makes the tissue more pliable, resulting in ligaments and tendons that are inherently more elastic or lax than those with average joint mobility.
The underlying issue is a defect in collagen quality or assembly, rather than a lack of the protein itself, which compromises its supportive function. This increased laxity allows the joint to exceed its normal boundaries, directly resulting in the hypermobility observed. Genetic factors play a significant role in determining collagen structure, which is why hypermobility often runs in families.
When Hypermobility Becomes a Medical Concern
For many, joint hypermobility remains a benign trait that is simply a form of increased flexibility, sometimes offering an advantage in activities like gymnastics or dance. However, when hypermobility begins to cause symptoms like chronic joint pain, frequent injuries, or instability, it transitions from a trait to a medical concern. This symptomatic state is often classified as Hypermobility Spectrum Disorder (HSD). People with HSD experience issues directly related to the lax joints, such as frequent joint dislocations or partial dislocations, known as subluxations.
A more severe, genetically defined condition is hypermobile Ehlers-Danlos Syndrome (hEDS), which is considered a connective tissue disorder. While hEDS shares the joint-related symptoms of HSD, it also involves a wider range of systemic issues. These can include chronic fatigue, easy bruising, and issues with the nervous or gastrointestinal systems. If a person with hypermobility experiences persistent joint pain, instability, or other unexplained health problems, consulting a doctor is advisable.