Joint Hypermobility: Understanding Causes, Symptoms, and Management

Why are joints hypermobile?

Joints are hypermobile, or "double-jointed," primarily due to inherent variations in the composition and structure of connective tissues, particularly collagen, which provides elasticity and strength to ligaments and joint capsules. This often results from genetic predispositions that influence the integrity and laxity of these supporting structures.

Understanding Joint Hypermobility

Joint hypermobility refers to the ability of a joint to move beyond its normal anatomical range of motion. While often colloquially referred to as being "double-jointed," it does not imply having extra joints, but rather an unusual degree of flexibility. This spectrum ranges from isolated hypermobility in a single joint to generalized joint hypermobility (GJH) affecting multiple joints throughout the body. For many, hypermobility is benign and asymptomatic, but for others, it can be associated with pain, instability, and a range of systemic symptoms, falling under the umbrella of Hypermobility Spectrum Disorder (HSD) or specific hereditary connective tissue disorders like Ehlers-Danlos Syndromes (EDS).

The Underlying Anatomy and Physiology

The stability of a joint is determined by several factors: the shape of the articulating bone surfaces, the strength and integrity of the joint capsule, the tautness of ligaments, the dynamic support from surrounding muscles and tendons, and the neurological control (proprioception). In individuals with hypermobility, the primary factors contributing to excessive range of motion are often related to the inherent properties of their connective tissues.

• Connective Tissue Composition: The most significant factor is the structure and quantity of proteins like collagen and elastin. Collagen provides tensile strength and structure to ligaments, tendons, and joint capsules, while elastin allows tissues to stretch and recoil. In hypermobile individuals, there may be:
  • Abnormal Collagen Structure: Genetic variations can lead to collagen that is more stretchy or "faulty," meaning it's less robust or organized than typical collagen. This makes ligaments and joint capsules less effective at limiting joint movement. Type I and Type III collagen are particularly relevant.
  • Increased Elastin Content or Function: While less common than collagen issues, variations in elastin can also contribute to increased tissue elasticity.
• Ligamentous Laxity: Ligaments are fibrous bands of connective tissue that connect bones and stabilize joints. When these ligaments are inherently more elastic or "loose," they allow for greater joint excursion. This laxity can be a hallmark of generalized hypermobility.
• Joint Capsule Properties: The joint capsule, a fibrous sac enclosing the joint, also contributes to stability. A more distensible or less rigid joint capsule will permit increased range of motion.
• Bony Anatomy: In some cases, the shape of the articulating bone ends can contribute. For example, shallower joint sockets or flatter bone surfaces may allow for greater movement compared to deeper, more restrictive configurations.

Primary Causes of Joint Hypermobility

The reasons for excessive joint flexibility are largely rooted in an individual's genetic makeup and the subsequent impact on their connective tissue.

• Genetic Predisposition: This is the most common underlying cause. Many forms of hypermobility are inherited, meaning they run in families.
  • Benign Joint Hypermobility: Often, hypermobility is simply a familial trait without significant associated problems. It's considered a normal variation in the population.
  • Hereditary Connective Tissue Disorders (HCTDs):
    • Ehlers-Danlos Syndromes (EDS): A group of inherited disorders primarily affecting collagen and connective tissues. Hypermobile EDS (hEDS) is the most common type and is characterized by widespread joint hypermobility, skin hyperextensibility, and tissue fragility, alongside other systemic manifestations. The genetic basis for hEDS is still being fully elucidated, but it involves defects in collagen synthesis or processing.
    • Marfan Syndrome: Another HCTD primarily affecting fibrillin-1, a protein essential for elastic fibers in connective tissue. While known for affecting the cardiovascular and ocular systems, joint hypermobility, especially in the fingers and wrists, is a common musculoskeletal feature.
    • Other Rare Syndromes: Conditions like Loeys-Dietz syndrome or Osteogenesis Imperfecta can also present with joint hypermobility as a symptom.
• Developmental Factors: Connective tissue properties can vary throughout life. Children are often more flexible than adults, and flexibility tends to decrease with age as collagen cross-links increase. Hormonal factors, such as increased relaxin during pregnancy, can also transiently increase ligamentous laxity.

Secondary or Acquired Hypermobility

While less common as a primary cause of widespread hypermobility, certain factors can contribute to localized or acquired joint laxity.

• Repetitive Training and Activity: Athletes involved in sports requiring extreme flexibility (e.g., gymnasts, dancers, contortionists) can develop increased range of motion over time through stretching and specific training. This is a deliberate adaptation of the musculoskeletal system, though it can sometimes push genetically predisposed individuals into symptomatic hypermobility.
• Trauma or Injury: Severe sprains or dislocations can stretch or tear ligaments, leading to permanent laxity in a specific joint.
• Neurological Conditions: Certain neurological conditions affecting muscle tone or proprioception can indirectly lead to increased joint range of motion due to lack of dynamic stabilization.
• Systemic Conditions: Some inflammatory conditions or endocrine disorders can rarely contribute to joint laxity.

Differentiating Benign Hypermobility from Hypermobility Spectrum Disorder (HSD) and Hypermobility Syndromes

It's crucial to understand that not all hypermobility is problematic.

• Benign Joint Hypermobility (BJH): Refers to hypermobility that is asymptomatic or causes only minor, infrequent symptoms. It's often a positive attribute in certain activities.
• Hypermobility Spectrum Disorder (HSD): This diagnosis is given when an individual experiences symptoms (like chronic pain, fatigue, dislocations, or subluxations) directly related to their hypermobility, but they do not meet the full diagnostic criteria for a specific hereditary connective tissue disorder like hEDS. HSD acknowledges the symptomatic nature of hypermobility across a spectrum.
• Hypermobile Ehlers-Danlos Syndrome (hEDS): This is a specific genetic connective tissue disorder with distinct diagnostic criteria that include generalized joint hypermobility along with specific skin findings, chronic pain, autonomic dysfunction, and other systemic manifestations.

Clinical Assessment and Diagnosis

Assessment of joint hypermobility typically involves a physical examination using standardized measures. The Beighton Score is the most widely used screening tool, assessing hypermobility in nine specific joints:

1. Passive dorsiflexion of the 5th metacarpophalangeal joint >90 degrees (bilateral)
2. Passive apposition of the thumb to the forearm (bilateral)
3. Hyperextension of the elbow >10 degrees (bilateral)
4. Hyperextension of the knee >10 degrees (bilateral)
5. Forward flexion of the trunk with palms resting on the floor

A score of 4 or higher (out of 9) is generally indicative of generalized joint hypermobility in adults, though criteria vary slightly for children and adolescents. However, the Beighton Score alone is insufficient for diagnosing HSD or hEDS, which require a more comprehensive clinical evaluation based on established criteria.

Implications and Management

While hypermobility can be an asset in activities like gymnastics or dance, it can also predispose individuals to certain issues:

• Joint Instability: Increased risk of sprains, subluxations (partial dislocations), and full dislocations.
• Chronic Pain: Often due to repetitive microtrauma, muscle fatigue from overcompensation, or nerve impingement.
• Proprioceptive Deficits: Reduced joint position sense can lead to clumsiness and increased injury risk.
• Fatigue: The body's constant effort to stabilize joints can be energy-intensive.

Management strategies for symptomatic hypermobility focus on improving joint stability and reducing pain:

• Strengthening: Building strong muscles around hypermobile joints is crucial for providing dynamic stability and support, compensating for lax ligaments. Focus on controlled, concentric, and eccentric movements.
• Proprioceptive Training: Exercises that improve balance, coordination, and the body's awareness of joint position help enhance stability and reduce injury risk. Examples include single-leg stands, unstable surface training, and plyometrics (when appropriate).
• Avoiding Hyperextension: Learning to move within a "safe" range of motion, avoiding locking out or hyperextending joints during daily activities and exercise.
• Pain Management: Physical therapy, manual therapy, and sometimes medication to address chronic pain.
• Education: Understanding one's own body and the implications of hypermobility is key to self-management.

Conclusion

Joint hypermobility is fundamentally a characteristic influenced by the unique properties of an individual's connective tissues, largely determined by genetic factors affecting collagen and elastin. While often benign, when symptomatic, it can significantly impact quality of life, necessitating a comprehensive approach that emphasizes strengthening, proprioceptive training, and a deep understanding of one's own body mechanics to promote stability and reduce potential complications.