Intrinsic tightness, also known as intrinsic contracture, is fundamentally caused by the shortening of the interosseous muscles in the hand. This shortening can severely limit the hand's ability to function normally, affecting movements like finger extension and abduction.
Understanding Intrinsic Tightness
The interosseous muscles are small muscles located between the metacarpal bones in the hand. They play a crucial role in flexing the metacarpophalangeal (MCP) joints (knuckles) and extending the interphalangeal (IP) joints (finger joints), as well as aiding in finger abduction and adduction. When these muscles become tight or contractured, it leads to a characteristic "intrinsic plus" posture of the hand, where the MCP joints are flexed and the IP joints are extended.
Key Causes of Interosseous Muscle Shortening
Several factors can lead to the shortening of the interosseous muscles, resulting in intrinsic tightness. These include:
- Ischaemia: A reduction or complete cessation of blood flow to the muscle tissue. Prolonged ischaemia can lead to muscle tissue death and subsequent fibrosis (scar tissue formation), causing the muscles to become stiff and shortened.
- Adhesions: The formation of scar tissue within or around the interosseous muscles. These adhesions can bind the muscles to surrounding structures, preventing their normal gliding and extension, leading to a fixed shortened state.
- Displacement: Abnormal positioning or dislocation of bones or soft tissues within the hand can alter the normal length-tension relationship of the interosseous muscles, forcing them into a shortened position that can become permanent over time if uncorrected.
- Spasticity: Often seen in neurological conditions such as stroke, cerebral palsy, or spinal cord injury, spasticity involves increased muscle tone and involuntary muscle contractions. Persistent spasticity in the interosseous muscles can lead to their chronic shortening and stiffness.
Each of these underlying causes contributes to the diminished flexibility and range of motion characteristic of intrinsic tightness, impacting fine motor skills and overall hand dexterity.
