The Z deformity of the thumb is a condition where the thumb collapses due to the imbalance of tendon forces, resulting in a characteristic Z-shape.
Understanding the Z Deformity
Here's a breakdown of the condition, based on the reference provided:
The Z deformity occurs when the tendons controlling the thumb's movement have an altered force, specifically:
- The tendon's new placement forces the Metacarpophalangeal (MCP) joint of the thumb into flexion.
- This flexion of the MCP joint then secondarily causes the Interphalangeal (IP) joint to hyperextend.
This combination of MCP flexion and IP hyperextension creates the Z-shape and prevents the thumb from performing its crucial pinching function.
Key Characteristics of Z Deformity
| Feature | Description |
|---|---|
| Shape | The thumb assumes a "Z" shape. |
| MCP Joint | Flexion of the MCP joint. |
| IP Joint | Hyperextension of the IP joint. |
| Function | Impedes the thumb's ability to pinch. |
Impact on Thumb Function
The Z deformity significantly compromises hand function because:
- It disrupts the alignment necessary for the thumb to effectively oppose the fingers.
- It hinders the ability to grip and manipulate objects, especially fine motor tasks.
The reference states that the primary consequence of this condition is the inability to pinch, highlighting its severe functional impact.
In summary, the Z deformity of the thumb is characterized by:
- MCP joint flexion.
- IP joint hyperextension.
- An overall Z shape to the thumb.
- A compromised ability to pinch.
