Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA
Intrinsic Tightness vs Extrinsic Tightness of the Hand
Intrinsic Tightness
Definition
Intrinsic tightness refers to contracture or shortening of the intrinsic muscles of the hand, including:
- Lumbricals
- Interossei
Causes
Common causes include:
- Crush injury to the hand
- Post-traumatic fibrosis
- Intrinsic muscle contracture
Pathophysiology
The intrinsic muscles become:
- Shortened
- Fibrotic
Normally, intrinsic muscles:
- Flex the MCP joints
- Extend the PIP and DIP joints
When these muscles become tight, they restrict PIP joint flexion, especially when the MCP joint is extended.
Clinical Test: Bunnell Test (Intrinsic Tightness Test)
Method
- Hold the MCP joint in extension
- Attempt to flex the PIP joint
- Then flex the MCP joint and reassess PIP flexion
Interpretation
Positive for Intrinsic Tightness
- PIP flexion is limited when the MCP joint is extended
- PIP flexion improves when the MCP joint is flexed
Mechanism
When the MCP joint is extended:
- The intrinsic muscles are stretched across the PIP joint
- Tight intrinsic muscles restrict PIP flexion
When the MCP joint is flexed:
- The intrinsic muscles relax
- PIP flexion improves
Treatment
Non-operative Treatment
- Physiotherapy
- Stretching exercises
- Splinting
Surgical Treatment
In resistant cases:
- Release of intrinsic muscles
- Lateral band release
Extrinsic Tightness
Definition
Extrinsic tightness refers to tightness or adhesions involving the extrinsic extensor tendons.
Causes
Common causes include:
- Extensor tendon adhesions
- Metacarpal fractures
- Dorsal hand trauma
Pathophysiology
The extensor tendons become:
- Shortened
- Adherent to surrounding tissues or bone
This limits normal finger flexion.
Clinical Findings
Extrinsic tightness produces the opposite pattern compared with intrinsic tightness.
Pattern of Motion
MCP Joint Extended
- PIP flexion improves
MCP Joint Flexed
- PIP flexion worsens
Mechanism
When the MCP joint is flexed:
- The extensor tendons are stretched
- Tight extensor tendons restrict PIP flexion
When the MCP joint is extended:
- The extensor tendons relax
- PIP flexion improves
Diagnosis
Diagnosis is based on:
- Reversed findings on Bunnell testing
- Clinical examination of tendon tightness and finger motion
Treatment
Conservative Treatment
- Physiotherapy
- Mobilization exercises
Surgical Treatment
If symptoms persist:
- Tenolysis to release tendon adhesions
Comparison Between Intrinsic and Extrinsic Tightness
| Feature | Intrinsic Tightness | Extrinsic Tightness |
|---|---|---|
| Structure involved | Intrinsic muscles | Extrinsic extensor tendons |
| MCP extended | Decreased PIP flexion | Improved PIP flexion |
| MCP flexed | Improved PIP flexion | Decreased PIP flexion |
| Main cause | Muscle fibrosis | Tendon adhesions |
| Treatment | Stretching or muscle release | Therapy or tenolysis |
Key Clinical Points
- Intrinsic tightness limits PIP flexion when the MCP joint is extended.
- Extrinsic tightness limits PIP flexion when the MCP joint is flexed.
- Bunnell’s test is essential for differentiating the two conditions.
- Post-traumatic fibrosis commonly causes intrinsic tightness.
- Extensor tendon adhesions after dorsal hand injuries commonly cause extrinsic tightness.
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