Purpose of Intrinsic Hand Position
The intrinsic hand position serves to create a functional grasp by enabling proper finger kinematics, allowing for greater fingertip-to-palm distance during grasping, and preventing the "roll-up" finger movement that can push objects out of grasp. This position is critical for maintaining hand function and preventing contractures that can significantly impact quality of life.
Biomechanical Function of Intrinsic Hand Position
The intrinsic hand position is characterized by:
- Proper balance between intrinsic and extrinsic hand muscles
- Metacarpophalangeal (MCP) joint flexion occurring before proximal interphalangeal (PIP) and distal interphalangeal (DIP) joint flexion
- Maintenance of the natural cascade of the fingers
Research demonstrates that intrinsic muscle function significantly alters finger kinematics during grasping:
- Without intrinsic muscle contribution, finger flexion begins at the PIP joint, followed by the DIP joint, and then the MCP joint 1
- With proper intrinsic muscle function, flexion initiates at the MCP joint, followed by the PIP and DIP joints 1
- This altered joint flexion order results in a larger maximal fingertip-to-palm distance during finger flexion (up to 19mm difference) 1
Clinical Importance
Prevention of Intrinsic Contractures
Intrinsic contractures can lead to:
- Hyperflexed MCP joints and hyperextended PIP joints
- Deformation of the natural cascade of the fingers
- Significant disability including weakness in grip strength
- Difficulty grasping larger objects
- Problems with hand hygiene 2
Functional Benefits
Maintaining proper intrinsic hand position provides:
- Improved grip strength
- Enhanced ability to grasp objects of varying sizes
- Better hand coordination for daily activities
- Prevention of deformities that can lead to long-term disability 1, 2
Management of Intrinsic Hand Function
Exercise Programs
The European League Against Rheumatism strongly recommends exercise programs for maintaining proper intrinsic hand function:
- Range of motion exercises
- Strengthening exercises for intrinsic hand muscles
- Regular daily practice 3, 4
Orthoses/Splints
Hand orthoses are recommended for:
- Prevention or correction of lateral angulation and flexion deformity
- Support of the thumb base and other affected joints
- Long-term management of hand position 3, 4
The American College of Rheumatology strongly recommends hand orthoses for first carpometacarpal (CMC) joint issues and conditionally recommends them for other hand joints 3.
Therapeutic Interventions
For patients with impaired intrinsic hand function:
- Occupational therapy focusing on hand exercises and functional activities
- Heat application before exercise to improve tissue extensibility
- Kinesiotaping for support while maintaining range of motion 3, 4
Clinical Assessment
Assessment of intrinsic hand function can be performed using:
- Observation of finger flexion patterns during grasping
- Evaluation of fingertip-to-palm distance during grasp
- Assessment of independence of digit movements 5
- Specialized tests such as the Chedoke Arm and Hand Inventory or the Motor Activity Log 3
Conclusion
The intrinsic hand position is fundamental to proper hand function, enabling effective grasping and manipulation of objects. Maintaining this position through appropriate exercise, orthoses, and therapeutic interventions is essential for preventing contractures and preserving quality of life.