• The fine motor movements of the thumb and fingers allow normal full upper extremity function. Detailed examination of the hand is critical to determining the patient’s pattern of injury.
• The muscles acting here can be denervated in brachial plexus as well as direct peripheral nerve injury patterns.
• Restoration of thumb and finger movement must be a priority in peripheral nerve injury patients.
• Function can be restored in patients with single or multiple peripheral nerve injury patterns by use of nerve and tendon transfer and other procedures.
• Restoration of hand function in complete or lower brachial plexus injury patterns is challenging and the ability to restore individual digit fine motor function extremely limited although with the expansion of nerve transfer techniques (for example, brachialis to median nerve anterior interosseous branch) this pessimism may change.
Structures of the Hand (composed of thumb, index/long/ring/small fingers)
• Carpal bones
• Metacarpal bones
• Carpal-metacarpal (CMC) joint (saddle joint formed by trapezius and thumb metacarpal)
• Metacarpal-phalangeal (MCP) joint (condyloid joint formed by thumb metacarpal and proximal phalanx)
• Inter-phalangeal (IP) joint (hinge joint formed by the thumb proximal and distal phalanges)
• Index, long, ring and small fingers:
• Carpal-metacarpal (CMC) joint (at index/long/ring fingers this is an ellipsoid joint at the small finger this is more of a saddle joint)
• Metacarpal-phalangeal (MCP) joint (condyloid joint formed by the respective metacarpal and proximal phalanx of each finger)
• Proximal (PIP) and Distal (DIP) Interphalangeal joints (condyloid joints formed by the proximal and middle phalanges--PIP joint; and middle and distal phalanges--DIP joint)
Movements of the Hand (composed of thumb, index/long/ring/small fingers)
Movement of the thumb and fingers is complex:
• Movement of the thumb occurs at the CMC, MCP and IP joints and allows for opposition--a critical function of the hand.
• Movement of the fingers occurs primarily at the MCP and IP joints and allows for grasp/grip, palpation and other fine finger motions.
• The small finger has some additional movement compared to the index/long/ring finger due to its greater mobility at the CMC joint as well as the added motor function provided by the hypothenar musculature.
• Dysfunction of hand motion seen in peripheral nerve injury can range from mild sensory disturbances seen in nerve compression to complete loss of function and claw deformity that can even limit the ability to perform basic hygiene to the affected hand.
• Because normal hand function is so critical to daily, work and recreational activity even minor deficits can be devastating to patients.
Key movements of the thumb:
• The carpal-metacarpal joint adducts/abducts, flexes/extends, and performs slight rotation, opposition and circumduction.
• The metacarpal-phalanageal flexes/extends and slightly abducts/adducts and rotates.
• The interphlangeal joint flexes and extends.
Key movements of the fingers:
• There is minimal motion at the carpal-metacarpal joints of the index/long and ring fingers.
• The carpal-metacarpal joint of the small finger has some motion—rotation.
• The metacarpal-phalangeal joint flexes/extends, abducts/adducts, and performs some circumduction and opposition (mainly at the small finger).
• The proximal and distal interphalangeal joints flex and extend.