Metacarpal Diaphysis Anatomical Definition
The metacarpal diaphysis refers to the shaft of the metacarpal bone, which is the long central portion between the base (proximal end) and the neck (distal end).
Anatomical Terminology
The metacarpal bone is divided into three distinct anatomical regions:
- Base: The proximal end that articulates with the carpal bones (or trapezium for the first metacarpal) 1
- Shaft (Diaphysis): The long tubular central portion of the bone between the base and neck 2, 3, 4
- Head: The distal rounded end that articulates with the proximal phalanx 1
- Neck: The narrow region between the head and shaft 2, 5
Clinical Relevance
Metacarpal diaphyseal fractures specifically refer to fractures occurring in the shaft region, which is biomechanically and clinically distinct from base, neck, or head fractures 2, 3, 4.
Key Distinguishing Features:
- Diaphyseal (shaft) fractures can be transverse, short oblique, long oblique, or spiral in pattern and typically occur in the mid-portion of the metacarpal 2, 3, 5
- These fractures are treated differently than metacarpal neck fractures (commonly called "boxer's fractures") or base fractures (such as Bennett's or Rolando's fractures of the thumb) 6
- Surgical fixation techniques for diaphyseal fractures include dorsal plating, intramedullary pinning, lag screws, and headless compression screws—all specifically designed for shaft fractures 3, 4, 5
Common Clinical Pitfall
Do not confuse the diaphysis (shaft) with the neck—the neck is the narrow transition zone just proximal to the metacarpal head, while the diaphysis comprises the entire central tubular portion of the bone 2, 3. This distinction is critical for treatment planning, as neck fractures tolerate more angulation and are often managed conservatively, whereas diaphyseal fractures may require surgical intervention for rotational deformity, significant angulation, or shortening 2, 6.