What is an Impacted Metacarpal Fracture?
An impacted metacarpal fracture is a specific fracture pattern where the bone fragments are driven or compressed into each other, resulting in telescoping or shortening of the metacarpal bone with the fracture ends wedged together under axial loading forces.
Fracture Characteristics
An impacted fracture represents a compression injury where the cortical bone on one side buckles while the opposite cortex remains intact or minimally disrupted, creating inherent stability through the interlocking of bone fragments. This mechanism typically occurs from direct axial loading, such as punching a solid object or falls onto a closed fist.
Key Features:
- The fracture fragments are compressed together rather than displaced apart, which provides inherent mechanical stability 1, 2
- Axial shortening is the hallmark finding, distinguishing impacted fractures from other metacarpal fracture patterns 3
- These fractures are generally more stable than transverse or oblique fractures because the bone ends are wedged together 4, 5
Diagnostic Evaluation
Radiographic Assessment:
- Obtain minimum 3-view radiographs (posteroanterior, lateral, and 45° semipronated oblique) to properly assess the fracture pattern and degree of impaction 3
- An internally rotated oblique projection should be added to the standard externally rotated oblique to increase diagnostic yield for metacarpal fractures 3
- Look specifically for axial shortening on the lateral view, which confirms the impacted nature of the fracture 3
Common Pitfall:
- Relying on only 2 views is inadequate and may miss the degree of impaction or associated rotational deformity 6, 3
Clinical Implications
Stability Considerations:
- Impacted fractures are generally more stable than non-impacted patterns due to the mechanical interdigitation of bone fragments 4, 5
- The majority can be managed non-operatively with immobilization 1, 2
Indications for Surgical Intervention:
- Operative fixation becomes necessary when there is >2 mm of residual articular surface step-off if the fracture extends into the joint 3
- Significant axial shortening, malrotation, or loss of reduction during immobilization may require surgical stabilization 2, 7
Management Approach
Non-operative Treatment:
- Most impacted metacarpal fractures can be treated conservatively with reduction and/or immobilization 2, 4
- Active finger motion exercises should be initiated immediately following diagnosis and treatment to prevent stiffness, which is the most common functionally disabling complication 3