Medial Projection of First Metacarpal: Causes and Management
The medial projection of the first metacarpal is most commonly associated with fractures, osteoarthritis, or anatomical variations that require radiographic evaluation with multiple views for proper diagnosis and treatment planning. 1
Potential Causes
- Fractures of the first metacarpal base: Extra-articular fractures can lead to displacement with medial projection, potentially causing retraction of the first web space and weakness of pinch strength 2
- Trapeziometacarpal osteoarthritis: Progressive joint degeneration can cause the first metacarpal to adopt a medial position, often accompanied by adduction contracture 3, 4
- Metacarpal head shape variations: The shape of the first metacarpal head (round vs. flat) influences joint mechanics and can contribute to abnormal positioning 5
- Malunion after previous trauma: Improper healing of previous fractures can result in permanent medial projection 6
- Congenital anatomical variations: Some individuals may have normal anatomical variations that present as medial projection on imaging 1
Diagnostic Approach
Radiographic Evaluation
- Standard 3-view wrist examination: Posteroanterior (PA), lateral, and 45° semipronated oblique views are essential for comprehensive evaluation 1, 7
- Proper positioning: The palm should be flat against the detector with fingers extended and thumb slightly abducted to avoid rotational artifacts that may obscure the medial process 1
- Technical considerations: The wrist should be in neutral position without ulnar or radial deviation for optimal visualization 1
Advanced Imaging
- CT without IV contrast: When initial radiographs are equivocal but clinical suspicion remains high, CT is recommended for detailed evaluation 1, 7
- 3D reconstructions: Particularly helpful for detailed evaluation of the first metacarpal's morphology, including the medial process 1
- MRI: May be indicated if soft tissue injuries are suspected in conjunction with the medial projection 7
Management Options
Conservative Treatment
- Indicated for stable, non-displaced fractures with:
- No joint involvement
- No malrotation
- Displacement less than 30 degrees
- Shortening less than 5mm 6
- Early functional treatment should be implemented for stable fractures 6
- Short-term immobilization: Cast in extended finger position with metacarpophalangeal joint flexed 60-90 degrees 6
- Twin-tape fixation: Allows functional treatment after soft-tissue swelling subsides 6
Surgical Management
- Indications for surgery:
- Open fractures
- Serial fractures of metacarpal bone
- Displacement greater than 30 degrees
- Shortening greater than 5mm 6
- Fixation options:
- Double-row locking plates: Provide stable fixation allowing early mobilization (2 weeks) 2
- Intramedullary stabilization: Particularly useful for displaced fractures of the fifth metacarpal but applicable to the first metacarpal as well 6
- Metacarpal osteotomy: For cases related to trapeziometacarpal osteoarthritis, abduction-extension osteotomy can provide lasting pain relief and correct adduction contracture 3, 4
Post-Treatment Considerations
- Early mobilization: Possible after 2 weeks with appropriate fixation techniques 2
- Monitoring for complications: Secondary displacement can occur, particularly with T-shaped plates 2
- Radiological consolidation: Typically occurs at 4-6 weeks post-treatment 2
Common Pitfalls to Avoid
- Inadequate imaging: Relying on a single view can miss important aspects of the deformity 1
- Poor positioning during radiography: Can significantly alter the appearance of the first metacarpal 1
- Failure to correlate with clinical findings: Radiographic appearance should always be interpreted in context of symptoms and examination 1
- Delayed treatment of unstable fractures: Closed reduction of significantly displaced fractures is often unsuccessful 6
By understanding the causes and appropriate management options for medial projection of the first metacarpal, clinicians can effectively diagnose and treat this condition to optimize hand function and prevent long-term complications.