What Does "Nearly Fused" Radial Physis Mean?
When the physis (growth plate) of the radius is "nearly fused," it means the cartilaginous growth plate is in the final stages of closing, with bone progressively replacing cartilage, indicating that longitudinal growth of the radius is almost complete and skeletal maturity is approaching.
Understanding the Process
The physis is the cartilaginous growth plate responsible for longitudinal bone growth. During late adolescence, this structure undergoes progressive closure through a process where:
- Bone replaces cartilage systematically - The growth plate becomes progressively mineralized and replaced by bone tissue
- Closure follows a specific pattern - In the distal radius, bony bridging begins centroradially and ends with a small limbus dorsoradially 1
- The process is rapid - Once fusion begins, complete closure occurs within less than a year, typically just a few months 1
Age and Timing Considerations
In Females:
- Fusion begins at 13-14 years (10% of population)
- Complete fusion occurs by 17-18 years (100% of population) 2
- The process takes place at 15-18 years on average 1
In Males:
- Fusion begins at 15-16 years (20% of population)
- Complete fusion occurs by 18-19 years (100% of population) 2
Females consistently fuse earlier than males by approximately 1 year 2.
Clinical Significance
Growth Implications:
- Minimal remaining growth potential - Once the physis is nearly fused, very little longitudinal growth remains
- Skeletal maturity approaching - This indicates the individual is nearing adult height
- No correlation with menarche - In females, there is no significant correlation between menarche timing and physeal closure (P = 0.091) 1
Radiographic Assessment:
When evaluating "nearly fused" physes, the growth plate appears:
- Narrowed and irregular compared to open physes
- Partially bridged by bone with only small cartilaginous remnants remaining
- Best visualized on plain radiographs of the wrist in AP view 2
Important Caveats
Avoid using MRI criteria applied to plain radiographs - Plain radiographs significantly overrate the grading of fusion compared to MRI (p<0.001 in most age groups), which can lead to misinterpretation of skeletal maturity 3. If precise staging is needed, use the imaging modality for which the grading system was designed.
Individual variation exists - While population averages are useful, there is considerable individual variation in timing of physeal closure based on genetic, nutritional, and hormonal factors 1, 2.