https://youtube.com/shorts/bnAkePlUUQM
More structured MSK MRI guidance is available in my book,
Visualizing MSK Radiology: A Practical Guide to Radiology Mastery on Amazon.
https://www.amazon.com/dp/B0DJGMHMFS
how the Tram-Track Appearance Reveals PCL Mucoid Degeneration—not a Tear
1. What Is the Tram-Track Appearance?
A characteristic MRI pattern of PCL mucoid degeneration, analogous to the “celery-stalk sign” in ACL mucoid degeneration.
Diagnostic MRI features:
- Homogeneous central high signal on proton-density and T2 sequences
- Surrounded by a well-defined rim of intact low-signal PCL fibers
- Visible on all three planes
→ Creating the classic parallel “tram-track” lines
This pattern indicates intact ligament structure with internal mucinous change.
2. Why It Matters
The tram-track appearance strongly correlates with a mechanically stable PCL.
- 0% instability on posterior drawer exam
- No laxity at arthroscopy
- Ligament appears intact, bulbous, yellowish
- Most patients had other causes of pain, not the PCL
3. How to Differentiate From a PCL Tear
| Feature | Mucoid Degeneration | PCL Tear |
| Fiber integrity | Completely intact | Often disrupted or avulsed |
| Signal pattern | Homogeneous central streak | Heterogeneous, amorphous |
| Peripheral rim | Intact on all planes | Discontinuous on axial/coronal |
| Thickness | 8.5 mm avg | 8.8 mm avg |
| Signal reliability | High signal ≠ tear | 30% show low T2 |
Key point:
Integrity of peripheral fibers is the best discriminator—not signal intensity or thickness.
4. Common Associated Findings
Supports the degenerative origin:
- PCL ganglion: 80%
- ACL mucoid degeneration: 45%
- Meniscal cysts: 35%
Bottom Line
The tram-track appearance is a highly reliable sign of PCL mucoid degeneration,
helping radiologists distinguish an intact, stable ligament from a true PCL tear.
#radiology, #mskradiology, #kneemri, #pcl, #mripearls, #radiologyeducation, #sportsmedicine, #pclmucoiddegeneration, #orthopedics, #drslothic
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