Follow-up to 2nd MTP Joint Osteoarthosis Mimicking an Interdigital Neuroma

The question from the related post was, “How do you decipher capsular thickening from synovial hypertrophy?”

Here are a few key points to help clarify the distinction:

I find that differentiating the joint capsule from the synovium is best done in the long-axis (LAX) plane. The synovium is an intra-articular structure. In the first video, which shows a normal 2nd MTP joint, I highlight the capsule, synovium, and articular cartilage for comparison.

The second video is from the Post and demonstrates capsular thickening. Again, I highlight both the capsule and synovium. Notice that the synovium remains hyperechoic—whereas synovial hypertrophy associated with synovitis typically appears hypoechoic.

The final video is from a patient with early rheumatoid arthritis. The capsule remains relatively normal in thickness, while the synovium is both hypoechoic and enlarged.

I hope this helps in clarifying the distinction between capsular thickening, which is common in osteoarthrosis, and synovial hypertrophy, which is most often associated with synovitis.