Age / Sex : 21 / M

Age/Sex: 21/M

Chief Complaint: Lt knee pain (one year ago)

active enthesitis around knee in patient with akyloisng spondylitis

Discussion

Findings:

Pelvis AP radiograph shows bilateral sacroiliitis and entheophytes at bilateral ischial tuberosities, suggesting ankylosing spondylitis.

Localized BM edema in the lateral femoral condyle (at the insertion site of LCL and the origin of the popliteus muscle) and the patella ( at the insertion site of quadriceps tendon, patellar tendon, and lateral patellar retinaculum) is depicted. Also, we can see the localized thickening of adjacent tendons or ligament with T2 hyperintense signal. Moderate amount of suprapatellar effusion along with inflamed and thickened synovial membrane is also present.

Diagnosis: Active enthesitis in ankylosing spondylitis

Discussion:

 1. Entheses

- sites where tendons, ligaments, joint capsules or fascia attach to bone

- dissipate biomechanical stress at the bony interface

- subjected to repeated micro-trauma

- enthesitis: inflammation of the entheses

- enthesopathies: insertional disorders in general

2. Two types of enthuses

    - fibrous type: typical of the metaphses and diaphyses of long bones

    - fibrocartilaginous type: mc, typical of the epiphyses, affected in SpA

3. MR findings of enthesitis in the knee

    - insertion of the quadriceps tendon at the upper patellar pole

    - insertion of the patellar tendon at the lower patellar pole and tibial tubercle

    - femoral condyle muscle insertions (less common)

    - peri-entheseal soft tissue edema

    - bone marrow edema at entheseal sites

    - adjacent bone erosion or enthesophytes

    - thickening and increased signal intensity of tendons and ligaments

    - additional joint or bursal fluid

References:

 Eshed et al. MRI of enthesitis of the appendicular skeleton in spondyloarthritisMRI of enthesitis of the appendicular skeleton in spondyloarthritis. Ann Rheum Dis 2007;66:1553-1559.