extensor digitorum communis tendons ( RID2379 ) At the level of the distal radius and proximal carpus the 4th Ext compartment retinaculum is thick and the EDC tendons are all clumped together (red arrows). Distal to the segmental constriction there is intratendinous and peritendinous ganglion arising from the EDC of the index finger, which appears normal more distally where there is mild fluid signal distension of the tendon sheath. I find that the clumped tendons in stenosing tenosynovitis of the 4th compartment are often clinically mistaken for a mass, though in this case the ganglion was clinically obvious. Would you aspirate this under US guidance? Would you fenestrate the thickened retinaculum? I will attach an ancient article reporting a series predominanty affecting the EDC, treated surgically, unrelated to RA or other arthropathy. This patient has no arthritis.