Chronic ischio-femoral impingement
Severe posterior hip pain not relieved by physiotherapy or steroid injection into the hip joint.
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Narrowed ischio-femoral interspace to 7mm (ie between the ischial tuberosity and lesser trochanter). The interposed quadratus femoris muscle shows focal increased T2 signal and attenuation of muscle fibers as compared with the remainder of the muscle that has a rather square appearance (best seen on the coronal) thus the anatomical name.
This is a classic case of ischio-femoral impingement with a narrowed channel through which the quadratus femoris is positioned. The muscle acts to externally rotate and adduct the thigh which opens up this channel whereas internal rotation of the hip tends to reduce the space by bringing the lesser trochanter closer to the ischial tuberosity. Note the channel is made even narrower by the additional hamstring tendon origins from the ischial tuberosity.
In this study, the muscle is not only edematous but also attenuated on the PD axial image (just in the channel) indicating the chronicity of impingement. This is not a neuropathic phenomenon as the whole muscle would be affected.