Abstract
Musculus piriformis is an important muscle for human biomechanics. It is the most powerful and resistant external rotator of the hip joint as well as a strong abductor.
In many locomotive activities including sports it is the subject to reflex long term hyperactivation, and we therefore encounter excessive tonus (hypertonus) and often hypertrophy and shortened muscle. In view of the intimate contact with the narvus ischiadicus the nervous filaments are irritated.
It is either due to the pressure of the hypertrophic muscle or the situation when the nerve passes at least partly through the muscle and a traction neuropathy develops. It results to ischialgia which belongs to the low back pain group.
Several clinical tests used in practice include the FAIR text (flexion, adduction, internal rotation), which stretches the muscle and in case of increased or provoked ischialgia it is evaluated as positive. In our study we paid attention to the correlation of the FAIR results with MRI finding.
Our cohort included 25 patients with chronic ischialgia, 11 men and 14 women with normal clinical neurological findings. We excluded root lesion S1, discopathy L5/S1, rheumatological or infectious disease and a pathology of the hip joint.
After a clinical examination the patients were examined on the MRI projection to the area of m. piriformis. In 11 out of the 25 patients examined by NRI we found compression of n. ischiadicus (ischiadic nerve) in foramen infrapiriforme, compression the nerve in passing the muscle in four, no sign of irritation of the nerve in other four patients and other kinds of pathology in six.
The results indicated high sensitivity of the GFSAIR test in diagnostics of irritation of n. ischiadicus in the region of foramen infrapiriforme or in passage through the muscle. At the same time the results revealed that without adequate imaging it is impossible to differentiate functional irritation of ischiadic nerve from an irritation by another pathological process.
Therefore, from the point of view of correct diagnostics until the recommendation to make it a part of precise diagnostics.