Piriformis Trigger Points

Introduction – Piriformis Muscle

The piriformis is a flat, oval-shaped muscle that is situated in the gluteal area of the hip and proximal thigh.(1) Between the sacrum and the greater trochanter in the center of the buttocks, this muscle is the largest of six short hip rotator muscles. The piriformis is able to powerfully spin the leg outward due to the leverage provided by the different attachments.(2)

Anatomy

Origin

The muscle origins from multiple locations which includes the anterior surface of the lateral process of the sacrum, the spinal region of the gluteal muscles, and the superior surface of the ilium near the margin of the greater sciatic notch.

Insertion

After it exits the pelvis through the greater sciatic foramen, its tendon joins the tendons of the obturator internus and the inferior and superior gemellus (i.e. the conjoint tendon) before inserting on the superior border of greater trochanter of the femur.(1)(3)

**Figure 1:** Attachments of the right piriformis muscle (red). A, seen from inside the pelvis in midsagittal view showing the attachment of the muscle on the inside of the sacrum, usually between the first four anterior sacral foramina. The fourth foramen is not shown. B, seen from behind (posterior view). In this figure, a relatively small muscle exits the pelvis through a relatively large sciatic foramen. Its rounded tendon attaches laterally to the superior surface of the greater trochanter. The muscle traverses the greater sciatic foramen just above the sacrospinous ligament. Most of the muscle is accessible to external palpation and nearly half of the muscle belly is accessible to palpation inside the pelvis. (Source: Myofascial Pain and Dysfunction- The Trigger Point Manual -Volume 2- The Lower Extremities, Chapter 10, Page 207)

The piriformis muscle divides the greater sciatic foramen into a superior and inferior segment which is used to name the nerves and vessels related.(1)

Action

The primary function of the piriformis is a lateral rotator of the hip and abducting the thigh during the flexion of the hip. It is frequently required in weight-bearing exercises to limit forceful and/or rapid medial thigh rotation, for instance, in the early stance phase of walking and running.

This muscle is also believed to help keep the femoral head in the acetabulum and stabilize the hip joint.(3)

Innervation

Ventral rami of lumbar nerve, L(5) and sacral nerves, S1 and S2.(4)

Trigger Points

For an auxiliary line for localizing trigger points (TrPs), connect the proximal end of the greater trochanter to that point of the sacrum corresponds to the ilium. The upper edge of the piriformis lies approximately on this line:

TrP 1: when you divide the described auxiliary line into thirds, this trigger point lies slightly lateral to the transition from the middle to the lateral third

TrP 2: At the medial end of the auxiliary line. (5)

Satellite trigger points are the gluteus medius and gluteus minimus muscles.(6)

Pain Pattern

Trigger points (TrPs) in the piriformis frequently play a key role in the complex myofascial pain disorders affecting the pelvic and hip areas. It could be challenging to distinguish between additional pain referred from TrPs in the nearby members of this lateral rotator group and pain coming from the piriformis TrPs.(3)

There are two strong zones of pain which includes a 3 to 4 cm zone lateral to coccyx and a 7 to 10 cm zone posterolateral buttock/hip joint. It may also involve a diffuse pain between the two areas and the proximal two-thirds of the posterior thigh.(4)(6)

The piriformis muscle pain has also been described to cause lumbago or low back pain following a sciatic radiation. Additionally, the greater trochanter and the inguinal region pain were noted.(3)

The piriformis syndrome caused by nerve-entrapment pain as the sciatic and other nerves pass through the greater sciatic foramen with the piriformis, has a different origin than the myofascial pain referred by active TrPs in the piriformis muscle.(3)

Perpetuating Factors

It includes prolonged flexing of the thighs with the knees spread (such as during medical procedures), sitting upright after a Cesarean delivery, chronic pelvic infections, arthritis of the hip, low back or hip surgery, sitting all day in one place with the hip flexed, prolonged seated positions in sports (such as rowing or cycling), body asymmetry, Morton’s foot, flat feet, sitting on one leg, sitting with legs crossed, gait irregularities, locked or otherwise dysfunctional sacroiliac joint, sexual activity, repetitive sports (such as running), squat lifts, twisting sideways while bending and lifting a heavy weight (such as stacking firewood or shoveling snow), and even sitting with a fat wallet in a back pocket.(7)

References

Varacallo M. Anatomy , Bony Pelvis and Lower Limb , Piriformis Muscle Anatomy , Bony Pelvis and Lower Limb , Piriformis Muscle. 2018;(December).
Claire Davies AD. The Trigger Point Therapy Workbook- Your Self-Treatment Guide for Pain Relief. 2013.
Travell JG, Simons DG. Myofascial pain and dysfunction, The trigger point manual Volume 2. 1997.
Niel-asher S. The Concise Book of Trigger Points. 2nd editio. 2008.
Richler P, Hebgrn E. Trigger Points and Muscle Chains in Osteopathy. 2009.
Finando D, Finando S. Trigger Point Therapy for Myofascial Pain. 2005.
Starlanyl DJ, Sharkey J. Healing through trigger point therapy – a guide to fibromyalgia, myofascial pain and dysfunction. Vol. 15. 2016.

Dr. Marcus Yu Bin Pai

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MD, PhD. Physical Medicine & Rehabilitation Physician from São Paulo - Brazil. Pain Fellowship in University of São Paulo.