Sciatic nerve movement in the deep gluteal space during hip rotations maneuvers

Key Points

1. Passive hip internal rotation and contraction of the obturator internus-gemellus complex is associated with ‘crimping’ of the sciatic nerve in the deep gluteal space.
2. Structures other than the piriformis muscle impose mechanical loads on the sciatic nerve in the deep gluteal space.
3. Further research is required to clarify the relevance for deep gluteal pain.

BACKGROUND & OBJECTIVE

The sciatic nerve travels from within the pelvis into the deep gluteal space via the greater sciatic notch. Its pathway is most commonly beneath the piriformis (90%), with the second most common variation being through the piriformis muscle (7%) (1). The nerve then travels over the obturator internus and gemelli complex to exit the deep gluteal space via the ischial tunnel (between the ischium and the femur).

The sciatic nerve can get impinged or irritated by adjacent structures within the deep gluteal space (the ‘space’ beneath the gluteus maximus) which may result in pain at the site of local impingement and in the distribution of the sciatic nerve (true sciatica). The piriformis muscle, however, is only one of a number of structures that may impinge the sciatic nerve in the deep gluteal space, so while ‘piriformis syndrome’ has been grossly over diagnosed, sciatic nerve impingement or irritation in the deep gluteal space does occur and should not be overlooked in the differential diagnosis of buttock pain.

This study explored the relationship between the sciatic nerve and the deep hip external rotators in the deep gluteal space.

The sciatic nerve’s pathway is most commonly beneath the piriformis (90%), with the second most common variation being through the piriformis muscle (7%).

This new paper provides evidence that stretch or contraction of the obturator internus-gemelli complex will create some ‘crimping’ in the sciatic nerve at this level.

METHODS

Sciatic nerve behavior was assessed in 58 healthy volunteers (30 males, mean age 20.4 ± 7.7 years), using real-time ultrasound and MATLAB software to quantify the change in shape of the nerve during hip actions. Participants were positioned in prone with the pelvis stabilized and one knee flexed to 90 degrees.

Sciatic nerve behavior was recorded during 4 actions:

1. Passive hip external rotation
2. Passive hip internal rotation
3. Maximal isometric external rotation
4. Maximal isometric internal rotation.

Force produced during isometric contractions was measured with a dynamometer (“Commander Muscle Tester”).

RESULTS

• During passive internal rotation and during isometric contraction of the external rotators, the sciatic nerve appeared to ‘crimp’ – a curve developed in the nerve at the level of the obturator internus – gemelli complex.

• During passive external rotation and isometric contraction of the internal rotators, the curve along the long axis of the nerve flattened out.

• In the short axis, the sciatic nerve tended to move laterally and forward during passive internal rotation and medially and backwards during passive external rotation.

• Less transverse movement occurred during isometric contractions than during passive through-range hip actions.

LIMITATIONS

• Only healthy individuals were examined in this study.

• The relationship between sciatic nerve motion or aberrant behavior of the nerve at the level of the deep hip external rotators and deep gluteal pain is yet to be determined.

CLINICAL IMPLICATIONS

At this point, the relationship between sciatic nerve motion through the deep gluteal space and pain is unclear, although dynamic ultrasound sciatic nerve assessments are commonly performed by radiologists and ‘adhesiolysis’ procedures performed to try to improve nerve motion and reduce buttock pain (2).

It is important that normal sciatic nerve behavior is established, so that aberrant patterns of motion can be clearly identified and correlations with pain explored. Sciatic nerve motion is most commonly visualized as a longitudinal motion occurring with sagittal plane hip and knee movements (flexion/extension). Longitudinal movements in the order of 1-2cms have been demonstrated at the posterior thigh (3,4) but limited information is available regarding movement of the nerve through the buttock or with other hip actions.

Balius and colleagues have previously demonstrated that the sciatic nerve is normally lightly tethered to the obturator internus tendon (5). This new paper provides evidence that stretch or contraction of the obturator internus-gemelli complex will create some ‘crimping’ in the nerve at this level. This is something to consider in those presenting with deep gluteal pain, but further research is required before firm links can be established.

+STUDY REFERENCE

Balius R, Pujol M, Pérez‐Cuenca D, Morros C, Susin A, Corominas H, Sala-Blanch X (2021) Sciatic nerve movement in the deep gluteal space during hip rotations maneuvers. Clinical Anatomy, 35(4), 482-491.

SUPPORTING REFERENCE

1. Beaton L, Anson B. The relation of the sciatic nerve and of its subdivisions to the piriformis muscle. Anat Rec. 1937;70(1):1-5.
2. Burke C, Walter W, Adler R. Targeted Ultrasound-Guided Perineural Hydrodissection of the Sciatic Nerve for the Treatment of Piriformis Syndrome. Ultrasound Q. 2018;35(2):125-129.
3. Ridehalgh, C, Moore, A, Hough, A. Sciatic nerve excursion during a modified passive straight leg raise test in asymptomatic participants and participants with spinally referred leg pain. Man Ther. 2015; 20(4):564–569.
4. Coppieters MW, Andersen LS, Johansen R, Giskegjerde PK, Høivik M, Vestr, S, Nee RJ. Excursion of the sciatic nerve during nerve mobilization exercises: An in vivo cross-sectional study using dynamic ultrasound imaging. JOSPT. 2015;10(10):731–737.
5. Balius R, Susín A, Morros C, Pujol M, Pérez-Cuenca D, Sala-Blanch X. Gemelli-obturator complex in the deep gluteal space: an anatomic and dynamic study. Skeletal Radiol. 2017;47(6):763-770.