Hip Short External Rotator Muscles Injuries

Fig. 18.1

Anterior view of the sacrum with the insertion site of the piriformis muscle

Course: The body of the piriformis is triangular with a medially oriented base. It is disposed transversally, pressed against the ventral surface of the sacrum (Fig. 18.2 and 18.3). At its origin, its fibers are in contact with the roots of the sacral plexus. It leaves the true pelvis through the greater sciatic foramen, thus forming the suprapiriform foramen and the infrapiriform foramen (through which the sciatic nerve usually passes). It then travels transversally and dorsally to the hip joint and inserts into the superior medial surface of the greater trochanter (Fig. 18.4).

Fig. 18.2

Posterior view of the piriformis (1), internal obturator (2), quadratus femoris (3), and superior (4) and inferior gemellus (5) muscles. The piriformis is bounded above by the suprapiriform foramen (6) and below by the infrapiriform foramen (7), through which the sciatic nerve usually passes

Fig. 18.3

MRI anatomy of the short external rotator muscles of the hip. (a) Axial T1-weighted MRI of the piriformis muscle (Pirif.), (b) the internal obturator (IO), (c) and the quadratus femoris muscle (QF) and external obturator (EO), (d) Coronal T1-weighted MRI of all the previous muscles (except the external obturator) but also of the inferior and superior gemellus muscles (IG and SG)

Fig. 18.4

Internal view of the greater trochanter with the insertion sites of the short external rotator muscles

There are numerous anatomical variants around the greater sciatic notch, and these explain some of the impingements with the sciatic nerve and the repercussions of some injuries to it.

Innervation: this muscle is innervated by branches of the sacral plexus (1st and 2nd sacral nerves).

Function: action of external rotation of the leg, but also abduction when the leg is flexed. While walking, it goes through successive phases of contraction and stretching, harmonizing, and synchronizing movement of the sacrum relative to the iliac bone, thus preventing overuse of the sacroiliac joints.

18.2.2 The Quadratus Femoris

Origin: it arises at the lateral surface of the ischial tuberosity of the hip bone (Figs. 18.2 and 18.5).

Fig. 18.5

External view of the coxal bone and the insertion sites of the quadratus femoris muscle (violet), superior (yellow) and inferior (orange) gemellus muscles, and the external obturator muscle (green)

Course: quadrilateral-shaped muscle placed transversely and horizontally (Fig. 18.3).

Insertion: it is inserted into the quadrate tubercle of the intertrochanteric crest (Fig. 18.4).

Innervation: Nerve to the quadratus femoris (collateral of the sacral plexus, S1 and S2).

Action: it is an external rotator and accessory adductor.

18.2.3 The External Obturator

Origin: it arises from the outer surface of the hip bone, on the anterior rim of the obturator foramen and external surface of the obturator membrane (Fig. 18.5).

Course: this triangular muscle has a medially oriented base and passes obliquely by the inferior and then posterior surfaces of the femoral neck, then dorsally in the external obturator groove, which is marked obliquely on the posterior and then postero-supero-external surfaces of the femoral neck (Figs. 18.2, 18.3, and 18.6).

Fig. 18.6

Posterior view of the external obturator muscle

Insertion: it arrives at the trochanteric fossa, where it inserts into the digital fossa (Fig. 18.4).

Innervation: it is innervated by the obturator nerve, the terminal branch of the lumbar plexus.

Action: it is an external rotator and accessory adductor.

18.2.4 The Internal Obturator

Origin: it arises from the internal surface of the hip bone, and more specifically, from the rim of the obturator foramen and the internal surface of the obturator membrane (Figs. 18.2 and 18.3).

Course: the muscle body is triangular with a base oriented medially and ventrally. Its path is first oblique, dorsal and lateral, until it reaches the lesser sciatic foramen, which it crosses, pressing against the lesser sciatic notch, through a bursa. It then changes direction and becomes transversal, passing to the dorsal surface of the hip joint.

Insertion: it inserts into the medial surface of the greater trochanter, in the trochanteric fossa, ventral to the digital fossa (imprinted above the digital fossa) (Fig. 18.4).

Innervation: it is innervated by the nerve to the internal obturator muscle, a collateral branch of the sacral plexus (S1 and S2).

Action: it is an external rotator and accessory abductor of the thigh in a flexed position at the level of the hip joint.

18.2.5 The Gemellus Muscles

There are two: the superior gemellus and the inferior gemellus. They surround the terminal portion of the internal obturator muscle (Figs. 18.2 and 18.3).

Origins: – superior gemellus: ischial spine (Fig. 18.5).

– inferior gemellus: arises at the superior part of the ischial tuberosity, immediately above and outside of the sacrotuberous ligament (also called the great or posterior sacrosciatic ligament) (Fig. 18.5).

Course: each is on opposites sides and a satellite of the internal obturator muscle, following its course outside the pelvis (Figs. 18.2 and 18.3).

Termination: on the terminal tendon of the internal obturator muscle; they do not have their own terminal insertions.

Innervation: superior gemellus muscle: nerve of the internal obturator muscle

inferior gemellus muscle: nerve of the quadratus femoris muscle

Action: identical to that of the internal obturator muscle.

18.3 Traumatic Injuries to the Piriformis Muscle

The piriformis syndrome has been regularly reported in the literature [3, 4] for many years. It results from an impingement of this muscle with the sciatic nerve, when both anatomical structures are normal but also when they are anatomical variants [5]. On the other hand, traumatic injuries of this muscle appear to be reported only sparsely in the literature [6].

18.3.1 Injury Mechanism

The most frequent mechanisms of injury: direct contact or a strong, resisted contraction of the muscle during a movement of sometimes limited amplitude but using a great deal of energy.

internal rotation: repeated sudden movements and/or sudden tensing,
adduction: sudden adduction movement, with the thigh flexed relative to the pelvis.

Traumatic injuries affect the muscle belly, which has a T2-weighted hyperintense signal on MRI (Fig. 18.7) — more or less intense, with more or less substantial disorganization of the muscle fibers depending on the extent of the tears. These images are nonetheless not specific.

Fig. 18.7

A 25-year-old professional rugby player with a traumatic piriformis muscle injury. Axial T2-weighted fat-suppressed MRI at different levels (a–d) of the piriformis muscle (arrows) showing an area of hyperintense focus in the piriformis muscle belly with partial disorganization of the muscle fibers (Reproduced with the permission of Drs Alain Silvestre and Philippe Meyer, Center of Osteoarticular Imaging, Sports Clinic, Mérignac, France)

18.3.2 Traumatizing Activities

Bicycling: the problems are related to the positions cyclists use to try to improve hamstring efficiency (by riding “off the saddle” or “on the nose”). The settings used on the bicycle — especially high gears — can increase constraints on the piriformis. This piriformis pain is associated with pudendal neuralgia in 30 % of cases.

Running: the natural attitude of the legs in medial rotation during forward steps leads to reflex contraction of the pirformis in eccentric work to maintain the leg in neutral rotation. The repetition of this phenomenon at each step can cause overuse and injury.

Asymmetric sports: these require positions in which the leg is in lateral rotation, either repeated or permanent. They lead to overuse of these short external rotator muscles, principally the piriformis (e.g., hockey, tennis, fencing).

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