Iliopsoas Pathology

Iliopsoas Anatomy and Function

The iliopsoas tendon-muscle complex is composed of the iliacus, psoas major, and psoas minor muscles ( Fig. 82.1 ). The psoas major is a long fusiform muscle that originates on the T12 to L5 vertebrae and intervertebral disks and is innervated by the ventral rami of L1 to L4. The iliacus is a triangular fan-shaped muscle composed of the medial, lateral, and ilioinfratrochanteric bundles ; it originates from the ilium and sacral ala and is innervated by the femoral nerve (L1-L2). The psoas major and iliacus muscles converge at the level of the L5 to S2 vertebrae to form the iliopsoas muscle. Prior to this convergence, the psoas major tendon originates above the level of the inguinal ligament from within the center of the psoas major muscle. As the tendon courses distally, it rotates clockwise (right hip) and migrates posteriorly within the muscle, lying immediately anterior to the hip joint, and inserts on the lesser trochanter ( Fig. 82.2 ). The iliopsoas bursa is positioned between the musculotendinous unit and the bony surfaces of the pelvis and proximal femur. It typically extends from the iliopectineal eminence to the lower portion of the femoral head, with an average length of 5 to 6 cm and width of 3 cm. The psoas minor is a long slender muscle that originates from the vertebral bodies of T12 and L1 and is present in only 60% to 65% of individuals. Distally it merges with the iliac fascia and psoas major tendon, and in 90% of specimens it has a firm bony attachment to the iliopectineal eminence.

Significant variability in the iliopsoas musculotendinous unit has been reported in the literature. In a cadaveric study, Tatu and colleagues reported the presence of two tendinous structures—the psoas major and iliacus. The medial iliacus muscle bundle was shown to insert onto the iliacus tendon, which progressively converges with the larger and more medial psoas major tendon. The lateral muscle bundle of the iliacus courses distally, without any tendinous attachments, and inserts on the anterior surface of the lesser trochanter and infratrochanteric ridge. These findings were corroborated in a study by Guillin and colleagues using ultrasound (US) to map the iliopsoas anatomy. Conversely, in a study utilizing magnetic resonance imaging (MRI) with cadaveric correlation, Polster and coworkers noted the medial iliacus bundle merged directly into the psoas major tendon, whereas the medialmost fibers of the lateral iliacus bundle inserted on a distinct thin intramuscular tendon. Philippon et al. examined 53 fresh frozen cadavers and demonstrated, at the level of the hip joint, the prevalence of a single-, double-, and triple-banded iliopsoas tendon was noted 28.3%, 64.2%, and 7.5% of the time, respectively. However, in the pediatric population, the presence of two distinct tendons was observed in only 21% of patients undergoing MRI. Gómez-Hoyos and coworkers observed a double (psoas and iliacus) tendinous footprint in 70% and a single tendon in 30% of specimens, which inserted on the anteromedial tip of the lesser trochanter, occupying 19% of its total surface. Conversely, in a separate study by Philippon and coworkers, the iliopsoas insertion was described as having an inverted teardrop shape that occupied the entire posterior surface of the lesser trochanter. Although controversy exists regarding the number of tendons, the relative contributions of the different muscle fibers to each tendon, and the location of the insertion point on the lesser trochanter, the current literature challenges historical descriptions of a single common conjoint tendon.

Reports of communication of the iliopsoas bursa with the hip joint through a congenital defect between the iliofemoral and pubofemoral ligaments are also variable. Tatu and colleagues reported no communication in 14 cadaveric dissections; however, others have observed a direct communication between the joint and bursa in 15% of patients. It is important to consider this communication during diagnostic injections, as the anesthetic material can move between the intra-articular and bursal compartments, thus confounding the results of the test.

The iliopsoas unit functions primarily as a powerful hip flexor, but it also has important functions in femoral external rotation and with lateral bending, flexion, and balance of the trunk. The iliacus and psoas major have been shown to have individual and task-specific activation patterns. The iliacus is important for stabilizing the pelvis and for early rapid hip flexion while running. The psoas major is important for sitting in an erect position and for stability of the spine in the frontal plane. Variable contributions of each muscle are observed during situps depending on the angle of hip flexion. The exact function of the psoas minor has not been fully defined, but given its attachment to both the iliac fascia and bony pelvis, it has been hypothesized that it may assist in partially controlling the position and mechanical stability of the underlying iliopsoas as it crosses the femoral head.

Iliopsoas Snapping

Iliopsoas snapping, also known as coxa saltans interna or internal hip snapping, is a disorder characterized by painful audible or palpable snapping of the iliopsoas during hip movement. In 1951, Nunziata and Blumenfled first described the mechanism of internal coxa saltans as snapping of the iliopsoas tendon over the iliopectineal eminence of the pelvis. Since then, dynamic US has been used in several studies to confirm this mechanism as the primary source of iliopsoas snapping. Most studies report a sudden “jerky” movement and audible or palpable snap of the iliopsoas over the iliopectineal eminence as the hip is brought from a position of flexion, abduction, and external rotation (FABER) to extension and neutral. Even so, more recent studies have demonstrated a sudden flipping of the psoas tendon over the iliacus muscle as the source of snapping ( Fig. 82.3A–C ). In these studies, dynamic US revealed that as the hip was placed in the FABER position, the iliacus became interposed between the psoas tendon and the superior pubic rami (see Fig. 82.3A ). As the hip was brought to neutral, part of the medial iliacus muscle became trapped as the tendon follows a reverse path to its original position (see Fig. 82.3B ). The trapped iliacus is suddenly released, resulting in an audible snap of the tendon against the pubic bone (see Fig. 82.3C ). Contrary to the original mechanism described by Nunziata and Blumenfeld, the iliopectineal eminence was medial to the psoas tendon and not involved with the observed snapping phenomenon.

Although abnormal movement of the tendon over the bony pelvis is commonly described as the source of the snapping phenomenon, alternative mechanisms have been proposed. Several studies have proposed that soft tissue abnormalities—such as an accessory iliopsoas tendinous slip, a paralabral cyst, and or stenosing tenosynovitis—are the source of snapping. Other authors have determined the iliopsoas snapping occurs over a bony prominence other than the pelvis, such as the lesser trochanters or femoral head. Overall, the exact mechanism of snapping remains controversial, and the lack of consensus regarding the mechanism supports the possibility of several potential etiologies for iliopsoas snapping.

Iliopsoas Bursitis and Tendonitis

Iliopsoas bursitis and tendonitis have been shown to be closely associated with the repetitive pathologic movement of the tendon observed in symptomatic coxa saltans interna. The irregular movement of the tendon during the snapping phenomenon is thought to cause irritation and inflammation of the underlying bursa. Even so, some studies have demonstrated no objective abnormality of the bursa in patients undergoing open surgery for symptomatic snapping. Nevertheless, these conditions coexist so frequently that Johnson and coworkers suggested they be considered a single entity referred to as “iliopsoas syndrome.” Correspondingly, the diagnostic workup and treatment for these conditions are the same.

Iliopsoas Impingement

Iliopsoas impingement (IPI) is a pathomechanical process whereby an excessively tight iliopsoas tendon impinges upon the underlying acetabular labrum, resulting in labral injury. This phenomenon was first described by Heyworth and colleagues in 2007 in a study (LOE IV) on revision hip arthroscopy; there they noted IPI and corresponding labral injury in 7 of 24 patients. After iliopsoas release at the level of the acetabulum, they noted that the tendon no longer impinged on the anterior labrum during hip extension. Domb and coworkers (LOE IV) further defined the pathophysiology of IPI in a series of patients with direct anterior labral tears at the 3 o'clock position (right hip) in the absence of bony abnormalities. They noted that the labral injury occurred directly beneath the iliopsoas tendon at the iliopsoas notch ( Fig. 82.4 ), which significantly differs from the traditional 1 to 2 o'clock location observed in femoroacetabular impingement (FAI). Pathologic findings at the time of arthroscopy included labral tearing, labral inflammation (referred to as the IPI sign ), or adjacent tendinous inflammation and scarring of the tendon to the anterior capsule. The authors concluded that the labral injury was possibly the result of a tight iliopsoas impinging on the anterior labrum or a repetitive traction injury to the labrum from adherence of the tendon to the adjacent capsulolabral complex. Similar to the observations of Heyworth and colleagues, Domb and coworkers found that releasing the tendon decreased compression on the underlying labrum in all cases. A cadaveric study by Yoshio et al. demonstrated that maximal pressure underneath the iliopsoas tendon occurs at the joint level during hip extension, supporting the possibility that excessive pathologic force from the iliopsoas possibly results in labral injury. Although the exact cause of the excessive tightening of the iliopsoas is unknown, Gómez-Hoyos and colleagues observed that lesser trochanteric retroversion was significantly increased in patients with IPI compared with a control group. The authors postulated that because the iliopsoas tendon makes an obtuse angle as it crosses over the iliopectineal eminence, increasing retroversion of the lesser trochanter may elevate contact pressures underneath the tendon and contribute to impingement of the iliopsoas on the labrum.

History

Physical Exam

Iliopsoas Snapping

Physical examination should include a complete musculoskeletal evaluation of the hip and focused specialty tests specific for the suspected diagnosis. The “active iliopsoas snapping test” is the most commonly described examination maneuver for detecting internal hip snapping. This test is performed by having the patient actively move the hip from the FABER position to extension and neutral ( Fig. 82.5A–C ). The examiner's hand should be placed on the groin to palpate the iliopsoas snapping, which typically occurs with the hip between 30 and 45 degrees of flexion. Iliopsoas strength is assessed by resisted hip flexion with the patient in the sitting position, which may result in groin pain but does not usually recreate snapping. Localized swelling of the inguinal region has been reported in up to 59% of patients with painful internal snapping. Diagnostic US-guided injections of the iliopsoas bursa are useful in the evaluation of iliopsoas snapping ( Fig. 82.6 ). A pre- and postinjection examination can be performed to determine whether the patient experiences pain relief; if so, it supports the diagnosis of painful snapping.

It is important also to evaluate patients for external snapping of the iliotibial band (ITB) over the greater trochanter, which may present in a similar manner to iliopsoas snapping. Patients often report a sensation of the hip dislocating during the snapping event. The examination is the most efficient way to distinguish between internal and external hip snapping. Our preferred exam technique—the “bicycle test”—for determining the presence of external hip snapping is performed by having the patient actively cycle the affected extremity from flexion to extension while lying in the lateral decubitus position ( Fig. 82.7A and B ). A palpable snap or clunk over the greater trochanter is confirmatory for this diagnosis.

Imaging

Although iliopsoas snapping is typically diagnosed with a thorough history and physical exam, imaging studies can be valuable for confirming the diagnosis and identifying concomitant hip pathology. Radiographic evaluation should begin with anteroposterior (AP) radiographs of the pelvis and lateral hip to rule out acute or chronic osseous abnormalities and evaluate for radiographic signs of FAI. In cases where the source of snapping is uncertain, dynamic US can be used to visualize the iliopsoas tendon or ITB during provocative maneuvers such as the active iliopsoas snapping and bicycle tests. US is also useful in identifying joint effusions and synovitis, rectus femoris tendinopathy, and iliopsoas bursitis and tendonitis. In addition to also being able to detect iliopsoas tendinitis and bursitis, MRI is useful in diagnosing associated chondral and labral pathology, which is present in 67% to 100% of patients presenting with painful iliopsoas snapping. MRI can determine the pathologic reason for snapping in up to 100% of patients. For patients with suspected IPI, plain film x-rays may show signs of FAI ; however, the most pertinent radiographic finding is a labral tear at or near the 3 o'clock position as seen on MRI.