Snapping Hip (Coxa Saltans)

Snapping hip, also known as coxa saltans (coxa=hip, saltans=dance/jump), refers to a snapping sensation about the hip on motion. It can be divided into intra-articular and extra-articular. The extra-articular category is further divided into external and internal.

Intra-articular snapping hip can be caused by a torn labrum, chondral defect, or loose bodies. The external type is due to snapping of the posterior iliotibial band or the anterior edge of the gluteus maximus muscle over the greater trochanter.

The internal type thought to occur when the musculotendinous iliopsoas snaps over the femoral head or the anterior capsule of the hip; however, a recent study with dynamic ultrasound suggests that the sudden flipping of the iliopsoas tendon over the iliac muscle is the most common cause of snapping hip. Snapping iliopsoas tendon can also be caused by acetabular dysplasia, as the tendon snaps over the uncovered femoral head. Therefore, hip dysplasia must be ruled out in patients with snapping iliopsoas tendon.

Coxa Saltans Externa

On MRI, patients with external snapping hip demonstrate thickening of the iliotibial tract or focal thickening of the anterior edge of gluteus maximus muscle. There may also be atrophy of the rest of the gluteus maximus muscle.

Coxa Saltans Interna

On MRI, patients with internal snapping hip will demonstrate edema around the iliopsoas tendon. The MRI image shown here shows edema (pink arrows) surrounding the iliopsoas tendon (blue arrow) on axial (A), coronal (B), and sagittal fluid-sensitive images from an MR arthrogram.

References

• Allen WC, Cope R. Coxa Saltans: The Snapping Hip Revisited. J Am Acad Orthop Surg. 1995 Oct;3(5):303-308.
• Deslandes M, Guillin R, Cardinal E, Hobden R, Bureau NJ. The snapping iliopsoas tendon: new mechanisms using dynamic sonography. AJR Am J Roentgenol. 2008 Mar;190(3):576-81.
• Garbuz DS, Masri BA, Haddad F, Duncan CP. Clinical and radiographic assessment of the young adult with symptomatic hip dysplasia. Clin Orthop Relat Res. 2004 Jan;(418):18-22.
• Krishnamurthy G, Connolly BL, Narayanan U, Babyn PS. Imaging findings in external snapping hip syndrome. Pediatr Radiol. 2007 Dec;37(12):1272-4.