A snapping hip, also referred to as coxa saltans, can be the result of external, internal, and intra-articular causes.1–3 In 1984, Schaberg and colleagues3 first classified the distinction between internal and external snapping hip. External snapping hip is the most common type, and is caused by the posterior iliotibial band or anterior border of the gluteus maximus slipping over the greater trochanter with hip flexion and extension. Intra-articular snapping hip can be caused by various pathologies within the hip joint, such as labral tears, loose bodies, articular cartilage flaps, displaced fracture fragments, or synovial chondromatosis.4,5 Recently, Byrd2 has suggested that the term snapping hip should only be used for extra-articular causes, because various intra-articular pathologies can be identified as causes of these symptoms.
This chapter focuses on internal snapping hip, which refers to a symptom complex most commonly attributed to catching of the iliopsoas tendon when it moves laterally to medially as the hip moves from a flexed, abducted, and externally rotated position to extension and internal rotation (Fig. 8-1).1 In 1951, Nunziata and Blumenfeld6 first described internal snapping tendon in a case series of three patients. Although the exact cause of the snapping remains controversial, it has been most often hypothesized to originate from the movement of the tendon over the anterior femoral head, joint capsule of the hip, or iliopectineal eminence at the pelvic brim.2,7,8 Less commonly, the snapping may be caused by the iliopsoas tendon sliding over exostoses of the lesser trochanter.3 Alternate theories suggest that internal snapping may be caused by the iliopsoas tendon slipping over the iliopsoas bursa—the anterior inferior iliac spine—by stenosing tenosynovitis of the iliopsoas tendon at its insertion into the lesser trochanter, or by movement of the iliofemoral ligament over the anterior femoral head and joint capsule.9 In actuality, it is likely that various patients may have different sources for their snapping. Different surgical approaches have been suggested for treatment based on the specific structure believed to be responsible for the snapping,10 although it is basically a tight iliopsoas musculotendinous unit that most agree is part of the problem.
Internal snapping hip has been estimated to exist incidentally in 5% of the population.2 Although the snapping phenomenon is frequently asymptomatic, in certain individuals it is accompanied by pain. Certain populations, such as ballet dancers and professional athletes, are more prone to painful snapping secondary to overuse.1,5,11,12 In one cross-sectional study, 91% of elite ballerinas reported experiencing snapping hip, with 80% having symptoms bilaterally but only 58% experiencing painful snapping. Clinical examination revealed the vast majority of these to be of the internal snapping type. The incidence of snapping hip has been noted to increase after total hip arthroplasty, often when a curved stem has been used. Usually, this can be classified as an external type of snapping hip, and it is thought to be related to catching of the posterior iliotibial band over the greater trochanter when the femoral component is placed too medially.1 With the advent of surface replacements, and the larger femoral head component, there appears to be an increased incidence of internal snapping hip following this procedure, as compared with a standard total hip arthroplasty, because the iliopsoas snaps over a more prominent acetabular component.
Internal snapping hip pain can manifest as groin pain that radiates to the anteromedial thigh and/or toward the knee. A dull ache after the snapping may be reported, and can last from minutes to hours.13 Rarely, internal snapping hip has been reported to cause pain in the lower back, flank, buttock, or sacroiliac joint.2,14 This type of pain is related to the posterior origins of the psoas (lumbar spine) and iliacus (posterior pelvis). The patient may report a history of painless snapping that has progressed to painful snapping. Internal snapping can occur unilaterally or bilaterally, and patients may or may not report a history of trauma. For internal or external snapping hip, the reported history of trauma is often minor and/or remote, whereas an acute history of significant trauma is often associated with intra-articular pathology. With intra-articular causes for snapping, patients more often report an intermittent clicking rather than a snapping sensation.
During the physical examination, it is critical to assess the patient for other causes of hip pain, including intra-articular causes. The Thomas test should be done to evaluate the patient for a flexion contracture of the iliopsoas or rectus femoris muscles. Patients may exhibit weak external rotation of the hip when it is in flexion and/or weak flexion of the hip while seated. Patients with internal snapping hip may also demonstrate an antalgic gait, most often externally rotated and abducted.5 The patient may also have pain and/or weakness with a resisted straight leg raise with the hip flexed at 15 degrees.
