The snapping hip, also known as coxa saltans or dancer’s hip, is defined as an audible or palpable clicking that usually is accompanied by pain during movement of the hip joint. Initially this phenomenon was classified in two main categories, intraarticular and extraarticular. More recently, use of the term “intraarticular snapping hip” has been discontinued because of increasing knowledge of intraarticular hip pathology. Currently snapping hip is divided into internal and external cases, based on whether the snap occurs on the medial or lateral aspect of the thigh, respectively.
Snapping hip was described in the literature in the first third of the last century. This pathology was usually attributed to the iliotibial band until Nunziata and Blumenfeld proposed an alternate etiology—slippage of the psoas tendon over the iliopectineal eminence. During the past 20 years, several reports have attempted to clarify the pathoanatomic features, assessment, and treatment of these hip disorders. Schaberg et al. distinguished “external” from “internal” etiologies, and the term “coxa saltans” was later introduced as a general description encompassing all different types. Occasionally we encounter a patient with painful clicking or popping symptoms without identifiable intraarticular pathology or lesions of the iliopsoas tendon or iliotibial band, known as idiopathic etiologies.
Internal snapping hip is an unusual but potentially debilitating disorder produced by the iliopsoas tendon slipping over underlying bony prominences. It was first recognized and described in 1951 by Nunziata and Blumenfeld in Argentina. The question of whether the iliopsoas tendon snaps over the anterior brim, femoral head, or lesser trochanter is debated. Gruen et al. and Spina have reported that the tight iliopsoas tendon is tethered over the pelvic brim and contributes to the anterior hip and pelvic pain. The snap may be painful and can relate to exercise or sports activity. Snapping of the iliopsoas tendon can be difficult to differentiate from intraarticular pathology because the symptoms may mimic a mechanical intraarticular process and both emanate from deep in the anterior groin (immediately adjacent to the joint).
Snapping of the iliotibial band, or external coxa saltans, is a more evident phenomenon, initially described by Binnie in 1913. Potential causes include snapping of the proximal hamstring tendon over the ischial tuberosity, or more commonly, snapping of the iliotibial band, fascia lata, gluteus maximus, or a combination of the aforementioned over the greater trochanter. Although iliotibial snapping may occur after trauma, symptomatic cases are usually associated with repetitive activities, especially sports. Other possible causes have been reported as iatrogenic processes after surgical procedures that leave the greater trochanter more prominent or in a lateral displacement position after hip arthroplasty, especially when a longer neck is used and a higher offset is created.
Epidemiology
Internal snapping hip occurs in between 5% to 10% of the population, and a significant number of painless cases may be incidental. Iliopsoas tendon snapping may be present as a bilateral disease with progressive unilateral or bilateral pain. Sometimes the patient has a history of trauma, and in some cases it is possible that the asymptomatic snapping was not recognized until it became painful. Patients involved in certain activities, such as ballet, may be at risk for the development of this pathology as an insidious overuse phenomenon.
The frequency of snapping hip syndrome has been reported in up to 90% of elite ballet dancers and with bilateral involvement in 80%. The clinician must be careful to differentiate whether snapping hip is the true cause of groin pain and whether the problem is solely intraarticular, extraarticular, or both.
Pathophysiology
The internal snapping phenomenon occurs as the iliopsoas tendon subluxes from lateral to medial, which typically occurs as the hip moves from flexion, abduction, and external rotation to extension and internal rotation. The structure responsible for transiently impeding the translation of the iliopsoas, thus creating the snapping phenomenon, is a source of continuous controversy. The most popular theories are that the tendon snaps back and forth across the anterior aspect of the femoral head or the capsule or over the pectineal eminence. Other authors believe that an exostosis of the lesser trochanter can be the cause of the snapping.
The external coxa saltans is frequently produced by a band formed by posterior thickening of the iliotibial band and anterior thickening of the gluteus maximus fibers. In hip extension, this band lies posterior to the greater trochanter but snaps over the greater trochanter with flexion. In more severe cases, the phenomenon also may be reproduced with hip rotation. Tightness of the iliotibial band may be an exacerbating feature. The iliotibial band is a long, nonelastic collagen structure that crosses both the hip and knee joints on the lateral thigh. The complex origin and insertion of this structure allows it to be taut during all motions of the hip. Any increase in this tension combined with repetitive motion can result in increased friction over the greater trochanter that may produce irritation and inflammation of the trochanteric bursa, as well as chronic degenerative changes such as fibrosis.
Various biomechanical causes have been proposed to act as predisposing anatomic factors to increase tension, including femoral retroversion or anteversion, internal tibial torsion, excessive foot pronation, and ipsilateral long leg. Another anatomic issue to consider is the wide insertion of the gluteus maximus muscle into the iliotibial tract. The broad coverage and wide area of action of this structure may be responsible for residual snapping, even after surgical release. A case of snapping hip as a result of fibrosis of the band muscle attributed to repeated intramuscular injections has also been reported.
Diagnosis
Clinical Presentation
Patients with internal snapping hip syndrome have chronic symptoms that begin with mildly painful snapping that grows in frequency and intensity over a period of months to years. When this phenomenon is asymptomatic, no treatment is required. Persons with a symptomatic internal snapping hip characteristically describe a painful clicking sensation emanating from deep within the anterior groin. Sometimes the pain may also be found at the ipsilateral flank. Patients can commonly pinpoint the area of pain on the groin and often volunteer to demonstrate the snapping. Surgical treatment is indicated only for symptomatic cases that do not improve with conservative measures.
Most external snapping hips are asymptomatic; however, repetitive motion in sports such as running, dancing, and rowing may also incite inflammation, pain, and disability. The patient will describe a snapping or subluxation type sensation on the lateral aspect of the hip. The iliotibial snapping can be detected with the patient lying on his or her side and then passively flexing and extending the hip. In some cases the snapping phenomenon may be visible under the skin, and in other cases it may be palpated over the area of the greater trochanter by placing the fully extended palm over the area.
A different form of external snapping hip is also described by some patients as the ability to “dislocate the hip,” which is often demonstrated by rotating the affected hip while tilting the pelvis in the standing position. The voluntary “dislocators” are more frequently painless and should only be treated with stretching exercises of the iliotibial band.
Physical Examination
Examination of patients with internal snapping hip reveals medial groin pain centered at or just below the pelvic brim. Physical examination of the internal snapping hip is performed with the patient in the supine position. The affected hip is flexed more than 90 degrees and extended to the neutral position ( Fig. 86-1 ). This maneuver will reproduce the snapping phenomenon at the front of the groin. The snapping phenomenon usually cannot be observed through the skin but often produces an audible snap. Upon palpation, the snapping phenomenon is felt by placing the hand over the affected groin. The examiner can frequently reproduce the painful snapping by abduction and external rotation in flexion and by adduction and internal rotation while extending. Painful snapping with this maneuver is key to the diagnosis. Occasionally the patient can reproduce the snapping phenomenon when walking as the hip goes into extension during the late stance phase of gait. When the snapping is symptomatic, the patient always has an apprehension response when it occurs. Other related findings are the presence of a C sign, a positive log roll test, or a positive impingement; however, those findings are more often associated with intraarticular hip pathology. More than 50% of patients with internal snapping hip have concomitant intraarticular hip pathology.
Symptomatic external snapping hip syndrome is always accompanied with pain in the greater trochanteric region ( Fig. 86-2 ). The pain is a result of greater trochanteric bursitis, inflammation of the iliotibial band itself, or abductor tendon pathology. A positive Ober test may also be found at physical examination ( Fig. 86-3 ). The Trendelenburg gait may be seen in a person with an associated abductor muscle tear or weakness. A pathologic gait may not be present initially but will develop with fatigue of the abductor complex, which can be elicited with a Trendelenburg test ( Fig. 86-4 ). This test consists of asking the patient to perform a single leg stand over periods of 10 seconds with a 10-second increment in each period; if abductor pathology is present, the sign becomes positive within 20 seconds. The test is carried out comparatively.
Imaging
Plain radiographs usually appear normal, although in some cases a femoroacetabular impingement deformity may be documented. Iliopsoas bursography is useful and may document the snapping phenomenon dynamically when combined with fluoroscopy. The main disadvantage of this technique is that it is dependent on the ability of the technician to reproduce the snapping during hip motion within the range of view of the C arm. Ultrasound is becoming increasingly useful as a dynamic noninvasive study that may document pathologic changes with the iliopsoas tendon and bursa, as well as the snapping phenomenon. With use of dynamic ultrasound, slippage of the tendon over bony prominences while the hip is extended may be demonstrated. Iliopsoas ultrasonography also depends on the ability and experience of the examiner. More recently, ultrasonography has also been used to describe new mechanisms of iliopsoas snapping, such as the bifid iliopsoas tendon or snapping of the iliopsoas over the iliacus muscle and snapping of the iliopsoas tendon over paralabral cysts. Conventional magnetic resonance imaging can show tendonitis of the psoas or bursitis in some cases. Magnetic resonance arthrography, however, is the preferred diagnostic study to evaluate persons who have a painful hip with internal snapping, because almost half of the patients with internal snapping hip syndrome have associated intraarticular hip pathology ( Fig. 86-5 ). Magnetic resonance arthrography can show intraarticular pathology in addition to changes related to the iliopsoas tendon and bursa.
Anteroposterior pelvis radiographs should always be performed to identify bony abnormalities, calcifications, or other pathology. Dynamic ultrasonography may document the snapping phenomenon and can also detect associated pathology such as tendonitis, bursitis or muscle tears, and iliopsoas bursitis. Ultrasound can be useful to measure tendon thickness and bursa size. Magnetic resonance imaging is complementary. Axial T1-weighted images best demonstrate thickening of the iliotibial tract or the focal thickening of the anterior edge of the gluteus muscle, and with these images it also is possible to identify secondary atrophy of the remainder of the gluteus maximum muscle.
Treatment
Nonoperative
Treatment of internal hip snapping is initially nonoperative and includes rest, stretching exercises, and use of oral antiinflammatory medications. Steroid injections of the iliopsoas bursa have also been used to treat this problem, with studies demonstrating relief of up to 3 months in 80% of the patients who received an injection. In a series of 30 patients reported by Gruen et al., 19 patients (63%) improved with a 3-month period of stretching of the hip internal and external rotators and eccentric strengthening of the hip flexor and extensors.
In most cases of external snapping hip, nonoperative treatment should be attempted initially. The patient should be educated about which offending activities to avoid, and most patients with symptoms improve with activity modification, stretching, and nonsteroidal antiinflammatory therapy. Formal physical therapy and corticosteroid infiltration of the greater trochanter bursa may also be helpful. Surgery should be considered for persons who do not respond to conservative treatment.
Operative Treatment: Internal Snapping Hip
Surgical treatment of internal snapping hip is reserved for symptomatic patients who do not improve after undergoing conservative treatment. Surgical approaches include open and endoscopic procedures that involve either a release of the iliopsoas tendon or a lengthening of the muscle-tendon unit (MTU).
Evaluation of the surgical anatomy of the iliopsoas tendon is important when performing a release. The level of the release will determine the volume of the tendon that is cut and the resulting volume of the muscle fibers that are not released. In a cross-sectional anatomic study of the iliopsoas tendon, Blomberg et al. reported the average diameter and percentage of tendon and muscle at different levels. Using 20 embalmed cadavers, they measured the diameter of the MTU of the iliopsoas at the level of the labrum and the hip periphery and its insertion on the lesser trochanter. At each one of the described levels, they looked at the percentage of tendon and muscle. They reported that the average circumference of the iliopsoas MTU at the level of the labrum, the hip periphery, and the lesser trochanter was 68.3, 58, and 45.7 mm in diameter, respectively. The MTU consisted of 40% tendon and 60% muscle at the level of the labrum, 53% tendon and 47% muscle at the level of the hip periphery, and 60% tendon and 40% muscle at the level of the lesser trochanter insertion ( Fig. 86-6 ). Based on this information, a more proximal release will leave more muscle tissue intact and have less of an affect on the overall volume of the MTU. In theory, this approach may produce less functional compromise but also could be related to more frequency of recurrence of the snapping phenomenon after release.
