Athletic injuries to the hip flexors and iliopsoas have been described in populations across all levels of competitive sports. Overall estimates of hip flexor pathology have ranged from 5% to 28% of injuries among high-risk sport specific groups. Although most of these injuries are successfully treated with conservative management, and high rates of return to play are observed, significant rehabilitation time can be involved. As the understanding of hip pathology with imaging modalities such as MRI has advanced, greater importance has been placed on accurately diagnosing hip flexor injuries and initiating rehabilitation protocols early to minimize time loss from sport.
Key points
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Hip flexor anatomy is intricate and relies on combination of history, physical examination, and advanced imaging for early and accurate diagnosis.
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Most hip flexor injuries can be treated conservatively; however, operative indications exist for those who fail conservative therapy alone.
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Most hip flexor injuries result in minimal time loss from sport, despite a relatively high incidence in athletic populations.
Introduction
Athletic injuries to the hip flexors and iliopsoas have been described in populations across all levels of competitive sports. Overall estimates of hip flexor pathology in the literature have ranged from 5% of injuries all the way to 28% of injuries among high-risk sport-specific groups. Although most of these injuries are successfully treated with conservative management, and high rates of return to play are observed, significant rehabilitation time can be involved. , As understanding of hip pathology with imaging modalities such as MRI has advanced, greater importance has been placed on accurately diagnosing hip flexor injuries and initiating rehabilitation protocols early to minimize time loss from sport and maximize long-term function.
Anatomy of the hip flexors
In order to accurately diagnose and treat hip flexor injuries in athletes, it is critical to understand their anatomy and function. The hip flexors consist of 6 key muscles that contribute to hip flexion: iliacus, psoas major, psoas minor, pectineus, rectus femoris, and sartorius. The iliacus is a triangular muscle arising from the wing of the ilium and inserting on the lateral psoas tendon and lesser trochanter of the femur. , The psoas major originates from the transverse processes and vertebral margins of T12-L5 and merges at the L5-S2 level with the iliacus to travel beneath the inguinal ligament and form the iliopsoas. The psoas minor is a normal anatomic variant present in approximately 60% of people. , It originates from the T12 to L1 vertebral bodies, lies anterior to the psoas major, and inserts into the iliopectineal eminence. The iliacus and psoas muscles are often grouped together as the iliopsoas musculotendinous unit secondary to overlapping function and anatomic proximity. The action of this group is to flex the femur at the hip joint and provide secondary lateral flexion to the lower vertebrae. In addition, these muscles contribute to postural stability while standing erect and elevating the torso from a supine position. The iliopsoas has an associated bursa that is the largest bursa in the body and lies between the iliopsoas and the hip capsule/pubis. The psoas major and iliacus are innervated by the L2-L3 nerve roots of the femoral nerve, while the psoas minor is supplied by L1 alone.
The rectus femoris acts as a hip flexor with 2 distinct anatomic origins—the direct and indirect heads of the rectus. The direct head originates at the anterior inferior iliac spine, and the indirect head originates on the anterior/superior acetabular rim and hip capsule. Distally, it becomes a part of the quadriceps tendon and ultimately inserts on the proximal pole of the patella, providing the primary force for knee extension. The sartorius, the longest muscle in the body, crosses the hip and the knee joints. It originates at the anterior superior iliac spine and inserts superficially on the pes anserinus as a broad fascial insertion. It functions to flex the hip, and secondarily to adduct the thigh and externally rotate the leg. Finally, the pectineus acts as a hip flexor and secondary adductor from its origin on the superior pubic ramus and insertion on the pectineal line of the femur. All 3 of these hip flexors are innervated by branches of the femoral nerve and are supplied by distinct arterial branches off the femoral artery.
Epidemiology of hip flexor injuries
The epidemiology of hip flexor injuries can be challenging to delineate. However, some studies have described incidences at differing levels of athletic competition. Because of the high degree of functional overlap and compact anatomic space, they are often described together as hip flexor injuries and not separated by specific hip flexor muscle pathology. Iliopsoas or rectus femoris injuries may occasionally be specified uniquely, especially with advanced imaging. Another limitation in characterizing these injuries is that they are often grouped with groin injuries to the adductor muscles.
Overall, injuries to the hip have been shown to represent 9.3% of all injuries in high school athletes and 17.3% of all injuries in college athletes. A 2018 study demonstrated that hip and groin injuries occurred at a rate of 53.06 injuries per 100,000 athlete-exposures (AEs) in college athletes. Men’s soccer players have been shown to have the highest rates of hip flexor strains (3.77 injuries per 10,000 AEs). At the professional level, muscle strains are the most common hip injury in National Football League players (59%), and strains of the hip flexors account for 63% of these injuries. Strains of the hip flexors are the second most common college football hip injury (28.55%).
Hip flexor injuries in the athlete
The diagnosis of these injuries can be particularly difficult because of the numerous pain generators surrounding the hip. Pain in this location can be referred from many different structures including the lumbar spine, intra-abdominal organs, genitourinary tract, hip joint, surrounding capsule, ligaments, and crossing muscles and tendons. As mentioned previously, most athletic injuries to the hip flexors are muscle strains in nature. Muscle strains often occur in larger muscles, especially ones that cross multiple joints during an eccentric contraction. Muscle strains and tears most frequently occur at the myotendinous junction, but may also occur in the muscle belly. In the pediatric population, avulsion injuries can occur at the apophysis, especially of the anterior superior and inferior iliac spines, as there is a mismatch in apophyseal strength versus musculotendinous strength. The large iliopsoas bursa can also contribute to bursitis pain in this anatomic region. This article will focus on several of the most common hip flexor injuries in athletes individually.
Iliopsoas Pathologies: Strains, Tears, Tendinosis, and Bursitis
Strains, tears, tendinosis, and bursitis of the iliopsoas muscle can all present similarly. Strains or tears are often the result of overuse or eccentric hip flexion against resistance. Bursitis or tendinosis is caused by overuse of the iliopsoas tendon resulting in friction as the tendon glides over the iliopectineal eminence. The most common symptom of an iliopsoas strain or tear is typically groin or proximal medial thigh pain. These symptoms are exacerbated by actively flexing the hip against resistance. There is also pain with passive extension of the hip by placing the iliopsoas tendon on stretch regardless of knee position. Tenderness over the femoral triangle and swelling may also be appreciated. Rarely a palpable muscle defect maybe noted. Qualitative strength assessment is important but often limited secondary to pain. In addition, the surrounding uninjured muscles may compensate for weakness in the injured muscle. This makes these injuries difficult for the patient to localize and for the physician to assess. It takes an average of 31 to 42 months from the onset of symptoms for a diagnosis to be made in most of these cases. A specific test for iliopsoas injury can be performed by having the patient lie supine and raise his or her heels 15° up from the table. In this position, the only hip flexor active is the iliopsoas.
When an iliopsoas injury is suspected, imaging studies are helpful in making the diagnosis. Plain radiographs are often normal, but can reveal avulsion injuries in the skeletally immature patient. MRI is often the imaging study of choice. Axial images typically give the best view for detailed evaluation; however, the muscle and tendon can be appreciated on sagittal and coronal images as well. Magnetic resonance is sensitive enough to detect other less common pathologies within the iliopsoas, including myositis ossificans or an acute hematoma. Tendinosis presents on MRI as attenuation of the tendon along its course or even at the insertion site on the lesser trochanter, and it is best appreciated on an axial image. High-intensity signal on T2 weighted images ischaracteristic. , MRI has been shown to be an accurate method of detecting iliopsoas bursitis also. The bursa can be appreciated as an elongated fluid collection medial and posterior to the iliopsoas muscle. It will appear hypointense on T1 and hyperintense on T2 weighted images. If enlarged, it may displace the muscle laterally and can sometimes extend into the pelvis. Distinct tears of the muscle can be visualized on axial, coronal, or sagittal images and are associated with edema around the muscle and a defect with attenuation.
Treatment of iliopsoas injuries is typically conservative in nature, initially with rest, stretching, strengthening, physical therapy, oral anti-inflammatory drugs, and possibly ultrasound-guided injection therapy. There is sparse literature evaluating specific therapy regimens for iliopsoas bursitis and tendinosis. Some centers have attempted to develop specific treatment protocols, but data are limited and mostly anecdotal. There have not been any randomized studies evaluating conservative management of iliopsoas bursitis, tendinopathy, or strains/tears.
Corticosteroid injections may have a role in treatment of these pathologies. Studies are limited to case reports and small series. Vaccaro demonstrated good results in 7 of 8 patients who underwent bursal injections with up to 2 years of symptomatic relief. However, 4 of these patients ultimately underwent surgery. Further studies comparing injection versus physical therapy alone are warranted prior to definitive recommendations.
Surgical management of iliopsoas strains/tears or tendinosis is not usually indicated unless patients have persistent disabling symptoms despite an adequate trial of conservative therapy. Patients who have persistent symptoms of iliopsoas pain greater than 6 months who have failed conservative measures may be surgical candidates. Most often, surgery involves the release of the iliopsoas tendon from its insertion on the lesser trochanter and can be performed open or endoscopically ( Fig. 1 ). Symptom alleviation and return to play data for high-level athletes are limited after this surgical procedure; however, recreational athletes seem to have high rates of return to play.
Coxa Sultans Interna (Internal Snapping Hip)
Internal snapping hip is a cause of groin pain in athletes that presents often with pain and a snapping sensation that can be perceived or audible. The snapping is often appreciated with activity, especially with hip flexion while running. Snapping hip syndrome can be broken down into external, internal, or intra-articular. An external snapping hip is caused by the iliotibial band snapping over the greater trochanter. An intra-articular snapping hip is caused by loose bodies, labral tears, synovial chondromatosis, synovial folds, or fracture fragments. An internal snapping hip, also known as coxa sultans interna, is caused by the iliopsoas snapping over the iliopectineal eminence or the femoral head. Specifically, it occurs when the hip extends and the tendon travels from an anterolateral to a posteromedial position. An internal snapping hip is often associated with chronic iliopsoas bursitis, likely caused by the motion of the tendon irritating the underlying bursa. The ideal imaging modality to appreciate the snapping hip is a dynamic ultrasound. It allows the physician to visualize the pathology and correlate this with the patient’s symptoms. The iliopsoas tendon is visualized under ultrasound with the patient supine and the hip moved from external rotation and slight flexion/abduction to extension and adduction. In addition, diagnostic injections can be utilized at the time of imaging. Bursography can also be performed, which allows visualization of the movement of the tendon, although this is less common.
Treatment begins with conservative management. This consists of activity modification and physical therapy for stretching, especially if the patient has decreased hip extension. Previous studies have demonstrated success with conservative management with specific stretching routines. Injection therapy with corticosteroids may also have a role, but evidence is limited to case reports and small series. , , Wahl and colleagues reported a 4-week return to play in 2 high-level athletes who underwent corticosteroid ultrasound-guided injection for an internal snapping hip, with long-term resolution at 26 months.
Surgical management may be considered if the patient fails 3 months of conservative management. There are 2 methods of surgical management, surgical release of the iliopsoas tendon , or lengthening of the tendon. , , , Endoscopic surgical release has been described in several studies with good results; however, some of the studies are confounded by simultaneous intra-articular arthroscopy for concomitant pathology or transcapsular release ( Fig. 2 ). Ilizaliturri reported on 6 patients who underwent this procedure and had complete symptom resolution but loss of hip flexion. Contreras and colleagues reported similar results with no residual hip snapping in 7 patients. Other literature has demonstrated good results with complete return of strength at 3 months. Byrd evaluated 9 patients who underwent endoscopic release from the lesser trochanter and reported 100% success; however, more than half of the patients had concomitant intra-articular hip pathology. In a second study, Ilizaturri compared 2locations of release, at the level of the capsule versus at the lesser trochanter, and found no difference.
