INTRODUCTION
Hip and pelvic injuries in the pediatric and adolescent population are receiving increased attention as youth sports participation grows. Most injuries in young athletes are soft-tissue injuries or apophyseal injuries that heal with supportive treatment. However, it is important to be aware that young athletes are prone to specific injuries of the hip that differ from the adult population. With recent improvements in hip imaging, new surgical techniques to address intraarticular pathology, and new theories on structural predisposition to intraarticular injuries, it is important to recognize pathology early in life that may lead to more significant problems with age.
This article reviews injuries of the hip in young athletes and discusses recent advancements in the evaluation, diagnosis, and treatment of these injuries.
COMMON CAUSES OF HIP PAIN IN THE YOUNG ATHLETE
Apophyseal Injuries
Traumatic injuries in the adult that result in muscle or tendon strains are potentially more serious in pediatric and adolescent patients. There are significant differences between the adult and the skeletally immature patient because the skeletally immature patient has open apophyses that are inherently weak, placing adolescents at risk for avulsion injury (15).
Apophyseal avulsion injuries of the hip and pelvis are common in and unique to adolescents, and their incidence has been on the rise with increased participation in competitive sports. Avulsion injuries commonly occur with indirect trauma that occurs with sudden forceful contraction of muscles. The hip and pelvis are common sites of these injuries in the adolescent and often occur with participation in soccer, gymnastics, football, hockey, and sprinting (11). Essentially any sport involving kicking, rapid acceleration or deceleration, and jumping can result in these injuries. These injuries typically occur in athletes between the ages of 10 and 25 yr. The pelvic and femoral apophyses remain cartilaginous later than other areas in the hip, and are particularly prone to repetitive microtrauma and apophysitis or acute rupture.
Avulsion fractures can occur at the site of attachment of any major muscle. The most common sites of avulsion injury include the anterior superior iliac spine (ASIS) (sartorius), the anterior inferior iliac spine (AIIS) (rectus femoris), and the ischial tuberosity (hamstrings, adductor magnus). Avulsion fractures of the lesser trochanter (iliopsoas) also can occur, although they are less common (15). Acute apophyseal avulsion injuries typically present in the adolescent following strenuous exercise, and patients may report experiencing a "pop." Focal pain, tenderness, and swelling commonly are reported. On examination, patients are directly tender over the site of the avulsion injury, and passive or active stretching of the affected muscle group reproduces their pain.
This diagnosis often can be made on clinical history and examination alone, but plain radiographs of the pelvis and orthogonal views are necessary to evaluate the size of the avulsed fragment as well as evaluating the degree of bony displacement. All adolescents also should have a frog-leg lateral view to rule out slipped capital femoral epiphysis (SCFE) (11). Plain radiographs typically are sufficient to diagnose an avulsion fracture; however, when a fracture is minimally displaced and not visible on plain films, magnetic resonance imaging (MRI) may confirm clinical suspicion.
Surgical intervention in apophyseal avulsion fractures rarely is necessary. Typically indications are bony displacement of greater than 2 cm, persistent symptoms that fail conservative therapy, painful nonunion, and exostosis formation. Some authors feel that any displaced greater trochanter avulsion fractures should be treated operatively due to the significant role of the abductor musculature in both hip mechanics and gait causing functional disability (15,20). While controversy does exist with respect to optimal management of avulsion fractures, typically they are treated conservatively with rest, ice, and protected weight-bearing with crutches. Gentle range of motion and stretching exercises follow an initial period of rest. Strengthening exercises begin with resolution of pain, and patients may return to full activity once they have full strength and are pain-free. Repeat radiographs to confirm bony healing should be obtained.
SLIPPED CAPITAL FEMORAL EPIPHYSIS
SCFE is the most common adolescent hip disorder, with a reported incidence of 10.8 cases per 100,000 children. The incidence rate is approximately four times higher in African-American children, two and one-half times higher in Hispanic children, is more prevalent in males, and is associated with an elevated body mass index (BMI) (18). The peak age of onset is approximately 11 yr of age.
SCFE occurs when the capital femoral epiphysis displaces posteriorly on the femoral neck at the level of the physis. This displacement can be acute with a severe presentation or more chronic with a mild presentation. Traditionally, SCFE has been classified on acuity of symptoms and severity of slip. However, recently more emphasis has been placed on mechanical stability because of its greater prognostic value (15). Those with a stable slip are able to bear weight on the affected leg with or without support, while those with an unstable slip are unable to bear weight. The majority of slips, greater than 90%, are stable (9).
The pathophysiology of SCFE likely is multifactorial and due to both biomechanical and biochemical factors. Retroversion of the femur and increased BMI are thought to subject the physis to greater stress and biochemical factors such as increased growth hormone, hypotestosteronism, hypothyroidism, and hypoestrogenism are thought to weaken the physis (9).
Patients may present with hip, groin, or thigh pain that can be confused as knee pain; however, a painless limp also is a common presentation. On physical examination, they classically have an externally rotated lower extremity and antalgic gait. The most consistent physical finding is limited internal rotation of the affected hip. While limited internal rotation easily is appreciated when the contralateral hip is normal, it is important to remember that SCFE commonly is bilateral, and patients can present with bilateral limited internal rotation (9).
Early diagnosis of SCFE is important to prevent acute and long-term complications. Plain radiographs with both anteroposterior (AP) and frog-leg views should be obtained. The frog-leg lateral view is more sensitive for early slip than the AP view. On the normal AP view, a line drawn along the superior femoral neck (Klein's line) should intersect a portion of the femoral head. In a patient with a SCFE, the line does not intersect the femoral head (Figure). Asymmetric physeal widening or blurring also can be a subtle early change with SCFE. In cases with high clinical suspicion for SCFE but normal radiographs, more advanced imaging with MRI or computed tomography (CT) can be obtained (6).
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Figure: Frog leg views demonstrating Klein's line normal (A) and with slipped capital femoral epiphysis (SCFE) (B).
Possible short-term complications of SCFE include avascular necrosis of the femoral head as well as chondrolysis, while long-term problems include hip dysfunction and osteoarthritis. Patients with a stable slip have a nearly negligible increased risk of osteonecrosis, while patients with an unstable slip have a nearly 50% risk of osteonecrosis (6). SCFE should be treated surgically as soon as it is recognized. The patient should be made nonweight-bearing and immediately referred to an orthopedic surgeon, as early intervention can prevent slip progression and complications (9). Presently, there is little evidence-based literature regarding optimal management of the acute, unstable SCFE. However, the majority of pediatric orthopedic surgeons report using a single threaded screw for fixation, with a minority using three stable screws for fixation. Optimal management of the contralateral hip in a unilateral SCFE remains controversial (15).
Legg-Calve-Perthes Disease
Legg-Calve-Perthes (LCP) is an idiopathic, self-limited condition involving avascular necrosis of the femoral head. It typically presents in boys aged 4 to 8 yr old. The pathogenesis is poorly understood and complex. The natural course involves avascular necrosis of the femoral head, followed by resorption, collapse, and then repair of the capital femoral epiphysis. The natural history of the disease can be quite variable, but outcomes are dependant on the age at which this occurs and can be greatly influenced by intervention (15). Half of those who had childhood LCP disease and did not receive treatment went on to develop osteoarthritis in the fifth decade of life.
LCP disease typically presents as a unilateral painless limp, although it can present with mild pain exacerbated with exercise that refers to the knee. On exam, patients often have decreased internal rotation with abduction and external rotation being the position of comfort.
While etiology of this disease remains unclear, it has been suggested that impairment of the blood supply due to extrinsic compression of the vessels or intravascular occlusion is a cause of LCP. Coagulation abnormalities that can result in a hypercoagulable state such as antithrombin deficiency, protein C or S deficiencies, factor V Leiden mutations, and prothrombin mutations and their possible association with LCP have been investigated. Results from some of these studies have been conflicting; however, more recent larger studies support this hypothesis (25). In a 2010 study by Vosmaer et al. (25) that investigated 169 patients diagnosed with LCP, the incidence of LCP was associated with the presence of the factor V Leiden mutation, prothrombin G20210A mutation, elevated Factor VIII levels, and protein S deficiency. The risk of LCP also increased with a growing number of coagulation abnormalities in boys (25).
With these recent studies demonstrating an association between LCP and mutations that predispose one to hypercoagulability, the question arises as to whether patients should be screened for hypercoagulability. At this time it likely would not change the management of a patient with LCP. It recently has been demonstrated in adults with osteonecrosis of the hip associated with thrombophilia or hypofibrinolysis that treatment with enoxaparin may prevent the progression of primary hip osteonecrosis (10). The authors of the study and other researchers have postulated that the sequences for development of LCP in children and osteonecrosis of the hip in adults are similar. They advocate in future studies investigating whether 3 months of enoxaparin thromboprophylaxis may shorten or even reverse the acute phase of LCP in childhood and reduce the chance of adult onset osteoarthritis. It is possible in the future that anticoagulation in the patients with LCP will result in improved outcome; however, no data advocate this treatment as of now.
There currently are no guidelines on screening for thrombophilia in children who develop LCP. The authors of this review suggest following recommendations from the American Society of Hematology regarding which pediatric patients to test for thrombophilia (22). There are situations in which an inherited defect may influence medical decision-making in pediatric patients; however, these situations are in adolescent-aged children who typically are outside the age range at which LCP presents. For instance, adolescent women considering oral contraceptive pills may benefit from thrombophilia screening. Knowledge of a congenital thrombosis would allow the patient and her physician to discuss the increased risk of thrombosis with estrogen-containing contraception (22). Other populations who may be likely to benefit from thrombophilia screening include adolescents who have had a history of spontaneous thrombosis (22).
In children who are asymptomatic but have a family history of thrombosis, it has been recommended that the decision to perform thrombophilia testing should be made on an individual basis. This decision should be made only after counseling the family regarding the potential benefits and limitations, and the results should be interpreted by a physician experienced in the management of children with thrombosis (24). Identification of a thrombophilia defect in a child may result in increased anxiety, despite the fact that the absolute risk of thrombosis in children is exceedingly low. At the moment, there is very little opportunity for thrombophilia testing to benefit a young child. The incidence of venous thromboembolism in healthy children is extremely low (0.07·100,000-1), so it is unwarranted to consider long-term anticoagulation in an asymptomatic child (22).
Treatment of LCP is highly controversial regarding conservative versus surgical intervention. Primary goals of intervention are maintenance of hip motion, pain relief, and containment. A number of radiological classification systems have been developed that attempt to stratify patients according to the severity of their disease, predict prognosis, and stratify treatment approaches (15). The most commonly used classification systems include the Catterall, Salter Thompson, and Herring (Lateral Pillar). Currently there is a lack of conclusive data within the literature regarding the indications for surgery and its benefits. Because of this, surgical intervention largely reflects the personal preference of the surgeon (15). In general, children who have onset at an earlier age tend to have more time for remodeling and have more favorable outcomes than children who present later.
Stress Fracture
Stress fractures of the hip, pelvis, or sacrum can result in hip or groin pain. While painful, stress fractures of the pelvis and sacrum rarely are associated with significant complications (19). Stress fractures of the femoral neck are a definite concern as they can progress to complete, pathologic fracture and can have significant complications.
Stress fractures can occur anywhere along the length of the femur, although the most common sites are the femoral neck and shaft. The true incidence of stress fractures of the femur is difficulty to determine because of variability in studies and because they are often thought to be underdiagnosed. Stress fractures of the femoral neck may account for up to 11% of stress fractures in athletes. Stress fractures of the femoral shaft previously have been reported with an incidence of approximately 3.5%. Recently it has been reported that stress fractures of the femoral shaft commonly are underdiagnosed, and the incidence of femoral shaft stress fractures may be higher than what has previously been reported, with some studies reporting incidences of approximately 20% (5). Stress fractures of the femoral neck occur more commonly in runners and endurance athletes and have been reported more commonly in female athletes. They have been associated with the female athlete triad of amenorrhea, eating disorders, and premature osteoporosis (11).
Patients often complain of groin or hip pain and may have referred knee pain on the ipsilateral side. Often their pain is most severe when their foot strikes the ground. Patients also may complain of nighttime pain. Many runners and athletes describe a sudden increase in their training regimen or a new form of exercise that stresses the hip.
Physical exam may be entirely normal. Unlike other bones subject to stress fracture that have minimal subcutaneous tissue over them and are easily palpable such as the tibia or metatarsals, the area of maximal tenderness over the proximal femur can be difficult to identify. However, palpation of the groin over the hip joint can reproduce a patient's symptoms from stress fracture of the femoral neck. Pain at the extremes of passive range of motion and axial loading of the hip also may reproduce pain, but the absence of pain does not rule out a stress fracture. Other tests that may be positive include inability to straight leg raise against resistance, Trendelenburg's test, and the "hop test," which is positive when patients complain of pain with hopping or the inability to hop on one foot (5,11). Clinical suspicion for stress fracture even in the absence of positive findings on physical exam necessitates further workup given the potentially serious complications of complete fracture.
Plain radiographs typically are performed to evaluate for stress fracture, although they usually are negative in the early stages of injury. Fewer than 10% of radiographs demonstrate changes consistent with stress fracture within the first week of injury. Even 2 to 3 wk after onset of pain, most patients may not have periosteal changes consistent with stress fracture. Changes initially visible on plain films usually demonstrate early fracture healing with changes of periosteal and endosteal bone formation being greatest at approximately 6 wk.
Over the past 30 yr, bone scans have developed into the gold standard for the identification of stress fractures within 72 h after injury (5). However, the false positive rate of bone scintigraphy for femoral neck stress fractures has been reported as high as 32%, and recently MRI has played a more important role in the diagnosis of stress fractures (2,5). On MRI, stress injury characteristically appears as a diffuse ill-defined hypointense area of T1-weighted images with increased signal on fat suppressed T2-weighted and short tau inversion recovery images (2). Overall MRI can precisely define the anatomic location and extent of injury in femoral stress fracture as well as any soft-tissue conditions. MRI recently has become a more popular diagnostic tool for evaluating stress fractures (5).
Early diagnosis and appropriate treatment of femoral neck stress fractures is imperative, as displaced fractures of the femoral neck can result in nonunion, malunion, osteonecrosis, and arthritic changes. The prognosis for young athletes after femoral neck fractures is particularly poor, with 20% to 86% going on to develop avascular necrosis (5). The majority of the published data on femoral stress fractures is observational and comes from the athletic population and military recruits. Most reports come from case reports and case series in these populations, so the literature is somewhat limited. Most athletes with femoral stress fractures have excellent results with nonoperative treatment consisting of rest. In the literature, rest ranges from bed rest, to nonweight-bearing, to weight-bearing as tolerated. Fracture healing typically takes approximately 6 to 8 wk, and repeat radiographs to assess for bony healing are necessary at follow-up.
Stress fractures of the femoral neck can be classified into three categories: tension, compression, and displaced. Tension stress fractures occurring on the superolateral aspect of the femoral neck are at increased risk for fracture displacement. Compression stress fractures occur on the inferomedial aspect of the femoral neck and have a low risk of displacement. This is an important distinction in management as they have differing likelihoods in going on to become a displaced fracture. Surgical management of stress fractures of the femur is based upon the likelihood of the injury to progress to a complete fracture. This is based on an assessment of each individual patient and each individual injury. Surgical management is considered when there is a failure of nonoperative management, a tension-side femoral neck stress fracture, any displaced stress fracture, malunion or nonunion, or when the hip is judged to be at high risk for displacement (5,17).
In any athlete who is diagnosed with a stress fracture, it is imperative to evaluate possible causes, including training error, nutritional issues, and underlying medical causes of the injury. In the female athlete, it is important to evaluate for the female athletic triad with particular emphasis on a dietary and menstrual history. One must be thoughtful of an underlying metabolic or hormonal disorder that could result in deficiencies of calcium, vitamin D, copper, or magnesium that can affect bone health.
Snapping Hip Syndrome
Snapping hip syndrome occurs when a painful or audible snap is associated with certain movements of the hip and lower extremity. Most commonly, it can be caused by the movement of a thickened iliotibial band, tensor fasciae latae, or gluteus maximus tendon over the greater trochanter or by the iliopsoas tendon passing over the anterior hip capsule, lesser trochanter, femoral head, or iliopectineal eminence. Less commonly, it may be caused by the biceps femoris passing over the ischial tuberosity, the iliofemoral ligament moving over the femoral head, or Iliopsoas bursitis (21). It is important to distinguish these etiologies of painful or audible snapping from other possible causes such as acetabular labral tears, intraarticular loose bodies, and osteochondral fractures.
Athletes with snapping hip typically complain of symptoms lateral to the greater trochanter or in the anterior groin, depending on the origin of the snapping. Symptoms sometimes can be reproduced by moving the affected hip from flexion to extension or by moving the affected hip from a flexed, abducted, and externally rotated position to full extension and internal rotation (21).
Plain radiographs, CT, and MRI of the hip often are normal, but they are helpful to exclude intraarticular pathology as a cause of the patient's symptoms. In the past, radiographic techniques such as bursography or tenography followed by fluoroscopy have been used to document abnormal movement of the Iliopsoas tendon. However these injection techniques are invasive and sometimes difficult to perform. Because of this, sonography has emerged as the preferred technique for evaluating the Iliopsoas tendon. In addition to being noninvasive, sonography has the advantage of both static and dynamic evaluation of the soft tissues around the hip joint (3). Sonography also provides an accurate method for injection of the Iliopsoas bursa.
The prognosis for snapping hip syndrome generally is excellent. Treatment consists of rest, analgesics, and physical therapy. Goals of physical therapy include stretching, regional muscle strengthening, and addressing biomechanical abnormalities. Injections of corticosteroids into the Iliopsoas bursa can be helpful, and ultimately if conservative therapy fails, surgical treatment can be beneficial (3,21).
Femoroacetabular Impingement, Labral Tears, Intra-articular Pathology, and Hip Arthroscopy in the Child and Adolescent
Over the past 20 yr, interest in hip arthroscopy has increased significantly, and over the past 5 to 10 yr, there has been a dramatic increase in the number of hip arthroscopies being performed. This increase has coincided with advancements in hip MRI techniques, as well as the use of MRI arthrogram and our improved understanding of hip disorders such as labral tears and femoroacetabular impingement (7).
Acetabular labral tears recently have garnered increased attention as a cause of hip pain in young athletic patients, and with recent advances in imaging and clinical examination, they have been diagnosed with increasing frequency. Recently, numerous studies have reported an association between labral tears and the early onset of osteoarthritis (1,8). Labral tears have been reported to result from acute hip trauma or injury from acetabular dysplasia; however, recently femoroacetabular impingement (FAI) has been identified as the predominant cause of labral tears in the nondysplastic hip (8).
A number of structural abnormalities in the morphology of the hip can limit range of motion in the hip and result in repeated contact between the femoral neck and the acetabular labrum and its cartilage. Impingement can occur with a decrease in femoral head-neck offset (cam effect), an overgrowth of the bony acetabulum (pincer effect), excessive acetabular retroversion, or a combination of these deformities (1). FAI can result in limited range of motion in the hip, pain, and alterations in the labrum and cartilage that over time now are thought to be associated with early onset osteoarthritis.
As our understanding progresses of how these structural abnormalities lead to degeneration of the labrum and possibly lead to early onset of osteoarthritis in the hip, we must consider labral pathology as an etiology of hip pain in the young athlete. While the prevalence of degenerative tears in the elderly hip is very high, up to 70% in some cadaveric studies, these tears are not considered amenable to repair because of the concomitant arthritis and decreased blood supply to the labrum that limits healing. In the young athlete with a labral tear, the labrum is much more amenable to healing as it has an excellent vascularity (7).
Patients with FAI typically complain of anterolateral hip pain. They often cup the anterolateral hip with the thumb and forefinger in the shape of a "C," often called the "C-Sign" (16). Pain with prolonged sitting or participation in sports also may be a symptom of FAI but could be secondary to a labral tear. Snapping in the hip with or without pain or catching or locking in the hip may be the result of intraarticular pathology including a labral tear, tear of ligamentum teres, or a loose body (7).
The flexion, adduction, and internal rotation (FADIR) test is the most sensitive physical examination test for FAI. Comparison with the contralateral side is prudent as minor discomfort with this test can occur in people without hip joint pathology (16).
Plain radiographs should be performed in patients with a history and physical exam consistent with FAI. A standard AP and lateral view is valuable in evaluating for osteoarthritis, assessing the acetabulum for dysplasia, anteversion, or retroversion, and evaluates the femoral head for osteonecrosis. For any patient with suspected FAI, a modified Dunn view also should be obtained. A modified Dunn view evaluates the hip flexed at 90° and abducted at 20°. The modified Dunn view is more sensitive for detecting cam lesions and osteophytes on the anterior femoral neck (16). To further evaluate the hip for FAI, labral pathology, or loose body and MRI arthrogram, is recommended. Initial imaging studies of the acetabular labrum utilizing MRI without arthrogram were limited in their ability to detect labral tears because of a tendency for the joint capsule to collapse against the acetabular rim (13). These initial MRI studies were only able to detect 25% to 30% of labral tears when done without contrast. MRI arthrography usually is accompanied by a diagnostic injection of bupivicaine. This has the added benefit of serving as diagnostic injection confirming the intraarticular origin of the patient's pain if they get relief of their pain. In one retrospective study it was found that intraarticular injection of the hip with local anesthetic during MRI has a 92% sensitivity, 97% specificity, and 90% accuracy for diagnosis of intraarticular disorder (4). However, recently with the use of new MRI techniques, researchers have reported equivalent if not better results utilizing MRI without arthrography to detect labral and cartilage abnormalities (12). Currently in the literature there is active debate on whether arthrogram is necessary for intraarticular imaging of the hip, although it is likely this depends largely on the techniques being used by the radiologists at different sites.
There are no published studies for nonsurgical treatment of FAI, although a trial of physical therapy for FAI and labral injury prior to surgical referral is reasonable. Conservative treatment goals focus on improving hip muscle flexibility and strength, posture, and sport technique modification (13,16).
With recent advancements in clinical and radiographic diagnosis of intraarticular hip pathology, there has been a recent rise in the application of hip arthroscopy to address these injuries. Most literature on these techniques has been in the adult population, and the literature evaluating surgical outcomes after open and arthroscopic approaches has been limited. The majority of studies are small retrospective case series with only level IV evidence (1). The studies that are available indicate arthroscopic treatment is effective for treatment of labral tears with at least 67% and as many as 100% of patients being satisfied with their outcomes. Patients treated arthroscopically for labral tears and FAI also did well, with as many as 93% of patients being able to return to sports and 78% remaining active at 1.5 yr out from surgery (1). New data currently are emerging regarding the use of arthroscopy for the treatment of FAI in the adolescent athlete (23).
Most of the experience in hip arthroscopy has been with adult hip disorders. While certain conditions now commonly being addressed with arthroscopy such as FAI, labral tears, and loose bodies are both pediatric and adult issues, other pediatric specific conditions are being investigated as possible applications for arthroscopy. Overall, the indications and outcomes for hip arthroscopy have been less well characterized in children and adolescents. Hip arthroscopy in children and adolescents may be efficacious for isolated labral tears, loose bodies, and chondral flaps associated with Legg-Perthes disease, hip dysplasia, or inflammatory arthritis. Possible future applications of hip arthroscopy in the pediatric population include treatment of various hip dysplasias, inflammatory arthritis, avascular necrosis, and ligamentum teres tears (23). However, further development of hip arthroscopy in children and adolescents is necessary to refine indications, evaluate longer-term results, and develop pediatric-specific instrumentation (14,23).
Other Causes of Pain
It is important for the clinician to keep in mind that there are other disorders that can cause pain, which are not reviewed in depth in this article. One must consider other possible diagnoses such as hip dislocation, hip fracture, rheumatoid arthritis, septic arthritis, nerve entrapment, intraabdominal disorders, genitourinary disorders, lumbar spine disease, inguinal hernia, and sports hernia.
CONCLUSION
There is a wide array of afflictions that can result in hip pain in the young athlete. Many of these disorders are unique to the pediatric and adolescent population and require special consideration with regard to diagnosis and treatment. The primary care sports medicine physician should be aware of the injuries both common and specific to this population. As youth sports participation increases, it is likely we will see an increase in the number of pediatric and adolescents complaining of hip pain. Our diagnostic and surgical techniques to address hip pathology in the young athlete likely will improve over time, as will our understanding of the natural progression of degenerative disease of the hip.
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