Femoroacetabular Impingement in Athletes

The implication that abnormal hip structure leads to secondary joint damage has been variously described for almost 100 years. However, the concept of femoroacetabular impingement (FAI) as a cause of osteoarthritis is credited to Professor Reinhold Ganz and his colleagues from Bern, Switzerland. Early-onset osteoarthritis among adults in their fourth and fifth decades is often attributed to this process. It is now recognized that FAI can cause serious joint damage among young athletes, even in their second and third decades. As athletes push their bodies beyond physiologic limits, breakdown occurs. Among these athletes with impingement, the threshold for breakdown is much lower and occurs with loads and activities that are tolerated by their counterparts with normal joint structure. Thus severe joint damage is often encountered in these athletes who, if they were less active, would only start to present with findings of osteoarthritis at a later age. FAI refers to the process by which a misshapen hip joint secondarily leads to breakdown of the intraarticular structures causing pain and associated dysfunction, followed by the premature development of osteoarthritis. Three types of FAI have been identified: a pincer type, a cam type, and combined impingement.

Pincer impingement is caused by an excessive prominence of the anterolateral rim of the acetabulum. This condition can occur simply from overgrowth of the anterior edge or as a result of retroversion of the acetabulum, which is a condition in which the face of the acetabulum tilts slightly backward instead of being in its normal forward position. Sometimes a separate piece of bone is found along the anterolateral rim, which is referred to as an os acetabulum . With hip flexion, the prominent rim of the acetabulum crushes the labrum against the femoral neck ( Fig. 84-1 ). This cyclical submaximal repetitive microtrauma leads to breakdown and failure of the acetabular labrum. Secondarily, over time, a variable amount of articular failure within the adjacent acetabulum occurs. Pincer impingement occurs just about equally in males and females and more commonly starts to cause symptoms in middle age.

Cam impingement refers to the cam effect caused by a nonspherical femoral head rotating inside the acetabulum. This condition has long been recognized as a sequela of a slipped capital femoral epiphysis in which posterior displacement of capitis leaves a prominence of the anterior neck, resulting in severely limited internal rotation of the hip. Operations performed to excise this bony prominence have been referred to as a cheilectomy . However, more subtle forms of an aspherical femoral head are much more common and have only more recently been recognized as a cause of problems. This “pistol-grip” deformity is seen in association with early-onset osteoarthritis in adults. It may be due to premature eccentric closure of the capital physis in adolescence, resulting in the nonspherical shape of the femoral head. It has been postulated that intense physical activity at a young age may somehow precipitate this partial physeal arrest and cause the cam lesion. This concept has not yet been substantiated. Thus although cam impingement is clearly a causative factor in joint damage among athletic persons, it is not clear whether athletic activity caused the impingement. With flexion, the nonspherical portion of the head rotates into the acetabulum, creating a shear force on the anterolateral edge of the acetabular articular surface ( Fig. 84-2 ). With repetitive motion, this force eventually results in articular delamination and failure of the acetabular cartilage. Persons with this condition have preferential articular pathology and relative labral preservation. Over time the labrum eventually starts to fail, but only after the process is advanced on the articular surface. Cam impingement has approximately a 3:1 predilection for males and often presents with problems in young adulthood.

Combinations of pincer and cam impingement can occur. The demographics are intermediate between pincer and cam forms. One pattern or the other may predominate, or athletes may have an equal contribution from both, which may have some influence on the optimal method of treatment.

Impingement (or FAI) has gained much attention in the past few years. In the past, this pathologic process simply went undiagnosed. Athletes often experienced poorly explained groin pain that remained an ill-defined, unsolved problem, eventually ending their competitive careers. With growing recognition and treatment, many athletes have been able to resume competitive activities and thus have created more awareness of this disorder. It is important not to neglect findings of impingement, but it is also important not to overtreat all abnormal radiographic findings. We have much to learn about why some athletes with impingement-shaped hips continue to function at high levels for years without experiencing secondary joint damage.

History

The onset of symptoms associated with FAI in athletes is variable, but the damage results from the cumulative effect of cyclical abnormal wear associated with the altered joint structure. The onset may be gradual, but athletes often recount an acute precipitating episode or event, prior to which they were relatively asymptomatic. However, on close questioning, the athlete frequently recalls prior nonspecific symptoms of a groin strain. Also, many athletes who experience pathologic impingement recount that, in their early years, they were never as flexible as other teammates. Although they may demonstrate specific examples of loss of flexibility, it is rarely a functional problem for them. Diminished range of motion is better compensated in the hip than in other joints by increased pelvic and lumbosacral motion. These compensatory pathomechanics create other problems that commonly coexist with FAI such as athletic pubalgia, trochanteric or iliopsoas bursitis, and/or sacroiliac pain.

Hip joint disorders often go undetected for a protracted period. In one study of athletes, 60% were treated for an average of 7 months before it was recognized that the joint could be the source of symptoms. As the athlete attempts to compensate for the damaged joint, he or she may experience symptoms associated with secondary disorders created by compensating for the hip. For example, chronic gluteal discomfort may be present, or lateral pain from trochanteric bursitis and abductor irritability may be experienced. On examination, these secondary findings may be more evident and obscure the underlying element of primary hip dysfunction.

Hip joint symptoms typically emanate from the anterior groin and may radiate to the medial thigh. Athletes often demonstrate the C sign when describing deep interior hip pain ( Fig. 84-3 ); that is, the hand is cupped above the greater trochanter with the fingers gripping into the anterior groin. Mechanical symptoms associated with intraarticular pathology are typically characterized by intermittent sharp stabbing pain or catching. These symptoms are often precipitated by turning, twisting, pivoting, or lateral movement. Maximal flexion is uncomfortable and extension of the flexed hip against resistance, such as rising from a squatted or seated position, may elicit pain. With chronic degeneration, the symptoms may become more constant with activities and less intermittent.

Physical Examination

Physical examination usually elicits evidence of hip joint irritability. However, keep in mind that, as an examiner, you may not create the level of forces across the joint that an athlete can generate with physical activities that precipitate symptoms.

The trademark feature of FAI is diminished internal rotation caused by the altered bony architecture of the joint. However, much variation is found in the normative data on hip range of motion. Also, although only one hip may be symptomatic, the altered structure is usually present in both hips, and there may not be much asymmetry in motion when comparing the symptomatic with the asymptomatic side. Be aware that many athletes may demonstrate reduced internal rotation and still not have pathologic impingement. Also, pathologic impingement may occasionally be observed in athletes with normal or even increased internal rotation.

The log roll test, although not sensitive, is the most specific test for hip joint pathology independent of its etiology ( Fig. 84-4 ). Rolling the leg back and forth rotates only the femoral head in relation to the acetabulum and the capsule, without stressing any of the surrounding structures. Forced flexion, adduction, and internal rotation is called the impingement test in reference to eliciting symptoms associated with impingement ( Fig. 84-5 ). However, virtually any person with an irritable hip, regardless of the etiology, will be uncomfortable with this maneuver. Thus although it is quite sensitive, it is not necessarily specific for impingement. This maneuver may normally be a little uncomfortable, and thus the symptomatic side must be compared with the asymptomatic side. Most important is whether this maneuver recreates the characteristic type of pain that the athlete experiences with activities. Less frequently, posterior impingement may be encountered and is assessed by external rotation of the extended hip ( Fig. 84-6 ).

These conditions often have a chronic component, even at the time of initial evaluation, and thus secondary findings may be present as a result of compensatory mechanisms. Lateral pain may be present from trochanteric bursitis, and posterior tenderness within the gluteal muscles may be present from overfiring in an attempt to splint the joint. These secondary features may be more easily recognized on examination and can obscure the underlying primary joint pathology.

The anterior groin and lower abdominal and adductor area must be carefully palpated to localize tenderness suggestive of athletic pubalgia. This tenderness can mimic or coexist with FAI. Tenderness with resisted sit-ups and hip flexion or adduction should raise an index of suspicion for athletic pubalgia. Pain with passive flexion and internal rotation is more indicative of an intraarticular source.

Snapping of the iliopsoas tendon is assessed by bringing the hip from a flexed, abducted, externally rotated position into extension with internal rotation. Alternatively, the athlete may better demonstrate the audible clunk when taking the hip from a flexed to an extended position. The snapping can be a source of symptoms and warrant treatment, or it may just be an incidental finding. Because it is usually noticeable to the athlete, it is important to assess its contribution to the individual’s symptoms when determining the appropriate treatment algorithm.

Diagnostic Intraarticular Injection

The athlete’s history and examination are the most powerful clinical assessment tools. Beyond that, a diagnostic intraarticular injection with an anesthetic provides the greatest clinical relevance with regard to the presence of hip pathology as a cause of symptoms and disability. Historically, this injection has been performed under fluoroscopic guidance, commonly in association with gadolinium arthrography for magnetic resonance imaging (MRI). The proficiency with which clinicians perform fluoroscopic-guided intraarticular injections can be variable and, if the test causes pain, it may be difficult to reliably assess the response to the anesthetic. Also, anecdotal observations by experienced clinicians have suggested that when the test is performed in conjunction with gadolinium, use of the contrast material may negate the expected response to the anesthetic, resulting in a false-negative interpretation.

More recently, office-based ultrasound injection of the hip has gained some popularity. With training, it is simple to perform and is much easier on the athlete than alternate methods. It is also much more convenient because it can be performed during the course of a normal office visit ( Fig. 84-7 ).

Examining the athlete before and after the injection can provide valuable information. However, most important is the athlete’s subjective sense of pain relief. Sometimes symptoms are provoked only by vigorous activities and cannot be elicited simply by an examiner. Thus it can often be helpful to inject anesthetic into the joint and send the athlete to therapy or a training room to perform activities that would normally precipitate symptoms. For this purpose, it is preferable to use a long-acting anesthetic so the athlete can more reliably assess the level of pain relief that may be too brief with a short-acting anesthetic.

When the history and examination findings are clearly indicative of a joint problem, diagnostic injections are not necessary. However, sometimes the clinical presentation may not be entirely clear or other factors may be contributing to the generation of pain. The response to the injection aids the clinician but, more importantly, may help educate the athlete about which portion of the symptoms is emanating from the joint. This information is important because treatment of the hip may ultimately only be successful at treating part of the symptoms.

Imaging

Radiographs

If an athlete has symptoms troublesome enough to warrant management beyond a couple of training room treatments, then radiographs should be obtained. Radiographs should include a well-centered anteroposterior pelvis view and a lateral view of the affected hip. These views are important for assessing impingement, as well as evaluating joint space preservation and other acute or chronic bony changes. Overcoverage of the anterior acetabulum, characteristic of pincer impingement, is evaluated by the presence of a crossover sign ( Fig. 84-8 ). Overcoverage can be due to acetabular retroversion, indicated by the posterior wall sign ( Fig. 84-9 ) and the prominent ischial spine sign ( Fig. 84-10 ). Global overcoverage may be associated with acetabular profunda ( Fig. 84-11 ) and protrusio ( Fig. 84-12 ), which are commonly accompanied by an excessive center-edge angle. The presence of an os acetabulum can also be evaluated ( Fig. 84-13 ). The etiology and the significance of an os acetabulum are variable, ranging from an unfused apophysis, a traction phenomenon from pull of the rectus femoris origin, or a rim fracture as a result of cam impingement.