On the other hand, pincer-type impingement is defined as an overcoverage of the anterior acetabulum, which with motion leads to abnormal contact between the acetabular rim and a normal femoral head and neck which leads to labral damage and eventually chondral damage. It is more typical of middle-aged women who participate in athletic activities. This type of impingement can derive from conditions such as coxa profunda or acetabular retroversion [4, 28, 29]. Labral damage is initially low; however with repeated contact, degenerative changes ensue with ganglion formation and rim ossification which in turn lead to further deepening of the acetabulum and worsening of the overcoverage. The levering of the femoral neck on the rim will lead to contact between the head and the posteroinferior acetabulum creating a countercoup lesion [12, 30].

These are a variety of disorders which cause pain in the nonarthritic young patient especially in athletes.

Psoas impingement is first described by Heyworth in 2007 [31]. It is characterized by labral tears in the anterior region (3 o’clock position) of the acetabulum which is not typical of FAI. He noticed that by releasing the iliopsoas tendon, there would be an impingement-free range of motion. As supported by further studies, a tight iliopsoas tendon is responsible for anterior labrum tears.

Subspine impingement occurs between a prominent anteroinferior iliac spine (AIIS) and the femoral neck with extreme flexion [32, 33]. This prominence is associated with AIIS avulsion injuries which consolidated in inferior position.

Ischiofemoral impingement occurs because of a narrowing of the ischiofemoral space [34] with resultant impingement of the lesser trochanter on the ischial tuberosity.

Greater trochanteric pelvic impingement (GTPI) is generally a sequela of Perthes disease and takes place in extremes of abduction [35]^.

Other dynamic causes of hip pain which must be considered when dealing with young adults with hip pain include true acetabular retroversion in which the anterior wall of the acetabulum is prominent while the posterior is shallow creating an anterior impingement in flexion, femoral retroversion which diminishes internal rotation [35, 36], and femoral varus which results in GTPI.

These conditions must be taken into account when dealing with the young adult with complains of hip pain once the treatment may be quite different.

It is difficult to establish the true epidemiology of FAI. In fact, it is difficult, in the arthritic population, to distinguish pre-arthritic changes that might have led to arthritis from those secondary to arthritis itself. In fact, even in the young, there are many asymptomatic people who exhibit morphological abnormalities associated with FAI. Reichenbach et al. [37] reported on asymptomatic military recruits with a mean age of 19.9 years old in whom cam-type deformity is present in 24% of them. The same author, in a different study [38], also showed that the presence of cam deformity in asymptomatic hips was associated with magnetic ressonance imaging (MRI) evidence of labral lesions and herniation pits as well as a decrease in acetabular cartilage width. Hack et al. [39] showed a presence of imaging changes associated with FAI in 14% of asymptomatic people.

Frank et al. [40], in 2015, did a systematic review on prevalence of FAI imaging findings in asymptomatic volunteers. They showed that the cam-type deformity was present in 37% subjects and that the pincer type was present in 67% of subjects even though pincer-type deformity was more heterogeneously defined. The average alpha angle was 54° which is the borderline abnormal. Also, there was a 3:1 ratio in cam-type deformity when comparing athletes with nonathletes.

In particular, the athletic population seems to be particularly at risk of developing imaging characteristics of FAI as well as symptomatic impingement. There has been a great amount of work being done here. Nepple et al. [41] showed that, in the National Football League, players who have been previously evaluated for groin pain have evidenced signs of FAI in 94.3% of the players, most of the times mixed-type impingement. Also, males participating in certain sports activities show a higher probability of osteoarthritis later in life [19, 27]. Siebenrock et al. [42, 43] showed significantly greater prevalence of cam deformity (alpha angle >55) in elite basketball players (89%) compared with controls (9%). Philippon et al. [44] reported on a significantly higher prevalence of cam deformity among hockey players (75%) compared with skiers (42%). Agricola et al. [45] investigated elite football players and found a nonsignificant increase in prevalence of cam-type deformity in football athletes (26%) compared with controls (17%), whereas Johnson [46] did not show statistical difference between football players and control groups in both female and male population. In this way, there is a clear association between participation in sports activities especially basketball, hockey, and other jumping sports and the development of cam-type deformity. These sports might be linked to at-risk positions for stress to the proximal femoral physis [21, 24, 27, 47]. It is suggested that repetitive axial loading (i.e., jumping) or hip flexion (i.e., squatting) can stimulate anterolateral extension of the physis that ultimately results in bony overgrowth of the cam deformity.

Current literature shows a clear increase in prevalence of radiographic signs associated with hip impingement in athletes participating in high-intensity sports in adolescence, namely, cam-type impingement. Cam-type impingement is particularly associated with the development of labral and chondral injuries and the development of early arthritis. However, we cannot say at this time that engaging in sports will increase the likelihood of symptomatic hip disease or arthritis.

As previously stated, FAI imaging abnormalities will not suffice in making the diagnosis and treating the patient because these are very common in the general population. There must be a clear correlation between clinical picture and imaging before initiating the endeavor of treating an athlete suspected of suffering from FAI-related disability.

In order to evaluate the hip, one must be aware that there are many causes of groin pain both arising in the musculoskeletal system and in visceral organs. On the other hand, the athlete should be evaluated for coexisting disease, compensatory disease, or coincidences.

Coexisting diseases are common such as lumbar pathology where pain can be referred to buttocks or trochanteric region or athletic pubalgia with pain referred to the groin area. Athletic pubalgia and intra-articular problems coexist often [48, 49]. Increase pelvic motion puts greater stress in stabilizing structures. Athletic pubalgia is more associated with pain on palpation of the pubic rami, adductor, and rectus abdominis insertions and should not be aggravated by hip range of motion but by coughing or performing sit-ups.

As for compensatory diseases, athletes compensate for their joint disease in overloading surrounding hip structures leading to gluteal fatigue, trochanteric bursitis, and abductor pain or tears. These secondary pathologies have its origin, most of the times intra-articularly.

As for incidental findings, a snapping of the iliopsoas tendon is present in 10% of the population [50], and an asymptomatic one should not be confused with one that causes labral tears or even should not be treated in case of labral tears caused by conditions other than the snapping itself.

Pain in FAI usually begins gradually. Athletes might recall an inciting event, but most of the times there is not one. In one study [51], there was an average of 29.6 months between the onset of symptoms and surgery. Poor flexibility is usually present, but oftentimes it is not a problem because they can be compensated by lumbar or pelvic hyper mobility. Pain is usually located in the groin and radiates to the medial thigh. Athletes can exhibit the C sign of Byrd [52] with the hand cupped around the greater trochanter and gripping the fingers to the groin. Pain is worse with turning, twisting, pivoting, and ascending and descending inclined surfaces. Pain also aggravates with maximal flexion, and extending from this position is also uncomfortable. With advanced degenerative changes, symptoms may become constant. Snapping and clicking are also present in 25% of the patients operated for FAI [51].

Physical examination should begin on the standing position looking for pelvic asymmetry, spinal deformity, or limb length discrepancies. Gait should be evaluated. At least three to four walking strides should be visualized in order to distinguish normal gait from an antalgic one (generally with shorter steps) or a Trendelenburg-type gait because of abductor insufficiency [53]. Also, the patient should perform the single stance test whereby he stands on the affected leg and holds the other leg in about 45° hip flexion and 45° knee flexion. A positive test is a drop or shift on the contralateral pelvis of more than 2 cm.

Much of the exam takes place in the supine position.

Palpation of anterior and lateral structures can be performed as the anterior iliac spines, pubic symphysis, adductor tubercle, inguinal and abdominal regions as well as the trochanteric region.

ROM is evaluated. Internal and external rotations are measured with the hips at 90° of flexion. It can also be performed in the sited position where pelvis is stabilized at the ischial tuberosity. ROM should also be measured in the prone position and thus alter relative contributions of the ligamentous structures – flexion relaxed the iliofemoral ligament, but the main contributor to internal rotation is the ischiofemoral ligament [54]. ROM is dictated by a firm end point or pain.

Several provocative maneuvers can be performed. The dynamic external rotatory impingement test (DEXTRIT) is executed by instructing the patient to hold the contralateral leg eliminating lumbar lordosis and taking the affected leg to 90° and beyond and moving it through an arc of external rotation and abduction. The dynamic internal rotatory impingement test is similar except for the arc which is done in adduction and internal rotation. Both tests are positive with recreation of the patient’s pain. The flexion/abduction/external rotation test (FABER) or Patrick test can elicit lumbar, sacroiliac, or posterior hip pain. The straight leg raise against resistance test (RSLR) also known as the Stinchfield test [55] evaluates flexors of the hip, namely, the iliopsoas and intra-articular problems. The passive supine rotation test (log roll) [52] assesses rotation of both hips noting differences of guarding and laxity. Pain or locking can elicit intra-articular or extra-articular pathology. The flexion/adduction/internal rotation (FADDIR) tests or impingement test [56] can be performed in the supine or lateral position. The affected leg is brought to 90° flexion, adduction, and internal rotation. Again, reproduction of the patient’s pain indicates a positive test.

The lateral exam allows for inspection and palpation of the lateral structures (trochanteric region) as well as posterior iliac spines, iliac wing, and ischial tuberosity. Special tests can be performed as well. In the passive adduction tests, the examiner stands behind the patient and assesses adduction with the knee and hip in extension (contraction of the tensor fascia lata), with the hip in extension and the knee at 45° (contractures of the gluteus tendons), and with the hip in flexion, the knee in flexion, and the shoulders against the table (gluteus maximus contracture).

In the prone position, palpation of the posterior structures is possible, and the femoral neck version can be assessed with the Craig test [55]. The limb is rotated so that the lateral prominence of the greater trochanter is maximal. The angle between the leg (tibia) and a vertical line is indicative of femoral anteversion. ROM can also be assessed as well as contractures of the flexors by passively extending the hip.

Philippon et al. [51] showed that patients operated on by FAI had less mobility in all plains of motion versus the contralateral leg. Flexion was the more affected with a 9° side to side difference. The impingement test was present in 99% of patients. Abnormalities in the FABER test were also noted in 97% of the patients.

However, it must be noted that although most of these tests are quite sensible for hip pathology, their specificity is low. In a systematic review, Tijssen et al. [57] included 21 studies to evaluate their validity. All studies were either level IV or V. Many of the tests were object of previous studies, but results showed there was a lack of diagnostic accuracy. The authors found it difficult to interpret results as the variation of populations was high as well as there was a bias in population selection. In this way there was heterogeneity of results. For instance, the sensitivity of the anterior impingement test’s varied from 0.59 to 0.99 and for the FABER test from 0.41 to 0.97. Also the positive predictive value and negative predictive values obtained are not applicable once the populations studied were at high suspicion of disease or even had labral tears and FAI confirmed and were not the general population. Burgess et al. [58] also concluded that there is too little information to draw a conclusion for clinical practice. Leibold et al. [59] referred that a negative result in the anterior impingement test, the flexion adduction axial compression test, and the Fitzgerald test provided the clinician confidence that labral pathology was absent. There is, however, to date, little evidence pertaining the accuracy and validity of most of the abovementioned tests.

For athletes with suspected FAI, a true AP view of the pelvis and a lateral radiograph of the hip should be obtained. In the AP view, the coccyx should point to the symphysis with a distance of 1–2 cm between them, and obturator foramens should be symmetrical so that there is no rotation or pelvic tilt. It is of the upmost importance to obtain the adequate projection once variations in pelvic tilt can change our ability to ascertain acetabular version and coverage.

In the AP projection, the joint space, impingement, overcoverage, and other bony alterations that can be present are evaluated. Overcoverage of the anterior acetabulum is suggested by the crossover sign (the anterior wall of the acetabulum crosses the posterior wall) (Fig. 20.2) which should be distinguished from global overcoverage and acetabular retroversion indicated by the posterior wall sign (the posterior wall does not reach half of the femoral head).

The sphericity of the femoral head should be evaluated in both the AP view as well as the lateral view which can be the 40° Dunn view or the frog lateral view. Both seem adequate in assessing the cam lesion [60, 61]. Herniation pits can be present at the head and neck junction indicating FAI. X-rays are extremely useful, but they depict a two-dimensional image when we are dealing with three-dimensional deformity.

Computed tomography (CT) scans can be used to further evaluate osseous anatomy at which it is much better than other imaging modalities. CT scans enable visualization of an os acetabulum otherwise not visible on MRI and can determine the degree of joint narrowing. Two-dimensional images obtained by CT scan underestimate the size of the cam lesion once it is necessary to bisect the apex of the lesion. So three-dimensional CT images are best to ascertain the morphology of the lesion both in the acetabulum providing additional information. In this way CT scans provide additional information as to the amount of resection necessary if surgical treatment is planned and for this reason can be an invaluable tool for preoperative planning.

MRI is a necessary exam when dealing with FAI and labral tears. High-resolution small-field images are necessary requiring at least a 1.5 T magnet with surface coils [62]. There is high sensitivity with conventional MRI to detect labral tears, but the ability to detect intra-articular cartilage damage associated with FAI is poor. If labral pathology is present, there is likely articular damage associated. Increased signal on T2-weighted images in anterior acetabulum wall is suggestive of articular damage. Also, increased activity within the herniation pit in the femoral neck may be associated with degenerative disease secondary to cam impingement. A paralabral cyst is pathognomonic for labral pathology, whereas subchondral cysts usually indicate articular pathology (Fig. 20.3a).

Also, MRI can be used to better define the alpha angle. This was first described by Notzli et al. [14] as the angle between a line from the center of the femoral head to the middle of the femoral neck and a second line between the center of the femoral and the point where the contour of the head and neck junction exceeds the radius of the femoral head. An angle over 55° is considered abnormal [17].

MRI can be performed as well with arthrography, whereby intra-articular contrast (gadolinium diethylenetriamine pentaacetate) is injected under fluoroscopy prior to image acquisition. MRI arthrograms (Fig. 20.3b) are very sensitive and specific for detecting labral tears and chondral injuries, but they lack the ability to detect undetached chondral separations [63]. A normal separation between the rim and the labrum can be evident which is different from a tear because its margins are smooth and it lacks the interdigitation of labral tissue. Anterior labral tears are more common.

Magnetic ressonance arthrography (MRA) has disadvantages as contrast injection does not allow for evaluation of effusion and can masquerade signal changes on osseous structures, so, ideally, sequences should be obtained prior and after contrast administration.

MRA also allows injection of a long-lasting anesthetic agent into the joint. The temporary relief of pain is a much important information as to whether the complaints actually come from inside the joint. If there is no pain relief, other causes for pain should be sought, once a poor relief of pain with surgical treatment for FAI can be expected [64]^.

Biochemical T2 mapping and dGEMRIC have been shown to improve accuracy in detecting chondral damage [65–68].

Pain in an athlete with FAI must be taken into consideration cautiously as it can be a sign of progressive articular damage. Many athletes exhibit great tolerance to pain, and this can postpone the awareness of the situation and further aggravate chondral damage.

It is, nonetheless, appropriate to perform a trial of conservative treatment initially, especially if symptoms are mild and stable. This includes activity modification which naturally includes restriction of athletic activities and nonsteroidal anti-inflammatory medications. For instance, squatting, which is part of most weight training programs associated with the majority of sports, can be quite deleterious for hips at risk and should be limited. Physical therapy aimed at improving range of motion and stretching is counterproductive as it exacerbates the impingement phenomenon and can increase symptoms. Initially, treatment should be oriented toward avoiding position which causes symptoms to exacerbate. Movement errors should be addressed afterward. Progressive strengthening in movements that mimic the athletes’ activity is the final goal. This can be attained with several eccentric and concentric exercises. A maintenance program is ensued next, and follow-up prior to sports resuming is advised.

However, because of the high activity level of football athletes and personal ambitions, such treatment regimen usually fails to control symptoms. There is limited data concerning the results of nonsurgical treatment for FAI. Emara et al. [69] reported on 37 patients with cam-type FAI (mild deformity – alpha angle <60°) who were treated conservatively. At 2 years, 11% chose surgical intervention, and another 16% had recurrent symptoms. The 89% patients who chose not to have surgery exhibited an improvement in the mean Harris Hip Score of 19 points. Hunt et al. [70] reported on 17 patients treated conservatively – 6 (35.3%) improved modestly but did not require surgery. Patients who required surgery were more active than the group who did not (p = 0.02). Long-term results of patients treated conservatively are unknown.

Such patients, following conservative treatment, should be monitored closely as continued FAI can further cause damage to the hip joint, and surgery could be warranted.

The ideal candidate for FAI surgery is one who exhibits classical symptoms (activity-related pain in the inguinal region that radiates to the trochanteric region), compatible physical examination (diminished internal rotations, positive provocative maneuvers), and typical radiographic morphology with concomitant labral tear on MRI and who failed conservative treatment and has a positive response to intra-articular anesthetic injection. Most of the times, not all these criteria are met. It is, in our view, imperative to exclude other causes for pain and to have positive response to intra-articular injection test.

The goal with surgical treatment is to address chondrolabral junction pathology as well as bone morphology abnormalities [11].

This can be achieved either through open – surgical dislocation or miniopen – or arthroscopic approaches. Open surgical dislocation was the initial description by Ganz et al. [71], whereas arthroscopic approach has gained recent popularity [72]. Surgical approach can be dictated by patients’ characteristics and surgeon preference.

When dealing with cam-type deformity, the severity of the deformity is usually bigger on the anterosuperior head-neck junction which is easily accessible through arthroscopic approach. If this extends posteriorly to the retinacular vessels, it is not accessible arthroscopically to most surgeons. More complex proximal femur deformities can possibly be more easily corrected by open surgical dislocation.

The type of pincer deformity also dictates approach. Anterior overcoverage can be dealt with arthroscopic techniques. The amount of anterior and lateral resection should be noted preoperatively as not to create a dysplastic acetabulum. True acetabular retroversion which implies posterior undercoverage should be treated by an anteverting periacetabular osteotomy (PAO).