Discussion

FAI was described by Ganz et al3 as a condition of “abnormal contact that may arise as a result of either abnormal morphological features…or as a result of subjecting the hip to excessive and supraphysiological range of motion”. Sankar et al13 further developed this definition, describing ‘five essential elements’:

• Abnormal morphology of the femur and/or acetabulum;

• Abnormal contact between these two structures;

• Especially vigorous supraphysiological motion that results in such abnormal contact and collision;

• Repetitive motion resulting in the continuous insult;

• The presence of soft-tissue damage.

We felt that these definitions do not sufficiently emphasise patients' symptoms. Ambiguity as to the role of symptoms in making a diagnosis of FAI has led to the introduction of new terms such as ‘asymptomatic FAI’ or ‘radiological FAI’,35–37 apparently to describe hip morphologies rather than a clinical disorder.19 We agreed that this creates confusion when trying to define the clinical disorder.

To make clear the need for symptoms to be present, the panel proposed the new term ‘femoroacetabular impingement syndrome’, or ‘FAI syndrome’.38 We considered other terms, for example, hip impingement syndrome, but preferred FAI syndrome as this did not include extra-articular hip impingement such as ischiofemoral or greater trochanteric impingement. We considered whether ‘syndrome’ might apply a negative label to patients, but the expert patient member of the panel did not feel this would be the case.

We defined FAI syndrome as a triad of symptoms, clinical signs and imaging findings.3 ,13 This term and its definition build on the definitions of FAI from Ganz et al and Sankar et al, but emphasise that symptoms, clinical signs and relevant imaging findings must all be present for diagnosis

To ensure that there is a distinction between patients with FAI syndrome and those with cam or pincer morphology but no clinical disorder, the panel recommends that certain terminology be used while we cease to use other terms that were considered confusing (see table 1).

Discussion

The primary symptom of FAI syndrome is pain.3 However, there is wide variation in the location, nature, radiation, severity and precipitating factors that characterise this pain. Most patients report pain in the groin or hip, but pain is also reported in the lateral hip, anterior thigh, buttock, knee, lower back, lateral and posterior thigh.39 Pain in FAI syndrome is typically motion-related or position-related; we recognised that this encompasses a wide range of patients, from those who experience symptoms during or after vigorous activity (eg, football), to those who have pain with a supraphysiological range of motion (eg, dance, gymnastics), to those who get symptoms despite leading a sedentary lifestyle (seated for long periods).3 ,39 ,40 We agreed that mechanical symptoms, such as clicking, catching, locking, giving way or stiffness are also reported by many patients with FAI syndrome.39

We discussed the common problem of determining whether pain is really arising from the hip joint or from other structures in the groin and hip region. We agreed that image-guided (X-ray or ultrasound) local anaesthetic injections are useful in helping to resolve this situation.41 ,42 Pain relief following a local anaesthetic injection would support a diagnosis of FAI syndrome, when the other diagnostic criteria are met.43

In most patients who seek treatment for FAI syndrome, symptoms are not mild or subtle. They are often severe and limiting in everyday life. The panel felt that this is especially important because patients are usually young, economically active adults. Symptoms of FAI syndrome therefore lead to a significant and lasting cost burden for society as well as being individually debilitating.44

Discussion

We discussed the need for a comprehensive hip and groin examination, as part of the determination of a diagnosis of FAI syndrome.45

Many examination techniques and clinical signs for FAI syndrome have been described, but we agreed that there are several problems. Different clinicians apply and interpret clinical tests differently, with little consistency between professional groups or among peers.45 ,46 Even when tests are well defined, they have often been evaluated in populations with a high likelihood of a positive test,18 so their performance in a different environment (such as primary care) is not known. The most well-known test, the FADIR impingement test, is sensitive (usually positive when FAI syndrome is present), but not specific (often positive when FAI syndrome is not the correct diagnosis).18 The evidence on hip range of motion (ROM) in FAI syndrome is surprisingly contradictory,16 ,47 but the panel felt that on balance FAI syndrome is associated with a restricted hip ROM.

We also recognised that abnormal movement patterns around the hip and pelvis are present in patients with FAI syndrome.47 ,48 These movement patterns, associated with FAI syndrome, may lead to pain or dysfunction in other regions, such as the spine, pelvis, posterior hip or abdominal wall.47 Furthermore, muscles around the hip are frequently weak in patients with FAI syndrome.16

The panel concluded that when FAI syndrome is suspected, it is important to examine gait, single leg control, muscle tenderness around the hip and hip ROM including internal rotation in flexion and the FABER distance (flexion abduction external rotation). Impingement testing should be performed, and to be positive it must reproduce the patient's familiar pain. It is essential to examine the groin for other structures that can produce similar pain.

Discussion

Morphological assessment of the hip is required in order to diagnose FAI syndrome, identifying cam or pincer morphology. Cam morphology refers to a flattening or convexity at the femoral head neck junction.3 Pincer morphology refers to either global or focal overcoverage of the femoral head by the acetabulum.3 The panel emphasised that their presence, in the absence of appropriate symptoms and clinical signs, does not constitute a diagnosis of FAI syndrome. A substantial proportion of people in the general population are thought to have cam or pincer morphology.19 ,49

We agreed that radiological assessment is best achieved initially with plain radiographs. A pelvic radiograph allows an overall assessment of the pelvis and hips, and exclusion of other painful conditions such as fracture, acetabular dysplasia and osteoarthritis. Ideally, this radiograph should be centred on the pubic symphysis, without rotation, and with neutral pelvic tilt.3 ,50 The shape of the acetabulum can be interpreted from this radiograph,51 but visualising the shape of the proximal femur requires an orthogonal view of the femoral neck. A number of such views have been described such as the cross-table lateral, Dunn and frog laterals.52

There are some difficulties in interpreting three-dimensional (3D) shapes from plain radiographs. For example, the spatial orientation of the acetabulum may be affected by the position of the pelvis. Posterior tilt increases in standing position and the parameters that describe anterior and posterior acetabular coverage, which are important in describing pincer morphology, may change.50 ,53 Also, two orthogonal views of the femoral neck may not be sufficient to identify all instances of cam morphology.21 In combination, these radiographs are only moderately sensitive for identifying the typical morphology of FAI syndrome, but are specific.21

We agreed that morphology can be better characterised through cross-sectional imaging, either CT or MRI.21 ,54 This is particularly important if surgery is being considered. MR arthrography is usually more accurate than plain MRI to assess the labrum and articular cartilage.55 ,56 MRI may also identify other soft tissue lesions that may result in hip or groin pain. When performing cross-sectional imaging of the hip in FAI syndrome, limited images of the distal femoral condyles allow assessment of femoral torsion, while 3D reformatting of CT or radial MRI allows assessment of focal morphological abnormalities, particularly of the proximal femur.57

Many radiographic measures of cam and pincer morphology have been described including the α angle (cam), cross-over sign and centre-edge angle (pincer).58–60 Some clinical trials (e.g. UK FASHIoN) of treatments for FAI syndrome have included patients with an α angle >55° at any position on the head neck junction for cam morphology and a positive cross-over sign or a centre edge angle >39° for pincer morphology.14 However α angles cannot accurately discriminate between patients with cam type FAI syndrome and asymptomatic volunteers, despite changes to the threshold value.20

The panel was unable to recommend precise diagnostic values for any of the common measures to define cam or pincer morphology in routine clinical practice. This is because we recognised that impingement is the result of a complex interaction, during motion, between the acetabulum and femoral neck. We agreed that the depth, orientation and rim of the acetabulum, and the head–neck profile, neck angle and torsion of the proximal femur all vary in the general population. It is when a particularly unfavourable combination of these characteristics occur together, along with provocative movement or position, that a patient may present with FAI syndrome. It has not been possible to capture all of this in a single measurement or even a simple set of shape criteria.

Discussion

Treatment strategies for FAI syndrome have included conservative care, rehabilitation and surgery. The panel agreed that each of these may have a role in different patients, but that there is little evidence to compare their effectiveness. Figure 1 is a suggested pathway for the management of FAI syndrome.

There is currently no high-level evidence to support the choice of a definitive treatment for FAI syndrome.22 ,23 For any one patient, the panel agreed that it is appropriate to consider the different treatment options. This is best done in a shared decision-making process, supporting the individual patient to make an informed preference decision on the best treatment option for them.61 ,62 We agreed that those treating FAI syndrome, particularly in secondary and tertiary care, should be part of a multidisciplinary group with knowledge of, and access to, all the treatment options.

Conservative care of patients with FAI syndrome is poorly described but could include patient education, activity and lifestyle modification, oral analgesia including non-steroidal anti-inflammatory drugs, intra-articular steroid injection and watchful waiting.23 There are no reports of what effect such an approach, in isolation, has on the symptoms of FAI syndrome. Similar conservative strategies are recommended in other musculoskeletal disorders such as hip osteoarthritis.63 ,64

Physiotherapist-led rehabilitation aims to reduce patients' symptoms by improving hip stability, neuromuscular control and movement patterns.23 The treatment targets for rehabilitation are wide-ranging and include improving sagittal and frontal plane hip range of motion, hip muscle strengthening and lumbopelvic dissociation.14 ,47 ,48 ,65 However, details of what should be incorporated in such a programme has not been well tested and it would appear that different physiotherapists are delivering different treatments.23

Surgery aims to correct hip morphology to achieve impingement-free motion. Cam morphology can be reshaped and femoral torsion or neck angle adjusted; the acetabulum can be reorientated or its rim trimmed. Where there is damage to the labrum or articular cartilage, this can be resected, repaired or reconstructed. Often, these procedures can be done by either arthroscopic or open surgery.2 ,4 An arthroscopic approach may be preferable in many patients to allow rapid recovery, but some of these procedures will require an open approach. Postoperative physiotherapy protocols have been described but their value is uncertain.66–68

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Figure 1

Pathway for the management of femoroacetabular impingement (FAI) syndrome.

Discussion

The panel agreed that patients with FAI syndrome who are not treated probably experience a gradual deterioration of symptoms.69 We do not know of any reports of the outcomes of conservative care. Physiotherapy-led rehabilitation seems to be associated with an improvement in symptoms for at least 2 years.23 ,70 However, the studies supporting this are only a few observational studies with small sample sizes and important methodological weaknesses.23 Reports of the results of surgery are more numerous and describe significant improvement in symptoms up to 5 years,71 but they suffer similar issues of poor design and therefore high risk of bias.22 Longer term results have been reported for open surgery, including improved symptoms persisting in most patients for at least 10 years.72

All prospective cohort studies available demonstrate an association between cam morphology and osteoarthritis of the hip.73–76 These studies have not found a similar association between pincer morphology and osteoarthritis. We are unable to say whether FAI syndrome is associated with a higher risk of osteoarthritis than isolated cam morphology, but the panel thought it was likely. There is no evidence that treatment for FAI syndrome alters the risk of subsequent osteoarthritis.

Discussion

There is no evidence that treating people who do not have pain, but who do have cam or pincer morphology, will alter the risk of them developing FAI syndrome or osteoarthritis, and so it is rarely indicated to offer surgery to these people. Preventative physiotherapy-led rehabilitation and conditioning strategies may be appropriate in professional athletes where the prevalence of cam morphology is high, such as professional football teams.77 In exceptional circumstances, and in a shared decision-making process with a patient, surgery may occasionally be appropriate for high-risk patients. An example of such a patient could be an active young adult who has had surgery for FAI syndrome in one hip and in whom chondrolabral injury is seen to be developing in the other (painless) hip.78 In such cases, careful consideration must be given to the risks of surgery and its unknown long-term outcome as well as to the uncertain risks of worsening degeneration and the onset of symptoms.

Discussion

The iHOT-12 and iHOT-33, HAGOS, and HOS are valid measures to assess young adults with hip joint pain. We recommend these instruments for use in clinical practice and research.33 ,34 ,79 ,80 For FAI syndrome in particular, iHOT and HAGOS were patient-derived in populations of patients including those treated for FAI syndrome, and so can be expected to perform well in this group. Both have sound psychometric properties including test-retest reliability, responsiveness, content validity, and construct validity.

In addition to the hip-specific outcome measures, general quality of life instruments such as the EQ-5D, SF12/36 or PROMIS are recommended.81–83 These instruments may not be necessary for routine clinical decision-making and assessment of FAI syndrome, but they have a role in facilitating economic analyses and relative comparisons to other conditions and treatments as part of clinical research and health policy development.