Femoroacetabular impingement: the past, current controversies and future perspectives

KEYWORDS:

• Hip
• arthroscopy
• femoroacetabular impingement
• sports medicine

Introduction

Femoroacetabular impingement (FAI) is a clinical syndrome in which morphological abnormalities of the femoral head and/or the acetabulum result in an abnormal contact between the femur and acetabulum during normal hip motion, leading to cartilage and/or labral damage and hip pain. It is subdivided into two distinct morphologies: the cam-type wherein there is a reduction in the femoral head–neck offset or the pincer type wherein there is focal or global over-coverage of the acetabulum. There is also mixed-type FAI in which both cam- and pincer-type deformities are seen in the same hip. FAI has gained significant importance in the recent past and the main reason for this is because it has been considered a precursor to osteoarthritis (OA) especially in cam-type impingement, but there is still no conclusive evidence about pincer-type impingement leading to OA [1].

In the United States, the rate of FAI surgery increased sevenfold among newly trained orthopedic surgeons between 2006 and 2010, and this is projected to increase even further [2]. The number of FAI-related publications increased fivefold between 2005 and 2010, showing a recent boom in FAI-related research [3]. Despite the large increase in the number of hip arthroscopies performed on patients with FAI, the optimal diagnostic approach and ideal treatment of FAI remains controversial.

Diagnosis

The clinical presentation of FAI is normally anterior or anterolateral hip/groin pain, which occasionally radiates down the anterior or anterolateral aspect of the thigh. Patients often grasp the affected hip with their hand, demonstrating the classical ‘C-sign’ [4]. The most commonly used test in physical examination is the hip flexion–adduction–internal rotation (FADIR) test, which is used by 74.0–87.9% of surgeons [5]. Because of the high sensitivity (99%; 95% confidence interval (CI): 98–100%) and low specificity (5%; 95% CI: 1–18%) of that test as a diagnostic test for FAI, the use of the FADIR test is recommended only as a screening tool [5]. The other common clinical finding elicited in these patients is the limited internal rotation in 90° of hip flexion. Confirmation of diagnosis is usually achieved in combination with radiographs, computed tomography (CT) scan, and magnetic resonance imaging (MRI). It should be noted that radiographic features of FAI can differ between standing and supine radiographs [6]. The obliquity and tilt of the pelvis vary among patients according to gender, the pattern of activity and body position, and patients often compensate for abnormal morphology with a dynamic alteration in the pelvic tilt [6]. The most commonly used measure is the α-angle – the angle at which the femoral head–neck junction leaves sphericity. An increase in α-angle was reported to correlate with a decrease in range of movement, as well as with the degree of labral/chondral damage [7]. However, surgeons should be aware that the definition of an abnormal α-angle is still controversial and inconsistent; it should always be considered with other parameters because the presence of an abnormal α-angle alone does not mean a decrease in the clearance between the acetabular rim and the femoral head [8]. MRI and MRA are commonly used after initial radiographs. For the diagnosis of labral tears, the sensitivity and specificity of plain MRI were reported to be 66% (95% CI: 59–73%) and 79% (95% CI: 67–91%), respectively [9]. As for magnetic resonance arthrogram (MRA), the sensitivity was 87% (95% CI: 84–90%) and specificity was 64% (95% CI: 54–74%) [9]. Surgeons should evaluate MRI/MRA results carefully because the interobserver reliability of MRA has been found to be too low [10]. A CT scan is very useful for determining proximal femoral morphology and version and also for accurately determining the acetabular version especially in cases of pincer impingement. Most patients with long-standing history also undergo a diagnostic hip injection to confirm the diagnosis. If the pain disappears following the injection of local anesthetic or steroid, it is confirmed that the patient has intra-articular pathology and they may benefit from surgical intervention. However, it should be noted that a positive result after the injection test does not always predict an improvement in short-term functional outcome after surgical intervention, despite the fact that a negative result has been proved to be a strong predictor of a poor postoperative outcome [11].

Treatment

Although high-quality evidence is lacking, short-term improvement in functional outcomes has been reported following open/arthroscopic surgical management of FAI. However, because the relationship between FAI and hip OA is still evolving, current literature does not show any benefit of prophylactic surgical interventions in the asymptomatic population who have radiological signs of FAI [12]. Once a patient is diagnosed with FAI, nonoperative management including rest, activity modification, physiotherapy, and intake of non-steroidal anti-inflammatory drugs are generally prescribed. Wall et al. reported that conservative treatment of FAI might benefit patients, but no specific duration of time for this approach before proceeding to surgery has been agreed upon [13]. In some cases, patients with symptomatic FAI and labral pathology undertake intra-articular injection as a therapy aiming to avoid surgery; however, this is reported to have very limited clinical benefits as a therapeutic modality in the longer term [14].

Two large-scale clinical trials, FAIT and FASHION, are currently active in the U.K. to determine the difference between surgical intervention and physical therapy in patients with FAI. Early results of both presented at the recent British Hip Society meeting in March 2018 show that surgery performs better than physical therapy in the shorter term for patients with FAI. In another recent randomised controlled trial (RCT), Mansell et al. reported that there was no significant difference in clinical outcomes including Hip Outcome Score between patients undergoing hip arthroscopy and those undergoing supervised physical therapy at 2 years [15]. Therefore, more work in this arena is certainly warranted.

Surgical treatment of FAI has been divided into open surgical dislocation, arthroscopy and arthroscopy-assisted surgery combined with mini-open techniques. Open approaches remain an effective tool for correction of intra- and extra-articular deformity. Almost the same functional outcome scores in patients undergoing open dislocation and those with arthroscopic treatment were reported; however, in health-related quality of life scores, the arthroscopy group tends to show greater improvements postoperatively [16]. It should also be kept in mind that the minimally invasive arthroscopic approach may not safely address conditions such as cam-type deformities with considerable posterolateral extension, deficient acetabular coverage, protrusio acetabuli, or coxa profunda [17]. The labrum plays an important role with regard to hip stability through the suction-seal effect, as well as protecting cartilage by distributing the mechanical load. Labrum repair was reported to be associated with significant improvement in the modified Harris Hip Score in comparison with labral debridement [18]. There have been several labral repair techniques described, but thus far no definitive evidence exists to support any particular method of repair, and no significant improvement in one technique over another has been reported using an objective outcome measure [19]. Labral reconstruction is also an option, especially in young patients whose labrum is deficient due to prior debridement or other reasons. However, there has been no strong comparative evidence except large case series and cohort studies addressing labral reconstruction thus far [20].

There is also controversy surrounding routine hip capsular closure after arthroscopic surgery. Routine capsular closure has been reported to decrease the risk of subtle iatrogenic instability [21], but further research is of paramount importance to clarify its effectiveness. It also remains to debate as to how large the capsulotomy should be prior to it requiring regular closure.

Toward the future

How can we predict success after hip arthroscopy for patients with FAI? Severe OA (Grade III and IV) and age over 60 were reported to be related with poor prognosis [22]. Recently, MRI techniques including delayed gadolinium-enhanced MRI of cartilage, T2 mapping, and T1ρ mapping have received great attention from the viewpoint of assessment for cartilage degeneration before arthroscopic surgery. They are mainly expected to identify patients with OA that is not seen on radiographs, for whom surgical intervention may not improve the outcome [23]. Whether surgical intervention can alter the natural history of FAI or not, in terms of prevention or delay OA, is still not clear, and neither is the relationship between hip morphology and future development of OA in young adults [7]. Further long-term prospective studies are needed to clarify the natural course of this interesting abnormal morphology. Smart technologies with regard to motion/gait analysis, computer-assisted surgery, and biomarkers are beginning to be of importance. Gait analysis following hip arthroscopy has been done for a decade now, but the definition of a standardized protocol for kinematic assessment of hip function has not reached a consensus yet. The recent advancement of computer-assisted surgery as a resource for preoperative planning and intraoperative assistance in hip arthroscopy has provided more precise surgical planning and the potential for improved operative results. There have been several studies published describing various technologies which have shown potential for increasing surgical precision in treating FAI; however, they are not without limitations, including a steep learning curve, lack of insight into soft tissue pathology, and restriction only to concentric hips [24]. Serum biochemical markers of cartilage breakdown and inflammation such as C-reactive protein and cartilage oligomeric matrix protein also have potential in the assessment and management of the pre-arthritic hip, but the amount of data currently available about the precise role they have in the setting of FAI is limited [25]. The relationship between genetics and developmental factors and the progression of FAI is also an interesting topic; no specific genes, alleles, or chromosomal loci have yet been proved to be associated with FAI. For example, the difference in the prevalence of certain morphological features between genders may indicate different levels of activity, but it may also suggest genetic involvement [26]. Also, the prevalence and the severity of the cam deformity, as well as the degree of femoral neck anteversion and the diameter of the head of the femur, differs significantly between the Asian and the European Caucasian populations [27]. FAI might increase the risk of injury to joints proximal and distal in the kinetic chain, such as the pelvis and knee [28]; anterior cruciate ligament (ACL) injury is increasingly recognized as being associated with FAI. Clinical and radiological studies have somewhat established a correlation between restricted hip and ACL injury, but have been unable to demonstrate an increased risk of future ACL injury in individuals with restricted hip movement [28]. Also, there was reported to be a high incidence of symptoms of athletic pubalgia in professional athletes with FAI [29]. Alternations in the hip mechanics due to underlying impingement may result in excessive strains to the posterior inguinal wall, resulting in symptomatic athletic pubalgia [29].

Many questions remain with regard to diagnosis and treatments of FAI and further research is required. We can focus on improved understanding of etiology, which may allow earlier screening/identification of symptoms at a younger age to allow earlier treatment. Also, it is important to use judicious patient selection by being aware of known negative prognostic factor (e.g. OA, obesity). The education of general orthopedic surgeons, as well as health-care practitioners, to recognize FAI and refer patients to young adult hip specialists in good time is warranted.

Declaration of interest

The authors have disclosed that they have no significant relationships with or financial interests in any commercial companies related to this study or article. The Physician and Sportsmedicine peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This manuscript was not funded.