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What’s New in Femoroacetabular Impingement Surgery

Context: Femoroacetabular impingement (FAI) has been described as a common cause of hip pain in young adults. This leads to abnormal hip joint mechanics and contact pressures. The associated pathomechanics can lead to the development of early osteoarthritis. Better understanding of the anatomy and pathophysiology, biomechanics, and diagnostic and therapeutic advances has led to improved clinical outcomes. A growing body of evidence has set the foundation for future progress in the treatment of this commonly encountered condition. Evidence Acquisition: The PubMed database was searched for English-language articles pertaining to FAI over the past 15 years (1998-2013). Study Design: Retrospective literature review. Level of Evidence: Level 4. Results: The authors evaluated and discussed the current evidence regarding the anatomy, physiology, biomechanics, imaging, and clinical outcomes of surgical intervention for FAI. Based on this information, future directions for improving the diagnosis and management of FAI are proposed. Conclusion: There remains a diverse approach to the diagnosis and management of cam- and/or pincer-type FAI. Recent advances in clinical diagnosis, imaging, indications, and arthroscopic techniques have led to improved outcomes and have set the foundation for future progress in the management of this condition. Strength of Recommendation Taxonomy (SORT): B

F emoroacetabular impingement (FAI) is a common cause of hip pain in young adults. FAI can be the result of an acetabular-sided "pincer" deformity or a femoral-sided "cam" deformity. Each type of bony abnormality can be seen in isolation or in combination and can lead to FAI. 11,15,17,23 In the past 2 decades, many advances have been made in the recognition and management of this condition that have led to improved patient outcomes. Despite improved outcomes, there remains the opportunity for future advancements. The purpose of this review is to describe the current evidence and future directions of the anatomy and pathophysiology, imaging, biomechanics, clinical decision making, and clinical outcomes of FAI treatment options.

AnAtomy And PAthoPhysiology
Femoroacetabular impingement can result from a cam deformity, 11,13 where there is loss of sphericity of the femoral head, or from a pincer deformity, 11,52 where there is focal or global acetabular overcoverage of the femoral head. There is a sex-related difference, with cam lesions more prevalent in men and acetabular overcoverage more prevalent in women. 13,42,53 Recent studies, however, have demonstrated that such findings are less likely to be seen in isolation. 11,13 Rather, a combination of these pathologies is more commonly present, and failure to identify and treat this can lead to undesirable outcomes. 11,13,42,52,53 What's New in Femoroacetabular Impingement Surgery: Will We Be Better in 2023?
Up to 90% of patients with labral pathology have a morphologic abnormality of the femoral head-neck junction or acetabulum. 13,16,19,23 Asphericity of the femoral head can lead to early contact and shear stresses of the anterior-superior acetabular rim as the hip is brought into flexion and internal rotation. 2,6,7 This can lead to prearthritic pain, early chondral delamination, and associated labral pathology. 8 Similarly, acetabular overcoverage, both focal and global, can cause abnormal impaction at the labrum during hip joint motion, as well as a contrecoup injury to the posteroinferior acetabulum. 23 Bedi et al 8,9 described static and dynamic factors associated with prearthritic hip pain. Static factors include anterior or lateral acetabular undercoverage, femoral anteversion, and femoral valgus. These factors lead to asymmetric joint loading and chondral wear during static activities (ie, stance). 8,9 Dynamic factors include cam-type deformity and acetabular overcoverage. As the hip is dynamically flexed, there is abnormal engagement between the femoral head and acetabulum. This alters the mechanics of the joint and surrounding musculature, leading to pain and early chondrolabral degeneration. 8,9 Dynamic extra-articular impingement factors, including femoral retroversion, femoral varus, trochanteric impingement, and anterior-inferior iliac spine (AIIS) impingement, also occur as the hip is brought into flexion and/or abduction. 8,9 imAging Radiographs Radiographic assessment of FAI, including true anteroposterior pelvis, false-profile, cross-table lateral, frog-leg lateral, and 45° lateral Dunn views, provides useful static evaluation for femoral or acetabular-sided bony lesions. 5,12,58 The ability to extrapolate spherical pathology from 2-dimensional imaging, however, can be difficult. For this reason, multiple radiographic views have been suggested to diagnose cam and pincer deformities. In a comparative study, Nepple et al 48 evaluated the sensitivity and specificity of specific radiographic views in predicting camtype FAI diagnosed by radial-oblique CT reformats (considered gold standard). They found that a complete radiographic series, including an anteroposterior pelvis, 45° lateral Dunn, crosstable lateral, and frog-leg lateral, was 86% to 90% sensitive in detecting abnormal alpha angles on CT. In an evaluation of the alpha angle measured on a cross-table lateral view with the leg in 15° of internal rotation or on the Dunn view, Beaule et al 5 found that patients with an alpha angle greater than 65° had significantly increased risk of cartilage damage.
Radiographic imaging to detect pincer-type deformity can be challenging. For example, alterations in pelvic tilt and rotation can influence interpretations of acetabular pathomorphology; as a result, pincer deformities can be either unrecognized or falsely identified. In a cadaveric assessment of the normal pelvis, Siebenrock et al 55 demonstrated a correlation between pelvic tilt and acetabular version. At 9° of pelvic inclination, all specimens demonstrated positive crossover and posterior wall signs despite a lack of acetabular retroversion. This study exposed the need for standardized techniques in radiographic imaging to account for this variability. Furthermore, in a recent retrospective study, Nepple et al 47 found that coxa profunda, a commonly accepted radiographic finding demonstrating global acetabular overcoverage, should be considered a normal radiographic finding in women.

Computed Tomography and 3-dimensional Modeling
Inaccurate or inconclusive preoperative assessment of plain radiographs can lead to inadequate or excessive resection of presumed lesions contributing to FAI. Failure to adequately address the offending 3-dimensional (3D) deformity causing FAI is the most common reason for failed arthroscopy and need for revision. 29,52 High-resolution CT allows for precise evaluation of osseous morphology about the hip joint ( Figure  1). Three-dimensional modeling is a recent advancement that has demonstrated promise with regard to dynamic hip analysis for preoperative planning (Figure 2). Using a noninvasive 3D CT-based kinematic technique to create a virtual hip model, Kubiak-Langer et al 35 were able to identify the location of impingement and assess the changes in range of motion before and after virtual resection of isolated cam, pincer, or combined lesions. Similarly, Bedi et al 9 performed patient-specific 3D CT modeling of hips with cam and/or pincer deformities. Models were dynamically assessed for location and extent of impingement. The location of impingement was unique in each case and did not correlate with radiographic imaging. Virtual acetabular rim trimming and/or femoral head-neck osteochondroplasty was performed to remove areas of impingement, which improved hip kinematics and range of motion. 9 Dynamic 3D CT modeling may also help decipher deformities that are symptomatic from those that are asymptomatic. Two recent studies demonstrated the prevalence of cam-type deformities in asymptomatic individuals. In an evaluation of 200 asymptomatic volunteers who underwent MRI, Hack et al 26 found a 14% incidence of cam morphology and 10.5% with an elevated alpha angle. Similarly, Jung et al 31 found a 14.3% incidence of cam-type deformity in asymptomatic male patients and a 5.6% incidence in asymptomatic female patients based on abnormal alpha angle measurements on anterior-posterior CT scout images. Although these patients had evidence of bony abnormality on static imaging, dynamic imaging comparison was not performed. 31 In a study comparing patients with symptomatic FAI, asymptomatic patients with 3D CT evidence of FAI, and asymptomatic controls, Audenaert et al 2 demonstrated increasing hip internal rotation among groups, respectively. They found that cam size, acetabular overcoverage, and decreased femoral anteversion all contributed to the loss of internal rotation.
Dynamic 3D CT analysis has also recently shed light on potential extra-articular causes of impingement. In a dynamic CT model of 53 hips of patients with impingement, Hetsroni et al 28 described varying AIIS morphology based on the relationship between the AIIS and the acetabular rim. They demonstrated that a prominent AIIS can lead to "subspine impingement" with loss of hip flexion and internal rotation. Evaluation of contact points also showed varied sites of contact on the femoral neck depending on the relative extent of the prominence. 28 Thus, along with intra-articular evaluation, 3D dynamic CT has tremendous future potential for identifying additional causes and locations of extra-articular impingement, including dysplasia, malunion, and heterotopic ossification. This will allow for a more comprehensive surgical approach in treating patients with FAI.

Magnetic Resonance Imaging
Magnetic resonance imaging is considered the most sensitive and specific modality to diagnose labral pathology and associated bony and soft tissue abnormalities associated with FAI (ie, subchondral cysts, bony edema, capsular thickening, synovitis, paralabral cysts, gluteus medius tendinopathy, adductor longus strain) as well as those independent of FAI (ie, osteonecrosis of the femoral head, bone tumors, synovial chondromatosis). Abnormal head-neck morphology and anterior-superior chondrolabral lesions can been seen in up to 90% of cases of FAI. 32 For the best results, a 1.5-or 3.0-T magnet with a 2-part shoulder coil, small field-of-view wrap coil, or multiple-channel cardiac coil should be used. 25 Axialoblique images oriented along the femoral neck are typically utilized in the evaluation of a cam deformity, labral tears, and partial-and full-thickness cartilage defects. 25 Cartilage delamination is the early result from focal camtype FAI. 25 This is commonly seen at the chondrolabral junction of the anterior-superior acetabulum. It is diagnosed by fluid extravasation deep to the cartilage (Figure 3). Magnetic resonance arthrography, which is typically performed to improve visualization of labral tears, has a 22% sensitivity and 100% specificity in detecting chondral delamination. 1,25 Delamination was most commonly identified on sagittal T1-weighted and proton-density sequences with fat saturation. 1 Recently, delayed gadolinium-enhanced MRI of cartilage  (dGEMRIC) has been used to evaluate proteoglycan depletion to predict early cartilage degeneration. Contrast uptake correlates inversely to the amount of glycosaminoglycan content present. 25 dGEMRIC in symptomatic FAI shows promise for detecting early cartilage degeneration. 1,25 BiomechAnics Abnormal contact resulting from FAI leads to labral damage and a cascade of events resulting in the development of osteoarthritis. Finite element modeling has demonstrated that the absence of a functioning labrum results in an increase (up to 92%) in contact stress of the acetabular cartilage. 21 In addition, the contact area of the femoroacetabular cartilage shifts laterally toward the acetabular rim. Labral tearing and/ or deficiency can lead to instability. 17,18,57 Three-dimensional motion analysis of cadaveric hips with simulated labral tears has shown increased distraction. 18 The altered contact pressures, eccentric loading, and loss of stability that results from labral dysfunction may contribute to the development of osteoarthritis. In a cadaveric study, Smith et al 57 demonstrated that removal of 2 cm or more of the labrum reduced hip stability. In addition, strain in the anteriorsuperior labrum was increased with a circumferential-type tear. 57 In an in vitro biplanar fluoroscopy study, Myers et al 44 demonstrated that the labrum served as a secondary stabilizer to the iliofemoral ligament in limiting external rotation and anterior translation.
The labrum may also contribute to the suction-seal effect of the joint. 17,57 Loss of the suction-seal can lead to subclinical instability and abnormal articular cartilage contact loading. 17,44,57 In a cadaveric study, Cadet et al 17 demonstrated that labral repair results in lower capsular fluid efflux than do partial labral resection and/or iliotibial band autograft reconstruction. Repair, however, was not as effective as the intact labral state.

clinicAl decision mAking
Nonoperative management of symptomatic FAI can help alleviate pain and restore function. 3,15,23 In a prospective observational study of patients with symptomatic prearthritic intra-articular hip disorders, 44% of patients treated conservatively had a satisfactory outcome at 1 year. 30 In comparing the nonoperative versus operative groups, both groups demonstrated improved outcomes without a significant difference. 30 The impact of these nonoperative modalities on the natural history of the development of degenerative osteoarthritis from FAI is not known, largely because there is no consensus at this time on the natural history of asymptomatic and symptomatic FAI.
Intra-articular cortisone injection is often performed to decipher intra-articular from extra-articular pathology. In a retrospective review comparing physical examination, MRI, magnetic resonance arthrography, and intra-articular injection of anesthetic, Byrd and Jones demonstrated that injection was 90% accurate at diagnosing intra-articular pathology. 15 In a retrospective review of patients who underwent injection before arthroscopy, Kivlan et al 34 found that patients with acetabular chondral damage had significant pain relief compared with those without chondral damage. The presence and severity of FAI and labral pathology did not influence the percentage relief from injection. 34 Therefore, in patients with isolated FAI, there is a possibility that they may not obtain significant benefit from injection if there is no associated chondrolabral pathology.
The decision to pursue open versus arthroscopic intervention depends on the pathomorphology as well as surgeon experience. Open surgical dislocation may be the best treatment option for posterior cam deformities or global pincer deformities in the event that appropriate access to the joint cannot be attained through traction only. Studies have demonstrated improved outcomes at midterm follow-up with this technique, including return to play in high-level athletes. 45,46 This technique, however, is technically demanding, with complications including trochanteric nonunion, heterotopic ossification, and avascular necrosis of the femoral head with acetabular retroversion and/or posterior wall insufficiency; open reverse periacetabular osteotomy is effective at reorienting the acetabulum. This is a technically difficult procedure with risk of neurovascular injury, symptomatic hardware, and nonunion. 8 Studies have demonstrated improved pain relief, function, and range of motion when performed effectively. 56 Recent technical advances in hip arthroscopy have enabled surgeons to address osseous and soft tissue pathologies that were once managed by open surgery. In a comparative series, Bedi et al 10 demonstrated that arthroscopic osteochondroplasty has similar efficacy to open surgical dislocation for restoring headneck offset, depth, and arc of resection for anterior and anteriorsuperior cam and focal pincer pathology. Similarly, Buchler et al 12 demonstrated similar efficacy of osseous correction of cam-type deformity between the 2 techniques. Success of arthroscopy, however, depended on surgeon experience. 12 Current limitations of arthroscopy for FAI, including posterior-superior cam and acetabular lesions, may become routinely manageable via arthroscopy and mitigate the morbidity associated with open procedures.

Long-term Follow-up Studies
Unfortunately, there is a paucity of level 1 or 2 data available. In a cohort of 50 consecutive patients with 100% follow-up at 10 years, Byrd and Jones 16 reported improved functional outcome scores in patients who were younger and had a shorter duration of symptoms and a normal center-edge angle.

Investigations Examining Outcomes Following FAI Treatment
With some exceptions, studies examining outcomes for patients undergoing treatment for FAI are mostly limited to smaller patient populations with short-to mid-term follow-up (Table 1). In one of the larger studies on FAI treatment, Larson et al 39 investigated the effect of radiographic arthritis on clinical outcomes in cohorts with FAI only and those with FAI and radiographic osteoarthritis. A total of 210 patients were included and followed for a minimum of 1 year (mean, 27 months). Improvements in Harris Hip Score (HHS), SF-12 (Short Form-12), and visual analog scale (VAS) for pain were greater in the group without osteoarthritis so that those with less than 50% joint space narrowing or more than 2 mm of joint space remaining fared better. Chondral damage noted on MRI and longer duration of preoperative symptoms were associated with worse clinical outcomes. 39 Byrd and Jones 14 studied the results of FAI surgery in athletes, including 23 professional and 56 intercollegiate athletes. A total of 200 patients was followed for a minimum of 1 year, with a majority of patients having cam pathology. There was significant improvement in the modified HHS (to a mean of 96 postoperatively) as compared with preoperative values, and 95% of professional athletes and 85% of intercollegiate athletes were able to return to sports. 14 Philippon et al 51 examined clinical outcomes in 112 patients following arthroscopic treatment for FAI. Mean patient age was 40.6 years, and mean follow-up was 2.3 years. Most patients underwent treatment for mixed (cam and pincer) impingement, 23 underwent osteoplasty only, and 3 had acetabuloplasty alone. The mean modified HSS improved from 58 preoperatively to 84 postoperatively, with 10 patients undergoing total hip arthroplasty at an average of 16 months. The preoperative HHS, joint space greater than 2 mm, and repair of labral pathology rather than debridement were predictors for a more favorable outcome. 51 Malviya et al 41 prospectively followed a cohort of 80 patients (40 professional athletes and 40 recreational athletes) to examine differences in return to sport and activity following arthroscopic treatment for FAI. Compared with preoperative values, there was a 2.6-fold improvement in training time and a 3.2-fold increase in time spent competing in the patients' desired sport 1 year following surgery. Overall, mean time to return to sport was 5.2 months, with professional athletes returning at an average of 4.2 months and recreational athletes at 6.8 months. Professional athletes also returned to their preinjury level of sport at a higher rate than that of recreational athletes at the 1-year mark. 41

Studies Examining Arthroscopic Treatment of Labral Pathology in FAI
When intrasubstance tears of the labrum are present, some favor debridement while others prefer maintaining labral tissue and refixation (Table 2). 22,33,36 Larson et al, 38 in a cohort study of 94 patients undergoing either labral debridement or refixation, showed that postoperative HHS, SF-12, and VAS were all significantly better in the refixation group at a mean follow-up of 42 months. Good to excellent results were noted in 68% of the debridement group versus 92% of the refixation group. 37 Limitations of this investigation include the use of a historical control population.
Schilders et al 54 investigated labral resection versus refixation in 96 patients at a mean 2.4 years postoperatively. HHS in the labral repair group improved from 60 to 94 and from 63 to 89 in the labral resection group. Based on a regression model, the mean benefit of performing labral fixation over resection was 7.3 points on the HHS grading system. 54 Preserving labral tissue when possible seems reasonable because of the sealing function of the labrum; the decision to perform labral debridement/resection versus refixation typically depends on a variety of factors: the type and location of the tear, healing capacity, the size of the labrum, the status of the articular cartilage, and the skill of the surgeon. 33,53 Outcomes following refixation versus debridement/ resection may be more dependent on the status of the labrum at the time of arthroscopy rather than the treatment provided.
When the labrum is not salvageable, some surgeons turn to labral reconstruction. 50 Philippon et al 50 reported clinical results of labral reconstruction using autograft iliotibial band in patients with advanced labral degeneration or labral deficiency. The mean HHS significantly improved preoperatively to postoperatively in the 47 patients, with a mean patient satisfaction score of 8 (scale, 1-10) over the 18-month follow-up. Four patients went on to total hip arthroplasty, with age being a significant independent predictor of patient outcome. 50 In a cohort of 19 patients undergoing labral reconstruction, 3 underwent total hip arthroplasty within the 3 years, and 14 of 16 patients had improved subjective functional scores. 59 Open Versus Arthroscopic Treatment of FAI Treatment of FAI was initially performed through an open surgical dislocation. 23 Treatment for FAI now includes open surgical dislocation, 23 all-arthroscopic, [10][11][12] and combined miniopen and arthroscopic techniques. 40 Comparison between techniques is difficult because of the varying outcome measures.
In a group of patients with FAI, 23 underwent arthroscopy and 15 open dislocation. 60 Ten patients were randomly allocated to a treatment group while the others made their own decision. The arthroscopy group had a significantly better follow-up, up to 1 year postoperatively. Shorter hospital stay and time off work were noted in the arthroscopy group; additionally, there was overcorrection of morphologic abnormalities at the head-neck junction in the arthroscopy group. 60 A systematic review of outcomes and complications of arthroscopic, mini-open, and surgical dislocation techniques showed that all 3 methods were effective in the treatment of FAI. 43 The arthroscopic group had a lower rate of complications (0%-5% major complication rate). 43 The open dislocation group had a relatively high rate of postoperative complications (0%-20% major complication rate), mostly related to trochanteric osteotomy-related issues. 43 The mini-open group had a lower complication rate than the open group (0%-17% major complication rate) but a higher incidence of lateral femoral cutaneous nerve injury versus the arthroscopic group. 43