Femoroacetabular Impingement—Cam, Mixed, and Pincer-Type Treatment Decision-Making

INTRODUCTION

Femoroacetabular impingement (FAI) is an abnormal hip kinematics that can lead to joint damage and pain. The modern concept of FAI was proposed by Professor Reinhold Ganz and was based on observations of intra-articular pattern of joint damage and its association with hip morphology, as seen via the surgical hip dislocation approach. Subsequent work demonstrated femoral retroversion, anterior inferior iliac spine (AIIS), prominent anterior trochanter, and other extra-articular morphology as sources of impingement. Surgical management of FAI started via the surgical dislocation approach, but as arthroscopic techniques developed, they gained popularity. At present, there are a range of surgical techniques available to treat the underlying morphologic cause (Table 11.1). Optimizing the treatment of patients with FAI-related hip pain requires a thorough thoughtful approach to evaluating the sources of impingement to maximize the outcome of nonoperative measures or surgical correction.

Questions that must be answered during the diagnostic evaluation include:

What pathomorphology is the source of FAI?
Can the FAI-related symptoms be managed nonoperatively?
In cases with multiple sources of pain, how much can reasonably be treated by surgical intervention?
What is the safest, most reliable means of addressing the sources of FAI?

TABLE 11.1 Surgical Procedures That Can Be Performed via Surgical Dislocation Vs. Arthroscopic Approaches

Surgical Dislocation	Hip Arthroscopy
Labral debridement, repair, reconstruction	Labral debridement, repair, reconstruction
Cartilage debridement, restoration (microfracture, autologous matrix-induced chondrogenesis, osteoarticular transfers)	Cartilage debridement, restoration (microfracture, autologous matrix-induced chondrogenesis)
Acetabular osteoplasty	Acetabular osteoplasty
Femoral head/neck osteoplasty	Femoral head/neck osteoplasty
Capsular repair/plication	Capsular repair/plication
Femoral neck lengthening
Trochanteric osteoplasty/transfer
Intertrochanteric/subtrochanteric osteotomy

This chapter will delve into the comprehensive evaluation of FAI symptoms and potential treatment options.

CLINICAL EVALUATION

History

A complete history is essential to the accurate diagnosis of FAI-related hip pain. Important topics to address include location and radiation of pain, activities that alleviate or exacerbate the pain, and the presence of mechanical symptoms such as clicking or locking. Most, but not all, patients with intra-articular pain report the anterior groin or C-sign region as the most common area of pain and describe it as a deep ache or stabbing type of pain. FAI-related pain rarely radiates to the lower leg, unlike pathology commonly encountered in the
lumbar spine. Positions of flexion and high-impact activities are typically more bothersome for patients with FAI, and complaints of pain or fatigue with prolonged standing or upright activity could suggest the presence of structural instability. Clicking or locking can be from multiple etiologies, including unstable labral tears, iliopsoas snapping, or capsular pathology. It is also important to get a broader perspective on the impact that hip pain has had on the patient’s functionality and lifestyle. Often, patients will have been managed by other providers, including physical therapists or primary care physicians, and their previous treatments should be identified. Lastly, it is important to clearly identify the patient’s functional goals following treatment, as this may influence the treatment strategy.

Physical Examination

Examination starts with inspection and palpation. Palpation of the greater trochanter can elicit trochanteric bursitis or tendinopathy, which patients often confuse with hip pain. Gait should be evaluated in all patients. A Trendelenburg stance or gait is indicative of gluteal (abductor) dysfunction and may exacerbate the degree of FAI. True abductor tears are rarely encountered in the cohort of young patients undergoing FAI surgery most commonly, but this diagnosis should be considered in older patients with hip pain and evidence of abductor dysfunction.

Supine physical examination should comprehensively evaluate the range of impingement-free motion in all planes of motion. When testing motion, it is essential to quantify the degree of motion specific to the femoroacetabular joint. Compensatory motion through the lumbar spine or rotation through the pelvis can give an inaccurate representation of true femoroacetabular motion. The pelvis should be palpated or observed during motion evaluation, and the limits of femoroacetabular motion should be noted at the onset of pelvic motion. Diminished flexion and flexion/internal rotation (FIR) is commonplace with FAI. When a firm stop is felt during internal rotation testing, femoral retroversion may be present, while offset deformities of the proximal femur typically examine with a softer end point. Diminished hip abduction may indicate lateral sources of impingement either at the proximal femur or at the acetabulum. Prone examination of hip range of motion in extension can provide a good measure of femoral version, with a lack of internal rotation raising suspicion for relative femoral retroversion.

Provocative tests include the following:

Anterior Impingement Test: Flexion/adduction/internal rotation (FADIR) serves to bring the anterolateral femoral head in contact with the anterior-superior rim. A positive test elicits pain in the anterior groin and may be indicative of cam and/or pincer pathomorphology (Figure 11.1).
Straight Flexion Test: Anterior groin pain elicited with straight hip flexion may be indicative of AIIS impingement on the anteromedial femoral neck.
Flexion, abduction, and external rotation (FABER) test could indicate sacroiliac joint pathology, superior/posterior acetabular rim impingement, or psoas irritation depending on the location of pain elicited by this physical examination test (Figure 11.2).
Posterior Impingement Test: Hip extension/external rotation may cause posterior buttock pain (extra-articular impingement) or anterior apprehension/pain (instability).

FIGURE 11.1. Impingement test (flexion, adduction, internal rotation [FADIR]) is performed with the hip in FADIR. Anterior groin pain is produced with this maneuver and is a nonspecific test that can indicate anterior labral tear, joint inflammation, and anterior impingement.

Chapter 16 outlines the physical examination test and associated anatomic and ultrasound findings in more detail.

FIGURE 11.2. The FABER (flexion, abduction, external rotation) test can indicate superior rim impingement, anterior instability, or sacroiliac joint irritation depending on the location of the pain with this maneuver.

Imaging

A comprehensive radiographic evaluation of the proximal femur and acetabulum is recommended to fully evaluate hip morphology. The standing anteroposterior (AP) pelvic radiograph evaluates lateral acetabular coverage, anterior and posterior wall coverage, and femoral morphology at the 12 o’ clock position (Figure 11.3). The false-profile radiograph evaluates anterior acetabular coverage and the femoral morphology at the 3 o’ clock position (Figure 11.4). The 45° Dunn view evaluates the anterior-superior to superior-anterior (1:30) position on the anterolateral femur, where typical cam deformities are most pronounced (Figure 11.5). The combination of these radiographic views provides a comprehensive evaluation of both acetabular and femoral morphology. Important measurements of acetabular coverage include the lateral center-edge angle (AP), Tönnis roof angle (AP), anterior and posterior wall indices (AP), and anterior center-edge angle (FP). Measures of femoral-sided impingement include the alpha angle and femoral head-neck ratio on all three radiographic views. Acetabular retroversion is evaluated on the AP view by the crossover sign, the posterior wall sign, the ischial spine sign, and anterior/posterior wall index (Figure 11.6).

Advanced imaging options include magnetic resonance imaging (MRI) and computed tomography (CT) scans. MRI more effectively images the soft tissues, including the labrum and capsule, whereas CT scan more effectively evaluates bony deformity. Three-dimensional reconstruction of CT data can be the most useful in qualitatively evaluating prior cam resection. MRI with cartilage-specific sequences can be helpful in evaluating the quality of the cartilage in the dysplastic or borderline dysplastic hips. Our cartilage imaging of choice is the delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) (Figure 11.7). The dGEMRIC index has been shown to determine the early failure of

periacetabular osteotomy for acetabular dysplasia, but its utility in FAI surgery is not well characterized. T2 mapping and T1-rho are other cartilage sequences that are being developed to evaluate cartilage health to help with the identification of early joint degeneration.

FIGURE 11.3. In a normal hip that is imaged properly with an anteroposterior pelvic x-ray, the symphysis should be right below the coccyx, and the obturator foramina should be symmetric. The Shenton’s line should be intact, with the sourcil roughly horizontal and on top of the femoral head. The anterior and posterior walls should meet at the edge of the joint, with the posterior wall just lateral to the femoral head center.

FIGURE 11.4. The false-profile view is obtained in the standing position and is a lateral view of the acetabulum. In a normal hip, the superior joint space is wider than the posterior joint space and is a sensitive view to detect early osteoarthritis as well as anterior hip instability.

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