The most commonly identified deformity among patients with femoral acetabular impingement syndrom (FAIS) is the cam-type lesion.1 Improvements in modern equipment and technology have made it easier to identify and provide arthroscopic correction by resecting the aspherical bone. However, hip arthroscopy has a steeper learning curve compared to arthroscopy in other joints.2,3 Addressing the cam-type deformity is arguably the most technically challenging aspect of this procedure and plays a pivotal role in obtaining desired outcomes.4 Performing a femoral osteoplasty is a unique technical skill within orthopedics, as there are very few procedures in our profession that require bony reshaping with a theoretical goal of creating sphericity. An inadequate decompression of the deformity is the leading cause of recurrent pain after hip arthroscopy.5 Over-resection is also less than ideal as this can jeopardize hip stability and the integrity of the femoral head and neck6 (Figure 1). Consequently, it is important to understand how to properly assess the extent of a cam deformity and to have the requisite techniques to optimize the femoral osteoplasty. This article provides a brief review of the preoperative workup of cam-type impingement and a systematic approach to ensure an “ideal” femoroplasty, in hopes of maximizing surgical outcomes and minimizing subsequent revision procedures.

Proximal femoral morphology varies widely, with certain patterns imparting a higher risk of impingement. The cam-type lesion describes an abnormality at the femoral head neck junction that decreases the head neck offset leading to pathologic abutment of the femoral head neck junction against the labrum and acetabular rim. The size and location of cam lesions are variable7. Increased cam size may be associated with a higher risk for developing osteoarthritis secondary to impingement.8

However, the size of the cam-type lesion is not the sole determinant for the development of hip impingement. This dynamic process may also be influenced by other structural elements of the proximal femur and their biomechanical interplay, such as neck shaft angle, neck length, and femoral version.9,10 In the setting of a cam-type lesion, varus femoral necks may create impingement and also lead to increased stress at the chondrolabral junction.9 Femoral version and torsion are other important components to consider when assessing the global risk for impingement. Impingement may occur in patients with relative retroversion at lower degrees of internal rotation and hip flexion than seen in patients with normal version.10

The etiology of primary FAI is somewhat controversial. Some authors have suggested the possibility of a genetic proclivity for the development of primary FAI.11 There has also been persuasive evidence that involvement in high intensity sports leads to repetitive microtrauma which, over time, stimulates aberrant bone formation extending from the physis and ultimately results in a cam-type deformity.12 Others have suggested that the cam-type deformity may be sequelae from subclinical hip physeal pathology during childhood.13

This last theory is the result of the observed structural abnormality seen in cam-type impingement, which shares similar characteristics to the deformity seen in patients who previously had slipped capital femoral epiphysis or Legg-Calve-Perthes.13,14 Consequently, cam-type impingement may be part of a spectrum of deformities where primary FAI is on one end with secondary FAI on the other as a result of residual deformity from a known history of hip pathology. Even rarer causes of hip pathology such as osteoid osteoma have also been implicated.15 It should be noted that some of these pre-existing hip pathologies may lead to residual deformity in not only the proximal femur but also in the acetabulum and extra-articular structures like the greater trochanter.16,17 Delineating the exact cause of impingement may be complex in these unique circumstances.

The most common presenting symptom in FAIS is the insidious onset of pain in the groin.18 However, one should not exclude FAIS from the differential if this particular clinical picture is not present. Additionally, chronic hip pain may cause or be caused by other sources of pain due to alterations in the kinetic chain. Obtaining a comprehensive history and physical exam is paramount in the workup of hip pain.

A comprehensive physical examination is important in working up FAIS. A systematic approach to hip examination should be performed for every patient. While many exam maneuvers are previously described, maneuvers that are specific to FAIS will be highlighted.

First, flexion-adduction-internal rotation or FADDIR is likely the most commonly used provocative maneuver for FAI.19 The test is performed in the supine position, and a positive test consists of reproduction of the patient's pain with passive flexion, adduction and internal rotation. A variation of FADDIR is the anterior impingement test where the hip is held in 90 degrees of hip flexion while it is adducted and internally rotated.20 Another variation of the FADDIR maneuver is the internal rotation overpressure (IROP) maneuver where the flexed and internally rotated hip is axially compressed.21 The scour test can be thought of as the McMurray test of the hip.20 It is another provocative maneuver that involves a repetitive movement of the hip from flexion and internal rotation to an abduction and extended position all while axial load is applied. A positive test is indicated by reproduction of pain and/ or mechanical symptoms.

Routine preoperative imaging obtained in the workup for FAI is imperative to identify the location of the deformity, which can be discerned by an area of subchondral sclerosis in the anterosuperior femoral neck.22,23 Considering the structural and locational variability of cam-type lesions within the head-neck junction, a radiographic series should include specific views optimized to accurately assess femoral sphericity, and determine the extent of aberrant growth. Uemura and colleagues simulated 10 different radiographic views using a control group of femurs against a group of femurs with a cam deformity.22 A different clock-face position on the head- neck junction was visualized with each view. Based on these findings, our preferred radiographic series to visualize the femoral head neck junction includes the following: a standing anteroposterior (AP) view, maximizing visualization at the 12:00-1:00 o'clock positions, a 45° modified Dunn lateral, optimized for 1:00-2:00 o'clock position, and the frog leg lateral, optimized for the 3:00 o'clock position(Figure 2A-C). Moreover, these images allow for clear visualization of the sclerosis depth from the cortical bone, which may be helpful in approximating appropriate resection depth during femoroplasty. If radiographs alone are deemed insufficient, additional 3D imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), may also be used to spatially analyze the femoral head and surrounding tissues (Figure 2D,E).

Many radiologic measures have been described to assess the asphericity of the femoral head. Among these, alpha angle is the most widely used. First described by Nötzli and colleagues, the alpha angle was assessed on MRI.24 However, MRI and MR arthrogram (MRA) are most useful in assessing articular cartilage and labrum, two structures that may incur damage secondary to impingement. Despite its use in first describing the alpha angle, MRI and MRA are limited in their ability to visualize the bony contour as it depends on the soft tissue transparency around the bone. As a result, computed tomography (CT) and post-processing measurements made on images obtained by rotating the femur about the axis of the femoral neck have given providers a perspective of the head neck contour that may be more representative of what can be seen intraoperatively.25 Given the concerns with increased radiation exposure, CT studies are usually obtained following the decision to proceed to surgery or in unique cases such as prior hip surgery or grossly abnormal hip osseous morphology.

There are many effective published techniques on performing a femoroplasty. What follows is an outline of the senior author's (SKA) technique. Three standard portals are used: anterolateral (AL), mid-anterior (MAP), and distal anterolateral (DALA). Central compartment work is completed prior to femoroplasty. Usually, no additional portals are necessary to perform the femoroplasty. Traction is released and the hip is brought into flexion in neutral rotation.

Visualization is paramount to performing a femoroplasty. There are many different capsulotomy techniques: periportal, interportal, T-capsulotomy, and extra-capsular approaches. Regardless of the capsular approach, the priority should be placed on access and visualization to adequately perform the femoroplasty. While capsulotomy size should be minimized, surgeons should not lose focus on the primary goal of performing a complete femoral cam resection. In order to comfortably perform a complete resection, visualization of the entire cam lesion must be obtained, and the capsulotomy should be adjusted accordingly. Without adequate visualization, one would risk an inadequate resection or risk damaging the surrounding soft tissues with the working instruments. When using a periportal or interportal approach, the extremity must be mobilized in order to visualize different areas of the head neck junction. In contrast, the T-type capsulotomy allows for a wide exposure view of the head neck junction and requires minimal manipulation of the extremity to visualize the cam lesion.