Emerging Ideas: Novel 3-D Quantification and Classification of Cam Lesions in Patients With Femoroacetabular Impingement

Background

Femoroacetabular impingement (FAI) can lead to labral injury, osseous changes, and even osteoarthritis. The literature contains inconsistent definitions of the alpha angle and other nonthree-dimensional (3-D) radiographic measures. We present a novel approach to quantifying cam lesions in 3-D terms. Our method also can be used to develop a classification system that describes the exact location and size of cam lesions.

Questions/Hypotheses

We asked whether automated quantification of CAM lesions based on CT data is a reasonable way to detect CAM lesions and whether they may be classified based on location.

Method of Study

We developed a method to quantify femoral head cam lesions using 3-D modeling of CT scans. By segmenting raw DICOM data, we can determine the distance from the cam lesion’s surface points to the centroid of the femoral head to quantify the mean bump height, volume, and location. The resulting 3-D femoral and acetabular models will be analyzed with custom software. We then will quantify the cam lesion with 3-D parameters using a modified zoning method. The mean bump height, volume, and location on the clock face, and relative zoning will be calculated. Zonal differences will be statistically analyzed. To assess the ability of this method to predict arthroscopic findings, we will obtain preoperative CT scans for 25 patients who undergo hip arthroscopy for FAI. We will compare measurements with the method with our measurements from arthroscopy. The clinical implications of our method’s measurements then will be reviewed and refined for future prospective studies.

Significance

We present a novel approach that can quantify a cam lesion’s location and size. This method will be used to provide guidelines for the exact amount of bony resection needed from a specific location of the proximal femur. There is also potential to develop software for ease of use so this method can be more widely applied.     

In Vivo Pelvic and Hip Joint Kinematics in Patients With Cam Femoroacetabular Impingement Syndrome: A Dual Fluoroscopy Study

Femoroacetabular impingement syndrome (FAIS) may alter the kinematic function of the hip, resulting in pain and tissue damage. Previous motion analysis studies of FAIS have employed skin markers, which are prone to soft tissue artifact and inaccurate calculation of the hip joint center. This may explain why the evidence linking FAIS with deleterious kinematics is contradictory. The purpose of this study was to employ dual fluoroscopy (DF) to quantify in vivo kinematics of patients with cam FAIS relative to asymptomatic, morphologically normal control participants during various activities. Eleven asymptomatic, morphologically normal controls and seven patients with cam FAIS were imaged with DF during standing, level walking, incline walking, and functional range of motion activities. Model-based tracking calculated the kinematic position of the hip by registering projections of three-dimensional computed tomography models with DF images. Patients with FAIS stood with their hip extended (mean [95% confidence interval], −2.2 [−7.4, 3.1]°, flexion positive), whereas controls were flexed (5.3 [2.6, 8.0]°; p = 0.013). Male patients with cam FAIS had less peak internal rotation than the male control participants during self-selected speed level-walking (−0.2 [−6.5, 6.1]° vs. −9.8 [−12.2, −7.3]°; p = 0.007) and less anterior pelvic tilt at heel-strike of incline (5°) walking (3.4 [−1.0, −7.9]° vs. 9.8 [6.4, 13.2]°; p = 0.032). Even during submaximal range of motion activities, such as incline walking, patients may alter pelvic motion to avoid positions that approximate the cam lesion and the acetabular labrum. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:823-833, 2020     

Editorial Commentary: Femoroplasty May Not Be Necessary in All Patients With Hip Femoroacetabular Impingement,But Cam Lesions Should Not Be Ignored in Patients With Significant Femoral Head-Neck Offset

Our knowledge of appropriate arthroscopic management of femoroacetabular impingement (FAI) continues to evolve. However, few studies exist evaluating mid- to long-term surgical outcomes to guide optimal treatment. The recent focus has been on the importance of cam femoroplasty in addition to labral treatment; however, studies have shown that correction of the alpha angle to normal does not correlate with patient outcomes. Furthermore, in cases of mixed impingement, an optimal degree of acetabuloplasty as measured by the lateral center-edge angle has not been determined. Few studies have evaluated isolated pincer decompression with omission of cam treatment. In select patients with small or negligible cam lesions who do not have acetabular dysplasia, a small, isolated acetabular rim resection of 1 to 3 mm may provide adequate FAI decompression as well as reduce surgical time and complications. Nonetheless, individualized FAI treatment is necessary that includes a comprehensive 180° femoroplasty in patients with sizable cam lesions to prevent future labral and chondral damage. An intraoperative dynamic examination is important to determine sufficient resolution of FAI. Predictive modeling may play an increasingly important role to ensure appropriate bony resection and to optimize long-term patient outcomes.     

Editorial Commentary: Cam Femoroacetabular Impingement Requires Dynamic Assessment of Beta-Angle (Femoroacetabular Excursion Angle) and Consideration of Femoral and Acetabular Version: Cam Impingement in Patients With Acetabular or Femoral Retroversion May Warrant Greater Osteoplasty

Radiographs, magnetic resonance imaging, and computed tomography scans have been commonly used to evaluate femoroacetabular impingement (FAI) and are well accepted forms of surgical planning. Assessing and addressing both the femoral and acetabular sides result in a combination of “one-sided” treatments that, in sum, net a successful treatment of FAI. However, combining one-sided approaches may not consider the dynamic interaction of the femoral head with the acetabulum. Elevated alpha angles alone can be indicative of a cam-type lesion without necessitating the presence of functional FAI. The presence of a cam-type lesion on lateral radiographs, as suggested by a positive alpha angle, does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle. Assessment of the beta angle, or femoroacetabular excursion angle, has the potential to address dynamic nature of FAI more accurately by directly measuring the degree of clearance between the femoral head and acetabulum. In addition, a comprehensive assessment of physical examination findings, particularly range of motion, as well as a summation of acetabular and femoral version (as measured by the McKibbin Index), are required. Cam-type of FAI poses a larger challenge in the patient with acetabular or femoral retroversion, which may warrant greater and more localized osteoplasty, distally, during hip arthroscopy.     

Hip Capsule Dimensions in Patients With Femoroacetabular Impingement: A Pilot Study

Background

Joint-preserving hip surgery, either arthroscopic or open, increasingly is used for the treatment of symptomatic femoroacetabular impingement (FAI). As a consequence of surgery, thickening of the joint capsule and intraarticular adhesions between the labrum and joint capsule and between the femoral neck and the joint capsule have been observed. These alterations are believed to cause persistent pain and reduced range of motion. Because the diagnosis is made with MR arthrography, knowledge of the normal capsular anatomy and thickness on MRI in patients is important. To date there is no such information available.

Questions/Purposes

The purpose of this study was to establish thickness, length of the hip capsule, and the size of the perilabral recess in patients with FAI.

Methods

We reviewed the preoperative MR arthrography of 30 patients (15 men) with clinical symptoms of FAI. We measured capsular thickness and made observations on the perilabral recess.

Results

The joint capsule was thickest (6 mm) anterosuperiorly between 1 and 2 o’clock. The average length from the femoral head-neck junction to the femoral insertion of the capsule ranged from 19 to 33 mm. A perilabral recess was present circumferentially, even across the acetabular notch, where the labrum is supported by the transverse acetabular ligament. The shortest recess occurred superiorly.

Conclusions

Knowledge of the capsular anatomy in patients with FAI before surgery is important to judge the postoperative changes and to plan potential further therapy including arthroscopic treatment of intraarticular adhesions.     

No Evidence of Systemic Inflammation in Symptomatic Patients With Femoroacetabular Impingement

Femoroacetabular impingement (FAI) is a common cause of hip pain and represents a major cause of early osteoarthritis. The role of systemic inflammation in pre‐arthritic hip conditions remains largely unknown and uninvestigated. Serum‐free light chains (sFLCs) are inflammatory markers produced by B cells. This study aimed to determine whether there was evidence of systemic inflammation in patients with FAI, defined by sFLCs, and whether this correlated with markers of disease severity. Participants for this study were recruited from a single center (Nuffield Orthopedic Center, Oxford) and were taking part in the Femoroacetabular Impingement Trial. The cohort comprised 115 individuals (38 male, 77 female, mean age 37 years): 57 individuals received surgical intervention and 58 received physiotherapy. All individuals provided patient‐reported outcome measures and serum samples at baseline and follow‐up 8 months post‐randomization. sFLC concentrations were measured in serum samples by immunoturbidimetry. At baseline, for all individuals, mean polyclonal sFLC concentrations were 30.36 mg/l (standard deviation [SD] 9.23). At follow‐up, the mean polyclonal sFLC concentrations were 31.68 mg/l (SD 9.61) in the surgical intervention cohort, and 29.48 mg/l (SD 7.85) in the physiotherapy intervention cohort. There was no significant correlation between sFLC concentrations and any of the patient reported outcome measures, or radiographic measures: average or maximum alpha angle, or center edge angle. In conclusion, in patients with symptomatic FAI there was no systemic inflammation, as defined by sFLC concentrations, and no correlation between sFLC concentrations and measures of disease severity. The lack of inflammation suggests FAI is a mechanical phenomenon. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2189–2196, 2019