CORR Insights®: Radiographically Apparent Acetabular Sourcil Landmarks Are Created by Comparable Regions of the Pelvis With Extraarticular Bone Variably Confounding Estimates of Joint Coverage

Where Are We Now?

Recent evidence highlights the importance of the lateral center-edge angle (LCEA) and anterior center-edge angle (ACEA) in assessing hip stability and dysplasia risk [3, 6, 7]. Moreover, uncertainty remains about how best to assess and manage patients with borderline dysplasia, and even how to define that term [19]. Studies have emphasized the need for standardized measurement techniques to enhance reliability across different populations, and they have suggested that both angles are important in anticipating outcomes after hip preservation surgery [5, 8]. For instance, research has demonstrated that a comprehensive evaluation combining the LCEA and ACEA provides a more nuanced understanding of hip morphology, aiding in tailored treatment strategies [4, 11]. Moreover, advances in imaging technology, such as three-dimensional (3D) reconstruction using CT and MRI, are being explored to refine these measurements, with the goal of improving diagnostic accuracy and patient management [9, 10]. This growing body of evidence underscores the importance of these radiologic measurements in guiding clinical decisions and improving patient outcomes for treatment of these problems.

Specific research focused on utilizing advanced imaging methodologies has revealed interesting results that deepen our understanding of the complexity of femoroacetabular motion and loading, some of which have been implemented into management algorithms. In 2017, Wylie et al. [21] compared the clockface acetabular position of the bony and sourcil lateral center-edge using standing plain AP radiographs and CT scans, and they suggested a more anterior clockface position when using the sourcil LCEA. However, these data were limited to patients who had symptoms of femoroacetabular impingement and who did not have a retroverted acetabulum. Interestingly, this study found minimal differences between the standing AP pelvic and supine CT digitally reconstructed radiographs (DRRs) similar to prior data [18]. In another study, Needell et al. [15] utilized CT false profile views to measure ACEA with excellent reproducibility, suggesting this technique may be clinically useful. Subsequent studies evaluated the sourcil and bone ACEA, and they reached a similar conclusion that sourcil and bone ACEAs represent more anterior and posterior clockface positions, respectively [6, 13]. These studies were also limited by a paucity of patients with dysplasia, and thus the conclusions may not be directly applicable to this population. Additionally, controversy remains as evidenced by responses to these studies and continued dialogue in this area [1, 14].

The study in this issue of Clinical Orthopaedics and Related Research® by Rivas et al. [16] advances our knowledge and addresses some of these controversies by utilizing a novel 3D methodology to evaluate which osseous areas of the acetabulum may combine to create the radiographic sourcil and where these osseous areas map on the acetabular clockface. These data support prior research suggesting that the acetabular sourcil correlates to anterior positions on the clockface of 12:31 and 12:48 on AP and false profile radiographs, respectively [13, 21]. Interestingly, Rivas et al. [16] demonstrated that a subgroup of patients had other anatomic locations such as the anterior inferior iliac spine (AIIS) that contributed to the sourcil, thus suggesting that advanced 3D evaluation of the acetabular morphology is crucial when considering surgical decision-making—especially when considering modifying the native acetabular osseous structure. This study highlights the importance of and mechanism by which treating physicians can develop a comprehensive preoperative understanding of 3D acetabular osseous anatomy that will aid preoperative planning and intraoperative decision-making—particularly when considering addressing subspinous or pincer pathology.

Where Do We Need to Go?

The current study raises some critical questions: (1) What specific periacetabular osseous regions are included in creating the sourcil on standing AP and false profile pelvic radiographs? (2) Can these regions, including the LCEA and ACEA, be reliably measured and are the measurement thresholds such as dysplasia acceptable for individual patient decision-making? (3) What is the most effective imaging methodology to evaluate acetabular morphology to guide clinical decision-making?

Advanced imaging technology, such as 3D reconstruction from CT and MRI, have afforded complex morphologic evaluation including angular measurements of the LCEA, ACEA, and acetabular and femoral version, among others. These techniques have been increasingly used to assist in surgical indications and planning [9, 10]. Interestingly, Rivas et al. [16] highlighted a subpopulation of patients in which the AIIS contributes to the acetabular sourcil, thus providing further evidence that the subspinous region should be considered when acetabular osseous evaluations are performed. Subspinous morphology and clinical impingement has been suggested previously [9], but the study data from Rivas et al. [16] suggest that the importance of this morphologic area may extend to dysplastic patients as well. Utilization of advanced imaging for acetabular morphologic evaluation has also highlighted the existing controversy regarding the importance of 3D imaging on reliable radiographic acetabular measurements. This controversy extends to the importance of weightbearing imaging and the relative effect of weightbearing on pelvic and hip radiographic anatomy. Questions remain about how the absence of weightbearing with supine 3D imaging may affect the functional position of the acetabulum and thus the position and measurements of the LCEA and ACEA.

Accurate radiologic evaluation and measurement of acetabular morphology remains of paramount importance in diagnosis and treatment or hip pathology with continued reliance on effective imaging methodology, including advanced imaging. Prior data have suggested that weightbearing may influence pelvic position and therefore, the functional weightbearing acetabular position [12]. However, other studies have suggested that minimal to no change occurs between supine and standing positions [20, 21]. For this reason, questions remain regarding whether acetabular morphologic measurements, including the LCEA and ACEA, obtained from supine advanced imaging should be used in surgical planning as they may not represent the functional, weightbearing position of the pelvis. The current study methodology eloquently accounted for this potential shortcoming by modifying the position of the DRR to correlate with the acetabular position of the standing pelvic radiographs. Further evaluation using this similar methodology to compare a DRR that is not adjusted to a weightbearing radiograph to one that is adjusted using the current study methodology would be very useful in exploring this current controversy. These data would be particularly important given that surgical interventions in the form of both arthroscopic acetabuloplasty and periacetabular osteotomy are not only performed in a supine position but also guided by supine intraoperative fluoroscopy.

How Do We Get There?

Future research on the LCEA and ACEA should focus on several key areas to enhance understanding and clinical application. Recent data would suggest minimal differences in some of these parameters, but limitations exist that restrict widespread application [12, 20]. Additionally, investigation into the long-term outcomes associated with specific LCEA, ACEA, and other morphologic measurement thresholds could provide deeper insights into their prognostic significance and the efficacy of individualized surgical intervention. Although current imaging advancements have shown promise, research should aim to establish standardized protocols for emerging technologies like 3D MRI as well as in- and out-of-phase MRI sequencing to ensure consistency and reliability in measurements. Ultimately, a more comprehensive and patient-specific understanding of these angles and their implications will enhance diagnostic accuracy and treatment strategies in hip preservation.

A multifaceted approach is essential to advance research on acetabular morphology including the LCEA and the ACEA. Although these two measurements of acetabular coverage are commonly used, and thus are the focus of the current study by Rivas et al. [16], they remain a two-dimensional evaluation of a three-dimensional structure. The data from the current study demonstrate the similarity of the evaluation of sourcil coverage on both AP and false-profile reconstructions, suggesting that minimal additional data are obtained by using both measurements to define dysplasia. Kitamura et al. [12] suggested that patient-specific and postural differences may affect physiologic pelvic tilt and hip contact pressure, and they recommended that future research focus on the pathogenesis of hip dysplasia, including patient-specific evaluation. Atkins et al. [2] expanded on these data by demonstrating the importance of patient-specific modeling in developing a clear understanding of acetabular dysplasia. For this reason, future study of acetabular morphology should incorporate patient-specific evaluation rather than an evaluation of the mean measurements of a patient population. Moreover, incorporation of other morphologic measurements into advanced imaging methodologies will be crucial to guide a comprehensive patient-specific 3D understanding of the acetabulum. Specifically, future advanced imaging utilizing 3D reconstructions should consider weightbearing sequences or reformatting techniques that orient the pelvis and acetabulum into a weightbearing position.

The current study by Rivas et al. [16] also highlighted a unique anatomic variability among patient subgroups in which regions such as the AIIS contribute to radiographic angular measurements. These subgroup variations demonstrate the clear need for large-scale, multicenter studies that evaluate the normative values of these angles across diverse populations, including variations by age, sex, ethnicity, and morphology (such as spinopelvic tilt and obliquity), to guide the application of these thresholds to an individual patient. Collaborative efforts among orthopaedic surgeons, radiologists, and researchers can facilitate the establishment of large, multicenter databases to collect and analyze radiologic data from diverse patient populations. Moreover, implementing standardized protocols for measuring the LCEA and ACEA using both traditional radiographs and advanced imaging techniques, such as 3D MRI, will enhance consistency and comparability across studies. Extending these protocols to other osseous measurements will similarly extend our understanding of the complex 3D acetabular morphology [18]. Thoughtful incorporation of other osseous morphologic contributors such as the AIIS into these measurements and their potential effects on acetabular joint mechanics will also be crucial.

Engaging in multidisciplinary research that evaluates the aforementioned factors in combination with patient-specific spinopelvic and bipolar femoroacetabular osseous morphology will deepen the understanding of hip morphology and its implications for young adult hip pain, paving the way for more individualized, patient-specific diagnostic and therapeutic hip preservation strategies.

Read This Next

• The hip is a complex, bipolar joint with an ROM and pathology that are affected by spinopelvic, specific acetabular, and femoral osseous morphology; this study highlights the role of individual and combined femoral and acetabular anatomy on hip pathology [17].

• Multiple radiographic measurements are utilized to understand complex hip osseous morphology; this study provides a clear and comprehensive description of these measurements and how they should be used to develop effective diagnostic and treatment algorithms [18].

• The spectrum of morphology and pathomorphology extending from true dysplasia through pincer impingement can be complex and requires thoughtful evaluation of these definitions and future research to quantify these patient subpopulations [19].