The Femoro-Epiphyseal Acetabular Roof (FEAR) Index: A New Measurement Associated With Instability in Borderline Hip Dysplasia?

Abstract

Background The definition of osseous instability in radiographic borderline dysplastic hips is difficult. A reliable radiographic tool that aids decision-makingspecifically, a tool that might be associated with instability-therefore would be very helpful for this group of patients. Questions/purposes (1) To compare a new radiographic measurement, which we call the Femoro-Epiphyseal Acetabular Roof (FEAR) index, with the lateral centeredge angle (LCEA) and acetabular index (AI), with respect to intra-and interobserver reliability; (2) to correlate AI, neck-shaft angle, LCEA, iliocapsularis volume, femoral antetorsion, and FEAR index with the surgical treatment received in stable and unstable borderline dysplastic hips; and (3) to assess whether the FEAR index is associated clinical instability in borderline dysplastic hips. Methods We defined and validated the FEAR index in 10 standardized radiographs of asymptomatic controls using two blinded independent observers. Interrater and intrarater coefficients were calculated, supplemented by Bland-Altman plots. We compared its reliability with LCEA and AI. We performed a case-control study using standardized radiographs of 39 surgically treated symptomatic borderline radiographically dysplastic hips and 20 age-matched controls with asymptomatic hips (a 2:1 ratio), the latter were patients attending our institution for trauma unrelated to their hips but who had standardized pelvic radiographs between January 1, 2016 and March 1, 2016. Patient demographics were assessed using univariate Wilcoxon two-sample tests. There was no difference in mean age (overall: 31.5 ± 11.8 years [95% CI, 27.7-35.4 years]; stable borderline group: mean, 32.1± 13.3 years [95% CI, 25.5-38.7 years]; unstable borderline group: mean, 31.1 ± 10.7 years [95% CI, 26.2-35.9 years]; p = 0.96) among study groups. Treatment received was either a periacetabular osteotomy (if the hip was unstable) or, for patients with femoroacetabular impingement, either an open or arthroscopic femoroacetabular impingement procedure. The association of received treatment categories with the variables AI, neck-shaft angle, LCEA, iliocapsularis volume, femoral antetorsion, and FEAR index were evaluated first using Wilcoxon two-sample tests (two-sided) followed by stepwise multiple logistic regression analysis to identify the potential associated variables in a combined setting. Sensitivity, specificity, and receiver operator curves were calculated. The primary endpoint was the association between the FEAR index and instability, which we defined as migration of the femoral head either already visible on conventional radiographs or recentering of the Each author certifies that he or she, or a member of his or her immediate family, has no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Results The FEAR index showed excellent intra-and interobserver reliability, ...

Three‐dimensional hip joint congruity evaluation of the borderline dysplasia: Zonal‐acetabular radius of curvature

“…Our study showed that borderline dysplastic acetabulum has significantly enlarged curvature in the anterior zone compared to the control. Although the zonal‐acetabular curvature and the FEAR index differ in the underlying biomechanical concept, both our research and recent reports based on the FEAR index suggest that borderline dysplasia may have evidence of instability 14,15 . Further investigations are necessary to evaluate whether there are correlations between zonal‐acetabular curvatures and joint instability.…”

“…Above all, the functional characterization of hip stability is important to guide surgical decision‐making. Wyatt et al 14 reported that the FEAR index, which is formed by the angle between the acetabular roof and the central third of the femoral growth plate, has a high value to predict the stability of the hip. This evaluation method is based on the biomechanical concept that the growth plate orients itself perpendicularly to the joint reacting forces during growth 14 .…”

“…Therefore, the functional characterization of hip stability is of paramount importance to guide surgical decision‐making 10 . However, it is difficult to characterize the pathological mechanism as impingement (stable) or dysplasia (unstable) by two‐dimensional radiographic measurements alone 10 although the recently introduced Femoro‐epiphyseal Acetabular Roof (FEAR) index seems to have a high association with instability 14,15 . As for the femoral side, there are several reports that evaluated the three‐dimensional morphology in the borderline dysplastic hips with concomitant cam deformity 4,9,16–18 .…”

Three-dimensional curvature mismatch of the acetabular radius to the femoral head radius is increased in borderline dysplastic hips

“…were excellent for ARO and fair to good for LCEA [41,42]. It is recognized that since we should determine the center of the femoral head to measure LCEA, the reliability of LCEA is slightly worse than that of ARO [43].…”

Diagnosis and Management of Borderline Hip Dysplasia and Acetabular Retroversion

“…Wyatt et al hypothesized that instability of the hip could be predicted by measuring the angle between the physeal scar of the femoral head and the sclerotic sourcil of the acetabulum. 3 This was based on knowledge that the orientation and growth of the subcapital physis respond to the direction of forces applied across the hip joint during development. They refer to this measurement as the femoroepiphyseal acetabular roof (FEAR) index.…”