Can the Femoro-Epiphyseal Acetabular Roof (FEAR) Index Be Used to Distinguish Dysplasia from Impingement?

How useful are indirect radiographic measurements of hip instability in borderline hip dysplasia? An MRI-based comparison to a healthy cohort

PURPOSE

Symptomatic hips with borderline hip dysplasia (BHD) morphology pose a challenge in differentiating stable from unstable hips. The current study aims to compare indirect radiographic signs of instability in a symptomatic BHD population to those in a healthy cohort.

METHODS

The study group consisted of patients with a lateral centre-edge angle (LCEA) with values 18° ≤ LCEA < 25° who underwent corrective periacetabular osteotomy (PAO) and reported an improvement in patient-reported outcome measures (PROMs). The comparison group consisted of a healthy cohort of athletes who did not complain of any hip-related symptoms and who had normal values of their hip morphological parameters (LCEA, acetabular index (AI°), alpha angle (α°), femoral version, acetabular version). Indirect signs of instability consisting of the femoro-epiphyseal acetabular roof index (FEAR), iliocapsularis-to-rectus-femoris (IC/RF) ratio and labral dimensions (height-to-length ratio) were assessed in both groups. Partial Pearson correlation, logistic multiple regression analysis and Receiver-Operating Characteristic (ROC) curve analysis were performed to determine correlations, as well as the sensitivity and specificity of these signs to differentiate between healthy hips and BHD.

RESULTS

On binary logistic multiple regression analysis, the FEAR Index was the only independent predictor to differentiate between BHD and healthy hips (p < 0.001). The IC/RF ratio did not achieve significance. The calculated area under the curve (AUC) was 0.93 (0.87 - 0.99, CI 95%, p < 0.001) for the FEAR Index and 0.81 (0.70 - 0.92, CI 95%, p < 0.001) for the height-length ratio. Using the predefined cut-off values (dysplastic-FEAR Index ≥ 5° or labral height-to-length ratio ≤ 0.5), 27% sensitivity/100% specificity and 20% sensitivity/ 100% specificity, were achieved. ROC analysis provided the following new thresholds: FEAR Index ≥ -5° (73% sensitivity/97% specificity); labral height-to-length ratio ≤ 0.8 (70% sensitivity, 79% specificity).

CONCLUSION

In our cohort, the FEAR index was an independent parameter that could differentiate between borderline dysplastic and asymptomatic hips. The previously published values for both the FEAR index and labral hypertrophy ratio had a poor sensitivity in differentiating symptomatic unstable BHD from healthy hips. The cut-off values of ≥ -5° (FEAR index) and ≤ 0.8 (labral height-to-length ratio) provided acceptable sensitivity and specificity when comparing to morphological healthy hips.

A Modified Approach to Measuring Femoro-Epiphyseal Acetabular Roof Index Has Better Intraobserver and Interobserver Reliability Compared With the Original Femoro-Epiphyseal Acetabular Roof Index

PURPOSE

To propose a modified approach to measuring the femoro-epiphyseal acetabular roof (FEAR) index while still abiding by its definition and biomechanical basis, and to compare the intra- and interobserver reliabilities of the original and the modified FEAR index. To propose a classification for medial sourcil edges.

METHODS

We retrospectively reviewed a consecutive series of patients treated with periacetabular osteotomy and/or hip arthroscopy at a single institute. Patients with unilateral or bilateral symptomatic borderline hip(s) were included. Hips with remarkable osteoarthritis, deformities, history of previous surgery, or without symptoms were excluded. A modified FEAR index was defined using a best-fit circle to determine the sourcil line and 2 ancillary lines connecting femoral head and sourcil edges to determine epiphyseal line. Lateral center-edge angle, Sharp angle, Tönnis angle on all hips, as well as FEAR index with original and modified approaches, were measured. Intra- and interobserver reliability were calculated as intraclass correlation coefficients (ICCs) for the FEAR index with both approaches and other alignments. A classification was proposed to categorize medial sourcil edges. ICCs for the 2 approaches across different sourcil groups also were calculated.

RESULTS

After we reviewed 411 patients, 49 were finally included. Thirty-two patients (40 hips) were identified as having borderline dysplasia defined by a lateral center-edge angle of 18 to 25°. Intraobserver ICCs for the modified method were good to excellent for borderline hips; poor to excellent for developmental dysplasia of the hip; and moderate to excellent for normal hips. As for interobserver reliability, the modified approach outperformed original approach with moderate-to-good interobserver reliability (developmental dysplasia of the hip group, ICC = 0.650; borderline dysplasia group, ICC = 0.813; normal hip group, ICC = 0.709). The medial sourcil edge was classified to 3 groups upon its morphology. Type II (39.0%) and III (43.9%) sourcil were the dominant patterns. The sourcil classification had substantial intraobserver agreement (observer 4, kappa = 0.68; observer 1, kappa = 0.799) and moderate interobserver agreement (kappa = 0.465). The modified approach to FEAR index possessed greater interobserver reliability in all medial sourcil edge patterns.

CONCLUSIONS

The modified FEAR index has better intra- and interobserver reliability compared with the original approach in all hip groups and sourcil groups. Type II and III sourcil types account for the majority, to which the modified approach is better.

LEVEL OF EVIDENCE

Level II, development of diagnostic criteria (consecutive patients with consistently applied reference standard and blinding).

No Difference in Patient-Reported Outcomes for Periacetabular Osteotomy and Hip Arthroscopy With Capsular Plication in the Setting of Borderline Hip Dysplasia: A Propensity-Matched Multicenter Study With Minimum 5-Year Follow-Up

PURPOSE

To compare minimum 5-year patient-reported outcome measures after hip arthroscopy (HA) and periacetabular osteotomy (PAO) for borderline hip dysplasia.

METHODS

Hips with a lateral center-edge angle (LCEA) between 18° and less than 25° that underwent either PAO or HA were selected from 2 institutions. The exclusion criteria were as follows: LCEA less than 18°, Tönnis osteoarthritis grade greater than 1, prior hip surgical procedures, active inflammatory disease, Workers' Compensation, and concomitant surgery. Patients underwent propensity matching based on age, sex, body mass index, and Tönnis osteoarthritis grade. Patient-reported outcome measures included the modified Harris Hip Score, as well as calculation of the minimal clinically important difference, patient acceptable symptom state, and maximum outcome improvement satisfaction threshold. Preoperative radiographic predictors included comparison of the Femoro-epiphyseal Acetabular Roof index and ligamentum teres lesions.

RESULTS

A total of 28 PAO patients underwent propensity matching to 49 HA patients. The 2 groups were similar in terms of mean age, sex, preoperative body mass index, and LCEA. The PAO group had a longer mean follow-up period (95.8 months vs 81.3 months, P = .001). The mean Femoro-epiphyseal Acetabular Roof index was significantly lower preoperatively in the HA group (P < .001). The 2 groups showed similar and significant improvements in the mean modified Harris Hip Score from preoperatively to latest follow-up (P < .001). The relative risk of subsequent surgery in the PAO group was 3.49 (P = .024), mostly attributed to hardware removal (25%). The revision rate was 3.6% in the PAO group and 8.2% in the HA group (P = .65). One patient in the PAO group required revision HA for intra-articular adhesions. Three of the patients requiring revision in the HA group underwent PAO because of persistent pain, and one underwent revision HA alone. Conversion to total hip arthroplasty was required in 1 patient in the HA group and no patients in the PAO group.

CONCLUSIONS

Both PAO and HA with capsular plication provide borderline hip dysplasia patients with clinically significant improvements and low revision rates at a minimum of 5 years postoperatively.

LEVEL OF EVIDENCE

Level III, retrospective, comparative therapeutic trial.

A New Arthroscopic Classification for Chondrolabral Disease in Patients Undergoing Surgery for Developmental Dysplasia of the Hip

BACKGROUND

Current classification systems for intra-articular pathology intraoperatively have been described for patients with femoroacetabular impingement rather than dysplasia.

PURPOSE

To (1) describe intra-articular findings in dysplastic hips undergoing combined hip arthroscopy and periacetabular osteotomy (PAO); (2) propose a new chondrolabral classification system for dysplastic hips based on these findings; and (3) correlate patient-reported outcome measures (PROM) with the newly proposed classification.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A total of 46 hips underwent combined hip arthroscopy and PAO at our institution between September 2013 and December 2014, irrespective of symptoms or radiographic findings. PROMs were evaluated preoperatively and at 2 years postoperatively. At the time of hip arthroscopy, the chondrolabral junction was classified as normal without tear (1 hip, type 1); hypertrophic labrum without chondrolabral disruption (19 hips, type 2); chondrolabral disruption on the articular side, not extending into the capsular side (16 hips, type 3A); chondrolabral disruption extending through the capsular side (3 hips, type 3B); and exposed acetabular subchondral bone (7 hips, type 4).

RESULTS

There was a significant difference in postoperative modified Harris Hip Score (mHHS) (P = .020), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain scores (P = .037), and WOMAC total scores (P = .049) between chondrolabral junction types. Post hoc analyses demonstrated significant differences between type 2 (84.9 ± 12.9) and type 3A (67.8 ± 20.7; P = .198), and between type 2 and type 4 (59.3 ± 24.3; P = .011) in postoperative mHHS scores; and between type 2 (83.9 ± 12.9) and type 3A (68.9 ± 23.7; P = .045) in postoperative WOMAC total scores. In multivariate analysis, chondrolabral type 3 or type 4, age >35 years, and previous surgery were significantly correlated with worse mHHS scores at 2 years.

CONCLUSION

This new chondrolabral classification is proposed to describe intra-articular pathology seen during combined hip arthroscopy and PAO, specifically in dysplastic hips. More advanced chondrolabral disease was associated with worse PROMs at 2 years.

The Radiographic Femoroepiphyseal Acetabular Roof Index Is a Reliable and Reproducible Diagnostic Tool in Patients Undergoing Hip-Preservation Surgery: A Systematic Review

PURPOSE

To assess the utility of the femoroepiphyseal acetabular roof (FEAR) index as a diagnostic tool in hip-preservation surgery.

METHODS

MEDLINE, EMBASE, and PubMed were searched from database inception until May 2022 for literature addressing the utility of the FEAR index in patients undergoing hip-preservation surgery, and the results are presented descriptively.

RESULTS

Overall, there were a total of 11 studies comprising 1,458 patients included in this review. The intraobserver agreement for the FEAR index was reported by 3 of 11 studies (intraclass correlation coefficient range = 0.86-0.99), whereas the interobserver agreement was reported by 8 of 11 studies (intraclass correlation coefficient range = 0.776-1). Among the 5 studies that differentiated between hip instability and hip impingement, the mean FEAR index in 319 patients in the instability group ranged from 3.01 to 13.3°, whereas the mean FEAR index in 239 patients in the impingement group ranged from -10 to -0.77° and the mean FEAR index in 105 patients in the control group ranged from -13 to -7.7°. Three studies defined a specific cutoff value for the FEAR index, with 1 study defining a cutoff value of 5°, which correctly predicted treatment decision between periacetabular osteotomy versus osteochondroplasty 79% of the time with an AUC of 0.89, whereas another defined a cutoff of 2°, which correctly predicted treatment 90% of the time and the last study set a threshold of 3°, which provided an AUC of 0.86 for correctly predicting treatment decision.

CONCLUSIONS

This review demonstrates that the FEAR index has a high agreement and consistent application, making it a useful diagnostic tool in hip-preservation surgery particularly in patients with borderline dysplastic hips. However, given the variability in FEAR index cutoff values across studies, there is no absolute consensus value that dictates treatment decision.

LEVEL OF EVIDENCE

Level IV; Systematic Review of Level II-IV studies.

Radiographic Predictors of Reoperation in Adolescents Undergoing Hip Preservation Surgery for Femoroacetabular Impingement

BACKGROUND

Femoroacetabular impingement (FAI) is a condition caused by repetitive abutment of a morphologically abnormal proximal femur and/or acetabulum that may result in chondral and labral pathology. An understanding of radiographic parameters associated with successful primary surgery has not been well established.

PURPOSE

To determine preoperative radiographic parameters that predict reoperation for FAI and correlate radiographic measurements with outcomes in these patients.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

A prospectively collected institutional registry of adolescent patients (age, <19 years) who underwent surgery for FAI (arthroscopic/open) was reviewed. Preoperative standing anteroposterior pelvic radiographs were analyzed for femoroepiphyseal acetabular roof (FEAR) index, as well as lateral center-edge angle (LCEA) and alpha, Tönnis, and Sharp angles. Patient-reported outcomes (PROs) (modified Harris Hip Score, Hip disability and Osteoarthritis Outcome Score) were analyzed preoperatively and at 1- and 2-year followup. Radiographic indication of risk for reoperation was evaluated using receiver operating characteristic (ROC) analysis. Spearman correlation was calculated between radiographic measurements and PROs at 2 years postoperatively.

RESULTS

A total of 81 patients (91 hips) underwent primary surgery (57 surgical dislocations vs 34 arthroscopies) for FAI. The mean age at time of primary operation was 16.23 years (range, 10.4-19.6 years) (73.6% female). Eleven hips (12.1%) underwent reoperation at a mean of 20.6 months from primary surgery. The LCEA, FEAR index, Tönnis angle, and Sharp angle before index surgery were significantly different (P < .05) between patients who underwent reoperation and those who did not. ROC analysis indicated that LCEA <22°, FEAR index >-8.7°, Tönnis angle >6.0°, and Sharp angle >44° were predictors for increased risk of reoperation. Using the cutoff values from the ROC analysis in this series, 43% of patients with an LCEA ≤22° had a repeat procedure, while only 8% of those with an LCEA >22° had a repeat procedure. Similar trends were seen with the other aforementioned acetabular radiographic measurements (FEAR index, Tönnis angle, Sharp angle). Patients who did not require a reoperation demonstrated significant improvement in all PRO categories from their preoperative to 2-year postoperative visits (P < .0001).

CONCLUSION

In patients undergoing treatment for FAI, a reoperation was associated with radiographic signs of hip dysplasia, indicating that patients with a shallower acetabulum are at risk for a repeat operation.

External Validation of the FEAR Index in Borderline Acetabular Dysplasia

Background

Given the lack of established, externally validated criteria for the diagnosis of unstable hips, the Femoro-Epiphyseal Acetabular Roof (FEAR) index has been proposed as a useful tool for identifying hips with instability in the setting of borderline acetabular dysplasia.

Purposes

To (1) determine the external performance of the FEAR index in identifying hips with a clinical diagnosis of instability in the setting of borderline dysplasia and (2) assess the performance of the FEAR index compared with acetabular inclination or physeal scar angle alone.

Study Design

Cohort study (diagnosis); Level of evidence, 3.

Methods

The authors reviewed 176 patients with borderline acetabular dysplasia (lateral center-edge angle, 20°-25°). A positive FEAR index was defined as ≥5°. An alternative threshold ≥2° was also assessed. Significant instability was determined by the senior surgeon based on the combination of patient and radiographic features; unstable hips were treated with periacetabular osteotomy (with or without hip arthroscopy), and stable hips were treated with isolated hip arthroscopy.

Results

Only 18% of borderline hips had a positive FEAR index. The ≥5° positive FEAR index threshold had a sensitivity of 33% (23/70) and specificity of 92% (98/106) in predicting the clinical diagnosis of instability. The ≥2° FEAR index threshold had a sensitivity of 39% (27/70) and specificity of 89% (94/106) in predicting the clinical diagnosis of instability. No alternative threshold for the FEAR index resulted in high levels of sensitivity and specificity. A threshold of -5° was required to reach an adequate sensitivity of 74%. The FEAR index remained a significant predictor of hip instability even after controlling for acetabular inclination (odds ratio, 1.12; P < .001) or physeal scar angle (odds ratio, 1.6; P < .001).

Conclusion

In the current study, a positive FEAR index was generally indicative of the presence of clinical instability, but the FEAR index alone remained inadequate to fully define the instability of a given hip, as it demonstrated low sensitivity (only 33%) in the external validation. The FEAR index is best used in the context of other clinical and radiographic features.

Hip Morphology in Periacetabular Osteotomy (PAO) Patients Treated for Developmental Dysplasia of the Hip (DDH) as Infants Compared With Those Without Infant Treatment

BACKGROUND

A subset of patients successfully treated for developmental dysplasia of the hip (DDH) as infants have symptomatic acetabular dysplasia at skeletal maturity leading to periacetabular osteotomy (PAO). The purpose of this study was to compare femoral and acetabular morphology in PAO patients with late acetabular dysplasia after previous treatment for DDH with PAO patients who do not have a history of DDH treatment.

METHODS

A single surgeon's patients who underwent PAO between 2011 and 2021 were retrospectively reviewed. Patients previously treated for infantile DDH with a Pavlik harness, abduction brace, closed reduction and spica casting, or open reduction and spica casting were included. Patients with previous bony hip surgery were excluded. Preoperative radiographic measurements of each hip were recorded including lateral center edge angle, anterior center edge angle, and Femoro-Epiphyseal Acetabular Roof index. Computed tomography measurements included the coronal center edge angle, sagittal center edge angle, Tönnis angle, acetabular anteversion at 1, 2, and 3 o'clock, femoral neck-shaft angle, femoral version, and alpha angle. Control PAO cases without a history of DDH diagnosis or treatment were matched with the infantile DDH treatment group in a 2:1 ratio based on coronal center edge angle, age, and sex.

RESULTS

There were 21 hips in 18 patients previously treated for infantile DDH (13 patients Pavlik harness, 3 abduction brace, 1 closed reduction, and 1 open reduction). The control PAO cohort was 42 hips in 42 patients who did not have previous DDH treatment. There was no statistically significant difference in any of the recorded measurements between patients previously treated for DDH and those without previous treatment including femoral version (P=0.494), anteversion at 1 o'clock (P=0.820), anteversion at 2 o'clock (P=0.584), anteversion at 3 o'clock (P=0.137), neck-shaft angle (P=0.612), lateral center edge angle (P=0.433), Femoro-Epiphyseal Acetabular Roof index (P=0.144), and alpha angle (P=0.156).

CONCLUSIONS

Femoral and acetabular morphology is similar between PAO patients with persistent symptomatic acetabular dysplasia following DDH treatment and patients presenting after skeletal maturity with acetabular dysplasia and no previous history of DDH treatment.

LEVEL OF EVIDENCE

Level III-case-control, prognostic study.

Predictive radiological parameters of failure following surgical management of femoroacetabular impingement associated with borderline acetabular dysplasia

INTRODUCTION

The role of arthroscopic treatment of femoroacetabular impingement (FAI) in mild or borderline hip dysplasia (lateral center edge angle=18-25) is controversial. It is recommended to combine capsular plication with femoral neck osteoplasty and suture repair of the labrum. Few studies have investigated which radiological parameters are associated with failure of this procedure.

HYPOTHESIS

A larger number of radiological signs of mild or borderline hip dysplasia than radiological signs of FAI negatively influence the outcomes of arthroscopic treatment.

METHODS

This was a retrospective study done with data collected prospectively after a minimum of 2 years' follow-up in patients who underwent arthroscopic treatment of FAI due to cam impingement combined with mild to moderate hip dysplasia. Patients with hip osteoarthritis graded as ≥ Tönnis 2 were excluded. Functional outcome scores (mHHS and NAHS) were determined along with the need for reoperation. Three groups were defined based on the outcomes: success (mHHS ≥ Patient Acceptable Symptomatic State [PASS]); moderate improvement (improvement in mHHS + mHHS<PASS) and failure (worsening of the mHHS). Demographic data, radiographic parameters (LCEA, Tönnis angle, alpha angle, offset, FEAR index, Shenton's line, Cliff sign, anterior wall index [AWI], posterior wall index [PWI]) and intraoperative findings were compared between these three groups. The area under the curve (AUC) for the most relevant data identified during the univariate analysis were then modeled to define which factors were the best at predicting failed arthroscopic treatment a posteriori.

RESULTS

The study analyzed 39 patients. The mean mHHS was 76±15 [40-92]. The "success" group consisted of 21 patients (56%, 21/39), the "moderate improvement" group of 12 patients (31%, 12/39) and the failure group of 6 patients (13%, 6/39) (2 subsequently underwent total hip replacement, 4 underwent shelf acetabuloplasty). The FEAR index was significantly higher and the AWI and VCE were significantly lower in the "failure" group. The FEAR index was the best predictive factor; an index ≥ 4° detected 100% of failures with 96% specificity. The patients in the "moderate improvement" group were significantly older (37 years±8 [18-45]<p= 0.04) with a significantly higher offset (2mm±3 [-5-5]<p=0.004); an offset ≥ 2mm could detect 73% of them with a specificity of 72%.

CONCLUSION

A FEAR index ≥ 4° and offset ≥ 2mm is best able to detect patients at risk of failure and unsatisfactory results, respectively, in the mild clinical cam-type impingement in a population of FAI patients.

LEVEL OF EVIDENCE

IV, retrospective series.

Editorial Commentary: Hip Arthroscopy for Femoroacetabular Impingement in Patients With Borderline Dysplasia Does Not Result in Inferior Outcomes Compared With Outcomes in Patients Without Dysplasia: Do Not Fear

The treatment of adult borderline hip dysplasia remains challenging and continues to be a subject of controversy. The preferred treatment for hip instability and acetabular undercoverage is periacetabular osteotomy. However, patients with painful hips and associated femoroacetebular impingement, microinstability, or no instability may benefit from arthroscopic surgery. Short-term studies have reported favorable clinical outcomes. Traditionally, the lateral center-edge angle was used to determine hip dysplasia. More recently the femoro-epiphyseal acetabular roof (FEAR) index was introduced as a measure for borderline dysplasia. In general, a FEAR index of less than 5° indicates hip instability. When using a FEAR index of more than 2° as a cut-off for hip instability and borderline dysplasia, arthroscopic hip surgery can achieve very similar clinical outcomes to patients with a FEAR index of less than 2°. However low and unequal sample sizes have potentially resulted in both type I and II errors, reducing internal study validity. Although this may be a step in the right direction, further high-quality studies are required to understand patients' characteristics on diagnosis, prognosis, outcomes of surgical interventions, and long-term disease progression for adult borderline hip dysplasia.

Association of Radiographic Markers of Hip Instability and Worse Outcomes 2 to 4 Years After Hip Arthroscopy for Femoroacetabular Impingement in Female Patients

BACKGROUND

Reported outcomes of patients undergoing hip arthroscopy for femoroacetabular impingement (FAI) with underlying borderline acetabular dysplasia are mixed. This may in part be the result of mixed-sex reporting.

PURPOSE

To determine the effect of radiographic measures of acetabular dysplasia and hip instability on outcomes of female patients undergoing hip arthroscopy for FAI.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

This was a retrospective study of female patients undergoing arthroscopic surgery for FAI. All patients had preoperative radiographs including a standing anteroposterior pelvic view on which lateral center-edge angle (LCEA), anterior wall index (AWI), posterior wall index (PWI), and femoroepiphyseal acetabular roof (FEAR) index were measured. Patient outcomes were quantified by preoperative and postoperative 12-Item International Hip Outcome Tool (iHOT-12) scores. All patients had follow-up at 2 to 4 years postoperatively. Published values for minimal clinically important difference (MCID), substantial clinical benefit (SCB), Patient Acceptable Symptom State (PASS), and a normal (iHOT-12 > 86 points) or abnormal (iHOT-12 < 56 points) hip were used to determine outcome, as well as the final iHOT-12 score and iHOT-12 preoperative to postoperative difference.

RESULTS

The cohort consisted of 249 female patients (83% follow-up) with iHOT-12 scores at 2 to 4 years after surgery (mean, 34.6 months). Female patients with combined LCEA ≤25° and AWI <0.35 had lower final iHOT-12 score and iHOT-12 difference and were less likely to meet MCID, SCB, and PASS and have a normal hip and were more likely to have an abnormal hip as determined by iHOT-12 cutoffs when compared with those patients who had an LCEA >25° and an AWI ≥0.35 (all P < .05). There was no effect of PWI on outcomes. Similarly, female patients with combined LCEA ≤25° and a laterally oriented (positive) FEAR index were less likely to meet MCID, SCB, and PASS and have a normal hip and were more likely to have an abnormal hip compared with those patients who had an LCEA >25° and a negative (medial) FEAR index (all P < .05). In multivariate regression, an LCEA between 18° and 25° was an independent predictor of worse outcomes.

CONCLUSION

An LCEA of 18° to 25°, in combination with an AWI of <0.35 or a laterally opening FEAR index, was predictive of worse outcomes in female patients undergoing hip arthroscopy for FAI.