Does hip bone morphology differ depending on the presence of Cam lesions in Borderline Developmental Dysplasia of the Hip?

doi:10.21203/rs.3.rs-5229544/v1

Objective. The purpose of this study was to divide patients with borderline developmental dysplasia of the hip (BDDH) into two groups according to the presence of Cam lesions, and compare radiographs related to bone morphology between them.

Materials and Methods.We retrospectively analyzed consecutive patients with BDDH who underwent hip arthroscopy (HA) or periacetabular osteotomy (PAO) at our institution between October 2013 and October 2019. The patients were classified into two groups according to the presence of Cam lesions. Radiographic measurements including lateral center-edge angle (LCEA), acetabular roof obliquity (ARO), cliff sign, femoral epiphyseal acetabular roof (FEAR) index, vertical center anterior angle (VCA), and Sourcil Index were compared between the two groups. The cutoff values were calculated using a receiver operating characteristic curve.

Results. Sixty-nine hips were analyzed in this study (Cam+: 34, Cam-: 35). The ARO and FEAR indexwere significantly higher in the Cam- group (P<0.001, P<0.001). The LCEA, VCA, and Sourcil Index was significantly lower in the Cam- group than that in the Cam+group (P<0.001, P<0.001, P<0.001). The cut-off values were 21.0° for LCEA, 15.1° for the ARO, 22.5° for the VCA angle, -2.2° for the FEAR index, and 49.5° for the Sourcil Index

Conclusion. Patients with BDDH exhibited significant differences in bone morphology depending on the presence of Cam lesions. Moreover, those without Cam lesions displayed similarities to patients with DDH. For such patients, performing HA alone risks poor clinical outcomes, and surgery to improve acetabular coverage, such as PAO, may be indicated.

hip arthroscopy

dysplasia

borderline developmental dysplasia of the hip

periacetabular osteotomy

Cam

Femoroacetabular impingement

Hip arthroscopy (HA) is a successful therapeutic procedure for a growing number of hip conditions because of advances in surgical skill and technology over the last decade. Recent studies have reported favorable results following HA in patients with a lateral center-edge angle (LCEA) between 18° and 25° or between 20° and 25°, that is, borderline developmental dysplasia of the hip (BDDH) [1, 2]. Using capsular plication/closure in conjunction with labral repair during HA could compensate for potential mild instability in patients with BDDH and provide good results [2, 3]. However, if HA is performed on a patient whose main symptom is due to instability, instability-related symptoms may persist and lead to poor clinical outcomes [4].

Some studies have reported good outcomes with HA for patients with BDDH with Cam lesions[5], while others have reported excellent results with periacetabular osteotomy (PAO) for patients with BDDH without Cam lesions[6]. Thus, there may be a mix of patients with impingement and joint instability among patients with BDDH, which may be due to the paucity of definitions of BDDH. Dornacher et al. showed that a high proportion of BDDH suggests that these hips might be mislabeled using LCEA alone [7]. In particular, few studies have evaluated whether there are differences in hip bone morphology between patients with BDDH with and without Cam lesions causing femoroacetabular impingement syndrome (FAIS), and this is still unknown.

Therefore, the purpose of this study was to divide patients who underwent HA and PAO for BDDH at our institution into two groups according to the presence of Cam lesions, and to compare radiographs related to hip bone morphology between the two groups. In particular, in assessing DDH, a number of radiographic measurements have been reported in addition to LCEA, including acetabular roof obliquity (ARO) and femoral epiphyseal acetabular roof (FEAR) index [4, 8], which may differ. We hypothesized that patients with BDDH without Cam lesions would have radiographic results that are significantly more similar to DDH than those with Cam lesions.

We retrospectively analyzed consecutive patients who underwent HA or PAO at our institution between October 2013 and October 2019. Patients who were not BDDH were excluded. BDDH was defined as an LCEA of 18–25° [1]. Further exclusion criteria were Tönnis osteoarthritis grade >1 and history of hip surgery. This study was approved by the Institutional Review Boards of the authors’ affiliated institutions.

Imaging Protocol and Measurements

In terms of radiographic analysis, the radiological measurement of Cam deformities was assessed by the α angle, with a value of 55° or greater defined as the presence of Cam lesions [9]. The LCEA, ARO, cliff sign, FEAR index on pelvic anteroposterior views, and vertical center anterior (VCA) angle on the false-profile view were measured. In the pelvic anteroposterior view, the coccyx was centered 1–3 cm above the pubic symphysis, and the hips were positioned at 0° abduction and 10° internal rotation. The center of the femoral head was estimated from a circle passing through the medial, lateral, and inferior contours of the femoral head, and the vertical axis was defined as perpendicular to a line connecting the bilateral inferior ischial tuberosities. The LCEA was measured as the angle between a line parallel to the vertical axis from the center of the femoral head and a line from the center of the femoral head to the outermost acetabular sourcil edge [10] (Figure 1). ARO was defined as the angle between the line connecting the most medial and lateral parts of the acetabular sourcil and line parallel to the bilateral pelvic teardrops [11] (Figure 1). For the cliff sign, a perfect circle was drawn around the femoral head. If the lateral side of the femoral head did not completely fill the perfect circle, it was considered positive [12] (Figure 1). The FEAR index was defined as the angle between the physeal scar line on the femoral head and line connecting the most medial and lateral points of the acetabular sourcil. In the physeal scar, the medial-most and lateral-most points of the straight section located in the middle third of the epiphyseal line were identified and connected. The angle was considered positive when the connected lines intersected medially and diverge laterally [4] (Figure 1). The VCA angle was defined as the angle between the vertical longitudinal line passing through the center of the femoral head and line connecting the center of the femoral head to the most anterior point of the acetabular sourcil [13] (Figure 1).

Furthermore, the size of the sourcil, the load-bearing portion of the acetabulum, is also considered a very important factor affecting hip instability [14], and the angle between the two lines connecting the center of the femoral head to the medial and lateral sides of the sourcil was defined as the Sourcil Index [15] (Figure 1).

Evaluation and Statistical Analysis

To analyze the reproducibility of all measurements, intra- and interobserver reliabilities were examined using an intraclass correlation coefficient (ICC) and Cohen's kappa coefficient test in a subset of 20 cases. To calculate the intraobserver reliability, measurements were taken twice at 6-week intervals by a single surgeon. For interobserver reliability, the measurements were performed by two surgeons. The ICCs and kappa coefficients for intra- and interobserver reliabilities were >0.8 (range, 0.82–0.96) for all measurements (Table 1). Based on the reliability observed, the means of the two measurements made by the initial observer were used for all analyses. All values are reported as mean±standard deviation, and the results were evaluated using the Bell Curve for Excel (Social Survey Research Information Co., Ltd, Tokyo, Japan).

Patient demographic data such as age, sex ratio, and body mass index (BMI), and radiographic measurements including LCEA, ARO, cliff sign, FEAR index, VCA angle, and Sourcil Index were compared between the two groups with and without Cam lesions. The unpaired t-test was used to compute differences in continuous variables, and the chi-square test was used for intergroup comparisons of categorical variables. Cutoff values and their accuracies for the LCEA, ARO, cliff sign, FEAR index, VCA angle, and Sourcil Index were calculated using a receiver operator characteristic (ROC) curve. ROC analysis allows for the graphical representation of a binary model, while also enabling the determination of a discriminatory threshold. The area under the curve (AUC) measures the accuracy of outcome classification according to the model. AUC values of 0.50, 0.7–0.8, 0.8, or greater, and 1.0 were considered random assignment, acceptable discrimination, excellent discrimination, and perfect assignment, respectively [16]. Cutoff values were identified by analyzing specificity and sensitivity. To establish the optimal cutoff value, the Youden index, the point on the curve representing the highest sensitivity and specificity, was used [16].

A probability value (P) of <0.05 was considered statistically significant. Comparing two groups, a power analysis showed that a minimum sample size of 26 patients in each group would be required using G*Power version 3.121 [17], when alpha was set as 0.05, power (1 − β) at 0.80, and an effect size at 0.7.

A total of 179 hips that underwent consecutive surgeries at our institution were included in the study (HA: 88, PAO: 86, combined: 5). Of the 179 hips, 106 were excluded because they did not have BDDH. Patients who had Tönnis osteoarthritis grade >1 (n=3) and history of hip surgery (n=1) were excluded. Finally, 69 hips were included and analyzed in this study (Figure 2). None of the patients underwent a bilateral surgery. Based on the definition of α angle, 34 hips were classified as having Cam lesions (Cam+ group) and 35 hips as having none (Cam- group). There were no significant differences in the background characteristics of the patients, including age, sex ratio, and BMI, between the two groups (Table 2).

In the radiographic evaluation, LCEA was significantly higher in the Cam+ group than that in the Cam- group (Cam+: 22.4±2.5, Cam-: 19.9±2.0, P<0.001) (Table 3). ARO and FEAR index were significantly higher in the Cam- group (ARO; Cam+: 10.3±4.5, Cam-: 18.6±4.0, P<0.001, FEAR index; Cam+: -6.7±6.8, Cam-: 3.4±4.4, P<0.001), and VCA angle was significantly higher in the Cam+ group (Cam+: 25.5±7.6, Cam-: 18.2±5.7, P<0.001) (Table 3). The positive rate of cliff sign was not significantly different between the two groups (P=0.546) (Table 3). Sourcil Index was significantly higher in the Cam+ group than that in the Cam- group (Cam+: 57.4±5.6, Cam-: 44.5±6.0, P<0.001) (Table 3).

The AUCs of the ROC curves for the LCEA, ARO, VCA, FEAR index, and sourcil area angle were 0.79, 0.92, 0.65, 0.91, and 0.94, respectively. The ROC curves for ARO, FEAR index, and sourcil area angle demonstrated excellent discrimination. Using the Youden index, the cutoff values for discriminating between Cam+ and Cam- groups were determined to be 21.0° for LCEA (sensitivity, 0.86; specificity, 0.77), 15.1° for the ARO (sensitivity, 0.86; specificity, 0.91), 22.5° for the VCA angle (sensitivity, 0.85; specificity, 0.52), -2.2° for the FEAR index (sensitivity, 0.97; specificity, 0.77), and 49.5° for the Sourcil Index (sensitivity, 0.83; specificity, 0.91) (Figure3).

The most important finding of this study was that even among patients with BDDH, bone morphology differed significantly depending on the presence or absence of Cam lesion. Classifying BDDH as stable or unstable is necessary for successful treatment of these hips. However, this is difficult in practice and may lead to incorrect treatment outcomes. For example, if HA is performed on a patient whose problem is hip instability, the symptoms associated with instability are likely to persist. [4]. The present results suggest that patients with BDDH without Cam lesions have significantly more DDH-like bone morphology than those with Cam lesions, which may indicate that performing HA on these patients is at risk for leading to poor clinical outcomes.

　In a previous systematic review, BDDH was defined as an LCEA of 18–25° or 20-25° [1]. McQuivey et al. also reported higher rates of failure to reach the minimal clinically important difference and revision surgery when HA was performed in patients with BDDH and LCEA<20° [18]. Considering that the cutoff value for LCEA with and without Cam in this study was 21°, it is possible that the percentage of patients with BDDH and correctable Cam lesions who have LCEA of 18–20° is very low. Dornacher et al. reported that 192 of 397 patients who underwent triple pelvic osteotomy for acetabular dysplasia had an LCEA of 18–25°, and suggested that this high proportion may indicate the presence of a substantial acetabular deficiency that cannot be recognized by LCEA alone [7]. They also reported that 17.2% of patients with BDDH had anterolateral acetabular defects [7]. In this study, the VCA angle was significantly lower in the Cam- group, with a cutoff value of 22.5°. Patients with BDDH without Cam lesions should be checked especially for anterior acetabular coverage insufficiency.

In this study, the ARO was significantly different between the two groups with and without Cam lesions, with a cutoff value of 15.1°. Grammatopoulos et al. identified radiographic and intraoperative features that could predict the success of HA in patients with DDH and LCEA<25°. At a mean follow-up of 4.5 years, they concluded that HA could be associated with an excellent chance of hip preservation in patients with mild dysplasia and an ARO<15° [19]. Hatakeyama et al. also reported that a preoperative predictor of poorer outcomes after hip arthroscopic labral preservation, capsular plication, and cam osteoplasty in BDDH is ARO≥15° on preoperative radiograph [20]. Interestingly, this cutoff value is consistent with that of our study, and it may be that few patients with BDDH with Cam lesions who are more amenable to HA have an ARO<15°.

Wyatt et al. introduced the FEAR index as a new radiographic marker to help distinguish between stable and unstable hips with BDDH according to the biomechanical concept that the growth plate orients itself perpendicular to the joint reaction forces during growth. They suggested that painful hips with LCEA≤25° and FEAR index≥5° are likely associated with instability and are not recommended for HA. [4]. However, in other studies that subsequently analyzed the FEAR index and hip instability, the cutoff values varied from 2° or 3° [21, 22]. A Systematic review assessing the utility of the FEAR index concluded that although there is no absolute consensus value that determines treatment because the cutoff value of the FEAR index varies from study to study, a value greater than 0 to 5 suggests hip instability and that a preservation procedure such as PAO is more likely to be effective than HA [23]. In this study, the FEAR index was significantly different between the two groups with and without Cam lesions. However, the cutoff value was -2.2°, which was not within the above-mentioned range indicating hip instability.

Packer et al. observed a high rate of steep drop-off at the lateral edge of the femoral head in patients with hip microinstability who underwent HA, which they named the cliff sign. They reported that 89% of the patients diagnosed with microstability during HA had a cliff sign. [12]. In this study, there was no significant relationship between the presence of Cam lesions and the presence of the cliff sign. Therefore, the cliff sign, which suggests hip instability, is a factor completely independent of Cam lesions and should be confirmed thoroughly preoperatively. Horberg JV et al. described the Sourcil Index, a new factor of the weight bearing surface of the acetabulum[15]. They reported the average Sourcil Index in dysplastic hips was 55.4° and in non-dysplastic hips was 66.9°. In this study, patients without Cam lesion had significantly lower FI, with the same trend as for dysplastic hips.

Therefore, patients with BDDH without Cam lesions are likely to have significantly more DDH-like bone morphology and instability than those with Cam lesion. Uchida et al. reported good clinical results with endoscopic shelf acetabuloplasty for patients with BDDH and DDH [24]. McClincy et al. described that the patients with BDDH showed improvement in hip symptoms after PAO with minimal complications and reoperations at a minimum 2-year follow-up [6]. Thus, the surgery to improve acetabular coverage as described above may be a likely indication for patients with BDDH without Cam lesions.

This study has several limitations. First, the number of subjects in this study was relatively small. Therefore, further studies with larger sample sizes are warranted. Secondly, the sample was limited to Japanese patients. Therefore, an analysis of other populations, such as those in the United States and Europe, is required to confirm the generalizability of our results.

Patients with BDDH exhibited significant differences in bone morphology depending on the presence of Cam lesions. Moreover, those without Cam lesions displayed similarities to patients with DDH. For such patients, performing HA alone risks poor clinical outcomes, and surgery to improve acetabular coverage, such as PAO, may be indicated.

Funding

No funding was received by any of the authors in support of or in any relationship to the study.

Conflict of interests

The authors have no competing interests to declare.

Ethics approval

Our hospital’s ethics committee approved the protocol of this study.

Consent to participate and consent for publication

All subjects in this study were informed of the study protocol and written informed consent to participate and publish was obtained.

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Table 1. Intraclass correlation coefficients and Kappa coefficients for intra- and inter-observer reliabilities of measurements

Variable	Intra-observer	Inter-observer
LCEA	0.94	0.90
ARO	0.93	0.87
FEAR index	0.90	0.82
VCA angle	0.92	0.81
Cliff sign	0.90	0.80
Sourcil Index	0.96	0.90

LCEA, lateral center-edge angle

ARO, acetabular roof obliquity

FEAR index, femoral epiphyseal acetabular roof index

VCA angle, vertical center anterior angle

Table 2. Comparison of patient background characteristics between Cam+ and Cam- groups

	Cam+	Cam-	P-value
Number of patients	34	35
Age	36.2±14.3	31.1±12.3	0.113
Gender: Female ratio	19/34	27/35	0.106
BMI	22.9±2.9	22.7±4.0	0.832

BMI, body mass index

The data are expressed as mean ± SD values.

Table 3. Comparison of radiographic factors between Cam+ and Cam- groups

	Cam+	Cam-	P-value
LCEA	22.4±2.5	19.9±2.0	<0.001*
ARO	10.3±4.5	18.6±4.0	<0.001*
FEAR index	-6.7±6.8	3.4±4.4	<0.001*
VCA angle	25.5±7.6	18.2±5.7	<0.001*
Cliff sign	15/34 (44.1%)	19/35 (54.3%)	0.546
Sourcil Index	57.4±5.6	44.5±6.0	<0.001*

LCEA, lateral center-edge angle

ARO, acetabular roof obliquity

FEAR index, femoral epiphyseal acetabular roof index

VCA angle, vertical center anterior angle

* P<0.05

The data are expressed as mean ± SD values.

No competing interests reported.

Does hip bone morphology differ depending on the presence of Cam lesions in Borderline Developmental Dysplasia of the Hip?

Status:

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Abstract

Figures

Introduction

Materials and Methods

Results

Discussion

Conclusions

Declarations

References

Tables

Additional Declarations

Status:

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