Acetabular deficiency in borderline hip dysplasia is underestimated by lateral center edge angle alone

INTRODUCTION

In hip preservation surgery, the term "borderline hip dysplasia" was used when the lateral center edge angle (LCEA), historically described by Wiberg, measured 18-25°. In recent years, several radiographic parameters have been described to assess the antero posterior coverage of the femoral head, for example, the anterior and posterior wall index (AWI and PWI). This allowed an increasingly comprehensive understanding of acetabular morphology and a questioning of the borderline definition.

MATERIAL AND METHODS

A retrospective review of 397 consecutive hips was performed, all treated with triple pelvic osteotomy (TPO) due to symptomatic hip dysplasia. On all preoperative pelvic radiographs with a LCEA of 18-25°, acetabular index (AI), AWI and PWI were measured. With these values, the hips were categorized into laterally, antero-laterally and postero-laterally dysplastic and stratified by gender. Intra- and interobserver correlation of the parameters was analyzed by intraclass correlation coefficient (ICC).

RESULTS

According to LCEA, 192 hips were identified as "borderline dysplastic". Based on AWI and PWI, the categorization resulted in 116 laterally dysplastic (60.4%), 33 antero-laterally (17.2%) and 43 postero-laterally dysplastic hips (22.4%). Gender stratification revealed that male acetabula seemed to be slightly more postero-laterally deficient than female (mean PWI 0.80 vs 0.89; p = 0.017). ICC confirmed highly accurate and reproducible readings of all parameters.

CONCLUSION

The rather high proportion of symptomatic hips labelled borderline dysplastic suggested, that there might be substantial acetabular deficiency not recognizable by LCEA. Comprehensive deformity analysis using LCEA, AI, AWI and PWI showed, that 40% of these hips were deficient either antero-laterally or postero-laterally. Male acetabula were more deficient postero-laterally than female.

Evaluation of lateral and anterior center-edge angles according to sex and anterior pelvic plane tilt angle: a three-dimensional quantitative analysis

BACKGROUND

This study aimed to quantitatively evaluate lateral center-edge angle (LCEA) and anterior center-edge angle (ACEA) according to sex and the anterior pelvic plane (APP) tilt angle and analyze the correlation between these measurements and acetabular coverage.

METHODS

Computed tomography scans of 71 adults (38 men and 33 women) with normal hip joints were obtained. LCEA, anterior ACEA, and acetabular coverage were measured with APP tilt every 5° from - 30° to + 30° and were compared between the sexes. The correlation between acetabular coverage and LCEA/ACEA was also analyzed.

RESULTS

(1) LCEA, ACEA, and acetabular coverage were statistically larger in men than in women at all APP tilt angles (with the exception of acetabular coverage ≥ 25°). (2) LCEA, ACEA, and acetabular coverage differed according to APP tilt angle. LCEA and acetabular coverage showed maximum values at 10°. ACEA showed a tendency to increase by an average of 3.6° for every 5° increase in the APP tilt angle. LCEA demonstrated strong and very strong associations across all APP tilting angles, whereas ACEA showed a moderate association at angles ≥ 15° in men and ≥ 30° in women.

CONCLUSIONS

The LCEA and ACEA are adequate measurement methods that reflect actual acetabular coverage unless the pelvis is tilted excessively anteriorly. While pelvic tilting does not need to be considered for LCEA within the physiologic range, it should always be taken into account for ACEA, as it increases by an average of 3.6° for every 5° increase in APP tilt angle.

LEVEL OF EVIDENCE

Level III: retrospective cohort study.

Does hip morphology correlate with proximal femoral fracture type?

PURPOSE

To determine if boney morphology influences the anatomic location of hip fractures in elderly patients.

METHODS

All patients with hip fractures between 2008 and 2012 who had hip radiographs taken prior to the fracture were reviewed. Fractures were classified as intracapsular or extracapsular and hip morphology was measured on the pre-fracture x-rays. Hip morphology was determined by alpha angle, lateral central edge angle, acetabular index, neck-shaft angle, hip axis length, femoral neck diameter, Tönnis classification for hip osteoarthritis (OA) and the presence of a crossover sign.

RESULTS

148 subjects (78.4% female, age 83.5 years) with proximal femur fractures were included. 44 patients (29.7%) had intracapsular fractures and 104 (70.3%) had extracapsular fractures. 48% of patients had previous hip fractures on the contralateral side and 74.6% had the same type of fracture bilaterally. The rates of bilateral intracapsular and extracapsular fractures were similar (33.7% vs. 40.9% respectively, p = 0.39). Extracapsular fractures had a statically significant higher neck-shaft angle, a shorter hip axis length, a narrower femoral neck diameter and a higher grade of Tönnis classification of OA (p = 0.04, 0.046, 0.03, 0.02 respectively). Acetabular coverage and the proximal femoral head-neck junction, which were evaluated by lateral centre-edge angle (LCEA), acetabular index and the presence of a crossover sign, did not correlate with fracture type. The alpha angle > 40° had a statistically significant higher likelihood for extracapsular fractures (p = 0.013).

CONCLUSIONS

Acetabular coverage and proximal femoral head-neck junction morphology, were found to partially correlate with the location of hip fractures and do not fully elucidate fracture type susceptibility.

Validation of a new 2.5D radiographic index evaluating acetabular coverage using ACX software

BACKGROUND

Several radiographic signs have been described to assess acetabular coverage. However, plain radiographs only have 2 dimensions (2D) and cannot accurately show acetabular coverage.

QUESTIONS/PURPOSES

We developed the ACX Dynamics software to calculate the radial centre-edge angle (RCEA), which represents the acetabular coverage of the femoral head at each acetabular edge point on the radial plane. This study validated the accuracy of the RCEA, as calculated by ACX Dynamics, as a quantitative parameter for acetabular coverage.

PATIENTS AND METHODS

We reviewed the anteroposterior (AP) pelvic radiographs and computed tomography (CT) of 650 hips from 325 patients who presented with chief complaint of symptoms at the hip joint. Of 109 hip radiographs (68 patients) that satisfied the criteria, 50 randomised, blinded AP pelvic radiographs were chosen. We determined the absolute RCEA difference (°) [= RCEA ACX (°) - RCEA CT (°)], determined the correlation between RCEA ACX (°) and RCEA CT (°), and examined the RCEA's intra-observer and inter-observer reliability in 50 hips.

RESULTS

The absolute RCEA difference from A45° to P75° was 1.9-3.1°. The correlation between the RCEA ACX (°) and RCEA CT (°) was > 0.7 in all lesions (p < 0.001). Using the intraclass correlation coefficient, the intra-observer reliability of the RCEA was 0.83-0.97 in the whole range, which is a highly reproducible and reasonable parameter, and the inter-observer reliability was > 0.80 in A45°-P0°.

CONCLUSIONS

The RCEA ACX (°) can be used as a simple quantitative parameter for assessing acetabular coverage using AP pelvic radiograph.

Does acetabular coverage influence the clinical outcome of arthroscopically treated cam-type femoroacetabular impingement (FAI)?

Aims

What represents clinically significant acetabular undercoverage in patients with symptomatic cam-type femoroacetabular impingement (FAI) remains controversial. The aim of this study was to examine the influence of the degree of acetabular coverage on the functional outcome of patients treated arthroscopically for cam-type FAI.

Patients and Methods

Between October 2005 and June 2016, 88 patients (97 hips) underwent arthroscopic cam resection and concomitant labral debridement and/or refixation. There were 57 male and 31 female patients with a mean age of 31.0 years (17.0 to 48.5) and a mean body mass index (BMI) of 25.4 kg/m² (18.9 to 34.9). We used the Hip2Norm, an object-oriented-platform program, to perform 3D analysis of hip joint morphology using 2D anteroposterior pelvic radiographs. The lateral centre-edge angle, anterior coverage, posterior coverage, total femoral coverage, and alpha angle were measured for each hip. The presence or absence of crossover sign, posterior wall sign, and the value of acetabular retroversion index were identified automatically by Hip2Norm. Patient-reported outcome scores were collected preoperatively and at final follow-up with the Hip Disability and Osteoarthritis Outcome Score (HOOS).

Results

At a mean follow-up of 2.7 years (1 to 8, sd 1.6), all functional outcome scores significantly improved overall. Radiographically, only preoperative anterior coverage had a negative correlation with the improvement of the HOOS symptom subscale (r = -0.28, p = 0.005). No significant difference in relative change in HOOS subscale scores was found according to the presence or absence of radiographic signs of retroversion.

Discussion

Our study demonstrated the anterior coverage as an important modifier influencing the functional outcome of arthroscopically treated cam-type FAI. Cite this article: Bone Joint J 2018;100-B:831-8.

Radiographic evaluation of early periprosthetic acetabular bone contrast and prosthetic head acetabular coverage after uncemented and cemented total hip prosthesis in dogs

BACKGROUND

Coxofemoral osteoarthritis is a chronic, disabling condition affecting people and dogs, with THA providing an excellent return to function in severely affected joints. The principal role of THA is to restore an adequate range of motion to the hip joint while transferring load from the acetabulum in order to improve the survival of the implant and enhance the limb function in the short and long terms. The objectives of the study reported here were, therefore, to radiographically evaluate periprosthetic acetabular bone GV and to assess prosthetic head acetabular coverage after 4 months of uncemented and cemented THA in dogs. Means periprosthetic acetabular GV for each and combined 3 regions of interest (zones 1, 2 and 3) were calculated immediately and 4 months after THA. Prosthetic head Norberg (PHN) angle was also measured to assess the degree of prosthetic head acetabular coverage after 4 months of surgery.

RESULTS

Zones 2 and 3 showed a significant increase in the mean bone GV after 4 months of uncemented THA. No differences in zones 1-3 after 4 months of cemented THA. Combined zones showed a significant increase in overall mean bone GV 4 months after uncemented THA; whereas, no changes were identified after 4 months of cemented THA. The PHN angles did not change after 4 months of uncemented and cemented THA and did not differ significantly between the 2 designs of hip arthroplasty.

CONCLUSIONS

Regional periprosthetic acetabular bone GV varies with the design of THA. None of the designs showed periprosthetic acetabular bone lucency. No differences identified in the degree of prosthetic head acetabular coverage in both designs, indicating proper implant stability after 4 months of surgery. Further longer-term investigation on larger population is however still warranted.

Toward automated classification of acetabular shape in ultrasound for diagnosis of DDH: Contour alpha angle and the rounding index

BACKGROUND AND OBJECTIVES

The diagnosis of Developmental Dysplasia of the Hip (DDH) in infants is currently made primarily by ultrasound. However, two-dimensional ultrasound (2DUS) images capture only an incomplete portion of the acetabular shape, and the alpha and beta angles measured on 2DUS for the Graf classification technique show high inter-scan and inter-observer variability. This variability relates partly to the manual determination of the apex point separating the acetabular roof from the ilium during index measurement. This study proposes a new 2DUS image processing technique for semi-automated tracing of the bony surface followed by automatic calculation of two indices: a contour-based alpha angle (αA), and a new modality-independent quantitative rounding index (M). The new index M is independent of the apex point, and can be directly extended to 3D surface models.

METHODS

We tested the proposed indices on a dataset of 114 2DUS scans of infant hips aged between 4 and 183 days scanned using a 12MHz linear transducer. We calculated the manual alpha angle (αM), coverage, contour-based alpha angle and rounding index for each of the recordings and statistically evaluated these indices based on regression analysis, area under the receiver operating characteristic curve (AUC) and analysis of variance (ANOVA).

RESULTS

Processing time for calculating αA and M was similar to manual alpha angle measurement, ∼30s per image. Reliability of the new indices was high, with inter-observer intraclass correlation coefficients (ICC) 0.90 for αA and 0.89 for M. For a diagnostic test classifying hips as normal or dysplastic, AUC was 93.0% for αA vs. 92.7% for αM, 91.6% for M alone, and up to 95.7% for combination of M with αM, αA or coverage.

CONCLUSIONS

The rounding index provides complimentary information to conventional indices such as alpha angle and coverage. Calculation of the contour-based alpha angle and rounding index is rapid, shows potential to improve the reliability and accuracy of DDH diagnosis from 2DUS, and could be extended to 3D ultrasound in future.