A quantitative method to assess focal acetabular overcoverage resulting from pincer deformity using CT data

Deep learning-based workflow for hip joint morphometric parameter measurement from CT images

Objective.Precise hip joint morphometry measurement from CT images is crucial for successful preoperative arthroplasty planning and biomechanical simulations. Although deep learning approaches have been applied to clinical bone surgery planning, there is still a lack of relevant research on quantifying hip joint morphometric parameters from CT images.Approach.This paper proposes a deep learning workflow for CT-based hip morphometry measurement. For the first step, a coarse-to-fine deep learning model is designed for accurate reconstruction of the hip geometry (3D bone models and key landmark points). Based on the geometric models, a robust measurement method is developed to calculate a full set of morphometric parameters, including the acetabular anteversion and inclination, the femoral neck shaft angle and the inclination, etc. Our methods were validated on two datasets with different imaging protocol parameters and further compared with the conventional 2D x-ray-based measurement method.Main results. The proposed method yields high bone segmentation accuracies (Dice coefficients of 98.18% and 97.85%, respectively) and low landmark prediction errors (1.55 mm and 1.65 mm) on both datasets. The automated measurements agree well with the radiologists' manual measurements (Pearson correlation coefficients between 0.47 and 0.99 and intraclass correlation coefficients between 0.46 and 0.98). This method provides more accurate measurements than the conventional 2D x-ray-based measurement method, reducing the error of acetabular cup size from over 2 mm to less than 1 mm. Moreover, our morphometry measurement method is robust against the error of the previous bone segmentation step. As we tested different deep learning methods for the prerequisite bone segmentation, our method produced consistent final measurement results, with only a 0.37 mm maximum inter-method difference in the cup size.Significance. This study proposes a deep learning approach with improved robustness and accuracy for pelvis arthroplasty planning.

Sex differences in the anatomy of the anterior-superior acetabular rim in relation to pincer-type femoroacetabular impingement in Koreans: a three-dimensional quantitative analysis

PURPOSE

The aim of this study was to compare the anatomical structures of the acetabular rim around the anterior inferior iliac spine (AIIS) ridge that indicate anterior focal coverage of acetabulum between the sexes using a three-dimensional (3D) model.

METHODS

3D models of 71 adults (38 men and 33 women) with normal hip joints were used. Based on the location of the inflection point (IP) of the acetabular rim around the AIIS ridge, the patients were classified into anterior and posterior types, and the ratios thereof for each sex were compared. Coordinates for the IP, the most anterior point (MAP), and the most lateral point (MLP) were obtained and compared between the sexes and between anterior and posterior types.

RESULTS

Coordinates for IPs in men were located anterior and inferior to those in women. MAP coordinates for men were located inferior to those for women, and MLP coordinates for men were located lateral and inferior to those for women. Comparing AIIS ridge types, we noted that coordinates for IPs of the anterior type were located medial, anterior, and inferior to those of the posterior type. Meanwhile, MAP coordinates of the anterior type were located inferior to those of the posterior type, and MLP coordinates of the anterior type were located lateral and inferior to those of the posterior type.

CONCLUSION

Anterior focal coverage of the acetabulum appears to differ between the sexes, and this difference may affect the development of pincer-type femoroacetabular impingement (FAI). Additionally, we found that anterior focal coverage differs according to anterior or posterior positioning of the bony prominence around the AIIS ridge, which may affect development of FAI.

Pelvic Bone Deformity and Its Correlation with Acetabular Center-edge Angle

Objective  The purpose of the present study was to evaluate the pelvic bone deformities and its correlation with the acetabular center-edge (CE) angle. Methods  Between August 2014 and April 2015, we prospectively evaluated patients aged between 20 and 60 years old. The exclusion criteria were: metabolic disease, previous hip or spine surgery, radiograph showing hip arthrosis ≥ Tönnis two, severe hip dysplasia, global acetabular overcoverage, acetabular crossover sign, hip deformities from slipped capital femoral epiphysis (SCFE) or Leg-Perthes-Calveé, and bad quality radiographs. At anteroposterior (AP) pelvic radiographs, we have evaluated: the CE angle, the acetabular index (IA), the acetabular crossover sign, the vertical and horizontal superior and inferior pelvic axis (H1: Horizontal line 1, superior pelvic axis; H2: Horizontal line 2, superior pelvic axis; V1: Vertical line, superior pelvic axis; HR: Horizontal line, inferior pelvic axis; VR: Vertical line, inferior pelvic axis). The superior and inferior pelvic axis were considered asymmetric when there was a difference ≥ 5 mm between both sides. Patients were divided into two groups: control and group 1. Results  A total of 228 patients (456 hips) were evaluated in the period. According to the established criteria, 93 patients were included. The mean age was 39.9 years old (20 to 60 years old, standard deviation [SD] = 10,5), and the mean CE angle in the right hip was 31.5° (20 ^o to 40°), and in the left 32.3° (20 ^o to 40°). The control group had 38 patients, with asymmetric H1 in 4 cases (10.5%), H2 in 5 (13.1%), V1 in 7 (18.4%), HR in 5 (13.1%) and VR in 1 (2.63%). Group 1 had 55 patients, with asymmetric H1 in 24 cases (43.6%), H2 in 50 (90.9%), V1 in 28 (50.9%), HR in 16 (29.09%) and VR in 8 (14.5%). Comparing both groups, there was statistical significance for H1, H2 and V1 asymmetry ( p  < 0.001). Conclusion  In the present paper, we observed the correlation between variation in the acetabular CE angle and asymmetry of the superior hemipelvis. The present authors believe that a better understanding of the pelvic morphologic alterations allows a greater facility in the diagnosis of hip articular deformities.

The association between anterior femoroacetabular impingement and femoral neck fractures: An observational study

The impact between acetabulum and femoral neck is another possible mechanism of femoral neck fracture.Direct trauma of the greater trochanter may not be able to fully explain the mechanism underlying femoral neck fracture. In this study, we sought to investigate whether anterior femoroacetabular impingement are associated with femoral neck fractures.A total of 36 patients with femoral neck fracture who had undergone total hip arthroplasty or hemiarthroplasty were included in this study. These patients were divided into 2 groups: labrum tear group and normal labrum group. Patients' age, gender, body mass index, muscle injury, injury pattern, trauma severity, femoral head-neck offset, femoral head-neck ratio, Cam deformity alpha angle, acetabular anteversion, femoral head diameter, acetabular index, cortical index, hip axis length, and neck stem angle were recorded and analyzed. SPSS 18.0 software was used for statistical analyses.According to intraoperative findings, 22 patients exhibited a labrum tear. Magnetic resonance imaging examination revealed bone contusion on the anterolateral margin of the acetabulum with muscle damage surrounding the hip. Among 14 cases without a labrum tear, no bone contusion and obvious muscle injury were found on the anterolateral margin of the acetabulum. Notably, muscle injury, injury pattern, trauma severity and femoral head-neck offset differed significantly (P < .05) between labrum tear and normal labrum groups.Previous studies have focused more on direct lateral trauma. In this study, the impact between acetabulum and femoral neck is another possible mechanism besides lateral impact. Specifically, the abnormal anatomy of the hip, such as femoral head-neck offset, may promote the fracturing process.

Femoroacetabular impingement with chronic acetabular rim fracture - 3D computed tomography, 3D magnetic resonance imaging and arthroscopic correlation

Femoroacetabular impingement is uncommonly associated with a large rim fragment of bone along the superolateral acetabulum. We report an unusual case of femoroacetabular impingement (FAI) with chronic acetabular rim fracture. Radiographic, 3D computed tomography, 3D magnetic resonance imaging and arthroscopy correlation is presented with discussion of relative advantages and disadvantages of various modalities in the context of FAI.

Variability of acetabular coverage between supine and weightbearing pelvic radiographs

BACKGROUND

Radiographic measures of acetabular coverage are essential screening tools used to characterize bony structure contributing to femoroacetabular impingement (FAI). Small changes in pelvic tilt result in altered radiographic measures of acetabular coverage. Positional changes in pelvic tilt are known to occur between the supine and weightbearing positions. It is unclear whether alteration of pelvic tilt between these positions is clinically sufficient to influence measures of acetabular coverage.

PURPOSE/HYPOTHESIS

To determine whether, and to what degree, imaging position (supine vs weightbearing) is capable of altering several measures of acetabular orientation: pubic symphysis to sacrococcygeal distance (PSSC), angle of Sharp (SA), Tönnis angle (TA), percentage of acetabular crossover (CO), and lateral center-edge angle of Wiberg (LCEA). The hypothesis was that imaging position would significantly alter all measures of acetabular orientation.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 2.

METHODS

A total of 50 consecutive symptomatic hips referred to a single provider for FAI were evaluated with standardized supine and weightbearing anteroposterior pelvic radiographs. Two independent reviewers blinded to patient positioning reviewed each radiograph at 2 separate time points. Mean measurements in each position were compared by use of paired Student t tests, and a Bonferroni-adjusted significance level of P = .01 was used to represent significance.

RESULTS

Statistically significant differences between the supine and weightbearing radiographs were identified for PSSC and all measures of acetabular coverage (P < .003). The mean PSSC decreased between the supine and weightbearing positions by an average of 13.4 mm (P < .001), thereby resulting in decreased mean LCEA, TA, SA, and CO of 1.2°, 1.3°, 0.8°, and 6.3%, respectively (P < .002). The change in positional pelvic tilt was not uniformly predictable and accounted for large measurement changes in some individuals. PSSC also demonstrated considerable inter- and intrasubject variability but averaged 55.8 mm supine and 44.9 mm weightbearing for females and 37.0 mm supine and 20.6 mm weightbearing for males.

CONCLUSION

In this study of nonarthritic adult patients with hip pain, the data indicate that positional changes are capable of significantly altering pelvic tilt and radiographic measures of acetabular coverage. It appears that the weightbearing position typically, but not universally, correlates with additional posterior pelvic tilt and decreased measures of acetabular coverage. Individual positional variability can contribute to large-magnitude changes in radiographic acetabular measures.

Bony abnormalities of the hip joint: a new comprehensive, reliable and radiation-free measurement method using magnetic resonance imaging

OBJECTIVES

To develop comprehensive and reliable radiation-free methods to quantify femoral and acetabular morphology using MRI.

METHODS

32 hips (16 subjects, 6 with intra-articular hip disorder (IAHD); 10 controls) were included. A 1.5T magnetic resonance system was used to obtain 3D fat suppressed gradient echo images at the pelvis and distal femora. After acquisition, pelvic images were post-processed to correct for coronal, axial and sagittal rotation. Measurements performed included acetabular version (AV), femoral version (FV), lateral center edge angle (LCEA), femoral neck angle (FNA) and alpha angle (AA) at 3, 2, 1 and 12 o'clock. Two experienced raters, a musculoskeletal radiologist and an orthopaedic physical therapist, and a novice rater, a research assistant, completed reliability testing. Raters measured all hips twice with minimum 2 weeks between sessions. Intraclass Correlation Coefficients were used to determine rater reliability; standard error of measurements was reported to estimate the reasonable limits of the expected error in the different raters' scores.

RESULTS

Interrater reliability was good to excellent for all raters for AV, FV, FNA, and LCEA (ICCs: 0.82-0.98); good to excellent between experienced raters (ICCs: 0.78-0.86) and poor to good between novice and experienced raters (ICCs: 0.23-0.78) for AA. Intrarater reliability was good to excellent for all raters for AV, FV and FNA (ICCs: 0.93-0.99); for one experienced and novice rater for LCEA (ICCs: 0.84-0.89); moderate to excellent for the experienced raters for AA (ICCs: 0.72-0.89). Intrarater reliability was poor for the second experienced rater for LCEA (ICC: 0.56), due to a single measurement error and for the novice rater for AA (ICCs: 0.17-0.38).

CONCLUSION

We described MRI methods to comprehensively assess femoral and acetabular morphology. Measurements such as AV, FV and FNA and the LCEA can be made reliably by both experienced and novice raters, however the AA measurement was reliable only among experienced raters.

The effect of pelvic tilt on radiographic markers of acetabular coverage

BACKGROUND

Radiographic indices of acetabular coverage are crucial to objectively characterize femoroacetabular impingement and plan bony decompression. It is established that changes in pelvic inclination result in alterations of acetabular crossover; however, it is unclear what influence this has on other measures of acetabular anatomy.

HYPOTHESIS

The objective of the present study was to determine if, and to what degree, a variation in pelvic tilt alters 4 measures of acetabular anatomy: the angle of Sharp, Tönnis angle, percentage of acetabular crossover, and lateral center edge angle (LCEA). The hypothesis was that pelvic tilt would significantly alter all measures of acetabular coverage.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Fluoroscopic images of 8 adult hemipelvises were obtained at 7 positions of rotation in the sagittal plane to investigate the change of each measurement in response to pelvic orientation. Two reviewers obtained measurements from each image at 2 separate time points.

RESULTS

Each increment of pelvic inclination resulted in increased measures of acetabular coverage for all measurements, whereas each increment of decreased pelvic inclination resulted in decreased measures of acetabular coverage for all measurements. Significant differences in the measured LCEA, acetabular crossover, and Tönnis angle were identified at each increment of tilt as compared with neutral radiographs. No significant differences could be identified for the angle of Sharp.

CONCLUSION

Pelvic tilt significantly alters the measures of LCEA, crossover, and Tönnis angle in this cadaveric study. Pelvic inclination results in increased measures of acetabular coverage, whereas decreasing inclination decreases each measure.

CLINICAL RELEVANCE

Given the known individual and positional pelvic tilt variability, standing anteroposterior pelvic radiographs may provide a more physiological representation of acetabular coverage in the young adult population.

The relevance of the radiological signs of acetabular retroversion among patients with femoroacetabular impingement

Orthopaedic surgeons have accepted various radiological signs to be representative of acetabular retroversion, which is the main characteristic of focal over-coverage in patients with femoroacetabular impingement (FAI). Using a validated method for radiological analysis, we assessed the relevance of these signs to predict intra-articular lesions in 93 patients undergoing surgery for FAI. A logistic regression model to predict chondral damage showed that an acetabular retroversion index (ARI) > 20%, a derivative of the well-known cross-over sign, was an independent predictor (p = 0.036). However, ARI was less significant than the Tönnis classification (p = 0.019) and age (p = 0.031) in the same model. ARI was unable to discriminate between grades of chondral lesions, while the type of cam lesion (p = 0.004) and age (p = 0.047) were able to. Other widely recognised signs of acetabular retroversion, such as the ischial spine sign, the posterior wall sign or the cross-over sign were irrelevant according to our analysis. Regardless of its secondary predictive role, an ARI > 20% appears to be the most clinically relevant radiological sign of acetabular retroversion in symptomatic patients with FAI.