Patient-Specific 3-D Magnetic Resonance Imaging-Based Dynamic Simulation of Hip Impingement and Range of Motion Can Replace 3-D Computed Tomography-Based Simulation for Patients With Femoroacetabular Impingement: Implications for Planning Open Hip Preservation Surgery and Hip Arthroscopy

3.0T magnetic resonance imaging-based hip bone models for femoroacetabular impingement syndrome are equivalent to computed tomography-based models

This study aimed to compare three-dimensional (3D) proximal femoral and acetabular surface models generated from 3.0T magnetic resonance imaging (MRI) to the clinical gold standard of computed tomography (CT). Ten intact fresh-frozen cadaveric hips underwent CT and 3.0T MRI scans. The CT- and MRI-based segmented models were superimposed using a validated 3D-3D registration volume-merge method to compare them. The least surface-to-surface distance between the models was calculated by a point-to-surface calculation algorithm using a custom-written program. The variables of interest were the signed and absolute surface-to-surface distance between the paired bone models. One-sample t-tests were performed using a signed and absolute test value of 0.16 mm and 0.37 mm, respectively, based on a previous study that validated 1.5T MRI bone models by comparison with CT bone models. For the femur, the average signed and absolute surface-to-surface distance was 0.18 ± 0.09 mm and 0.30 ± 0.06 mm, respectively. There was no difference in the signed surface-to-surface distance and the 0.16 mm test value (t = 0.650, p = 0.532). However, the absolute surface-to-surface difference was less than the 0.37 mm test value (t = -4.025, p = 0.003). For the acetabulum, the average signed and absolute surface-to-surface distance was -0.06 ± 0.06 mm and 0.26 ± 0.04 mm, respectively. The signed (t = -12.569, p < 0.001) and absolute (t = -8.688, p < 0.001) surface-to-surface difference were less than the 0.16 mm and 0.37 mm test values, respectively. Our data shows that 3.0T MRI bone models are more similar to CT bone models than previously validated 1.5T MRI bone models. This is likely due to the higher resolution of the 3T data.

Hip-spine relationship: clinical evidence and biomechanical issues

The hip-spine relationship is a critical consideration in total hip arthroplasty (THA) procedures. While THA is generally successful in patient, complications such as instability and dislocation can arise. These issues are significantly influenced by the alignment of implant components and the overall balance of the spine and pelvis, known as spinopelvic balance. Patients with alteration of those parameters, in particular rigid spines, often due to fusion surgery, face a higher risk of THA complications, with an emphasis on complications in instability, impingement and dislocation. For these reasons, over the years, computer modelling and simulation techniques have been developed to support clinicians in the different steps of surgery. The aim of the current review is to present current knowledge on hip-spine relationship to serve as a common platform of discussion among clinicians and engineers. The offered overview aims to update the reader on the main critical aspects of the issue, from both a theoretical and practical perspective, and to be a valuable introductory tool for those approaching this problem for the first time.

Femoroacetabular Impingement Measurements Obtained From Two-Dimensional Radiographs Versus Three-Dimensional-Reconstructed Computed Tomography Images Result in Different Values

Purpose

To compare the reliability and accuracy of radiographic measurements obtained from 2-dimensional (2D) radiographs and 3-dimensional (3D)-reconstructed computed tomography (CT) images in the assessment of femoroacetabular impingement syndrome (FAIS).

Methods

Consecutive patients with FAIS from January 2018 to December 2020 were identified and included in this study. Two fellowship-trained surgeons and 2 fellows performed blinded radiographic measurements. Lateral center-edge angle (LCEA) and Tönnis angles were measured on anteroposterior pelvic radiographs, and alpha angles were measured on frog lateral radiographs. Reliability coefficients for individual measurement accuracy were performed using the Cronbach alpha and intra- and inter-rater intraclass correlation coefficients (ICCs). Composite measurements for LCEA, Tönnis angle, and alpha angle were compared with the corresponding 3D value using paired sample t-tests.

Results

Fifty-three patients with FAIS with standardized 2D radiographic and 3D-reconstructed CT imaging were included. All reliability metrics met thresholds for internal reliability. Inter-rater ICCs for LCEA, Tönnis angle, and alpha angle were (0.928, 0.888, 0.857, all P < .001). When we compared 2D radiographic measurements with 3D-reconstructed CT values, there was a significant difference in the LCEA for 2 authors: surgeon 1 (mean [M] = -9.14, standard deviation [SD] = 5.7); t(52) = -11.6, P < .001, and surgeon 2 (M = -5.9°, SD = 4.7); t(52) = -9.2, P < .001. Significant differences were seen for Tönnis angle for 2 authors: fellow 2 (M = 3.9°, SD = 5.6); t(52) = 5.1, P < .001, and surgeon 2 (M = -2.6°, SD = 4.1); t(52) = -4.6, P < .001. Alpha angle measurements compared to the 3D-reconstructed alpha angle at 2 o'clock was significantly different for 3 authors: fellow 1 (M = 11.9°, SD = 16.2); t(52) = 5.3, P < .001; fellow 2 (M = 10.4°, SD = 18.6); t(52) = 4.1, P = .002; and surgeon 2 (M = -6.5°, SD = 16.2); t(52) = -2.9, P = .005. Positive mean values indicate 2D radiographic measurements overestimated 3D reconstruction values and negative mean values indicate underestimation.

Conclusions

The use of 2D radiographs alone for preoperative planning of FAIS may lead to inaccuracies in radiographic measurements.

Level of Evidence

Level, III retrospective cohort study.

Evaluating computed bony range of motion (BROM) by registering in-vitro cadaver-based functional range of motion (FROM) to a hip motion simulation

BACKGROUND

While modern hip replacement planning relies on hip motion simulation (HMS), it lacks the capability to include soft-tissues and ligaments restraints on computed bony range of motion (BROM), often leading to an overestimation of the in-vivo functional range of motion (FROM). Furthermore, there is a lack of literature on BROM assessment in relation to FROM. Therefore, the study aimed to assess computed BROM using in-vitro cadaver-derived FROM measurements, registered to a CT-based in-house HMS, and to further investigate the effect of functional and anatomical hip joint centres (FHJC and AHJC) on BROM.

METHOD

Seven limiting and three non-limiting circumducted passive FROM of four cadaver hips were measured using optical coordinate measuring machine with reference spheres (RSs) affixed to the pelvis and the femur, following CT-scan of the specimen. The RSs' centres were used to register the measured FROM in HMS, enabling its virtual recreation to compute corresponding BROM by detecting nearest bony impingement. FHJC, estimated from non-limiting FROM, was compared with AHJC to examine their positional differences and effect on BROM.

RESULTS

Differences in BROM and FROM were minimal in deep flexion (3.0° ± 4.1°) and maximum internal rotation (IR) at deep flexion (3.0° ± 2.9°), but substantially greater in extension (53.2° ± 9.5°). Bony impingement was observed during flexion, and IR at deep flexion for two hips. The average positional difference between FHJC and AHJC was 3.1 ± 1.2 mm, resulting in BROM differences of 1°-13° across four motions.

CONCLUSIONS

The study provided greater insight into the applicability and reliability of computed BROM in pre-surgical planning.

Magnetic resonance imaging-based bone imaging of the lower limb: Strategies for generating high-resolution synthetic computed tomography

This study aims at assessing approaches for generating high-resolution magnetic resonance imaging- (MRI-) based synthetic computed tomography (sCT) images suitable for orthopedic care using a deep learning model trained on low-resolution computed tomography (CT) data. To that end, paired MRI and CT data of three anatomical regions were used: high-resolution knee and ankle data, and low-resolution hip data. Four experiments were conducted to investigate the impact of low-resolution training CT data on sCT generation and to find ways to train models on low-resolution data while providing high-resolution sCT images. Experiments included resampling of the training data or augmentation of the low-resolution data with high-resolution data. Training sCT generation models using low-resolution CT data resulted in blurry sCT images. By resampling the MRI/CT pairs before the training, models generated sharper images, presumably through an increase in the MRI/CT mutual information. Alternatively, augmenting the low-resolution with high-resolution data improved sCT in terms of mean absolute error proportionally to the amount of high-resolution data. Overall, the morphological accuracy was satisfactory as assessed by an average intermodal distance between joint centers ranging from 0.7 to 1.2 mm and by an average intermodal root-mean-squared distances between bone surfaces under 0.7 mm. Average dice scores ranged from 79.8% to 87.3% for bony structures. To conclude, this paper proposed approaches to generate high-resolution sCT suitable for orthopedic care using low-resolution data. This can generalize the use of sCT for imaging the musculoskeletal system, paving the way for an MR-only imaging with simplified logistics and no ionizing radiation.

Posterior Hip Impingement at Maximal Hip Extension in Female Patients With Increased Femoral Version or Increased McKibbin Index and Its Effect on Sports Performance

Background

The location of posterior hip impingement at maximal extension in patients with posterior femoroacetabular impingement (FAI) is unclear.

Purpose

To investigate the frequency and area of impingement at maximal hip extension and at 10° and 20° of extension in female patients with increased femoral version (FV) and posterior hip pain.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

Osseous patient-specific 3-dimensional (3D) models were generated of 50 hips (37 female patients, 3D computed tomography) with a positive posterior impingement test and increased FV (defined as >35°). The McKibbin index (combined version) was calculated as the sum of FV and acetabular version (AV). Subgroups of patients with an increased McKibbin index >70° (24 hips) and FV >50° (20 hips) were analyzed. A control group of female participants (10 hips) had normal FV, normal AV, and no valgus deformity (neck-shaft angle, <139°). Validated 3D collision detection software was used for simulation of osseous impingement-free hip extension (no rotation).

Results

The mean impingement-free maximal hip extension was significantly lower in patients with FV >35° compared with the control group (15° ± 15° vs 55° ± 19°; P < .001). At maximal hip extension, 78% of patients with FV >35° had osseous posterior extra-articular ischiofemoral hip impingement. At 20° of extension, the frequency of posterior extra-articular ischiofemoral impingement was significantly higher for patients with a McKibbin index >70° (83%) and for patients with FV >35° (76%) than for controls (0%) (P < .001 for both). There was a significant correlation between maximal extension (no rotation) and FV (r = 0.46; P < .001) as well as between impingement area at 20° of extension (external rotation [ER], 0°) and McKibbin index (0.61; P < .001). Impingement area at 20° of extension (ER, 0°) was significantly larger for patients with McKibbin index >70° versus <70° (251 vs 44 mm²; P = .001).

Conclusion

The limited hip extension found in our study could theoretically affect the performance of sports activities such as running, ballet dancing, or lunges. Therefore, although not examined directly in this study, these activities are not advisable for these patients. Preoperative evaluation of FV and the McKibbin index is important in female patients with posterior hip pain before hip preservation surgery (eg, hip arthroscopy).

A radiomics approach to the diagnosis of femoroacetabular impingement

Introduction

Femoroacetabular Impingement (FAI) is a hip pathology characterized by impingement of the femoral head-neck junction against the acetabular rim, due to abnormalities in bone morphology. FAI is normally diagnosed by manual evaluation of morphologic features on magnetic resonance imaging (MRI). In this study, we assess, for the first time, the feasibility of using radiomics to detect FAI by automatically extracting quantitative features from images.

Material and methods

17 patients diagnosed with monolateral FAI underwent pre-surgical MR imaging, including a 3D Dixon sequence of the pelvis. An expert radiologist drew regions of interest on the water-only Dixon images outlining femur and acetabulum in both impingement (IJ) and healthy joints (HJ). 182 radiomic features were extracted for each hip. The dataset numerosity was increased by 60 times with an ad-hoc data augmentation tool. Features were subdivided by type and region in 24 subsets. For each, a univariate ANOVA F-value analysis was applied to find the 5 features most correlated with IJ based on p-value, for a total of 48 subsets. For each subset, a K-nearest neighbor model was trained to differentiate between IJ and HJ using the values of the radiomic features in the subset as input. The training was repeated 100 times, randomly subdividing the data with 75%/25% training/testing.

Results

The texture-based gray level features yielded the highest prediction max accuracy (0.972) with the smallest subset of features. This suggests that the gray image values are more homogeneously distributed in the HJ in comparison to IJ, which could be due to stress-related inflammation resulting from impingement.

Conclusions

We showed that radiomics can automatically distinguish IJ from HJ using water-only Dixon MRI. To our knowledge, this is the first application of radiomics for FAI diagnosis. We reported an accuracy greater than 97%, which is higher than the 90% accuracy for detecting FAI reported for standard diagnostic tests (90%). Our proposed radiomic analysis could be combined with methods for automated joint segmentation to rapidly identify patients with FAI, avoiding time-consuming radiological measurements of bone morphology.

Limited External Rotation and Hip Extension Due to Posterior Extra-articular Ischiofemoral Hip Impingement in Female Patients With Increased Femoral Anteversion: Implications for Sports, Sexual, and Daily Activities

BACKGROUND

Posterior femoroacetabular impingement (FAI) is poorly understood. Patients with increased femoral anteversion (FV) exhibit posterior hip pain.

PURPOSE

To correlate hip impingement area with FV and with combined version and to investigate frequency of limited external rotation (ER) and hip extension (<40°, <20°, and <0°) due to posterior extra-articular ischiofemoral impingement.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Osseous patient-specific three-dimensional (3D) models based on 3D computed tomography scans were generated of 37 female patients (50 hips) with positive posterior impingement test (100%) and increased FV >35° (Murphy method). Surgery was performed in 50% of patients (mean age, 30 years; 100% female). FV and acetabular version (AV) were added to calculate combined version. Subgroups of patients (24 hips) with increased combined version >70° and patients (9 valgus hips) with increased combined version >50° were analyzed. The control group (20 hips) had normal FV, normal AV, and no valgus. Bone segmentation was performed to generate 3D models of every patient. Validated 3D collision detection software was used for simulation of impingement-free hip motion (equidistant method). Impingement area was evaluated in combined 20° of ER and 20° of extension.

RESULTS

Posterior extra-articular ischiofemoral impingement occurred between the ischium and the lesser trochanter in 92% of patients with FV >35° in combined 20° of ER and 20° of extension. Impingement area in combined 20° of ER and 20° of extension was larger with increasing FV and with higher combined version; correlation was significant (P < .001, r = 0.57, and r = 0.65). Impingement area was significantly (P = .001) larger (681 vs 296 mm²) for patients with combined version >70° (vs <70°, respectively) in combined 20° of ER and 20° of extension. All symptomatic patients with increased FV >35° (100%) had limited ER <40°, and most (88%) had limited extension <40°. The frequency of posterior intra- and extra-articular hip impingement of symptomatic patients (100% and 88%, respectively) was significantly (P < .001) higher compared with the control group (10% and 10%, respectively). The frequency of patients with increased FV >35° with limited extension <20° (70%) and patients with limited ER <20° (54%) was significantly (P < .001) higher compared with the control group (0% and 0%, respectively). The frequency of completely limited extension <0° (no extension) and ER <0° (no ER in extension) was significantly (P < .001) higher for valgus hips (44%) with combined version >50° compared with patients with FV >35° (0%).

CONCLUSION

All patients with increased FV >35° had limited ER <40°, and most of them had limited extension <20° due to posterior intra- or extra-articular hip impingement. This is important for patient counselling, for physical therapy, and for planning of hip-preservation surgery (eg, hip arthroscopy). This finding has implications and could limit daily activities (long-stride walking), sexual activity, ballet dancing, and sports (eg, yoga or skiing), although not studied directly. Good correlation between impingement area and combined version supports evaluation of combined version in female patients with positive posterior impingement test or posterior hip pain.

Femoral impingement in maximal hip flexion is anterior-inferior distal to the cam deformity in femoroacetabular impingement patients with femoral retroversion : implications for hip arthroscopy

AIMS

Femoroacetabular impingement (FAI) patients report exacerbation of hip pain in deep flexion. However, the exact impingement location in deep flexion is unknown. The aim was to investigate impingement-free maximal flexion, impingement location, and if cam deformity causes hip impingement in flexion in FAI patients.

METHODS

A retrospective study involving 24 patients (37 hips) with FAI and femoral retroversion (femoral version (FV) < 5° per Murphy method) was performed. All patients were symptomatic (mean age 28 years (SD 9)) and had anterior hip/groin pain and a positive anterior impingement test. Cam- and pincer-type subgroups were analyzed. Patients were compared to an asymptomatic control group (26 hips). All patients underwent pelvic CT scans to generate personalized CT-based 3D models and validated software for patient-specific impingement simulation (equidistant method).

RESULTS

Mean impingement-free flexion of patients with mixed-type FAI (110° (SD 8°)) and patients with pincer-type FAI (112° (SD 8°)) was significantly (p < 0.001) lower compared to the control group (125° (SD 13°)). The frequency of extra-articular subspine impingement was significantly (p < 0.001) increased in patients with pincer-type FAI (57%) compared to cam-type FAI (22%) in 125° flexion. Bony impingement in maximal flexion was located anterior-inferior at femoral four and five o'clock position in patients with cam-type FAI (63% (10 of 16 hips) and 37% (6 of 10 hips)), and did not involve the cam deformity. The cam deformity did not cause impingement in maximal flexion.

CONCLUSION

Femoral impingement in maximal flexion was located anterior-inferior distal to the cam deformity. This differs to previous studies, a finding which could be important for FAI patients in order to avoid exacerbation of hip pain in deep flexion (e.g. during squats) and for hip arthroscopy (hip-preservation surgery) for planning of bone resection. Hip impingement in flexion has implications for daily activities (e.g. putting on shoes), sports, and sex.Cite this article: Bone Joint Res 2023;12(1):22-32.

Efficient cascaded V-net optimization for lower extremity CT segmentation validated using bone morphology assessment

Semantic segmentation of bone from lower extremity computerized tomography (CT) scans can improve and accelerate the visualization, diagnosis, and surgical planning in orthopaedics. However, the large field of view of these scans makes automatic segmentation using deep learning based methods challenging, slow and graphical processing unit (GPU) memory intensive. We investigated methods to more efficiently represent anatomical context for accurate and fast segmentation and compared these with state-of-the-art methodology. Six lower extremity bones from patients of two different datasets were manually segmented from CT scans, and used to train and optimize a cascaded deep learning approach. We varied the number of resolution levels, receptive fields, patch sizes, and number of V-net blocks. The best performing network used a multi-stage, cascaded V-net approach with 128³ -64³ -32³ voxel patches as input. The average Dice coefficient over all bones was 0.98 ± 0.01, the mean surface distance was 0.26 ± 0.12 mm and the 95th percentile Hausdorff distance 0.65 ± 0.28 mm. This was a significant improvement over the results of the state-of-the-art nnU-net, with only approximately 1/12th of training time, 1/3th of inference time and 1/4th of GPU memory required. Comparison of the morphometric measurements performed on automatic and manual segmentations showed good correlation (Intraclass Correlation Coefficient [ICC] >0.8) for the alpha angle and excellent correlation (ICC >0.95) for the hip-knee-ankle angle, femoral inclination, femoral version, acetabular version, Lateral Centre-Edge angle, acetabular coverage. The segmentations were generally of sufficient quality for the tested clinical applications and were performed accurately and quickly compared to state-of-the-art methodology from the literature.

Correlation of femoral version measurements between computed tomography and magnetic resonance imaging studies in patients presenting with a femoroacetabular impingement-related complaint

Computed tomography (CT) is considered the gold standard for femoral version measurement. However, recent data have shown magnetic resonance imaging (MRI) as another modality to measure femoral version. This study aimed to correlate MRI and CT femoral version measurements in patients presenting with a femoroacetabular impingement (FAI)-related complaint. Patients (18-35 years old) who presented to the hip preservation clinic and radiology department with a suspected FAI diagnosis from 26 December 2018 to 4 March 2020 were included. All patients had a CT and MRI of the hip, with images including both hips and knees, as per our institution's protocol for possible hip preservation surgery. Patients were excluded if they were missing views of the knees, or if they had a history or imaging appearance of any condition affecting femoral version at the femoral head (e.g. slipped capital femoral epiphysis). Femoral version was measured by three reviewers. Fifty-eight patients were included, and 36 (62%) were female. Femoral version averaged 6.1° ± 11.8° on CT and 6.5° ± 10.8° on MRI. A strong positive correlation was reported between the two imaging modalities (r: 0.81; P < 0.001). Inter-rater reliability among the three reviewers was excellent and statistically significant for measurements on both MRI [intraclass correlation coefficient (ICC): 0.95; 95% CI: 0.85, 0.99; P < 0.001] and CT (ICC: 0.97; 95% CI: 0.92, 0.99; P < 0.001). Our finding suggests that MRI is a sufficient method for measuring femoral version to determine disease etiology and treatment progression. To avoid exposing patients to ionizing radiation, physicians should not obtain CT scans to evaluate femoral version.

Arthroscopic Treatment for Femoroacetabular Impingement Syndrome in Adolescents: A Systematic Review and Meta-Analysis

OBJECTIVE

The objective of this review was to analyze the effect of arthroscopic surgery for femoroacetabular impingement syndrome (FAI) in adolescents and factors that may influence the revision rate.

DESIGN

Systematic review and meta-analysis.

SETTING

PubMed, Scopus, Cochrane Library, EMBASE, and MEDLINE were searched from their earliest records to May 2021.

PATIENTS

Adolescents who underwent primary arthroscopic treatment for FAI.

INTERVENTIONS

Hip arthroscopic treatment.

MAIN OUTCOME MEASURES

Patient-reported outcomes (PROs), alpha angle, revision rates, and the rate of complications.

RESULTS

A total of 832 hips in 753 patients were included in this study. All PROs improved significantly. The modified Harris Hip Score pooled mean difference was 24.99 (95% CI, 22.88-27.10, P < 0.0001, I2 = 19.9%), Hip Outcome Score (HOS)-Sports-Specific Subscale was 35.88 (95% CI, 33.07-38.68, P < 0.0001, I2 = 0%), HOS-Activities of Daily Living was 23.53 (95% CI, 21.21-25.85, P < 0.0001, I2 = 0%), and the Nonarthritic Hip Score was 22.34 (95% CI, 18.40-26.28, P < 0.0001, I2 = 40.9%). The visual analog scale for pain decreased by 40.39 (44.39-36.40, P < 0.0001, I2 = 0%). The alpha angle decreased by 22.0 degrees from 62.9 degrees to 40.9 degrees after arthroscopic surgery. The rate of complication and revision surgery was 1.2% (10/832) and 3.4% (28/832), respectively, with high postoperative patient satisfaction.

CONCLUSIONS

All PROs significantly improved after surgery, with a low rate of complications and reoperation. High postoperative patient satisfaction was also reported.

Limited Hip Flexion and Internal Rotation Resulting From Early Hip Impingement Conflict on Anterior Metaphysis of Patients With Untreated Severe SCFE Using 3D Modelling

INTRODUCTION

Slipped capital femoral epiphysis (SCFE) is the most common hip disorder in adolescent patients that can result in complex 3 dimensional (3D)-deformity and hip preservation surgery (eg, in situ pinning or proximal femoral osteotomy) is often performed. But there is little information about location of impingement.Purpose/Questions: The purpose of this study was to evaluate (1) impingement-free hip flexion and internal rotation (IR), (2) frequency of impingement in early flexion (30 to 60 degrees), and (3) location of acetabular and femoral impingement in IR in 90 degrees of flexion (IRF-90 degrees) and in maximal flexion for patients with untreated severe SCFE using preoperative 3D-computed tomography (CT) for impingement simulation.

METHODS

A retrospective study involving 3D-CT scans of 18 patients (21 hips) with untreated severe SCFE (slip angle>60 degrees) was performed. Preoperative CT scans were used for bone segmentation of preoperative patient-specific 3D models. Three patients (15%) had bilateral SCFE. Mean age was 13±2 (10 to 16) years and 67% were male patients (86% unstable slip, 81% chronic slip). The contralateral hips of 15 patients with unilateral SCFE were evaluated (control group). Validated software was used for 3D impingement simulation (equidistant method).

RESULTS

(1) Impingement-free flexion (46±32 degrees) and IRF-90 degrees (-17±18 degrees) were significantly ( P <0.001) decreased in untreated severe SCFE patients compared with contralateral side (122±9 and 36±11 degrees).(2) Frequency of impingement was significantly ( P <0.001) higher in 30 and 60 degrees flexion (48% and 71%) of patients with severe SCFE compared with control group (0%).(3) Acetabular impingement conflict was located anterior-superior (SCFE patients), mostly 12 o'clock (50%) in IRF-90 degrees (70% on 2 o'clock for maximal flexion). Femoral impingement was located on anterior-superior to anterior-inferior femoral metaphysis (between 2 and 6 o'clock, 40% on 3 o'clock and 40% on 5 o'clock) in IRF-90 degrees and on anterior metaphysis (40% on 3 o'clock) in maximal flexion and frequency was significantly ( P <0.001) different compared with control group.

CONCLUSION

Severe SCFE patients have limited hip flexion and IR due to early hip impingement using patient-specific preoperative 3D models. Because of the large variety of hip motion, individual evaluation is recommended to plan the osseous correction for severe SCFE patients.

LEVEL OF EVIDENCE

Level III.

Noninvasive shape-fitting method quantifies cam morphology in femoroacetabular impingement syndrome: Implications for diagnosis and surgical planning

There are considerable limitations associated with the standard 2D imaging currently used for the diagnosis and surgical planning of cam-type femoroacetabular impingement syndrome (FAIS). The aim of this study was to determine the accuracy of a new patient-specific shape-fitting method that quantifies cam morphology in 3D based solely on preoperative MRI imaging. Preoperative and postoperative 1.5T MRI scans were performed on n = 15 patients to generate 3D models of the proximal femur, in turn used to create the actual and the virtual cam. The actual cams were reconstructed by subtracting the postoperative from the preoperative 3D model and used as reference, while the virtual cams were generated by subtracting the preoperative 3D model from the virtual shape template produced with the shape-fitting method based solely on preoperative MRI scans. The accuracy of the shape-fitting method was tested on all patients by evaluating the agreement between the metrics of height, surface area, and volume that quantified virtual and actual cams. Accuracy of the shape-fitting method was demonstrated obtaining a 97.8% average level of agreement between these metrics. In conclusion, the shape-fitting technique is a noninvasive and patient-specific tool for the quantification and localization of cam morphology. Future studies will include the implementation of the technique within a clinically based software for diagnosis and surgical planning for cam-type FAIS.

Hip Impingement Location in Maximal Hip Flexion in Patients With Femoroacetabular Impingement With and Without Femoral Retroversion

BACKGROUND

Symptomatic patients with femoroacetabular impingement (FAI) have limitations in daily activities and sports and report the exacerbation of hip pain in deep flexion. Yet, the exact impingement location in deep flexion and the effect of femoral version (FV) are unclear.

PURPOSE

To investigate the acetabular and femoral locations of intra- or extra-articular hip impingement in flexion in patients with FAI with and without femoral retroversion.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

An institutional review board-approved retrospective study involving 84 hips (68 participants) was performed. Of these, symptomatic patients (37 hips) with anterior FAI and femoral retroversion (FV <5°) were compared with symptomatic patients (21 hips) with anterior FAI (normal FV) and with a control group (26 asymptomatic hips without FAI and normal FV). All patients were symptomatic, had anterior hip pain, and had positive anterior impingement test findings. Most of the patients had hip/groin pain in maximal flexion or deep flexion or during sports. All 84 hips underwent pelvic computed tomography (CT) to measure FV as well as validated dynamic impingement simulation with patient-specific CT-based 3-dimensional models using the equidistant method.

RESULTS

In maximal hip flexion, femoral impingement was located anterior-inferior at 4 o'clock (57%) and 5 o'clock (32%) in patients with femoral retroversion and mostly at 5 o'clock in patients without femoral retroversion (69%) and in asymptomatic controls (76%). Acetabular intra-articular impingement was located anterior-superior (2 o'clock) in all 3 groups. In 125° of flexion, patients with femoral retroversion had a significantly (P < .001) higher prevalence of anterior extra-articular subspine impingement (54%) and anterior intra-articular impingement (89%) compared with the control group (29% and 62%, respectively).

CONCLUSION

Knowing the exact location of hip impingement in deep flexion has implications for surgical treatment, sports, and physical therapy and confirms previous recommendations: Deep flexion (eg, during squats/lunges) should be avoided in patients with FAI and even more in patients with femoral retroversion. Patients with femoral retroversion may benefit and have less pain when avoiding deep flexion. For these patients, the femoral location of the impingement conflict in flexion was different (anterior-inferior) and distal to the cam deformity compared with the location during the anterior impingement test (anterior-superior). This could be important for preoperative planning and bone resection (cam resection or acetabular rim trimming) during hip arthroscopy or open hip preservation surgery to ensure that the region of impingement is appropriately identified before treatment.

Automated measurement of alpha angle on 3D-magnetic resonance imaging in femoroacetabular impingement hips: a pilot study

BACKGROUND

Femoroacetabular impingement (FAI) syndrome is an established pre-osteoarthritic condition. Diagnosis is based on both clinical and radiographic parameters. An abnormal manually calculated alpha angle in magnetic resonance imaging (MRI) is traditionally utilized to diagnose abnormal femoral head-neck offset. This pilot study aimed to assess the feasibility of automated alpha angle measurements in patients with FAI syndrome, and to compare automated with manual measurements data with regard to the time and effort needed in each method.

METHODS

Alpha angles were measured with manual and automated techniques, using postprocessing software in nineteen hip MRIs of FAI syndrome patients. Two observers conducted manual measurements. Intra- and inter-observer reproducibility and correlation of manual and automated alpha angle measurements were calculated using intra-class correlation (ICC) analysis. Both techniques were compared regarding the time taken (in minutes) and effort required, measured as the amount of mouse button presses performed.

RESULTS

The first observer's intra-observer reproducibility was good (ICC 0.77; p < 0.001) while the second observer's was good-to-excellent (ICC 0.93; p < 0.001). Inter-observer reproducibility between both observers in the first (ICC 0.45; p < 0.001) and second (ICC 0.56; p < 0.001) manual alpha angle assessment was moderate. The intra-class correlation coefficients between manual and automated alpha angle measurements were ICC = 0.24 (p = 0.052; observer 1, 1st measurement), ICC = 0.32 (p = 0.015; observer 1, 2nd measurement), ICC = 0.50 (p < 0.001; observer 2, 1st measurement), and ICC = 0.45 (p < 0.001; observer 2, 2nd measurement). Average runtime for automatic processing of the image data for the automated assessment was 16.6 ± 1.9 min. Automatic alpha angle measurements took longer (time difference: 14.6 ± 3.9 min; p < 0.001) but required less effort (difference in button presses: 231 ± 23; p < 0.001). While the automatic processing is running, the user can perform other tasks.

CONCLUSIONS

This pilot study demonstrates that objective and reliable automated alpha angle measurement of MRIs in FAI syndrome hips is feasible. Trial registration The Ethics Committee of the University of Düsseldorf approved our study (Registry-ID: 2017084398).

MRI-- and CT--based metrics for the quantification of arthroscopic bone resections in femoroacetabular impingement syndrome

The purpose of this in vitro study was to quantify the bone resected from the proximal femur during hip arthroscopy using metrics generated from magnetic resonance imaging (MRI) and computed tomography (CT) reconstructed three-dimensional (3D) bone models. Seven cadaveric hemi-pelvises underwent both a 1.5 T MRI and CT scan before and following an arthroscopic proximal femoral osteochondroplasty. The images from MRI and CT were segmented to generate 3D proximal femoral surface models. A validated 3D--3D registration method was used to compare surface--to--surface distances between the 3D models before and following surgery. The new metrics of maximum height, mean height, surface area and volume, were computed to quantify bone resected during osteochondroplasty. Stability of the metrics across imaging modalities was established through paired sample t--tests and bivariate correlation. Bivariate correlation analyses indicated strong correlations between all metrics (r = 0.728--0.878) computed from MRI and CT derived models. There were no differences in the MRI- and CT-based metrics used to quantify bone resected during femoral osteochondroplasty. Preoperative- and postoperative MRI and CT derived 3D bone models can be used to quantify bone resected during femoral osteochondroplasty, without significant differences between the imaging modalities.

Less in-toeing after femoral derotation osteotomy in adult patients with increased femoral version and posterior hip impingement compared to patients with femoral retroversion

In-toeing of the foot was associated with high femoral version (FV), while Out-toeing was associated with femoral-retroversion. Therefore, we report on (i) foot-progression-angle (FPA), (ii) prevalence of In-toeing and Out-toeing, and (iii) clinical outcome of patients treated with femoral-derotation-osteotomy (FDO). We performed a retrospective analysis involving 20 patients (20 hips) treated with unilateral FDO (2017–18). Of them, 14 patients had increased FV, 6 patients had femoral-retroversion. Follow-up time was mean 1 ± 1 years. All patients had minimal 1-year follow-up and the mean age was 29 ± 8 years. Patients with increased FV (FV > 35°) presented with positive posterior-impingement-test and mean FV was 49 ± 11° (Murphy method). Six patients with femoral-retroversion (FV < 10°) had positive anterior impingement test and mean FV of 5 ± 4°. Instrumented gait analysis was performed preoperatively and at follow-up using the Gaitrite system to measure FPA and was compared to a control group of 18 healthy asymptomatic volunteers (36 feet, mean age 29 ± 6 years). (i) Mean FPA increased significantly (P = 0.006) from preoperative 1.3 ± 7° to 4.5 ± 6° at follow-up for patients with increased FV and was not significantly different compared to the control group (4.0 ± 4.5°). (ii) In-toeing decreased from preoperatively (five patients) to follow-up (two patients) for patients with increased FV. Out-toeing decreased from preoperatively (two patients) to follow-up (no patient) for patients with femoral-retroversion. (iii) Subjective-hip-value of all patients increased significantly (P < 0.001) from preoperative 21 to 78 points at follow-up. WOMAC was 12 ± 8 points at follow-up. Patients with increased FV that underwent FDO walked with less In-toeing. FDO has the potential to reduce In-toeing and Out-toeing and to improve subjective satisfaction at follow-up.

MRI-based synthetic CT shows equivalence to conventional CT for the morphological assessment of the hip joint

This study evaluated the accuracy of synthetic computed tomography (sCT), as compared to CT, for the 3D assessment of the hip morphology. Thirty male patients with asymptomatic hips, referred for magnetic resonance (MR) imaging and CT, were included in this retrospective study. sCT images were generated from three-dimensional radiofrequency-spoiled T1-weighted multi-echo gradient-echo MR images using a commercially available deep learning-enabled software and were compared with CT images through mean error and surface distance computation and by means of eight clinical morphometric parameters relevant for hip care. Parameters included center-edge angle (CEA), sharp angle, acetabular index, extrusion index, femoral head center-to-midline distance, acetabular version (AV), and anterior and posterior acetabular sector angles. They were measured by two senior orthopedic surgeons and a radiologist in-training on CT and sCT images. The reliability and agreement of CT- and sCT-based measurements were assessed using intraclass correlation coefficients (ICCs) for absolute agreement, Bland-Altman plots, and two one-sided tests for equivalence. The surface distance between CT- and sCT-based bone models were on average submillimeter. CT- and sCT-based measurements showed moderate to excellent interobserver and intraobserver correlation (0.56 < ICC < 0.99). In particular, the inter/intraobserver agreements were good for AV (ICC > 0.75). For CEA, the intraobserver agreement was good (ICC > 0.75) and the interobserver agreement was moderate (ICC > 0.69). Limits of agreements were similar between intraobserver CT and intermodal measurements. All measurements were found statistically equivalent, with average intermodal differences within the intraobserver limits of agreement. In conclusion, sCT and CT were equivalent for the assessment of the hip joint bone morphology.

Most of patients with femoral derotation osteotomy for posterior extraarticular hip impingement and high femoral version would do surgery again

AIMS

To assess (1) hip pain and function and ROM; (2) subsequent surgeries, complications; and (3) subjective satisfaction and PROMs in patients undergoing femoral derotation osteotomies.

METHODS

Femoral derotation subtrochanteric osteotomies to treat symptomatic posterior extraarticular ischiofemoral hip impingement were performed in 23 patients (25 hips) between 2013 and 2017. The mean age was 26 ± 8 years (96% female) with a minimum 2-year follow-up (mean follow-up of 4 ± 1 years). Surgical indication was a positive posterior impingement test and limited external rotation (mean 16° ± 8°) in extension in patients with abnormal high femoral version (mean 46° ± 9, measured on CT scans with the Murphy method) and high McKibbin instability index (mean 67°). Femoral osteotomies were combined with a surgical hip dislocation in 96% for cam resection and labrum or cartilage treatment. Preoperative MRI and 3D-CT with dynamic impingement simulation were evaluated.

RESULTS

(1) The posterior impingement test decreased significantly from preoperatively 100% to 4% (p < 0.001). External rotation in extension increased significantly (p < 0.001) from preoperative 16° ± 8 to 44° ± 16°. The MdA score increased significantly from 14 ± 1 to 16 ± 2 (p < 0.001) points.(2) At follow-up, all 25 hips were preserved. No conversion to THA and no revision osteosynthesis was performed. 64% underwent complete hardware removal.(3) 80% of the patients reported at follow-up that they would undergo surgery again. Subjective satisfaction (SHV) increased significantly (p < 0.001) from preoperatively 24% to 84% postoperatively.

CONCLUSIONS

Femoral derotation subtrochanteric osteotomies for the treatment of posterior extraarticular ischiofemoral hip impingement are safe and improve posterior hip pain and function and external rotation in mostly female patients with high femoral version and a high McKibbin instability index.

Magnetic Resonance Imaging Versus Computed Tomography for Three-Dimensional Bone Imaging of Musculoskeletal Pathologies: A Review

Magnetic resonance imaging (MRI) is increasingly utilized as a radiation‐free alternative to computed tomography (CT) for the diagnosis and treatment planning of musculoskeletal pathologies. MR imaging of hard tissues such as cortical bone remains challenging due to their low proton density and short transverse relaxation times, rendering bone tissues as nonspecific low signal structures on MR images obtained from most sequences. Developments in MR image acquisition and post‐processing have opened the path for enhanced MR‐based bone visualization aiming to provide a CT‐like contrast and, as such, ease clinical interpretation. The purpose of this review is to provide an overview of studies comparing MR and CT imaging for diagnostic and treatment planning purposes in orthopedic care, with a special focus on selective bone visualization, bone segmentation, and three‐dimensional (3D) modeling. This review discusses conventional gradient‐echo derived techniques as well as dedicated short echo time acquisition techniques and post‐processing techniques, including the generation of synthetic CT, in the context of 3D and specific bone visualization. Based on the reviewed literature, it may be concluded that the recent developments in MRI‐based bone visualization are promising. MRI alone provides valuable information on both bone and soft tissues for a broad range of applications including diagnostics, 3D modeling, and treatment planning in multiple anatomical regions, including the skull, spine, shoulder, pelvis, and long bones.

Prävalenz, Biomechanik und Diagnostik femoraler Achs- und Torsionsfehler

Abweichungen der Anatomie des proximalen Femurs (Torsionspathologien, Coxa valga/vara) führen zu Veränderungen der Biomechanik des Hüftgelenks. Dies kann sich in einem femoroazetabulären Impingement (FAI), einer Mehrbelastung durch erhöhten intraartikulären Druck oder einer Fehl- oder Überbelastung der Hüftgelenkabduktoren manifestieren. Die Morphologie des Beckens, insbesondere die Version und Überdachung des Azetabulums, kann einen kompensatorischen oder verstärkenden Effekt haben und muss in die globale Beurteilung des Hüftgelenks miteinbezogen werden. Eine ausführliche klinische und radiologische Evaluation ist für eine korrekte Diagnosestellung von entscheidender Bedeutung. Die Patienten berichten meist von inguinalen, z. T. aber auch von glutealen Schmerzen. Diese sind häufig von mechanischem Charakter und können durch bestimmte Bewegungen provoziert werden. Der Bewegungsumfang der Hüfte ist beim FAI vermindert, und es zeigt sich ein positiver vorderer und/oder hinterer Impingement-Test. Torsionspathologien führen häufig zu einem veränderten Gangbild. So präsentieren sich Patienten mit erhöhter femoraler Torsion oft mit einem innenrotierten, bei verminderter Torsion mit einem außenrotierten Gangbild. Zudem zeigt sich häufig eine Abduktoreninsuffizienz. Während zur Bestimmung des Collum-Diaphysen-Winkels (CCD-Winkel) eine zentrierte Beckenübersichtsröntgenaufnahme im a.-p.-Strahlengang verwendet werden kann, sollte die Bestimmung der Torsion anhand einer Computertomographie (CT) oder Magnetresonanztomographie (MRT) von Knien und Hüftgelenk erfolgen. Von entscheidender Bedeutung ist die Angabe der verwendeten Messmethode der femoralen Torsion, da große systematische Unterschiede der Torsionswerte zwischen den verschiedenen Messmethoden bestehen.

Three-Dimensional Magnetic Resonance Imaging Bone Models of the Hip Joint Using Deep Learning: Dynamic Simulation of Hip Impingement for Diagnosis of Intra- and Extra-articular Hip Impingement

Background:

Dynamic 3-dimensional (3D) simulation of hip impingement enables better understanding of complex hip deformities in young adult patients with femoroacetabular impingement (FAI). Deep learning algorithms may improve magnetic resonance imaging (MRI) segmentation.

Purpose:

(1) To evaluate the accuracy of 3D models created using convolutional neural networks (CNNs) for fully automatic MRI bone segmentation of the hip joint, (2) to correlate hip range of motion (ROM) between manual and automatic segmentation, and (3) to compare location of hip impingement in 3D models created using automatic bone segmentation in patients with FAI.

Study Design:

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

Methods:

The authors retrospectively reviewed 31 hip MRI scans from 26 symptomatic patients (mean age, 27 years) with hip pain due to FAI. All patients had matched computed tomography (CT) and MRI scans of the pelvis and the knee. CT- and MRI-based osseous 3D models of the hip joint of the same patients were compared (MRI: T1 volumetric interpolated breath-hold examination high-resolution sequence; 0.8 mm³ isovoxel). CNNs were used to develop fully automatic bone segmentation of the hip joint, and the 3D models created using this method were compared with manual segmentation of CT- and MRI-based 3D models. Impingement-free ROM and location of hip impingement were calculated using previously validated collision detection software.

Results:

The difference between the CT- and MRI-based 3D models was <1 mm, and the difference between fully automatic and manual segmentation of MRI-based 3D models was <1 mm. The correlation of automatic and manual MRI-based 3D models was excellent and significant for impingement-free ROM (r = 0.995; P < .001), flexion (r = 0.953; P < .001), and internal rotation at 90° of flexion (r = 0.982; P < .001). The correlation for impingement-free flexion between automatic MRI-based 3D models and CT-based 3D models was 0.953 (P < .001). The location of impingement was not significantly different between manual and automatic segmentation of MRI-based 3D models, and the location of extra-articular hip impingement was not different between CT- and MRI-based 3D models.

Conclusion:

CNN can potentially be used in clinical practice to provide rapid and accurate 3D MRI hip joint models for young patients. The created models can be used for simulation of impingement during diagnosis of intra- and extra-articular hip impingement to enable radiation-free and patient-specific surgical planning for hip arthroscopy and open hip preservation surgery.

Automated Morphometric Analysis of the Hip Joint on MRI from the German National Cohort Study

Purpose

To develop and validate an automated morphometric analysis framework for the quantitative analysis of geometric hip joint parameters in MR images from the German National Cohort (GNC) study.

Materials and Methods

A secondary analysis on 40 participants (mean age, 51 years; age range, 30-67 years; 25 women) from the prospective GNC MRI study (2015-2016) was performed. Based on a proton density-weighted three-dimensional fast spin-echo sequence, a morphometric analysis approach was developed, including deep learning-based landmark localization, bone segmentation of the femora and pelvis, and a shape model for annotation transfer. The centrum-collum-diaphyseal, center-edge (CE), three alpha angles, head-neck offset (HNO), and HNO ratio along with the acetabular depth, inclination, and anteversion were derived. Quantitative validation was provided by comparison with average manual assessments of radiologists in a cross-validation format. Paired-sample t tests with a Bonferroni-corrected significance level of .005 were employed alongside mean differences and 10th/90th percentiles, median absolute deviations (MADs), and intraclass correlation coefficients (ICCs).

Results

High agreement in mean Dice similarity coefficients was achieved (average of 97.52% ± 0.46 [standard deviation]). The subsequent morphometric analysis produced results with low mean MAD values, with the highest values of 3.34° (alpha 03:00 o'clock position) and 0.87 mm (HNO) and ICC values ranging between 0.288 (HNO ratio) and 0.858 (CE) compared with manual assessments. These values were in line with interreader agreements, which at most had MAD values of 4.02° (alpha 12:00 o'clock position) and 1.07 mm (HNO) and ICC values ranging between 0.218 (HNO ratio) and 0.777 (CE).

Conclusion

Automatic extraction of geometric hip parameters from MRI is feasible using a morphometric analysis approach with deep learning.Keywords: Computer-Aided Diagnosis (CAD), Interventional-MSK, MR-Imaging, Neural Networks, Skeletal-Appendicular, Hip, Anatomy, Computer Applications-3D, Segmentation, Vision, Application Domain, Quantification Supplemental material is available for this article. © RSNA, 2021.

3D MRI Models of the Musculoskeletal System

Computed tomography (CT) is most commonly used to produce three-dimensional (3D) models for evaluating bone and joint morphology in clinical practice. However, 3D models created from magnetic resonance imaging (MRI) data can be equally effective for comprehensive and accurate assessment of osseous and soft tissue structure morphology and pathology. The quality of 3D MRI models has steadily increased over time, with growing potential to replace 3D CT models in various musculoskeletal (MSK) applications. In practice, a single MRI examination for two-dimensional and 3D assessments can increase the value of MRI and simplify the pre- and postoperative imaging work-up. Multiple studies have shown excellent performance of 3D MRI models in shoulder injuries, in the hip in the setting of femoroacetabular impingement, and in the knee for the creation of bone surface models. Therefore, the utility of 3D MRI postprocessed models is expected to continue to rise and broaden in applications. Computer-based and artificial intelligence-assisted postprocessing techniques have tremendous potential to improve the efficiency of 3D model creation, opening many research avenues to validate the applicability of 3D MRI and establish 3D-specific quantitative assessment criteria. We provide a practice-focused overview of 3D MRI acquisition strategies, postprocessing techniques for 3D model creation, MSK applications of 3D MRI models, and an illustration of cases from our daily clinical practice.

Complications of hip preserving surgery

Preoperative evaluation of the pathomorphology is crucial for surgical planning, including radiographs as the basic modality and magnetic resonance imaging (MRI) and case-based additional imaging (e.g. 3D-CT, abduction views).

Hip arthroscopy (HAS) has undergone tremendous technical advances, an immense increase in use and the indications are getting wider. The most common indications for revision arthroscopy are labral tears and residual femoroacetabular impingement (FAI).

Treatment of borderline developmental dysplastic hip is currently a subject of controversy. It is paramount to understand the underlining problem of the individual hip and distinguish instability (dysplasia) from FAI, as the appropriate treatment for unstable hips is periacetabular osteotomy (PAO) and for FAI arthroscopic impingement surgery.

PAO with a concomitant cam resection is associated with a higher survival rate compared to PAO alone for the treatment of hip dysplasia. Further, the challenge for the surgeon is the balance between over- and undercorrection.

Femoral torsion abnormalities should be evaluated and evaluation of femoral rotational osteotomy for these patients should be incorporated to the treatment plan.

Cite this article: EFORT Open Rev 2021;6:472-486. DOI: 10.1302/2058-5241.6.210019

Sex differences in the prevalence of radiographic findings of structural hip deformities in patients with symptomatic femoroacetabular impingement

The purpose of this study was to determine the sex differences in the overall prevalence of radiographic femoroacetabular impingement (FAI) deformity patients presenting with hip pain and to identify the most common radiographic findings in male and female patients. A geographic database was used to identify patients between the age of 14 and 50 years with hip pain from 2000 to 2016. A chart and radiographic review was performed to identify patients with cam, pincer and mixed-type FAI. A total of 374 (449 hips) out of 612 (695 hips) male patients and 771 (922 hips) out of 1281 (1447 hips) female patients had radiographic features consistent with FAI. Ninety-four male hips (20.9%) and 45 female hips (4.9%) had cam type, 20 male hips (4.5%) and 225 female hips (24.4%) had pincer type and 335 male hips (74.6%) and 652 female hips (70.7%) had mixed type. The overall prevalence of radiographic findings consistent with FAI in male and female patients with hip pain was 61.1% and 60.2%, respectively. Mixed type was the most prevalent. The most common radiographic finding for cam-type FAI was an alpha angle >55°, and the most common radiographic finding for pincer-type FAI was a crossover sign. Male patients were found to have a higher prevalence of cam-type deformities, whereas female patients were found to have a higher prevalence of pincer-type deformities.

Posterior Extra-articular Ischiofemoral Impingement Can Be Caused by the Lesser and Greater Trochanter in Patients With Increased Femoral Version: Dynamic 3D CT-Based Hip Impingement Simulation of a Modified FABER Test

Background:

Posterior extra-articular hip impingement has been described for valgus hips with increased femoral version (FV). These patients can present clinically with lack of external rotation (ER) and extension and with a positive posterior impingement test. But we do not know the effect of the combination of deformities, and the impingement location in early flexion is unknown.

Purpose:

To evaluate patient-specific 3-dimensional computed tomography (3D CT) scans of hips with increased FV and control hips for differences in range of motion, location and prevalence of osseous posterior intra- and extra-articular hip impingement.

Study Design:

Case series; Level of evidence, 4.

Methods:

Osseous 3D models based on segmentation of 3D CT scans were analyzed for 52 hips (38 symptomatic patients) with positive posterior impingement test and increased FV (>35°). There were 26 hips with an increased McKibbin instability index >70 (unstable hips). Patients were mainly female (96%), with an age range of 18 to 45 years. Of them, 21 hips had isolated increased FV (>35°); 22 hips had increased FV and increased acetabular version (AV; >25°); and 9 valgus hips (caput-collum-diaphyseal angle >139°) had increased FV and increased AV. The control group consisted of 20 hips with normal FV, normal AV, and no valgus (caput-collum-diaphyseal angle <139°). Validated 3D CT–based collision detection software for impingement simulation was used to calculate impingement-free range of motion and location of hip impingement. Surgical treatment was performed after the 3D CT–based impingement simulation in 27 hips (52%).

Results:

Hips with increased FV had significantly (P < .001) decreased extension and ER at 90° of flexion as compared with the control group. Posterior impingement was extra-articular (92%) in hips with increased FV. Valgus hips with increased FV and AV had combined intra- and extra-articular impingement. Posterior hip impingement occurred between the ischium and the lesser trochanter at 20° of extension and 20° of ER. Impingement was located between the ischium and the greater trochanter or intertrochanteric area at 20° of flexion and 40° of ER, with a modification of the flexion-abduction-ER (FABER) test.

Conclusion:

Posterior extra-articular ischiofemoral hip impingement can be caused by the lesser and greater trochanter or the intertrochanteric region. We recommend performing the modified FABER test during clinical examination in addition to the posterior impingement test for female patients with high FV. In addition, 3D CT can help for surgical planning, such as femoral derotation osteotomy and/or hip arthroscopy or resection of the lesser trochanter.

Does the Rule of Thirds Adequately Detect Deficient and Excessive Acetabular Coverage?

BACKGROUND

Assessment of AP acetabular coverage is crucial for choosing the right surgery indication and for obtaining a good outcome after hip-preserving surgery. The quantification of anterior and posterior coverage is challenging and requires either other conventional projections, CT, MRI, or special measurement software, which is cumbersome, not widely available and implies additional radiation. We introduce the "rule of thirds" as a promising alternative to provide a more applicable and easy method to detect an excessive or deficient AP coverage. This method attributes the intersection point of the anterior (posterior) wall to thirds of the femoral head radius (diameter), the medial third suggesting deficient and the lateral third excessive coverage.

QUESTION/PURPOSE

What is the validity (area under the curve [AUC], sensitivity, specificity, positive/negative likelihood ratios [LR(+)/LR(-)], positive/negative predictive values [PPV, NPV]) for the rule of thirds to detect (1) excessive and (2) deficient anterior and posterior coverages compared with previously established radiographic values of under-/overcoverage using Hip2Norm as the gold standard?

METHODS

We retrospectively evaluated all consecutive patients between 2003 and 2015 from our institutional database who were referred to our hospital for hip pain and were potentially eligible for joint-preserving hip surgery. We divided the study group into six specific subgroups based on the respective acetabular pathomorphology to cover the entire range of anterior and posterior femoral coverage (dysplasia, overcoverage, severe overcoverage, excessive acetabular anteversion, acetabular retroversion, total acetabular retroversion). From this patient cohort, 161 hips were randomly selected for analysis. Anterior and posterior coverage was determined with Hip2Norm, a validated computer software program for evaluating acetabular morphology. The anterior and posterior wall indices were measured on standardized AP pelvis radiographs, and the rule of thirds was applied by one observer.

RESULTS

The detection of excessive anterior and posterior acetabular wall using the rule of thirds revealed an AUC of 0.945 and 0.933, respectively. Also the detection of a deficient anterior and posterior acetabular wall by applying the rule of thirds revealed an AUC of 0.962 and 0.876, respectively. For both excessive and deficient anterior and posterior acetabular coverage, we found high specificities and PPVs but low sensitivities and NPVs.

CONCLUSION

We found a high probability for an excessive (deficient) acetabular wall when this intersection point lies in the lateral (medial) third, which would qualify for surgical correction. On the other hand, if this point is not in the lateral (medial) third, an excessive (deficient) acetabular wall cannot be categorically excluded. Thus, the rule of thirds is very specific but not as sensitive as we had expected.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Biochemical MRI With dGEMRIC Corresponds to 3D-CT Based Impingement Location for Detection of Acetabular Cartilage Damage in FAI Patients

Background

Anterior femoroacetabular impingement (FAI) is associated with labral tears and acetabular cartilage damage in athletic and young patients. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) is an imaging method for detecting early damage to cartilage.

Purpose

We evaluated the following questions: (1) What is the sensitivity and specificity of morphological magnetic resonance imaging (MRI) and dGEMRIC for detecting cartilage damage? Do the mean acetabular and femoral dGEMRIC indices differ between (2) superior acetabular clock positions with and without impingement and (3) between cam- and pincer-type FAI?

Study Design

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

Methods

This was a retrospective comparative study of 21 hips (20 patients with symptomatic anterior FAI) without osteoarthritis on anteroposterior radiographs. Morphological MRI and dGEMRIC (3.0-T, 3-dimensional [3D] T1 maps, dual-flip angle technique) of the same hip joint were compared. Intraoperative acetabular cartilage damage was assessed in patients who underwent surgical treatment. Computed tomography (CT)-based 3D bone models of the same hip joint were used as the gold standard for the detection of impingement, and dGEMRIC indices and zones of morphologic damage were compared with the CT-based impingement zones.

Results

Of the 21 hips, 10 had cam-type FAI and 8 had pincer-type FAI according to radiographs. The mean age was 30 ± 9 years (range, 17-48 years), 71% were female, and surgical treatment was performed in 52%. We found a significantly higher sensitivity (69%) for dGEMRIC compared with morphological MRI (42%) in the detection of cartilage damage (P < .001). The specificity of dGEMRIC was 83% and accuracy was 78%. The mean peripheral acetabular and femoral dGEMRIC indices for clock positions with impingement (485 ± 141 and 440 ± 121 ms) were significantly lower compared with clock positions without impingement (596 ± 183 and 534 ± 129 ms) (P < .001). Hips with cam-type FAI had significantly lower acetabular dGEMRIC indices compared with hips with pincer-type FAI on the anterosuperior clock positions (1 to 3 o'clock) (P = .018).

Conclusion

MRI with dGEMRIC was more sensitive than morphological MRI, and lower dGEMRIC values were found for clock positions with impingement as detected on 3D-CT. This could aid in patient-specific diagnosis of FAI, preoperative patient selection, and surgical decision making to identify patients with cartilage damage who are at risk for inferior outcomes after hip arthroscopy.

Best Practices: Hip Femoroacetabular Impingement

OBJECTIVE. Imaging plays a critical role in the assessment of patients with femoroacetabular impingement (FAI). With better understanding of the underlying pathomechanics and advances in joint-preserving surgery, there is an increasing need to define the most appropriate imaging workup. The purpose of this article is to provide guidance on best practices for imaging of patients with FAI in light of recent advances in corrective FAI surgery. CONCLUSION. Pelvic radiography with dedicated hip projections is the basis of the diagnostic workup of patients with suspected FAI to assess arthritic changes and acetabular coverage and to screen for cam deformities. Chondrolabral lesions should be evaluated with unenhanced MRI or MR arthrography. The protocol should include a large-FOV fluid-sensitive sequence to exclude conditions that can mimic or coexist with FAI, radial imaging to accurately determine the presence of a cam deformity, and imaging of the distal femoral condyles for measurement of femoral torsion. CT remains a valuable tool for planning of complex surgical corrections. Advanced imaging, such as 3D simulation, biochemical MRI, and MR arthrography with application of leg traction, has great potential to improve surgical decision-making. Further research is needed to assess the added clinical value of these techniques.

Inclusion of the Acetabular Labrum Reduces Simulated Range of Motion of the Hip Compared With Bone Contact Models

Purpose

To determine whether inclusion of the acetabular labrum affects the maximum range of motion (ROM) during simulation of the flexion–adduction–internal rotation impingement examination.

Methods

Three-dimensional surface reconstructions of the femur, hemi-pelvis, and labrum from computed tomography arthrography images of 19 participants were used to simulate maximum ROM during the flexion–adduction–internal rotation examination. Simulations were conducted for positions between 70° and 110° flexion and 0° and 20° adduction at 10° increments to measure maximum internal rotation and the position of contact between the femur and acetabular rim (bone-to-bone) or the femur and labrum (bone-to-labrum). Internal rotation angles and clock-face position values were compared between the 2 contact scenarios for each position.

Results

The ROM in the bone-to-labrum contact model was significantly less than that of the bone-to-bone contact model for all evaluated positions (P ≤ .001, except at 110° flexion and 20° adduction, P = .114). The inclusion of the labrum reduced internal rotation by a median [interquartile range] of 18 [15, 25]° while altering the position of contact on the acetabular clock-face by –0:01 [–0:27, 0:16]. The variability in contact location for the bone-to-labrum contact scenario was nearly double that of the bone-to-bone contact scenario, as indicated by the interquartile range.

Conclusions

Inclusion of the anatomy of the acetabular labrum in collision models used to simulate impingement examinations reduced the internal rotation ROM by approximately 20° and increased variability in the location of contact relative to the acetabular rim.

Clinical Relevance

While standard bone-to-bone contact ROM simulations may be informative with respect to the relative change in ROM based on a surgical intervention (e.g., pre- and post-osteochondroplasty for cam-type femoroacetabular impingement), they may not accurately represent the clinical ROM of the joint or the kinematic position at which damage may occur due to shape mismatch between the femur and acetabulum.

MRI-based 3D models of the hip joint enables radiation-free computer-assisted planning of periacetabular osteotomy for treatment of hip dysplasia using deep learning for automatic segmentation

Introduction

Both Hip Dysplasia(DDH) and Femoro-acetabular-Impingement(FAI) are complex three-dimensional hip pathologies causing hip pain and osteoarthritis in young patients. 3D-MRI-based models were used for radiation-free computer-assisted surgical planning. Automatic segmentation of MRI-based 3D-models are preferred because manual segmentation is time-consuming.To investigate(1) the difference and(2) the correlation for femoral head coverage(FHC) between automatic MR-based and manual CT-based 3D-models and (3) feasibility of preoperative planning in symptomatic patients with hip diseases.

Methods

We performed an IRB-approved comparative, retrospective study of 31 hips(26 symptomatic patients with hip dysplasia or FAI). 3D MRI sequences and CT scans of the hip were acquired. Preoperative MRI included axial-oblique T1 VIBE sequence(0.8 mm³ isovoxel) of the hip joint. Manual segmentation of MRI and CT scans were performed. Automatic segmentation of MRI-based 3D-models was performed using deep learning.

Results

(1)The difference between automatic and manual segmentation of MRI-based 3D hip joint models was below 1 mm(proximal femur 0.2 ± 0.1 mm and acetabulum 0.3 ± 0.5 mm). Dice coefficients of the proximal femur and the acetabulum were 98 % and 97 %, respectively. (2)The correlation for total FHC was excellent and significant(r = 0.975, p < 0.001) between automatic MRI-based and manual CT-based 3D-models. Correlation for total FHC (r = 0.979, p < 0.001) between automatic and manual MR-based 3D models was excellent.(3)Preoperative planning and simulation of periacetabular osteotomy was feasible in all patients(100 %) with hip dysplasia or acetabular retroversion.

Conclusions

Automatic segmentation of MRI-based 3D-models using deep learning is as accurate as CT-based 3D-models for patients with hip diseases of childbearing age. This allows radiation-free and patient-specific preoperative simulation and surgical planning of periacetabular osteotomy for patients with DDH.

Prevalence of combined abnormalities of tibial and femoral torsion in patients with symptomatic hip dysplasia and femoroacetabular impingement

AIMS

The prevalence of combined abnormalities of femoral torsion (FT) and tibial torsion (TT) is unknown in patients with femoroacetabular impingement (FAI) and hip dysplasia. This study aimed to determine the prevalence of combined abnormalities of FT and TT, and which subgroups are associated with combined abnormalities of FT and TT.

METHODS

We retrospectively evaluated symptomatic patients with FAI or hip dysplasia with CT scans performed between September 2011 and September 2016. A total of 261 hips (174 patients) had a measurement of FT and TT. Their mean age was 31 years (SD 9), and 63% were female (165 hips). Patients were compared to an asymptomatic control group (48 hips, 27 patients) who had CT scans including femur and tibia available for analysis, which had been acquired for nonorthopaedic reasons. Comparisons were conducted using analysis of variance with Bonferroni correction.

RESULTS

In the overall study group, abnormal FT was present in 62% (163 hips). Abnormal TT was present in 42% (109 hips). Normal FT combined with normal TT was present in 21% (55 hips). The most frequent abnormal combination was increased FT combined with normal TT of 32% (84 hips). In the hip dysplasia group, 21% (11 hips) had increased FT combined with increased TT. The prevalence of abnormal FT varied significantly among the subgroups (p < 0.001). We found a significantly higher mean FT for hip dysplasia (31°; SD 15)° and valgus hips (42° (SD 12°)) compared with the control group (22° (SD 8°)). We found a significantly higher mean TT for hips with cam-type-FAI (34° (SD 6°)) and hip dysplasia (35° (SD 9°)) compared with the control group (28° (SD 8°)) (p < 0.001).

CONCLUSION

Patients with FAI had a high prevalence of combined abnormalities of FT and TT. For hip dysplasia, we found a significantly higher mean FT and TT, while 21% of patients (11 hips) had combined increased TT and increased FT (combined torsional malalignment). This is important when planning hip preserving surgery such as periacetabular osteomy and femoral derotation osteotomy. Cite this article: Bone Joint J 2020;102-B(12):1636-1645.

Hip preservation

Classical indications for hip preserving surgery are: femoro-acetabular impingement (FAI) (intra- and extra-articular), hip dysplasia, slipped capital femoral epiphysis, residual deformities after Perthes disease, avascular necrosis of the femoral head.

Pre-operative evaluation of the pathomorphology is crucial for surgical planning including radiographs as the basic modality and magnetic resonance imaging (MRI) and/or computed tomography (CT) to evaluate further intra-articular lesions and osseous deformities.

Two main mechanisms of intra-articular impingement have been described:

(1) Inclusion type FAI (‘cam type’).

(2) Impaction type FAI (‘pincer type’).

Either arthroscopic or open treatment can be performed depending on the severity of deformity.

Slipped capital femoral epiphysis often results in a cam-like deformity of the hip. In acute cases a subcapital re-alignment (modified Dunn procedure) of the femoral epiphysis is an effective therapy.

Perthes disease can lead to complex femoro-acetabular deformity which predisposes to impingement with/without joint incongruency and requires a comprehensive diagnostic workup for surgical planning.

Developmental dysplasia of the hip results in a static overload of the acetabular rim and early osteoarthritis. Surgical correction by means of periacetabular osteotomy offers good long-term results.

Cite this article: EFORT Open Rev 2020;5:630-640. DOI: 10.1302/2058-5241.5.190074

Use of a 3D virtual dynamic hip model to quantify the amount of osteoplasty required in femoroacetabular impingement patients

OBJECTIVE

Compare required osteoplasty predicted by a 3D virtual dynamic hip model in femoroacetabular impingement patients to actual osteoplasty performed.

MATERIALS AND METHODS

Retrospective study on 20 consecutive FAI patients with a preoperative CT who underwent arthroscopy from October 2016 to September 2017. A 3D virtual dynamic hip model was created from the CT. The model displayed virtual osteoplasty depth required to restore physiologic range of motion on an osteoplasty map. Depths of virtual osteoplasty and actual osteoplasty at surgery were compared and correlated with alpha angle, lateral center edge angle, femoral version, and acetabular version.

RESULTS

Actual femoroplasty depth correlated with alpha angle (r = 0.85, p ≤ 0.001) and actual acetabuloplasty depth correlated with lateral center edge angle (r = 0.83, p < 0.001). Virtual osteoplasty depth did not correlate with alpha angle (p = 0.25), lateral center edge angle (p = 0.50), femoral version (p = 0.09), or acetabular version (p = 0.09). The 3D model predicted a mean virtual osteoplasty of 6.2 ± 0.3 mm compared to mean actual osteoplasty of 5.9 ± 1.1 mm. There was no significant difference between the two means (p = 0.26), though there was a significant difference in variance (p = 0.001). There was poor test reliability between virtual osteoplasty compared with actual osteoplasty (ICC = 0.30).

CONCLUSION

3D model predicted virtual osteoplasty depths varied with actual osteoplasty and was independent of 2D measurements.

Computer assistance in hip preservation surgery-current status and introduction of our system

INTRODUCTION

Preservation surgery of the hip with open or arthroscopic approach has always been challenging as complex 3-D anatomy and limited surgical access make intraoperative evaluation difficult. Recent advances in computer technology offer a wide range of innovative solutions with a goal to improve accuracy and safety of corrective procedures on human joints.

METHOD

The author critically reviews currently available literature in the field of computer assistance in hip preservation surgery. Basic features of unique planning software and navigation surgical system used in treatment of femoroacetabular impingement and hip dysplasia are introduced.

RESULTS

Currently available software provides preoperative identification of hip deformity on CT-based 3-D model and planning of the surgical correction using kinematic protocols. Real-time intraoperative 3-D orientation is possible, and execution of surgical correction can be performed either with navigation of surgical tools or with printed templates. Computer assistance in hip preservation surgery is in the developing phase. First clinical experiences of its use in treatment of femoroacetabular impingement, hip dysplasia, hip tumors, and avascular necrosis of the femoral head are promising.

CONCLUSION

Computer assistance has been applied for treatment of several hip disorders. Technical advances are suggested and quality basic studies and clinical trials are encouraged for the novel technology to become more user friendly and widely accepted.

Advances in FAI Imaging: a Focused Review

PURPOSE OF REVIEW

Femoroacetabular impingement (FAI) is one of the main causes of hip pain in young adults and poses clinical challenges which have placed it at the forefront of imaging and orthopedics. Diagnostic hip imaging has dramatically changed in the past years, with the arrival of new imaging techniques and the development of magnetic resonance imaging (MRI). This article reviews the current state-of-the-art clinical routine of individuals with suspected FAI, limitations, and future directions that show promise in the field of musculoskeletal research and are likely to reshape hip imaging in the coming years.

RECENT FINDINGS

The largely unknown natural disease course, especially in hips with FAI syndrome and those with asymptomatic abnormal morphologies, continues to be a problem as far as diagnosis, treatment, and prognosis are concerned. There has been a paradigm shift in recent years from bone and soft tissue morphological analysis towards the tentative development of quantitative approaches, biochemical cartilage evaluation, dynamic assessment techniques and, finally, integration of artificial intelligence (AI)/deep learning systems. Imaging, AI, and hip preserving care will continue to evolve with new problems and greater challenges. The increasing number of analytic parameters describing the hip joint, as well as new sophisticated MRI and imaging analysis, have carried practitioners beyond simplistic classifications. Reliable evidence-based guidelines, beyond differentiation into pure instability or impingement, are paramount to refine the diagnostic algorithm and define treatment indications and prognosis. Nevertheless, the boundaries of morphological, functional, and AI-aided hip assessment are gradually being pushed to new frontiers as the role of musculoskeletal imaging is rapidly evolving.

The Effect of Modality and Landmark Selection on MRI and CT Femoral Torsion Angles

Background Assessment of femoral torsion at preoperative hip imaging is commonly recommended. However, it is unclear whether MRI is as accurate as CT and how different methods affect femoral torsion measurements. Purpose To compare MRI- and CT-based assessment of femoral torsion by using four commonly used measurement methods in terms of agreement, reproducibility, and reliability and to compare femoral torsion angles between the four different measurement methods. Materials and Methods This retrospective study evaluated patients with hip pain who underwent CT and 3-T MRI of the hip including sequences of the pelvis and distal condyles between May 2017 and June 2018. The four measurement methods differed regarding the landmark levels for the proximal femoral reference axis and included measurements at the level of the greater trochanter, femoral neck, base of the femoral neck, and level of the lesser trochanter. Intraclass correlation coefficients (ICCs) were calculated, and Bland-Altman analysis was performed. Results Forty-five patients (mean age ± standard deviation, 19 years ± 5; 27 female) and 57 hips were evaluated. Inter- and intrarater reliability were excellent for each of the four CT- and MRI-based measurement methods (ICC range, 0.97-0.99). Mean difference between CT- and MRI-based measurement ranged from 0.3° ± 3.4 (P = .58) to 2.1° ± 4.1 (P < .001). Differences between CT and MRI were within the corresponding ICC variation for all four measurement methods. Mean torsion angles were greater by 17.6° for CT and 18.7° for MRI (all P < .001) between the most proximal to the most distal measurement methods. Conclusion MRI- and CT-based femoral torsion measurements showed high agreement and comparable reliability and reproducibility but were dependent on the level of selected landmarks used to define the proximal reference axis. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Zoga in this issue.

Location of Intra- and Extra-articular Hip Impingement Is Different in Patients With Pincer-Type and Mixed-Type Femoroacetabular Impingement Due to Acetabular Retroversion or Protrusio Acetabuli on 3D CT-Based Impingement Simulation

BACKGROUND

Diagnosis and surgical treatment of hips with different types of pincer femoroacetabular impingement (FAI), such as protrusio acetabuli and acetabular retroversion, remain controversial because actual 3-dimensional (3D) acetabular coverage and location of impingement cannot be studied via standard 2-dimensional imaging. It remains unclear whether pincer hips exhibit intra- or extra-articular FAI.

PURPOSE

(1) To determine the 3D femoral head coverage in these subgroups of pincer FAI, (2) determine the impingement-free range of motion (ROM) through use of osseous models based on 3D-computed tomography (CT) scans, and (3) determine the osseous intra-and extra-articular 3D impingement zones by use of 3D impingement simulation.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

This is a retrospective, comparative, controlled study involving 70 hips in 50 patients. There were 24 patients (44 hips) with symptomatic pincer-type or mixed-type FAI and 26 patients (26 hips) with normal hips. Surface models based on 3D-CT scans were reconstructed and compared for hips with acetabular retroversion (30 hips), hips with protrusio acetabuli (14 hips), and normal asymptomatic hips (26 hips). Impingement-free ROM and location of impingement were determined for all hips through use of validated 3D collision detection software based on CT-based 3D models. No abnormal morphologic features of the anterior iliac inferior spine were detected.

RESULTS

(1) Mean total femoral head coverage was significantly (P < .001) increased in hips with protrusio acetabuli (92% ± 7%) and acetabular retroversion (71% ± 5%) compared with normal hips (66% ± 6%). (2) Mean flexion was significantly (P < .001) decreased in hips with protrusio acetabuli (104°± 9°) and acetabular retroversion (116°± 6°) compared with normal hips (125°± 13°). Mean internal rotation in 90° of flexion was significantly (P < .001) decreased in hips with protrusio acetabuli (16°± 12°) compared with normal hips (35°± 13°). (3) The prevalence of extra-articular subspine impingement was significantly (P < .001) higher in hips with acetabular retroversion (87%) compared with hips with protrusio acetabuli (14%) and normal hips (0%) and was combined with intra-articular impingement. The location of anterior impingement differed significantly (P < .001) between hips with protrusio acetabuli and normal hips.

CONCLUSION

Using CT-based 3D hip models, we found that hips with pincer-type and mixed-type FAI have significantly larger femoral head coverage and different osseous ROM and location of impingement compared with normal hips. Additionally, intra- and extra-articular subspine impingement was detected predominantly in hips with acetabular retroversion. Acetabular rim trimming during hip arthroscopy or open surgical hip dislocation should be performed with caution for these hips. Patient-specific analysis of location of impingement using 3D-CT could theoretically improve diagnosis and planning of surgical treatment.

Bone-to-Bone and Implant-to-Bone Impingement: A Novel Graphical Representation for Hip Replacement Planning

Bone-to-bone impingement (BTBI) and implant-to-bone impingement (ITBI) risk assessment is generally performed intra-operatively by surgeons, which is entirely subjective and qualitative, and therefore, lead to sub-optimal results and recurrent dislocation in some cases. Therefore, a method was developed for identifying subject-specific BTBI and ITBI, and subsequently, visualising the impingement area on native bone anatomy to highlight where prominent bone should be resected. Activity definitions and subject-specific bone geometries, with planned implants were used as inputs for the method. The ITBI and BTBI boundary and area were automatically identified using ray intersection and region growing algorithm respectively to retain the same ‘conical clearance angle’ obtained to avoid prosthetic impingement (PI). The ITBI and BTBI area was then presented with different colours to highlight the risk of impingement, and importance of resection. A clinical study with five patients after 2 years of THA was performed to validate the method. The results supported the study hypothesis, in that the predicted highest risk area (red coloured zone) was completely/majorly resected during the surgery. Therefore, this method could potentially be used to examine the effect of different pre-operative plans and hip motions on BTBI, ITBI, and PI, and to guide bony resection during THA surgery.