Femoroacetabular impingement: role of imaging

Inter-observer concordance in normal and pathological findings of the hip joint in plain radiographs

Background and aim:

The purpose of the study was to compare the data obtained by two independent observers and statistically analyse the results using Cohen’s K to highlight the concordance or discordance in the diagnosis of normality, pathology and, in particular, the type of femoroacetabular impingement (FAI) on plain films.

Methods:

the study was conducted retrospectively. The only inclusion criterium was the minimum age of 20 years. All patients underwent a radiographic examination of the pelvis in standard anteroposterior projection in orthostasis.

Results:

A hundred patients were evaluated. A good concordance between the two operators in the examination of normal hip joint (k= 0.68 right/ 0,74 left) was found; a similar grade of agreement was found for the analysis of “pincer” type FAI (k = 0.73 right, 0,67 left). The best results in concordance were achieved in the examination of “cam” type FAI (k= 0.82 right, 0,88 left), “mixed” type FAI (k = 0.85 right, 0,86 left), and in findings of “coxa profunda” (k = 0.92 right, 0,88 left).

Conclusion:

We found a good concordance between the two readers; a few cases of disagreement were found in the diagnosis of “pincer” type FAI and absence of disease. This discrepancy may be due to the different weight given by the single observer to the clinical indication that leads the patient to examination, but also by the difficulty of a not dedicated radiologist to show some subtle signs indicative of early FAI.

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.

Proximal Femoral Rotational Osteotomy for Symptomatic Femoral Retroversion : A Case Report

The Rotational osteotomy for femoral retroversion has been extremely rare despite the known association between femoral neck retroversion, hip pain, and osteoarthritis. Here, we describe a case of femoral neck retroversion for which proximal femoral rotation osteotomy. A 16-year-old boy with a past history of developmental dysplasia of the both hip treated conservatively presented with a complaint of pain in left hips. On physical examination, flexion of the left hip was limited to 90° with terminal pain. Internal rotation was also limited to 10°. Computed tomography (CT) showed -7.1° anteversion of the left femur. We performed rotational osteotomy to increase femoral anteversion because conservative treatment was not effective. The postoperative course was uneventful. At 12 postoperative months, his left hip pain was completely disappeared and femoral anteversion was 34° on CT scans. Retroversion of the femur is a distinct dynamic factor that should be considered in the evaluation of mechanical causes of hip pain. Restoring the normal rotational alignment of the hip resulted in cure of the impingement due to femoral retroversion. J. Med. Invest. 67 : 214-216, February, 2020.

Prevalence of radiographic parameters on CT associated with femoroacetabular impingement in a Chinese asymptomatic population

BACKGROUND

Imaging evaluation of femoroacetabular impingement (FAI) plays a major role in early diagnosis and treatment, preventing irreversible degenerative changes in hip joints.

PURPOSE

To investigate the anatomical parameters associated with FAI in a Chinese asymptomatic population by computed tomography (CT) and to evaluate the prevalence of the radiographic features of cam and pincer types in Chinese patients.

MATERIAL AND METHODS

We reviewed the CT images of 470 hips in 235 Chinese patients who underwent abdominal and pelvic CT scans for reasons unrelated to hip symptoms at our hospital between February and October 2017. The following measurements were made on each hip joint: acetabular version angle (AV); anterior acetabular sector angle (AASA); posterior acetabular sector angle (PASA); the lateral center edge angle (LCE); the alpha angle (AA); and femoral head-neck offset (FHNO).

RESULTS

Significant differences in all parameters were seen between men and women. Young men and elderly women showed more retroversion in our study. LCE, AA, and FHNO were all larger in men than women. The data showed 25% of female joints and 34.5% of male joints had at least one predisposing factor for FAI using measurement parameters by CT images in Chinese asymptomatic patients, and the prevalence of pincer lesion (19.1%) was larger than cam lesion (9.1%).

CONCLUSION

Morphological features associated with FAI are also present in Chinese asymptomatic patients. The threshold values for abnormal parameters should be reconsidered based on gender, age, and other factors in order to improve the accuracy of diagnosis.

Interchangeability of CT and 3D "pseudo-CT" MRI for preoperative planning in patients with femoroacetabular impingement

OBJECTIVE

To determine whether a 3D magnetic resonance imaging (MRI) sequence with postprocessing applied to simulate computed tomography (CT) ("pseudo-CT") images can be used instead of CT to measure acetabular version and alpha angles and to plan for surgery in patients with femoroacetabular impingement (FAI).

MATERIALS AND METHODS

Four readers retrospectively measured acetabular version and alpha angles on MRI and CT images of 40 hips from 20 consecutive patients (9 female patients, 11 male patients; mean age, 26.0 ± 6.5 years) with FAI. 3D models created from MRI and CT images were assessed by 2 orthopedic surgeons to determine the need for femoroplasty and/or acetabuloplasty. Interchangeability of MRI with CT was tested by comparing agreement between 2 readers using CT (intramodality) with agreement between 1 reader using CT and 1 using MRI (intermodality).

RESULTS

Intramodality and intermodality agreement values were nearly identical for acetabular version and alpha angle measurements and for surgical planning. Increases in inter-reader disagreement for acetabular version angle, alpha angle, and surgical planning when MRI was substituted for CT were - 2.1% (95% confidence interval [CI], - 7.7 to + 3.5%; p = 0.459), - 0.6% (95% CI, - 8.6 to + 7.3%; p = 0.878), and 0% (95% CI, - 15.1 to + 15.1%; p = 1.0), respectively, when an agreement criterion ≤ 5° was used for angle measurements.

CONCLUSION

Pseudo-CT MRI was interchangeable with CT for measuring acetabular version and highly favorable for interchangeability for measuring alpha angle and for surgical planning, suggesting that MRI could replace CT in assessing patients with FAI.

Intraoperative radiation exposure in hip arthroscopy: a systematic review

Fluoroscopy is used in hip arthroscopy (HA) for portal placement, instrument localisation, and guidance in bony resection. The recent increase in arthroscopic hip procedures may place patients and surgeons at risk for increased radiation exposure and radiation-induced complications. The purpose of the current systematic review was to assess intraoperative radiation exposure in HA. The systematic review was conducted according to PRISMA guidelines; inclusion criteria were studies assessing radiation exposure in HA. 9 studies including 994 patients were included. Mean age was 38.6 years and 48% (436 of 906) were female. Mean time of fluoroscopy exposure was 0.58 minutes. Dose area product was 129.5 cGycm². Mean intraoperative absorbed radiation dose studies was 12.6 mGy. Mean intraoperative effective dose was 0.48 mSv. The mean occupational exposure to the surgeon per case was 0.0031 mSv. Higher patient body mass index (BMI) correlated to greater patient effective and cumulative dose (p < 0.05, r = 0.404), and greater occupational exposure (p < 0.001, r = 0.460). Increasing surgeon experience decreased fluoroscopy time (p = 0.039) and radiation dose (p = 0.002). Radiation dose and effective dose were well under the thresholds for deterministic effects (2 Gy) and annual radiation exposure for occupational workers (20 mSv). Intraoperative radiation exposure to patients and surgeons is within acceptable annual radiation limits. Ensuring careful selection of perioperative imaging modalities, proper protective shielding, specifically the use of leaded eyeglasses, and optimal C-arm positioning are key strategies to reduce radiation exposure to patients and surgeons alike.

The Prevalence of Radiographic Findings of Structural Hip Deformities for Femoroacetabular Impingement in Patients With Hip Pain

BACKGROUND

Radiography is the initial imaging modality used to evaluate femoroacetabular impingement (FAI), and diagnostic radiographic findings are well-established. However, the prevalence of these radiographic findings in patients with hip pain is unknown.

PURPOSE

The purpose was 3-fold: (1) to determine the overall prevalence of radiographic FAI deformities in young patients presenting with hip pain, (2) to identify the most common radiographic findings in patients with cam-type FAI, and (3) to identify the most common radiographic findings in patients with pincer-type FAI.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

A geographic database was used to identify patients aged 14 to 50 years with hip pain between the years 2000 to 2016. The following were evaluated on radiographs: cam type: typical pistol grip deformity, alpha angle >55°; pincer type: crossover sign (COS), coxa profunda or protrusio acetabuli, lateral center edge angle (LCEA) ≥40°, Tönnis angle <0°; and mixed type: both cam- and pincer-type features. Posterior wall sign (PWS) and ischial spine sign (ISS) were also evaluated. The prevalence of each was determined. Descriptive statistics were performed on all radiographic variables.

RESULTS

There were 1893 patients evaluated, and 1145 patients (60.5%; 1371 hips; 374 male and 771 female; mean age, 28.8 ± 8.4 years) had radiographic findings consistent with FAI. Of these hips, 139 (10.1%) had cam type, 245 (17.9%) had pincer type, and 987 (72.0%) had mixed type. The prevalence of a pistol grip deformity and an alpha angle >55° was 577 (42.1%) and 1069 (78.0%), respectively. The mean alpha angle was 66.9°± 10.5°. The prevalence of pincer-type radiographic findings was the following: COS, 1062 (77.5%); coxa profunda, 844 (61.6%); ISS, 765 (55.8%); PWS, 764 (55.7%); Tönnis angle <0°, 312 (22.8%); LCEA ≥40°, 170 (12.4%); and protrusio acetabuli, 7 (0.5%).

CONCLUSION

The overall prevalence of radiographic findings consistent with FAI in young patients with hip pain was 60.5%. Radiographic findings for mixed-type FAI were the most prevalent. The most common radiographic finding for cam-type FAI was an alpha angle >55°. The most common radiographic finding for pincer-type FAI was the COS.

Acetabular posterior wall morphology. A CT-based method to distinguish two acetabular posterior wall types

Background

The anatomy of the posterior wall of the acetabulum is important for the hip stability. We wanted to know whether differences can be observed.

Material and methods

On lateral 3D pelvic CT reconstruction of the pelvis two types were identified. On axial CT-images acetabular angles were determined.

Results

We observed 35 type I acetabular and 61 type II acetabular. Posterior acetabular sector angle was 114° in type I and 94° in type II acetabular (p < 0.01). At an cut-off angle of 100° we could predict the type of acetabulum.

Conclusions

We could describe reference values for the posterior wall to distinguish two morphological types.

The Extension-Thickness-Damage (ETD) score: a pre-operative hip MR arthrography-based classification to predict type of labrum surgery

INTRODUCTION

Hip magnetic resonance arthrography (MRA) is the pre-operative imaging modality of choice in patients with labral damage, with several classifications of labral tears having been reported based on MRA findings. Nevertheless, none of the available classification systems allows the surgeon to predict before surgery how a labral tear could be treated. Our purpose was to develop a new MRA-based scoring system of labral tears to predict before surgery the treatment option more suitable for labral tears.

MATERIALS AND METHODS

Forty-seven patients (29 males and 18 females; mean age: 35.9 ± 12.4) performed hip MRA for suspicious of femoroacetabular impingement and were afterwards subjected to arthroscopic treatment. Two musculoskeletal radiologists reviewed all pre-operative examinations and provided the Extension-Thickness-Damage score for each patient, based on Extension of tear, Thickness of labrum, and type of Damage. Chondral lesions grading was based on the arthroscopic findings according to Konan classification. For statistical purposes, patients were divided into two groups, depending on the type of treatment: labral repair or debridement. Mann-Whitney U, Chi-square, receiver operator curves, and Cohen kappa statistics were used.

RESULTS

35/47 underwent repair, while 12/47 were debrided. In both groups, the median chondral damage was grade III, with no significant differences (p = 0.439). The median Extension-Thickness-Damage score in the repair group (6) was significantly lower (p < 0.001) than that in the debridement group (8). The highest diagnostic performance (area under the curve) of Extension-Thickness-Damage was 0.819. The inter-observer agreement was substantial in the evaluation of Extension (k = 0.626) and Thickness (k = 0.771), and almost perfect for Damage (k = 0.827). Higher scores of Extension and Thickness were more frequently associated with debridement (p < 0.001; p = 0.0016, respectively), with no significant differences on the basis of Damage parameter (p = 0.284).

CONCLUSIONS

The MRA-based Extension-Thickness-Damage score could represent a helpful pre-operative tool, expressing the extent of the damage and its reparability before arthroscopy.

Minimal Clinically Important Difference and Substantial Clinical Benefit After Revision Hip Arthroscopy

PURPOSE

To define minimal clinically important difference (MCID) and substantial clinical benefit (SCB) in revision hip arthroscopy.

METHODS

The modified Harris Hip Score (mHHS), the Hip Outcome Score (HOS), and the international Hip Outcome Tool (iHOT-33) were administered to revision hip arthroscopy patients. At 1 year postoperatively, patients graded their hip function based on anchor responses. SCB was defined as both a net change and an absolute value. Receiver operating characteristic analysis with area under the curve was used to confirm psychometric values. A distribution-based method was used for MCID.

RESULTS

Forty-nine patients were included with a mean age of 29.7 (±8.6) years. The most common indication for revision hip arthroscopy was residual femoroacetabular impingement (FAI; N = 34; 69.4%) followed by capsular management (N = 8; 16.3%). At 1-year follow-up, 34 patients reported feeling improved. Outcome score change corresponding to MCID and SCB net change for the mHHS, HOS Activities of Daily Living (ADL), HOS Sports, and iHOT-33 was 7.9/23.1, 7.9/16.2, 13.1/25.0, and 12.8/25.5, respectively. A higher proportion of patients with residual FAI achieved MCID compared with patients with other diagnoses. On the preoperative HOS ADL, HOS Sports, and iHOT-33, patients scoring below 67.7 (0.78), 55.6 (0.81), and 35.7 (0.73) were significantly more likely to achieve SCB postoperatively. Thirty-four patients (73.9%) were classified as receiving physical function improvement, and on the HOS Sports, MCID was achieved by 65% whereas 43% met the SCB criteria.

CONCLUSIONS

MCID values ranged from 7.9 on the mHHS and the HOS ADL to 13.1 on the HOS Sports. SCB net change ranged from 16.2 on the HOS ADL to 25.2 on the iHOT-33, whereas absolute SCB ranged from 82.4 on the iHOT-33 to 84.7 on the mHHS. Residual FAI and capsular management were the most common indications for revision surgery with patients who underwent surgery for the former found to be most likely to achieve clinically significant improvement.

LEVEL OF EVIDENCE

Level IV, case series.

Arthroscopic Treatment of Femoroacetabular Impingement in Adolescents Provides Clinically Significant Outcome Improvement

PURPOSE

To define minimal clinically important difference (MCID) and substantial clinical benefit (SCB) for adolescents undergoing arthroscopic femoroacetabular impingement (FAI) surgery.

METHODS

A prospective institutional hip preservation registry was reviewed to identify hip arthroscopies performed for FAI. Patients with pre-existing hip conditions such as slipped capital femoral epiphysis and Legg-Calve-Perthese were excluded. Included patients were 18 years and younger. The modified Harris Hip Score (mHHS), the Hip Outcome Score (HOS), and the international Hip Outcome Tool (iHOT-33) were administered as part of the registry. MCID was calculated using a distribution-based method, and SCB was calculated using a physical function anchor question. Receiver operating characteristic analysis with area under the curve (AUC) was used for psychometric analyses.

RESULTS

Forty-seven adolescents were identified. The majority of patients were female (n = 32, 68.1%) with a mean age of 16.5 (±1.1) years. The MCID (% achieving) for the mHHS, HOS activities of daily living (ADL), HOS Sport, and iHOT-33 was 9.5 (85%), 9.8 (79%), 12.1 (85%), and 10.7 (94%), respectively. Ninety-two percent of adolescents reported some form of improved hip physical ability on the anchor question. The following 1-year absolute outcome scores were significantly representative of an SCB state on the mHHS, HOS ADL, HOS Sport, and mHHS, respectively (AUC): 93.5 (0.79), 98.5 (0.84), 96.9 (0.81), and 85.9 (0.76).

CONCLUSIONS

Adolescents undergoing arthroscopic FAI surgery achieve clinically significant outcome improvement. We found that the vast majority of adolescents achieve MCID on hip-specific patient-reported outcome tools. However, although adolescents readily achieve MCID, a considerable improvement in postoperative outcome score is often needed to perceive a substantial benefit (SCB). The available hip outcome tools may be subject to ceiling effects for measuring clinically significant outcome improvement in adolescents.

LEVEL OF EVIDENCE

Level IV, case series.

Preoperative Outcome Scores Are Predictive of Achieving the Minimal Clinically Important Difference After Arthroscopic Treatment of Femoroacetabular Impingement

BACKGROUND

There is increasing interest in defining meaningful improvement in patient-reported outcomes. Knowledge of the thresholds and determinants for successful femoroacetabular impingement (FAI) outcomes is evolving.

PURPOSE

To define preoperative outcome score thresholds and determine clinical/demographic patient factors predictive for achieving the minimal clinically important difference (MCID) after arthroscopic FAI surgery.

STUDY DESIGN

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

METHODS

A prospective institutional hip preservation registry was reviewed to identify patients undergoing arthroscopic FAI surgery. The modified Harris Hip Score (mHHS), the Hip Outcome Score (HOS), and the international Hip Outcome Tool (iHOT-33) were administered at baseline and 1 year postoperatively. The MCID was calculated using a distribution-based method. Receiver operating characteristic (ROC) analysis was used to calculate cohort-based threshold values predictive of achieving the MCID. The area under the curve (AUC) was used to define predictive ability, with AUC >0.7 considered acceptably predictive. Multivariable analysis identified patient factors associated with achieving the MCID. Sensitivity analysis was performed to derive the MCID by an alternative anchor-based method.

RESULTS

There were 364 patients (mean [±SD] age, 32.5 ± 10.3 years), and 57.1% were female. The MCID for the mHHS, HOS-Activities of Daily Living (HOS-ADL), HOS-Sports, and iHOT-33 was 8.2, 8.3, 14.5, and 12.1, respectively. ROC analysis findings (threshold, percentage achieving the MCID, and strength of association) for these tools were as follows: mHHS (60.5, 77.2%, and 0.68, respectively), HOS-ADL (83.3, 68.1%, and 0.85, respectively), HOS-Sports (58.3, 65.9%, and 0.76, respectively), and iHOT-33 (53.9, 81.9%, and 0.65, respectively). The likelihood for achieving the MCID significantly declined above these thresholds. In multivariable analysis, a higher sagittal center-edge angle (CEA) (odds ratio [OR], 1.04; 95% CI, 1.01-1.08) was a positive predictor of achieving the MCID on the iHOT-33, while a higher Outerbridge grade for the acetabulum was a negative predictor (OR, 0.56; 95% CI, 0.32-0.99) on the mHHS. Sensitivity analysis confirmed these variables and identified relative femoral retroversion as another negative predictor (OR, 0.40; 95% CI, 0.17-0.94).

CONCLUSION

The HOS had excellent predictive ability for identifying patient thresholds of achieving the MCID; patients with preoperative scores below identified thresholds were most likely to achieve the MCID. Additionally, anterior acetabular undercoverage, chondral injuries, and relative femoral retroversion were clinically significant negative modifiers of outcomes. These findings have implications for managing preoperative expectations of FAI surgery.

Orthopaedic surgeons' use and knowledge of ionizing radiation during surgical treatment for femoroacetabular impingement

PURPOSE

To better understand how radiograph imaging is currently used throughout perioperative care for femoroacetabular impingement (FAI) and to define surgeon knowledge and perspective on radiation safety when treating FAI.

METHODS

An online questionnaire was designed to be completed by hip arthroscopists on the imaging modalities and projections they use during evaluation and treatment of FAI and the associated radiation exposures and safety. A sample of practicing attending orthopaedic surgeons was surveyed via an anonymous survey link emailed to corresponding authors on publications related to FAI. The anonymous survey link was also provided to orthopaedic surgeons at the 2014 Vail Hip Symposium.

RESULTS

Ninety-one surgeons completed the survey. Of these participants, 72 surgeons (79.1 %) indicated they use pre-operative radiographs and intra-operative spot fluoroscopic images during FAI treatment. Thirty-three surgeons (36.3 %) use pre-operative computed tomography (CT). Twenty-three surgeons (25.3 %) use real-time moving fluoroscopy. A majority of surgeons incorrectly answered multiple-choice questions about which C-arm positions and settings result in the lowest doses of radiation to the surgeon or patient. Eighty-three surgeons (91.2 %) indicated they believe most orthopaedic surgeons need to be more informed about radiation safety.

CONCLUSIONS

This study gives a quantitative representation of the imaging modalities and projections utilized during perioperative treatment for FAI. This study also identified a lack of knowledge of radiation safety among orthopaedic surgeons treating patients with FAI and demonstrates the need for greater education.

LEVEL OF EVIDENCE

IV.

The prevalence of femoroacetabular impingement in radiographs of asymptomatic subjects: a cross-sectional study

BACKGROUND

There is a lack of uniformity in the diagnostic criteria for femoroacetabular impingement (FAI), and few studies discuss the prevalence of radiographic changes in asymptomatic individuals. These factors make it difficult to establish a natural history of this disease. The aim of this study was to assess the prevalence of radiographic signs of CAM and Pincer FAI in an asymptomatic population.

METHODS

A cross-sectional study was performed from July 2013 to December 2013. A total of 185 subjects were analysed.

INCLUSION CRITERIA

no history of hip pain or orthopedic disease; and being 20-60 years old.

EXCLUSION CRITERIA

athletically active; or patients who would not allow acquisition of appropriate radiographs for analysis. Radiographs were obtained in anteroposterior and Dünn 45° view to access: alpha angle (AA), triangular index (TI), crossover sign (CS), lateral-centre edge (LCE) angle and acetabular index (AI).

RESULTS

Median age was 34 years (27-49.5) and FAI was present in 53% of all subjects. 32.44% (60) was the overall CAM-type prevalence and 42.7% (79) the overall Pincer-type prevalence. Only 2 subjects presented the 3 overcoverage signs (AI, LCE and CS). An association was noted between the presence of AI &lt;0° and the LCE &gt;40° (p = 0.05).

CONCLUSIONS

Our study established a higher prevalence of radiographic markers of FAI in an asymptomatic population.

Coxa profunda in the diagnosis of pincer-type femoroacetabular impingement and its prevalence in asymptomatic subjects

In many papers, the diagnosis of pincer-type femoroacetabular impingement (FAI) is attributed to the presence of coxa profunda. However, little is known about the prevalence of coxa profunda in the general population and its clinical relevance. In order to ascertain its prevalence in asymptomatic subjects and whether it is a reliable indicator of pincer-type FAI, we undertook a cross-sectional study between July and December 2013. A total of 226 subjects (452 hips) were initially screened. According to strict inclusion criteria, 129 asymptomatic patients (257 hips) were included in the study. The coxa profunda sign, the crossover sign, the acetabular index (AI) and lateral centre-edge (LCE) angle were measured on the radiographs. The median age of the patients was 36.5 years (28 to 50) and 138 (53.7%) were women. Coxa profunda was present in 199 hips (77.4%). There was a significantly increased prevalence of coxa profunda in women (p < 0.05) and a significant association between coxa profunda and female gender (p < 0.001) (92% vs 60.5%). The crossover sign was seen in 36 hips (14%), an LCE > 40° in 28 hips (10.9%) and an AI < 0º in 79 hips (30.7%). A total of 221 normal hips (79.2%) (normal considering the crossover) had coxa profunda, a total of 229 normal hips (75.5%) (normal considering the LCE) had coxa profunda and a total of 178 normal hips (75.3%) (normal considering AI) had coxa profunda. When the presence of all radiological signs in the same subject was considered, pincer-type FAI was found in only two hips (one subject). We therefore consider that the coxa profunda sign should not be used as a radiological indicator of pincer-type FAI. We consider profunda to be a benign alteration in the morphology of the hip with low prevalence and a lack of association with other radiological markers of FAI. We suggest that the diagnosis of pincer-type FAI should be based on objective measures, in association with clinical findings.

A 3D active model framework for segmentation of proximal femur in MR images

PURPOSE

Segmentation of osseous structures from clinical MR images is difficult due to acquisition artifacts and variable signal intensity of bones. Segmentation of femoral head is required for evaluation of hip joint abnormalities such as cam- type femoroacetabular impingement. A parametric deformable model (PDM) framework was developed for segmentation of 3D magnetic resonance (MR) images of the hip.

METHOD

A two-phase segmentation scheme was implemented: (i) Radial basis function interpolation was performed for semi-automatic piecewise registration of a proximal femur atlas model to an MRI scan region of interest. User-defined control points on the mesh model were registered to the corresponding landmarks on the image. (ii) An active PDM was then used for coarse-to-fine level segmentation. The segmentation technique was tested using 3D synthetic image data and clinical MR scans of the hip with varying resolution.

RESULTS

The segmentation method provided a mean target overlap of 0.95 and misclassification error of 0.035 for the synthetic data. The average target overlap was 0.88, and misclassification error rate was 0.12 for the clinical MRI data sets.

CONCLUSION

A framework for segmentation of proximal femur in hip MRI scans was developed and tested. This method is robust to artifacts and intensity inhomogeneity and resistant to leakage into adjacent tissues. In comparison with slicewise segmentation techniques, this method features inter-slice consistency, which results in a smooth model of the proximal femur in hip MRI scans.