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.

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

Journal of Hip Preservation Surgery ◽

10.1093/jhps/hnab050 ◽

2021 ◽

Author(s):

Jun Zhou ◽

Heath P Melugin ◽

Rena F Hale ◽

Bryant M Song ◽

Kelechi R Okoroha ◽

...

Keyword(s):

Sex Differences ◽

Femoroacetabular Impingement ◽

Mixed Type ◽

Alpha Angle ◽

Radiographic Finding ◽

Hip Pain ◽

Radiographic Findings ◽

Male And Female ◽

Female Patients ◽

Male Patients

ABSTRACT 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.

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Prevalence of Morphological Variations Associated With Femoroacetabular Impingement According to Age and Sex: A Study of 1878 Asymptomatic Hips in Nonprofessional Athletes

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967120977892 ◽

2021 ◽

Vol 9 (2) ◽

pp. 232596712097789

Author(s):

Rodolfo Morales-Avalos ◽

Adriana Tapia-Náñez ◽

Mario Simental-Mendía ◽

Guillermo Elizondo-Riojas ◽

Michelle Morcos-Sandino ◽

...

Keyword(s):

Femoroacetabular Impingement ◽

Alpha Angle ◽

Cross Sectional Study ◽

Level Of Evidence ◽

Crossover Sign ◽

Cross Sectional ◽

Radiographic Findings ◽

Morphological Variations ◽

Pelvic Radiographs ◽

Center Edge

Background: Radiographic findings related to the cam and pincer variants of femoroacetabular impingement (FAI) include measurements of the alpha angle and lateral center-edge angle (LCEA). The function of these radiographic findings has been put into question because of high heterogeneity in reported studies. Purpose: The aim of this study was 3-fold: (1) to determine the prevalence of cam and pincer variants according to sex and age on anteroposterior (AP) pelvic radiographs from an asymptomatic nonathletic population, (2) to identify the most common radiographic signs of cam- and pincer-type variants, and (3) to determine if there are variations in the prevalence of these radiographic signs according to sex and age. Study Design: Cross-sectional study; Level of evidence, 3. Methods: There were 3 independent observers who retrospectively analyzed the 939 AP pelvic radiographs (1878 hips) of patients aged 18 to 50 years who did not have hip symptoms and who were not professional athletes. The prevalence of the cam and pincer variants according to the alpha angle and LCEA, respectively, and the presence of other radiographic signs commonly associated with these variables were determined in the overall population and by subgroup according to sex and age group (18-30, 31-40, and 41-50 years). Descriptive and inferential statistics were used to analyze the study sample. Results: The mean age of the included population was 31.0 ± 9.2 years, and 68.2% were male. The prevalence of the cam-type variant was 29.7% (558/1878), and that of the pincer-type variant was 24.3% (456/1878). The radiographic signs that were most associated with the cam and pincer variants were a pistol-grip deformity and the crossover sign, respectively. Significant differences ( P < .001) in the prevalence of these variants were identified between men and women in both variants. No differences were observed in the alpha angle or LCEA according to sex or age. Conclusion: Radiographic findings suggestive of FAI had significant variations with respect to sex and age in this study sample. This study provides information to determine the prevalence of these anatomic variants in the general population.

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Prevalence of Femoral and Acetabular Version Abnormalities in Patients With Symptomatic Hip Disease: A Controlled Study of 538 Hips

The American Journal of Sports Medicine ◽

10.1177/0363546517726983 ◽

2017 ◽

Vol 46 (1) ◽

pp. 122-134 ◽

Cited By ~ 41

Author(s):

Till D. Lerch ◽

Inga A.S. Todorski ◽

Simon D. Steppacher ◽

Florian Schmaranzer ◽

Stefan F. Werlen ◽

...

Keyword(s):

Hip Dysplasia ◽

Alpha Angle ◽

Young Patients ◽

Hip Pain ◽

Controlled Study ◽

Control Group ◽

Acetabular Version ◽

Neck Shaft Angle ◽

Femoral Version ◽

Center Edge

Background: Variations in femoral and acetabular version are becoming increasingly recognized as contributing factors to the development of hip pain in patients with femoroacetabular impingement (FAI) and hip dysplasia. It is still unknown what the true prevalence of these rotational abnormalities is in this patient population. Purpose: To determine (1) the prevalence of femoral version abnormalities in symptomatic hips with FAI and hip dysplasia, (2) the prevalence of combined abnormalities of femoral and acetabular version in these patients, and (3) which specific hip morphologies are associated with abnormalities of femoral version. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 462 symptomatic patients (538 hips) were included who had hip pain attributed to FAI or hip dysplasia and who presented to our tertiary referral center for hip preservation surgery between 2011 and 2015. We retrospectively examined femoral and acetabular version among 11 subgroups with predefined hip morphologies and compared findings with a control group. The allocation to each subgroup was based on morphologic reference values for femoral head coverage, lateral center edge angle, alpha angle, and neck-shaft angle calculated on plain radiographs. Results: Of the 538 hips included, 52% were found to have abnormal femoral version; severe abnormalities were found in 17%. Severely decreased femoral version (<0°) was found in 5%; moderately decreased femoral version (0°-10°), in 17%; moderately increased femoral version (26°-35°), in 18%; and severely increased femoral version (>35°), in 12%. The most frequent abnormal combination was increased femoral version combined with normal acetabular version (22%). We found significantly lower mean femoral version for the cam-type FAI group (15°) and significantly higher mean femoral version for the Perthes hips (32°; ie, Legg-Calvé-Perthes disease) as compared with the control group (22°). The mean femoral version of the study group was 19°; for male patients, 15°; and for female patients, 22°. Conclusion: Abnormalities in femoral version are highly prevalent in patients with hip pain who are eligible for hip preservation surgery, and severe abnormalities are prevalent in 1 of 6 patients (17%). Based on these results, the evaluation of young patients with hip pain should always include an assessment of femoral version and acetabular version to best decide what treatment approach should be undertaken to optimize outcomes.

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IDENTIFICATION OF FACTORS ASSOCIATED WITH DISEASE PROGRESSION IN THE CONTRALATERAL HIP OF PATIENTS WITH SYMPTOMATIC FEMOROACETABULAR IMPINGEMENT

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967121s00145 ◽

2021 ◽

Vol 9 (7_suppl3) ◽

pp. 2325967121S0014

Author(s):

Adam Khan ◽

Craig R. Louer ◽

Wahid Abu-Amer ◽

Gail Pashos ◽

Cecilia Pascual Garrido ◽

...

Keyword(s):

Disease Progression ◽

Femoroacetabular Impingement ◽

External Rotation ◽

Univariate Analysis ◽

Alpha Angle ◽

Hip Osteoarthritis ◽

Symptom Development ◽

Ucla Activity Score ◽

Center Edge ◽

Imaging Characteristics

Introduction: Femoroacetabular Impingement (FAI) is one of the most common causes of hip osteoarthritis. Nevertheless, the factors contributing to symptom development and FAI disease progression are poorly understood. Hypothesis/Purpose: The purpose of this study was to (1) investigate rates of initial and subsequent symptom development in the contralateral hip of patients with FAI, and (2) identify predictors of disease progression (symptom development) in the contralateral hip. Methods: This prospective study included a minimum 5 year follow-up of the contralateral hip in 179 patients undergoing FAI surgery. Symptoms (moderate pain) were monitored over the study course. Univariate analysis compared patient and FAI imaging characteristics of patients developing symptoms to those who remained asymptomatic. Results: 146 patients (146 hips, 81.5%) were included (min 5 year, mean 6.7 years). Thirty-nine (26%) presented with symptoms in the contralateral hip while 34 (23%) developed symptoms. Head-neck offset ratio (HNOR) on AP pelvis radiographs was significantly lower among hips that developed symptoms (0.164 vs. 0.153 p=0.025). Maximum alpha angle (p=0.413), lateral center edge angle (p=0.704), and crossover sign (p=0.115) were not predictive of symptoms. Patients with a UCLA activity score greater than 9 were less likely to develop symptoms (14% vs. 46%, p=0.081), but this was not statistically significant. The total arc of rotation in extension (35.740 vs 45.140, p=0.012) and 900 of flexion (40.00 vs 50.800, p=0.009) as well as external rotation at 900 of flexion (28.940 vs 36.590, p=0.020) were decreased in hips developing symptoms. Internal Rotation in flexion was not significantly decreased in symptomatic patients (11.060 vs 14.20, p=0.113). Conclusions: We identified unique radiographic and physical exam findings that are associated with symptom development in patients with FAI. Specifically, decreased hip rotation arc and decreased HNOR were strongly associated with disease progression and may represent important factors for future risk modeling in FAI patients.

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Identification of Factors Associated with Disease Progression in the Contralateral Hip of Patients with Symptomatic Femoroacetabular Impingement. (139)

Orthopaedic Journal of Sports Medicine ◽

10.1177/2325967121s00278 ◽

2021 ◽

Vol 9 (10_suppl5) ◽

pp. 2325967121S0027

Author(s):

Adam Khan ◽

Craig Louer ◽

Wahid Abu-Amer ◽

Gail Pashos ◽

Cecilia Pascual Garrido ◽

...

Keyword(s):

Disease Progression ◽

Femoroacetabular Impingement ◽

External Rotation ◽

Alpha Angle ◽

Hip Osteoarthritis ◽

Symptom Development ◽

Ucla Activity Score ◽

Center Edge ◽

Imaging Characteristics

Objectives: Femoroacetabular Impingement (FAI) is one of the most common causes of hip osteoarthritis. Nevertheless, the factors contributing to symptom development and FAI disease progression are poorly understood. The purpose of this study was to (1) investigate rates of symptom development in the contralateral hip of patients with FAI at mid-term follow-up, and (2) identify predictors of disease progression (symptom development) in the contralateral hip. Methods: This prospective study included 179 patients undergoing ipsilateral FAI surgery with no history of previous contralateral hip surgery. In the current study, the contralateral hip was assessed at minimum 5 year follow-up. Symptoms (defined as moderate pain) and the need for surgery were monitored over the study course. Statistical analysis compared patient and FAI imaging characteristics of patients developing symptoms to those who remained asymptomatic. Results: A total of 146 hips (81.5%) were included at a mean 6.7 years of follow-up. Thirty-nine (26.7%) presented with symptoms in the contralateral hip, while an additional 35 (23.9%) developed symptoms during the follow-up period. Twenty-Six (17.8%) progressed to surgery for their contralateral hip. Head-neck offset ratio (HNOR) on AP pelvis radiographs was significantly lower among hips that developed symptoms (0.16 vs. 0.15 p=0.03). Maximum alpha angle (p=0.41), lateral center edge angle (p=0.70), and crossover sign (p=0.12) were not predictive of symptoms. Patients with a UCLA activity score greater than 9 were less likely to develop symptoms (14% vs. 46%, p=0.081), but this was not statistically significant. The total arc of rotation in 90° of flexion (40.0° vs 50.8°, p=0.01) as well as external rotation at 900 of flexion (28.9° vs 36.6°, p=0.02) were decreased in hips developing symptoms. Internal rotation in flexion was not significantly decreased in symptomatic patients (11.1° vs 14.2°, p=0.11). Kaplan Meier survival analysis demonstrated 53% and 45% of patients remaining asymptomatic at 5 and 8 year time points (Figure). Conclusions: At a mean follow-up of 6.7 years, significant symptoms in the contralateral hip of patients with FAI are present in 50.7% of patients, while 49.3% remain asymptomatic or minimally symptomatic. We identified unique radiographic and physical exam findings that are associated with symptom development in patients with FAI. Specifically, decreased hip rotation arc and decreased HNOR were strongly associated with disease progression and may represent important factors for future risk modeling in FAI patients.

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Risk Factors for Long-term Hip Osteoarthritis in Patients With Femoroacetabular Impingement Without Surgical Intervention

The American Journal of Sports Medicine ◽

10.1177/0363546520949179 ◽

2020 ◽

Vol 48 (12) ◽

pp. 2881-2886

Author(s):

Heath P. Melugin ◽

Rena F. Hale ◽

Jun Zhou ◽

Matthew LaPrade ◽

Christopher Bernard ◽

...

Keyword(s):

Risk Factors ◽

Femoroacetabular Impingement ◽

Mixed Type ◽

Surgical Intervention ◽

Significant Risk ◽

Hip Osteoarthritis ◽

Hip Pain ◽

Male Sex ◽

Time Of Presentation

Background: Femoroacetabular impingement (FAI) is a common cause of hip pain and a known risk factor for hip osteoarthritis (OA) and total hip arthroplasty (THA) at a young age. Unfortunately, little is known about the specific factors associated with an increased risk of OA. Purpose: To (1) report the overall rate of symptomatic hip OA and/or THA in patients with FAI without surgical intervention and (2) identify radiographic features and patient characteristics associated with hip OA. Study Design: Case-control study; Level of evidence, 3. Methods: A geographic database was used to identify all patients with hip pain and radiographs between 2000 and 2016. Chart review was performed to identify patients with FAI. Patient medical records were reviewed to obtain demographic information, clinical history, physical examination findings, imaging details, and treatment details. Kaplan-Meier analysis was used to determine the rate of hip OA. Univariate and multivariate proportional hazard regression models were performed to determine risk factors for OA. Results: The study included 952 patients (649 female; 303 male; 1104 total hips) with FAI. The majority of hips had mixed type (n = 785; 71.1%), 211 (19.1%) had pincer type, and 108 (9.8%) had cam type. Mean age at time of presentation was 27.6 ± 8.7 years. Mean follow-up time was 24.7 ± 12.5 years. The rate of OA was 13.5%. THA was performed in 4% of patients. Male sex, body mass index (BMI) greater than 29, and increased age were risk factors for OA (male sex: hazard ratio [HR], 2.28; P < .01; BMI >29: HR, 2.11; P < .01; per year of increased age: HR, 1.11; P < .01.). Smoking and diabetes mellitus were not significant risk factors. No radiographic morphological features were found to be significant risk factors for OA. Conclusion: At mean follow-up of 24.7 years, 14% of hips had symptomatic OA and 4% underwent THA. BMI greater than 29, male sex, and increased age at the time of presentation with hip pain were risk factors for hip OA. The cohort consisted of a large percentage of mixed-type FAI morphologies, and no specific radiographic risk factors for OA were identified.

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The prevalence of femoroacetabular impingement anatomy in Division 1 aquatic athletes who tread water

Journal of Hip Preservation Surgery ◽

10.1093/jhps/hnaa009 ◽

2020 ◽

Vol 7 (2) ◽

pp. 233-241

Author(s):

Joanna L Langner ◽

Marianne S Black ◽

James W MacKay ◽

Kimberly E Hall ◽

Marc R Safran ◽

...

Keyword(s):

Femoroacetabular Impingement ◽

Young Patients ◽

Hip Pain ◽

Water Polo ◽

Increased Risk ◽

Division 1 ◽

Mri Scans ◽

Asymptomatic Individuals ◽

Cam Morphology ◽

Pincer Morphology

Abstract Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes. Increased stress on the hip during development has been associated with increased risk of cam morphology. The specific forces involved are unclear, but may be due to continued rotational motion, like the eggbeater kick. The goal of this prospective cohort study was to use magnetic resonance imaging (MRI) to identify the prevalence of FAI anatomy in athletes who tread water and compare it to the literature on other sports. With university IRB approval, 20 Division 1 water polo players and synchronized swimmers (15 female, 5 male), ages 18–23 years (mean age 20.7 ± 1.4), completed the 33-item International Hip Outcome Tool and underwent non-contrast MRI scans of both hips using a 3 Tesla scanner. Recruitment was based on sport, with both symptomatic and asymptomatic individuals included. Cam and pincer morphology were identified. The Wilcoxon Signed-Rank/Rank Sum tests were used to assess outcomes. Seventy per cent (14/20) of subjects reported pain in their hips yet only 15% (3/20) sought clinical evaluation. Cam morphology was present in 67.5% (27/40) of hips, while 22.5% (9/40) demonstrated pincer morphology. The prevalence of cam morphology in water polo players and synchronized swimmers is greater than that reported for the general population and at a similar level as some other sports. From a clinical perspective, acknowledgment of the high prevalence of cam morphology in water polo players and synchronized swimmers should be considered when these athletes present with hip pain.

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Femoroacetabular Impingement Syndrome: An Underrecognized Cause of Hip Pain and Premature Osteoarthritis?

The Journal of Rheumatology ◽

10.3899/jrheum.091186 ◽

2010 ◽

Vol 37 (7) ◽

pp. 1395-1404 ◽

Cited By ~ 31

Author(s):

GRAHAM D. REID ◽

CALLUM G. REID ◽

NADIA WIDMER ◽

PETER L. MUNK

Keyword(s):

Femoral Head ◽

Femoroacetabular Impingement ◽

Early Recognition ◽

Hip Osteoarthritis ◽

Hip Pain ◽

Impingement Syndrome ◽

Predisposing Factor ◽

Radiographic Findings ◽

Hip Arthritis ◽

Femoroacetabular Impingement Syndrome

Acetabular dysplasia is well recognized as a potential predisposing factor to the development of hip osteoarthritis (OA). In the orthopedic literature, other dysmorphic and orientation abnormalities of the femoral head, femoral head-neck junction, and the acetabulum have been reported, with increasing frequency in recent years, under the term femoroacetabular impingement syndrome (FAI). The studies have shown a clear association of these structural anomalies with patients’ symptoms and signs, radiographic and pathologic abnormalities, and the development of degenerative hip arthritis. FAI is now believed to be a very important predisposing factor for the development of degenerative hip arthritis, particularly in younger adults. Although the results of longterm studies are awaited, the hope is that early surgical intervention in patients with FAI will change the course or prevent the development of hip OA. It is well documented that early recognition of potential FAI surgical candidates, before OA is advanced, determines the postsurgical outcome. FAI has not been reported in the rheumatology literature, but since patients with FAI likely often initially present to rheumatology clinics for assessment of hip pain, it is important for rheumatologists to be aware of this condition and refer to orthopedics when appropriate. The objective of this review is to provide an outline of the basic concepts of FAI, including clinical presentation and radiographic findings, so that rheumatologists become more familiar with this important emerging entity.

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Femoroacetabular impingement: presence of FAI-like features on conventional radiography in young patients presenting to primary care with hip pain

Acta Radiologica ◽

10.1177/0284185113481592 ◽

2013 ◽

Vol 54 (6) ◽

pp. 690-697 ◽

Cited By ~ 7

Author(s):

Carl Sullivan ◽

Julian Chakraverty ◽

Kieran Foley ◽

Srikanth Narayanaswamy ◽

Sridhar Kamath

Keyword(s):

Primary Care ◽

Femoroacetabular Impingement ◽

Young Patients ◽

Conventional Radiography ◽

Hip Pain

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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

The American Journal of Sports Medicine ◽

10.1177/0363546519897273 ◽

2020 ◽

Vol 48 (3) ◽

pp. 661-672 ◽

Cited By ~ 1

Author(s):

Till D. Lerch ◽

Mathias Siegfried ◽

Florian Schmaranzer ◽

Christiane S. Leibold ◽

Corinne A. Zurmühle ◽

...

Keyword(s):

Surgical Treatment ◽

Femoral Head ◽

Femoroacetabular Impingement ◽

Mixed Type ◽

Acetabular Retroversion ◽

Ct Scans ◽

Controlled Study ◽

3D Ct ◽

Femoral Head Coverage ◽

Protrusio Acetabuli

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.

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