Anterior Inferior Iliac Spine Morphology: Comparison of Symptomatic Hips With Femoroacetabular Impingement and Asymptomatic Hips

How to Best Identify Acetabular Retroversion on Radiographs: Thresholds to Guide Clinical Practice

BACKGROUND

Acetabular retroversion is associated with impingement and instability. An adequate interpretation of acetabular version and coverage on radiographs is essential to determine the optimal treatment strategy (periacetabular osteotomy vs hip arthroscopic surgery). The crossover sign (COS) has been associated with the presence of acetabular retroversion, and the anterior wall index (AWI) and posterior wall index (PWI) assess anteroposterior acetabular coverage. However, the radiographic appearance of the acetabulum is sensitive to anterior inferior iliac spine (AIIS) morphology and pelvic tilt (PT), which differs between the supine and standing positions.

PURPOSE

To (1) identify differences in the acetabular appearance between the supine and standing positions among patients presenting with hip pain; (2) determine factors (acetabular version, AIIS morphology, and spinopelvic characteristics) associated with the crossover ratio (COR), AWI, and PWI; and (3) define relevant clinical thresholds to guide management.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Patients who presented to a hip preservation surgical unit (n = 134) were included (mean age, 35 ± 8 years; 58% female; mean body mass index, 27 ± 6). All participants underwent supine and standing anteroposterior pelvic radiography to assess the COS, COR, AWI, and PWI as well as standing lateral radiography to determine standing PT. Computed tomography was used to measure supine PT, acetabular version, and AIIS morphology. Acetabular version was measured at 3 transverse levels, corresponding to the 1-, 2-, and 3-o'clock positions. The correlation between radiographic characteristics (COR, AWI, and PWI) and acetabular version, AIIS morphology, and PT was calculated using the Spearman correlation coefficient. Receiver operating characteristic curve analysis was performed to define thresholds for the COR, AWI, and PWI to identify retroversion (version thresholds: <10°, <5°, and <0°).

RESULTS

The COS was present in 55% of hips when supine and 30% when standing, with a mean difference in the COR of 12%. The supine COR (rho = -0.661) and AWI/PWI ratio (rho = -0.618) strongly correlated with acetabular version. The COS was more prevalent among patients with type 2 AIIS morphology (71%) than among those with type 1 AIIS morphology (43%) (P = .003). COR thresholds of 23% and 28% were able to identify acetabular version <5° (sensitivity = 81%; specificity = 80%) and <0° (sensitivity = 88%; specificity = 85%), respectively. An AWI/PWI ratio >0.6 was able to reliably identify acetabular version <0° (sensitivity = 83%; specificity = 84%). In the presence of a COR >30% and an AWI/PWI ratio >0.6, the specificity to detect retroversion was significantly increased (>90%).

CONCLUSIONS

The presence of the COS was very common among patients with hip pain. False-positive results (high COR/normal version) may occur because of AIIS morphology/low PT. Relevant thresholds of COR >30% and AWI/PWI ratio >0.6 can help with diagnostic accuracy. In cases in which either the COR or AWI/PWI ratio is high, axial cross-sectional imaging can further help to avoid false-positive results.

Ultrasound Assessment of Hip Subspine Bone Morphology Soft-tissue Correlates with Clinical Diagnosis of Impingement

PURPOSE

To determine the ultrasound imaging manifestations associated with subspine impingement (SSI), including the osseous and soft-tissue injuries adjacent to anterior inferior iliac spine (AIIS) and to investigate the diagnostic value of ultrasound for SSI.

METHODS

We retrospectively evaluated patients who attended the sports medicine department of our hospital and underwent arthroscopic treatment for femoroacetabular impingement (FAI) between September 2019 and October 2020, with preoperative hip joint ultrasound and computed tomography (CT) examination within 1 month before surgery. All of the FAI patients were divided into the SSI group and non-SSI group, according to the clinical and intraoperative findings. The preoperative ultrasound and CT findings were assessed. The sensitivity, specificity, and positive predictive value (PPV) of some indicators were calculated and compared. Multivariable logistic regression and receiver operating characteristic curve (ROC) were also used.

RESULTS

A total of 71 hips were included, with a mean age of 35.4 ± 10.4 years, 56.3% were women. Of these, 40 hips had clinically confirmed SSI. The bone morphology type III, heterogeneous hypoecho in anterosuperior joint capsule and the direct head of rectus femoris (dRF) tendon adjacent to AIIS on the Standard Section of the dRF in ultrasound were associated with SSI. Among them, the heterogeneous hypoecho in the anterosuperior joint capsule had the best diagnostic value for the SSI (85.0% sensitivity, 58.1% specificity, AUC = 0.681). The AUC of the ultrasound composite indicators was 0.750. The AUC and PPV of CT low-lying AIIS for the SSI diagnosis was 0.733 and 71.7%, which could be improved when CT was combined with the ultrasound composite indicators with AUC = 0.831 and PPV = 85.7%.

CONCLUSIONS

Bone morphology abnormalities and soft-tissue injuries adjacent to the AIIS through sonographic evaluation were associated with SSI. Ultrasound could be used as a feasible method to predict SSI. The diagnostic value for SSI could be improved when ultrasound is combined with CT.

LEVEL OF EVIDENCE

Level IV, case series.

Subspine femoroacetabular impingement: retrospective study of a series of patients treated by hip arthroscopic resection

BACKGROUND

Femoroacetabular impingement syndrome (FAIS) is a common hip pathology that causes pain and functional limitation in young patients. subspine femoroacetabular impingement (SFAI) is an increasingly diagnosed extra-articular subtype that occurs from mechanical conflict of the anteroinferior iliac spine (AIIS) with the cervico-diaphyseal junction during hip flexion, which is poorly described in the literature.

QUESTIONS/PURPOSES

We aimed to describe the clinical, functional, and radiological results of the arthroscopic treatment of a group of patients with SFAI treated in our Hip Unit.

STUDY DESIGN

Case series.

METHODS

We present a retrospective study of ten patients with SFAI treated between 2013 and 2020 with arthroscopic resection. Clinical results were assessed with scales such as visual analog scale (VAS); modified Harris Hip Score (mHHS), and Hip disability and Osteoarthritis Outcome Score (HOOS). Radiological results were assessed with radiological measurements, magnetic resonance imaging (MRI), and computed tomography (CT) reconstructions.

RESULTS

Six patients had a Type III AIIS and four of them had Type II. Two patients had previously been surgically treated for FAIS. The range of motion improved in flexion from 107 ± 11 degrees before surgery to 127.5 ± 6 degrees (p = 0.005). MHHS improved from 48.1 (38-75.3) before surgery to 83.1 (57-91) (p = 0.007) and HOOS improved from 65.2 (58-75) to 89 (68.1-100) (p = 0.007). VAS improved from 7.3 (5-9) pre-surgical to 2.5 (0-8) post-surgical (p = 0.005). We did not have significant complications except for an asymptomatic case of heterotopic ossification (Brooker I).

CONCLUSION

Arthroscopic decompression of AIIS in SFAI patients is a safe procedure that provides satisfactory short-term functional results, improving clinical symptoms, function, sports performance, and range of motion in our study.

A comparison between ultrasound-guided AIIS injection and radiography in the diagnosis of subspine impingement in patients with FAI

BACKGROUND

Subspine impingement (SSI) does not have effective diagnostic criteria, especially in patients who also have femoroacetabular impingement (FAI). The classification of anterior inferior iliac spine (AIIS) morphology via three-dimensional CT is controversial.

PURPOSE

To propose a method for ultrasound-guided AIIS injection as a way to diagnose SSI and evaluate the accuracy of radiography methods, including 3-D CT and MRI, as well as intraoperative findings.

METHODS

Patients diagnosed with FAI between September 2020 and December 2021 were evaluated in this prospective study. Those who met the criteria were included in the ultrasound-guided AIIS injection test. Whether the pain was relieved after injection was recorded in the radiology report. Patients who experienced significant relief of the anterior groin pain (more than 50%) after the AIIS injection were considered positive responders. Among these patients, radiography materials, including AIIS morphology as measured by 3-D CT as well as superior capsular oedema on MRI, were compared. The presence of congestion or bruising on the capsule side of the labrum corresponding to the AIIS during hip arthroscopy was recorded.

RESULTS

A total of 73 patients with FAI underwent the ultrasound-guided AIIS injection test. Prevalence rates of 13.70% (10/73), 58.90% (43/73), 23.29% (17/73) and 4.11% (3/73) were recorded for Type I, Type IIA, Type IIB and Type III AIISs, respectively. Thirty-six patients had positive responses to injection, and 37 patients had negative responses to injection. None of the patients with Type I, 23 (53.49%) patients with Type IIA, 11 (64.71%) patients with Type IIB and 2 (66.7%) patients with Type III AIISs had positive responses to the injection. A total of 57.14% of patients with Type II or Type III AIIS had positive responses to the injection. The proportions of patients with superior capsular oedema on MRI in the Type I, Type IIA, Type IIB, and Type III AIIS groups was 0, 30.23, 29.41 and 0%, respectively. Among non-Type I AIIS patients, those who reported positive responses to the injection had a higher incidence of superior capsular oedema (38.89% vs. 14.81%, P = 0.036), but they had no significant differences in the proportion of congestion or bruising of the labrum (47.22% vs. 37.04%, P = 0.419). The results showed that no pairs of methods-ultrasound-guided injection, MRI, and intraoperative findings-achieved good consistency (κ = 0.222, κ = 0.098 and κ = - 0.116).

CONCLUSIONS

Radiographic methods including 3-D CT and MRI as well as the intraoperative findings of the labrum cannot be considered an accurate and reliable basis for the diagnosis and treatment of SSI in FAI patients. It is suggested that ultrasound-guided AIIS injections be combined with radiography to better diagnose SSI.

LEVEL OF EVIDENCE

IV, case series.

The narrow subspine space and relatively large labrum are radiographic features of subspine impingement: a case-control study

Background

Subspine impingement is considered a source of residual hip symptoms after primary hip arthroscopy, and the role of the subspine space and soft tissue is not clear. The purpose of this study was to analyze the relationship between the subspine space and labrum size in subspine impingement patients.

Methods

We performed a retrospective study of patients with femoroacetabular impingement between July 2016 and July 2020. Sixteen patients without hip symptom relief after primary hip arthroscopic treatment of femoroacetabular impingement and undergoing revision surgery for anterior inferior iliac spine compression were included as the study group. Forty-eight matched patients who underwent only primary surgery and whose hip discomfort was relieved without a diagnosis of subspine impingement were included as the control group. The patients’ preoperative computerized tomography data were reviewed, and the anterior inferior iliac spine dimensions and the size of the subspine space were measured. The size of the labrum at the 11:30, 1:30, and 3 o’clock positions was measured with the use of magnetic resonance imaging. The ratio of the subspine space to the labrum was also calculated.

Results

There was no significant difference in anterior inferior iliac spine dimensions between these two groups (p > 0.05). A relatively narrow subspine space was found in the study group, especially in the direction of the anterior inferior iliac spine. Compared with the control group, subspine impingement patients were identified with larger labrums at 11:30 (8.20 ± 1.95 mm vs. 6.81 ± 0.50 mm, p = 0.016), 1:30 (7.83 ± 1.61 mm and 6.25 ± 0.78 mm, p = 0.001) and 3:00 (9.50 ± 1.73 mm vs. 7.48 ± 0.99 mm, p = 0.001). A relative mismatch between the subspine space and the labrum was also identified in the study group. The ratios of the labrum width to the subspine area were significantly larger in the study group than in the control group.

Conclusion

This study reported potential additional criteria for subspine impingement—a large labrum and a relatively narrow subspine space—instead of abnormal anterior inferior iliac spine dimensions. For those with a large labrum and narrow subspine space, the diagnosis of subspine impingement should be carefully made, and arthroscopic anterior inferior iliac spine decompression may be important.

Subspine Hypertrophy: Higher Incidence of Symptomatic versus Asymptomatic Hips in Patients with Unilateral Femoroacetabular Impingement

Objective

To compare the difference of anterior inferior iliac spine (AIIS) and subspine hypertrophic deformity between symptomatic and asymptomatic hips in patients traditionally diagnosed with femoroacetabular impingement (FAI), and investigate the correlation of subspine decompression with AIIS variation and subspine hypertrophic deformity.

Methods

We retrospectively reviewed 70 patients with unilateral symptomatic FAI who underwent hip arthroscopy. The operative hips and contralateral hips naturally formed the symptomatic groups and asymptomatic control groups, respectively. The morphometric comparison of the hip joint was performed between the operative and contralateral sides of each patient. Radiological assessment was performed by two observers (an experienced musculoskeletal radiologist and an experienced surgeon). Three‐dimensional (3D)‐CT images of each patient were blindly reviewed to determine the AIIS variation and subspine hypertrophic deformity. Reformatted two‐dimensional (2D)‐CT images and anterior–posterior (AP) pelvic plain radiographs were blindly reviewed to determine FAI‐related morphological measurements. Moreover, the surgical assessment was reviewed by one experienced surgeon to interpret whether subspine decompression was performed. The correlation of subspine decompression with AIIS variation and subspine hypertrophy was analyzed.

Results

Out of 70 patients with unilateral symptomatic FAI, 37 were males (52.9%) and 23 (32.9%) had symptoms involving the left hip. The mean age was 39.3 ± 10.4 years and the mean BMI was 24.3 ± 3.6. The distribution of AIIS variants in symptomatic hips did not differ significantly from that in asymptomatic hips (χ² = 3.092, P = 0.213). Twenty‐nine hips in the symptomatic group (41.4%) and 12 hips in the asymptomatic group (17.1%) were identified as positive for subspine hypertrophy. The incidence of positive subspine hypertrophy was significantly higher in the symptomatic hips compared to the asymptomatic hips (χ² = 9.968, P = 0.002). FAI‐related morphological parameters including α angle, lateral center‐edge angle, acetabular anteversion, crossover sign, and Tonnis grade were highly symmetrical and did not show significant differences between symptomatic and asymptomatic hips. Fifty‐four of 70 hips (77.1%) had labral tears extended to the acetabular rim corresponding to the AIIS. Forty‐seven hips of 70 hips (67.1%) underwent subspine decompression, which was significantly correlated with AIIS variation and subspine hypertrophic deformity (P = 0.019 and 0.001, respectively).

Conclusion

Subspine hypertrophic deformity was found to be more common in symptomatic side vs asymptomatic side in patients with unilateral symptomatic femoroacetabular impingement. Subspine hypertrophy may be considered as an underlying indication for subspine decompression besides low‐lying AIIS.

Prominent Anterior Inferior Iliac Spine Morphologies Are Common in Patients with Acetabular Dysplasia Undergoing Periacetabular Osteotomy

BACKGROUND

The anterior inferior iliac spine (AIIS) prominence is increasingly recognized in the setting of femoroacetabular impingement (FAI). The AIIS prominence may contribute to decreased hip flexion after acetabular reorientation in patients with acetabular dysplasia. AIIS morphologies have been characterized in numerous populations including asymptomatic, FAI, and athletic populations, but the morphology of the AIIS in patients with symptomatic acetabular dysplasia undergoing periacetabular osteotomy (PAO) has not been studied. In acetabular dysplasia, deficiency of the anterosuperior acetabular rim is commonly present and may result in the AIIS being positioned closer to the acetabular rim. Understanding morphological variation of the AIIS in patients with symptomatic dysplasia, and its relationship to dysplasia subtype and severity may aid preoperative planning, surgical technique, and evaluation of postoperative issues after PAO.

QUESTIONS/PURPOSES

In this study, we sought to determine: (1) the variability of AIIS morphology types in hips with symptomatic acetabular dysplasia and (2) whether the differences in the proportion of AIIS morphologies are present between dysplasia pattern and severity subtypes.

METHODS

Using our hip preservation database, we identified 153 hips (148 patients) who underwent PAO from October 2013 to July 2015. Inclusion criteria for the current study were (lateral center-edge angle [LCEA] < 20°), Tönnis Grade of 0 or 1 on plain AP radiographs of the pelvis, preoperative low-dose CT scan, and no prior surgery, trauma, neuromuscular, ischemic necrosis, or Perthes-like deformity. A total of 50 patients (50 hips) with symptomatic acetabular dysplasia undergoing evaluation for surgical planning of PAO remained for retrospective evaluation; we used these patients' low-dose CT scans for analysis. The median (range) age of patients in the study was 24 years (13 to 49). Ninety percent (45 of 50) of the hips were in female patients, whereas 10% (5 of 50) were in male patients. The morphology of the AIIS was classified on three-dimensional CT reconstructions according to a previously published classification to define the relationship between the AIIS and the acetabular rim. The morphology of the AIIS was classified as Type I (AIIS well proximal to acetabular rim), Type II (AIIS extending to level of acetabular rim), or Type III (AIIS extending distal to acetabular rim). Acetabular dysplasia subtype was characterized according to a prior protocol as either predominantly an anterosuperior acetabular deficiency, a posterosuperior acetabular deficiency, or a global acetabular deficiency. Acetabular dysplasia severity was distinguished as mild (LCEA 15° to 20°) or moderate/severe (LCEA < 15°). To answer our first question, regarding the proportions of each AIIS morphology in the dysplasia population, we calculated proportions and 95% CI estimates. To answer our second question, regarding the proposition of AIIS type between subtypes of dysplasia type and severity, we used a chi-square test or Fisher's exact test to compare categorical variables. A p value of < 0.05 was considered significant.

RESULTS

Seventy-two percent (36 of 50; 95% CI 58% to 83%) of patients had a Type II or III AIIS morphology. Type I AIIS morphology was found in 28% of patients (14 of 50; 95% CI 18% to 42%), Type II AIIS morphology in 62% (31 of 50; 95% CI 48% to 74%), and Type III AIIS/morphology in 10% (5 of 50; 95% CI 4% to 21%). A Type I AIIS was seen in seven of 15 of patients with anterosuperior acetabular deficiency, three of 18 of patients with global deficiency, and four of 17 patients with posterosuperior deficiency (p = 0.08). There was no difference in the variability of AIIS morphologies between the different subtypes of acetabular dysplasia pattern and no difference in AIIS morphology variability between patients with mild versus moderate/severe dysplasia.

CONCLUSIONS

The morphology of the AIIS in patients with acetabular dysplasia is commonly prominent, with 72% of hips having Type II or Type III morphologies.

CLINICAL RELEVANCE

The AIIS is often prominent in patients with acetabular dysplasia undergoing PAO, regardless of dysplasia pattern or severity. Prominent AIIS morphologies may affect hip flexion ROM after acetabular reorientation. AIIS morphology is a variable that should be considered during preoperative planning for PAO. Future studies are needed to assess the clinical significance of a prominent AIIS on intraoperative findings and postoperative status after PAO.

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.

Prevalence of Anterior Inferior Iliac Spine Dysmorphism and Development of a Novel Classification System: An Anatomic Study of 1,797 Cadaveric Specimens

Purpose: Subspine impingement occurs due to a morphologically abnormal anterior inferior iliac spine (AIIS), capable of causing impingement against the distal femoral neck. The purpose of this investigation was to determine the prevalence of AIIS dysmorphism based on specimen sex, race, and age, while introducing a novel anatomic-based classification system.

Methods: A total of 1,797 adult cadaveric specimens (n = 3,594 hemipelvises) were analyzed. AIIS with the potential for subspine impingement (SSI) was recorded in each specimen by two independent authors. Specimens with AIIS dysmorphism were then reexamined to determine SSI subtype using a novel descriptive anatomic classification system.

Results: AIIS dysmorphism was present in 6.4% (n = 115 of 1,797 specimens) of specimens and 5.2% (n = 186 of 3,594) of hemipelvises. Dysmorphism was significantly more common in male specimens (p = 0.04) and African–American specimens (p = 0.04). No significant overall difference in prevalence was appreciated based on specimen age (p = 0.89). Subtype classification found that 67% of hemipelvises possessed a columnar type AIIS, 30% were bulbous and 3% hook type. Males possessed a significantly higher prevalence of columnar type AIIS dysmorphism (p < 0.001). No significant overall differences in anatomic classification were appreciated based on race (p = 0.12) or when analyzed based on age (p = 0.34).

Conclusion: AIIS dysmorphism was present in 6.4% of the 1,797 cadaveric specimens evaluated. African-American and male specimens possessed significantly higher prevalence of AIIS dysmorphism, with no significant difference based on specimen age. Columnar type AIIS dysmorphism was most common. Anatomic classification was not significantly different based on specimen race or age.

Level of Evidence: Case Series, Level IV.

Functional Results of Arthroscopic Treatment in Patients With Femoroacetabular and Subspine Impingement Diagnosed With a 3-Dimensional Dynamic Study

Purpose

To describe the functional results of arthroscopic treatment in patients with femoroacetabular impingement (FAI) and subspine impingement (SSI) evaluated with a 3-dimensional (3D) dynamic study.

Methods

This was a retrospective observational study of patients with a diagnosis of FAI and SSI, evaluated with a 3D dynamic computed tomography scan with Move Forward software, who underwent hip arthroscopy between February 2015 and December 2017. Measurements of the alpha angle, femoral anteversion, acetabular anteversion, lateral center-edge angle, and Tönnis angle were extracted from the 3D dynamic study. Functionality was evaluated using the Western Ontario McMaster Universities Osteoarthritis Index before and 12 months after surgery.

Results

We analyzed 22 hips in 17 patients (9 female and 8 male patients) with an average age of 34.6 ± 14.3 years. Of the 22 hips, 15 had cam morphology, 6 had mixed morphology, and 1 had pincer morphology. Of the hips, 11 had a type I spine, 10 had type II, and 1 had type III. The average alpha angle, Tönnis angle, femoral anteversion, and acetabular anteversion were 61.9° ± 11.1°, 2.5° ± 6.4°, 8.8° ± 6.8°, and 15.1° ± 7.1°, respectively. The median lateral center-edge angle was 38.1° (interquartile range, 32.6°-43.5°). At 1-year follow-up, a decrease in the Western Ontario McMaster Universities Osteoarthritis Index score (P = .001) and an increase in the flexion angle (P < .001) were observed. No cases needed posterior surgical revision because of persistent pain.

Conclusions

Arthroscopic treatment provides symptom relief and good functional results in patients with FAI and SSI.

Level of Evidence

Level IV, therapeutic case series.

MRI Assessment of Subspine Impingement: Features beyond the Anterior Inferior Iliac Spine Morphology

Background The MRI manifestations of subspine impingement (SSI) other than morphologic features of anterior inferior iliac spine (AIIS) have not been extensively explored and validated. Purpose To determine the MRI findings associated with SSI, including AIIS morphologic features, femoral distal cam, and associated soft-tissue injuries. Materials and Methods This is a retrospective study of symptomatic patients who underwent arthroscopic treatment for femoroacetabular impingement between December 2014 and March 2017, with preoperative MRI within 6 months before surgery. The SSI group included patients with clinical and intraoperative findings of SSI; the remaining patients comprised the non-SSI group. Preoperative MRI findings were independently assessed by two radiologists who were blinded to clinical information. Interreader agreement was assessed, and multivariable logistic regression was also used. Results A total of 62 patients (mean age ± standard deviation, 42.1 years ± 11.9; 38 women) were included. SSI was diagnosed in 20 of the 62 patients (32%) (mean age, 43 years ± 12); 42 patients (68%) did not have SSI (mean age, 41 years ± 10). Reader 1 detected distal cam in 16 of the 20 patients with SSI (80%) and eight of the 42 patients without SSI (19%), and reader 2 detected distal cam in 15 of the 20 patients with SSI (75%) and eight of the 42 patients without SSI (19%) (P < .001 for both). Reader 1 detected signs of impingement on the distal femoral neck (IDFN) in 18 of the 20 patients with SSI (90%) and seven of the 42 patients without SSI (16%), and reader 2 detected signs of IDFN in 13 of the 20 patients with SSI (65%) and nine of the 42 patients without SSI (21%) (P < .001 and P = .001, respectively). Reader 1 detected superior capsular edema in 15 of 20 patients with SSI (75%) and three of 42 patients without SSI (7%), and reader 2 detected superior capsular edema in 17 of 20 patients with SSI (85%) and 22 of 42 patients without SSI (52%) (P < .001 and P = .02, respectively). Distal cam was a predictor of SSI after adjustment for IDFN. Interreader agreement was substantial for distal cam (κ = 0.80) and moderate for IDFN (κ = 0.50). Conclusion Soft-tissue injuries and osseous findings other than morphologic features of the anterior inferior iliac spine were associated with subspine impingement. © RSNA, 2019 See also the editorial by Guermazi in this issue.

The prevalence of a prominent anterior inferior iliac spine

INTRODUCTION

Impingement of the prominent anterior inferior iliac spine (AIIS) against the femoral neck has recently been described as another type of impingement. The purpose of this study is to provide a distribution of AIIS types using the classification proposed by Hetsroni and thus report on the prevalence of prominent types.

MATERIALS AND METHODS

A total of 400 patients were included in the study with an average age 27.3 ± 6.9 years (range 18-40). All patients received a whole-body polytrauma computer tomography (CT) scan in the emergency room (ER) upon arrival. The classification of AIIS proposed by Hetsroni et al., which describes three morphological types, was used. Type II and III were grouped as prominent types. The measurements were performed in all three planes by two examiners.

RESULTS

Male to female ratio was 71:29. Type I was observed in 367 (91.7%) patients. Type II was observed in 31 (7.8%) patients and type III was observed in 2 (0.5%) patients, unilaterally. Prominent types were much more prevalent in men (10.5%) than in women (2.6%). The CT assessment demonstrated excellent intra- and interreliability (overall: 0.926, I/II: 0.906, III: 1.000).

CONCLUSION

A young population demonstrates a prevalence of a prominent AIIS of 11.5%. Prominent AIIS is more common in men than in women.