Do normal radiographs exclude asphericity of the femoral head-neck junction?

Imaging of femoroacetabular impingement-current concepts

Following the recognition of femoroacetabular impingement (FAI) as a clinical entity, diagnostic tools have continuously evolved. While the diagnosis of FAI is primarily made based on the patients' history and clinical examination, imaging of FAI is indispensable. Routine diagnostic work-up consists of a set of plain radiographs, magnetic resonance imaging (MRI) and MR-arthrography. Recent advances in MRI technology include biochemically sensitive sequences bearing the potential to detect degenerative changes of the hip joint at an early stage prior to their appearance on conventional imaging modalities. Computed tomography may serve as an adjunct. Advantages of CT include superior bone to soft tissue contrast, making CT applicable for image-guiding software tools that allow evaluation of the underlying dynamic mechanisms causing FAI. This article provides a summary of current concepts of imaging in FAI and a review of the literature on recent advances, and their application to clinical practice.

Ultrasound is as reliable as plain radiographs in the diagnosis of cam-type femoroacetabular impingement

INTRODUCTION

In the diagnosis of femoroacetabular impingement (FAI), plain radiographs are accepted as the initial imaging method. However, there is no consensus regarding the optimal lateral view, and radiographs can underestimate the asphericity of the head-neck junction. Our research question was if ultrasound has at least the same reliability as X-ray and can be used as an alternative or additional method in the initial imaging of FAI.

MATERIALS AND METHODS

Forty patients with a median age of 39 years were consecutively included after diagnosis of cam-type FAI on magnetic resonance imaging (MRI). All patients underwent radiography involving a plain anteroposterior-view, frog-leg lateral view, and ultrasound of the hip joint in the ventral longitudinal section at 20° internal rotation. Parameters measured by MRI, radiographs, and ultrasound were the alpha angle, anterior offset, offset ratio, and anterior femoral distance.

RESULTS

No significant difference between the alpha angle on MRI (64.8°), the frog-leg view (66.3°), or ultrasound (65.6°) could be detected. Comparable correlation was found between the alpha angle on MRI and the frog-leg lateral view (r = 0.73; p < 0.0001) and between the alpha angle on MRI and sonograms (r = 0.77; p < 0.0001). The intra-class correlation coefficient for measurements using ultrasound was 0.81-0.98, and using radiographs was 0.83-0.99, with the exception of measurements involving the anterior offset on the frog-leg lateral view (0.61 and 0.64).

CONCLUSIONS

Ultrasound is as reliable as plain radiographs in the diagnosis of cam-type FAI and can serve as an alternative or additional method in initial imaging.

Prevalence of cam hip shape morphology: a systematic review

OBJECTIVE

Cam hip shape morphology is a recognised cause of femoroacetabular impingement (FAI) and is associated with hip osteoarthritis. Our aim was to systematically review the available epidemiological evidence assessing the prevalence of cam hip shape morphology in the general population and any studied subgroups including subjects with and without hip pain.

DESIGN

All studies that reported the prevalence of cam morphology, measured by alpha angles, in subjects aged 18 and over, irrespective of study population or presence of hip symptoms were considered for inclusion. We searched AMED, MEDLINE, EMBASE, CINAHL and CENTRAL in October 2015. Two authors independently identified eligible studies and assessed risk of bias. We planned to pool data of studies considered clinically homogenous.

RESULTS

Thirty studies met inclusion criteria. None of the included studies were truly population-based: three included non-representative subgroups of the general population, 19 included differing clinical populations, while eight included professional athletes. All studies were judged to be at high risk of bias. Due to substantial clinical heterogeneity meta analysis was not possible. Across all studies, the prevalence estimates of cam morphology ranged from 5 to 75% of participants affected. We were unable to demonstrate a higher prevalence in selected subgroups such as athletes or those with hip pain.

CONCLUSIONS

There is currently insufficient high quality data to determine the true prevalence of cam morphology in the general population or selected subgroups. Well-designed population-based epidemiological studies that use homogenous case definitions are required to determine the prevalence of cam morphology and its relationship to hip pain.

The 2015 Frank Stinchfield Award: Radiographic Abnormalities Common in Senior Athletes With Well-functioning Hips but Not Associated With Osteoarthritis

BACKGROUND

It is not known whether morphological abnormalities of the hip are compatible with lifelong hip function and avoidance of osteoarthritis (OA). Our purpose was to investigate the prevalence of radiographic findings consistent with femoroacetabular impingement (FAI) and dysplasia (DDH) in senior athletes with well-functioning hips.

QUESTIONS/PURPOSES

(1) What is the prevalence of FAI and DDH in senior athletes with well-functioning hips? (2) Are radiographic findings of FAI and DDH associated with OA? (3) Is a history of longer duration or more intense activity associated with hip pathomorphology? (4) Were the modified Harris hip scores and the Hip Outcome Scores lower (legacy scales) in patients with evidence of hip pathomorphology than those without?

METHODS

Five hundred forty-seven individuals (55% men, 45% women; 1081 hips, 534 bilateral and 13 unilateral), mean age 67 years (SD 8 years), gave consent and qualified for this institutional review board-approved cross-sectional study of senior athletes. Hips were independently evaluated for radiographic signs of FAI, DDH, and OA. Additionally, a lifetime activities questionnaire and outcome instruments were used to assess pain and function. Hips that had previously undergone arthroplasty or fracture surgery were excluded.

RESULTS

Eighty-three percent (898 of 1081) of hips had radiographic abnormalities consistent with FAI, of which 67% (599 of 898) were cam-type FAI. Ten percent (103 of 1081) of hips had radiographic evidence for dysplasia. Radiographic findings of FAI were not predictive of OA after controlling for age and sex (odds ratio [OR], 1.79; 95% confidence interval [CI], 0.48-6.62; p = 0.390). Similarly, radiographic findings of DDH were not predictive of OA (OR, 1.48; 95% CI, 0.31-7.21; p = 0.62). Our data suggest an increased risk of FAI-type morphologies in athletes who participated in competitive sporting events during early adult years (OR, 1.49; 95% CI, 1.04-2.11; p = 0.020). Additionally, participants who reported lifetime participation in competitive sports were at an increased risk of OA compared with those who did not (OR, 1.75; 95% CI, 1.14-2.69; p = 0.007). There were no differences in outcome scores between athletes with and without morphologic abnormalities.

CONCLUSIONS

Radiographic findings consistent with FAI in these senior athletes were common and were not associated with the presence of OA. These data suggest that the need to screen for asymptomatic young athletes for radiographic evidence of FAI and DDH may not be necessary.

LEVEL OF EVIDENCE

Level III, prognostic study.

Open-MRI measures of cam intrusion for hips in an anterior impingement position relate to acetabular contact force

Open MRI in functional positions has potential to directly and non-invasively assess cam femoroacetabular impingement (FAI). Our objective was to investigate whether open MRI can depict intrusion of the cam deformity into the intra-articular joint space, and whether intrusion is associated with elevated acetabular contact force. Cadaver hips (9 cam; 3 controls) were positioned in an anterior impingement posture and imaged using open MRI with multi-planar reformatting. The β-angle (describing clearance between the femoral neck and acetabulum) was measured around the entire circumference of the femoral neck. We defined a binary "MRI cam-intrusion sign" (positive if β < 0°). We then instrumented each hip with a piezoresistive sensor and conducted six repeated positioning trials, measuring acetabular contact force (F). We defined a binary "contact-force sign" (positive if F > 20N). Cam hips were more likely than controls to have both a positive MRI cam-intrusion sign (p = 0.0182, Fisher's exact test) and positive contact-force sign (p = 0.0083), which represents direct experimental evidence for cam intrusion. There was also a relationship between the MRI cam-intrusion sign and contact-force sign (p = 0.033), representing a link between imaging and mechanics. Our findings indicate that open MRI has significant potential for in vivo investigation of the cam FAI mechanism.

Prevalence of Cam Morphology in Females with Femoroacetabular Impingement

Cam and pincer are two common morphologies responsible for femoroacetabular impingement (FAI). Previous literature has reported that cam deformity is predominantly a male morphology, while being significantly less common in females. Cam morphology is commonly assessed with the alpha angle, measured on radiographs. The purpose of this study is to determine the prevalence of cam morphology utilizing the alpha angle in female subjects diagnosed with symptomatic FAI. All females presenting to the senior author’s clinic diagnosed with symptomatic FAI between December 2006 and January 2013 were retrospectively reviewed. Alpha (α) angles were measured on anteroposterior and lateral (Dunn 90°, cross-table lateral, and/or frog-leg lateral) plain radiographs by two blinded physicians, and the largest measured angle was used. Using Gosvig et al.’s classification, alpha angle was characterized as (pathologic > 57°), borderline (51–56°), subtle (46–50°), very subtle (43–45°), or normal (≤42°). Three hundred and ninety-one patients (438 hips) were analyzed (age 36.2 ± 12.3 years). Among the hips included, 35.6% were normal, 14.6% pathologic, 15.1% borderline, 14.6% subtle, and 20.1% very subtle. There was no correlation between alpha angle and patient age (R = 0.17) or body mass index (R = 0.05). The intraclass correlation coefficient for α-angle measurements was 0.84. Sixty-four percent of females in this cohort had an alpha angle >42°. Subtle cam deformity plays a significant role in the pathoanatomy of female patients with symptomatic FAI. As the majority of revision hip arthroscopies are performed due to incomplete cam correction, hip arthroscopists need to be cognizant of and potentially surgically address these subtle lesions.

What Is the Association Between Sports Participation and the Development of Proximal Femoral Cam Deformity? A Systematic Review and Meta-analysis

BACKGROUND

Femoroacetabular impingement (FAI) is recognized as a common cause of hip pain and intra-articular disorders in athletes. Studies have suggested a link between participation in athletics during adolescence and the development of cam-type deformities of the proximal femoral head-neck junction.

PURPOSE

To investigate the association of sporting activity participation during adolescence and the development of cam deformity.

STUDY DESIGN

Systematic review.

METHODS

The PubMed, EMBASE, and Cochrane databases were searched to identify potential studies. Abstracts and manuscripts (when applicable) were independently reviewed by 2 reviewers. Nine studies met the inclusion criteria, including 8 studies that compared the prevalence of cam deformity in athletes with that in controls and 3 studies that compared the prevalence of cam deformity before and after physeal closure (2 with both). A meta-analysis was performed with pooling of data and random-effects modeling to compare rates of cam deformity between athletes and controls.

RESULTS

High-level male athletes are 1.9 to 8.0 times more likely to develop a cam deformity than are male controls. The pooled prevalence rate (by hip) of cam deformity in male athletes was 41%, compared with 17% for male controls. The pooled mean alpha angle among male athletes was 61°, compared with 51° for male controls.

CONCLUSION

Males participating in specific high-level impact sports (hockey, basketball, and possibly soccer) are at an increased risk of physeal abnormalities of the anterosuperior head-neck junction that result in a cam deformity at skeletal maturity.

The False-Profile View May Be Used to Identify Cam Morphology

PURPOSE

To identify the accuracy of measuring the alpha angle on the false-profile, anteroposterior (AP), and 90° Dunn lateral views of the hip as compared with computed tomography (CT) scan findings.

METHODS

Forty patients were needed to have power greater than 80%. Forty-five consecutive patients undergoing hip arthroscopy were retrospectively reviewed with preoperative radial oblique CT reformatted scans and plain radiographs. Alpha angles were measured on plain radiographs (AP, 90° Dunn lateral, and false profile) and CT reformatted views. Abnormal alpha angles were considered greater than 50.5°. Two orthopaedic surgeons independently measured the images, and the results were compared between imaging modalities.

RESULTS

The false-profile view was 60% sensitive and 89.0% specific for diagnosing cam deformities of the hip. All radiographs combined were 86% sensitive and 75% specific for diagnosing cam deformities. The false-profile view most strongly correlated with the 2-o'clock (R = 0.746, P = .001) and 3-o'clock (R = 0.698, P < .0001) positions. An intraclass correlation coefficient of 0.81 was found for measurement of the alpha angle on the false-profile view.

CONCLUSIONS

This study has proved that the false-profile view effectively characterizes cam deformity, especially anterior deformity at the 3-o'clock position. Measuring the alpha angle on the false-profile view appears to be reproducible. The false-profile view along with standing AP pelvis and 90° Dunn lateral views of the hip comprises a good screening radiographic series for patients presenting with symptoms of femoroacetabular impingement.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Relationship between the alpha and beta angles in diagnosing CAM-type femoroacetabular impingement on frog-leg lateral radiographs

PURPOSE

Alpha and beta angles are commonly used radiographic measures to assess the sphericity of the proximal femur and distance between the pathologic head-neck junction and the acetabular rim, respectively. The aim of this study was to explore the relationship between these two measurements on frog-leg lateral hip radiographs.

METHODS

Fifty frog-leg lateral hip radiographs were evaluated by two orthopaedic surgeons and two radiologists. Each reviewer measured the alpha and beta angles on two separate occasions to determine the relationship between positive alpha and beta angles and the inter- and intra-observer reliability of these measurements.

RESULTS

There was no significant association between positive alpha and beta angles, [kappa range -0.043 (95 % CI -0.17 to 0.086) to 0.54 (95 % CI 0.33-0.75)]. Intra-observer reliability was high [alpha angle intra-class correlation coefficient (ICC) range 0.74 (95 % CI 0.58-0.84) to 0.99 (95 % CI 0.98-0.99) and beta angle ICC range 0.86 (95 % CI 0.76-0.92) to 0.97 (95 % CI 0.95-0.98)].

CONCLUSIONS

There is no statistical or functional relationship between readings of positive alpha and beta angles. The radiographic measurements resulted in high intra-observer and fair-to-moderate inter-observer reliability. Results of this study suggest that the presence of a CAM lesion on lateral radiographs as suggested by a positive alpha angle does not necessitate a decrease in clearance between the femoral head and acetabular rim as measured by the beta angle and thus may not be the best measure of functional impingement. Understanding the relationship between these two aspects of femoroacetabular impingement improves a surgeon's ability to anticipate potential operative management.

The Antiquity of the Cam Deformity: A Comparison of Proximal Femoral Morphology Between Early and Modern Humans

BACKGROUND

The precise etiology of cam impingement continues to be incompletely understood. The prevailing hypothesis posits that the deformity arises as a developmental injury prior to skeletal maturation. There is a possible evolutionary role, with an aspherical femoral head affording upright humans better stability. We set out to identify the antiquity of the cam deformity to better understand the comparative roles of modern behavior and evolution in its development.

METHODS

We used 249 physical specimens of femora from the Libben osteological collection, a set of bones from an ancient population who lived between the eighth and the eleventh century. These femora were photographed in four different orientations, and six specific proximal femoral angles were measured. The values were also compared with those from modern human femora using the Student t test, with a two-tailed p value of 0.05 denoting significance.

RESULTS

In total, 249 femora from 175 individuals were included in the final analysis. The ages of the individuals ranged between seventeen and fifty-five years. Interobserver and intraobserver correlation was good or excellent for all variables measured. Compared with modern populations, ancient human hips were significantly more anteverted (19.96° versus 12.85°; p < 0.001) and varus (true neck-shaft angle, 121.96° versus 129.23°; p < 0.001). The alpha angle was significantly lower in ancient humans (35.33° versus 45.61°; p < 0.001), and none of the ancient femora met the modern criteria for a cam deformity (an alpha angle of >50°).

CONCLUSIONS AND CLINICAL RELEVANCE

It appears that the cam deformity was nonexistent among ancient humans and is perhaps predominantly a product of modern-day stresses. Further clinical investigation into behavioral modifications in adolescence is warranted to potentially prevent the development of deformity and impingement.

Subradiological cam deformity of the head-neck junction: an occult cause of hip pain and chondrolabral damage

PURPOSE

The goal of this study was to determine how frequently the conventionally defined "idiopathic" chondrolabral hip injuries are associated with subradiological cam deformities of the head-neck junction and whether a protective femoral osteochondroplasty may improve the outcome of their arthroscopic treatment.

METHODS

All the non-arthritic or pre-arthritic painful hips diagnosed as having a primary chondrolabral injury were retrospectively evaluated. Coxometric data, clinical history and physical findings were reviewed to rule out any possible secondary lesion. The medical records of the selected cases were analyzed as for imaging features, surgical findings and post-arthroscopy outcome.

RESULTS

Three cases out of 79 chondrolabral injuries were identified as "primary" on the basis of the preoperative assessment. All the three patients were female in their fourth decade and showed a joint damage consistent with undetected cam FAI (cartilage delamination in the anterolateral acetabular quadrant, minor pathology of the adjacent labrum with or without chondrolabral separation, abrasion signs and herniation pits along the anterolateral head-neck junction). The first patient received a simple chondrolabral treatment whose benefits deteriorated few months after surgery; the second patient underwent chondrolabral repair and femoral osteochondroplasty and is still pain-free; and the third patient had a beneficial revision arthroscopy for femoral osteochondroplasty after prior unsuccessful chondrolabral surgery.

CONCLUSIONS

If a chondrolabral injury of the hip is associated with MR arthrographic and arthroscopic indirect signs of cam FAI, a subradiological head-neck deformity should be considered despite normal alpha angles. In such cases, a protective femoral osteochondroplasty may increase the success rate of the chondrolabral repair.

LEVEL OF EVIDENCE

IV.

Validation of a standardized mapping system of the hip joint for radial MRA sequencing

OBJECTIVE

Intraarticular gadolinium-enhanced magnetic resonance arthrography (MRA) is commonly applied to characterize morphological disorders of the hip. However, the reproducibility of retrieving anatomic landmarks on MRA scans and their correlation with intraarticular pathologies is unknown. A precise mapping system for the exact localization of hip pathomorphologies with radial MRA sequences is lacking. Therefore, the purpose of the study was the establishment and validation of a reproducible mapping system for radial sequences of hip MRA.

MATERIALS AND METHODS

Sixty-nine consecutive intraarticular gadolinium-enhanced hip MRAs were evaluated. Radial sequencing consisted of 14 cuts orientated along the axis of the femoral neck. Three orthopedic surgeons read the radial sequences independently. Each MRI was read twice with a minimum interval of 7 days from the first reading. The intra- and inter-observer reliability of the mapping procedure was determined.

RESULTS

A clockwise system for hip MRA was established. The teardrop figure served to determine the 6 o'clock position of the acetabulum; the center of the greater trochanter served to determine the 12 o'clock position of the femoral head-neck junction. The intra- and inter-observer ICCs to retrieve the correct 6/12 o'clock positions were 0.906-0.996 and 0.978-0.988, respectively.

CONCLUSIONS

The established mapping system for radial sequences of hip joint MRA is reproducible and easy to perform.

Ultrasonography can quantify the extent of osteochondroplasty after treatment of Cam-type femoroacetabular impingement

PURPOSE

Surgical resection of femoroacetabular Cam impingement (cam-FAI) is now a generally accepted treatment, producing adequate hip score increases. Insufficient resection at the head-neck junction is the main reason for revision. The anterolateral region of the head-neck junction is visualized only suboptimally by radiography, which can be inadequate for monitoring resection results postoperatively. Our aim was to investigate the extent of Cam resection by ultrasonography (US) and determine if there is any correlation with clinical outcome.

METHODS

Altogether, 40 consecutive patients (mean age 39 years) were enrolled in this prospective study following arthroscopic Cam resection. All patients underwent standardized US examination in the ventral longitudinal section at 20° external rotation, neutral position, and 20° internal rotation the day before arthroscopy and two days afterward. Alpha angle, anterior offset, offset ratio, and anterior femoral distance were measured on sonograms. Hip Disability and Osteoarthritis Outcome Score (HOOS) and Western Ontario and McMaster University Index of Osteoarthritis (WOMAC) were conducted the day before surgery and 6 weeks postoperatively (at the earliest).

RESULTS

Alpha angle was significantly smaller on postoperative US in all hip joint positions. At 20° internal rotation, the alpha angle decreased from 65.6 to 36.9° (p < 0.0001). All but two (5%) patients had alpha angles <50°. Anterior offset increased significantly on US in neutral position and at 20° internal rotation. HOOS and WOMAC increased significantly. No correlation was found between measurements for Cam-FAI and the scores.

CONCLUSIONS

US may be a useful tool for monitoring Cam-FAI resection results postoperatively.

Cam-type deformities: Concepts, criteria, and multidetector CT features

Interpreting imaging studies of a painful hip requires detailed knowledge of the regional anatomy. Some variants of the proximal femur, such as cam-type deformities, can course asymptomatically or cause femoroacetabular impingement. The principal numerical criterion for defining cam-type deformities, the alpha angle, has some limitations. In this article, we review the anatomic variants of the anterior aspect of the proximal femur, focusing on cam-type deformities. Using diagrams and multidetector CT images, we describe the parameters that are useful for characterizing these deformities in different imaging techniques. We also discuss the potential correspondence of imaging findings of cam-type deformities with the terms coined by anatomists and anthropologists to describe these phenomena.

Femoral Neck Stress Fractures and Imaging Features of Femoroacetabular Impingement

BACKGROUND

Prior literature has suggested an association between the radiographic signs of femoroacetabular impingement (FAI) and femoral neck stress fractures (FNSF) or femoral neck stress reactions (FNSR). At the time of the writing of this article, no study has described the association of FAI and FNSF/FNSR along with the need for surgical intervention and outcomes.

OBJECTIVE

To determine the prevalence of radiographic features of FAI in patients diagnosed with FNSF.

DESIGN

Retrospective case series.

SETTING

Tertiary care, institutional setting.

PATIENTS

A medical records search program (Stanford Translational Research Integrated Database Environment, Stanford University, California) was used to retrospectively search for patients 18-40 years old with a history of FNSF or FNSR. The records were obtained from the period July 25, 2003, to September 23, 2011.

METHODS

For assessment of risk factors, plain radiographs and magnetic resonance imaging studies were reviewed for features of cam or pincer FAI. Medical records were reviewed to determine whether patients required operative intervention.

MAIN OUTCOME MEASURES

Incidence of abnormal alpha (α) angle, abnormal anterior offset ratio, abnormal femoral head-neck junction, coxa profunda, positive crossover sign, and abnormal lateral center-to-edge angle.

RESULTS

Twenty-one female and 3 male participants (mean age 27 years, range 19-39 years) were identified with magnetic resonance imaging evidence of femoral neck stress injury. Cam morphology was seen in 10 patients (42%). Pincer morphology could be assessed in 18 patients, with coxa profunda in 14 (78%) and acetabular retroversion in 6 (14%). Features of combined pincer and cam impingement were observed in 4 patients (17%). Seven patients (29%) had operative intervention, with 3 (12%) requiring internal fixation of their femoral neck fractures, and all had radiographic evidence of fracture union after surgery. Four patients (17%) had persistent symptoms after healing of their FNSF with conservative treatment and eventually required surgery for FAI, 3 had no pain at final follow-up 1 year post-surgery, and one patient was lost to follow-up.

CONCLUSION

The results of the current study suggest that patients in the general population with femoral neck stress injuries have a higher incidence of bony abnormalities associated with pincer impingement, including coxa profunda and acetabular retroversion, although it is unclear whether pincer FAI is a true risk factor in the development of FNSF.

Clinical presentation and disease characteristics of femoroacetabular impingement are sex-dependent

BACKGROUND

Cam-type femoroacetabular impingement (FAI) is generally described as being more common in males, with pincer-type FAI being more common in females. The purpose of this study was to determine the effect of sex on FAI subtype, clinical presentation, radiographic findings, and intraoperative findings in patients with symptomatic FAI.

METHODS

We compared cohorts of fifty consecutive male and fifty consecutive female patients who were undergoing surgery for symptomatic FAI. Detailed information regarding clinical presentation, radiographic findings, and intraoperative pathology was recorded prospectively and analyzed. FAI subtype was classified on the basis of clinical diagnosis and radiographic evaluation.

RESULTS

Female patients had significantly greater disability at presentation, as measured with use of the modified Harris hip score (mHHS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Hip Disability and Osteoarthritis Outcome Score (HOOS), and the SF-12 (12-Item Short Form Health Survey) physical function subscore (all p ≤ 0.02), despite a significantly lower UCLA (University of California at Los Angeles) activity score (p = 0.03). Female patients had greater hip motion (flexion and internal rotation and external rotation in 90° of flexion; all p ≤ 0.003) and less severe cam-type morphologies (a mean maximum alpha angle of 57.6° compared with 70.8° for males; p < 0.001). Males were significantly more likely to have advanced acetabular cartilage lesions (56% of males compared with 24% of females; p = 0.001) and larger labral tears with more posterior extension of these abnormalities (p < 0.02). Males were more likely than females to have mixed-type FAI and thus a component of pincer-type FAI (combined-type FAI) (62% of males compared with 32% of females; p = 0.003).

CONCLUSIONS

We found distinct, sex-dependent disease patterns in patients with symptomatic FAI. Females had more profound symptomatology and milder morphologic abnormalities, while males had a higher activity level, larger morphologic abnormalities, more common combined-type FAI morphologies, and more extensive intra-articular disease.

LEVEL OF EVIDENCE

Prognostic Level I. See Instructions for Authors for a complete description of levels of evidence.

MRI of the hip for the evaluation of femoroacetabular impingement; past, present, and future

The concept of femoroacetabular impingement (FAI) has, in a relatively short time, come to the forefront of orthopedic imaging. In just a few short years MRI findings that were in the past ascribed to degenerative change, normal variation, or other pathologies must now be described and included in radiology reports, as they have been shown, or are suspected to be related to, FAI. Crucial questions have come up in this time, including: what is the relationship of bony morphology to subsequent cartilage and labral damage, and most importantly, how is this morphology related to the development of osteoarthritis? In this review, we attempt to place a historical perspective on the controversy, provide guidelines for interpretation of MRI examinations of patients with suspected FAI, and offer a glimpse into the future of MRI of this complex condition.

Comparative study of the femoroacetabular impingement (FAI) prevalence in male semiprofessional and amateur soccer players

INTRODUCTION

Femoroacetabular impingement (FAI) represents a novel approach to the mechanical etiology of hip osteoarthritis. The cam-type femoroacetabular impingement deformity occurs frequently in young male athletes. The aim of our study was to evaluate the prevalence of FAI in male semiprofessional soccer players using clinical examination and magnetic resonance imaging (MRI), compared to amateur soccer players. In MRI, the α angle of Nötzli is determined for quantifying FAI.

MATERIALS AND METHODS

According to power analysis, a total of 22 asymptomatic semiprofessional soccer players with a median of 23.3 years of age (range 18-30 years) and 22 male amateur soccer players with a median of 22.5 years of age (control group, range 18-29 years) underwent an MRI to measure the hip α angle of Nötzli. The α angle of the kicking legs of the semiprofessional group and the amateur group were analyzed. The study group was moreover evaluated by the Hip Outcome Score (HOS) and a clinical hip examination including range of motion (ROM) and impingement tests.

RESULTS

In the semiprofessional group, 19 soccer players had a right kicking leg and 1 soccer player had a left kicking leg. 2 soccer players kicked with two feet. In the semi-professional group, the mean value of the α angle of the kicking leg (57.3 ± 8.2°) was significantly higher than in the amateur group (51.7 ± 4.8°, P = 0.008). In the semi-professional group, 15 (62.5 %) of 24 kicking legs had an increased α angle >55°, while 5 (27.3 %) kicking legs of the amateur group had an α angle >55°. Five semi professional soccer players had findings in clinical examination, whereof 4 had an increased α angle >55°. No participant of the amateur group showed pathological results in the clinical examination (P = 0.0484). Overall, semiprofessional soccer players had a higher proportion of an increased α angle than the amateur group.

CONCLUSIONS

Semiprofessional players have a higher prevalence of an increased α angle in the kicking leg than the amateur group at the same age. The kicking leg is predisposed for FAI.

Reliability of a new hip lateral view to quantify alpha angle in femoroacetabular impingement

BACKGROUND

Radiographic measurement of the alpha angle (AA) in femoroacetabular impingement (FAI) is not well codified and invasive techniques such as MR- or CT-arthrography remain the gold standard. Excessive acetabular coverage described in pincer-type FAI can be seen on plain radiographs but has never been quantified and anterior center edge (ACE) angle, described on the false-profile view (FP) to measure anterior acetabular coverage has never been evaluated in FAI.

HYPOTHESIS

In this study we wanted to determine if a plain radiograph could efficiently measure AA compared to CT-arthrography and if ACE could quantify the acetabular coverage in FAI.

MATERIALS AND METHODS

We developed a hip view combining a lateral view and a FP, called profile view in impingement position (PIP). Twenty-six patients operated for FAI had CT-arthrography, PIP and FP. Nineteen control subjects had the PIP. AA were measured twice by three raters and ACE once. We compared AA measured on patients between CT and PIP, on PIP between patients and controls, ACE measured on patients between PIP and FP, and did a reproducibility analysis. Means were compared by paired or unpaired t-tests; reproducibility was measured by intraclass correlation coefficient (ICC).

RESULTS

Mean AA was 65.8° (range, 48-85°) on CT-arthrography and 63.9° (range, 50-87°) on PIP (P>0.05). ICC for PIP measures were 0.8-0.9 for intra-rater and 0.6-0.9 for inter-rater reliability. Mean AA on PIP in patients was 63.3° (range, 52-87°) and 44.9° (range, 34-67°) in controls (P<0.001). Mean ACE was 26.8° (range, 14-41°) on PIP and 32.8° (range, 18-56°) on the FP (P=0.015).

DISCUSSION

The PIP is a reliable view to measure the AA in FAI as measures on PIP and CT-arthrography were not significantly different with a good reproducibility. All of the painful hips and 2 controls had an AA>50°. PIP was not efficient to measure ACE.

LEVEL OF EVIDENCE

Level III, case-control study.

Radiographic findings of femoroacetabular impingement in capoeira players

PURPOSE

Capoeira is a Brazilian martial art that requires extreme movements of the hip to perform jumps and kicks. This study evaluated a group of capoeira players to assess the prevalence of femoroacetabular impingement (FAI) in athletes practicing this martial art.

METHODS

Twenty-four experienced capoeira players (14 men, 10 women) underwent a diagnostic assessment, including clinical examination and standard radiographs of the pelvis and hips. The α-angle, head-neck offset, crossover sign, acetabular index, lateral centre-edge angle, and the Tönnis grade were assessed using the radiographs. Clinical relationships for any radiographic abnormalities indicating FAI were also evaluated.

RESULTS

Four subjects (17 %) reported pain in their hips. Forty-four hips (91.7 %) had at least one radiographic sign of CAM impingement, and 22 (45.8 %) had an α-angle of more than 60°. Eighteen hips (37.5 %) had at least one sign of pincer impingement and 16 (33.3 %) a positive crossover sign. Sixteen hips (33.3 %) had mixed impingement. There was a significant positive association between having an α-angle of more than 60° and the presence of groin pain (P = 0.002). A reduced femoral head-neck offset (P < 0.001) and an increased α-angle on the anteroposterior radiograph (P = 0.008) were independently associated with a higher Tönnis grade.

CONCLUSION

High prevalence of radiographic CAM-type FAI among these skilled capoeira players was found. In these subjects, a negative clinical correlation for an increased α-angle was also detected. Additional caution should be exercised whenever subjects with past or present hip pain engage in capoeira.

The alpha angle in cam-type femoroacetabular impingement

We report on gender-specific reference intervals of the alpha angle and its association with other qualitative cam-type findings in femoroacetabular impingement at the hip, according to a population-based cohort of 2038 19-year-olds, 1186 of which were women (58%). The alpha angle was measured on standardised frog-leg lateral and anteroposterior (AP) views using digital measurement software, and qualitative cam-type findings were assessed subjectively on both views by independent observers. In all, 2005 participants (837 men, 1168 women, mean age 18.6 years (17.2 to 20.1) were included in the analysis. For the frog-leg view, the mean alpha angle (right hip) was 47° (26 to 79) in men and 42° (29 to 76) in women, with 97.5 percentiles of 68° and 56°, respectively. For the AP view, the mean values were 62° (40 to 105) and 52° (36 to 103) for men and women, respectively, with 97.5 percentiles of 93° and 94°. Associations between higher alpha angles and all qualitative cam-type findings were seen for both genders on both views. The reference intervals presented for the alpha angle in this cross-sectional study are wide, especially for the AP view, with higher mean values for men than women on both views.

Cite this article: Bone Joint J 2014;96-B:449–54.

A local reference frame for describing the proximal human femur: application in clinical settings

OBJECTIVE

The conventional reference frame for the femur has limited relevance for the planning of hip surgery as the femoral neck axis, a crucial reference for surgeons, has to be independently derived. The purpose of this study is to develop and validate a reliable frame of reference for the proximal femur that can be applied in clinical settings.

MATERIALS AND METHODS

Ten three-dimensional models of femurs were obtained. An iterative method was developed to find the femoral neck axis (X-axis). A second axis was also created from the lesser trochanter to the piriformis fossa (LTPF). The origin was defined as the femoral head centre. The cross product of the neck and LTPF axes provided the Z-axis and the third axis (Y-axis) was perpendicular to the other two. Intra-/inter-investigator reliability was assessed on the ten femur models; ten times by one investigator and twice by three investigators respectively. The results were then compared with the conventional reference frame using landmarks on the distal femur.

RESULTS

The femoral neck and LTPF axes had mean intra-/inter-investigator angle differences of 0.5° (SD 0.4°) and 0.7° (SD 0.5°), and 0.8° (SD 0.5°) and 0.9° (SD 0.6°) respectively while the variations of the X-, Y- and Z- axes were SD 0.6°, 0.7° and 0.5°.

CONCLUSIONS

A reliable method of obtaining the three-dimensional proximal femoral frame was developed, using the femoral neck axis, with greater relevance to clinical settings, preoperative planning and accurate assessment of procedures post-operatively.

Correlations between the alpha angle and femoral head asphericity: Implications and recommendations for the diagnosis of cam femoroacetabular impingement

OBJECTIVE

To determine the strength of common radiographic and radial CT views for measuring true femoral head asphericity.

PATIENTS AND METHODS

In 15 patients with cam femoroacetabular impingement (FAI) and 15 controls, alpha angles were measured by two observers using radial CT (0°, 30°, 60°, 90°) and digitally reconstructed radiographs (DRRs) for the: anterior-posterior (AP), standing frog-leg lateral, 45° Dunn with neutral rotation, 45° Dunn with 40° external rotation, and cross-table lateral views. A DRR validation study was performed. Alpha angles were compared between groups. Maximum deviation from a sphere of each subject was obtained from a previous study. Alpha angles from each view were correlated with maximum deviation.

RESULTS

There were no significant differences between alpha angles measured on radiographs and the corresponding DRRs (p=0.72). Alpha angles were significantly greater in patients for all views (p≤0.002). Alpha angles from the 45° Dunn with 40° external rotation, cross-table lateral, and 60° radial views had the strongest correlations with maximum deviation (r=0.831; r=0.823; r=0.808, respectively). The AP view had the weakest correlation (r=0.358).

CONCLUSION

DRRs were a validated means to simulate hip radiographs. The 45° Dunn with 40° external rotation, cross-table lateral, and 60° radial views best visualized femoral asphericity. Although commonly used, the AP view did not visualize cam deformities well. Overall, the magnitude of the alpha angle may not be indicative of the size of the deformity. Thus, 3D reconstructions and measurements of asphericity could improve the diagnosis of cam FAI.

Cam impingement: defining the presence of a cam deformity by the alpha angle: data from the CHECK cohort and Chingford cohort

INTRODUCTION

Cam impingement is characterized by abnormal contact between the proximal femur and acetabulum caused by a non-spherical femoral head, known as a cam deformity. A cam deformity is usually quantified by the alpha angle; greater alpha angles substantially increase the risk for osteoarthritis (OA). However, there is no consensus on which alpha angle threshold to use to define the presence of a cam deformity.

AIM

To determine alpha angle thresholds that define the presence of a cam deformity and a pathological cam deformity based on development of OA.

METHODS

Data from both the prospective CHECK cohort of 1002 individuals (45-65 years) and the prospective population-based Chingford cohort of 1003 women (45-64 years) with respective follow-up times of 5 and 19 years were combined. The alpha angle was measured at baseline on anteroposterior radiographs, from which a threshold for the presence of a cam deformity was determined based on its distribution. Further, a pathological alpha angle threshold was determined based on the highest discriminative ability for development of end-stage OA at follow-up.

RESULTS

A definite bimodal distribution of the alpha angle was found in both cohorts with a normal distribution up to 60°, indicating a clear distinction between normal and abnormal alpha angles. A pathological threshold of 78° resulted in the maximum area under the ROC curve.

CONCLUSION

Epidemiological data of two large cohorts shows a bimodal distribution of the alpha angle. Alpha angle thresholds of 60° to define the presence of a cam deformity and 78° for a pathological cam deformity are proposed.

Femoroacetabular impingement: fact, fiction, or fantasy?

OBJECTIVE

Proponents of femoroacetabular impingement (FAI) now claim that FAI is an important risk factor for hip osteoarthritis and argue that early, aggressive treatment is indicated to stave off long-term complications. The result is more young patients undergoing corrective surgery; does the literature support these claims or has hype trumped reality? This article critically reviews these assertions together with the current scientific evidence that defends (or refutes) them.

CONCLUSION

Each reader will need to weigh the evidence carefully when interpreting images or planning management for patients with possible FAI.

Anteroinferior acetabular rim damage due to femoroacetabular impingement

BACKGROUND

The most common location of labral tears and chondral damage in the hip is the anterosuperior region of the acetabulum, which is associated with pain in flexion and rotation. We describe a case series of patients with labral tears, ganglion formation, and chondromalacia isolated to the anteroinferior acetabulum. Clinically, patients had pain in extension and internal rotation.

CASE DESCRIPTIONS

Isolated anteroinferior labral hypertrophy and ganglion were first observed in a patient with coxa valga. We retrospectively reviewed clinical and radiographic records and identified nine hips in seven patients with isolated anteroinferior damage. One patient with bilateral valgus femoral head tilt after slipped capital femoral epiphysis (SCFE) had impingement of the anteromedial metaphysis on the acetabulum from 3 to 6 o'clock. Five of seven had valgus neck-shaft angles and all had acetabular anteversion with damage isolated to the anteroinferior acetabular rim.

LITERATURE REVIEW

Series on the diagnostic efficacy of MR arthrogram have noted anteroinferior damage adjacent to superior acetabular rim lesions. However, these do not describe isolated anteroinferior rim damage. In addition, available case series of patients with valgus SCFE do not describe a location of impingement or intraarticular damage.

PURPOSES AND CLINICAL RELEVANCE

In this small case series of patients with isolated anteroinferior chondrolabral damage, there are two potential causative mechanisms: (1) primary anteroinferior impingement with femoral extension and internal rotation and (2) posterior extraarticular ischiotrochanteric impingement causing secondary anterior instability of the femur. The pathoanatomy appears to be multifactorial, necessitating an individualized treatment approach.

Development of a fully automatic shape model matching (FASMM) system to derive statistical shape models from radiographs: application to the accurate capture and global representation of proximal femur shape

OBJECTIVE

To evaluate the accuracy and sensitivity of a fully automatic shape model matching (FASMM) system to derive statistical shape models (SSMs) of the proximal femur from non-standardised anteroposterior (AP) pelvic radiographs.

DESIGN

AP pelvic radiographs obtained with informed consent and appropriate ethical approval were available for 1105 subjects with unilateral hip osteoarthritis (OA) who had been recruited previously for The arcOGEN Study. The FASMM system was applied to capture the shape of the unaffected (i.e., without signs of radiographic OA) proximal femur from these radiographs. The accuracy and sensitivity of the FASMM system in calculating geometric measurements of the proximal femur and in shape representation were evaluated relative to validated manual methods.

RESULTS

De novo application of the FASMM system had a mean point-to-curve error of less than 0.9 mm in 99% of images (n = 266). Geometric measurements generated by the FASMM system were as accurate as those obtained manually. The analysis of the SSMs generated by the FASMM system for male and female subject groups identified more significant differences (in five of 17 SSM modes after Bonferroni adjustment) in their global proximal femur shape than those obtained from the analysis of conventional geometric measurements. Multivariate gender-classification accuracy was higher when using SSM mode values (76.3%) than when using conventional hip geometric measurements (71.8%).

CONCLUSIONS

The FASMM system rapidly and accurately generates a global SSM of the proximal femur from radiographs of varying quality and resolution. This system will facilitate complex morphometric analysis of global shape variation across large datasets. The FASMM system could be adapted to generate SSMs from the radiographs of other skeletal structures such as the hand, knee or pelvis.

The deviation of the mechanical leg axis correlates with an increased hip alpha angle and could be a predictor of femoroacetabular impingement

PURPOSE

This study was designed to evaluate whether the mechanical axis deviation (MAD) of the leg correlates with an increased hip alpha angle as described by Nötzli, which is associated with femoroacetabular impingement (FAI).

METHODS

In a retrospective analysis, standing full-length anteroposterior radiographs were analysed in patients who suffered from symptomatic leg alignment. The study included 85 radiographs of 80 patients with an average age of 43.11 years (range 18-60 years). Five patients underwent a bilateral long-leg X-ray examination. All radiographs were transferred as Digital Imaging and Communications in Medicine data files from the Picture Archiving and Communications System into the OrthoPlanner software version 2.3.2. The radiographs were measured by one orthopaedic surgeon and one independent radiologist.

RESULTS

The mean value of the alpha angle of Nötzli was 61.43° (49.07-74.04°). A total of 57 (67%) radiographs showed a varus deviation, 25 (29.5%) had a valgus malalignment and three (3.5%) a straight leg axis. Of 82 radiographs, 40 (48.8%) had a moderate axis deviation with a MAD <15 or > - 15 mm and a mean alpha angle of 57.81°, and 42 (51.2%) with extended axis deviation of a MAD > 15 or < - 15 mm had a mean alpha angle of 62.93°; 40 (95.2%) of these 42 showed an alpha angle > 55°. The alpha angle was significantly increased in extended axis deviation compared to moderate axis deviation (P = 0.001).

CONCLUSIONS

This study confirmed that increased alpha angles were found significantly at higher degrees of axis deviation on the full-length radiograph. In cases of a MAD >15 or < - 15 mm and symptomatic coxalgia, diagnostic tests must be pursued for FAI.

Femoroacetabular impingement: role of imaging

The femoroacetabular impingement (FAI) is an impingement characterized by repetitive abutment between the femur and the acetabular rim during hip motion due to loss of joint clearance (Imam and Khanduja in Int Orthop 35(10):1427-1435, 2011; James et al. in AJR Am J Roentgenol 187(6):1412-1419, 2006). Femoroacetabular impingement (FAI) can be classified as either cam or pincer type, and it can be differentiated on the basis of a predominance of either a femoral or an acetabular abnormality (Pfirrmann et al. in Radiology 244(2):626, 2007; Ganz et al. in Clin Orthop Relat Res 466(2):264-272, 2008). In cases of cam FAI, the nonspherical shape of the femoral head at the femoral head-neck junction and reduced depth of the femoral waist lead to abutment of the femoral head-neck junction against the acetabular rim. In cases of pincer FAI, acetabular overcoverage limits the range of motion and leads to a conflict between the acetabulum and the femur. The most important role of preoperative MR evaluation in patients affected by FAI is the accurate assessment of the damage's extension.

Symptomatic femoroacetabular impingement: does the offset decrease correlate with cartilage damage? A pilot study

BACKGROUND

Current measures of the reduced head-neck offset such as residual deformity of slipped capital femoral epiphysis (SCFE) including the alpha angle, which measures the femoral head-neck sphericity but does not account for acetabular abnormalities, do not represent the true magnitude of the deformity and the mechanical consequences. The beta angle (angle between the femoral head-neck junction and acetabular rim) accounts for the morphology of both the acetabulum and femur and, thus, may be the more appropriate parameter for assessing SCFE deformity.

QUESTIONS/PURPOSES

We determined (1) whether the beta angle could be reliably measured on MRI; and (2) whether the beta angle correlates with the cartilage status.

METHODS

We recruited 10 adult patients (mean age, 28 years) with symptomatic cam femoroacetabular impingement and 15 asymptomatic volunteers (mean age, 24 years) to have three-dimensional MRI including delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) for cartilage status assessment. Corresponding alpha angles, beta angles, and acetabular dGEMRIC indices were obtained in seven radial reformats to assess the hip in seven regions (anterior to superior and posterior).

RESULTS

We noted high reproducibility for both alpha and beta angle measurements. The dGEMRIC indices correlated with beta angles in the superoinferior and superior regions but not the alpha angles.

CONCLUSIONS

Beta angle measurement in radial MR images is reproducible and appears to correspond to cartilage damage in the superior regions of the hip. The beta angle may be a useful parameter to assess hip deformity in the followup of SCFE although further confirmation is warranted.

Femoroacetabular impingement predisposes to traumatic posterior hip dislocation

BACKGROUND

Traumatic posterior hip dislocation in adults is generally understood to be the result of a high-energy trauma. Aside from reduced femoral antetorsion, morphologic risk factors for dislocation are unknown. We previously noticed that some hips with traumatic posterior dislocations had evidence of morphologic features of femoroacetabular impingement (FAI), therefore, we sought to evaluate that possibility more formally.

QUESTIONS/PURPOSES

We asked whether hips with a traumatic posterior hip dislocation present with (1) a cam-type deformity and/or (2) a retroverted acetabulum.

METHODS

We retrospectively compared the morphologic features of 53 consecutive hips (53 patients) after traumatic posterior hip dislocation with 85 normal hips (44 patients) based on AP pelvic and crosstable axial radiographs. We measured the axial and the lateral alpha angle for detection of a cam deformity and the crossover sign, ischial spine sign, posterior wall sign, retroversion index, and ratio of anterior to posterior acetabular coverage to describe the acetabular orientation.

RESULTS

Hips with traumatic posterior traumatic dislocation were more likely to have cam deformities than were normal hips, in that the hips with dislocation had increased axial and lateral alpha angles. Hips with posterior dislocation also were more likely to be retroverted; dislocated hips had a higher prevalence of a positive crossover sign, ischial spine sign, and posterior wall sign, and they had a higher retroversion index and increased ratio of anterior to posterior acetabular coverage.

CONCLUSIONS

Hips with posterior traumatic dislocation typically present with morphologic features of anterior FAI, including a cam-type deformity and retroverted acetabulum. An explanation for these findings could be that the early interaction between the aspherical femoral head and the prominent acetabular rim acts as a fulcrum, perhaps making these hips more susceptible to traumatic dislocation.

A method of assessing the severity of cam type femoro-acetabular impingement in three dimensions

Femoroacetabular impingement is caused by abnormal morphology of either the femur or acetabulum or both. Diagnostic criteria currently include an alpha angle of over 50° on a lateral radiograph. In this study, CT scans of symptomatic hips (n = 37) were compared with normal hips (n = 34) obtained from CT colonoscopy procedures. The femoral head described in terms of a three dimensional (3D) alpha angle and a 3D head neck margin (epiphysis) angle '3Dμ' using a semi-automated algorithm. In normal hips 70% have a maximum 3Dα angle of more than 50° at some point around their femoral head (mean 53° ± 5°, range 42° - 64°), while in cam hips, it was significantly larger (mean 69° ± 10°, range 54° - 94°, p<0.001). The 3Dμ also varied significantly and had a reverse relationship to that of the alpha angle: cam hips have an articular extent that crossed over spherical limit of the hip joint (mean minimum 41° ± 7°) while the articular margin of normal hips always remained within the spherical limit (mean minimum 49° ± 6°). This semi-automated algorithm provides an objective measure of the femoral head in health and disease. It can reliably distinguish cam hips from normal, enabling cam hips to have their cam quantified and their surgery planned objectively.

Femoroacetabular impingement

Femoroacetabular impingement (FAI) is a common cause of early-onset osteoarthritis of the hip. It can be caused by morphologic abnormalities involving the proximal femur or acetabulum, leading to abnormal abutment of the femoral head-neck against the acetabular rim. This repetitive trauma causes mechanical wear of the labrum and articular cartilage, leading to osteoarthritis of the hip. Magnetic resonance imaging is an accurate noninvasive imaging modality that can detect acetabular labral lesions and adjacent cartilage damage, and is able to detect underlying subtle anatomic variations of the femoral head-neck junction and acetabulum associated with FAI.

Evaluation of Cam-type femoroacetabular impingement by ultrasound

PURPOSE

In the diagnosis of femoroacetabular impingement (FAI), magnetic resonance imaging (MRI) and X-ray are widely accepted methods for detection. When evaluating the hip head-neck junction using MRI, oblique axial sequences are required. However, the construction and analysis of these images are restricted to specialist radiologists and surgeons in the field of hip joint MRI. This study sought to investigate whether ultrasound, a simple and inexpensive method, can be used as a reliable tool for diagnosing Cam-type FAI.

METHODS

Forty patients, with a mean age of 39 years (range, 18-61 years), were consecutively included in this prospective study, following a diagnosis of Cam-type FAI on an oblique axial MRI. All patients underwent ultrasound examination in the ventral longitudinal section at 20° external rotation, neutral position and 20° internal rotation. The alpha angle, anterior offset, offset-ratio, and anterior femoral distance (AFD) were measured using MRI and ultrasound.

RESULTS

No significant differences were detected between the alpha angle on MRI and that using ultrasound in the neutral position or in 20° internal rotation, with strong correlations observed between these parameters (r = 0.67 for neutral position, r = 0.77 for 20° internal rotation). The Pearson's correlation coefficient for the alpha angle on MRI and the ratio of AFD/anterior offset on ultrasound in internal rotation was 0.76 (p < 0.0001).

CONCLUSIONS

The results show strong correlations between MRI and ultrasound measurements in patients with Cam-type FAI. Consequently, ultrasound may provide a useful tool for the early diagnosis of Cam-type FAI in daily practice.

The three-dimensional relationship between acetabular rim morphology and the severity of femoral cam lesions

We examined the relationship between the size of the femoral cam in femoroacetabular impingement (FAI) and acetabular pathomorphology to establish if pincer impingement exists in patients with a femoral cam.

CT scans of 37 symptomatic impinging hips with a femoral cam were analysed in a three-dimensional study and were compared with 34 normal hips. The inclination and version of the acetabulum as well as the acetabular rim angle and the bony acetabular coverage were calculated. These measurements were correlated with the size and shape of the femoral cams.

While the size of the femoral cam varied characteristically, the acetabular morphology of the two groups was similar in terms of version (normal mean 23° (sd 7°); cam mean 22° (sd 9°)), inclination (normal mean 57° (sd 5°); cam mean 56° (sd 5°)), acetabular coverage (normal mean 41% (sd 5%); cam mean 42% (sd 4%)) and the mean acetabular rim angle (normal mean 82° (sd 5°); cam mean 83° (sd 4°)).

We found no correlation between acetabular morphology and the severity of cam lesion and no evidence of either global or focal over-coverage to support the diagnosis of ‘mixed’ FAI. The femoral cam may provoke edge loading but removal of any acetabular bearing surface when treating cam FAI might induce accelerated wear.

Cite this article: Bone Joint J 2013;95-B:314–19.

Cam type femoro-acetabular impingement: quantifying the diagnosis using three dimensional head-neck ratios

OBJECTIVE

Cam hips are commonly quantified using the two-dimensional α angle. The accuracy of this measurement may be affected by patient position and the technician's experience. In this paper, we describe a method of measurement that provides a quantitative definition of cam hips based upon three-dimensional computed tomography (CT) images.

MATERIALS AND METHODS

CT scans of 47 (24 cam, 23 normal) femurs were segmented. A sphere was fitted to the articulating surface of the femoral head, the radius (r) recorded, and the femoral neck axis obtained. The cross sectional area at four locations spanning the head neck junction (r/4, r/2, 3r/4 and r), perpendicular to the neck axis, was measured. The ratios (Neck/Head) between the areas at each cut relative to the surface area at the head centre were calculated and aggregated.

RESULTS

Normal and cam hips were significantly different: the sum of the head-neck ratios (HNRs) of the cam hips were always smaller than normal hips (p < 0.01). A cut off point of 2.55 with no overlap was found between the two groups, with HNRs larger than this being cam hips, and smaller being normal ones.

CONCLUSION

Owing to its sensitivity and repeatability, the method could be used to confirm or refute the clinical diagnosis of a cam hip. Furthermore it can be used as a tool to measure the outcome of cam surgery.

Three-dimensional quantification of femoral head shape in controls and patients with cam-type femoroacetabular impingement

An objective measurement technique to quantify 3D femoral head shape was developed and applied to normal subjects and patients with cam-type femoroacetabular impingement (FAI). 3D reconstructions were made from high-resolution CT images of 15 cam and 15 control femurs. Femoral heads were fit to ideal geometries consisting of rotational conchoids and spheres. Geometric similarity between native femoral heads and ideal shapes was quantified. The maximum distance native femoral heads protruded above ideal shapes and the protrusion area were measured. Conchoids provided a significantly better fit to native femoral head geometry than spheres for both groups. Cam-type FAI femurs had significantly greater maximum deviations (4.99 ± 0.39 mm and 4.08 ± 0.37 mm) than controls (2.41 ± 0.31 mm and 1.75 ± 0.30 mm) when fit to spheres or conchoids, respectively. The area of native femoral heads protruding above ideal shapes was significantly larger in controls when a lower threshold of 0.1 mm (for spheres) and 0.01 mm (for conchoids) was used to define a protrusion. The 3D measurement technique described herein could supplement measurements of radiographs in the diagnosis of cam-type FAI. Deviations up to 2.5 mm from ideal shapes can be expected in normal femurs while deviations of 4-5 mm are characteristic of cam-type FAI.

Hip arthroscopy for challenging deformities: posterior cam decompression

Since the classic description of cam femoroacetabular impingement occurring in the anterolateral quadrant of the proximal femur, there has been growing evidence of cam impingement extending outside of this region. Although anteromedial cam decompression may be performed, posterior cam decompression is at higher theoretic risk of vascular embarrassment with osteonecrosis and/or tensile failure with fracture, leading some investigators to believe that these major deformities require open surgical correction. We present a less invasive method of arthroscopic posterior cam decompression using the modified midanterior portal while avoiding the posterolateral vasculature of the proximal femur.

Hip ontogenesis: how evolution, genes, and load history shape hip morphotype and cartilotype

BACKGROUND

Developmental hip disorders (DHDs), eg, developmental dysplasia of the hip, slipped capitis femoris epiphysis, and femoroacetabular impingement, can be considered morphology variants of the normal hip. The femoroacetabular morphology of DHD is believed to induce osteoarthritis (OA) through local cumulative mechanical overload acting on genetically controlled patterning systems and subsequent damage of joint structures. However, it is unclear why hip morphology differs between individuals with seemingly comparable load histories and why certain hips with DHD progress to symptomatic OA whereas others do not.

QUESTIONS/PURPOSES

We asked (1) which mechanical factors influence growth and development of the proximal femur; and (2) which genes or genetic mechanisms are associated with hip ontogenesis.

METHODS

We performed a systematic literature review of mechanical and genetic factors of hip ontogeny. We focused on three fields that in recent years have advanced our knowledge of adult hip morphology: imaging, evolution, and genetics. WHERE ARE WE NOW?: Mechanical factors can be understood in view of human evolutionary peculiarities and may summate to load histories conducive to DHD. Genetic factors most likely act through multiple genes, each with modest effect sizes. Single genes that explain a DHD are therefore unlikely to be found. Apparently, the interplay between genes and load history not only determines hip morphotype, but also joint cartilage robustness ("cartilotype") and resistance to symptomatic OA. WHERE DO WE NEED TO GO?: We need therapies that can improve both morphotype and cartilotype. HOW DO WE GET THERE?: Better phenotyping, improving classification systems of hip morphology, and comparative population studies can be done with existing methods. Quantifying load histories likely requires new tools, but proof of principle of modifying morphotype in treatment of DDH and of cartilotype with exercise is available.

Do plain radiographs correlate with CT for imaging of cam-type femoroacetabular impingement?

BACKGROUND

Three-dimensional imaging (CT and MRI) is the gold standard for detecting femoral head-neck junction malformations in femoroacetabular impingement, yet plain radiographs are used for initial diagnostic evaluation. It is unclear, however, whether the plain radiographs accurately reflect the findings on three-dimensional imaging.

QUESTIONS/PURPOSES

We therefore: (1) investigated the correlation of alpha angle measurements on plain radiographs and radial reformats of CT scans; (2) determined which radiographic views are most sensitive and specific in detecting head-neck deformities present on CT scans; and (3) determined if specific radiographic views correlated with specific locations on the radial oblique CT scan.

METHODS

We retrospectively reviewed 41 surgical patients with preoperative CT scans (radial oblique reformats) and plain radiographs (AP pelvis, 45° Dunn, frog lateral, and crosstable lateral). Alpha angles were measured on plain radiographs and CT reformats.

RESULTS

The complete radiographic series was 86% to 90% sensitive in detecting abnormal alpha angles on CT. The maximum alpha angle on plain radiographs was greater than that of CT reformats in 61% of cases. Exclusion of the crosstable lateral did not affect the sensitivity (86%-88%). The Dunn view was most sensitive (71%-80%). The frog lateral showed the best specificity (91%-100%). Substantial correlations (intraclass correlation coefficients, 0.64-0.75) between radiograph and radial oblique CT position were observed, including AP/12:00 (superior), Dunn/1:00 (anterolateral), frog/3:00 (anterior), and crosstable/3:00 (anterior).

CONCLUSIONS

For diagnostic and treatment purposes, a three-view radiographic hip series (AP pelvis, 45° Dunn, and frog lateral) effectively characterizes femoral head-neck junction malformations.

LEVEL OF EVIDENCE

Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Hip capsule dimensions in patients with femoroacetabular impingement: a pilot study

BACKGROUND

Joint-preserving hip surgery, either arthroscopic or open, increasingly is used for the treatment of symptomatic femoroacetabular impingement (FAI). As a consequence of surgery, thickening of the joint capsule and intraarticular adhesions between the labrum and joint capsule and between the femoral neck and the joint capsule have been observed. These alterations are believed to cause persistent pain and reduced range of motion. Because the diagnosis is made with MR arthrography, knowledge of the normal capsular anatomy and thickness on MRI in patients is important. To date there is no such information available.

QUESTIONS/PURPOSES

The purpose of this study was to establish thickness, length of the hip capsule, and the size of the perilabral recess in patients with FAI.

METHODS

We reviewed the preoperative MR arthrography of 30 patients (15 men) with clinical symptoms of FAI. We measured capsular thickness and made observations on the perilabral recess.

RESULTS

The joint capsule was thickest (6 mm) anterosuperiorly between 1 and 2 o'clock. The average length from the femoral head-neck junction to the femoral insertion of the capsule ranged from 19 to 33 mm. A perilabral recess was present circumferentially, even across the acetabular notch, where the labrum is supported by the transverse acetabular ligament. The shortest recess occurred superiorly.

CONCLUSIONS

Knowledge of the capsular anatomy in patients with FAI before surgery is important to judge the postoperative changes and to plan potential further therapy including arthroscopic treatment of intraarticular adhesions.