Femoroacetabular Impingement: Screening and Definitive Imaging

The borderline dysplastic hip: when and how is it abnormal?

Borderline acetabular dysplasia refers to mildly sub-normal patterns of acetabular shape and coverage that might predispose children to mechanical dysfunction and instability. Borderline dysplasia generally includes children with a lateral center edge angle (CEA) of 18-24°. Some children with borderline radiographic measurements have normal joint mechanics and function while others benefit from acetabular reorienting surgery. Although radiographic findings of borderline dysplasia might suggest instability, the ultimate diagnosis is based on history and physical exam in addition to imaging. Children with borderline acetabular dysplasia sometimes benefit from other cross-sectional imaging studies such as MR imaging to evaluate for secondary evidence of instability, including damage along the acetabular rim, or labral degeneration and hypertrophy. CT is also helpful for depiction of 3-D acetabular morphology for preoperative assessment and planning. Pediatric radiologists are often the first to identify borderline or mild dysplasia on radiographs. It is imperative that pediatric radiologists serve as effective consultants and offer appropriate recommendations as part of a cohesive multidisciplinary approach to this complex patient population.

Femoroacetabular Impingement: Prevalent and Often Asymptomatic in Older Men: The Osteoporotic Fractures in Men Study

BACKGROUND

The epidemiology of femoroacetabular impingement (FAI) is important but incompletely understood, because most reports arise from symptomatic populations. Investigating the prevalence of FAI in a community-based cohort could help us better understand its epidemiology and in particular the degree to which it might or might not be associated with hip pain.

QUESTIONS/PURPOSES

The purposes of this study were (1) to evaluate the proportion of older (≥65 years of age) men with morphologic abnormalities consistent with FAI; and (2) to assess the association of the morphologic abnormalities with prevalent radiographic hip osteoarthritis (OA) and hip pain.

METHODS

Anteroposterior radiographs were obtained in 4140 subjects (mean age±SD, 77±5 years) from the Osteoporotic Fractures in Men study. We assessed each hip for cam, pincer, and mixed FAI types using validated radiographic definitions. Both intra- and interobserver reproducibility were >0.9. Radiographic hip OA was assessed by an expert reader (intraobserver reproducibility, 0.7-0.8) using validated methods, and summary grades of 2 or greater (on a scale from 0 to 4) were used to define radiographic hip OA. Covariates including hip pain in the last 30 days were collected by questionnaires that were answered by all patients included in this report. Logistic regressions with generalized estimating equations were performed to evaluate the association of radiographic features of FAI and arthrosis.

RESULTS

Pincer, cam, or mixed types of radiographic FAI had a prevalence of 57% (1748 of 3053), 29% (886 of 3053), and 14% (419 of 3053), respectively, in this group of older men. Both pincer and mixed types of FAI were associated with arthrosis but not with hip pain (odds ratio [OR], 1.63; 95% confidence interval [CI], 1.25-2.13; p<0.001 for pincer and OR, 2.49; 95% CI, 1.65-3.76; p<0.001 for mixed type). Patients with hips characterized by cam-type FAI had slightly reduced hip pain without the presence of arthrosis compared with hips without FAI (OR, 0.82; 95% CI, 0.68-0.99; p=0.037). A center-edge angle>39° and a caput-collum-diaphyseal angle<125° were associated with arthrosis (OR, 1.53; 95% CI, 1.22-1.94; p<0.001 and OR, 2.09; 95% CI, 1.24-3.51; p=0.006, respectively), but not with hip pain (OR, 0.89; 95% CI, 0.77-1.03; p<0.108 and OR, 0.99; 95% CI, 0.67-1.45; p=0.945, respectively). An impingement angle<70° was associated with less hip pain compared with hips with an impingement angle≥70° (OR, 0.76; 95% CI, 0.61-0.95; p=0.015).

CONCLUSIONS

FAI is common in older men and represents more of an anatomic variant rather than a symptomatic disease. This finding should raise questions on how age, activities, and this anatomic variant each contribute to result in symptomatic disease.

LEVEL OF EVIDENCE

Level III, prognostic study.

Advanced Imaging in Femoroacetabular Impingement: Current State and Future Prospects

Symptomatic femoroacetabular impingement (FAI) is now a known precursor of early osteoarthritis (OA) of the hip. In terms of clinical intervention, the decision between joint preservation and joint replacement hinges on the severity of articular cartilage degeneration. The exact threshold during the course of disease progression when the cartilage damage is irreparable remains elusive. The intention behind radiographic imaging is to accurately identify the morphology of osseous structural abnormalities and to accurately characterize the chondrolabral damage as much as possible. However, both plain radiographs and computed tomography (CT) are insensitive for articular cartilage anatomy and pathology. Advanced magnetic resonance imaging (MRI) techniques include magnetic resonance arthrography and biochemically sensitive techniques of delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T1rho (T1ρ), T2/T2* mapping, and several others. The diagnostic performance of these techniques to evaluate cartilage degeneration could improve the ability to predict an individual patient-specific outcome with non-surgical and surgical care. This review discusses the facts and current applications of biochemical MRI for hip joint cartilage assessment covering the roles of dGEMRIC, T2/T2*, and T1ρ mapping. The basics of each technique and their specific role in FAI assessment are outlined. Current limitations and potential pitfalls as well as future directions of biochemical imaging are also outlined.

A review of imaging modalities for the hip

Hip arthroscopy is one of the fastest growing surgical procedures performed by orthopaedic surgeons, with the number of hip arthroscopies expected to double in 2013. The increase in surgical prevalence is at least in part due to an increased awareness of prearthritic hip pathology. The diagnoses of prearthritic hip conditions are made through a comprehensive history, physical examination, and selection of appropriate diagnostic imaging modalities. The purpose of this review article is to provide the practicing orthopaedic surgeon with an overview of the imaging modalities available for the diagnosis of prearthritic hip pathology, with a focus on literature supporting advancements in imaging techniques and new applications of existing modalities.

Orthopedic perspectives on femoroacetabular impingement

Femoroacetabular impingement (FAI) is a cause of hip pain in which there is abnormal and repetitive contact between the proximal femur and the acetabulum. FAI can occur as a primary condition in children with distinct anatomical abnormalities or can occur as a secondary process in cases of developmental hip conditions or trauma. There are two main categories of FAI, cam and pincer, which are distinguished based on whether the anatomical abnormality is on the femoral side or the acetabular side of the hip joint, respectively. Good outcomes have been achieved with early surgical intervention, but once advanced degenerative changes have occurred the chances for a successful surgical outcome are severely diminished. The orthopedic surgeon's ability to appropriately treat FAI depends on an accurate understanding of the etiology and features of each child. The ability to make an early, accurate diagnosis is enhanced with the use of imaging modalities such as radiographs, MRI and CT. This review will focus on orthopedic perspectives in the use of these imaging modalities in defining the anatomical features of and guiding treatment for FAI.

Evaluation of the painful athletic hip: imaging options and imaging-guided injections

OBJECTIVE

This article reviews diagnostic imaging tests and injections that provide important information for clinical management of patients with sports-related hip pain.

CONCLUSION

In the evaluation of sports-related hip symptoms, MR arthrography is often used to evaluate intraarticular pathology of the hip. The addition of short- and long-acting anesthetic agents with the MR arthrography injection adds additional information that can distinguish between symptomatic and asymptomatic imaging findings. Osseous abnormalities can be characterized with radiography, MRI, or CT. Ultrasound is important in the assessment of iliopsoas abnormalities, including tendon snapping, and to guide diagnostic anesthetic injection.

Relationship between proximal femoral and acetabular alignment in normal hip joints using 3-dimensional computed tomography

BACKGROUND

The bony architecture of the hip depends upon functional adaptation to mechanical usage via the dynamic interaction between the acetabulum and femoral head. Acetabular retroversion is thought to be a contributing factor of pincer-type femoroacetabular impingement. Studies of pathological hip joints suggest proximal femoral anatomy compensates for acetabular retroversion. HYPOTHESIS/ PURPOSE: The purpose of this study was to determine if a predictable relationship exists between proximal femoral and acetabular angles, age, and gender in normal hip joints. We hypothesized that, through functional adaptation to mechanical loading, a complementary developmental relationship exists between the acetabulum and proximal femur.

STUDY DESIGN

Descriptive laboratory study.

METHODS

The femoral neck version, femoral neck shaft angle, acetabular version, acetabular inclination, and center edge angle were measured in 230 normal hip joints in 115 adults using 3-dimensional reconstruction software. Correlations between the angles, age, and gender were examined using the methods of stepwise regression and backward elimination.

RESULTS

Regarding side-to-side comparison and variability, there was no statistically significant difference between the left and right sides in the average value of each angle measurement. The correlations specifically between angles, age, and gender were similar on the left and right sides for all pairs except femoral version and acetabular inclination. Regarding significant findings of the study, a positive correlation (P < .05) was found between femoral version and acetabular version (0.38° to 1°). A positive correlation was found between femoral neck shaft angle and acetabular version (0.21° to 1°). A negative correlation was found between femoral neck shaft angle and age (-0.17° to 1°). A positive correlation was found between acetabular version and female gender (2.6° to 1°). A positive correlation was found between center edge angle and female gender (2.8° to 1°). A negative correlation was found between femoral version and acetabular inclination (-0.49° to 1°), although this latter relationship was only observed unilaterally (ie, left hip).

CONCLUSION

This study demonstrates that a correlation exists between multiple proximal femoral and acetabular angles in normal hip joints. These findings support the hypothesis that a complementary developmental relationship occurs between the femoral head and acetabulum.

CLINICAL RELEVANCE

The results of this study suggest that, in some patients, what is thought to be pathological acetabular retroversion may actually be normal anatomy with a compensated femoral version. Investigating the relationship between these angles in patients with the signs and symptoms of pincer-type femoroacetabular impingement may alter a surgeon's approach to this patient population.