What is normal femoral head/neck anatomy? An analysis of radial CT reconstructions in adolescents

The morphogenesis of porcine femoral head mammillary processes: A structural mechanism of biomechanical stability

The capital femoral physis is a growth plate located between the head of the femur and femoral neck, which forms a temporary joint where growth plate cartilage is converted to bone by endochondral ossification. The bone-cartilage-bone interface develops a unique radial pattern of interdigitating mammillary processes that interlock the femoral head with the metaphysis, increasing biomechanical stability. The arrangement of these mammillary processes may not be a random occurrence and likely serves to provide mechanical mechanisms to enhance biomechanical stability. In this study, we provide a qualitative and quantitative analysis of porcine femoral head mammillary processes and focus on the analysis of six key points of development: the epiphyseal tubercle, epiphyseal cupping, growth plate slope angles, expansion of the epiphyseal subchondral bone plate, epiphyseal elongation, and the emergence of smaller, radially arranged mammillary processes. We introduce a metric of surface roughness analysis to quantify mammillary processes and apply it to analyze the development of the observed radial pattern of peripheral mammillary processes from birth to adolescence. We hypothesized that these processes develop to form a radial pattern with some degree of periodicity beginning relatively early in development of the joint and increase in prominence with age and weight of the animal. These findings may have important implications in the early diagnosis and treatment of the hip disorder slipped capital femoral epiphysis (SCFE). Underdevelopment of femoral head mammillary processes may reduce joint stability and could be a risk factor in SCFE.

Acetabular Coverage Decreases at the End of Skeletal Growth: A 3DCT Study of Healthy Hips

BACKGROUND

Abnormalities in size and position of the acetabulum have been linked to both developmental dysplasia of the hip and femoroacetabular impingement. Owing to its 3-dimensional (3D) complexity, plain radiography and cross-sectional studies [computed tomography (CT) and magnetic resonance imaging] have limitations in their ability to capture the complexity of the acetabular 3D anatomy. The goal of the study was to use 3D computed tomography reconstructions to identify the acetabular lunate cartilage and measure its size at varying ages of development and between sexes.

METHODS

Patients aged 10 to 18 years with asymptomatic hips and a CT pelvis for appendicitis were reviewed. Patients were stratified by sex and age: preadolescent (10 to 12), young adolescent (13 to 15), and old adolescent (16 to 18) in equal proportions. Materialise 3-matic was used to generate a 3D pelvic model, and the acetabular lunate cartilage surface area was calculated. The lunate cartilage was divided into anatomic segments: superior (11:00 to 1:00), anterior (1:00 to 4:00), and posterior (8:00 to 11:00). The femoral head surface area was calculated to control for patient size. Mixed effects models were generated predicting segment size where side was treated as a repeated measure. Absolute and relative (lunate cartilage to femoral head) models were generated.

RESULTS

Sixty-two patients (124 hips) were included. Females showed a significant decrease in femoral head coverage as age increased overall and in the 3 subsegments. The majority of changes occurred between the preadolescent and young adolescent groups. Males did not show an overall change, but the superior and anterior anatomic subgroups showed a significant decrease in coverage between the young and old adolescent groups. Male lunate cartilages were absolutely, but not relatively, larger than females. No clinically significant side-to-side differences were noted.

CONCLUSIONS

The relative femoral head coverage by the acetabular lunate cartilage reduced with increasing age, suggesting the growth of the femoral head outpaces the acetabular lunate cartilage's growth. This was more prominent in females. This study has important implications for expected acetabular coverage changes in the latter aspects of pediatric and adolescent development.

LEVEL OF EVIDENCE

Level III-diagnostic study.

Sclerotic lesions of the femoral head-neck junction for diagnosis of femoroacetabular impingement

The morphological characteristics associated with a diagnosis of femoroacetabular impingement (FAI) observed on plain radiographs can also be seen in subjects without hip joint symptoms. Therefore, the purpose of this study was to investigate whether sclerotic lesions on femoral head-neck junction (FHNJ) could be used as a supplemental diagnostic feature. A total of 128 hips from 119 patients (43 male and 76 female) diagnosed with FAI and 24 hips from 21 patients (2 male and 19 female) with other hip pathologies as control were compared in this study. Using standing frog-leg plain radiographs, the prevalence of sclerotic lesions on the FHNJ was established. Additionally, the pixel intensity (PI) of the sclerotic lesions between the FAI and the control groups were quantitatively compared. Sclerotic lesions were present in 96.1% of FAI hips (123 of 128) and only 37.5% of control hips (9 of 24) (p < 0.05). The ratio of PI in the FAI group was significantly higher (approximately 10%) than in the control group (p < 0.05). The evaluation of sclerotic lesions may be used as a supplement to aid in the diagnosis of FAI.

Normative Values for Capital Femoral Epiphyseal Extension of the Developing Hip Based on Age, Sex, and Oxford Bone Age

BACKGROUND

Recent evidence suggests that increasing capital femoral epiphyseal extension may be an adaptive response that underlies the development of most cam morphology, whereas slipped capital femoral epiphysis is associated with its deficiency. However, there is an absence of rigorous data on the normal development of epiphyseal extension in the hip joint in modern adolescents. The aim of this study was to establish normative values for anterior and superior epiphyseal extension in a normal adolescent control population.

METHODS

A total of 210 pediatric subjects (420 hips) between the ages of 8 and 17 years old at the time of presentation who received pelvic radiographs were retrospectively reviewed. Basic demographic data were collected. All subjects with underlying hip pathology were excluded. Epiphyseal extension ratio (EER) was measured, defined as the ratio of extension of the capital femoral epiphysis down the femoral neck relative to the diameter of the femoral head. Superior EER was measured on the anterioposterior view and anterior EER on the frog-leg lateral view bilaterally. Skeletal maturity was graded based on Oxford bone age (OBA) at the proximal femur.

RESULTS

The superior EER increased from 0.63±0.05 at age 8 to 0.80±0.05 at age 17. The anterior EER similarly increased from 0.56±0.06 at age 8 to 0.74±0.05 at age 17. The superior and anterior EERs increased with age in a linear fashion for males (r=0.80 and 0.75, respectively) and females (r=0.67 and 0.65) through physeal closure. When subjects were standardized by the OBA stage of the femoral head, females and males showed no statistical difference at OBA stages 6, 7 or 8.

CONCLUSIONS

Superior and anterior EER increased throughout adolescent development until physeal closure. When controlling for skeletal maturity, there were no significant differences between sexes. This normative data may help guide future management and research of slipped capital femoral epiphysis and cam morphology.

LEVEL OF EVIDENCE

Level II, Diagnostic.

Age- and gender-specific variations of the epiphyseal tilt and epiphyseal angle in adolescents without hip pathology

PURPOSE

To determine age-and gender-dependent variation of epiphyseal tilt and epiphyseal angle using CT in adolescents without hip pathology.

METHODS

Pelvic CT scans were obtained in 132 adolescents for evaluation of abdominal pain. Radially oriented planes around the femoral neck were reformatted and the epiphyseal tilt and angle were measured in the anterior, anterosuperior and superior planes. Variations in the tilt angle and epiphyseal angle were assessed by age group from 12 to 18 years and gender by using a linear mixed model analysis.

RESULTS

The epiphyseal tilt did not change (p = 0.97) with increasing age. Male patients exhibited smaller tilt angle in the anterosuperior plane (p = 0.003) but no difference was detected in the anterior (p = 0.17) or superior (p = 0.06) planes. The epiphyseal angle decreased with increasing age in the anterior (p = 0.03), anterosuperior (p = 0.001) and superior (p < 0.001) planes in male patients, with no variation in female patients (p = 0.92). Male patients had larger epiphyseal angles in the anterior (p = 0.02), anterosuperior (p < 0.001) and superior (p = 0.002) planes compared with female patients.

CONCLUSION

We found no age-specific variations in the epiphyseal tilt and no difference in the epiphyseal tilt in male and female patients in the superior and anterior plane. The epiphyseal angle was smaller in female patients, however, the epiphyseal angle decreased with increasing age in male patients which corresponds to an increase in epiphyseal extension. The reference values reported in this study may serve as additional information in the evaluation of adolescents with hip pain and as reference for future studies investigating slipped capital femoral epiphysis and femoroacetabular impingement development.

LEVEL OF EVIDENCE

Level III Diagnostic Study.

Hip shape is symmetric, non-dependent on limb dominance and gender-specific: implications for femoroacetabular impingement. A 3D CT analysis in asymptomatic subjects

OBJECTIVE

To determine the reference intervals (RefInt) of the quantitative morphometric parameters of femoroacetabular impingement (FAI) in asymptomatic hips with computed tomography (CT) and determine their dependence on age, side, limb dominance and sex.

METHODS

We prospectively included 590 patients and evaluated 1111 hips with semi-automated CT analysis. We calculated overall, side- and sex-specific parameters for imaging signs of cam [omega and alpha angle (α°)] and pincer-type morphology [acetabular version (ACvers), lateral centre-edge angle (LCEA) and cranio-caudal coverage].

RESULTS

Hip shape was symmetrical and did not depend on limb dominance. The 95% RefInt limits were sex-different for all cam-type parameters and extended beyond current abnormal thresholds. Specifically, the upper limits of RefInt for α° at 12:00, 1:30 and 3:00 o'clock positions were 56°, 70° and 58°, respectively, and 45° for LCEA. Acetabular morphology varied between age groups, with a trend toward an LCEA/ACvers increase over time.

CONCLUSION

Our morphometric measurements can be used to estimate normal hip morphology in asymptomatic individuals. Notably they extended beyond current thresholds used for FAI imaging diagnosis, which was most pronounced for cam-type parameters. We suggest the need to reassess α° RefInt and consider a 60° threshold for the 12:00/3:00 positions and 65-70° for other antero-superior positions.

KEY POINTS

• Hip shape is symmetrical regardless of limb dominance. • Pincer/cam morphology is frequent in asymptomatic subjects (20 and 71%, respectively). • LCEA and acetabular version increases with age (5-7° between opposite age groups). • Femoral morphology is stable after physeal closure (in the absence of pathology). • Alpha and omega angle thresholds should be set according to sex.

Femoroacetabular Impingement Is Associated With Sports-Related Posterior Hip Instability in Adolescents: A Matched-Cohort Study

BACKGROUND

Femoroacetabular impingement (FAI) deformity has been associated with posterior hip instability in adult athletes.

PURPOSE

To determine if FAI deformity is associated with posterior hip instability in adolescents, the femoral head-neck junction or acetabular structure in a cohort of adolescent patients who sustained a low-energy, sports-related posterior hip dislocation was compared with that in a group of healthy age- and sex-matched controls with no history of hip injury or pain.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

We identified 12 male patients (mean age, 13.9 years; range, 12-16 years) who sustained a sports-related posterior hip dislocation and underwent a computed tomography (CT) scan after closed reduction. For each patient, 3 age- and sex-matched healthy controls were identified. Femoral head-neck type was assessed by measurement of the alpha angle on the radially oriented CT images at the 12-, 1-, 2-, and 3-o'clock positions. Age, body mass index (BMI), alpha angle at each position, acetabular version, Tönnis angle, and lateral center-edge angle (LCEA) on the involved hip in the dislocation group were compared with those of the matched controls using a mixed-effects model. A logistic regression analysis using a generalized estimating equation was used to compare the percentage of subjects with cam-type FAI deformity (alpha angle >55°) in each group.

RESULTS

The dislocation and control groups were similar in age distribution and BMI (P > .05). The mean alpha angles were statistically significantly higher in the dislocation group compared with the control group at the superior (46.3° ± 1.1° vs 42.7° ± 0.6°; P = .0213), superior-anterior (55.5° ± 1.9° vs 46.0° ± 1.3°; P = .0005), and anterior-superior (54.9° ± 1.5° vs 48.9° ± 1.0°; P = .0045) regions. Cam deformity was present in a larger proportion of patients in the dislocation group than in the control group (P < .0035). An alpha angle greater than 55° was present in 16.7% of the dislocation group and 0% of the control group at the 12-o'clock position (P = .1213), 41.7% versus 0% at the 1-o'clock position (P = .0034), 58% versus 6% at the 2-o'clock position (P = .0004), and 25% versus 2.8% at the 3-o'clock position (P = .0929). Acetabular anteversion was lower in the dislocation group (9.6° ± 1.4°) compared with the control group (15.1° ± 0.8°) (P = .0068). Mean acetabular LCEA was within a normal range in both groups.

CONCLUSION

A significantly higher mean alpha angle from the superior to the anterior-superior regions of the femoral head-neck junction and lower acetabular version were found in adolescents who sustained low-energy, sports-related posterior hip dislocations.

Femoral Deformity May Be More Predictive of Hip Range of Motion Than Severity of Acetabular Disease in Patients With Acetabular Dysplasia: An Analysis of the ANCHOR Cohort

BACKGROUND

It is generally believed that acetabular dysplasia (AD) is associated with increased hip range of motion (ROM). The purpose of this study was to investigate the associations between dysplasia severity and hip ROM in a large multicenter cohort.

METHODS

A prospective registry of patients undergoing periacetabular osteotomy for symptomatic AD by 1 of 13 surgeons was used to analyze 1,051 patients (mean age, 26 ± 10 years). Multivariable linear regression modeling was used to investigate for associations between dysplasia severity (severe, <5°; moderate, 5° to 15°; mild, >15°), α angle, and hip ROM.

RESULTS

When controlling for age, sex, body mass index, and α angle, only internal (α = 1.94; P = 0.005) and external (α = -2.63; P < 0.001) rotation in extension were significantly different between groups with increasing dysplasia severity. Alpha angle was greater for those with severe AD compared with subjects with mild disease (60° ± 16° versus 57° ± 15°; P = 0.038). Alpha angle was also significantly correlated with rotational ROM parameters (internal and external rotation in flexion and extension) (Pearson r, range: -0.077 to -0.216; P < 0.05 for all), but not with linear motion.

CONCLUSIONS

Internal rotation in extension was directly associated with dysplasia severity, whereas external rotation in extension was inversely associated. Furthermore, α angle was greater with increasing dysplasia severity and predictive of rotational ROM parameters. Taken together, these data suggest that femoral-sided deformity, including α angle and possibly femoral version, may be responsible for differences in ROM based on dysplasia severity.

LEVEL OF EVIDENCE

Level III, Prognostic.

Femoroacetabular impingement in children and adolescents

PURPOSE OF REVIEW

The present review discusses the etiology, clinical presentation, and management of femoroacetabular impingement (FAI) in the pediatric population, including etiologic and diagnostic controversies, management options, and outcomes.

RECENT FINDINGS

New evidence demonstrates conflicting results regarding how and when primary FAI develops in relation to skeletal maturity. Recent studies also discuss the effects of sex, race, and sports on FAI development and radiographic considerations in the pediatric population. Recent literature demonstrates good to excellent outcomes in the operative management of FAI in children and adolescents.

SUMMARY

FAI is a source of pediatric hip pain and can occur primarily or secondarily. It is characterized by anterior hip pain, made worse with flexion activities, decreased hip internal rotation, and a positive impingement sign. Pathologic values for radiographic measures of FAI are not clearly defined in the pediatric population. As FAI is a risk factor for osteoarthritis, early intervention in specific patients may be indicated. Hip arthroscopy, surgical hip dislocation, or combined mini-open and arthroscopic approaches are utilized, with good to excellent short, and mid-term functional results. Further study is required in the pediatric population to identify potential preventive strategies, to delineate the pathologic radiographic values of FAI, to define specific indications for operative management, and to examine long-term outcomes to determine optimal management.