Age- and Sex-Specific Morphologic Variations of Capital Femoral Epiphysis Growth in Children and Adolescents Without Hip Disorders

Three-dimensional analysis of age and sex differences in femoral head asphericity in asymptomatic hips in the United States

BACKGROUND

The sphericity of the femoral head is a metric used to evaluate hip pathologies and is associated with the development of osteoarthritis and femoral-acetabular impingement.

AIM

To analyze the three-dimensional asphericity of the femoral head of asymptomatic pediatric hips. We hypothesized that femoral head asphericity will vary significantly between male and female pediatric hips and increase with age in both sexes.

METHODS

Computed tomography scans were obtained on 158 children and adolescents from a single institution in the United States (8-18 years; 50% male) without hip pain. Proximal femoral measurements including the femoral head diameter, femoral head volume, residual volume, asphericity index, and local diameter difference were used to evaluate femoral head sphericity.

RESULTS

In both sexes, the residual volume increased by age (P < 0.05). Despite significantly smaller femoral head size in older ages (> 13 years) in females, there were no sex-differences in residual volume and aspherity index. There were no age-related changes in mean diameter difference in both sexes (P = 0.07) with no significant sex-differences across different age groups (P = 0.06). In contrast, there were significant increases in local aspherity (maximum diameter difference) across whole surface of the femoral head and all quadrants except the inferior regions in males (P = 0.03). There were no sex-differences in maximum diameter difference at any regions and age group (P > 0.05). Increased alpha angle was only correlated to increased mean diameter difference across overall surface of the femoral head (P = 0.024).

CONCLUSION

There is a substantial localized asphericity in asymptomatic hips which increases with age in. While 2D measured alpha angle can capture overall asphericity of the femoral head, it may not be sensitive enough to represent regional asphericity patterns.

Association of Idiopathic Cam Morphology With Femoral and Acetabular Version: Analysis of 986 Cadaveric Hips

Background

Studies have correlated symptomatic femoroacetabular impingement (FAI) with femoral retroversion and cam lesions.

Purpose

To investigate any association between femoral and acetabular versions with cam deformity in a largely asymptomatic population.

Study Design

Descriptive laboratory study.

Methods

A total of 986 cadaveric hips were selected from a historical osteologic collection. Each hip was assessed to determine the femoral and acetabular versions, anterior offset, and alpha angle. Cam morphology was defined as an alpha angle >60°. Multiple regression analysis was performed to determine the relationship between age, femoral version, acetabular version, and either alpha angle or anterior femoral offset.

Results

The mean alpha angle and anterior offset for the sample population were 48.1°± 10.4° and 0.77 ± 0.17 cm, respectively, with cam morphology in 149 of the 986 (15.1%) specimens. No significant difference was observed between hips with and without cam morphology with respect to the femoral (10.8°± 10° vs 10.3°± 9.6°; P = .58) or acetabular versions (17.4°± 6° vs 18.2°± 6.3°; P = .14). Multiple regression analysis did not demonstrate an association between the femoral or acetabular versions and the alpha angle, and it showed a small association between the increasing femoral and acetabular versions and a decreased anterior femoral offset (both P < .01).

Conclusion

In a large random sample of cadaveric hips, cam morphology was not associated with femoral or acetabular retroversion. Combined with the existing literature, these findings suggest that retroversion is not associated with cam development.

Clinical Relevance

This study provides insight into the development of cam morphology, which may eventually aid in the evaluation and treatment of FAI.

Idiopathic Slipped Capital Femoral Epiphysis: Demographic Differences and Similarities between Stable, Unstable, and Valgus Types

Idiopathic slipped capital femoral epiphysis (SCFE) is a known disorder in pre/adolescent children with vague hip/knee pain. We wished to study the demographic differences between stable varus, unstable varus, and valgus idiopathic SCFEs using a retrospective review over a 10-year period of SCFE children seen at a tertiary children's hospital. Standard demographic data was collected, and radiographs were measured to determine the Southwick angle and status of the tri-radiate cartilage. There were 190 patients; 138 had stable varus SCFEs, 45 unstable varus SCFEs, and 7 valgus SCFEs. All unstable SCFEs were varus, and all valgus SCFEs were stable. There were significant differences between the three groups by age at diagnosis, sex, race, SCFE severity, weight percentile, and duration of symptoms. The average age at diagnosis was 11.0 ± 1.2, 11.8 ± 1.8, and 12.3 ± 1.7 years for the valgus, unstable varus, and stable varus groups (p = 0.019), and similarly, SCFE severity was 25° ± 15°, 48° ± 18°, and 35° ± 19° (p = 0.0002) for the three same groups. Patients with valgus SCFEs were mostly female (86%) compared to the stable varus (39.9%) and unstable (47%) groups (p = 0.05) and mostly non-White (86%) (0.011). The duration of symptoms was 4.1 ± 4.1, 2.3 ± 5.0, and 4.5 ± 5.0 months for the valgus, unstable varus, and stable varus groups (p = 0.00005). These three types of idiopathic SCFEs demonstrated differences by age at diagnosis, sex, race, weight percentile, and duration of symptoms.

Effects of joint loading on the development of capital femoral epiphysis morphology

INTRODUCTION

The deleterious influence of increased mechanical forces on capital femoral epiphysis development is well established; however, the growth of the physis in the absence of such forces remains unclear. The hips of non-ambulatory cerebral palsy (CP) patients provide a weight-restricted (partial weightbearing) model which can elucidate the influence of decreased mechanical forces on the development of physis morphology, including features related to development of slipped capital femoral epiphysis (SCFE). Here we used 3D image analysis to compare the physis morphology of children with non-ambulatory CP, as a model for abnormal hip loading, with age-matched native hips.

MATERIALS AND METHODS

CT images of 98 non-ambulatory CP hips (8-15 years) and 80 age-matched native control hips were used to measure height, width, and length of the tubercle, depth, width, and length of the metaphyseal fossa, and cupping height across different epiphyseal regions. The impact of age on morphology was assessed using Pearson correlations. Mixed linear model was used to compare the quantified morphological features between partial weightbearing hips and full weightbearing controls.

RESULTS

In partial weightbearing hips, tubercle height and length along with fossa depth and length significantly decreased with age, while peripheral cupping height increased with age (r > 0.2, P < 0.04). Compared to normally loaded (full weightbearing) hips and across all age groups, partially weightbearing hips' epiphyseal tubercle height and length were smaller (P < .05), metaphyseal fossa depth was larger (P < .01), and posterior, inferior, and anterior peripheral cupping heights were smaller (P < .01).

CONCLUSIONS

Smaller epiphyseal tubercle and peripheral cupping with greater metaphyseal fossa size in partial weightbearing hips suggests that the growing capital femoral epiphysis requires mechanical stimulus to adequately develop epiphyseal stabilizers. Deposit low prevalence and relevance of SCFE in CP, these findings highlight both the role of normal joint loading in proper physis development and how chronic abnormal loading may contribute to various pathomorphological changes of the proximal femur (i.e., capital femoral epiphysis).

Smaller epiphyseal tubercle in hips with slipped capital femoral epiphysis compared to the uninvolved contralateral hip

Recent investigations suggest that physeal morphologic features have a major role in the capital femoral epiphysis stability and slipped capital femoral epiphysis (SCFE) pathology, with a smaller epiphyseal tubercle and larger peripheral cupping of the femoral epiphysis being present in hips with progressive SCFE compared to healthy controls. Yet, little is known on the causal versus remodeling nature of these associations. This study aimed to use preoperative magnetic resonance imaging (MRI) of patients with unilateral SCFE to perform a comparison of the morphology of the epiphyseal tubercle, metaphyseal fossa, and peripheral cupping in hips with SCFE versus the contralateral uninvolved hips. Preoperative MRIs from 22 unilateral SCFE patients were used to quantify the morphological features of the epiphyseal tubercle (height, width, and length), metaphyseal fossa (depth, width, and length), and peripheral cupping height in three dimension. The quantified anatomical features were compared between hips with SCFE and the contralateral uninvolved side across the whole cohort and within SCFE severity subgroups using paired t-test. We found significantly smaller epiphyseal tubercle heights (p < 0.001) across all severities of SCFE when compared to their uninvolved contralateral side. There was a marginally smaller metaphyseal fossa length (p = 0.05) in SCFE hips compared to their contralateral uninvolved hips, with mild SCFE hips specifically having smaller fossa and epiphyseal lengths (p < 0.05) than their contralateral uninvolved side. There were no side-to-side differences in any other features of the epiphyseal tubercle, metaphyseal fossa and peripheral cupping across all severities (p > 0.05). These findings suggest a potential causal role of epiphyseal tubercle in SCFE pathogenesis.

Femoroacetabular impingement in ancient Nubia 1400-656 BC

INTRODUCTION

There is significant recent interest in femoroacetabular impingement (FAI) in orthopaedics. The etiology of the cam deformity is unknown but has been hypothesized to be due to stresses from sporting activities in our modern society. Few archeological studies exist of femora and FAI. This study reviewed proximal femoral anatomy in a skeletal collection from the ancient Nile valley archeological site at Tombos 1400-656 BC.

METHODS

Digital photographs of the femora were used to obtain angular measurements of the apparent neck shaft, true neck shaft, version, inclination, and α and β angles of Nötzli. All photographs were reviewed by two orthopaedic surgeons for cam and pincer lesions. Sex and age of the specimens was determined when possible. A cam lesion was defined as any femur demonstrating an α angle > 50° or when a cam deformity was seen on visual inspection by both orthopaedic surgeons. Pincer lesions were identified upon visual inspection by both orthopaedic surgeons, when the femoral neck demonstrated impaction lesions, as pelvis radiographs could not be obtained.

RESULTS

There were 126 unique femora; 69 female and 57 male. Age estimates were possible in 100 and was 15-24 years in 14, 25-34 years in 33, 35-49 years in 28, 50-69 years in 17, and ≥ 70 years in 8. There were nine femora (seven individuals) with cam lesions (7%) and five femora (four individuals) with pincer lesions (4%). One demonstrated a combined lesion.

CONCLUSION

FAI existed in ancient Nile valley inhabitants and is thus not only a product of modern day life style athletics. This contrasts with Native Americans living in Ohio 700-1000 AD where no FAI was identified. This difference is likely due to combinations of different types of activity, diet, and genetics. Further research of ancient populations is needed to further answer this question.

LEVEL OF EVIDENCE

IV-cohort study.

Slipped Capital Femoral Epiphysis Associated With Athletic Activity

BACKGROUND

Little data exist regarding the association of slipped capital femoral epiphysis (SCFE) and sporting activities.

HYPOTHESIS

There is no association between SCFE and sporting activities.

STUDY DESIGN

Retrospective review of all SCFE cases at our institution from 2010 through March 2021.

LEVEL OF EVIDENCE

Level 3.

METHODS

All patients with idiopathic SCFE were reviewed looking for the presence/absence of sporting activities and symptom onset. Also collected were the age, symptom duration, and weight/height of the patient, sex, race, and stable/unstable nature of the SCFE. The severity of the SCFE was measured using the lateral epiphyseal-shaft angle.

RESULTS

There were 193 children (110 boys, 83 girls) with idiopathic SCFEs. The SCFE was stable in 147, unstable in 45, and unknown in 1. The average age was 12.1 ± 1.8 years, average SCFE angle 38° ± 20° and symptom duration 4.0 ± 5.1 months. An association with a sporting activity was present in 64 (33%). The sporting activity was basketball (18), football (11), baseball/softball (10), and others (23). Football, basketball, and soccer predominated in boys, baseball and running sports were equal between boys and girls, and cheerleading/gymnastics/dancing predominated in girls. Differences showed that those involved in sports had a slightly lower body mass index (BMI) (88th percentile vs 95th percentile, P = 0.00). There were no differences between those involved and those not those involved in sporting activities for symptom duration, SCFE severity, sex, race, or stable/unstable SCFE type.

CONCLUSION

Sporting activities are associated with the onset of symptoms in 1 of 3 of patients with SCFE, refuting the null hypothesis.

CLINICAL RELEVANCE

A high level of suspicion for SCFE should be given when any peripubertal athlete presents with hip or knee pain regardless of BMI/obesity status, and appropriate imaging performed.

Does the Capital Femoral Physis Bony MorphologyDiffer in Children with Symptomatic Cam-type Femoroacetabular Impingement

BACKGROUND

The epiphyseal tubercle, the corresponding metaphyseal fossa, and peripheral cupping are key stabilizers of the femoral head-neck junction. Abnormal development of these features in the setting of supraphysiologic physeal stress under high forces (for example, forces that occur during sports activity) may result in a cam morphology. Although most previous studies on cam-type femoroacetabular impingement (FAI) have mainly focused on overgrowth of the peripheral cupping, little is known about detailed morphologic changes of the epiphyseal and metaphyseal bony surfaces in patients with cam morphology.

QUESTIONS/PURPOSES

(1) Does the CT-based bony morphology of the peripheral epiphyseal cupping differ between patients with a cam-type morphology and asymptomatic controls (individuals who did not have hip pain)? (2) Does the CT-based bony morphology of the epiphyseal tubercle differ between patients with a cam-type morphology and asymptomatic controls? (3) Does the CT-based bony morphology of the metaphyseal fossa differ between patients with a cam-type morphology and asymptomatic controls?

METHODS

After obtaining institutional review board approval for this study, we retrospectively searched our institutional database for patients aged 8 to 15 years with a diagnosis of an idiopathic cam morphology who underwent a preoperative CT evaluation of the affected hip between 2005 and 2018 (n = 152). We excluded 96 patients with unavailable CT scans and 40 patients with prior joint diseases other than cam-type FAI. Our search resulted in 16 patients, including nine males. Six of 16 patients had a diagnosis of bilateral FAI, for whom we randomly selected one side for the analysis. Three-dimensional (3-D) models of the proximal femur were generated to quantify the size of the peripheral cupping (peripheral growth of the epiphysis around the metaphysis), epiphyseal tubercle (a beak-like prominence in the posterosuperior aspect of the epiphysis), and metaphyseal fossa (a groove on the metaphyseal surface corresponding to the epiphyseal tubercle). A general linear model was used to compare the quantified anatomic features between the FAI cohort and 80 asymptomatic hips (aged 8 to 15 years; 50% male) after adjusting for age and sex. A secondary analysis using the Wilcoxon matched-pairs signed rank test was performed to assess side-to-side differences in quantified morphological features in 10 patients with unilateral FAI.

RESULTS

After adjusting for age and sex, we found that patients with FAI had larger peripheral cupping in the anterior, posterior, superior, and inferior regions than control patients who did not have hip symptoms or radiographic signs of FAI (by 1.3- to 1.7-fold; p < 0.01 for all comparisons). The epiphyseal tubercle height and length were smaller in patients with FAI than in controls (by 0.3- to 0.6-fold; p < 0.02 for all comparisons). There was no difference in tubercle width between the groups. Metaphyseal fossa depth, width, and length were larger in patients with FAI than in controls (by 1.8- to 2.3-fold; p < 0.001 for all comparisons). For patients with unilateral FAI, we saw similar peripheral cupping but smaller epiphyseal tubercle (height and length) along with larger metaphyseal fossa (depth) in the FAI side compared with the uninvolved contralateral side.

CONCLUSION

Consistent with prior studies, we observed more peripheral cupping in patients with cam-type FAI than control patients without hip symptoms or radiographic signs of FAI. Interestingly, the epiphyseal tubercle height and length were smaller and the metaphyseal fossa was larger in hips with cam-type FAI, suggesting varying inner bone surface morphology of the growth plate. The docking mechanism between the epiphyseal tubercle and the metaphyseal fossa is important for epiphyseal stability, particularly at early ages when the peripheral cupping is not fully developed. An underdeveloped tubercle and a large fossa could be associated with a reduction in stability, while excessive peripheral cupping growth would be a factor related to improved physeal stability. This is further supported by observed side-to-side differences in tubercle and fossa morphology in patients with unilateral FAI. Further longitudinal studies would be worthwhile to study the causality and compensatory mechanisms related to epiphyseal and metaphyseal bony morphology in pathogenesis cam-type FAI. Such information will lay the foundation for developing imaging biomarkers to predict the risk of FAI or to monitor its progress, which are critical in clinical care planning.

LEVEL OF EVIDENCE

Level III, prognostic study.

What Is the Association Among Epiphyseal Rotation, Translation, and the Morphology of the Epiphysis and Metaphysis in Slipped Capital Femoral Epiphysis?

BACKGROUND

Contemporary studies have described the rotational mechanism in patients with slipped capital femoral epiphysis (SCFE). However, there have been limited patient imaging data and information to quantify the rotation. Determining whether the epiphysis is rotated or translated and measuring the epiphyseal displacement in all planes may facilitate planning for surgical reorientation of the epiphysis.

QUESTIONS/PURPOSES

(1) How does epiphyseal rotation and translation differ among mild, moderate, and severe SCFE? (2) Is there a correlation between epiphyseal rotation and posterior or inferior translation in hips with SCFE? (3) Does epiphyseal rotation correlate with the size of the epiphyseal tubercle or the metaphyseal fossa or with epiphyseal cupping?

METHODS

We identified 51 patients (55% boys [28 of 51]; mean age 13 ± 2 years) with stable SCFE who underwent preoperative CT of the pelvis before definitive treatment. Stable SCFE was selected because unstable SCFE would not allow for accurate assessment of rotation given the complete displacement of the femoral head in relation to the neck. The epiphysis and metaphysis were segmented and reconstructed in three-dimensions (3-D) for analysis in this retrospective study. One observer (a second-year orthopaedic resident) performed the image segmentation and measurements of epiphyseal rotation and translation relative to the metaphysis, epiphyseal tubercle, metaphyseal fossa, and the epiphysis extension onto the metaphysis defined as epiphyseal cupping. To assess the reliability of the measurements, a randomly selected subset of 15 hips was remeasured by the primary examiner and by the two experienced examiners independently. We used ANOVA to calculate the intraclass and interclass correlation coefficients (ICCs) for intraobserver and interobserver reliability of rotational and translational measurements. The ICC values for rotation were 0.91 (intraobserver) and 0.87 (interobserver) and the ICC values for translation were 0.92 (intraobserver) and 0.87 (intraobserver). After adjusting for age and sex, we compared the degree of rotation and translation among mild, moderate, and severe SCFE. Pearson correlation analysis was used to assess the associations between rotation and translation and between rotation and tubercle, fossa, and cupping measurements.

RESULTS

Hips with severe SCFE had greater epiphyseal rotation than hips with mild SCFE (adjusted mean difference 21° [95% CI 11° to 31°]; p < 0.001) and hips with moderate SCFE (adjusted mean difference 13° [95% CI 3° to 23°]; p = 0.007). Epiphyseal rotation was positively correlated with posterior translation (r = 0.33 [95% CI 0.06 to 0.55]; p = 0.02) but not with inferior translation (r = 0.16 [95% CI -0.12 to 0.41]; p = 0.27). There was a positive correlation between rotation and metaphyseal fossa depth (r = 0.35 [95% CI 0.08 to 0.57]; p = 0.01), width (r = 0.41 [95% CI 0.15 to 0.61]; p = 0.003), and length (r = 0.56 [95% CI 0.38 to 0.75]; p < 0.001).

CONCLUSION

This study supports a rotational mechanism for the pathogenesis of SCFE. Increased rotation is associated with more severe slips, posterior epiphyseal translation, and enlargement of the metaphyseal fossa. The rotational nature of the deformity, with the center of rotation at the epiphyseal tubercle, should be considered when planning in situ fixation and realignment surgery. Avoiding placing a screw through the epiphyseal tubercle-the pivot point of rotation- may increase the stability of the epiphysis. The realignment of the epiphysis through rotation rather than simple translation is recommended during the open subcapital realignment procedure. Enlargement of the metaphyseal fossa disrupts the interlocking mechanism with the tubercle and increases epiphyseal instability. Even in the setting of a stable SCFE, an increased fossa enlargement may indicate using two screws instead of one screw, given the severity of epiphyseal rotation and the risk of instability. Further biomechanical studies should investigate the number and position of in situ fixation screws in relation to the epiphyseal tubercle and metaphyseal fossa.

LEVEL OF EVIDENCE

Level III, prognostic study.

The point of epiphyseal penetration affects rotational stability of screw fixation in slipped capital femoral epiphysis: A biomechanical study

The epiphyseal tubercle, a posterosuperior projection of the epiphysis into the metaphysis, serves as the axis of rotation in slipped capital femoral epiphysis (SCFE) and a source of physeal stability. We hypothesized that in a biomechanical model of single screw fixation of stable SCFE, a screw passing through the epiphyseal tubercle (the axis of rotation) would confer less rotational stability than a centrally placed screw. Three femurs were selected from a sample population of 8- to 15-year-old healthy hips to represent three stages of maturation: a "young" femur with a prominent epiphyseal tubercle and decreased epiphyseal cupping around the metaphysis, a "median" femur with a subsiding tubercle, and a "mature" femur with a subsided epiphyseal tubercle and increased peripheral epiphyseal cupping. Specimens were three-dimensional printed with one of two screw trajectories: passing centrally in the epiphysis or directly through the epiphyseal tubercle. Resistance to rotational displacement was measured through stiffness and maximum torque over 30° degrees of displacement. In the "young" model, epiphyseal tubercle screw position conferred less rotational stiffness and required less maximum torque during rotational displacement when compared to a centrally placed screw (P < .001). In the "median" and "mature" models where the tubercle has subsided and is replaced by peripheral epiphyseal cupping, screw position through the tubercle was associated with equal or greater rotational stiffness and maximum torque during displacement as a centrally placed screw.

Age- and sex-specific morphologic changes in the metaphyseal fossa adjacent to epiphyseal tubercle in children and adolescents without hip disorders

The epiphyseal tubercle plays an important role in epiphyseal stabilization. While the majority of studies have focused on tubercle morphology, there is a paucity of information on the morphological features of the metaphyseal fossa, where the tubercle sits on the metaphysis. The goal of this study was to determine the developmental changes in the capital femoral metaphyseal fossa. Computed tomography of the pelvis from 80 children and adolescents 8-15 years old were used to create three-dimensional models of the proximal femur. Depth, width, length, and surface area of the metaphyseal fossa were measured and the impact of age and sex on fossa morphology was assessed using the linear regression and two-way analysis of variance, respectively. The metaphyseal fossa was located in the posterosuperior quadrant of the metaphysis without any variations in the location with increasing age (P > .1). However, with increasing age, there was a reduction in all metaphyseal fossa measurements including the depth, length, width, and surface area (P < .01). No significant differences were noted for the metaphyseal fossa measurements between males and females (P > .1). The metaphyseal fossa reduces in size from 8 to 15 years of age in a similar fashion in males and females. As the metaphyseal fossa adjacent to the tubercle matches the area where a focal radiolucency has been observed in early slipped capital femoral epiphysis (SCFE), further studies should clarify the mechanisms by which the interlocking interaction of the epiphyseal tubercle and its fossa contributes to or is affected by SCFE.

Capital Femoral Epiphyseal Cupping and Extension May Be Protective in Slipped Capital Femoral Epiphysis: A Dual-center Matching Cohort Study

BACKGROUND

Peripheral cupping of the capital femoral epiphysis over the metaphysis has been reported as a precursor of cam morphology, but may also confer stability of the epiphysis protecting it from slipped capital femoral epiphysis (SCFE). The purpose of this study was to investigate the relationship between a novel morphologic parameter of inherent physeal stability, epiphyseal cupping, and the development of SCFE in a dual-center matched-control cohort study.

METHODS

We performed a dual-center age-matched and sex-matched cohort study comparing 279 subjects with unilateral SCFE and 279 radiographically normal controls from 2 tertiary children's hospitals. All SCFE patients had at least 18 months of radiographic follow-up for contralateral slip surveillance. Anteroposterior and frog lateral pelvis radiographs were utilized to measure the epiphyseal cupping ratio and the current standard measure of inherent physeal stability, the epiphyseal extension ratio.

RESULTS

Control hips were found to have greater epiphyseal cupping than the contralateral uninvolved hip of SCFE subjects both superiorly (0.28±0.08 vs. 0.24±0.06; P<0.001) and anteriorly (0.22±0.07 vs. 0.19±0.06; P<0.001). The 58/279 (21%) subjects who went on to develop contralateral slip had decreased epiphyseal cupping superiorly (0.25±0.07 vs. 0.23±0.05; P=0.03) and anteriorly (0.20±0.06 vs. 0.17±0.04; P<0.001). When we compared controls with hips that did not progress to contralateral slip and hips that further developed a contralateral SCFE, 1-way ANOVA demonstrated a stepwise decrease in epiphyseal cupping and epiphyseal extension ratio in the anterior and superior planes from control hips to contralateral hips without subsequent slip to contralateral hips that developed a SCFE (P<0.01 for each).

CONCLUSIONS

This study provides further evidence that epiphyseal cupping around the metaphysis is associated with decreased likelihood of SCFE and may reflect increased inherent physeal stability. Epiphyseal cupping may represent an adaptive mechanism to stabilize the epiphysis during adolescence at the long-term cost of the eventual development of associated cam-femoroacetabular impingement deformity.

LEVELS OF EVIDENCE

Level III-prognostic Study.

Increased body mass index percentile is associated with decreased epiphyseal tubercle size in asymptomatic children and adolescents with healthy hips

PURPOSE

To investigate whether body mass index (BMI) percentile impacts the morphology of the capital femoral epiphysis in children and adolescents without hip disorders.

METHODS

We assessed 68 subjects with healthy hips who underwent a pelvic CT for evaluation of appendicitis. There were 32 male patients (47%) and the mean age was 11.6 years (sd 2.3). The BMI (k/m²) was calculated for sex- and age-related percentiles according to the Centers for Disease Control and Prevention growth charts. CT images were segmented, and the epiphysis and metaphysis were reformatted using 3D software. We measured the epiphyseal tubercle (height, width and length), the metaphyseal fossa (depth, width and length) and the peripheral cupping of the epiphysis. All measurements were normalized to the diameter of the epiphysis. Pearson's correlation analysis was used to assess the correlations between the variables measured and BMI percentile adjusted for age.

RESULTS

Following adjustment to age, increased BMI correlated to decreased tubercle height (r =-0.34; 95% confidence interval (CI) -0.53 to -0.11; p = 0.005), decreased tubercle length (r = -0.32; 95%CI -0.52 to -0.09; p = 0.008) and decreased tubercle width (r = -0.3; 95% CI -0.5 to -0.07; p = 0.01). There was no correlation between BMI and metaphyseal fossa and epiphyseal cupping measurements.

CONCLUSION

The association between increased BMI percentile and decreased epiphyseal tubercle size, without changes of the metaphyseal fossa and peripheral cupping suggests another morphological change of the femur that may be associated with decreased growth plate resistance to shear stress. Further study is necessary to investigate whether the epiphyseal tubercle size plays a role in the pathogenesis of slipped capital femoral epiphysis in obese children and adolescents.

LEVEL OF EVIDENCE

Level IV.

The metaphyseal fossa surrounding the epiphyseal tubercle is larger in hips with moderate and severe slipped capital femoral epiphysis than normal hips

PURPOSE

To compare the 3D morphology of the metaphyseal fossa among mild, moderate and severe stable slipped capital femoral epiphysis (SCFE) and normal hips.

METHODS

We identified pelvic CT of 51 patients (55% male; mean 12.7 years (sd 1.9; 8-15)) with stable SCFE. In all, 16 of 51 hips (31%) had mild, 14 (27%) moderate and 21 (41%) severe SCFE. A total of 80 patients (50% male; mean age 11.5 years (sd 2.3; 8 to 15)) with normal hips who underwent pelvic CT due to abdominal pain made up the control cohort. CT scans were segmented, and the femur was reformatted using 3D software. We measured the metaphyseal fossa depth, width, length and surface area after the epiphysis was subtracted from the metaphysis in the 3D model.

RESULTS

The metaphyseal fossa width was significantly larger in severe (adjusted difference: 6.9%; 95% confidence interval (CI) 2.1 to 11.8; p = 0.001), moderate (6.5%; 95% CI 0.8 to 12.2; p = 0.02) and mild SCFE (6.2%; 95% CI 0.8 to 11.6; p = 0.01), in comparison with normal hips. Severe SCFE showed larger fossa length compared with mild SCFE (6.8%; 95% CI 0.6 to 13.0; p = 0.02) and normal hips (6.0%; 95% CI 1.4 to 10.6; p = 0.004). The fossa surface area was larger in severe (3.5%; 95% CI 1.3 to 5.7; p < 0.001) and moderate SCFE (2.7%; 95% CI 0.1 to 5.2; p = 0.03) when compared with normal hips. There were no differences in fossa depth between SCFE and normal hips.

CONCLUSION

The metaphyseal fossa is wider and more extensive but not deeper in hips with moderate and severe SCFE in comparison with normal hips. Although hips with severe SCFE had larger length and surface area than mild SCFE hips, further research is needed to clarify whether enlargement of the metaphyseal fossa is a consequence of slip progression.

LEVEL OF EVIDENCE

III.

What Is the Accuracy and Reliability of the Peritubercle Lucency Sign on Radiographs for Early Diagnosis of Slipped Capital Femoral Epiphysis Compared With MRI as the Gold Standard?

BACKGROUND

The diagnosis of slipped capital femoral epiphysis (SCFE) often is delayed. Although lack of clinical suspicion is the main cause of delayed diagnosis, typical radiographic changes may not be present during the initial phases of SCFE. The peritubercle lucency sign for follow-up of the contralateral hip in patients with unilateral SCFE may be beneficial in assisting the early diagnosis. However, the accuracy and reliability of this sign in patients with SCFE is unknown.

QUESTIONS/PURPOSES

(1) What is the accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the peritubercle lucency sign on radiographs for the early diagnosis of SCFE compared with MRI as the gold standard? (2) What are the interobserver and intraobserver reliabilities of the peritubercle lucency sign on radiographs?

METHODS

Between 2000 and 2017, 71 patients underwent MRI for an evaluation of pre-slip or a minimally displaced SCFE. Sixty percent of hips (43 of 71) had confirmed SCFE or pre-slip based on the presence of hip pain and MRI changes, and these patients underwent in situ pinning. Three independent experienced observers reviewed MR images of the 71 hips and agreed on the presence of a juxtaphyseal bright-fluid signal suggesting bone marrow edema in these 43 hips with SCFE, and absence MRI changes in the remaining 28 hips. The same three experienced observers and two inexperienced observers, including a general radiologist and an orthopaedic surgery resident, blindly assessed the radiographs for the presence or absence of the peritubercle lucency sign, without information about the diagnosis. Diagnostic accuracy measures including sensitivity, specificity, PPV, and NPV were evaluated. Intraobserver and interobserver agreements were calculated using kappa statistics.

RESULTS

The overall accuracy of the peritubercle lucency sign on radiographs was 94% (95% CI 91 to 96), sensitivity was 97% (95% CI 95 to 99), specificity was 89% (95% CI 90 to 96), PPV was 93% (95% CI 90 to 96), and NPV was 95% (95% CI 92 to 99). All accuracy parameters were greater than 85% for the five observers, regardless of experience level. Intraobserver agreement was perfect (kappa 1.0), and interobserver agreement was excellent for the peritubercle lucency sign on radiographs across the five observers (kappa 0.81 [95% CI 0.73 to 0.88]). The reliability was excellent for experienced observers (kappa 0.88 [95% CI 0.74 to 1.00]) and substantial for inexperienced observers (kappa 0.70 [95% CI 0.46 to 0.93]), although no difference was found with the numbers available (p = 0.18).

CONCLUSIONS

The peritubercle lucency sign on radiographs is accurate and reliable for the early diagnosis of SCFE compared with MRI as the gold standard. Improving the early diagnosis of SCFE may be possible with increased awareness, high clinical suspicion, and a scrutinized evaluation of radiographs including an assessment of the peritubercle lucency sign.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Smaller Epiphyseal Tubercle and Larger Peripheral Cupping in Slipped Capital Femoral Epiphysis Compared with Healthy Hips: A 3-Dimensional Computed Tomography Study

BACKGROUND

The inner surface of the capital femoral epiphysis is important for growth plate stability. However, abnormalities of epiphyseal morphology associated with the pathogenesis of slipped capital femoral epiphysis (SCFE) remain poorly understood. This study compares the 3-dimensional anatomy of the epiphyseal tubercle and peripheral cupping in hips with SCFE and normal hips.

METHODS

We created 3-dimensional models of the capital femoral epiphysis with use of computed tomography (CT) imaging from 51 patients with SCFE and 80 subjects without hip symptoms who underwent CT because of abdominal pain. The height, width, and length of the epiphyseal tubercle and the peripheral cupping were measured and normalized by the epiphyseal diameter and presented as a percentage. We used analysis of variance for the comparison of the measurements between SCFE and control hips after adjusting for age and sex.

RESULTS

Compared with normal hips, hips with mild SCFE had smaller mean epiphyseal tubercle height (0.9% ± 0.9% compared with 4.4% ± 0.4%; p = 0.006) and length (32.3% ± 1.8% compared with 43.7% ± 0.8%; p < 0.001). The mean epiphyseal tubercle height was also smaller in hips with moderate (0.6% ± 0.9%; p = 0.004) and severe SCFE (0.3% ± 0.8%; p < 0.001) compared with normal hips. No differences were observed for measurements of epiphyseal tubercle height and length between SCFE subgroups. The mean peripheral cupping was larger in hips with mild (16.3% ± 1.0%; p < 0.001), moderate (16.4% ± 1.1%; p < 0.001), and severe SCFE (18.9% ± 0.9%; p < 0.001) overall and when assessed individually in all regions compared with normal hips (10.6% ± 0.5%).

CONCLUSIONS

Hips with SCFE have a smaller epiphyseal tubercle and larger peripheral cupping compared with healthy hips. A smaller epiphyseal tubercle may be a predisposing morphologic factor or a consequence of the increased shearing stress across the physis secondary to the slip. Increased peripheral growth may be an adaptive response to instability as other stabilizers (i.e., epiphyseal tubercle and anterior periosteum) become compromised with slip progression. Future studies are necessary to determine the biomechanical basis of our morphologic findings.

A Novel Classification System for Slipped Capital Femoral Epiphysis Based on the Radiographic Relationship of the Epiphyseal Tubercle and the Metaphyseal Socket

Recent studies have suggested that the epiphyseal tubercle serves as a fulcrum for rotation in slipped capital femoral epiphysis (SCFE). However, radiographic evidence of the rotational mechanism is limited. In this study, we describe a novel radiographic staging system for SCFE based on the anatomic relationship between the epiphyseal tubercle and the metaphyseal socket.

Methods

We reviewed the cases of 469 patients with SCFE who were treated at our institution between 2000 and 2017. SCFE was classified according to our proposed staging system using the preoperative lateral radiograph. Normal hips were considered to be Stage 0. In Stage 1, the tubercle is concentric within its metaphyseal socket, which is enlarged and may present peritubercle radiolucency. In Stage 2, there is evidence of eccentricity of the tubercle, which remains in contact with the posterior wall of the socket. In Stage 3, the tubercle and metaphyseal lucency reach the posterior cortex of the femoral neck. A complete dislodgment of the tubercle from the metaphysis is present in Stage 4. Intra- and interobserver agreement, and correlations between the staging system and the traditional classifications of severity, stability, and chronicity, were estimated.

Results

The distribution by stage was as follows: 2% of the hips were classified as Stage 0, 19% were Stage 1, 48% were Stage 2, 15% were Stage 3, and 16% were Stage 4. The staging system had excellent intraobserver (κ = 0.89 [95% confidence interval (CI) = 0.83 to 0.96]) and interobserver agreement (κ = 0.87 [95% CI = 0.72 to 1.00]). There was a high correlation between the staging system and SCFE severity as assessed by the Southwick angle (r = 0.77 [95% CI = 0.73 to 0.82]; p < 0.001). There was a moderate correlation between the staging system and the Loder classification of stability (r = 0.55 [95% CI = 0.48 to 0.62]; p < 0.001) and a negligible correlation with the classification of chronicity (r = 0.19 [95% CI = 0.10 to 0.28]; p < 0.001).

Conclusions

The proposed staging system for SCFE is highly reliable and correlates well with the severity of SCFE based on the degree of displacement, with moderate correlation shown for stability. This new staging system helps in understanding the rotational mechanism of SCFE, warranting further investigation to determine its clinical application.

Clinical Relevance

The novel classification has the potential for the identification of hips that demonstrate subtle SCFE or are at pre-slip stage, or those at risk for osteonecrosis of the femoral head, failure of fixation, or slip progression.

Relative contribution of epiphyseal tubercle and peripheral cupping to capital femoral epiphysis stability during daily activities

Epiphyseal tubercle and peripheral cupping can influence the development of slipped capital femoral epiphysis (SCFE) and Cam morphology. During normal skeletal growth, epiphyseal tubercle shrinks while the peripheral cupping grows. We hypothesized that epiphyseal tubercle act as the primary stabilizer of the head-neck junction at early stages and this role is gradually transferred to epiphyseal cupping as the tubercle shrinks and cupping grows. From a cohort of 80 boys and girls (8-15 years old) with normal hips, CT scans of 5 subjects corresponding to minimum, 25th percentile, median, 75th percentile and maximum relative tubercle and cupping height were used to develop 3D finite element models. In vivo measured hip loads were used to study load sharing between the tubercle and peripheral cupping under combined and uniaxial loads exerted on femoral head during a range of daily activities. Lower epiphyseal tubercle height, larger epiphyseal cupping height and bigger differences in tubercle and cupping heights were strongly associated with increased epiphyseal cupping to epiphyseal tubercle stress ratios (R²  > 0.7). We found lower peripheral cupping stresses relative to the tubercle (cupping to tubercle stress ratio <1) in hips with larger tubercle and smaller cupping. The relative decreases in tubercle size along with increased in peripheral cupping in our models gradually shifted the load distribution to higher stresses in the periphery compared to the epiphyseal tubercle area (cupping to tubercle stress ratio >1). Both tubercle and cupping play a substantial role in sharing the generated stresses across the head-neck junction under all tested loading conditions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1571-1579, 2019.