Body Mass Index Affects Proximal Femoral but Not Acetabular Morphology in Adolescents Without Hip Pathology.

BACKGROUND: Increased mechanical load secondary to a large body mass index (BMI) may influence bone remodeling. The purpose of this study was to investigate whether BMI is associated with the morphology of the proximal part of the femur and the acetabulum in a cohort of adolescents without a history of hip disorders. METHODS: We evaluated pelvic computed tomographic (CT) images in 128 adolescents with abdominal pain without a history of hip pathology. There were 44 male patients (34%) and the mean patient age (and standard deviation) was 15 ± 1.95 years. The alpha angle, head-neck offset, epiphysis tilt, epiphyseal angle, and epiphyseal extension were measured to assess femoral morphology. Measurements of acetabular morphology included lateral center-edge angle, acetabular Tönnis angle, and acetabular depth. BMI percentile, specific to age and sex according to Centers for Disease Control and Prevention growth charts, was recorded. RESULTS: BMI percentile was associated with all measurements of femoral morphology. Each 1-unit increase in BMI percentile was associated with a mean 0.15° increase in alpha angle (p < 0.001) and with a mean 0.03-mm decrease in femoral head-neck offset (p < 0.001). On average, a 1-unit increase in BMI percentile was associated with a 0.0006-unit decrease in epiphyseal extension (p = 0.03), a 0.10° increase in epiphyseal angle (p < 0.001), and a 0.06° decrease in tilt angle (p = 0.02; more posteriorly tilted epiphysis). There was no detected effect of BMI percentile on acetabular morphology including lateral center-edge angle (p = 0.33), Tönnis angle (p = 0.35), and acetabular depth (p = 0.88). CONCLUSIONS: Higher BMI percentile was associated with increased alpha angle, reduced head-neck offset and epiphyseal extension, and a more posteriorly tilted epiphysis with decreased tilt angle and increased epiphyseal angle. This morphology resembles a mild slipped capital femoral epiphysis deformity and may increase the shear stress across the growth plate, increasing the risk of slipped capital femoral epiphysis development in obese adolescents. BMI percentiles had no association with measurements of acetabular morphology. Further studies will help to clarify whether obese asymptomatic adolescents have higher prevalence of a subclinical slip deformity and whether this morphology increases the risk of slipped capital femoral epiphysis and femoroacetabular impingement development.

Acetabular Version Increases After Closure of the Triradiate Cartilage Complex.

BACKGROUND: Although the etiology of primary femoroacetabular impingement (FAI) is considered developmental, the underlying pathogenic mechanisms remain poorly understood. In particular, research identifying etiologic factors associated with pincer FAI is limited. Knowledge of the physiologic growth patterns of the acetabulum during skeletal maturation might allow conclusions on deviations from normal development that could contribute to pincer-related pathomorphologies. QUESTIONS/PURPOSES: In a population of healthy children, we asked if there were any differences related to skeletal maturation with regard to (1) acetabular version; (2) acetabular depth/width ratio; and (3) femoral head coverage in the same children as assessed by MRIs obtained 1 year apart. METHODS: We prospectively compared 129 MRIs in 65 asymptomatic volunteers without a known hip disorder from a mixed primary/high school population (mean age, 12.7 years; range, 7-16 years). All participants underwent two MRI examinations separated by a minimum interval of 1 year. Based on the status of the triradiate cartilage complex (open versus closed [TCC]), all hips were allocated to the following groups: "open-open" = open TCC at both MRIs (n = 45 hips [22 bilateral]); "open-closed" = open TCC at initial and closed TCC at followup MRI (n = 26 hips [13 bilateral]); and "closed-closed" group = closed TCC at both MRIs (n = 58 hips [29 bilateral]). We assessed acetabular version in the axial plane at five different locations (5, 10, 15, 20 mm below the acetabular dome and at the level of the femoral head) as well as three-dimensional (3-D) acetabular depth/width ratio and 3-D femoral head coverage on six radial MRI sequences oriented circumferentially around the femoral neck axis. Using analysis of variance for multigroup comparisons with Bonferroni adjustment for pairwise comparisons, we compared the results between the initial and followup MRI examinations and among the three groups. RESULTS: Acetabular version was increased in hips of the "open-closed" group at the followup MRI compared with the initial MRI at 5 mm (-6 ± 4.6 [95% confidence interval {CI}, -7.6 to -3.6] versus -1 ± 5.0 [95% CI, -3.3 to 0.7]; p < 0.001), 10 mm (0 ± 4.0 [95% CI, -1.6 to 2.1] versus 7 ± 4.6 [95% CI, 4.4-8.7]; p < 0.001), and 15 mm (8 ± 5.0 [95% CI, 6.1-10.2] versus 15 ± 4.6 [95% CI, 13.3-17.4]; p < 0.001) below the acetabular dome. Acetabular version did not change between the initial and followup MRI in the "open-open" and "closed-closed" groups. Independently of the groups, acetabular version was increased in all hips with a fused TCC compared with hips with an open TCC (mean difference measured at 5 mm below the acetabular dome at initial MRI examination: 2° ± 5.9° [95% CI, 0.2°-3.4°] versus -9° ± 4.4° [95% CI, -9.9° to -7.8°]; p < 0.001; at followup MRI examination: 1° ± 5.7° [95% CI, 0.1°-2.7°] versus -9° ± 3.8° [95% CI, -10° to -7.6°]; p < 0.001). Both acetabular depth/width ratio and femoral head coverage did not differ among the groups or between the initial and followup MRI examinations within each group. CONCLUSIONS: Although acetabular depth/width ratio and femoral head coverage remain relatively constant, acetabular version increases with advancing skeletal maturity. There seems to be a relatively narrow timeframe near physeal closure of the TCC within which acetabular orientation changes to more pronounced anteversion. Further studies with greater numbers and longer followup periods are required to support these findings and determine whether such version changes may contribute to pincer-type pathomorphologies. LEVEL OF EVIDENCE: Level II, prospective study.

Biochemical MRI predicts hip osteoarthritis in an experimental ovine femoroacetabular impingement model.

BACKGROUND: Cam-type femoroacetabular impingement (FAI) resulting from an abnormal nonspherical femoral head shape leads to chondrolabral damage and is considered a cause of early osteoarthritis. A previously developed experimental ovine FAI model induces a cam-type impingement that results in localized chondrolabral damage, replicating the patterns found in the human hip. Biochemical MRI modalities such as T2 and T2* may allow for evaluation of the cartilage biochemistry long before cartilage loss occurs and, for that reason, may be a worthwhile avenue of inquiry. QUESTIONS/PURPOSES: We asked: (1) Does the histological grading of degenerated cartilage correlate with T2 or T2* values in this ovine FAI model? (2) How accurately can zones of degenerated cartilage be predicted with T2 or T2* MRI in this model? METHODS: A cam-type FAI was induced in eight Swiss alpine sheep by performing a closing wedge intertrochanteric varus osteotomy. After ambulation of 10 to 14 weeks, the sheep were euthanized and a 3-T MRI of the hip was performed. T2 and T2* values were measured at six locations on the acetabulum and compared with the histological damage pattern using the Mankin score. This is an established histological scoring system to quantify cartilage degeneration. Both T2 and T2* values are determined by cartilage water content and its collagen fiber network. Of those, the T2* mapping is a more modern sequence with technical advantages (eg, shorter acquisition time). Correlation of the Mankin score and the T2 and T2* values, respectively, was evaluated using the Spearman's rank correlation coefficient. We used a hierarchical cluster analysis to calculate the positive and negative predictive values of T2 and T2* to predict advanced cartilage degeneration (Mankin ≥ 3). RESULTS: We found a negative correlation between the Mankin score and both the T2 (p < 0.001, r = -0.79) and T2* values (p < 0.001, r = -0.90). For the T2 MRI technique, we found a positive predictive value of 100% (95% confidence interval [CI], 79%-100%) and a negative predictive value of 84% (95% CI, 67%-95%). For the T2* technique, we found a positive predictive value of 100% (95% CI, 79%-100%) and a negative predictive value of 94% (95% CI, 79%-99%). CONCLUSIONS: T2 and T2* MRI modalities can reliably detect early cartilage degeneration in the experimental ovine FAI model. CLINICAL RELEVANCE: T2 and T2* MRI modalities have the potential to allow for monitoring the natural course of osteoarthrosis noninvasively and to evaluate the results of surgical treatments targeted to joint preservation.

Reference values for proximal femoral anatomy in adolescents based on sex, physis, and imaging plane.

BACKGROUND: Morphological alterations of the hip joint are important contributors to the development of osteoarthritis. While plane-specific variations in the shape of the proximal femur have been described, there are no defined reference standards for measurements in adolescent patients. PURPOSE: To evaluate hips in asymptomatic adolescent patients using radially reformatted multidetector computed tomography (MDCT) to define the morphological characteristics of the femoral head-neck (FHN) junction with respect to patient sex and physeal status, and to establish reference values for α angle, FHN offset, and epiphyseal extension (EE). STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 132 pelvic MDCT scans in adolescent patients with abdominal pain were reformatted into radially oriented planes along the femoral necks. The diameter of the femoral head, α angle, EE, and FHN offset were measured. Reference values for α angle, EE, and FHN offset were determined, and the α angle, EE, and FHN offset were compared between open versus closed physeal status for each sex. RESULTS: The α angle measurements in male patients were higher than in female patients in anterior (A), anterosuperior (AS), and superior (S) planes (P < .001). The median α angle was highest for all patients in the AS plane (male, 52°; female, 49°). Open physes correlated with higher α angles compared with closed physes in all imaging planes except the AS plane. The FHN offset was lowest in the AS plane for all patients and was increased in female patients with closed physes compared with open physes in the A plane and in the A, S, posterosuperior, and posterior planes in male patients (P < .05). There were subtle plane-specific variations in EE. CONCLUSION: The α angle is higher and FHN offset is lower in the AS plane in patients with closed versus open physes, whereas the opposite is true in all other planes. The α angles in male patients were higher than in female patients, although there were no significant sex-based differences in the FHN offset. The α angles were highest and FHN offset was lowest in the AS plane. There were subtle variations in EE across all planes, and the EE was higher in patients with closed versus open physes. CLINICAL RELEVANCE: Plane- and sex-specific reference values for α angle, FHN offset, and EE in asymptomatic adolescent patients will assist orthopaedic surgeons and radiologists in appropriately suggesting femoroacetabular impingement based on the imaging evaluation of patients with hip pain, whose measurements lie at the periphery of or outside the reference intervals in the appropriate clinical context.

Evaluation of radial distribution of cartilage degeneration and necessity of pre-contrast measurements using radial dGEMRIC in adults with acetabular dysplasia.

BACKGROUND: The purpose of the present study was to investigate the radial distribution patterns of cartilage degeneration in dysplastic hips at different stages of secondary osteoarthritis (OA) by using radial delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC), and to assess whether pre-contrast measurements are necessary. METHODS: Thirty-five hips in 21 subjects (mean age ± SD, 27.6 ± 10.8 years) with acetabular dysplasia (lateral CE angle < 25°) were studied. Severity of OA was assessed on radiographs using Tönnis grading. Pre- (T1pre) and post-contrast T1 (T1Gd) values were measured at 7 sub-regions on radial reformatted slices acquired from a 3-dimensional (3D) T1 mapping sequence using a 1.5 T MR scanner. Values of radial T1pre, T1Gd and ΔR1 (1/T1Gd - 1/T1pre) of subgroups with different severity of OA were compared to those of the subgroup without OA using nonparametric tests, and bivariate linear Pearson correlations between radial T1Gd and ΔR1 were analyzed for each subgroup. RESULTS: Compared to the subgroup without OA, the subgroup with mild OA was observed with a significant decrease in T1Gd in the anterosuperior to superior sub-regions (mean, 476 ~ 507 ms, p = 0.026 ~ 0.042) and a significant increase in ΔR1 in the anterosuperior to superoposterior and posterior sub-regions (mean, 0.93 ~ 1.37 s-1, p = 0.012 ~ 0.042). The subgroup with moderate to severe OA was observed with a significant overall decrease in T1Gd (mean, 404 ~ 452 ms, p = 0.001 ~ 0.020) and an increase in ΔR1 (mean, 1.17 ~1.69 s-1, p = 0.001 ~ 0.020). High correlations were observed between radial T1Gd and ΔR1 for all subgroups (r = -0.869 ~ -0.944, p < 0.001). CONCLUSIONS: Radial dGEMRIC without pre-contrast measurements is useful for evaluating different patterns of cartilage degeneration in the entire hip joint of patients with hip dysplasia, particularly for those in early stages of secondary OA.

Femoral morphology and epiphyseal growth plate changes of the hip during maturation: MR assessments in a 1-year follow-up on a cross-sectional asymptomatic cohort in the age range of 9-17 years.

OBJECTIVES: The goal of this prospective study was to characterize the morphology and physeal changes of the femoral head during maturation using MRI in a population-based group of asymptomatic volunteers. MATERIALS AND METHODS: Sixty-four pupils (127 hips) of 331 pupils from a primary and high school were asked to take part in this study and were willing to participate. 3T MRI of the hip was obtained at baseline and 1-year follow-up. With these images, we analyzed the femoral morphology and epiphyseal changes related to age, status of the physis, and location on the femur. RESULTS: The radius of the femoral head and neck increased with age, as expected, (p < 0.001). The epiphyseal extension increased significantly with age (p < 0.05), but epiphyseal tilt and alpha angle showed no differences (p > 0.05). Building groups by using the epiphyseal status, we found that the epiphyseal extension had the highest changes in the "open" group and almost stopped in the "closed" group. The tilt angle did not change significantly (p > 0.05). Significant smaller alpha-angles were found in the "closed" group, however, these were in a normal range in all of them. Correlated to the position, the highest alpha-angle values were located in anterior-superior and superior-anterior position. CONCLUSIONS: Our data can be used as normative values, which can be compared to patients or cohorts with certain risk factors (e.g., professional athletes), this will offer the chance to detect and understand pathological changes.