Effects of Hindlimb Suspension on the Development of Hip Bone Morphologies in Growing Rats.

Abnormal hip bone morphologies are associated with various diseases of the hip joint. Weight bearing, especially during growth, may be important to achieve normal acetabulum development. This study aimed to investigate whether hip bone morphologies were affected by hindlimb suspension (HS) in 4 week-old rats. In HS groups, tail suspension was applied for 0, 2, 4, and 8 weeks. Age-matched rats were used as controls. The complex of hip bones with lumbar and sacral vertebrae were assessed based on morphological indexes using three-dimensional reconstructed images from X-ray computed tomography. Acetabular widths (measured from cranial to caudal) unchanged and depths became larger in both groups with age. Acetabular lengths (from the ventral side to the dorsal side) became larger in control groups but unchanged in HS groups with age. In HS groups, acetabular width, length, and depths were smaller than the control groups at 4 and/or 8 weeks. Acetabular versions became enlarged (rotated inwards) with age in both groups, although this was particularly pronounced in HS groups. Histologically, triradiate cartilage layers in the acetabulum were thinner with age and almost disappeared at 8 weeks in both groups. However, HS decreased Safranin O staining and prolonged the presence of hypertrophic chondrocyte indicating alterations in the chondral ossification processes. Iliac wing angles remained unchanged and anterior superior iliac crest (ASIC) distances increased with age in controls. In contrast, HS groups showed narrowed iliac wing angles with small ASIC distances. These results suggest that reduced mechanical loading during growth can interfere with hip joint formation. Keywords Hindlimb suspension, Hip joint, Acetabular morphology, Triradiate cartilage.

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.

Carry on With Raja Ravi Varma, Mary Cassatt, and Renoir.

Raja Ravi Varma's painting "There Comes Papa" depicts his daughter carrying her son astride her hip. The positive implication of the posture of the hips of the child while being carried in this manner on acetabular development is discussed.

Abduction treatment in stable hip dysplasia does not alter the acetabular growth: results of a randomized clinical trial.

Background The effect of bracing over natural history of stable dysplastic hips is not well known. This multicenter randomized trial aimed at objectifying the effect of abduction treatment versus active surveillance in infants of 3 to 4 months of age. Methods Patients were randomized to either Pavlik harness or active surveillance group. Ultrasound was repeated at 6 and 12 weeks post randomization. The primary outcome was the degree of dysplasia using the Graf α-angle at 6 months of age. The measurement of the acetabular index (AI) on plain pelvis X-rays was used to identify persistent dysplasia after 9 months and walking age (after 18 months). Findings The Pavlik harness group (n = 55) and active surveillance group (n = 49) were comparable for predictors of outcome. At 12 weeks follow-up the mean α-angle was 60.5° ± 3.8° in the Pavlik harness group and 60.0° ± 5.6° in the active surveillance group. (p = 0.30). Analysis of secondary outcomes (standard of care) showed no treatment differences for acetabular index at age 10 months (p = 0.82) and walking age (p = 0.35). Interpretation Pavlik harness treatment of stable but sonographic dysplastic hips has no effect on acetabular development. Eighty percent of the patients will have a normal development of the hip after twelve weeks. Therefore, we recommend observation rather than treatment for stable dysplastic hips.

Acetabular Version Increases During Adolescence Secondary to Reduced Anterior Femoral Head Coverage.

BACKGROUND: Acetabular version influences joint mechanics and the risk of impingement. Cross-sectional studies have reported an increase in acetabular version during adolescence; however, to our knowledge no longitudinal study has assessed version or how the change in version occurs. Knowing this would be important because characterizing the normal developmental process of the acetabulum would allow for easier recognition of a morphologic abnormality. QUESTIONS/PURPOSES: To determine (1) how acetabular version changes during adolescence, (2) calculate how acetabular coverage of the femoral head changed during this period, and (3) to identify whether demographic factors or hip ROM are associated with acetabular development. METHODS: This retrospective analysis of data from a longitudinal study included 17 volunteers (34 hips) with a mean (± SD) age of 11 ± 2 years; seven were male and 10 were female. The participants underwent a clinical examination of BMI and ROM and MRIs of both hips at recruitment and at follow-up (6 ± 2 years). MR images were assessed to determine maturation of the triradiate cartilage complex, acetabular version, and degree of the anterior, posterior, and superior acetabular sector angles (reflecting degree of femoral head coverage provided by the acetabulum anteriorly, posteriorly and superiorly respectively). An orthopaedic fellow (GG) and a senior orthopaedic resident (PJ) performed all readings in consensus; 20 scans were re-analyzed for intraobserver reliability. Thereafter, a musculoskeletal radiologist (KR) repeated measurements in 10 scans to test interobserver reliability. The intra- and interobserver interclass correlation coefficients for absolute agreement were 0.85 (95% CI 0.76 to 0.91; p < 0.001) and 0.77 (95% CI 0.70 to 0.84), respectively. All volunteers underwent a clinical examination by a senior orthopaedic resident (PJ) to assess their range of internal rotation (in 90° of flexion) in the supine and prone positions using a goniometer. We tested investigated whether the change in anteversion and sector angles differed between genders and whether the changes were correlated with BMI or ROM using Pearson's coefficient. The triradiate cartilage complex was open (Grade I) at baseline and closed (Grade III) at follow-up in all hips. RESULTS: The acetabular anteversion increased, moving caudally further away from the roof at both timepoints. The mean (range) anteversion angle increased from 7° ± 4° (0 to 18) at baseline to 12° ± 4° (5 to 22) at the follow-up examination (p < 0.001). The mean (range) anterior sector angle decreased from 72° ± 8° (57 to 87) at baseline to 65° ± 8° (50 to 81) at the final follow-up (p = 0.002). The mean (range) posterior (98° ± 5° [86 to 111] versus 97° ± 5° [89 to 109]; p = 0.8) and superior (121° ± 4° [114 to 129] to 124° ± 5° [111 to 134]; p = 0.07) sector angles remained unchanged. The change in the anterior sector angle correlated with the change in version (rho = 0.5; p = 0.02). The change in version was not associated with any of the tested patient factors (BMI, ROM). CONCLUSIONS: With skeletal maturity, acetabular version increases, especially rostrally. This increase is associated with, and is likely a result of, a reduced anterior acetabular sector angle (that is, less coverage anteriorly, while the degree of coverage posteriorly remained the same). Thus, in patients were the normal developmental process is disturbed, a rim-trim might be an appropriate surgical solution, since the degree of posterior coverage is sufficient and no reorientation osteotomy would be necessary. However, further study on patients with retroversion (of various degrees) is necessary to characterize these observations further. The changes in version were not associated with any of the tested patient factors; however, further study with greater power is needed. LEVEL OF EVIDENCE: Level II, prognostic study.

Does Orientation of the Femoral Head Affect Acetabular Development? An Experimental Study in Lamb.

BACKGROUND: Derotational osteotomy of the proximal femur has proved to be effective in the treatment of residual acetabular dysplasia. However, the reason why this osteotomy is effective remains debatable. The purpose of this study is to investigate if an alteration of femoral head orientation affects acetabular growth. METHODS: A proximal femoral osteotomy was performed in 21 lambs aged 3 months: 5 varus osteotomies (110 degrees), 4 valgus osteotomies (150 degrees), and 12 derotation osteotomies. Results were compared with a control group (5 animals). Osteotomy was fixed with a screw-plate device. Version was controlled intraoperatively with K-wires. Animals were killed 3 months after surgical procedure. A morphometric study of both proximal femur and acetabulum was performed, including deepness, volume and diameters of the acetabulum, neck-shaft angle and femoral version. RESULTS: The average neck-shaft angle for the normal, anteversion, and retroversion groups was 129 degrees, whereas it was 110 degrees for the varus group and 149 degrees for the valgus group. The average femoral version for the normal, valgus, and varus groups was 21 degrees of anteversion, whereas it was 38 degrees of anteversion for the so-called anteversion group and 17 degrees of retroversion for the retroversion group. Nor the neck-shaft angle, nor the femoral version correlated with the acetabular anteroposterior diameter (P=0.698, 0.6, respectively), the acetabular inferosuperior diameter (P=0.083, 0.451, respectively) or the acetabular deepness (P=0.14, 0.371, respectively). The neck-shaft angle correlated significantly with acetabular volume (P=0.023), so that the lower the neck-shaft angle, the higher the acetabular volume (r=-0.453). The femoral version did not correlated with acetabular volume (P=0.381). CONCLUSIONS: Decreasing the neck-shaft angle provokes an increase in acetabular volume, whereas changes in femoral version do not affect the acetabular growth. Extra-articular osteotomies that alter femoral orientation affect intra-articular gross morphology. LEVEL OF EVIDENCE: Level II-therapeutic study.

Predicting acetabular growth in developmental dysplasia of the hip following open reduction after walking age.

BACKGROUND: Acetabular dysplasia of the hip following open reduction can complicate the treatment of developmental dysplasia of the hip (DDH). The purposes of this retrospective study were to investigate the long-term results of open reduction performed via an extensive anterolateral approach for DDH after walking age and to predict acetabular development using postoperative radiographs and arthrograms. METHODS: From 1973 to 2001, we performed open reduction for 131 hips in 119 pediatric patients with DDH after failed closed reduction. Of these, 85 hips of 73 patients who underwent arthrography at 5 years old were followed-up radiologically until skeletal maturity. Mean age at the time of surgery was 17 ± 4.6 months (range, 10-33 months), and mean age at final survey was 19 ± 5.7 years (range, 14-33 years). Mean follow-up time was 17.7 ± 5.8 years (range, 13-32 years). Groups with satisfactory outcomes (66 hips) and unsatisfactory outcomes (19 hips) according to the Severin classification were compared. Factors predicting acetabular development were identified using univariate and multiple logistic analyses. RESULTS: Univariate analysis showed a significant between-group difference in acetabular index (AI) at 2 months postoperatively, and in center-edge (CE) angle, cartilaginous AI (CAI), and cartilaginous CE angle at 5 years old (p < 0.05 each). In multiple logistic regression analysis, CAI at 5 years old represented a predictor of acetabular development after open reduction for DDH (odds ratio, 1.81; 95% confidence interval (CI), 1.04-3.13; p < 0.05). Area under the receiver operating characteristic curve for CAI at 5 years old was 0.93 (95%CI, 0.85-1.0), and the optimal cut-off was 10° (81.8% sensitivity, 92% specificity). CONCLUSIONS: A CAI ≥10° on hip arthrograms at 5 years old may offer a useful indicator of the need for corrective surgery following open reduction after walking age.

Analysis of Acetabular Ossification From the Triradiate Cartilage and Secondary Centers.

BACKGROUND: Acetabular development is a complex process that involves both endochondral growth from the triradiate cartilage (TRC) and intramembranous growth from the primary and secondary ossification centers of the innominate bones. Ponseti and others have described these centers including their contribution toward the development of normal acetabular shape. Prior studies have not utilized advanced imaging to study the appearance and closure of these secondary centers. The purpose of this study was to determine the chronological age at which the secondary ossification centers of the acetabulum appear and close and where there are any sex differences. METHODS: Patients who underwent abdominal and pelvic computed tomography (CT) scans between January 2009 and December 2014 at a pediatric hospital were retrospectively reviewed. Patients between age 6 and 16 years with adequate imaging of acetabulum were included. CT scans were assessed for the appearance and closure of the 3 acetabular secondary ossification centers [anterior (os pubis), superior (os ilium), and posterior (os ischium)] and closure of the TRC. RESULTS: A total of 159 CT scans met inclusion criteria (66 males and 93 females). The median age of appearance of the secondary ossification centers was: posterior (10.1 females, 12.8 males), anterior (10.7 females, 13.4 males), and superior (11.1 females, 13.6 males). The median age of closure of the secondary ossification centers was: posterior (12.8 females, 13.6 males), anterior (12.8 females, 13.9 males), superior (14.5 females, 13.9 males), and TRC (14.5 females, 14.3 males). Most ossification centers in females appeared and closed approximately 2 to 3 years before males. CONCLUSIONS: Secondary ossification centers in the acetabulum appear sequentially (first posterior, then anterior, then superior), with almost all centers closing just before TRC. Closure occurs earlier in females than males. Knowledge of these centers and their closure patterns allows better radiologic readings (especially CT studies) and understanding of acetabular growth, allowing more informed management of childhood hip conditions including dysplasia, trauma, and over-use sports injuries. LEVEL OF EVIDENCE: Level III-Diagnostic.

A murine model for developmental dysplasia of the hip: ablation of CX3CR1 affects acetabular morphology and gait.

BACKGROUND: Developmental dysplasia of the hip (DDH) is a debilitating condition whose distinguishing signs include incomplete formation of the acetabulum leading to dislocation of the femur, accelerated wear of the articular cartilage and joint laxity resulting in osteoarthritis. It is a complex disorder having environmental and genetic causes. Existing techniques fail to detect milder forms of DDH in newborns leading to hip osteoarthritis in young adults. A sensitive, specific and cost effective test would allow identification of newborns that could be non-invasively corrected by the use of a Pavlik harness. Previously, we identified a 2.5 MB candidate region on human chromosome 3 by using linkage analysis of a 4 generation, 72 member family. Whole exome sequencing of the DNA of 4 severely affected members revealed a single nucleotide polymorphism variant, rs3732378 co-inherited by all 11 affected family members. This variant causes a threonine to methionine amino acid change in the coding sequence of the CX3CR1 chemokine receptor and is predicted to be harmful to the function of the protein To gain further insight into the function of this mutation we examined the effect of CX3CR1 ablation on the architecture of the mouse acetabulum and on the murine gait. METHODS: The hips of 5 and 8 weeks old wild type and CX3CR1 KO mice were analyzed using micro-CT to measure acetabular diameter and ten additional dimensional parameters. Eight week old mice were gait tested using an inclined treadmill with and without load and then underwent micro-CT analysis. RESULTS: (1) KO mice showed larger a 5-17% larger diameter left acetabula than WT mice at both ages. (2) At 8 weeks the normalized area of space (i.e. size discrepancy) between the femur head and acetabulum is significantly larger [38% (p = 0.001)-21% (p = 0.037)] in the KO mice. (3) At 8 weeks gait analysis of these same mice shows several metrics that are consistent with impairment in the KO but not the WT mice. These deficits are often seen in mice and humans who develop hip OA. CONCLUSION: The effect of CX3CR1 deletion on murine acetabular development provides suggestive evidence of a susceptibility inducing role of the CX3CR1 gene on DDH.

Combined Bone Ingrowth and Remodeling Around Uncemented Acetabular Component: A Multiscale Mechanobiology-Based Finite Element Analysis.

Bone ingrowth and remodeling are two different evolutionary processes which might occur simultaneously. Both these processes are influenced by local mechanical stimulus. However, a combined study on bone ingrowth and remodeling has rarely been performed. This study is aimed at understanding the relationship between bone ingrowth and adaptation and their combined influence on fixation of the acetabular component. Based on three-dimensional (3D) macroscale finite element (FE) model of implanted pelvis and microscale FE model of implant-bone interface, a multiscale framework has been developed. The numerical prediction of peri-acetabular bone adaptation was based on a strain-energy density-based formulation. Bone ingrowth in the microscale models was simulated using the mechanoregulatory algorithm. An increase in bone strains near the acetabular rim was observed in the implanted pelvis model, whereas the central part of the acetabulum was observed to be stress shielded. Consequently, progressive bone apposition near the acetabular rim and resorption near the central region were observed. Bone remodeling caused a gradual increase in the implant-bone relative displacements. Evolutionary bone ingrowth was observed around the entire acetabular component. Poor bone ingrowth of 3-5% was predicted around the centro-inferio and inferio-posterio-superio-peripheral regions owing to higher implant-bone relative displacements, whereas the anterio-inferior and centro-superior regions exhibited improved bone ingrowth of 35-55% due to moderate implant-bone relative displacement. For an uncemented acetabular CoCrMo component, bone ingrowth had hardly any effect on bone remodeling; however, bone remodeling had considerable influence on bone ingrowth.

Magnetic resonance imaging evaluation of the labrum to predict acetabular development in developmental dysplasia of the hip: A STROBE compliant study.

Recently, more attention has been paid to the role of the acetabular labrum. Therefore, we designed a retrospective cohort study of patients with residual hip dysplasia (RHD) who underwent magnetic resonance imaging (MRI). The objective of this study was to investigate an association between the MRI appearance of the labrum before school age and the natural history of RHD.We retrospectively investigated 45 hips of 40 patients who underwent MRI at about 3 and 4 years of age for RHD and were conservatively followed up with until 6 years of age or older. We evaluated the extent of eversion with a new method that measures the ß angle (MRI ß angle) using landmarks of the Graf method on MRI T2*-weighted images. The outcome measure was the Severin classification at the final follow-up. We compared the radiographic and MRI parameters at approximately 3 and 4 years of age between the good and poor outcome groups. The Student t test or one-way analysis of variance was used to compare the quantitative variables between groups. The Chi-square test was used to perform a ratio comparison.Although there was a significant difference in the center-edge (CE) angle, there was no significant difference in the acetabular index and the ratio of the presence of femoral head necrosis and the break in Shenton line between the good and poor groups. The MRI ß angle was significantly greater in the poor outcome group than in the normal and good outcome groups. The cut-off value of the MRI ß angle to differentiate the good and poor outcome groups was 65°, and its specificity and sensitivity were 92% and 53%, respectively.There was labral eversion on MRI scans in patients with RHD. Acetabular development before adolescence was poorer with greater labral eversion on MRI scans. The specificity for poor acetabular development was high when the MRI ß angle was 65° or more. The MRI ß angle has the potential to predict acetabular development.

Functional status and amount of hip displacement independently affect acetabular dysplasia in cerebral palsy.

AIM: Acetabular dysplasia is the one of main causes of hip displacement in patients with cerebral palsy (CP). Although several studies have shown a relationship between hip displacement and acetabular dysplasia, relatively few have evaluated the association between quantitative acetabular dysplasia and related factors, such as Gross Motor Function Classification System (GMFCS) level. METHOD: We performed a morphometric analysis of the acetabulum in patients with CP using multiplanar reformation of computed tomography data. The three directional acetabular indices (anterosuperior, superolateral, and posterosuperior) were used to evaluate acetabular dysplasia. Consequently, linear mixed-effects models were used to adjust for related factors such as age, sex, GMFCS level, and migration percentage. RESULTS: A total of 176 patients (mean age 9y 5mo, range 2y 4mo-19y 6mo; 104 males, 72 females) with CP and 55 typically developing individuals (mean age 13y 6mo, range 2y 5mo-19y 10mo; 37 males, 18 females) in a comparison group were enrolled in this study. Statistical modelling showed that all three directional acetabular indices independently increased with GMFCS level (p<0.001) and migration percentage (p<0.001). INTERPRETATION: Acetabular dysplasia was independently affected by both the amount of hip displacement and the GMFCS level. Thus, physicians should consider not only the migration percentage but also three-dimensional evaluation in patients at high GMFCS levels.

Influence of Implant Surface Texture Design on Peri-Acetabular Bone Ingrowth: A Mechanobiology Based Finite Element Analysis.

The fixation of uncemented acetabular components largely depends on the amount of bone ingrowth, which is influenced by the design of the implant surface texture. The objective of this numerical study is to evaluate the effect of these implant texture design factors on bone ingrowth around an acetabular component. The novelty of this study lies in comparative finite element (FE) analysis of 3D microscale models of the implant-bone interface, considering patient-specific mechanical environment, host bone material property and implant-bone relative displacement, in combination with sequential mechanoregulatory algorithm and design of experiment (DOE) based statistical framework. Results indicated that the bone ingrowth process was inhibited due to an increase in interbead spacing from 200 µm to 600 µm and bead diameter from 1000 µm to 1500 µm and a reduction in bead height from 900 µm to 600 µm. Bead height, a main effect, was found to have a predominant influence on bone ingrowth. Among the interaction effects, the combination of bead height and bead diameter was found to have a pronounced influence on bone ingrowth process. A combination of low interbead spacing (P = 200 µm), low bead diameter (D = 1000 µm), and high bead height (H = 900 µm) facilitated peri-acetabular bone ingrowth and an increase in average Young's modulus of newly formed tissue layer. Hence, such a surface texture design seemed to provide improved fixation of the acetabular component.

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.

Mechanobiological simulations of peri-acetabular bone ingrowth: a comparative analysis of cell-phenotype specific and phenomenological algorithms.

Several mechanobiology algorithms have been employed to simulate bone ingrowth around porous coated implants. However, there is a scarcity of quantitative comparison between the efficacies of commonly used mechanoregulatory algorithms. The objectives of this study are: (1) to predict peri-acetabular bone ingrowth using cell-phenotype specific algorithm and to compare these predictions with those obtained using phenomenological algorithm and (2) to investigate the influences of cellular parameters on bone ingrowth. The variation in host bone material property and interfacial micromotion of the implanted pelvis were mapped onto the microscale model of implant-bone interface. An overall variation of 17-88 % in peri-acetabular bone ingrowth was observed. Despite differences in predicted tissue differentiation patterns during the initial period, both the algorithms predicted similar spatial distribution of neo-tissue layer, after attainment of equilibrium. Results indicated that phenomenological algorithm, being computationally faster than the cell-phenotype specific algorithm, might be used to predict peri-prosthetic bone ingrowth. The cell-phenotype specific algorithm, however, was found to be useful in numerically investigating the influence of alterations in cellular activities on bone ingrowth, owing to biologically related factors. Amongst the host of cellular activities, matrix production rate of bone tissue was found to have predominant influence on peri-acetabular bone ingrowth.

Acetabular development after open reduction to treat dislocation of the hip after walking age.

BACKGROUND: Treatment of hip dislocation diagnosed after walking age is often difficult. We report the surgical treatment of these patients by open reduction with a soft tissue surgical procedure without osteotomy. METHODS: Thirty-eight children (43 hips) diagnosed with complete dislocation of the hip after walking age were included in this study. We radiographically analysed postoperative hip joint development up to 6 years of age. To assess the predictors of acetabular development, we evaluated the radiographs, using an acetabular index of ≤35° and a centre-edge angle of >5° at 6 years of age as satisfactory outcomes, and evaluated the advance of acetabular development over time. RESULTS: AI on the affected side was improved with time after open reduction. The diameter of the capital femoral ossific nucleus on the affected side was almost equivalent to that on the unaffected side at 6-12 months after surgery, after which the centre-edge angle improved gradually from one year after surgery. We compared hips classified as satisfactory to unsatisfactory at 6 years of age, and found that the centre-edge angle at one year after open reduction was significantly associated with acetabular development (P = 0.044). The cut-off value was -2° with sensitivity of 0.909 and specificity of 0.677. CONCLUSIONS: The results of the current study suggest that initial development of the capital femoral ossific nucleus after open reduction would be followed by improved joint congruity, and that this would facilitate acetabular development. The centre-edge angle at one year after surgery could be regarded as a potential predictor of acetabular development in open reduction surgery for late-diagnosed developmental dysplasia of the hip cases.

Hip Vascularity: A Review of the Anatomy and Clinical Implications.

Throughout development, the vascular supply to the proximal femur and acetabulum undergoes a series of changes during which it is susceptible to injury. Before age 3 months, the ligamentum teres and lateral epiphyseal arteries are the dominant supply to the developing head. The dominant supply shifts to the lateral epiphyseal vessels by age 18 months. The distinct metaphyseal and epiphyseal circulations of the adult proximal femur form in adolescence when an increasingly rich metaphyseal circulation supplies the subphyseal region, terminating at the physeal plate. The acetabular blood supply derives from two independent systems, with the dominance of each changing throughout maturity. Most descriptions of the vascular contributions to the proximal femur and acetabulum have been gross anatomic and histologic studies. Advanced imaging studies (eg, CT angiography, perfusion MRI) have added to our understanding of the vascular anatomy of the proximal femur and acetabulum, its changes throughout development, and its clinical implications.

A new predictive indicator by arthrography for future acetabular growth following conservative treatment of developmental dysplasia of the hip.

The aim of this study was to find a new predictive indicator for acetabular growth of developmental dysplasia of the hip. Seventy-three hips that were diagnosed with developmental dysplasia of the hip and treated by conservative reduction were included in our study. In 30 hips with center-edge angle ≤ 10° at age 4, the center-edge of the acetabular limbus angle (CEALA) in the arthrogram was measured. On the basis of the results, CEALA was significantly smaller in the secondary acetabular dysplasia group than in the normal group at maturity. In conclusion, CEALA is a more reliable and accurate predictive indicator for acetabular development than center-edge angle or acetabular index.

Bone ingrowth around porous-coated acetabular implant: a three-dimensional finite element study using mechanoregulatory algorithm.

Fixation of uncemented implant is influenced by peri-prosthetic bone ingrowth, which is dependent on the mechanical environment of the implant-bone structure. The objective of the study is to gain an insight into the tissue differentiation around an acetabular component. A mapping framework has been developed to simulate appropriate mechanical environment in the three-dimensional microscale model, implement the mechanoregulatory tissue differentiation algorithm and subsequently assess spatial distribution of bone ingrowth around an acetabular component, quantitatively. The FE model of implanted pelvis subjected to eight static load cases during a normal walking cycle was first solved. Thereafter, a mapping algorithm has been employed to include the variations in implant-bone relative displacement and host bone material properties from the macroscale FE model of implanted pelvis to the microscale FE model of the beaded implant-bone interface. The evolutionary tissue differentiation was observed in each of the 13 microscale models corresponding to 13 acetabular regions. The total implant-bone relative displacements, averaged over each region of the acetabulum, were found to vary between 10 and 60 µm. Both the linear elastic and biphasic poroelastic models predicted similar mechanoregulatory peri-prosthetic tissue differentiation. Considerable variations in bone ingrowth (13-88%), interdigitation depth (0.2-0.82 mm) and average tissue Young's modulus (970-3430 MPa) were predicted around the acetabular cup. A progressive increase in the average Young's modulus, interdigitation depth and decrease in average radial strains of newly formed tissue layer were also observed. This scheme can be extended to investigate tissue differentiation for different surface texture designs on the implants.

Developmental pattern of the hip in patients with hereditary multiple exostoses.

BACKGROUND: Coxa valga is a common clinical feature of hereditary multiple exostoses (HME). The current study aimed to determine the unique developmental pattern of the hip in patients with HME and evaluate the factors that influence its progression. METHODS: Thirty patients (57 hips) with HME were divided into two groups according to the Hilgenreiner epiphyseal angle (HEA). Twenty-two patients (44 hips) including 13 men and 9 women were assigned to group 1 (HEA <25°), and 8 patients (13 hips) including 3 men and 5 women were assigned to group 2 (HEA ≥25°). The mean age at the initial presentation was 6.0 (4-12) years with 6.8 (4-11) years of follow-up in group 1, and 10.4 (8-13) years with 5.4 (2-9) years of follow-up in group 2. We measured the HEA, neck-shaft angle (NSA), acetabular index (AI), center-edge angle (CEA), and migration percentage (MP) for radiographic evaluation. RESULTS: Among the hips, 50 (87.7%) hips had coxa valga and 27 (47.4%) hips had abnormal MP (42.1% were borderline and 5.3% were subluxated). There was a significant difference in the HEA and NSA between the groups (p < 0.001 and p < 0.05, respectively). The HEA significantly correlated with the development of the NSA and no correlation was found between the HEA and AI, CEA, and MP. CONCLUSIONS: There was a significant relationship between the HEA at the initial presentation and the NSA at skeletal maturity. We should consider guided growth for patients with lower HEA to prevent significant coxa valga deformity with close follow-up.