Vascular occlusion and cartilage disorders in osteonecrosis of the femoral head in rats

The role and underlying mechanisms of microRNA‑214 in Legg‑Calvé‑Perthes disease

Legg‑Calvé‑Perthes disease (LCPD) is a pediatric form of femoral head osteonecrosis with unknown etiology. MicroRNAs (miRs) have been revealed to serve an important role in LCPD. MiR‑214 serves an important role in chondrogenesis. The aim of the present study was to investigate the potential role of miR‑214 in LCPD and the underlying mechanisms. The expression levels of miR‑214 and B‑cell lymphoma 2 (Bcl‑2)‑associated X protein (Bax) in dexamethasone (DEX)‑treated TC28 cells, and the femoral head cartilage tissues, serum and primary chondrocytes of patients with LCPD, and healthy individuals were determined via reverse transcription quantitative polymerase chain reaction and western blot analysis. A luciferase reporter assay was conducted to investigate the association between miR‑214 and Bax, while cell viability was determined via an MTT assay, and flow cytometry was performed to investigate cell apoptosis. The results revealed that miR‑214 was downregulated and Bax was upregulated in DEX‑treated TC28 cells and tissues obtained from patients with LCPD. MiR‑214 was demonstrated to directly target Bax and negatively regulate its expression. DEX administration significantly suppressed cell proliferation, promoted apoptosis and decreased the Bcl‑2/Bax ratio in TC28 cells; overexpression of miR‑214 induced opposing effects, which were reversed by Bax overexpression. In conclusion, the results indicated that miR‑214 and Bax may be potential therapeutic targets for the future clinical treatment of LCPD.

Prevalence of Hypertension in Pediatric Tibia Vara and Slipped Capital Femoral Epiphysis

BACKGROUND

Slipped capital femoral epiphysis (SCFE) and tibia vara (Blount disease) are associated with childhood obesity. However, the majority of obese children do not develop SCFE or tibia vara. Therefore, it is hypothesized that other obesity-related biological changes to the physis, in addition to increased biomechanical stress, potentiate the occurrence of SCFE and tibia vara. Considering that hypertension can impose pathologic changes in the physis similar to those observed in these obesity-related diseases we set out to determine the prevalence of hypertension in patients with SCFE and tibia vara.

METHODS

Blood pressure measurements were obtained in 44 patients with tibia vara and 127 patients with SCFE. Body mass index and blood pressure were adjusted for age, sex, and height percentiles utilizing normative distribution data from the CDC. These cohorts were compared with age-matched and sex-matched cohorts derived from an obesity clinic who did not have either bone disease. A multivariable proportional odds model was used to determine association.

RESULTS

The prevalence of prehypertension/hypertension was significantly higher in the tibia vara (64%) and SCFE cohort (64%) compared with respective controls (43%). Patients diagnosed with either SCFE or tibia vara had 2.5-fold higher odds of having high blood pressure compared with age-matched and sex-matched obese patients without bone disease. Sex, age, and race did not have a significant effect on a patient's blood pressure.

CONCLUSIONS

This is the first study to establish that the obesity-related bone diseases, SCFE and tibia vara, are significantly associated with high blood pressure. These data have immediate clinical impact as they demonstrate that children with obesity-related developmental bone disease have increased prevalence of undiagnosed and untreated hypertension. Furthermore, this prevalence study supports the hypothesis that hypertension in conjunction with increased biomechanical forces together potentiate the occurrence of SCFE and tibia vara. If proven true, it is plausible that hypertension may represent a modifiable risk factor for obesity-related bone disease.

LEVEL OF EVIDENCE

Level III-case-control study.

Angiogenic activity mediates bone repair from human pluripotent stem cell-derived osteogenic cells

Human pluripotent stem cells provide a standardized resource for bone repair. However, criteria to determine which exogenous cells best heal orthopedic injuries remain poorly defined. We evaluated osteogenic progenitor cells derived from both human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs). Phenotypic and genotypic analyses demonstrated that these hESCs/hiPSCs are similar in their osteogenic differentiation efficiency and they generate osteogenic cells comparable to osteogenic cells derived from mesenchymal stromal cells (BM-MSCs). However, expression of angiogenic factors, such as vascular endothelial growth factor and basic fibroblast growth factor in these osteogenic progenitor cells are markedly different, suggesting distinct pro-angiogenic potential of these stem cell derivatives. Studies to repair a femur non-union fracture demonstrate only osteogenic progenitor cells with higher pro-angiogenic potential significantly enhance bone repair in vivo. Together, these studies highlight a key role of pro-angiogenic potential of transplanted osteogenic cells for effective cell-mediated bone repair.

Altered cellular kinetics in the growth plate of the femoral head of spontaneously hypertensive rats

PURPOSE

Pathologic changes in the growth plate remain unknown in Legg-Calvé-Perthes (LCP) disease. Spontaneously hypertensive rats have proven to be a good model for studying LCP disease. This study investigated the histopathologic changes and the expression of vascular endothelial growth factor in the growth plate of spontaneously hypertensive rats (SHR).

MATERIALS AND METHODS

Sixty SHR rats were divided into two groups: those showing osteonecrosis (SHR+n group: 32), and those showing normal ossification (SHR-n group: 28). Thirty Wister Kyoto rats served as a control. For histomorphological measurement, the length of each zone of the growth plate was measured. Cell kinetics was measured by 5-bromo-2'-deoxyuridin (BrdU) immunohistochemistry and transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) assays. Vascular endothelial growth factor (VEGF) immunohistochemistry was used to identify of expression of VEGF.

RESULTS

The lengths of growth plates of the SHR+n group were significantly shorter in the initial growth period than those of the other groups. The lowest proliferative rate and the highest apoptosis rate were observed in the SHR+n group at the initial growth period. The expression of VEGF in the growth plate of the SHR group was lower than the control group, and it was lower in the SHR+n group than in the SHR-n group.

CONCLUSION

The growth plate of the SHR+n group was found to be affected by disease process of ischemic necrosis of the femoral head, and this might explain the relative overgrowth of the greater trochanter in the later stages of LCP disease.

Compromised perfusion in femoral head in normal rats: distinctive perfusion MRI evidence of contrast washout delay

OBJECTIVES

The femoral head is prone to osteonecrosis. This study investigated dynamic contrast-enhanced (DCE) MRI contrast washout features of the femoral head and compared the data with data from other bony compartments in normal rats.

METHODS

7-month-old Wistar rats were used. DCE MRI of the right hip (n=18), right knee (n=12) and lumbar spine (n=10) was performed after an intravenous bolus injection of Gd-DOTA (0.3 mmol kg(-1)). Temporal resolution was 0.6 s for hip and spine, and 0.3 s for knee. The total scan duration was 8 min for hip and spine, and 4.5 min for knee. The regions of interest for enhancement measurement included femoral head, proximal femoral diaphysis, distal femoral diaphysis and epiphysis, proximal tibial epiphysis and diaphysis, and lumbar vertebrae L1-5.

RESULTS

Femoral head showed no enhancement signal decay during the DCE MRI period, while all other bony compartments showed a contrast washin phase followed by a contrast washout phase. In the knee joint, the contrast washout of the proximal tibia diaphysis was slower that of other bony compartments of the knee.

CONCLUSION

Based on the evidence of delayed contrast washout, this study showed that blood perfusion in the femoral head could be compromised in normal rats.

Scanning and transmission electron microscopic observation of femoral head feeding vessels in stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive rats (SHRSP) are known to show necrosis of the femoral head with a frequency of about 50%. This rat has thus been used as an animal model for necrosis of the femoral head in many studies. In a detailed investigation of feeding vessel disorders that cause femoral head necrosis, we observed changes over time in the feeding vessels using scanning electron microscopy and transmission electron microscopy. In scanning electron microscopy of vascular casts, abnormal findings in feeding vessels of SHRSP with aging from the immature stage included contortion and bending in the lumen with overall narrowing. Under transmission electron microscopy, decreased numbers of smooth muscle cells and increased amounts of collagen fibers were marked, and these changes with hypertrophy of vascular walls might be similar to those of arteriolosclerosis. The structural changes first revealed by transmission electron microscopic observation might cause the friability of the feeding vessels so that contortion and bending occurred, suggesting transient obstruction of blood flow to the femoral head and subsequent induction of femoral head necrosis. These findings should help in understanding the causes of femoral head necrosis in humans, including Perthes' disease.

Uncemented ceramic-on-ceramic THA in adults with osteonecrosis of the femoral head

Advanced osteonecrosis of the femoral head is increasingly treated with uncemented total hip arthroplasty (THA), particularly in the younger population. While early outcomes appear promising, little is known about the optimum bearing surface in this patient subpopulation. The goal of this study was to evaluate the clinical and radiological outcomes of uncemented ceramic-on-ceramic THA in young adults with osteonecrosis of the femoral head. Twenty-four consecutive patients (24 hips) with osteonecrosis of the femoral head and 24 patients (24 hips) with osteoarthritis were treated with an uncemented ceramic-on-ceramic THA. Mean patient age for the osteonecrosis group was 46 years and for the osteoarthritis group was 50 years. At a mean follow-up of 34 months, functional improvement was significant in both groups (P<.01). The outcome was good to excellent for 85% of patients (17 hips) in the osteonecrosis group and 90% of patients (19 hips) in the osteoarthritis group. Harris and Oxford Hip scores were significantly better (P<.05) in the osteoarthritis group than in the osteonecrosis group at 6 months postoperatively but at no other assessment visit. Our results suggest that ceramic-on-ceramic THA in osteonecrotic patients produces similar clinical and radiological outcomes to those with osteoarthritis at a minimum 24-month follow-up. Ceramic-on-ceramic uncemented THA is therefore a useful adjunct for the treatment of advanced osteonecrosis of the femoral head.

Towards a better understanding of the aetiology of Legg-Calvé-Perthes' disease: acetabular retroversion may cause abnormal loading of dorsal femoral head-neck junction with restricted blood supply to the femoral epiphysis

The most accepted part of the aetiology of Perthes' disease is an intermittent arterial occlusion. Many different reports now also suggest that some mechanical factor plays a role. In search of mechanical differences between normal hips and Perthes hips, many secondary morphologic differences of the proximal femur and the acetabulum are known. Recent research by the author has shown morphological changes of the acetabulum, independent of Perthes' disease in a large part of patients. In particular, retroversion of the acetabulum was found in a large part of adults who suffered from Perthes' disease as a child, and even in children who just developed Perthes' disease. The author suggest a relation of the two entities and hypotheses that due to the acetabular retroversion, there may be an intermittent, movement depending abnormal loading pressure on the dorsal femoral head-neck junction and the local blood vessels, which can lead to insufficient blood supply of the femoral epiphysis and to local necrosis, as these vessels are the only blood supply to the femoral epihysis in children.

CHONDROCYTE APOPTOSIS IN RESPONSE TO DISLOCATION OF THE HIP IN THE RAT MODEL

BACKGROUND

Joint dislocation is a traumatic event that can lead to osteoarthritis. The purpose of this paper is to study cartilage changes following prolonged joint dislocation for 1, 2 or 8 h.

METHODS

Sprague-Dawley rats (n = 27) were used in this study. Surgical dislocation of the hip under anaesthesia was carried out on the animals. The joints remained dislocated for 1, 2 or 8 h. The joints were subsequently harvested and terminal deoxnucleotidyl transferase-mediated dUTP nick-end labelling testing was carried out to show chondrocyte apoptosis in the femoral head and acetabulum. Using this test, the apoptotic index, which is the proportion of apoptotic chondrocytes to total number of chondrocytes, was calculated. A comparison of apoptotic indices was made among the three groups.

RESULTS

The mean apoptotic indices for the femoral head for the 1-, 2- and 8-h groups were 0.065 +/- 0.025, 0.162 +/- 0.031 and 0.201 +/- 0.030, respectively. There was a significant difference (P < 0.05) in the mean apoptotic indices between each of the three groups. For the acetabulum, the mean apoptotic indices were 0.046 +/- 0.012, 0.051 +/- 0.023 and 0.057 +/- 0.031 for the 1-, 2- and 8-h groups, respectively. There was no significant difference (P > 0.05) between each of the three groups.

CONCLUSIONS

Dislocation of a joint causes chondrocyte apoptosis. There is a progressive increase in the apoptotic index with prolonged dislocation of the rat hip.

Osteonecrosis induced by standing in growing Wistar Kyoto rats

BACKGROUND

Wistar Kyoto (WKY) rats bred in ordinary rat cages rarely develop osteonecrosis of the epiphyseal nucleus of the femoral head (OENFH), a pathological condition with findings similar to those of early-stage Perthes' disease in humans. OENFH occurs frequently in spontaneously hypertensive rats. Interestingly, when rats are forced to stand upright on the hindlimbs at feeding time, OENFH is frequently encountered.

METHODS

Experiment I investigated the stage of growth development at which osteonecrosis might be generated. Forty male WKY rats 5 weeks of age were kept and fed in high (27 cm height) rat cages. Twenty femora from 10 WKYs per observation time were resected under deep ether anesthesia at 9, 12, 15, and 20 weeks. Histologic examination of the femoral head focused on OENFH and abnormalities of the growth plate. Experiment II defined the period after postnatal week 5 when OENFH was generated while standing upright. The standing posture was lessened up to postnatal weeks 9 and 12 using a low (10 cm height) rat cage and then reenforced at feeding time with a high rat cage until 15 weeks. Forty femora from the 20 WKYs were then resected as in experiment I.

RESULTS

The onset of OENFH was observed only at 12 and 15 weeks of age in experiment I, revealing that OENFH occurred specifically during this growth period. In experiment II the osteonecrosis was minimal. Abnormalities in the growth plates of experiment II animals were less pronounced than those of rats killed 15 weeks after birth in experiment I.

CONCLUSIONS

Repetitive mechanical stress on the femoral heads from 5 to 9 weeks of age played an important role in the etiology of osteonecrosis in WKYs. This etiological finding could provide a clue to the pathogenesis and prevention of Perthes' disease in humans.

Zoledronic acid improves femoral head sphericity in a rat model of perthes disease

We hypothesized that the bisphosphonate zoledronic acid (ZA) could improve femoral head sphericity in Perthes disease by changing the balance between bone resorption and new bone formation. This study tests the effect of ZA in an established model of Perthes disease, the spontaneously hypertensive rat (SHR). One hundred and twenty 4-week old SHR rats were divided into three groups of 40: saline monthly, 0.015 mg/kg ZA weekly, or 0.05 mg/kg ZA monthly. At 15 weeks DXA measurements documented that femoral head BMD was increased by 18% in ZA weekly and 21% in ZA monthly compared to controls (p<0.01). Femoral head sphericity in animals with osteonecrosis was improved in ZA-treatment groups (p<0.01) as measured by epiphyseal quotient (EQ). The proportion of "flat" heads (EQ0.40) was significantly reduced from 32% in saline-treated animals to 12% in weekly ZA and 3% in monthly ZA (p<0.01). Histologically there was a similar prevalence of osteonecrosis in all groups. The prevalence of ossification delay was significantly reduced by ZA treatment (p<0.01). Zoledronic acid favorably altered femoral head shape in this spontaneous model of osteonecrosis in growing rats. Translation of these results to Perthes disease could mean that deformity of the femoral head may be modified in children, perhaps reducing the need for surgical intervention in childhood and adult life.

Etiologic factors in femoral head osteonecrosis in growing rats

Osteonecrosis of the epiphyseal nucleus of the femoral head, which resembles that in Perthes' disease in children, was studied in spontaneously hypertensive rats (SHRs) and ordinary Wistar Kyoto rats (WKYs). The SHRs were kept in ordinary cages and the WKYs in custom-made high cages from 5 weeks to 15 weeks after birth. The WKYs had to stand on their hind limbs to feed because the feed box and the drinking aperture were placed at a high level. At 15 weeks, the femurs were resected and examined radiographically and histologically. There was a relatively high incidence of avascular necrosis in the epiphyseal nuclei of the femoral heads; 45.8% in SHRs and 33.3% in WKYs. In the SHRs, there were ossification disturbances of the proximal femoral epiphysis and deformities of the proximal femurs, such as a flattened femoral head and short neck. These findings suggest that constitutional cartilage disorder in the SHRs and excessive mechanical stress on the femoral heads in the WKYs participated in the etiology of the osteonecrosis.