Rickets, Osteomalacia, and Renal Osteodystrophy

Hypophosphatemic Hypovitaminosis D Induces Osteomalacia in the Adult Female Rat

Osteomalacia is a bone-demineralizing disease of adulthood, often caused by hypovitaminosis D. Current animal models of the disease mimic osteomalacia as a consequence of gastric bypass or toxic exposure to metals, but a relevant model of diet-induced osteomalacia is lacking. For that purpose, 7-month-old female Sprague Dawley rats were randomly assigned into 2 weight-stratified groups and maintained for 4 months on synthetic diets containing negligible or normal levels of vitamin D. The dietary regimen resulted in vitamin D deficiency as measured by 25-hydroxyvitamin D serum levels; however, hypovitaminosis D per se did not affect biomarkers of calcium metabolism and bone turnover, nor did it result in increased osteoid. Thus, vitamin D depletion through the diet was found to be insufficient to induce an osteomalacia-like phenotype in the adult rat. After 4 months, the phosphate content of the vitamin D-depleted diet had decreased to 0.16% (calcium:phosphorus ratio of 5.85), resulting in an osteomalacic-like condition (trabecular osteoid surface/bone surface constituted 33%; CI, 26-40). The diet change also affected both metabolic and bone turnover biomarkers, including significantly suppressing serum fibroblast growth factor 23. Furthermore, decreased dietary phosphate in a vitamin D-depleted diet led to microarchitectural changes of trabecular and cortical bone, lower bone mass density, lower bone mass content and decreased bone strength, all indicating reduced bone quality. Taken together, our results show that osteomalacia can be induced in the adult female rat by depleting vitamin D and lowering phosphate content in the diet.

Bilateral spontaneous fracturing of the femoral neck in a patient with renal osteodystrophy

We report a case of bilateral fracturing of the femoral neck in a patient with renal osteodystrophy who was treated by means of osteosynthesis. In this type of patient, there is a need to remain watchful for the possibility of occurrences of spontaneous fracturing of the femoral neck, even if the initial radiographic examination is normal.

Comparison of fixator-assisted nailing versus circular external fixator for bone realignment of lower extremity angular deformities in rickets disease

PURPOSE

In rickets patients, limb deformities are usually multiapical and complex even with medical treatment; residual deformities remain necessitating surgical correction. In our study we aim to compare the results of correction of lower limb deformities, in rickets patients, treated with circular external fixator versus fixator-assisted intra-medullary nail.

MATERIALS AND METHODS

Seventeen rickets patients, with 39 deformed lower extremity segments (femur and or tibia), underwent deformity correction procedures in our institution. Ten patients with 26 segments were treated using fixator-assisted nailing. Nine patients with 17 segments were treated using Ilizarov technique with circular frame. All patients were evaluated by long-standing true anteroposterior and lateral orthoroentgenograms of lower extremities preoperatively. Joint alignment, joint orientation, and apices of deformities were calculated and noted. The postoperative results of MAD, MPTA, LDFA, PPPTA and functional criteria were compared with preoperative values and assessments made in SPSS 13.0 for Windows by using McNemar, Pearson Chisquare, and Fisher exact statistical tests.

RESULTS

Mean age for the fixator-assisted nailing (FAN) group patients at the time of surgery was 23.8 years (14-37 years). There were 16 femur and 10 tibiae operated on 6 female and 4 male patients. The mean follow up time is 42.6 months (6-71 months). In the Ilizarov group patients the mean age at the time of surgery was 16.7 years (13-22 years). There were 14 tibiae and 3 femur operated on 6 female and 3 male patients. The mean follow-up time was 19 months (6-48 months). Results were evaluated according to the Paley et al. classification of bone and functional results. According to those criteria we had 1 fair, 1 good, and 7 excellent bone results and 1 fair, 1 good, and 7 excellent functional results in the circular ring fixator group. In the FAN group we found 3 good and 7 excellent bone results; 1 fair, 2 good, and 7 excellent functional results. Nearly all patients complained of pain, limping, instability, and walking problems at their first preoperative visit. In both groups there was no union problem; in the FAN group, in one patient correction loss occurred and in another one screw loosening was encountered; in the Ilizarov group, 66% of patients had pin tract infections and one premature fibula consolidation occurred. Statistical analysis revealed no significant difference between two groups in correction ratios.(pearson chi square p = 0.332 for MAD; pearson chi square p = 0.477 for LDFA; Paley functional criteria fisher exact p = 0.684).

CONCLUSION

The results indicated that fixator-assisted nailing carries deformity correction accuracy comparable with Ilizarov-type external fixators. FAN provides great patient comfort and the total treatment time is less. In patients with rickets, the retained IM nail can further provide protection against recurrence even if the metabolic pathology reoccurs.

Erk pathways negatively regulate matrix mineralization

Skeletal mineralization is an important step regulating the mechanical properties of the calcified tissues, but molecular events underlying mineralization still remain elusive. We examined the role of extracellular signal-regulated kinase (Erk) pathways in matrix mineralization of osteogenic cells both in vitro and in vivo. Matrix mineralization by preosteocytic MLO-A5 cells and osteoblastic MC3T3-E1 cells was increased by either PD98059 Mek inhibitor treatment or adenovirus vector-mediated dominant negative Ras (Ras(DN)) expression and was suppressed by Erk activation by platelet-derived growth factor (PDGF) treatment or constitutively active Mek1 (Mek(CA)) expression. Administration of adenovirus vectors carrying Ras(DN) gene onto the calvaria of 1-day-old mice increased the mineralization of the tissues, while that of the Mek(CA) adenovirus suppressed it. These results suggest that the Erk pathway is a negative regulator of the matrix mineralization both in vitro and in vivo.

Renal osteodystrophy

The incidence of chronic renal disease is increasing, and the pattern of renal osteodystrophy seems to be shifting from the classic hyperparathyroid presentation to one of low bone turnover. Patients with persistent disease also live longer than previously and are more physically active. Thus, patients may experience trauma as a direct result of increased physical activity in a setting of weakened pathologic bone. Patient quality of life is primarily limited by musculoskeletal problems, such as bone pain, muscle weakness, growth retardation, and skeletal deformity. Chronic renal disease also increases the risk of comorbidity, such as infection, bleeding, and anesthesia-related problems. Current treatment strategies include dietary changes, plate-and-screw fixation, and open reduction and internal fixation.

Skeletal manifestations of rickets in infants and young children in a historic population from England

Gross and radiographic changes characteristic of inadequate bone mineralization due to rickets are described in 21 immature skeletons from a 19th century urban population from Birmingham, England. The aims of the study are as follows: to evaluate and if possible augment existing dry-bone criteria for the recognition of rickets in immature skeletal remains; to investigate the value of radiography for the paleopathological diagnosis of rickets; and to compare and contrast the expression of rickets in this group with that previously documented for a rural agrarian population from Wharram Percy, England. Some gross skeletal signs of rickets which were not previously well-documented in paleopathological studies are noted. The worth of radiography for evaluating structural changes to both cortical and trabecular bone in the disease is demonstrated, and features useful for the interpretation of vitamin D deficiency are discussed. The pattern of skeletal elements affected and the severity of changes differs in the Birmingham group from that seen in the comparative rural population. It is emphasized that a variety of factors may influence the expression of rickets in paleopathological material, including rate of skeletal growth, age cohort affected, and intensity of vitamin D deficiency. Nevertheless, careful analysis, not only of the frequency of rickets but also of the degree of severity of lesions and the patterning with respect to skeletal elements affected, may enable more nuanced understanding of the biocultural context of the disease in earlier populations.

Hypovitaminosis D in acutely injured pediatric burn patients

PROBLEM

The prevalence of vitamin D insufficiency, its etiology, and associated sequelae among acutely injured burn patients is unknown.

OBJECTIVE

This study assessed vitamin D and endocrine status, as well as the effect of anabolic agents, in pediatric patients who had sustained burns in excess of 25% total body surface area (TBSA).

SUBJECTS

Sixty-nine patients with a mean TBSA burn of 50.6+/-2.2% (range 27% to 94%) and full thickness injury of 41.3+/-3.0% (range 0% to 94%) were studied. Subjects ranged in age from 0.6 to 18 years (mean, 5.8+/-0.6 years). Main outcome measures Blood samples were obtained for serum 25-hydroxyvitamin D (D25), 1,25-dihydroxyvitamin D (D1,25), albumin, cortisol, triiodothyronine (T3), tetraiodothyronine (T(4)), thyroid stimulating hormone (TSH), and parathormone (PTH).

RESULTS

Two hundred eighty morning blood samples of D25 and D1,25 demonstrated that 45% and 26.2% were low and 8.9% and 11% were very low, respectively. At least one low D25 or D1,25 level occurred in 62.3% of all subjects. Very low levels were noted in 23.2% of all patients. There was an increased incidence of hyperparathyroidism in patients with very low serum D25. Vitamin D25 and D1,25 levels were lower in subjects with larger burns or inhalation injury, as well as those treated with thyroxine or oxandrolone. Serum albumin, cortisol, T(4), and TSH were not correlated with concentration of vitamin D.

CONCLUSIONS

Demonstration of a high incidence of low serum vitamin D indicates vitamin D status may be significantly compromised in burned children. It is unclear why vitamin D deficiency exists in this population. The most effective way to improve vitamin D status remains elusive at this time.

The development of rickets as a complication of chemotherapy for the treatment of Wilms' tumor

Musculoskeletal complaints were the presenting symptoms in four of 44 children (9%) treated for relapsed Wilms' tumors with ifosfamide, a derivative of cyclophosphamide. Subsequent radiologic examination revealed rachitic bone and joint changes. A fifth child manifested clinical and radiographic signs of rickets after presenting with hypophosphatemia, hypouricemia, and glycosuria. Recognition of a potential drug-induced Fanconi syndrome is important when managing pediatric oncology patients previously treated with ifosfamide. Early replacement therapy is recommended when proximal renal tubular abnormalities are detected to help prevent and control the severe metabolic bone disease associated with the Fanconi syndrome.

Lack of evidence for rickets in the osteopetrotic rat mutation, toothless

A common, but paradoxic, feature among osteopetrotic human infants is the presence of rickets. This disorder of mineralization is manifested radiographically and histologically by increased growth plate cartilage and hypertrophic cell zone thickness and excess metaphyseal osteoid and biochemically by decreased serum calcium and phosphorus concentrations. Rickets has also been reported in two osteopetrotic animal mutations, the osteosclerotic (oc) mouse and the toothless (tl) rat. Although the phenotypic expression of the rachitic lesion in the oc mouse closely resembles that in affected humans, the results of the present study show that the lesion in the tl rat does not. Compared with normal littermates, histologic and morphometric analyses of tibial growth plate cartilage in tl rats up to 5 weeks of age showed age-related increases in thickness of the proliferative cell zone and decreases in thickness of the hypertrophic cell zone that were most apparent within the central, but not lateral, regions of the growth plate and areas of acellularity and failure of chondrocytes to transform synchronously from proliferative cell to hypertrophic cell phenotypes. Femoral ash content, composition, and accretion rates did not differ from those in normal rats during the first 5 weeks of life. These findings do not support the rachitic nature of the cartilage lesion in the tl rat. Rather, a chondrodysplastic disorder is suggested, which more closely resembles the cartilage defect present in this mutation.

Surgically induced uremia in rats. II: Osseous PTH-susceptible signaling systems as predictors of bone resorption

Predicting the course of parathormone (PTH)-elicited bone turnover in both humans and experimental rat models with moderate chronic uremia, using only standard clinical chemistry analyses, is often difficult. Consequently, rat bone from 1 + 2/3 nephrectomized animals, after 230 days of progressive renal failure, was examined for PTH-stimulated adenylate cyclase (AC) and phospholipase C (PL-C) activities. Correlations to biological parameters related to the function of bone and kidney were made. Reduced renal function was demonstrated by increased serum creatinine; circulating 1,25 dihydroxyvitamin D3 below detection level; diminished renal PTH-elicited AC activity; and decreased urinary cAMP excretion. PTH-activated renal PL-C was also reduced. However, no significant differences were seen in urine creatinine, calcium, phosphate, and hydroxyproline, nor in serum PTH, alkaline phosphatase, calcium, and phosphate. Notwithstanding, renal osteodystrophy developed as estimated by increased plasticity of the long bones, as well as reduction of the diaphyseal (Dd) and inner femoral mid-shaft (Di) diameters. Femoral cancellous bone exhibited a substantial elevation of both eroded surface (ES) and osteoid surface (OS) as well as a marked reduction in trabecular bone volume (TBV). Calvarial PTH-activated AC was enhanced, whereas corresponding PL-C was markedly reduced. PTH-enhanced AC correlated positively with ES and negatively with Di, respectively. PTH-enhanced PL-C, however, correlated positively with bone calcium content and negatively with ES. Our results indicate that bone modeling and remodeling are to a large extent related to PTH-elicited signaling systems, and cannot easily be predicted by standard clinical chemistry analyses.

Surgically induced uremia in rats. I: Effect on bone strength and metabolism

During the course of chronic renal failure (CRF) in man, renal osteodystrophy (osteitis fibrosa and/or osteomalacia) gradually develops. The present study aimed to establish a similar type of CRF leading to renal osteodystrophy in rats. During progressive CRF development over 225 days after 5/6 nephrectomy, the following serum variables were measured: creatinine, immunoreactive parathyroid hormone (iPTH), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), a25-hydroxyvitamin D3, (25(OH)D3), alkaline phosphatase, albumin, phosphate, urea nitrogen, total calcium, and other blood electrolytes. Subsequent to sacrifice, mechanical properties of the rat femur, bone histomorphometry (osteoid and eroded surfaces) and bone contents of calcium, phosphate and hydroxyproline were also examined. Serum creatinine in rats with CRF gradually escalated by some 70%, while circulating 1,25(OH)2D3 was reduced beneath detection level. Total plasma calcium and phosphate concentrations were, however, almost unchanged indicating that PTH-induced bone remodeling due to moderate hyperparathyroidism sustained calcium homeostasis. Alkaline phosphatase levels were reduced by some 50%, which reflects chronically impeded bone formation. Bone histomorphometry assessment revealed substantial elevation of resorption with moderate accompanying fibrosis in about 70% of afflicted animals. Bone calcium, phosphate and hydroxypyrroline contents remained unaltered. However, hydroxyproline/calcium ratio was marginally reduced. These results, together with altered mechanical bending stress characteristics and diminished diaphysis cross section area, confirm development of mixed bone lesions in the uremic animals. Our results are compatible with the early development of CRF in man. The established rat model is therefore useful in elucidating the precipitation and early treatment of renal osteodystrophy in humans.

Nutritional rickets

Nutritional rickets was once felt to be a disease of the past. In recent years, dietary patterns and the prevalence of unsupplemented breast feeding has led to a mild resurgence in rickets. The cases presented show a wide spectrum of nutritional disease, illustrating the common risk factors, the usefulness of vitamin-D metabolite assays in making a definitive diagnosis, and the response to vitamin-D therapy.