Primary thoracolumbar scoliosis in pinealectomized chickens

Current models to understand the onset and progression of scoliotic deformities in adolescent idiopathic scoliosis: a systematic review

PURPOSE

To create an updated and comprehensive overview of the modeling studies that have been done to understand the mechanics underlying deformities of adolescent idiopathic scoliosis (AIS), to predict the risk of curve progression and thereby substantiate etiopathogenetic theories.

METHODS

In this systematic review, an online search in Scopus and PubMed together with an analysis in secondary references was done, which yielded 86 studies. The modeling types were extracted and the studies were categorized accordingly.

RESULTS

Animal modeling, together with machine learning modeling, forms the category of black box models. This category is perceived as the most clinically relevant. While animal models provide a tangible idea of the biomechanical effects in scoliotic deformities, machine learning modeling was found to be the best curve-progression predictor. The second category, that of artificial models, has, just as animal modeling, a tangible model as a result, but focusses more on the biomechanical process of the scoliotic deformity. The third category is formed by computational models, which are very popular in etiopathogenetic parameter-based studies. They are also the best in calculating stresses and strains on vertebrae, intervertebral discs, and other surrounding tissues.

CONCLUSION

This study presents a comprehensive overview of the current modeling techniques to understand the mechanics of the scoliotic deformities, predict the risk of curve progression in AIS and thereby substantiate etiopathogenetic theories. Although AIS remains to be seen as a complex and multifactorial problem, the progression of its deformity can be predicted with good accuracy. Modeling of AIS develops rapidly and may lead to the identification of risk factors and mitigation strategies in the near future. The overview presented provides a basis to follow this development.

The effect of exogenous melatonin on reducing scoliotic curvature and improving bone quality in melatonin-deficient C57BL/6J mice

It is well-documented that melatonin deficiency has been linked to the etiopathogenesis of adolescent idiopathic scoliosis. In this study, we intended to apply melatonin in melatonin-deficient mice to ascertain whether melatonin could reduce the incidence/severity of scoliosis, and investigate the role of melatonin on bone mineral density in scoliosis. A total of 80 mice were divided into 4 groups: 20 quadrupedal mice and 20 bipedal mice served as controls; 20 quadrupedal and 20 bipedal mice received oral melatonin (8 mg/kg BW) daily. After 5^th, 10^th, 15^th and 20^th weeks of treatment, radiographs and in vivo micro-CT were used to determine the incidence of scoliosis and bone qualities, respectively. Upon sacrifice, the levels of melatonin were measured in each group. At 20^th week, the occurrence of scoliosis was 80%, 30%, 22% and 5% in bipedal, quadrupedal, bipedal + melatonin and quadrupedal + melatonin group, respectively. The trabecular bone quality of the vertebral body was significantly ameliorated in the melatonin-treated bipedal models. Likewise, the number of osteoclasts was significantly less in those treated with melatonin. Our results indicated that melatonin deficiency may be crucial for scoliotic development, and restoration of melatonin levels can prevent scoliotic development with the improvement in bone density.

Mechanism of right thoracic adolescent idiopathic scoliosis at risk for progression; a unifying pathway of development by normal growth and imbalance

Adolescent idiopathic scoliosis is regarded as a multifactorial disease and none of the many suggested causal etiologies have yet prevailed. I will suggest that adolescent idiopathic scoliosis has one common denominator, namely that initial curve development is mediated through one common normal physiological pathway of thoracic rotational instability. This is a consequence of gender specific natural growth of the passive structural components of thoracic spinal tissues for the adolescent female. This causes an unbalanced mechanical situation, which progresses if the paravertebral muscles cannot maintain spinal alignment. The alteration in the coronal plane with the lateral curve deformity is an uncoupling effect due to a culmination of a secondary, temporary sagittal plane thoracic flattening and of a primary, temporary transverse plane rotational instability for the adolescent female. Treatment of adolescent idiopathic scoliosis should address this physiological pathway and the overall treatment strategy is early intervention with strengthening of thoracic rotational stability for small curve adolescent idiopathic scoliosis.

A review of pinealectomy-induced melatonin-deficient animal models for the study of etiopathogenesis of adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a common orthopedic disorder of unknown etiology and pathogenesis. Melatonin and melatonin pathway dysfunction has been widely suspected to play an important role in the pathogenesis. Many different types of animal models have been developed to induce experimental scoliosis mimicking the pathoanatomical features of idiopathic scoliosis in human. The scoliosis deformity was believed to be induced by pinealectomy and mediated through the resulting melatonin-deficiency. However, the lack of upright mechanical spinal loading and inherent rotational instability of the curvature render the similarity of these models to the human counterparts questionable. Different concerns have been raised challenging the scientific validity and limitations of each model. The objectives of this review follow the logical need to re-examine and compare the relevance and appropriateness of each of the animal models that have been used for studying the etiopathogenesis of adolescent idiopathic scoliosis in human in the past 15 to 20 years.

Pinealectomy in a broiler chicken model impairs endochondral ossification and induces rapid cancellous bone loss

BACKGROUND CONTEXT

Adolescent idiopathic scoliosis (AIS) in humans is a lateral curvature of the spine often associated with osteopenia. It has recently been accepted that the development of AIS is closely associated with spinal overgrowth. Pinealectomy (PNX) in a chicken model consistently induces scoliosis with anatomic features similar to human AIS; however, the mechanism of PNX inducing scoliosis is poorly understood.

PURPOSE

This experimental study attempts to improve the understanding of the mechanisms underlying the onset of scoliosis in a PNX broiler chicken model.

METHODS

A histomorphometric study was performed to analyze longitudinal bone growth and cancellous bone remodeling before the development of scoliosis. Static and dynamic parameters in cancellous bone and chondro-osseous junction of the 7th thoracic vertebral body at 9 days after hatching were compared between PNX chickens (n=9) and control chickens with no surgery (n=5).

RESULTS

PNX resulted in a rapid and marked loss of cancellous bone volume (7.9±0.9% vs. 14.2±1.8%, mean±SD, p<.0005) and profoundly disrupted trabecular structure with increases in dynamic formative parameters, such as mineralizing surface, mineralization apposition rate, and adjusted appositional rate. In the chondro-osseous junction, activated osteoclasts phagocytized degenerating chondrocytes, leaving a minimal amount of cartilage matrix and activated osteoblasts, losing their scaffolding for bone formation, and directly covering the hypertrophic zone cells. The osteoid surface and thickness in the chondro-osseous junction were significantly increased in PNX chickens (43.1±14.2% vs. 11.6±5.7% and 4.1±0.2 μm vs. 2.9±0.4 μm). In the subjacent cartilage regions being protected from further resorption, abundant labeled cartilage remained with higher cellularity.

CONCLUSIONS

It is known that fast-growing birds have a unique paradigm of rapid bone elongation with minimal metaphyseal bone production. A bone-forming surface exists at the front of cartilage ossification in the growth plate; therefore, papillae of hypertrophic chondrocytes become included between the trabeculae of metaphyseal bone and the overall thickness of the growth plate increases considerably in addition to distal expansion. Our results indicate that the unique mechanism for rapid bone elongation in chicken is more pronounced after PNX. PNX also induces high turnover osteoporosis, which may also contribute to the development of scoliosis in the chicken.

The role of melatonin in the pathogenesis of adolescent idiopathic scoliosis (AIS)

The cause of adolescent idiopathic scoliosis (AIS) in humans remains obscure and probably multifactorial. At present, there is no proven method or test available to identify children or adolescent at risk of developing AIS or identify which of the affected individuals are at risk of progression. Reported associations are linked in pathogenesis rather than etiologic factors. Melatonin may play a role in the pathogenesis of scoliosis (neuroendocrine hypothesis), but at present, the data available cannot clearly show the role of melatonin in producing scoliosis in humans. The data regarding human melatonin levels are mixed at best, and the melatonin deficiency as a causative factor in the etiology of scoliosis cannot be supported. It will be an important issue of future research to investigate the role of melatonin in human biology, the clinical efficacy, and safety of melatonin under different pathological situations. Research is needed to better define the role of all factors in AIS development.

Melatonin delays cell proliferation by inducing G1 and G2 /M phase arrest in a human osteoblastic cell line hFOB 1.19

A recent prospective study indicated that melatonin supplements may reduce the progression of idiopathic scoliosis, the most common deformity of the spine. This form of scoliosis occurs during rapid skeletal growth. To date, however, there is no direct evidence regarding an antiproliferative effect of melatonin at the level of osteoblasts. Herein, we investigated whether melatonin inhibits cell proliferation in a normal human fetal osteoblastic cell line hFOB 1.19. MTT staining showed that at 1 mm concentrations, melatonin significantly inhibited osteoblast proliferation in time-dependent manner. Flow cytometry demonstrated that melatonin significantly increased the fraction of cells in G(0) /G(1) phase of the cell cycle, while simultaneously reducing the proportion in the G(2) /M phase rather than the S phase. Western blot and real-time PCR analyses further confirmed that melatonin's inhibitory effect was possibly because of downregulation of cyclin D1 and CDK4, related to the G(1) phase, and of cyclin B1 and CDK1, related to the G(2) /M phase. There was no downregulation of cyclin E, CDK2, and cyclin A, which are related to G(1) /S transition and S phase. In addition, the trypan blue dye exclusion assay showed that cell viability was not changed by melatonin relative to control cells. These findings provide evidence that melatonin may significantly delay osteoblast proliferation in a time-dependent manner and this inhibition involves the downregulation of cyclin D1 and CDK4, related to the G(1) phase, and of cyclin B1 and CDK1, related to the G(2) /M phase.

Pinealectomy in the chicken: a good model of scoliosis?

The phenomenon of spinal deformity in the pinealectomized chicken has led researchers to postulate a disturbance of melatonin activity as a potential cause of adolescent idiopathic scoliosis (AIS). More recently, structural differences between curves seen in this model and those seen in scoliosis have been highlighted suggesting the deformities observed are not as similar as first thought. We examined melatonin levels, and the radiological and histological characteristics of scoliosis after pinealectomy in chickens. They underwent pinealectomy (P) at 2 days of age, sham surgery (S) or served as controls (C). Mean melatonin levels were 32.9 pmol/L (P), 175 pmol/L (S) and 227.3 pmol/L (C). Scoliosis developed in 75% of chickens after pinealectomy and 38% after a sham procedure. Nineteen percent of unoperated controls also developed scoliosis. A lower melatonin level was associated with the development of scoliosis (p < or = 0.001), but exceptions were seen with levels up to 265 pmol/L observed in one case. Most of the curves occurring spontaneously and after sham surgery and almost half after pinealectomy were short angular curves: distinct from those resembling idiopathic scoliosis. These occur over one or two segments and are characterized by marked apical wedging, frequently associated with subluxation or dislocation. The intervertebral joint in the chicken is more like a synovial joint histologically than an intervertebral disc. This study highlights important differences between the chicken and the human, and between their respective spinal deformities. Caution is advised when drawing conclusions regarding the pathogenesis of AIS from this model.

Idiopathic scoliosis and pineal lesions in Australian children

PURPOSE

To determine whether treatment of pineal lesions in children is associated with development of idiopathic scoliosis.

METHODS

38 boys and 10 girls with pineal lesions were identified. Their mean age at presentation was 10 years. The pineal pathology varied from cysts and epidermoid to teratoma, germinoma, pineocytoma, and glioblastoma. Treatment ranged from biopsy/extirpation to radiotherapy.

RESULTS

12 patients died. No scoliosis was found in any females or any of the deceased. Two boys had scoliosis: one had a 12-degree right upper thoracic curve with 32-degree kyphosis and the other had a 60-degree right thoracolumbar idiopathic curve, requiring a 2-stage arthrodesis.

CONCLUSION

Pineal ablation is not related to the development of idiopathic scoliosis in humans.

Biomechanical simulations of the scoliotic deformation process in the pinealectomized chicken: a preliminary study

BACKGROUND

The basic mechanisms whereby mechanical factors modulate the metabolism of the growing spine remain poorly understood, especially the role of growth adaptation in spinal disorders like in adolescent idiopathic scoliosis (AIS). This paper presents a finite element model (FEM) that was developed to simulate early stages of scoliotic deformities progression using a pinealectomized chicken as animal model.

METHODS

The FEM includes basic growth and growth modulation created by the muscle force imbalance. The experimental data were used to adapt a FEM previously developed to simulate the scoliosis deformation process in human. The simulations of the spine deformation process are compared with the results of an experimental study including a group of pinealectomized chickens.

RESULTS

The comparison of the simulation results of the spine deformation process (Cobb angle of 37 degrees ) is in agreement with experimental scoliotic deformities of two representative cases (Cobb angle of 41 degrees and 30 degrees ). For the vertebral wedging, a good agreement is also observed between the calculated (28 degrees ) and the observed (25 degrees - 30 degrees ) values.

CONCLUSION

The proposed biomechanical model presents a novel approach to realistically simulate the scoliotic deformation process in pinealectomized chickens and investigate different parameters influencing the progression of scoliosis.

Transverse plane pelvic rotation in adolescent idiopathic scoliosis: primary or compensatory?

Several studies have suggested that the pelvis is involved in the etiology or pathogenesis of adolescent idiopathic scoliosis (AIS). The purpose of this retrospective, cross-sectional radiographic study is to identify any correlation between the transverse plane rotational position of the pelvis in stance and operative-size idiopathic or congenital scoliosis deformities, using Scheuermann's kyphosis and isthmic spondylolisthesis patients for comparison. The hypothesis tested was that the direction of transverse pelvic rotation is the same as that for a thoracic scoliosis. As a group, AIS patients had a significant transverse plane pelvic rotation in the same direction as the thoracic curve. When subdivided into the six Lenke curve patterns, this was true for the groups with a major thoracic curve: thoracic (1), double thoracic (2) and double curve patterns (3). It was not true for patterns with a major thoracolumbar/lumbar curve: single thoracolumbar/lumbar (5) and double thoracic-thoracolumbar/lumbar (6). Nor was it true for triple (4) curves. The Lenke 1 and 2 major thoracic curves without compensatory thoracolumbar/lumbar curves did not have the predicted pelvic rotation. All congenital scoliosis patients studied had main thoracic curves and significant transverse plane pelvic rotation in the same direction as the thoracic curve. There was no transverse plane pelvic rotation in the Scheuermann's kyphosis or isthmic spondylolisthesis patients. We interpret these findings as consistent with a compensatory rotation of the pelvis in the same direction as the main thoracic curve in most patients with a compensatory thoracolumbar/lumbar curve as well as in patients with main thoracic congenital scoliosis.

Recent advances in the aetiology of adolescent idiopathic scoliosis

The aetiology of adolescent idiopathic scoliosis (AIS) is still unknown despite many years of research effort. Theories on AIS's aetiology have included mechanical, hormonal, metabolic, neuromuscular, growth, and genetic abnormalities. Amongst these, some factors may be epiphenomena rather than the cause itself. Other factors may even contribute to curve progression, rather than curve initiation. Current views maintain that AIS is a multifactorial disease with genetic predisposing factors [Lowe et al. in J Bone Joint Surg [Am] 82:1157-1168, 2000]. With improvements in diagnostic methods, imaging and genomics, there has been considerable recent work on aetiology. This review aims to bring readers up-to-date with the latest developments in scoliosis research.

Changes in melatonin receptors in relation to the development of scoliosis in pinealectomized chickens

STUDY DESIGN

The 2[125I]iodomelatonin binding assay was used to investigate the involvement of melatonin receptors in the development of scoliosis in pinealectomized chickens.

OBJECTIVE

To compare the binding properties of melatonin receptors in the thoracic spinal cord between pinealectomized chickens that had scoliosis develop and those that did not.

SUMMARY OF BACKGROUND DATA

Surgical pinealectomy in young chickens induced scoliosis with a reported incidence of 50% to 100%. The factors regulating the development of scoliosis in this animal model are unclear. Melatonin receptors have been shown in the spinal cord of chickens, but their functions are still unknown. This study addresses the question as to whether spinal cord melatonin receptors are related to the pathogenesis of scoliosis in pinealectomized chickens.

METHOD

Control and pinealectomized chickens were kept under controlled lighting conditions and monitored for scoliosis development. At 9-11 weeks after pinealectomy, thoracic spinal cords were removed for 2[125I]iodomelatonin binding assay, and blood was collected for serum melatonin assay at either the middle of the light period or middle of the dark period.

RESULTS

Pinealectomy in young chickens produced: (1) loss of diurnal variations in serum melatonin levels, (2) 50% incidence of scoliosis, and (3) attenuation in the diurnal variations in the receptor affinity to melatonin. No differences were detected in the serum melatonin levels or binding of spinal cord melatonin receptors between the pinealectomized chickens that had scoliosis develop and those that did not.

CONCLUSION

Changes are detected in melatonin receptor binding after pinealectomy. However, these changes cannot account for the reason why scoliosis develops in some chickens after pinealectomy, while it does not in others. Neither low melatonin serum level nor changes in spinal cord melatonin binding can be a sole etiologic factor in the pathogenesis of scoliosis in pinealectomized chickens.

The effect of pinealectomy on scoliosis development in young nonhuman primates

STUDY DESIGN

Prospective study on pinealectomy in primates.

OBJECTIVE

To evaluate whether pinealectomy in a bipedal nonhuman primate model will result in the development of scoliosis.

SUMMARY OF BACKGROUND DATA

Pinealectomy in newborn chickens consistently resulted in scoliosis development. Published data suggest that the surgical removal of the pineal, loss of melatonin secretion, and a bipedal posture are important elements in the development of scoliosis in lower animal models.

METHOD

There were 18 rhesus monkeys between 8 and 11 months old that underwent pineal excision. All monkeys were kept in a regulated 12-hour light-dark cycle. Monthly radiographs assessed scoliosis development. Completeness of pineal excision was assessed by measurement of a major metabolite of melatonin in the urine, 6-sulfatoxymelatonin, using an enzyme-linked immunosorbent assay assessed.

RESULTS

Mean follow-up was 28 months (range 10-41). Seven monkeys died prematurely, and 11 survived to date; the data from those that died could still be used, although follow-up was shortened. At the latest follow-up or death, scoliosis did not develop in any of the monkeys. Urinary 6-sulfatoxymelatonin measurements revealed 3 patterns. Group 1 consisted of 10 monkeys, which showed definite evidence of complete pineal excision. Group 2 consisted of an uncertain group of 2 monkeys in which the nighttime melatonin level is slightly high. Group 3 consisted of 6 monkeys that had incomplete pineal excision or ectopic melatonin production.

CONCLUSIONS

To our knowledge, this is the first report of pinealectomy in nonhuman primates. Of the 18 monkeys, 10 had a loss of melatonin secretion, for a mean of 29 months after surgery. Because none of the monkeys had scoliosis develop, this study strongly suggests that the possible etiologic factors producing idiopathic scoliosis in lower animals are different from primates, and findings in lower animals cannot necessarily be extrapolated to human beings.