Vertebral growth remains a mystery, especially with regards to the contribution of different growth plates and the mechanisms of growth after closure of these plates. As an example of vertebral growth in general, the growth of the vertebral canal was assessed in a rat model using fluorochromes. Although 80–90% of vertebral canal growth was due to growth plates, the remaining canal growth occurred via periosteal absorption and deposition. This is contrary to the traditional idea that periosteal mechanisms do not change the shape or dimensions of bone and suggests that the vertebrae exhibit a different model of growth than typical bones. Vertebral growth remains largely a mystery. The contributions of different growth plates and the mechanisms of growth after closure of these plates requires further exploration. As an example of vertebral growth, vertebral canal growth was assessed in a living rat model using fluorochromes. Vertebral canal growth and presumably vertebral growth in general occurred by different mechanisms at different phases of development. Growth plates accounted for the majority of growth although periosteal mechanisms also resulted in changes in the size and shape of the vertebrae. This is contrary to the traditional concept of periosteal growth and suggests that vertebrae may exhibit a different model of growth than typical bones. The growth of the vertebrae in a particular dimension and during a particular phase of development is dependent on different mechanisms of growth, which may play a role in interpreting vertebral growth anomalies. The interspinous junction closed by the end of the first week, whereas the neurocentral junction closed between weeks three and four. By four weeks, the vertebral canal had achieved 80–90% of its growth in area and diameter. After growth plate closure, the canal continued to grow by periosteal mechanisms and was displaced posteriorly. Thirty-six Sprague-Dawley rats (age one week-seven weeks) were injected with tetracycline and alizarin using a dosing interval of four days. Thoracic vertebrae were sectioned using a cryostat and examined under a fluorescence microscope. In addition to noting fluoro-chrome deposition, the dimensions of the growth plates and canal were noted.
This study was designed to examine the components of the MR image of the neurocentral junction (NCJ) and to explore the discrepancy between the age of closure of the NCJ as determined by anatomic and imaging studies. MR images of one hundred and fourteen porcine NCJs were correlated with anatomic and histologic sections. Whereas gross anatomic visualization did not reveal the NCJ site, MRI was sensitive for cartilage detection and accurately determined the age of NCJ closure although it overestimated the extent of closure. Based on this study, MRI characterization of the NCJ appears reliable and the NCJ cartilage does not close until adolescence. This study examined the composition of the MR image of the neurocentral junction (NCJ) and the discrepancy between the age of closure of the NCJ as determined by anatomic and imaging studies.
MRI was sensitive for cartilage detection and accurately determined the age of NCJ closure (i.e. absence of cartilage on histologic examination). MRI underestimated the extent of NCJ closure, with NCJs in the process of closure often presenting as completely open on MRI. MRI and histologic characterization of the NCJ provided better description of closure patterns than anatomic examination. Disparate NCJ development has been implicated as a potential cause of adolescent idiopathic scoliosis. Whereas autopsy studies have refuted this theory by suggesting that the NCJ closes before adolescence, MRI studies have resurrected this idea by suggesting later closure. MRI-histologic correlation suggests that the NCJ cartilage remains present until adolescence and therefore further exploration of the disparate growth hypothesis is required. Gross anatomic visualization did not reveal the NCJ site, even after removal of the periosteum. In contrast, the presence or absence of an NCJ image correlated with the presence or absence of cartilage although MRI overestimated the extent of this cartilage. Vertebrae were grossly examined for any evidence of the NCJ site. Sagittal and transverse MR images of one hundred and fourteen porcine NCJs in various stages of development (thirty-eight open, sixty-four closing, twelve closed) were correlated with anatomic and histologic sections acquired at the same position.
An instrumented extensively porous coated stem was implanted in composite femur models (n=3) and mechanically tested. The stem stresses resulting from proximal overbroaching, ETO, cable grips, and various cable and strut constructs were determined.
Stem stresses increased 98 when a proximally loose stem was combined with an ETO using laboratory tests. This stress was decreased by up to 37 percent when a long trochanteric plate was utilized.
An instrumented extensively porous coated stem was implanted in composite femur models (n=3) and mechanically tested. The stem stresses resulting from proximal overbroaching, ETO, cable grips, and various cable and strut constructs were determined.
Stem stresses increased 98 when a proximally loose stem was combined with an ETO using laboratory tests. This stress was decreased by up to 37 percent when a long trochanteric plate was utilized.
