Femoral Epiphysis Early Ischemic Magnetic Resonance Diagnostic Studies

Correlation between MRI Characteristics and Histologic Findings in Growth Cartilage of PigletPurpose: To determine the correlation between MR signal characteristics and histologic findings of growth cartilage. Materials and Methods: 24 knees including distal femur and proximal tibia of twelve 2-week-old piglets were imaged at 1.5 Tesla GE MR scanner. Comparison of signal intensity and thickness of cartilaginous regions seen on MR images with architecture and thickness of zones shown in corresponding histologic sections was made. Results: MR imaging delineated five regions between the secondary ossification center and the metaphysis corresponding histologically to zone of provisional calcification of secondary ossification center, physis of the secondary ossification center, epiphyseal cartilage, main physis and zone of provisional calcification. The thickness of regions shown on T₁- and T₂- weightedimaging correlated with that of histologic zone (r|- =0.88). Conclusion: MRI findingsdifferentiated the different regions of growth cartilage and correlated with histologic findings. Gadolinium-Enhanced MR Imaging in Normal Developing EpiphysisPurposes: To define the MR appearance of normal epiphyseal and physeal cartilage and that of normal epiphyseal and metaphyseal marrow on Gadolinium-enhanced MR. Materials and Methods: We studied Gd-enhanced MR appearance of epiphyseal and physeal cartilage in 20 proximal and distal femoral ends of 10 healthy piglets. In other 8 health piglets, the enhancement ratio of epiphyseal and metaphyseal marrow in different weeks-old piglets were analyzed. The correlation of MRI characteristics with histologic findings was studied. Results: Gd-enhanced MRI enabled to make differentiation between physeal and epiphyseal cartilage and reveal epiphyseal vascular canals. Enhanced ratios in physeal cartilage were bigger than those in epiphyseal cartilage (P<0.005). The metaphysis and the periphery of the secondary center of ossification were red marrow. Their enhancements were great on enhanced SE T1WI, and enhancement ratio in the both regions declined with age. The central regions of 2nd center of ossification and diaphyses were yellow marrow and showed low signal intensity on enhanced SE T1WI. Conclusion: Gd-enhanced MR imaging enabled to show difference in enhancement between physis and epiphyseal cartilage, and reveal epiphyseal vascular canals. Metaphysis (red marrow) and periphery of the 2nd center of ossification(red marrow) are enhanced more intensely than the central regions of 2nd ossification center (yellow marrow). The enhancements in all regions declined with age. Dynamic Gadolinium-enhanced MR Imaging in normal growing cartilagePurpose: To evaluate the blood perfusion of epiphysis, physis, spongiosa, metaphysis and 2nd ossification center in normal growing skeletons by using dynamic gadolinium-enhanced MR imaging. Materials and Methods: Ten 2-week-old piglets were studied, including 20 distal femurs. All piglets were imaged in a 1.5T GE scanner. For dynamic gadolinium enhanced imaging, spoiled gradient-recalled echo images with a temporal resolution of 3.0s were performed before, during and after the injection of gadolinium, and a total of 72 images were obtained. The histologic samples were examined after scanning. Enhancement ratios of the various anatomic regions on MRI were evaluated and compared with histologic findings. Results: The enhancement ratio of physeal cartilage was greater than that of epiphyseal cartilage (P<0.001). The enhancement ratio of metaphyseal spongiosa was greatest compared to those of all other anatomic regions (P<0.001). The epiphyseal cartilage enhanced most slowly, compared to physis and spongiosa (P<0.001). Dynamic enhancement on MR imaging coincided with histologic data showing the locations and concentrations of blood vessels in physes, epiphyses, metaphyses and other anatomic regions. Conclusion: Dynamic gadolinium-enhanced MR imaging can characterize the perfusion in the various anatomic regions of growing cartilage. Manifestation of Early Ischemia in Capital Femoral Epiphysis Induced by Hyperabduction and Its Reversal on Gadolinium-Enhanced MRIPurpose: To demonstrate that the early ischemia of capital femoral epiphysis induced by hip hyperabduction can be reversal and Gadolinium-enhanced MRI may detect early reversible ischemia. Materials and Methods: Eight 3- to 7-week-old piglets were placed in maximal hip abduction bilaterally. After 3 to 72 hours of consistent hyperabduction, gadolinium-enhanced MRI was used for 16 hips of eight piglets. After MR imaging was completed all piglets were allowed to ambulate freely for one or seven days and re-imaged. On enhanced MRI the characteristics of epiphyseal and physeal cartilage and 2nd ossification center in femoral heads were evaluated and lack of enhancement in epiphysis indicates ischemia. The comparison between MRI appearances and histological findings was made. Results: On gadolinium-enhanced MRI, regional decreased or absent enhancement was seen in 7 cartilaginous epiphyses and 6 physes of all 16 femoral heads. The reversal was seen in only one epiphysis and one physis after one day of ambulation and in all rest after 7 days of ambulation. The abnormality was not seen in histologic study after one or 7 days of ambulation. Conclusion: The early ischemia of capital femoral epiphysis induced by hip hyperabduction within 72 hours can be reversal and Gadolinium-enhanced MRI may detect the early reversible ischemia. Perfusion MR Imaging in super-early ischemia of growth cartilagePurpose: To evaluate the change of perfusion in super-early ischemia of growth cartilage of femoral head induced by hyperabduction. Materials and Methods: 14 femoral heads of seven 2-week-old piglets were studied. At beginning all piglets were placed with hips in neutral position and MR scans were performed . After MR exams, all piglets were placed with bilateral hips in consistent hyperabduction for 2 hours and the same MR exams were repeated . After that, all piglets were allowed to ambulate. After 24 hours the same MRI was performed again. The main MR sequences included perfusion MR imaging and conventional Gd-enhanced SE T1WI. Enhancement ratios of the various anatomic regions of femoral heads in hips with hyperabduction were compared with those in hips with neutral position. The corresponding histologic findings were evaluated. Results: The enhancement ratios of physes and spongiosas of femoral heads with hips in hyperabduction were significantly less than those in normal physes and spongiosas(P<0.05). Physes and spongiosas with hyperabduction enhanced significantly slower than those with neutral position(P<0.05). The MRI appearances of growth cartilage after ambulation were the same as those before abduction. Histologic findings showed no evidence of osteonecrosis or necrosis of chondrocyte. Conclusions: Perfusion MRI can detect super-early ischemia of growth cartilage of femoral head induced by hips with hyperabduction.