The first sample examined was the central piece of the distal femur. The differences between the peaks and valleys are visible. The structures in the valley appear to be more dense than those in the peak regions.
peak of distal femur
valley of distal femur
The difference in growth rates can be seen in this light microscope picture (3).
This picture is of the anterior distal femur. Although the other pictures are of the central distal femur, the expected growth differeces are visible.
Upon examination of the first sample, it was realized that the bone was not fractured well enough to see the matrix structure. We then refractured the sample and replated it with gold. This second look at the central portion of the distal femur provided us with better results. More details of the cell matrices are revealed in these photomicrographs.
Valley of distal femur after refracturing showed at443x magnification. The cell structure is much more noticeable than in the original piece. The cross pieces are called longitudinal septae, and they indicate where the cells used to be. The cells were destroyed in the fixation.
The peak of the distal femur after refracturing, shown at a magnification of 378 x.
A longitudinal septae shown at 23,000x.
IV. Discussion:
The structural differences between this piece and the valley are not very noticeable. This could be because the samples were fixed in formalin, when they should have been fixed in glutaraldehyde. Formalin is 37-50% formaldehyde and is a coagulant. Glutaraldehyde would have been the better fixative because it is a protein fixer. On some photos there were small round particles that were thought to be calcium crystals, but upon X-ray analysis, were found to be calcium phosphate, contamination from the 3% Biz solution.
It was thought that the anterior piece would show a more dramatic difference in the structure of the cell matrices. However, the results from this particular sample were not clear. The section of bone was thin, making it difficult to slice the sample into pieces for mounting and better viewing without ruining what was there. Perhaps better pictures would have resulted if the sample was sliced differently before mounting, but a thicker sample would have helped, too. It also seems as though the growth plate shrank together, most likely the result of the fixation process. Therefore the growth plate was not as visible as it was expected to be.
This project was useful for showing the overall structure of the growth plate region. However, it was not as helpful for seeing the individual structures up close. There was still a noticeable difference between the peaks and the valleys, mainly in the general structure of the growth plate region. This difference in shape may attribute to the different growth rates in the respective regions.
REFERENCES
1. Lerner, A.L "Variations in Bone Growth Rate in the Rabbit Distal Femur are Strongly Correlated to the Volume of Extracellular Matrix in the Hypertrophic Chondrocyte Domain." 44th Annual Meeting, Orthopaedic Research Society, March 16-19, 1998, New Orleans, Louisiana.
2. ibid
3. Photomicrograph supplied by Dr. Amy Lerner, Professor of Biomedical Engineering, University of Rochester.
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