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The vertebral column in general is made up of 33 vertebrae of different shape and size, although all of which share typical features. There are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral vertebrae that fuse into one at the age of about 20 years, and 4 coccygeal vertebrae that become one piece at middle age.
The study of human skeletons in the Gross Anatomy Laboratory, Faculty of Medicine, Khon Kaen University from 1975 to 2004 totalled 480 skeletons which we found a case with 6 lumbar vertebrae. The first and the sixth presented anatomical variations from the typical and normal lumbar vertebrae. We are interested in reporting the case that has never been reported in Thai.
- To study anatomy of the six lumbar vertebrae in Thai skeletons.
- To study the articulation between the sixth lumbar vertebra and sacrum.
The skeleton of a 57 year old male presents anatomical variations of lumbar vertebrae. He has six, in contrast to normal five lumbar vertebrae whereas the other levels are normally, 7 cervical, 12 thoracic, 1 sacral and 1 coccygeal vertebrae.
The first lumbar vertebra is obviously differently from others in that its transverse processes are short and articulated with the malformed ribs. The pair of this malformed ribs is the 13th, an extra pair additional to the normal 12 pairs. The right one is 4 centimeters long while the left is 3.5 centimeters. Additional malformed of pair of ribs in this case made 3 pairs of floating ribs. Anatomy of the second to fifth lumbar vertebrae are similar to the typical lumbar vertebrae.
The sixth lumbar vertebra situated below the fifth and articulated to the first sacral vertebra. Although in general the body of the sixth lumbar vertebra configuration is similar to the other lumbar vertebrae but its spinous process projected posterior, is short with a shape of plump ridge. The left transverse process is slender and longer than the right transverse process. The upper border of the body that is articulated to the intervertebral disc below the fifth lumbar vertebra is rough and extended around its rim. The lower border that articulated to the sacrum has a smoother surface than the upper. The inferior surface of the both transverse processes are the extended tubercles that projected downward anteriorly and articulate to the upper surface of ala of sacrum completely. The inferior articular process on inferior surface of both transverse processes were seen but the processes looked very small and short with tubercles that articulated to the small and short superior articular processes of the sacrum.
The sixth lumbar vertebra is the anomaly of the skeletal system that found in our study. This abnormality can be ascribed to the over-splitting of the embryonic somite and the subsequently complicated development process starting from the cellular level up to the naked eye observation. This is the first report on sixth lumbar vertebra in 480 skeletons. The incidence of this anomaly in Thai should be further researched.