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This comprehensive anatomical study on bones and X-rays regarding pedicles of lumbar …

Home » Biology Articles » Anatomy & Physiology » Anatomy, Human » Morphometry of Vertebral Pedicles: a Comprehensive Anatomical Study in the Lumbar Region » Discussion

- Morphometry of Vertebral Pedicles: a Comprehensive Anatomical Study in the Lumbar Region

Chaynes et al. reported a cadaveric study on vertebral pedicle anatomy in relation to pedicle screw fixation. They reported that the pedicular height in spine gradually increases from T1 to L5. On the contrary in the present study the vertical height (v) in bone specimens increased from LI to L2, decreased from L2 to L3, increased from L3 to L4 and markedly increased from L4 to L5. In the present work, the minimum horizontal diameter (d) in lumbar spine increased from LI to L5, whereas in the study reported by Chaynes et al. (2001), the pedicular width was greatest at the three junctional regions of the spine. Linear measurements of both vertebral pedicles were made in ten complete lumbar cadaveric spines using calipers in study reported by Chaynes et al. , whereas our study report the same was based on measurements of bone specimens of fully ossified 200 male and 200 female lumbar vertebrae greater than 20 years of age; hence the aforementioned differences may be one of the factors responsible for the different observations.

Analyses of the observations with prior works by other authors reveal many interesting facts. In previous reports by Amonoo- Koufi and Singel et al. , values for left and right pedicles of the lumbar vertebra were nearly the same, on the contrary in our study the results were different and hence presented separately. Singel et al. reported that nearly all the measurements were greater in females than the males, whereas in our report all the mean values of the parameters observed in male subjects scored significantly higher and this can be justified as they have to support greater upper body weight. The anteroposterior length from body of the vertebra to the transverse process along the long axis was not included in majority of the previous works, although it is important for screw fixation techniques. These values were maximum at L2 level and minimum at L5 level in both left and right pedicle in both the sexes. Short stature of average Indian population compared to the western world can be correlated for the decreased value of all the parameters bilaterally from LI to L5 in both the sexes. Greater vertical height (v) values of L2 vertebra than LI and L3 is due to the closer location of the first lumbar pedicle to the transitional junction of thoracolumbar spine, and is again the site of complex zygapophyseal joint. The brunt of this force transmission should then be on L2 vertebra which has adapted itself resulting in increased pedicle vertical height. This stable position makes the L2 vertebra less prone to dislocate as compared to LI transition vertebra. All the explanations given by previous authors (Amonoo-Kuofi; Coles et al. 1998; Fidler, 1988; Krenz & Troup, 1973; Postachini & Cinotti, 1992; Singel et al) regarding the greater vertical height of LI pedicle will finally apply to the L2 pedicle. The uniform increase in minimum horizontal diameter from L1 to L5 bilaterally in both males and females is similar to observations and explanations given by the earlier authors and is primarily related to the role of weight transmission.

Age related variations observed from X-rays concluded some facts which could not be assessed from direct gross measurements. The maximum horizontal diameter (t) of both right and left pedicles from radiographs of female subjects were significantly greater than male counterpart at all vertebral segments from LI to L5 in adolescent age group (10-20 years), this finding was contrary to the rest of all the age groups (>20 years), where it was significantly greater in males. Aforementioned observations can best be correlated with early pubertal growth spurts in females than males, which reflected as different trend in 10-20 years age group. Same explanation applies to the maximum vertical height (h), though the differences were not statistically significant, inferring that this parameter was relatively less affected by pubertal changes in both the sexes. Similar observations were reported by Amonoo- Kuofi, though his study was different as there were no differences between right and left pedicles measurement and the gender difference were not significant in majority of elder (> 50 years) age groups. He related the larger vertical diameter of the pedicle of the 1 st lumbar vertebra (in both males and females) as compared with the vertical diameters of 2nd and 3rd lumbar pedicles by the weight bearing functions and concluded that vertical diameter with its larger dimension and wider variations with age, contributes more to weight- bearing function than the horizontal diameter. He opined that after the 5th decade of life the horizontal and vertical diameters of pedicles in females showed a tendency to increase, while male diameters decreased (1995). On the contrary in the present study the aforementioned diameters in elder (>50 years) age group showed a tendency to decrease in both the sexes. Hence it can be hypothesized that age related osteoporosis along with wear and tear processes is responsible for decreasing diameters in the X-rays.

What are the factors contributing to the measured differences between specimens and the X-rays in the present study? Following possibilities can be hypothesized:

1. Partial volume effects are responsible for this phenomenon which resulted in greater values in the radiological study than the direct specimen observations.
2. In plain radiographs, magnification factor can only be roughly estimated, besides X-rays measurements had the common limitation of the two dimensional structures.
3. Bone specimen observations had the usual benefit of three dimensional structures; on the other hand, the fact that some dry bone properties differ from the in vivo bones was the main limitation.

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