MORPHOMETRIC STUDY OF THE ARTICULAR FACETS OF ATLAS VERTEBRA IN NORTH INDIAN POPULATION

Address for Correspondence: Dr Piyush Kumar, Department Of Anatomy, Pt. B. D. Sharma, PGIMS, Rohtak, Haryana, India. E-Mail: piyushkarnonline@gmail.com Introduction: The first cervical vertebra, Atlas (C1) has different anatomical features from the other cervical vertebrae. C1 vertebra is an important part of bony anatomy of Cranio-vertebral Junction (CVJ). The stability of the atlas is provided by two symmetrical lateral masses that are united by anterior and posterior arches. These lateral masses are thick, supportive elements composed of both superior and inferior articular facets. The stability of the cervical spine is violated by various traumatic and non-traumatic causes. Instability of CVJ needs surgical correction or long term immobility to attain a solid fusion. Materialsand Methods: For the study of various metric parameters, 50 atlas vertebrae were used. Maximum anteroposterior (AP) and transverse (T) diameter of SAF and IAF were measured and the data were analyzed. Discussion: SAF-AP: The average anteroposterior diameter of SAF on both the sides of atlas was maximum in European, American, Spanish and German population where as in Indian and Turkish population the values were less. SAF-T: The average transverse diameter of SAF was more or less similar in Indian, German, Turkish and Spanish population. IAF: IAF had maximum AP &T diameter in American and German population. The values of IAF in Spanish population correlated with the values in Indian population. The values were found more or less similar in all the Indian studies. Results and Conclusion: The mean values obtained for all the parameters were more or less symmetrical. In the present study, the AP diameters of SAFs were less as compared to the western population. The values of AP & T diameter of IAF was also found less in Indian population. The knowledge of the dimensions of the SAF (AP 20.25mm; T-10.93mm) and IAF (AP16.95mm; T14.95 mm) help in safe planning of the screw placement during CVJ surgery.

the study.
Measurements: For measuring the parameters of the bone reference points were obtained from published data of Naderi et al. [3] Maximum Antero-posterior Diameter (length) of superior articular facet: Two points were taken, one on the anterior limit of SAF and other on its posterior limit then length was measured (in mm) along its principal axis directed anteromedially.
Maximum Transverse Diameter (width) of superior articular facet: Two points were taken, one on the medial limit of SAF and other on its lateral limit then width was measured (in mm) perpendicular to the principal axis.
Maximum Antero-posterior Diameter (length) of inferior articular facet: Two points were taken, one on the anterior limit of IAF and other on its posterior limit then length was measured (in mm) along its principal axis directed anteromedially.
Maximum Transverse Diameter (width) of inferior articular facet: Two points were taken, one on the medial limit of IAF and other on its lateral limit then width was measured (in mm) perpendicular to the principal axis.
All the measurements were subjected to statistical analysis.The mean, median, range and standard deviation obtained were tabulated and presented for all the parameters.

MATERIALS AND METHODS
The

SAF-AP:
The average anteroposterior diameter of SAF on both the sides of atlas was maximum in European, American, Spanish and German population where as in Indian and Turkish population the values were less than the above mentioned population.for western population may be due to their heavy built and bigger stature which needs statistical verification.The parameter values of our present study when compared with Turkish population were found more or less similar.

INTRODUCTION
International Journal of Anatomy and Research, Int J Anat Res 2017, Vol 5(2.2):3829-32.ISSN 2321-4287 DOI: https://dx.doi.org/10.16965/ijar.2017.194this ring structure when fracture occurs there is disruption of the ring which results in segments that needs surgical repair.C1 vertebra is an important part of bony anatomy of Cranio-vertebral Junction (CVJ).It has articular relationship with occiput and C2.CVJ surgery is an important part of spinal surgery, which requires knowledge regarding the The first cervical vertebra, Atlas (C1) has different anatomical features from the other cervical vertebrae.The atlas holds the globe of the skull and is devoid of body and spine and is composed of an anterior arch and posterior arch with laterally projecting transverse processes which resemble an irregular ring: [1,2].Due to neuromuscular and musculoskeletal anatomy of this region [3].The stability of the atlas is provided by two symmetrical lateral masses that are united by anterior and posterior arches.The posterior arch of the atlas forms about 3/5th of the atlantal ring.These lateral masses are thick, supportive elements composed of both superior and inferior articular facets.SAFs which are present on the atlas vertebrae face superomedially and are well known for nodding movements and for bearing the weight of the head.Inferior articular facets are flat and facing posteromedially [1,2,4].The stability of the cervical spine is violated by various traumatic and non-traumatic causes.Instability of CVJ needs surgical correction or long term immobility to attain a solid fusion.Therefore reduction and rebuilding of the stability of this complex is important.A short segment posterior fixation technique is often adopted to preserve the motion of the CVJ.This study is undertaken to assess the safe site for different surgical methods for which morphometric measurements of SAFs and IAFs are necessary.No such work has been done on this bone in North Indian Haryanvi population.Various authors have attempted to study and throw some knowledge about the morphologic and morphometric details of atlas in European, Turkish, German, Spanish and American population.[4-9] Indian authors who have contributed to provide data for morphologic and morphometric parameters of atlas bone are Cacciola et al, Gosavi and Vatsalaswamy, Gupta et al, Jasveen Kaur et al and Rekha et al. [13-15].
present study was conducted in the Department of Anatomy, Pt.B.D Sharma Post Graduate Institute of Medical Sciences, Rohtak, India.For the study of various metric parameters, 50 atlas vertebrae were used.These bones were retrieved from the Department of Anatomy, Pt.B.D Sharma PGIMS, Rohtak.Digital Vernier Calliper was used for measuring the parameters.The fractured atlas vertebrae and pathologically deformed atlas vertebrae were excluded from The parameters mentioned (vide supra) were analyzed and are shown in : The average transverse diameter of SAF was more or less similar in Indian, German, Turkish and Spanish population.IAF: IAF had maximum AP & T diameter in American and German population.The values of IAF in Spanish population correlated with the values in Indian population.European data for IAF was not available.The values were found more or less similar in all the Indian studies.In general the variation in SAF & IAF parameters

CONCLUSION
In the present study, the AP diameters of SAFs were less as compared to the western population.The values of AP & T diameter of IAF was also found less in Indian population.The knowledge of the dimensions of the SAF (AP-20.25mm,T-10.93mm) and IAF (AP-16.95mm,T-14.95 mm) help in safe planning of the screw placement during CVJ surgery.

Table I : RESULTS Table 1 :
Showing the Parameters that were analyzed.
Paired T-test was carried out for comparison of readings from right and left sides.When these parameters were subjected to paired t-test the difference was found to be statistically insignificant.Few authors (Kandizora et al, Naderi et al, Cacciola et al and Gupta et al) have reported the results without considering the side (right / left) of facet.Their data was also considered for comparison in our study.DISCUSSION

Table 3 :
Comparison of Maximum Transverse Diameter of Superior Articular Facet of atlas.

Table 4 :
Comparison of Maximum Antero-Posterior Diameter of Inferior Articular Facet of atlas.

Table 5 :
Comparison of Maximum Transverse Diameter of Inferior Articular Facet of atlas.