Anatomical Variations Of The Occipital Condylar In The Post-lateral Approach To The Lesions Of Ventral Foramen Magnum

Objective: Through the quantitative study on correlated anatomy of foramen magnum in Chinese dry skulls, to provide anatomical evidence for whether or not removing the occipital condylar when dealing with the lesions of ventral FM.Methods: a series of anatomy data(including FML, FMW, AOCP and OCA) correlating FM of one hundred skulls were measured with slide gaudl .Then classified those into three types according to the ratio of AOCP/FML.Result: The mean distance of FML,FMW,AOCP and OCA are 34.81±4.39mm,29.11±4.39 mm,15.99±3.25mm,24.07±4.78mm respectively. Three groups were obtained after skulls classification, in which 8 cases of group I (8%) with small condylar, 74 cases of group II with middle condylar, and 18 cases of group III with big condylar.Conclusion: Great anatomical variations were found in the shape of occipital condylar. Before dealing with the lesions located in FM, indentifying the type of condylar using preoperative CT 3-D bony reconstruction will be helpful for the selection of suitble post-lateral approach.Objective: Through the skull measurements and quantitative analysis of correlated anatomical structure, to provide scientific basis for the selection of operative approach to lower clivus and ventral foramen magnum(FM).Methods: One hundred skulls was classified according to the shape of FM with the ratio of AOCP/FML, to statistically analyze the difference of exposing angle to the ventral FM by different approaches.Result: Three groups were obtained after skulls classification, in which 8 cases of group I (8%) with small condylar, 74 cases of group II with middle condylar, and 18 cases of group III with big condylar. There was no statistical difference between angle A and B in group I, but significant differnece was demonstrated in group II and III.(angle A and B is the exposing angle pre- and post 1/3 condylar resection respectively)Conclusion: Great anatomical variations were found in the shape of occipital condylar. When dealing with the lesions located in low clivus and FM, the suboccipital lateral approach will provide a satisfactory exposure in patients with small condylar. For those with middle and big condylar, partial resection of condylar will offer a wider exposing angle, thus the far lateral transcondylar approach seems necessary. Identifying the type of condylar using preoperative CT 3-D bony reconstruction will be helpful for the selection of surgical approach.