Skull radiograph measurements of normals and patients with basilar impression; use of Landzert's angle.

One hundred normal lateral skull radiographs were studied and those of ten patients with basilar impression attending Kenyatta Hospital, Nairobi. The mean shortest distance of the odontoid tip to McGregor's basal line was 1.2 +/- 2.28 mm below the basal line (range 6 mm below to 3 mm above basal line), in normals and 9 +/- 2.7 mm (6-14 mm) above basal line in patients. The mean basal angle was 113 degrees +/- 7 degrees (102 degrees-133 degrees) in normals and 122 degrees +/- 6 degrees (113 degrees-125 degrees) in patients. The mean nasion-basion-opisthion angle was 162 degrees +/- 4 degrees (154 degrees-169 degrees) in normals and 178 degrees +/- 5 degrees (173 degrees-185 degrees) in patients. The mean total length of clivus was 48 +/- 3.7 mm (43-56 mm) in normals and 44 +/- 6.6 (36-48 mm) in patients group. The mean median diameter of the foramen magnum was 39 +/- 5 mm (30-48 mm), atlas 21 +/- 3 mm (18-25 mm) axis 18 +/- 3 mm (14-23 mm), third cervical vertebra 16 +/- 2 mm (13-22 mm) in normals and in patients: 39 +/- 4 mm (36-45 mm), atlas 23 +/- 6 (15-30 mm) axis 19 +/- 4 mm (16-25 mm), third cervical vertebra 16 +/- 3 (14-20). There was a significant difference in the position of the odontoid tip and the nasion-basion-opisthion angle between the normal and patient groups. All the other parameters measured in this work did not differ significantly between the two groups.