If both the ala of the sacrum are absent, it is called :
Naegele's pelvis: This type of pelvis is extremely rare. It is produced due to arrested development of one ala of the sacrum. (i) Congenital or (ii) Acquired (osteitis of sacroiliac joint). Congenital variety may be associated with urinary tract and may of the same side. The pelvis is obliquely contracted at all levels but more marked in the outlet. Ilio-pectineal line on the affected side is almost straight. Scoliosis involving only the lumbar region will cause deformity of the pelvis. The acetabulum is pushed inwards on the weight bearing side. This may be pronounced if the disease occurs during early life. Oblique asymmetry of the pelvis results in contraction of one of the oblique diameters. Cesarean section is the only safe method of delivery. Robe's pelvis (transversely contracted pelvis): This is an extremely rare abnormality. Ala of both the sides are absent and the sacrum is fused with the innominate bones. Delivery is done by cesarean section. Kyphotic pelvis: It is secondary to the kyphotic changes of the veebral column either following tuberculosis or rickets.The sacrum is tilted backwards in the upper pa and forwards in the lower pa. It is narrow and straight. The anteroposterior diameter of inlet is increased but is diminished at the outlet. Subpubic angle is narrow. Thus, the feature is an extreme funnelling of the pelvis.Abdomen becomes pendulous due to the shoened distance between the symphysis pubis and xiphisternum. Malpresentation is common. Mechanical distress is evident. Cesarean section is ideal and one may have to do the classical operation because of poor formation of the lower segment or for technical reasons. RACHITIC FLAT PELVIS: Rickets is predominantly a disease of early childhood when the bones remain soft and unossified. In childhood changes occur in the bony pelvis due to weight bearing. Inlet: Sacral promontory is pushed downwards and forwards producing a "reniform" shape of the inlet with marked shoening of the antero-posterior diameter without affecting the transverse diameter, which is often increased. Cavity: Sacrum is flat and tilted backwards. There may be sharp angulation at the sacrococcygeal joint. Outlet: Body weight transmitted through the ischium in sitting position results in widening of the transverse diameter of the outlet and the pubic arch. OSTEOMALACIC PELVIS: The deformity is caused by softening of the pubic bones due to deficiency of calcium and vitamin D and lack of exposure to sunrays. It usually affects women after they have reached maturity. The promontory is pushed downwards and forwards and the lateral pelvic walls are pushed inwards causing the anterior wall to form a beak. The shape of the inlet thus becomes triradiate. Approximation of the two ischial tuberosities occurs. Sacrum is markedly shoened, Coccyx is pushed forward.Cesarean section is ideal. Reference: D C Dutta Textbook of Obstetrics 7th edition page 347,348.
Naegele's pelvis
Robe's pelvis
Triradiate pelvis
Rachitic pelvis
General obstetrics