The long-term effect of pelvic osteotomy on birth canal size.

The effect of pelvic osteotomy on birth canal size at skeletal maturity is unknown. This information would be useful to counsel women of reproductive age who have undergone pelvic osteotomy. It was the purpose of this study to answer that question. A retrospective review of girls who had undergone pelvic osteotomy in the period 1980-1999 was performed. Transverse plane birth canal dimensions (inlet, mid-pelvis, and outlet) were measured from radiographs before and after osteotomy and at final follow-up. Final follow-up diameters were compared to threshold values (obstetric pelvimetry and clinical guidelines). There were 37 patients (40 osteotomies: 31 Salter, 5 Steel, 2 Chiari, and 2 Ganz). The average age at osteotomy was 7.5 +/- 5.3 years (range 2.0-21.3 years), and at final follow-up was 16.0 +/- 4.7 years (range 2.9-25.7 years); the average follow-up was 8.5 +/- 5.2 years (range 0.5-17.6 years). The effect of osteotomy at skeletal maturity was investigated by analyzing the 30 children > or = 14 years of age at the final follow-up. The pelvic inlet was above the threshold for all 30 children. The mid-pelvis was below the low normal threshold (9.5 cm) in 3 of 21 Salter, 2 of 5 Steel, and 1 of 2 Chiari osteotomies. The pelvic outlet was below the threshold in 2 of 21 Salter and 2 of 5 Steel osteotomies. The mid-pelvis dimensions were narrower in those who underwent osteotomy when older: 7.1 +/- 4.9 years (n = 24) and 11.9 +/- 7.9 years (n = 6) (p = 0.06) for those above and below the 9.5 cm mid-pelvis threshold, respectively. In conclusion, 6 of the 30 cases had a mid-pelvis which was below threshold at skeletal maturity. If the transverse mid-pelvis diameter at skeletal maturity is < 9.5 cm, then the likelihood of Cesarean section is increased, and this information should be given to the patient.