DDH is a progressive disease with varying severity in children. The stability of the pelvic ring is mainly maintained by the posterior sacroiliac joint, the anterior pubic symphysis, and the surrounding ligaments, which tightly bind all bone blocks together to form the pelvic ring (13, 14). In this study, nine child cadaver specimens were subjected to unilateral and six of those were subjected to one-stage bilateral Salter pelvic osteotomy. We found that one-stage bilateral Salter osteotomy had a similar effect on sacroiliac joint stability, local stability, axial stiffness, and ultimate load as unilateral Salter pelvic osteotomy.
The sacroiliac joint, and especially the surrounding ligaments, play an important role in the stability of the posterior pelvic ring. Salter pelvic osteotomy damaged the pelvic ring, but we found that the sacroiliac joint at the operation side after unilateral Salter pelvic osteotomy was more stable than at the non-operation side. This may be caused by a bilateral asymmetrical force. In Barnes’s study, the researchers found that unilateral Salter pelvic osteotomy could lead to hip dysplasia on the healthy side(15). We think that the pelvic stress on the operation side was transferred to the contralateral pelvic ring, as force hinge, carrying more load which affected the stability of the non-operation side. However, one-stage bilateral Salter pelvic osteotomy cuts both the left and right ilium and both sides are fixed with the same treatment. This could lead to two hinge points making bilateral sacroiliac joint stress a symmetrical force.
Salter pelvic osteotomy cuts the ilium and is fixed with Kirschner wires. This study tested whether one-stage bilateral Salter pelvic osteotomy increases the risk of local stability. We found that the RVD of local stability for one-stage bilateral Salter pelvic osteotomy was between 0.50 and 0.52 mm, which is lower than that for unilateral Salter pelvic osteotomy. Moreover, we considered that one-stage bilateral Salter pelvic osteotomy created a bilateral symmetrical force on both the left and right pelvic ring.
The axial stiffness of the pelvis reflects the displacement of the pelvis when subjected to axial pressure(16). The greater the axial stiffness, the stronger the pelvic compressive capacity. We found that both unilateral and one-stage bilateral Salter pelvic osteotomy decreased the axial stiffness of the pelvis. In addition, this study showed axial stiffness of one-stage bilateral pelvic osteotomy (91.30 N/mm) to be lower than that of unilateral Salter pelvic osteotomy (119.06 N/mm) but the difference was not significant. The ultimate load reflects the stability of the whole pelvic ring, and we found that one-stage bilateral Salter pelvic osteotomy did not decrease ultimate load, which verified the stability of one-stage bilateral Salter pelvic osteotomy. Interestingly, the ultimate load test showed that, regardless of whether unilateral or bilateral pelvic Salter osteotomy was performed, the pelvic ring was first destroyed at the sacroiliac joint, and not at the Kirschner wire fixation site. According to the current weight estimation formula “Weight (kg) = 2(age + 4)”(17), the ultimate load of two Salter pelvic osteotomies is strong enough to support at least eight times the body weight of a child aged six years. All the results support the theory that one-stage bilateral pelvic Salter osteotomy is vertically stable. However, due to the preciousness of the cadaver specimens, the study did not test the ultimate load of a normal pelvic ring, so no comparison between a normal pelvic ring and a bilateral one-stage osteotomy pelvic ring was done in this study.
This study was the first to confirm the stability of one-stage bilateral Salter pelvic osteotomy. Some surgeons have tried one-stage surgery for DDH disease and have followed up on efficacy. In Ochoa’s study, 45 children suffering from congenital dislocation of the hip or acetabular dysplasia were assigned to one-stage bilateral Salter pelvic osteotomy (15 children) or successive Salter osteotomy (30 children). One-stage osteotomy was shown to be viable and had a better acetabular index and may be even better than that of a unilateral osteotomy(18). In another study(19) a one-stage operation (using a Pemberton osteotomy for one hip and a Salter osteotomy for the other hip) was more economical and allowed more rapid recovery than a two-stage procedure comprising consecutive operations. In addition to Salter osteotomy, the stability of a one-stage Pemberton's pericapsular osteotomy, which also damages the pelvic ring, has been verified. In Zorer’s study, twenty patients underwent a one-stage bilateral Pemberton's pericapsular osteotomy, and the results showed significant advantages over two separate consecutive interventions(20). Another study by Agus’s team evaluated the clinical outcome of 12 children (24 hips) who treated with one-stage bilateral Salter pelvic osteotomy and compared with 12 patients (12 hips) who received unilateral Salter pelvic osteotomy, and found one-stage bilateral Salter pelvic osteotomy didn’t increase the mortality and postoperative complications(21). And only the blood transfusion volume was higher in one-stage bilateral Salter pelvic osteotomy group than that of unilateral osteotomy group (170 cc vs 100 cc), which may be because bilateral osteotomy group needs longer operation time.
Although the stability of a one-stage bilateral Salter pelvic osteotomy was verified in this study, there were some limitations. First, there were a limited number of cadaveric pelvic specimens, and only six underwent one-stage bilateral Salter pelvic osteotomy. Second, the cadaver specimens belong to kids without any DDH, our model could not completely simulate live patients. The weight of the upper body is mainly transmitted to the pelvic ring through the bones, especially the spine, but some tissues such as skin, fascia, and muscle of psoas, gluteals, etc. also transmit pressure. Third, according to our clinical experience, children who undergo one-stage bilateral Salter pelvic osteotomy receive plaster fixation and are allowed to start some exercises in bed before pelvic osteotomy healing, whereas the specimens in the study were static and the early postoperative activities of children could not be simulated. Fourth, In Salter osteotomy the fulcrum point is the pubic symphysis, we evaluated the RVD of the surgical site, but did not evaluate the anterior and lateral displacement of the acetabulum on the contralateral side. In addition, the pubic symphysis, as the force hinge of Salter osteotomy, was very meaningful to explore the stability difference between unilateral and bilateral salter osteotomy. In future research, we need to further explore and improve these deficiencies. Despite these limitations, some important structures were protected, and showed that one-stage bilateral Salter pelvic osteotomy is viable and stability for bilateral DDH.
In summary, this study was based on the pelvis of children aged two to six years, and simulated one-stage bilateral Salter pelvic osteotomy. Compared with unilateral Salter pelvic osteotomy, one-stage bilateral Salter pelvic osteotomy is viable and stability from the aspect of sacroiliac joint stability, local stability, ultimate load, and axial stiffness. However, this finding was based on experimental research. Clinical treatment of patients is more complicated and is affected by many factors, such as the physical condition of the patient, hospital infrastructure, anesthesia level, doctor's experience, and patient compliance. We must carefully choose treatment options. In addition, a larger number of specimens and long-term clinical follow-up are necessary in future.