There is little prior research on the treatment for hip dislocation through the Smith-Peterson approach in AMC under the age of 12 months. Our study addresses this research gap, as it presents the experience in treating TDH in AMC using the aforementioned approach for children under 12 months old.
The teratologic dislocations in patients with AMC are much more rigid and irreducible than developmental dysplasia of the hip. Therefore, hip closed reduction generally results in increased stiffness and a high rate of subluxation and redislocation. Consequently, hip closed reduction is normally considered invalid.  Open reduction for teratologic dislocations was introduced for patients with AMC as a valid option and this approach is considered to prevent pelvic obliquity, sitting imbalance, gait abnormality, and secondary scoliosis. 
Concerning surgical time, Bahattin et al. suggest that early reduction (before six months) in patients with AMC does not lead to less hip surgery.  Several authors have suggested that operative treatment of hip dislocations in AMC can be performed at three to ten months. [3, 22, 23] The hip joint development is the result of an intricate balance between growing bony changes of acetabulum with the proximal femur.  Considering the severe deformity of hip dislocation in AMC and the corresponding need for earlier and longer acetabulum molding, we agree with their treatment time window which can be performed at three to ten months. In fact, the results of this study also confirm this viewpoint. The two patients (three hips) with secondary revision surgery were more than eight months old when they received open reduction; however, fifteen out of the total 18 participants did not require secondary revision surgery at less than eight months old. Recall that there was a significant difference in the age of surgery between the secondary revision surgery patients and the non-revision surgery patients. However, sometimes we could not receive the patient for treatment as early as we intended to because some children were abandoned by their families and sent to welfare institutions. In the literature, a relatively high proportion of the reported AMC case series required additional femoral or pelvic osteotomies along with open reduction. This result suggests that the effects of reduction age on acetabular shaping in TDH and developmental hip dysplasia are similar; in other words, reduction surgery at an older age is more likely to lead to residual acetabular deformities. 
Surgical approach with muscle protection
We used a modified anterior Smith-Peterson approach with rectus femoris intact for all the TDH in this research. There are several advantages to using this method to treat patients with AMC. Firstly, more attention should be paid to concentric reduction and reduction stability in hip dislocation in AMC, and the method used here addresses this issue. The acetabulum in AMC is small, shallow, and filled with fibrous-fatty tissue. The femoral head in AMC is hypoplastic and often flattened in its medial portion, which can be demonstrated by arthrography (Fig. 1b and 1c).  Compared with medial-approach open reduction, the anterior Smith-Peterson approach is demonstrably more effective in hip joint exposure, hip obstacle removal, and circumferential capsulotomy. The reports in the literature show that there are more frequent secondary procedures for progressive subluxation after open reduction when the anteromedial access route is used. [3, 8] Additionally, the medial approach is likely related to injury of the medial circumflex artery, which causes iatrogenic AVN especially in infants younger than 12 months with unclear hierarchical anatomy. The reported rate of significant AVN in medial-approach open reduction is as high as 43%. [26, 27] For the present study, we have kept rectus femoris and the tendon attachment of iliopsoas intact in this modified anterior Smith-Peterson approach, which minimizes muscle damage near the hip joint.
Avascular necrosis of the femoral head in open reduction through the Smith-Peterson approach in TDH is a risk when doing a complete capsulotomy of the hip. However, Akazawa et al. thought that hip capsulotomy adjacent to the acetabular rim does not affect the blood supply to the femoral head if the incision has a proper distance from the base of the femoral neck. The lateral epiphyseal artery comes from the femur greater trochanter and passes through the posterior capsule at the femoral neck base. [10, 12] In our series, seven hips demonstrate AVN, but only one hip showed Kalamchi and MacEwen grade IV AVN.
Open reduction was usually associated with increased stiffness of the hip joint in AMC.  In terms of the open reduction approach, Staheli et al. reported that the range of motion of AMC patients who received the medial approach was better than that in those treated using an anterolateral approach.  We consider that the limitation of hip joint motion is related to more soft tissue injury than that which occurs with the anterolateral approach. Therefore, we have retained rectus femoris and the attachment of iliopsoas in our Smith-Peterson approach, which also maximizes the postoperative hip joint function. In our series, most of the children retained a certain degree of hip joint activity, and none of them encountered joint stiffness after the operation.
Bahattin et al. suggested that open reduction for TDH at a late age may be preferable because open reduction and femoral osteotomy procedures can be performed simultaneously to reduce the need for additional surgeries.  However, when the femora-acetabular harmony is created early through the open reduction of the femoral head, the remodeling capacity of the femoral head and the acetabulum could be maximized and the need for additional surgeries may be reduced. In our study, 25 hips were IHDI I degree and three hips were IHDI II degree, without IHDI III or IV classification postoperatively. Only three hips received secondary revision surgery including femoral and pelvic osteotomy in the latest follow-up. These results indicate favorable results for femora-acetabular harmony after early open reduction through a modified Smith-Peterson approach with retained rectus femoris intact.
Bilateral and unilateral side
The reduction of bilateral teratologic hip dislocations in AMC remains controversial. Many authors have argued that bilateral TDH should be left untreated because the pelvis remains level and motion is satisfactory; leaving it untreated also circumvents the high rate of complications after surgery.  Some authors suggest that bilateral TDH should be reduced to restore femora-acetabular harmony and decrease the risk of later pain or stiffness. [3, 12] In our study group, eight patients with bilateral TDH received open reduction surgery simultaneously and seven of these patients did not receive secondary revision surgery. There was no statistically significant difference in surgical age and revision surgery between the bilateral and unilateral hip groups (P=0.188 and P=0.736). These results may suggest that simultaneous open reduction of bilateral hip joints does not affect the clinical results.
TDH in AMC is accompanied by multiple musculoskeletal disorders, such as contractures and other joint dislocations. Management of arthrogryposis is difficult because numerous surgical procedures are necessary for concomitant knee, shank, foot, elbow, and wrist deformities.  We dealt with lower limb deformities in the following order: foot, hip joint, and knee joint.
Our study had several limitations. Firstly, because it was a retrospective study, there was selective bias and no standardized indication for secondary revision surgery. Secondly, the AMC sample size was too small. Having a larger number of patients in future research may yield more definitive results concerning the best time for early open reduction surgery. Thirdly, we only evaluated medium-term clinical outcomes. Longer follow-up may lead to increased incidence of secondary revision surgery and complications and may provide additional clinical information.