There is little prior research on treating hip dislocation following the Smith-Petersen approach in AMC for infants. Our study addresses this research gap, as it presents an experience in treating TDH in AMC using the aforementioned approach for children under 12 months old.
The TDH in 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, reducing its favor among surgeons.  Open reduction for TDH was introduced for patients with AMC as a valid option due to its ability to prevent pelvic obliquity, sitting imbalance, gait abnormality, and secondary scoliosis. 
Concerning surgical age, Bahattin et al. argue that early reduction (before six months) in AMC does not reduce future hip surgeries.  Several authors have suggested that operative treatment of TDH in AMC can be performed at three to ten months. [3, 22, 23] Hip development involves an intricate balance between changes in the acetabulum and the proximal femur.  Considering the severe deformity of TDH and the corresponding need for earlier and longer acetabulum molding, we agree with their treatment window at three to ten months. In fact, the results in this study confirm this viewpoint. The two patients (three hips) requiring secondary revision surgery were more than eight months old when they received open reduction; however, 15 out of the total 18 participants did not require secondary revision surgery at less than eight months old. There was a significant difference in the age of surgery between the secondary revision surgery patients and the non-revision surgery patients. However, we sometimes did not receive the patients within the ideal timeframe because they 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. These results suggest 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. 
We used a modified anterior Smith-Petersen approach that preserved the rectus femoris for all the TDH in this research. There are several advantages to this method. First, it allows more attention to be paid to concentric reduction and reduction stability in TDH in AMC. 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-Petersen approach is demonstrably more effective in hip exposure, 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 using the anteromedial access route. [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] In the present research, we preserved the rectus femoris and the tendon attachment of iliopsoas in this modified anterior Smith-Petersen approach, thus minimizing muscle damage near the hip.
Avascular necrosis of the femoral head in open reduction through the Smith-Petersen approach in TDH is a risk when doing a complete capsulotomy of the hip. However, Akazawa et al. indicated that hip capsulotomy adjacent to the acetabular rim would not affect the blood supply to the femoral head if the incision is sufficiently distant 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 the Kalamchi and MacEwen grade IV AVN.
Open reduction often has been associated with increased stiffness of the hip 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 of those treated using an anterolateral approach.  We believe that the limited hip motion is related to the added soft tissue injury that occurs with the anterolateral approach. Therefore, we have preserved the rectus femoris and the attachment of iliopsoas in our Smith-Petersen approach, which also maximizes postoperative hip 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, the remodeling capacity of the femoral head and the acetabulum can be maximized, reducing the need for additional surgeries. 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-Petersen approach that preserves the rectus femoris.
The reduction of bilateral TDH 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 require 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 has little effect on clinical results.
TDH in AMC is accompanied by multiple musculoskeletal disorders. 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. First, 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 age-related opportunity 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; it may also provide additional clinical information.