Traumatic dislocation of normal hips in children is a rare injury [1] , accounting for 5% of all hip dislocation at any age [2] , with an incidence of 0.8 cases per million/year [3] . Posterior dislocation accounts for 80% of such cases [4] . It occurs predominantly in older boys, which is probably due to their higher traumatic morbility [5] . In younger children, dislocation may result from low energy trauma [6] , and this might be related to the anatomic characteristics of this age group [7] . The younger the child, the more predisposing factors there are and the higher the susceptibility of the hip dislocation to the minor trauma [5] . It constitutes an orthopedic emergency [8] . The treatment should be performed as early as possible [8] . The reduction is usually easy to achieve; but labral, capsule, and/or osteochondral fragment interposition may prevent concentric reduction [9] . There is usually a favorable outcome after expedient reduction, although avascular necrosis can occur [7] .

We report a case of a traumatic posterior hip dislocation in a 5 years old girl caused by low energy trauma.

A 5-year-old girl with no history of medical or surgical pathology, fell from the ground and landed on her right hip during a playful accident. She was received at the emergency department 1 hour later for closed trauma of the right hip with vicious attitude of the homolateral lower limb: combining flexed knee, adduction and internal rotation figure ( Figure 1 ). There was no evidence of sciatic nerve and/or vascular involvement. The standard radiograph in the lateral and anteroposterior views of the injured hip showed a posterior displacement of the femoral head without any associated bone injury ( Figure 1 ).

Two hours later, under general anesthesia, a closed reduction was performed in the operating room. The patient was in supine position on the standard table, the knee and the hip flexed in 90, a traction force was applied along the axis of the femur, while the pelvis was held by an assistant. The reduction occurred ( Figure 2 ). The control radiograph showed a coxa valga at 140, an external coverage angle of the acetabulum at 31, and the hip was congruent without any widening of the joint space compared to the non-traumatized side ( Figure 2 ). There was no evidence of sciatic nerve injury. Cutaneous traction for three weeks was done, followed by protection of the support for three more weeks.

At 4 months of follow-up, she had resumed her previous activities without any deficit. The radiograph showed no signs of early osteonecrosis of the femoral head; the reduction was maintained.

Traumatic posterior hip dislocation in children is uncommon, unlike in adults. This observation concerns a 5 year-old girl, victim of low energy trauma. The diagnosis was made using a standard radiograph. The reduction was performed earlier. The outcome was satisfactory in the short-term.

The rarity of this injury in children contrasts with the benign nature of the trauma in this age group [1] . This injury is more common in boys [10] [11] and may occur at any age among children, although the peak incidence occurs between 4 and 7 years of age and between 11 and 15 years of age [10] - [12] . In younger children, the acetabulum is very flexible, loose and cartilaginous; and the ligaments are weak [3] [7] [8] [13] , thus allowing trivial trauma to result in dislocation [14] - [17] . So these represent the most recognized predisposing factors [14] - [17] . Other anatomical conditions are also associated with this injury such as: coxa valga, defect in external coverage of the femoral head, an opening of the acetabular angle and a decrease in acetabular anteversion [1] [18] . There are probably other predisposing factors that are still unknown [1] . The flexibility of the periarticular structures may explain the absence of associated bone injuries [2] [7] . A vicious attitude of the limb in a context of low-energy trauma, without any pathological history or any medical warning signs, should make this injury suspect despite the similarity with other hip injuries such as a fracture separation of the proximal end of the femur. Good-quality radiographic evaluation is essential for confirming or discardind the diagnosis, revealing the type of dislocation and discarding the hypothesis of associated fractures [3] . Traumatic hip dislocation in children is an orthopedic emergency [4] [16] . There is a consensus that the reduction should be performed immediately, preferably using a closed procedure and under general anesthesia [12] [19] [20] or with relaxants [4] [12] , using the same maneuvers as used for reductions in adults (Stimson, Allis and Bigelow) [3] [8] [11] [12] [14] . After the reduction, the joint congruence should be evaluated, comparing the joint space, lateralization of the head [21] and breakage of Shenton’s line [11] with the contralateral side. There continues to be no consensus regarding the treatment to be followed after achieving reduction [8] . Despite the difference in post-reduction care methods, the duration of limb nonweightbearing of up to 6 weeks is noted by several authors, in order to allow the capsule to heal [3] [11] [13] [15] [22] . The outcome of traumatic hip dislocations in children is generally favorable compared to that in adults [8] . The younger the child, the fewer complications they experience [8] .

Traumatic posterior hip dislocation is rare in children. It occurs in a young girl, with a coxometric abnormality, after a low-energy trauma. Its closed reduction under general anesthesia is easy by external maneuver. The outcome is favorable in the short term after a maximum of 6 weeks of nonweightbearing.

A long-term follow up would be a beneficial option in order to look for late-onset complications such as aseptic femoral head osteonecrosis.