Introduction

Traumatic hip dislocation (THD) is a rare injury in young children with an incidence of 0.8 per million children aged < 14 years1. In contrast to THD in adults, lower-energy trauma can lead to hip dislocation in children because of the loosened hip capsule, larger range of motion of the femoral head, greater thickness of acetabular cartilage, and greater flexibility2,3. Hip dislocations can be classified as simple (without associated fractures) or complex (with associated fractures of the acetabulum, femoral head, or neck) depending on whether the fracture is complicated. THD is often associated with fractures due to high-energy injuries. Approximately 13% of children with THD are reported to have concomitant fractures. Ipsilateral femoral fracture is a relatively common fracture that often leads to missed diagnosis of hip dislocation4,5.

Previous studies have found that the magnitude of energy responsible for THD in children increases with age2 and THD in children should be reduced as soon as possible. Previous studies have shown that reduction within 6 h after dislocation can effectively reduce the incidence of avascular necrosis (AVN) of the femoral head3.

There are few studies on the evaluation of THD in children, and a consensus on treatment principles and protocols is lacking6,7,8. This study aimed to analyse THD in children at our clinical centre.

Patients and methods

Clinical data of children with THD treated at our clinical centre from 1 June 2012 to 1 January 2022 were collected. General data, injury mechanism, type of dislocation, other combined injuries, reduction time, reduction method, imaging findings before and after reduction, treatment after reduction, and complications were also recorded.

The inclusion criteria were as follows: patients aged < 18 years, patients diagnosed with THD with no pathological disease, and patients with intact clinical data. The exclusion criteria included patients aged > 18 years, those with other related diseases, and those lost to follow-up. The Merle d’Aubigné–Postel hip score (MDP) was used to assess hip function at the last follow-up9. The total score is 17–18 points for excellent, 13–16 points for good, 9–12 points for moderate, and less than 8 points for poor hip function. The ethics committee of our hospital approved this study and all guardians provided written informed consent for publication. All methods were performed in accordance with in accordance with the Declaration of Helsinki.

Results

Nineteen children with THD were enrolled, including 12 male and seven female patients. The mean age was 8.28 ± 0.99 years (range 2.3–15.3 years). The types of hip dislocation were posterior in 17 patients (89.47%), medial in one patient, and anterior in one patient. The left and right sides were involved in nine and 10 patients, respectively. Four patients had low-energy injuries, all of whom were less than 10 years old. Fifteen patients (78.95%) had high-energy injuries, of which nine (47.37%) were caused by traffic accidents. Among the high-energy injuries, there were six cases of THD with associated femoral head fracture or acetabulum fractures, three of which entailed associated femoral head fracture only, and one with associated acetabulum fractures. The remaining two cases entailed combined femoral head fractures and acetabulum fractures. There were seven cases of THD combined with fractures of parts other than the femoral head or acetabulum and six cases of simple dislocation without associated fractures.

A patient with suspected sciatic nerve injury had no associated neurological dysfunction after closed reduction and discharge (Table 1). Closed reduction was achieved in eight patients without anaesthesia, for whom the operating physician assessed the degree of muscle tightness of the affected limb and the feasibility of closed reduction in a nonaesthetic state. Four showed reductions in 6 h. The time from injury to reduction in the remaining four patients ranged from 8 h to 2 days. Closed reduction was performed in five patients under anaesthesia, and the time from injury to reduction was appreciably longer than 6 h, ranging from 10 h to 11 days with an average of 70.6 h. Six patients underwent open reduction due to femoral head or acetabular fractures, and the time from injury to reduction was > 6 h. The mean follow-up period was 6.18 ± 0.81 years. According to the MDP hip function score, 18 patients (94.74%) were rated as excellent. One patient presented osteonecrosis of the femoral head, with a hip function score of 10 (medium).

Table 1 Patient demographics, injury characteristics, and outcomes at the latest follow-up.
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Discussion

In this study, we observed that traffic accidents were the leading cause of THD in children and the general prognosis was good. Hamilton et al. suggested that hip dislocation was caused mainly by low-energy injuries in patients aged 2–8 years and high-energy injuries in patients aged 10–15 years10. In this study, the average age of children with low-energy injuries was 5 years and that of children with high-energy injuries was 8.9 years. Our findings are consistent with those of Braun et al., who found a predominance of moderate or high trauma in patients older than 8 years11. In a study involving 42 children, Mehlman et al. found that most of the dislocations (64%) were attributable to low-energy injury12. Vialle et al. found that low-energy injuries accounted for 52.38% (22/42) of paediatric patients with THD, and traffic accidents accounted for 40.48% of total injuries2. Bressan et al. reported that low-energy injuries were the most common trauma mechanism in 76 children aged < 7 years, with only five patients reporting a car accident injury1. In this study, the incidence of hip dislocation caused by car accidents was higher in both younger and older age groups.

Similar to adults, posterior dislocation is the most common hip dislocation pattern in children (up to 90%)13. The incidence of posterior dislocation in this study was similar to that reported in previous studies (89.47%). We encountered one patient with central dislocation, which occurred as a high-energy injury, and one patient had an anterior dislocation complicated by ipsilateral proximal femoral shaft fracture due to a traffic accident.

A reduction within 6 h can decrease the occurrence of postoperative complications, especially AVN of the femoral head14. Mehlman et al. found that patients whose reduction was delayed for > 6 h had a 20-fold higher risk of AVN than those whose reduction was reduced by ≤ 6 h12. Ahmed et al. performed a meta-analysis that reached the same conclusion15. However, the time from injury to reduction is not the only factor affecting AVN. According to Haram et al. and Yuksel et al., the appearance of AVN is related to a reduction in the time and severity of the trauma and age11,16. This was proved by Archer; all patients who developed AVN underwent reduction within 6 h and the appearance of AVN was related to severe trauma3. The incidence of AVN in patients with hip dislocation and proximal femoral epiphyseal fracture is extremely high (100%)13. In this study, one of 19 patients experienced an AVN that was caused by an epiphyseal fracture of the femoral head caused by a car accident and only 21.05% (4/19) of the patients underwent reduction within 6 h, (Fig. 1). We postulate that AVN was much more likely to be related to severe trauma than to reduction time.

Figure 1
figure 1

A 5 year-old boy with right femoral neck fracture combined with femoral shaft fracture. (A) Femur neck dislocation of the epiphysis, the green arrow indicates the dislocation of the epiphysis posteriorly. (B) Open surgery. Green arrow shows reduction and fixation using one screw and two Kirscher wires. (C) Radiograph 1 month postoperatively. Green arrow indicates the femoral head has turned white and the avascular necrosis (AVN) appeared. (D) Removal of the fixation material. Green arrow indicates the AVN of the femoral head 1 year postoperatively. (E) Magnetic resonance imaging of the AVN at 1.5 years postoperatively. Green indicates the femur head with no signals. (F) Computed tomography of the AVN. Green arrow indicates that the femur head was absorbed.

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Patients undergoing THD should be treated with closed reduction as soon as possible. Closed reduction is successful in most children with hip dislocation13. In this study, closed reduction was successful in all 13 children without ipsilateral hip or proximal femoral fractures. However, closed reduction may lead to separation of the proximal femoral epiphysis17. The prognosis for epiphyseal separation fractures of the femoral head is extremely poor, and the incidence of AVN is extremely high13,17. Archer et al.3 and Herrera et al.17 suggested that closed reduction should be performed under anaesthesia in the operating room, because medically induced muscle relaxation helps reduce the resistance to reduction. Additionally, fluoroscopy can be used during the recurrence process to detect whether the epiphysis is unstable. If instability is confirmed, open reduction should be performed13.

Radiographic examination is performed after closed reduction, and computed tomography (CT) is performed when the joint space is > 3 mm18. CT can detect small fracture fragments that cannot be found by radiography18. In this study, one patient with dislocation of the right hip after falling while riding a bicycle was treated with closed reduction in another hospital within 6 h of the injury; however, the symptoms were not significantly relieved. The radiograph showed that the space between the hip joint widened, and CT indicated a dislocation of the right hip with an acetabular avulsion fracture and a bone fragment in the hip joint. Open surgical reduction was performed 7 days after the injury (Fig. 1).

Non-concentric reduction was observed in up to 25% of patients2, which included not only incarceration of cartilage fragments from the posterior wall of the acetabulum or the femoral head, but also compression of soft tissues, such as the labrum or hip capsule19. Fractures due to compression of the hip labrum and the unossified posterior wall of the acetabulum are only visible on MRI, and thus, MRI is recommended as the standard radiographic imaging method for the diagnosis of THD in children and adolescents after closed reduction19. However, Vialle et al. suggested that CT is sufficient for distinguishing relevant lesions2. Although some studies have proposed that surgical exploration is required if the joint space is asymmetric after reduction14, Podeszwa et al. found that surgical treatment of non-concentric reduction of the hip joint is also a safe method20. We agree with the recommendations of previous studies that open surgical reduction should be performed in patients with dislocated or non-concentric reduction on CT after closed reduction3,11,18,21.

THD may be overlooked and missed and may be diagnosed after injury due to pain and abnormal gait22. The unreduced fibrous tissue in the hip was filled, thus causing difficulty in reducing the neglected dislocation of the hip23. Sulaiman et al. reported 13 patients in whom THD was overlooked closed reduction within 3 weeks could have been attempted24. In this study, THD was missed in one patient when the injury was diagnosed, and 3 weeks later the patient underwent open surgery with a good outcome (Fig. 2).

Figure 2
figure 2

A 13 year-old boy with neglected left hip dislocation. (A) Anteroposterior radiograph of the left hip diagnosed with subluxation of the femoral head 3 weeks after the injury. (B) Computed tomography of an avulsion fracture of the femoral head with subluxation of the femoral head. (C) Open reduction is performed, and hip subluxation is reduced.

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Sulaiman et al.24 pointed out that the most common surgical approach to the hip in children is the anterior approach, because this approach enters through the intermuscular and neural spaces, does not require severing of the muscles, and avoids injury to the medial femoral circumflex artery (MFCA), which is the vital artery supplying the femoral head25. Herrera et al. suggested that the surgical approach should be determined based on the direction of the dislocation13. Gardner et al. suggested that a posterior approach for neglected posterior dislocations would provide good hip exposure, allowing direct access to the dislocation and visualisation of the sciatic nerve26. Novais et al.27 reported that the surgical hip dislocation (SHD) approach allows for a full assessment of the acetabulum and femoral head, and is an excellent approach for traumatic posterior hip dislocation. However, Castillon et al.28 pointed to the possibility of sciatic nerve injury in the posterior approach. To expose the femoral neck, the external rotator muscles and the posterior joint capsule must be severed, although the intraoperative sutures are carefully performed, however, this technique still inevitably reduces the stability of the posterior hip joint and increases the risk of recurrence of posterior dislocation. Finally, the blood supply around the hip joint is relatively abundant, especially the MFCA, and the posterolateral entry into the joint capsule will inevitably cause damage to the peripheral blood vessels28. Many studies have indicated anterior open reduction as the preferred treatment for neglected traumatic anterior dislocation of the hip3,11,29. Morriset et al. reported that arthroscopy could be used to treat hip dislocations with failed closed reduction30. In this study, five patients with posterior dislocation with femoral fractures or acetabulum fractures underwent open reduction and were treated using the anterolateral approach, because it is more accessible to femoral head fractures, femoral neck fractures, and anterior acetabulum fractures is readily obtained from the anterior approach in most cases31. This surgical approach uses the Hueter space that consists of sartorius-rectus and tensor fascia lata intermuscular space to enter the hip joint, which avoids the vascular and nerve damage required for exposure, and the incision avoids proximity to the sciatic nerve, which can effectively avoid the possibility of sciatic nerve injury caused by long-term traction or compression. In addition, it preserves the posterior joint capsule, which avoids the occurrence of posterior dislocation32.

Although AVN is the most serious complication, the prognosis in children with THD appears to be better. Mehlman et al. reported an AVN of 12% in the study by Mehlman12. In a literature review, Bressan et al. found that among 76 children younger than 7 years with THD, most (76.32%) had normal hip function, and 11 patients had AVN1. Abul et al. described 13 patients with an average Harris hip score of 95.7 in a 10 year follow-up, and only one patient with AVN had a good prognosis33. In this study, 18 children had excellent hip scores and 31.57% (6/19) had mild claudication, which did not affect daily activities as of the last follow-up. One patient had AVN; however, the hip score was moderate (10 points).

This study had some limitations. First, the incidence of THD is generally low; thus, the study sample was relatively small. Second, MRI was not performed on any of the patients to diagnose AVN of the femoral head. Third, this was a single-centre retrospective study; thus, a prospective, multicentre study should be performed to obtain high-level evidence.

In conclusion, high-energy injuries, such as traffic accidents, were identified as the main cause of THD injuries in this study. We recommend that closed reduction should be performed first, and open reduction should be performed for patients with failed reduction, non-central reduction, ipsilateral hip fracture, or neglect of THD. The overall prognosis of paediatric patients with THD is good.