Pediatric pelvic fractures are rare injuries, accounting for 1% to 4% of all pediatric fractures, of which acetabular fractures account for 0.8% to 20%.1–3 During development, the acetabulum is composed of the triradiate cartilage, a Y-shaped epiphyseal plate located between the ilium, pubis, and ischium ossification centers.1,2,4 The triradiate cartilage undergoes bipolar growth due to a secondary ossification center at its central zone.4 This secondary ossification center typically appears around the age of 10 years and closes at around 14 years, that is, the conclusion of acetabular development. Acetabular fractures occurring in patients with immature (“open”) triradiate cartilage are rare due to its pliability.2,4 However, failure to appreciate a surgical acetabular fracture in this setting can lead to detrimental outcomes including posttraumatic acetabular dysplasia, residual pain, and instability.1–7 Therefore, surgical decision making must be taken with great care, and imaging must be scrutinized to evaluate fracture morphology and displacement.

Appreciation of pediatric acetabular fractures in patients with open triradiate cartilage is often inadequate when using radiograph or CT.8,9 Lack of ossification often makes fracture morphology and articular surface evaluation difficult. To supplement this, magnetic resonance imaging (MRI) is a sensitive imaging modality to evaluate the degree of displacement of nonossified areas of acetabulum without the risk of radiation from CT.2,8,10,11 Surgical treatment of these pediatric acetabular fractures is also rare—a recent retrospective analysis noted that only 12 English articles on this topic exist in the literature.4 Thus, there is value in reporting experience with cases in which MRI was used to guide management. We report three cases of pediatric posterior wall acetabulum fractures for which preoperative radiograph, CT, and MRI were obtained and describe our experience correlating imaging and intraoperative findings. All cases involved open reduction and internal fixation (ORIF) in patients with open triradiate cartilage who experienced football injuries.

This report has been approved by our institutional review board. The patient's parents were informed that their children's cases would be submitted for publication and provided consent.

Case Reports Case 1

A 10-year-old boy presented to an outside facility with right hip pain after an injury during football practice, recalling feeling a clunk and hip pain. Radiographs were negative for fracture (Figure 1). A hip sprain was diagnosed, and he referred to physical therapy. He presented to our clinic 3 weeks later with pain and difficulty ambulating. Examination revealed limited range of motion (ROM). CT showed a posterior wall acetabulum fracture fragment of 1.5 cm diameter at the widest point with 4 mm displacement (Figure 2, A). MRI showed a larger fracture fragment of 2.1 cm with 6.7 mm displacement (Figure 2, B).

Figure 1:

Case 1—Initial AP and frog leg radiographs of the pelvis and intraoperative fluoroscopy stress testing for hip instability.

Figure 2:

Case 1—Axial cuts depicting the largest fragment size on CT and MRI compared with the posterior wall fragment seen intraoperatively.

He was then scheduled for ORIF. Intraoperatively, instability was confirmed (Figure 1, B). A Kocher-Langenbeck approach revealed a large posterior wall osteochondral fragment. Notably, MRI most closely mirrored intraoperative findings regarding fragment size and displacement (Figure 2, C). The fragment largely consisted of nonossified cartilage, accounting for approximately 80% of the posterior wall (Figure 2, C). Once adequate reduction was achieved with 1.6 mm Kirschner wires (K-wires) (Synthes Holding AG), a 2.7 mm reconstruction plate (Synthes Holding AG) was fashioned into two spring plates for fixation by cutting a 12-hole plate because prefashioned plates were too large (Figure 3). Four 2.8 mm Qfix suture anchors (Smith & Nephew) were then used for labral repair and capsular plication. The patient discharged on postoperative day (POD) 2 without complication.

Figure 3:

Case 1—(A) Initial postoperative imaging and (B) imaging at final follow-up

Case 2

A 9-year-old boy presented after sustaining a closed right hip dislocation after a football tackle, which was reduced by Emergency Medical Services before presentation. Examination revealed ROM pain without gross instability and difficulty ambulating. A radiograph demonstrated a concentric reduction and was interpreted negative for fracture (Figure 4). CT depicted a comminuted posterior wall fracture with the largest fragment measuring 3.7 mm at its widest, with 4.5 mm displacement (Figure 5, A). MRI depicted the largest fragment measuring 11.1 mm at its widest, with 7.1 mm displacement (Figure 5, B).

Figure 4:

Case 2—Initial AP pelvis and lateral femur radiographs

Figure 5:

Case 2—Axial and sagittal cuts depicting fracture fragments seen on CT and MRI compared with intraoperative findings

He was then scheduled for ORIF. Intraoperatively, instability was confirmed. A Kocher-Langenbeck approach revealed a large osteochondral fragment consisting of 80% of the posterior wall with labral avulsion. MRI more closely matched intraoperative findings in fracture size and morphology (Figure 5, C). Similar to the previous case, once reduction was achieved with 1.6 mm K-wires (Synthes Holding AG), one 12-hole 2.7 mm reconstruction plate (Synthes Holding AG) was fashioned into spring plates for fixation (Figure 6). The labrum was repaired using one 2.4 mm Qfix suture anchor (Smith & Nephew). The patient discharged on POD 4 without complication.

Figure 6:

Case 2—(A) Initial postoperative imaging and (B) imaging at final follow-up

Case 3

A 13-year-old boy presented after sustaining a closed left hip dislocation during a football tackle, which was reduced at an outside facility before presentation. Initial examination revealed difficulty ambulating with painful but stable ROM. Radiographs demonstrated a concentric joint reduction and interpreted negative for fracture (Figure 7). CT showed a posterior wall fragment of 7.1 mm diameter with 2.2 mm displacement (Figure 8). MRI showed a larger fracture fragment of 16.3 mm with 4.8 mm displacement (Figure 8).

Figure 7:

Case 3—Initial AP pelvis and lateral femur radiographs.

Figure 8:

Case 3—Axial cuts depicting the largest fragment size on CT and MRI

He was then scheduled for ORIF. Intraoperatively, instability was confirmed. A Kocher-Langenbeck approach revealed a posterior wall fracture most similar in size and morphology to MRI. Once reduction was achieved with 1.6 mm K-wires (Synthes Holding AG), a 3.5 mm reconstruction spring plate (Synthes Holding AG) was used for fixation with a 2.8 QFix anchor (Smith & Nephew) for labral repair (Figure 9). The patient discharged on POD 2 without complication.

Figure 9:

Case 3—(A) Initial postoperative imaging and (B) imaging at final follow-up

Overall Outcomes

Intraoperatively, ROM stability was confirmed in all patients. All patients were discharged as touch-down weight bearing with a hip abduction brace and advanced to full weight bearing at week 6. Most recent clinical follow-up was—case 1: 29.1 weeks, case 2: 141 weeks, and case 3: 36.1 weeks. All patients were pain-free with full ROM and ambulation, without complication at final follow-up.

Discussion

We present 3 cases of posterior wall acetabulum fracture in pediatric patients with open triradiate cartilage in which radiograph, CT, and MRI were obtained prior to operative intervention. All patients sustained high-energy football injuries, with two closed dislocations. Notably, all initial radiographs were negative, which is consistent with previous literature listing the first missed diagnosis rate as high as 46.7%.12,13 Thus, having a high of suspicion for acetabular fracture, confirming with advanced imaging is essential for diagnosis in the setting of pediatric hip trauma.

When managing a surgical acetabular fracture, the main goals include restoration of articular surface congruency and joint stability.1 Management relies on fracture pattern, displacement, and stability. Fractures with <1 mm displacement are typically nonsurgical, whereas fractures with >1 to 2 mm displacement, >40% to 50% posterior wall involvement, or hip subluxation/instability are surgical.1,2,9 Management can also differ based on skeletal maturity, assessed by triradiate cartilage status.2,14,15 In acetabular development, changes in posterior wall ossification can occur up to 15 years with development starting around age 9 and complete fusion around age 17.9 As such, assessment of injury patterns in skeletally immature patients is challenging due to increased cartilaginous composition. Previous literature has noted that radiograph imaging is only useful in substantial fracture displacement. In addition, although CT can offer better visualization of fracture fragments/displacement, it too can fall short when compared with intraoperative findings.16

Underestimation of these fractures when using radiographs/CT has been reported in the literature.8,9,14 By contrast, MRI has the benefit of direct identification of acetabular cartilage injuries, constituting up to 11% of pediatric acetabular fractures.16–18 Hearty et al9 highlighted MRI as a more reliable indication of intraoperative findings, secondary to the fact that small osseous fragments viewed by CT fail to appreciate the magnitude of soft tissue findings. Similarly, Khair et al8 reported a skeletally immature patient in which MRI more closely represented the true extent of the posterior wall fracture. This was similar to our experience in which MRI was most representative of intraoperative findings. In addition to superior appreciation of severity and cartilaginous injury, MRI has the benefit of avoiding radiation in a vulnerable pediatric population.11 Therefore, MRI may be considered as the first/only form of advanced imaging when there is high index of suspicion for a pediatric acetabular fracture.

This study aims to add to the small amount of existing literature on a rare clinical entity—pediatric acetabular fractures. It is important to emphasize that although CT imaging indicated surgical intervention in all cases, the emphasis of this report is that MRI has multiple benefits including better agreement with intraoperative findings for preoperative planning and the ability to detect less displaced cartilaginous injuries and therefore should be obtained in patients for which acetabular fracture is suspected. Furthermore, one may consider only MRI in patients who present similar those in this report, especially at centers with expedient access to this advanced imaging modality. Given that this pathology can result in detrimental long-term outcomes when treated nonsurgically, assessment should occur with as much details as possible to ensure optimal patient outcomes.

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