Acetabular Fractures in Children

Epidemiology

Injuries of the pediatric acetabulum or triradiate cartilage are rare entities.¹^,²^,³^,⁴^,⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰^,¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶ Diagnostics and therapy are correspondingly inconsistent. Thus, the majority of early publications were only case reports.¹⁰^,¹⁷^,¹⁸^,¹⁹^,²⁰

Overall, the incidence of acetabular injuries within the group of pediatric fractures is reported to be between 0.03% and 0.3%¹^,¹⁶ and to be between 3.5% and 20.4% in pediatric patients with pelvic trauma.¹^,²^,³^,⁴^,⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰^,¹¹^,¹²^,¹³^,¹⁵^,²¹^,²²^,²³

Even more rare are patients sustaining injury to the triradiate cartilage.³^,¹⁷^,¹⁸^,²⁴

19.2 Anatomical Characteristics

A child’s pelvis differs significantly from the one found in adults. The pelvic bones are less brittle and are covered with a thick periosteum. In addition, the ligaments are relatively stronger and growth centers are present, which together with the sacroiliac (SI) joints and the pubic symphysis allow a significant absorption capacity.

Thus, the bone is more deformable and can absorb more energy due to the higher amount of cartilage before fractures occur.²⁵ Consequently, more energy is required to produce a fracture and energy can be transferred to the pelvic viscera even after fractures have been sustained.²⁵^,²⁶ Due to this elasticity, the intrapelvic viscera are not sufficiently protected and intrapelvic organ injuries can occur without the presence of pelvic fractures or dislocations.²⁶

Overall, injuries of the acetabulum (triradiate cartilage) tend to be more stable as the relatively thick periosteum restricts bony displacement.

The growing acetabulum consists of three primary ossification centers: the pubic, ischial, and iliac centers. These converge within the triradiate cartilage complex,¹⁴^,²⁰ which normally fuses at the age of 16 to 18 years.²⁰

The development of the child’s hip joint and the localization and the histological characteristics of the acetabular growth plates were described in detail by Poinsettia.²⁷

The growth plates lie between the three pelvic bones. They are composed of the nonarticular part medially (triradiate cartilage) with three flanges between the three pelvic bones, and the lateral cup-shaped (horseshoe-shaped) acetabular hyaline cartilage laterally. The iliac and ischial bone are directly connected, whereas the upper pubic bone is separated from both by a thick cartilage layer. Approximately two-thirds of this complex belong to the latter cartilage part.³^,²⁷

The greatest cellularity of these growth plates is found in the ilioischial flange.³^,²⁷^,²⁸ Therefore, injury to this part can result in growth disturbances. Interstitial growth (height, dimension) and appositional growth (depth) and some periosteal growth are the main contributors in this complex,¹⁴ whereas the femoral head is responsible for development of the acetabular concentricity.³^,²⁰^,²⁷

Several secondary ossification centers develop within the flanges of the acetabulum. The os acetabuli is the most common epiphysis of the superior pubic ramus that contributes to the anterior wall of the acetabulum. Its growth starts at 8 years of age and fuses by the age of 15 years.¹⁴^,²⁷ A superior epiphysis develops between 8 and 9 years and is fused by 18 years of age, whereas an ischial epiphysis appears between 9 and 10 years of age.³^,²⁰^,²⁷

The triradiate cartilage is proximally and posteriorly connected to the actual acetabular cartilage (▶ Fig. 19.1).

Fig. 19.1 Bone anatomy of the acetabular growth plate and the corresponding bones in an approximately 7- to 8-year-old child. The triradiate cartilage is simulated with plastilina. Imprint from lateral (a) and medial (b). The acetabular cavity shows cartilaginous parts anterior, superior, and posterior (c).

19.3 Mechanism of Injury

Pediatric pelvic fractures are the result of comparable external forces as in adults. But, the fracture pattern shows significant differences. Although lateral compression forces in adults often result in pelvic ring instability, the same mechanism is supposed to result in an acetabular fracture in children.¹⁰ The forces acting along the femoral neck to the acetabulum produce similar fracture types,²⁹ depending on the hip position.²⁹^,³⁰

Most pediatric acetabular injuries are the result of a high-energy trauma,³⁰ whereas injury to the triradiate cartilage is most often due to direct injury.²^,³^,¹⁴^,²⁸^,³¹^,³²

The predominant injury mechanism is a motor vehicle accident.³²^,³³ More complex injury mechanisms can lead to combined pelvic ring and triradiate cartilage injury.³⁴

As in adults, lateral compression forces with forces through the femoral neck and head to the acetabular surface can lead to an acetabular injury or fracture.¹⁰^,²⁹^,³⁰

19.4 Associated Injuries

Pediatric acetabular fractures are often associated with concomitant pelvic ring injuries, proximal femoral fractures, or femoral shaft fractures and additional head trauma. Some of these patients even experience a polytrauma situation.²³^,³⁵^,³⁶

Data from the German Pelvic Trauma Registry indicate an approximately 40% rate of multiple injuries with a mean Injury Severity Score (ISS) of 16.4 points.²³

The rate of additional pelvic ring injuries can be found in up to 58.6% and femoral head dislocation can occur.²⁴^,³⁵ The latter was found to result in less favorable long-term results.³⁷ Additionally, the combination of a triradiate injury and a traumatic epiphysiolysis of the femoral head is possible.³⁸ Also, acetabular fractures have been described as a marker of significant bleeding.¹²^,¹⁹

Clinical Relevance

Due to the anatomical and biomechanical differences of the pediatric skeleton, accompanying injuries occur twice as frequent as in adults.³⁹

19.5 Diagnostics

Clinical evaluation generally does not differ from that of adults (ATLS) but must be focused on possible concomitant intrapelvic lesions.³⁹ Beside inspection of the undressed patient, mechanical stability testing of the pelvis and analysis of the peripelvic orifices are mandatory. Soft tissue and bony injuries of the proximal femoral region should especially be suspected.³³^,³⁶

Radiological evaluation of the traumatized acetabulum in young children is often difficult.²⁸^,³¹^,⁴⁰ An anteroposterior (AP) pelvic X-ray is mandatory. Even with this single view several fractures cannot be detected. An os acetabuli might complicate the proper diagnosis.²⁶^,⁴¹^,⁴²

A follow-up X-ray after 2–4 weeks post injury was recommended to detect secondary periosteal signs indicating an acetabular injury³⁹ (▶ Fig. 19.2).

Fig. 19.2 Injury of the triradiate cartilage with periosteal signs after 4 weeks and secondary development of acetabular dysplasia.

Oblique views (Judet views) and inlet and outlet views can confirm the diagnosis of an injury to the triradiate cartilage. Radiation exposure should be considered; thus, MRI or CT scans are favored.³⁵

Classical radiographic signs of an acetabular fracture are⁴⁰:

Displacement of growth plates
Disruption of the iliopectineal line
Intraarticular effusion
A positive capsule sign
Asymmetric teardrop

The value of ultrasound examination for the detection of intraarticular effusion is unknown.

Data from the literature found a missed injury rate of 22–80% on primary X-rays.³^,³³^,⁴³^,⁴⁴ Therefore, in all suspected cases acetabular evaluation, a CT scan is recommended.²⁴^,³⁰^,³⁴^,⁴⁰^,⁴⁵^,⁴⁶ The main advantage is the more frequent detection of osteochondral injuries.⁴⁵

An MRI is recommended in all further unclear situations, in clinical suspicion of an inverted labrum or intraarticular osteochondral fragments, or suspected closure of the triradiate cartilage.⁴⁷ Additional anesthesia is not a contraindication for MRI evaluation.³⁵

For long-term evaluation, follow-up X-rays are recommended to detect significant growth disturbances.⁴⁸ Additionally, MRI evaluation is proposed for follow-up examination.

19.6 Classification

Several authors described pediatric acetabular classifications.²⁰^,³⁰^,⁴⁹ The most useful classification of injuries of the acetabulum in the immature group of patients (open triradiate cartilage) was proposed by Bucholz.³ This classification evaluates the injury in relation to the triradiate cartilage. Similar to the Salter-Harris classification, three injury types are distinguished:

Type I: epiphysiolysis of one part of the triradiate cartilage
Type II: epiphysiolysis with a bony fragment
Type V: crush injury to the growth plate

Fracture classification according to Letournel is rarely possible.⁵⁰ Heeg et al classified 17 of 23 acetabular fractures in children up to the age of 17 according to Letournel.³³ The remaining six cases were classified according to Bucholz.³ The classification of Letournel is often not feasible in young children, but many fractures can be classified with this classification in the transient age group of children (12–14 years).³^,²⁹^,⁵⁰

Injury to the triradiate cartilage with or without metaphyseal involvement can arise from shearing forces against the ischial bone, the pubic bone, or the proximal femur. These injuries are the most common types⁵¹^,⁵²^,⁵³ and have a relatively good prognosis regarding normal growth in the majority of cases.³^,⁵⁴ Often, an additional injury of the pelvic ring can be observed.² The second variant involves a crush injury of the triradiate cartilage (type V according to Salter) with a poor prognosis and risk of development of a premature closure due to a medial osseous bridge.

Others divide acetabular injuries mainly into four subgroups.²⁰^,³⁰^,⁴⁹ Alpar distinguished stable, nondisplaced fractures; unstable fractures; displaced fractures; and central fracture dislocations.³⁰ Heiss distinguished fractures with roof involvement, acetabular floor fractures, acetabular rim fractures, and central fracture dislocations.⁴⁹ The classification of Watts is comparable to that of Alpar, with further subdivision of the central fracture dislocations into two subtypes.²⁰

19.7 Treatment

The main goal in treating pediatric acetabular injuries is an absolute anatomical reduction, a congruent joint, and no damage to the blood supply of the triradiate cartilage.²⁰^,⁴⁸

For long time, conservative treatment was advocated as the treatment of choice in these injuries.²^,⁴⁹^,⁵⁵ The treatment options differ from functional to plaster and traction therapy. In stable, undisplaced fractures, bed rest, early physiotherapy, and partial weight bearing after one week were favored, whereas in unstable, displaced fractures, a 6-week traction therapy followed by non–weight bearing for an additional 6 weeks was proposed.³⁰ Others recommended supracondylar traction for 3–4 weeks, followed by 2–4 weeks of bed rest after anatomical reduction⁴⁸^,⁵⁶ or application of a pelvic cast for 3–4 weeks in stable injuries.⁵³

Overall, congruent reduction with a closed conservative treatment concept is difficult and often impossible to achieve.³³

According to present criteria, conservative treatment is reserved only for stable and undisplaced acetabular fractures (< 2 mm gap, no step, requires corresponding CT or MRI diagnostics).³⁵ Therefore, operative stabilization is proposed when anatomical reduction is not possible by closed means⁴⁸ or fracture is unstable or displaced.²⁰^,²⁸^,³⁰^,³³^,⁴⁸^,⁵¹^,⁵²^,⁵³^,⁵⁵^,⁵⁶^,⁵⁷^,⁵⁸

Accepted indications for operative stabilization of acetabular injury in children are³^,²⁰^,²⁸^,³⁰^,³³^,⁴⁸^,⁵¹^,⁵²^,⁵³^,⁵⁵^,⁵⁷^,⁵⁸:

Fractures with > 2 mm displacement of the weight-bearing articular surface
Hip joint instability
Posterior wall fractures involving more than 50% of the articular surface
Incarcerated fragments

Presently, only 1.5% of children were treated surgically in the recent German Pelvic Trauma Registry Study,²³ whereas others reported an osteosynthesis rate between 15% and 45%.⁴^,¹²^,⁴⁴^,⁵⁸

Treatment options include resorbable transosseous sutures,⁴⁸ single screw osteosynthesis, K-wire fixation, or plate osteosynthesis.³⁰^,³³^,⁴⁴^,⁴⁸^,⁴⁹^,⁵¹^,⁵³^,⁵⁶^,⁵⁹ Also, a CT-guided percutaneous stabilization was reported in a 14-year-old child.⁶⁰

Heeg et al reported a rate of 81.3% anatomical congruency after open reduction and internal fixation.³⁴

Postoperatively, non–weight bearing for 4–8 weeks⁵¹^,⁵³ or with additional traction is recommended.³³ Von Laer proposes further weight bearing, dependent on clinical impairments (pain).⁵³ However, Heeg permits partial weight bearing for an additional 6 weeks, followed by full weight bearing after 3 months.³³

However, the operative treatment should consist of a “sparse” osteosynthesis to avoid maldevelopment of the acetabulum⁴⁸^,⁵⁶

For children < 10–12 years, Slongo recommends the ilioinguinal approach or the Smith-Peterson approach for indirect reduction of anterior lesions of the bony acetabulum.³⁵ It is pointed out that plastic bone deformity can be present. Experiences using the intrapelvic approach are missing. For predominantly posterior lesions, surgical hip dislocation by transgluteal approach is recommended for children < 6–8 years and the classical surgical hip dislocation with trochanter flip osteotomy is recommended in children > 8–10 years.³⁵ Implant selection is based on the age-dependent anatomy.

In the six children from the German Pelvic Trauma Registry, four children had posterior plate osteosynthesis and two had percutaneous screw osteosynthesis.²³

The majority of pediatric acetabular fractures can nevertheless still be treated conservatively. Open reduction is recommended for severely displaced fractures and when unable to achieve closed reduction.⁶¹

Clinical Relevance

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