1.1 Triradiate physeal cartilage (Y-physis)

Histological studies have shown that these growth plates, contrary to the usual epiphyseal plates, are bipolar. The germinative zone extends along the three rami of the pelvis. In addition, there is a central zone rich in blood vessels. This is the center from which the 3-D growth of the acetabulum originates [3]. Contrary to a normal physis, which is peripherally delimited by the zone of Ranvier, the Y-physis has two portions: an intraarticular portion coated with cartilage and, as described by Ponseti [2], and an intrapelvic, strongly perichondral fibrous portion. This intrapelvic portion is highly resistant but produces a large amount of callus after injury, which may lead to growth disturbances in the acetabulum due to bridge formation ( Fig 2.16-3 ) [4, 5].

1.2 Classification

There exists no specific classification of pediatric acetabular fractures. Most surgeons therefore rely on the AO/OTA classification of adult fractures as proposed and published by Pennal and Tile [6] that basically comprises three groups, A to C ( Fig 2.16-4 ).

• 
  

  Type A: vertical fractures

  
  
• 
  

  Type B: T-type fractures

  
  
• 
  

  Type C: combined fractures

This classification does not account for acetabular rim fractures that are more frequent in children than in adults. Thus we propose two main classifications: (1) based purely on anatomy, and (2) a simple one based on outcome, analogous to the classification already proposed for pelvic fractures.

• 
  

  Lesions without expected severe late sequelae (avulsion fractures of the acetabular rim, simple vertical type A fractures)

  
  
• 
  

  Lesions with potentially severe late sequelae (all fractures involving the triradiate cartilage, including invisible crush injuries, such as Salter-Harris V fractures, and callus bridging of the perichondral ring). Contrary to injuries of other growth plates, such lesions of the acetabulum have negative sequelae only if they occur before 6–8 years probably because growth of the hip joint is completed before the rest of the skeleton and the hip joint thus attains its final size earlier [2, 7–9] ( Fig 2.16-3, Fig 2.16-5 ).

Anatomically, four fracture types exist:

• 
  

  Small fragments of the acetabular rim that mostly occur with hip dislocation, followed by an unstable hip, depending on fragment size [10] ( Table 2.16-1 )

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Table 2.16-1 Posterior acetabular fracture—dislocation (Vailas JC, Hurwitz S, Wiesel SW: Dept of Orthopedic Surgery, Washington).

  Posterior acetabular fractures and hip stability
  Intact posterior capsule
  Fragment size, %	Stable, %	Unstable, %
  25	100	0
  33	75	25
  50	0	100
  75	0	100
  Absent posterior capsule
  Fragment size, %	Stable, %	Unstable, %
  0	100	0
  25	89	11
  33	14	86
  50	0	100

  
  
• 
  

  Vertical or oblique linear fractures that occur in association with nondisplaced and stable pelvic fractures

  
  
• 
  

  Severe simple, linear acetabular fractures resulting in hip instability

  
  
• 
  

  Central fractures with central fracture-dislocation of the femoral head

2.1 Patient history

Whereas nearly 100% of all pelvic fractures are the result of direct trauma, acetabular fractures may also result from the so-called indirect trauma. Such indirect force is usually exerted axially toward the acetabulum. A typical injury mechanism is landing on the stretched leg after a vigorous jump; typical for sports such as snowboarding, skateboarding, or go-karting. Importantly, a relatively high level of kinetic energy is required. In children younger than 6–8 years, the cause in virtually all cases is extraneous force. A characteristic example is a father who holds his toddler between his legs while skiing. In case of a fall, the father will fall over the child and often cause dislocation of the child’s hip, accompanied by acetabular fracture ( Fig 2.16-9 ).

2.2 Patient selection and indication

Even more frequently than pelvic fractures, acetabular fractures in childhood are caused by high-energy trauma. At least in our geographical regions, the incidence of this severe injury appears to be rising, including among younger children. Reasons include greater mobility but also, and above all, the fact that ever younger children are engaging in increasingly risky high-energy sports. Emblematic of this development is the increasingly popular mini-trampoline.

Since acetabulum fractures are frequently caused by indirect trauma, additional injuries are less common than with pelvic fractures, at least in our case material. This is especially true for isolated hip joint fractures. The combination of pelvic and acetabular fractures is rare in childhood, with incidences that vary depending on the reference [15–19].

Table 2.16-2 presents the frequency of pelvic and acetabular fractures referred to a clinic in a large skiing region.

2.3 Indication

Acetabular fractures should be addressed and treated actively. The following principles applied:

• 
  

  There is a rule or consensus regarding both adults and children that basically all joint fractures should be anatomically reduced and fixated.

  
  
• 
  

  It is recommended or required to treat joint fractures by open surgery to achieve the best possible congruence of the articular surface.

  
  
• 
  

  In addition, at least in childhood, an unwritten rule requires that a gap or step exceeding 2 mm be eliminated [20].

For the three principles mentioned above, it appears evident that the treatment indications for acetabular fractures should be subjected to the same considerations as all joint fractures. The often-observed attitude of casualness and negligence toward the treatment of fractures of the second largest and one of the most important joints of the human body is therefore surprising. This is especially evident in the case of injuries to children’s hip joints. It is wrong to assume that a child is more tolerant than an adult. Any incongruence of the hip joint, regardless of age, represents a state of “prearthrosis.” It follows that active treatment of an acetabular fracture in children (regardless of age) is nearly always indicated. Exceptions: fissures, minimal posterior chondral acetabular rim fractures, compression of the Y-physis ( Fig 2.16-5 ).

Note: Since most acetabular fractures are isolated injuries, they rarely present an absolute emergency. This means that physicians with little experience in pediatric traumatology have enough time to consult a specialist or preferably transfer the child to a center. Initiating inadequate treatment should be avoided.

3.1 Nonoperative treatment (ie, nonactive; bed rest/crutches, etc)

Generally, all articular fractures, regardless of age, should be anatomically reduced and stabilized. In our view, this applies even more stringently to hip joint fractures. This means that a decision for nonoperative treatment should be made with caution and only on the basis of thorough analysis, ie, diagnostics:

• 
  

  In normal cases this applies only to stable and nondisplaced acetabular fractures (< 2 mm gap, no step) ( Fig 2.16-10 )

  
  
• 
  

  Insignificant acetabular rim fractures that do not impair the stability of the hip joint ( Table 2.16-3 ) ( Fig 2.16-11 )

  
  
• 
  

  So-called crush injuries of the triradiate cartilage (fateful)

These injuries usually become clearly visible only in the further course of growth—as already mentioned, most of these cases lead to secondary dysplasia ( Fig 2.16-3 ).