Pediatric hip fractures are rare injuries, accounting for 1 percent of fractures in children, but a high complication rate—most critically involving osteonecrosis—means they warrant elevated vigilance and, generally, prompt treatment with open or closed reduction.

At the AAOS 2018 Annual Meeting symposium titled “Staying out of Trouble in Pediatric Trauma,” Wudbhav N. Sankar, MD, of the Children’s Hospital of Philadelphia, offered guidance and tips for managing pediatric hip fractures as well as “unstable slips,” or slipped capital femoral epiphysis (SCFE).

Pediatric hip fractures typically result from a high-energy mechanism. For this reason, “You should always look for associated injuries, and in young children, I always consider nonaccidental trauma,” Dr. Sankar said.

A primary reason for the high complication rate associated with these injuries is the precarious vascular anatomy of the proximal femur, Dr. Sankar said. He explained that the primary blood supply at this site is the medial femoral circumflex artery, with the femoral head supplied by terminal retinacular branches.

“These small-end arteries are extremely vulnerable to intracapsular injury,” he said. “The obvious implication is a potentially devastating complication of injuries to the femoral head—osteonecrosis.”

Courtesy of Children’s Hospital of Philadelphia

Treatment principles

In managing a pediatric hip fracture, the first priority is to attain an anatomic reduction, Dr. Sankar said. “It is less important whether you favor a closed or open technique and more important that you get it as good as you can possibly get it,” he advised.

The second priority is to achieve a stable reduction. Although closed treatment with spica cast may be appropriate for young children with nondisplaced fractures, for most cases, surgical treatment with internal fixation is indicated.

Closed reduction with percutaneous fixation should be performed on a fracture table or radiolucent table. When closed reduction fails, open reduction with the Watson-Jones or Smith-Peterson approach, incorporating capsular decompression, is recommended.

Another treatment principle, Dr. Sankar said, is that “fracture risk outweighs the risk to the physis. Go ahead and cross the physis with the fixation if warranted.” In the very young patient “with a small amount of real estate, if there is any concern about fracture stability, I have a very low threshold for backing the treatment up with a spica cast,” he said.

The Delbet classification for femoral neck fractures is useful, especially for its correlation with the risk of osteonecrosis.

Delbet I fractures are transphyseal injuries and account for approximately 8 percent of pediatric hip fractures. They have the highest rate of osteonecrosis, with estimates ranging from 90 percent previously to 38 percent in a recent meta-analysis, with the lower number being “probably more accurate,” Dr. Sankar said. Half of such fractures are associated with dislocations, “and occasionally the fracture is revealed only after the relocation.”

In young children, smooth pins may be used to cross the physis, followed by a spica cast. In older patients, the physis is crossed with standard screw fixation, Dr. Sankar said (Fig. 1).

Delbet II fractures are the most common in children. They are transcervical injuries and account for 40 percent to 50 percent of such fractures. They have the next-highest osteonecrosis rate, at 28 percent. Fixation method is determined by age and fracture position. For children younger than two years, multiple pins are used, followed by spica cast. For ages three to 10 years, 4.5 mm or 6.5/7.3 mm cannulated screws are used, “stopping short of the physis if you have enough space,” Dr. Sankar advised (Fig. 2). Then a spica cast is applied.

In children older than 10 years, 6.5/7.3 mm screws are used, and the surgeon may “cross the physis liberally.”

Delbet III fractures are basicervical injuries and represent 34 percent of total pediatric hip fractures. They have an osteonecrosis rate of 18 percent; fixation is dictated by age and size of the femoral neck, much as with Delbet II fractures.

Delbet IV fractures are intertrochanteric injuries and have the lowest osteonecrosis rate—5 percent—primarily because they are extracapsular. Reduction may be closed, and fixation is determined by age, with multiple screws used in younger patients and sliding hip screws or locking plate used in older patients.

Courtesy of Children’s Hospital of Philadelphia

Complications and surgical timing

“Unfortunately, pediatric hip fractures have a fairly high complication rate,” Dr. Sankar noted. He described the most common complications as follows:

• Coxa vara (18.5 percent): It may be the result of deformity progression or initial malreduction. It can be prevented by anatomic reduction and stable fixation, and when it occurs, valgus osteotomy is indicated.
• Nonunion (10.8 percent): The risk factors are casting alone, poor fixation, and nonanatomic reduction. The treatment is valgus-producing osteotomy to improve the forces across the fracture site and revision fixation with or without bone grafting.
• Growth arrest (21.8 percent): It may occur either from the direct injury or iatrogenically from crossing the physis with implants, and it may lead to coxa vara or valga. The surgeon should consider corrective osteotomy or partial arrest of the functional physis.
• Osteonecrosis: Causes include a kinked or disrupted retinaculum and tamponade, and the risk is correlated with Delbet type (as previously noted). The risk is increased with older age (> 11 years), and it is thought that younger children may revascularize better. The issue of treatment-related causes is controversial. A systematic review found a lower osteonecrosis rate with closed reduction and internal fixation, whereas other studies found that open reduction and internal fixation reduces the risk. Several confounders are at play, Dr. Sankar said, and quality of reduction may be the best predictor. “Get it anatomic!” he implored.

After anatomic reduction, capsular decompression offers another strategy to reduce osteonecrosis risk. Such decompression, Dr. Sankar said, is “seemingly important” if tamponade is a causative factor. Release of the capsule is associated with a lower osteonecrosis rate in several studies, but a systematic review did not demonstrate a significant effect. Confounders include treatment method, initial displacement, and timing. Whether decompression is done percutaneously or open may also have an effect.

On the matter of timing of surgery, Dr. Sankar said early reduction “is accepted in adults, but the data are less clear in children.” A systematic review demonstrated a risk of osteonecrosis 4.2 times greater if surgery occurs more than 24 hours after injury. Other series have not demonstrated a benefit of early treatment.

SCFE

Dr. Sankar then discussed treatment approaches for unstable SCFE, which is defined by a slipped epiphysis in a child who is unable to bear weight with or without aids. The unstable form is a minority (< 10 percent) of SCFE cases and is generally seen in seemingly innocuous, low-energy injuries unlike transphyseal hip fractures; it usually is associated with prodromal symptoms.

Patients with unstable SCFE are at risk for osteonecrosis, with an incidence of 24 percent in one meta-analysis. The frequent cause is a tear or kink of the retinaculum or tamponade. Treatment priorities are to stabilize the epiphysis and to minimize residual deformity and the subsequent risk of femoroacetabular impingement.

With respect to intra-articular pressure in capsular decompression, Dr. Sankar explained that a study reported an average pressure of 48 mmHg on the affected side versus 23 mmHg in the contralateral hip. During reduction, the intracapsular pressure spiked to 75 mmHg. With capsulotomy, it dropped to 17 mmHg. Animal studies suggest that intracapsular pressures over 50 mmHg sustained for more than six hours may precipitate osteonecrosis.

One treatment option for unstable SCFE is in situ pinning, involving gentle positional reduction, timely treatment, multiple screws, and capsular decompression.

A recent advance, as described by a 2016 article published in The Journal of Bone & Joint Surgery, has been additional perfusion monitoring. An intracranial pressure probe is threaded through the cannulated screw into the small space left by the guide wire. This technique documented successful blood flow restoration in unstable “slips” after percutaneous decompression, with no instances of osteonecrosis in 13 cases at two-year follow-up.

Another option is the Watson-Jones open reduction. The capsule is decompressed. A fingertip is used to reduce the acute portion of the slip, which is then fixed with Smooth K wires. In a study, this approach yielded an “excellent Iowa hip score (94.5) and some of the lowest osteonecrosis rates in the literature (4.6 percent).”

A third method is the modified Dunn procedure, which refers to open capital realignment via a surgical dislocation approach. This approach can identify and preserve retinacular vessels and allows controlled, anatomic reduction. Reported osteonecrosis rates range from zero percent to 27 percent.

Some controversy remains regarding timing of surgery, although most studies in the United States favor treatment within 24 hours. The notion of a window of opportunity has been raised in Europe, with the risk of osteonecrosis rising after 24 hours, until it drops after 72 hours. Still, the consensus in the United States is, “Treat urgently,” Dr. Sankar said.

He concluded with the following take-home points:

• Pediatric hip fractures and unstable SCFEs require urgent treatment. “Worry most about osteonecrosis,” he said.
• The goal is to obtain stable fixation. In the case of femoral neck fractures, “Get an anatomic reduction,” he said.
• It is probably best to decompress the capsule.
• Treat injuries in a timely manner.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org.