Published 5/1/2011
Jennie McKee

The unique challenges of pediatric ACL tears

Preoperative assessment of maturity is crucial to reduce risks

Managing anterior cruciate ligament (ACL) tears in pediatric patients presents unique challenges, according to Allen F. Anderson, MD, who participated in the 2011 American Orthopaedic Society for Sports Medicine Specialty Day program.

“The literature clearly documents poor outcomes with nonsurgical treatment,” he noted, “but surgical intervention can cause iatrogenic physeal injury, resulting in leg length discrepancy or angular deformity.”

These management decisions are further complicated, said Dr. Anderson, “by deficiencies in basic science knowledge related to physeal response to injury, and the methodologic limitations of clinical studies that have evaluated the safety of surgical techniques for repairing pediatric ACL tears.”

The standard of care, he said, should be a surgical treatment approach appropriate for each patient’s potential for growth disturbance.

Assessing maturity and risk
The consequences of growth disturbance may be severe in children who have a great deal of growth remaining, but these consequences can be mitigated by careful preoperative evaluation of the patient’s skeletal and sexual maturity, noted Dr. Anderson.

“In general, chronologic age is an excellent predictor of maturity; however, because two children of the same age could have different skeletal ages, chronologic age alone is insufficient to predict how surgical treatment may disturb growth,” he said (Fig. 1).

Skeletal age may be predicted with radiographs or magnetic resonance imaging. One common method uses the Greulich-Pyle Atlas of Skeletal Maturation and compares radiographs of the left wrist and hand to a reference population. Physiologic age may be estimated using criteria developed by Tanner, which classifies sexual maturity from stage 1 (prepubescent) through stage 5 (adult) (Table 1).

Basic science studies may also provide some evidence that can aid in assessing risk factors for growth disturbance; however, much of the data are from animal models and are not entirely applicable to humans.

“In general, the risk for growth disturbance is associated with the extent of damage to the cross-sectional area of the physis,” said Dr. Anderson.

Conservative or surgical treatment
A conservative treatment strategy for pediatric ACL tears may present several problems, cautioned Dr. Anderson.

“It’s difficult to keep kids out of sports for years,” he said, “and they may be injured in free play.”

In addition, he said, the literature provides compelling evidence that nonsurgical treatment is associated with a high probability of long-term knee impairment. Patients often experience recurrent instability, meniscal damage, and sports-related instability.

“The risks of nonsurgical treatment are greater than the risks of surgery,” he said. “Consequently, the standard of care, in my opinion, should be surgical reconstruction for pediatric patients.”

Surgical options
For children with the highest risk of bone growth disturbance—those classified as being at Tanner Stages 1 or 2, with open epiphyses and no development of the tibial tubercle—either a transepiphyseal or modified physeal-sparing procedure should be considered.

“Transepiphyseal reconstruction uses a quadruple hamstring graft, with an endobutton and washer inserted proximally, and a screw and post used distally,” he said.

For patients in early Tanner Stage 3, said Dr. Anderson, the same procedures may be recommended as for patients at Tanner Stages 1 or 2, although this is a gray area.

Children rated as Tanner Stage 3, a time of accelerated growth, or Stage 4, when the physeal plates begin to close—are considered to be at intermediate risk.

For patients with a low risk of growth disturbance—those in later Tanner Stage 3 or 4—Dr. Anderson would recommend a transphyseal reconstruction using quadruple hamstring grafts.

Postpubescent Tanner Stage 5 patients are considered adults and can be treated with a standard ACL reconstruction.

Determining when a patellar tendon ACL reconstruction can be performed in males with a bone age of 16.5 to 17 years who have physes that are not significantly open can be challenging.

“In my experience, if there’s some ossification at the tip of the tibial tubercle, the distal tibial bone block will be a solid piece and not fragmented,” said Dr. Anderson.

Research directions
Additional basic science research is needed to learn more about the physeal response to injury, and more clinical studies are needed to evaluate the long-term outcomes of surgical techniques used to repair pediatric ACL tears. Safe drill size and graft tension must also be studied.

“The drill hole size or orientation that can cause growth disturbance is not completely understood, in either animal models or children,” said Dr. Anderson. “In animal models, however, the threshold for growth disturbance appears to be approximately 3 percent to 4 percent of the cross-sectional area.”

He also noted that studies assessing the safety of placing a soft-tissue graft across the physis have had mixed results.

“Three studies have found no or limited protection, and two studies have found that soft-tissue grafts are safe,” he said. “Despite this discrepancy in these animal studies, it is likely that soft-tissue grafts help prevent growth arrest.”

According to Dr. Anderson, multicenter trials are needed to clarify the contradictions in the literature and ultimately help determine the best treatment for pediatric patients with ACL injuries.

“Until we obtain this information, my recommendation would be to modify the procedure based on the patient’s physiologic and skeletal age to minimize the risk of a growth disturbance,” he stated.

Disclosure information: Dr. Anderson—Orthopaediatrics.

Bottom line

  • Choosing a treatment strategy for pediatric ACL injuries is challenging. Although nonsurgical treatment has been associated with poor outcomes, surgical procedures can cause iatrogenic physeal injury.
  • The surgical treatment approach should take each patient’s skeletal and sexual maturity into account.
  • Transepiphyseal reconstruction, a modified physeal sparing procedure, and transphyseal reconstruction are some of the surgical options that may be appropriate, depending on the patient’s level of risk for growth disturbance.
  • Multicenter trials on the physeal response to injury and more data on the long-term outcomes of surgical ACL repair techniques in pediatric patients are needed.

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org