Technical Information about ACL Injuries in Children.

Last updated Thursday, January 13, 2005

Introduction

Incidence Rate

Injuries of the anterior cruciate ligament (ACL) in children and adolescents were once felt to be infrequent. Less than 20 years ago, some accepted thinking was that complete ACL disruption occurs only after growth plate closure (1). This concept emerged from the observation that physeal injury occurs before ligament damage (2,3). Biomechanical studies have confirmed this clinical observation that the ligaments are generally stronger than the growth plate (4,5). There has also been postulation that the anatomic location of the insertion of knee ligaments in relation to the physis leads to the preferential injury to the physis (3).

More recently it has become recognized that ligamentous injury can occur in the pediatric population and in fact Cook et al have shown that the knee is the most frequently injured site in the child athlete (6). Avulsion injuries from the tibial spine (3,7,8), the femoral insertion (9,10), or both tibial and femoral insertions have been reported (11). More recently, there have been multiple reports of complete ACL tears in skeletally immature children (3,9,12-14), the youngest in a three year old (15).

Despite the above observations, ACL injuries in the skeletally immature are becoming more prevalent. DeLee (16) has identified three factors that have lead to an increased interest in children’s knee injuries:

  1. a greater number of children participating in organized sports,
  2. increased recognition of pediatric knee injuries by the medical community, and
  3. improved methods for diagnosing ligamentous disruptions in all age groups.

Operative treatment of ACL injuries in children, ideally, would be postponed until physeal closure. This more conservative approach, however, may actually result in greater risk to the knee. Controlling the activities of children can be impossible given the immaturity of the athlete and the increasing pressure to excel at younger ages.

Goal of treatment

The goal of treatment of the ACL insufficiency in the child is similar to that of the adult; the prevention of recurrent giving way episodes (17). Recurrent instability ACL insufficient patient leads to meniscal tears, and osteochondral damage predisposing to premature degenerative arthritis. If repeat injuries can be prevented by non operative means this is desirable in any age group, especially in the pediatric age group. One of the more important factors in preventing repeat injuries is activity modification, particularly avoiding high level athletic activities that require jumping, pivoting, contact, or participation on unpredictable surfaces.

Who should consider surgery?

ACL deficiency in the skeletally immature has resulted in a high incidence of secondary meniscal injuries, degenerative joint disease, and symptomatic instability in both sports and daily activities (13,18-20). Skeletally immature patients are in fact much less likely to limit their activities and adapt to ACL insufficiency than skeletally mature counterparts. Therefore, many skeletally immature patients must be considered surgical candidates; since the risk of injury from operative intervention may be less than the potential damage caused by repeated injury.

Types of surgery

Several surgical stabilization procedures have been described in the literature. Primary repair of interstitial tears of the ACL in children has been shown to be minimally successful (21,22).

As in adults primary repair alone of interstitial tears has a high failure rate and should not be considered as adequate or appropriate treatment for this injury. Primary repair with appropriate augmentation however may offer some advantages in this age group over reconstruction alone.

The primary repair of avulsion injuries have been shown to be more successful (23). This is particularly true when there is a bony avulsion that can be anatomically restored. It must be cautioned however that pure avulsion injuries are uncommon and frequently avulsion injuries exists in conjunction with interstitial ACL tears. Arthroscopic inspection is usually necessary to determine if a bony avulsion is truly an isolated avulsion or has occurred in conjunction with an interstitial tear.

Partial tears of the ACL in skeletally immature patients have been documented. Studies have shown that partial tears of the ACL can result in a satisfactorily result when treated without surgery (13,24). A good result with a partial injury is dependent on the degree of laxity. If laxity less is sufficient to allow a pivot shift phenomenon then an unsatisfactory result is more likely without surgery.

Extraarticular reconstructions have been suggested as a way of providing stability in this age group without compromising the physis. Although these procedures avoid drilling through the physis, the relative lack of isometrey of the graft can lead to increased laxity over time (14,19). It is also felt that extraarticular procedures that require dissection and fixation devices near the physis may run more risk of interfering with growth than the careful drilling of a central transphyseal hole. Extraarticular procedures in the skeletally immature patient are generally not recommended except for the primary repair of torn secondary restraints (25).

Intraarticular reconstruction without transphyseal drill holes have been described (26,27). These procedures generally utilize a groove over the front of the tibia and groove over the top of the femur or an "over the top" position on the femur thus avoiding transphyseal drill holes. The results of these procedures have been mixed. Like extraarticular reconstructions, this type of procedure decreases the relative graft isometry. The effect of hardware used for graft fixation near the growth plate is unclear. The anterior position of the graft on the tibia has resulted in graft impingement and persistently abnormal MRI signals within the graft tissue (27).

The most commonly accepted method for intraarticular ACL reconstruction in the skeletally immature patient utilizes a transphyseal tibial drill hole and an "over the top position" on the femur as noted in (12). It is felt that the relatively central tibial drill hole will not cause an angular deformity if disturbance in growth occurs. Avoidance of a femoral drill hole extending laterally lessens the possibility of asymmetrical growth arrest on the distal femur. The dissection on the distal lateral thigh however and the use of fixation devices near the lateral femoral physis may create some risk for growth disturbance (28).

Several studies have been reported of ACL reconstruction in skeletally immature patients utilizing both tibial and femoral drill holes (14,19). The reported results are generally acceptable, but most studies are reported on patients who are close to skeletal maturity. A recent study by Matava and Siegel however has shown symmetrical subsequent growth from both the tibial and femoral physes following the creation of transphyseal drill holes (29).

Considerations in treating ACL injuries in childre

All of the reported studies on ACL reconstruction in skeletally immature patients are complicated by the wide range of ages of the study subjects. Most studies deal with patients who are post pubertal and near skeletal maturity. This is clearly a different group when compared to the patient near skeletal maturity.

The important considerations for treatment in this age group include:

  1. determining biological age,
  2. appropriate classification of injury type,
  3. accurately quantifying laxity,
  4. the effect of transphyseal drill holes on subsequent growth,
  5. special considerations in graft selection in the skeletally immature, and
  6. complications.

Age

The determination of biologic age is necessary when comparing methods of treatment and when devising a treatment plan. The Tanner Staging of biologic age is an appropriate way to classify skeletally immature patients (30). A simplification of this system would be to combine groups I and II into a prepubescent category and groups III and IV into a pubescent category.

Those in the pubescent group have developed secondary sexual characteristics and are near full growth. Patients in this group can be generally treated as adults and make up the bulk of most published studies. Prepubescent patients ( groups I and II) constitute the group of most concern since they have considerable growth remaining. Most recommendations of this chapter pertain to the treatment of prepubescent patients.

Injury

The type of ACL injury is important in formulating a treatment plan and predicting outcome. Injuries can be classified as:

  1. bony avulsions,
  2. interstitial tears, or
  3. bony avulsions with associated interstitial tears.

It is generally agreed that bony avulsions have a better prognosis than interstitial tears. The determination of injury type may require arthroscopic inspection. Although, the use of magnetic resonance imaging has greatly improved the ability to determine the region and extent of injury. With true isolated bony avulsions, a good result can be expected with anatomic replacement of the avulsed fragment.

Laxity

The level of laxity following ACL injury in children is important in treatment decisions. Children in general have more normal laxity than adults and a comparison with the opposite knee is vital. Absolute laxity is also important since functional disability is closely related to absolute laxity. The pivot shift phenomenon usually occurs with anterior laxity of greater than 10 mm. Laxity less than this amount (negative pivot shift or pivot glide) should generally be treated nonoperatively particularly in the prepubescent population. When anterior laxity becomes greater than 15 mm not only are sporting activities dangerous, but everyday activities may become impaired making surgical intervention more necessary.

Tunnels

A review of available literature reveals incomplete knowledge as to the effect of drill holes upon the physis. Most data on physeal closures have been extrapolated from traumatic injuries (31). It is felt that a carefully placed drill hole is far traumatic to the growth plate than are the injuries that are included in most growth arrest studies. Care should be taken to minimize the trauma to the physis when creating drill holes. Several general principles regarding surgery near the physis can be made:

  • Drill holes should be as small as possible.
  • Centrally placed tunnels, if growth is affected, are less likely to cause an angular deformity.
  • Only soft tissue grafts should traverse the physis. Bone blocks or fixation devices that traverse the physis are more likely to cause growth arrest.
  • Extraarticular procedures that require extensive dissection or fixation devices near the physis may be more damaging than transphyseal tunnels.

Graft

Soft tissue grafts only should be considered when transphyseal drill holes are used for ACL reconstruction. Bone blocks traversing the physis have an increased risk for increasing the likelihood for premature physeal closure at that location. Harvesting of an autogenous bone-patellar tendon-bone graft also runs the risk of damaging the tibial tubercle apophysis. The use of allograft or synthetics in this age group has little indication. The most ideal graft for traversing the physis is one of autogenous hamstring tendons.

Complications

Since the potential exists for growth interference following ACL reconstruction through an open physis, there is understandable increased anxiety patient and their family. If a growth disturbance is recognized, a definitive treatment plan should be set in place to minimize the morbidity of this complication; appropriate consultation with a pediatric orthopaedic is helpful to determine the timing and most appropriate intervention. Rehabilitation may also need to be modified to make it more fun to entice cooperation and participation. Should stiffness (arthrofibrosis) develop in this age group, arthroscopy and release of adhesions is preferred over manipulation alone since less than gentle manipulation may potentially endanger the physis.

The goal of ACL reconstruction in the skeletally immature patient is to restore normal anterior laxity of the knee joint with the least amount of risk to subsequent growth. The preferred technique is the use of both tibial and femoral centrally placed drill holes, hamstring tendon autografts, fixation distant from the physis, and avoidance of dissection near the physis. The use of small centrally placed tunnels and soft tissue grafts minimizes the risk of physeal closure. Should closure occur the centrally placed tunnels would not likely result in an angular deformity. By not dissecting near either the tibial or femoral physis, interruption of blood supply is minimized. Keeping fixation devices distant from the physis avoids the chance of inadvertent influence. The use of an EndoButton CL (Acufex, Smith & Nephew; Mansfield, MA) avoids fixation devices such as interference fit screws that may traverse the physis.

Summary

  • Bony avulsions of the anterior cruciate ligament can be anatomically restored.
  • Partial tears of the ACL in this age group should normally be treated without surgery unless significant patholaxity is present.
  • Postpubertal patients who are nearing skeletal maturity should be treated as adults.
  • Centrally placed transphyseal drill holes of the smallest possible diameter are preferred by the authors.
  • Excessive dissection near a physis or placement of fixation devices near a physis should be avoided.
  • Soft tissue grafts only should be utilized in prepubescent patients. Bone blocks or fixation devices across the physis should be avoided.
  • A careful plan must be in place to monitor subsequent bone growth, and a plan for intervention should be in place if premature physeal closure occurs.

The effect of surgical intervention on subsequent growth in the skeletally immature patient is a major factor influencing treatment decisions. The risks of surgery must be weighed against the potential damage to the knee caused by repeated participation and instability, which are common in this age group. It is essential to prevent repeat injuries and if this can not be done in a non operative manner then surgical intervention should be considered.

References

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