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Managing ACL Injuries in Children: Are Kids' Injuries Different?

Michael Lastihenos, MD; Stephen J. Nicholas, MD

Pediatric Series
Editors: Barry Goldberg, MD, and Elliott B. Hershman, MD


In Brief: ACL injuries in children result in adultlike chronic instability problems. Physical tests and radiographs guide the diagnosis. Treatment depends on whether the ACL injury is an intrasubstance tear or, what is more common, an avulsion fracture of the tibial eminence. A case report of an 11-year-old boy describes a typical avulsion injury. Treatment of avulsion injuries consists of cast immobilization and open reduction and fixation for a displaced fragment.

Injuries to the anterior cruciate ligament (ACL) are less common in children and adolescents than in adults because children's ligaments are generally stronger than their growth plates and bones (1). Thus, knee trauma in children typically results in injuries to bone and growth plates rather than to ligaments.

However, ACL injuries in children should not be overlooked: One study (2) has shown that they occur more frequently than previously suspected. Seventy patients aged 18 or younger with acute knee hemarthroses were studied at Children's Hospital of Pittsburgh. Overall, this study of pediatric knee hemarthrosis revealed a 63% incidence of ACL tears; 16% had associated meniscus tears.

Injury Classification in Children

ACL deficiency may be congenital or traumatic. Congenital aplasia or hypoplasia of the ACL may be associated with congenital subluxation or dislocation of the knee; however, this condition is extremely rare, with an incidence of 0.017 per 1,000 live births (3).

Reports on traumatic ACL injuries in children are few and involve small numbers of patients (4-8). In general, traumatic ACL injuries are least common in children under age 14 (4,9). The injury can occur as an intrasubstance tear or, more commonly, as an avulsion fracture of the tibial eminence. The most common mechanism of injury is knee hyperextension coupled with a twisting force, similar to the mechanism seen in adults. Avulsion fractures can also be associated with injuries to other knee ligaments, especially the collaterals (7,9). (See "Anterior Cruciate Ligament Avulsion in Active Adults," May 1995 page 25.) Meyers and McKeever (10,11) have classified avulsion fractures of the tibial eminence into four types depending on displacement:

  • Type 1, minimal displacement of the anterior eminence;
  • Type 2, elevation of the anterior third to half of the eminence that hinges on its posterior portion;
  • Type 3, complete displacement or separation of the fragment (as in the case study); and
  • Type 3 with rotation: contact between the cartilaginous surface of the fragment and the fracture surface of the tibial plateau, which prohibits union.

Type 2 and type 3 injuries have about equal incidence and are more common than type 1 injuries (1).

Case Report

A healthy 11-year-old boy sustained a twisting injury of his right knee during a football game. He described hearing and feeling a pop inside the knee. He was unable to walk because of acute pain.

On field evaluation, the boy reported pain throughout the knee. The neurovascular status of his right leg was normal. Fluid was noted within the joint. He held his knee in mild flexion and was reluctant to move the joint. There was no significant medical or surgical history. The differential diagnosis included subluxation or dislocation of the patellofemoral or femorotibial articulation, fracture, torn ligaments, or a combination of these. The knee was splinted, and the patient was transferred to a hospital.

On presentation in the emergency room, the boy was in moderate distress. The neurovascular status had remained normal. The knee had a tense effusion and was held in 30° flexion. There was no joint line or patella tenderness. Range of motion was from 20° to 90°. The patient was able to actively extend his leg. Gross anterior instability was seen on Lachman and anterior drawer tests. There was a negative posterior drawer test. There was no varus or valgus instability.

Anteroposterior, lateral and tunnel view radiographs revealed a displaced type 3 avulsion fracture of the tibial eminence (figures 1a and 1b). A magnetic resonance image (MRI), obtained to rule out other intra-articular pathology such as torn menisci, also demonstrated the injury (figure 1c). It appeared that his skeletal and chronologic age were the same .


This fracture required treatment, primarily because the amount of displacement rendered the ACL incompetent to restrict anterior tibial translation. An attempt at closed reduction under general anesthesia was unsuccessful. The displaced fragment was then reduced arthroscopically and held in place with three percutaneous pins (figure 2). The leg was placed in a long-leg cast to maintain extension.


The child's postoperative course was uneventful. The cast and pins were removed at postoperative week 6, and the child began physical therapy including full weight bearing in a hinged brace. At that time he continued physical therapy until he regained his full range of motion and strength. At 42 weeks postsurgery the child had returned to full activity with no complaints of knee instability. Examination of the knee revealed full range of motion, a negative pivot shift, and a grade 1 anterior drawer test. Radiographs suggested that the fracture healed without disturbance of the tibial growth plate (figure 3).


The Exam Strategy

Ligaments must be thoroughly examined whenever a child presents with a knee injury (12). During the initial on-field evaluation, the patient or bystanders can provide information about the probable mechanism of injury, and therefore about the ligament that was likely injured. Twisting is associated with ACL and meniscus injuries; valgus stress, medial collateral ligament (MCL) injuries; varus stress, lateral collateral ligament (LCL) injuries; and blows to the anterior tibia, posterior cruciate ligament (PCL) injuries.

The initial evaluation should then proceed with assessment of the limb's vascular status. Evidence of ischemia dictates splinting of the knee and immediate transfer to a hospital. If the vascular status is normal, the leg's neurologic status is assessed and the knee examination is performed. The examiner observes for abrasions, soft-tissue swelling, and/or knee effusion, and palpates the femur, tibia, fibula, and patella for possible fractures. The medial and lateral joint lines are palpated for meniscal tenderness. The child's ability to perform a straight-leg raise indicates the function of the quadriceps and patellar tendons. During range-of-motion testing the examiner notes limitation secondary to pain or mechanical block. Knee joint opening to varus and valgus stress at 0° and 30° determines the status of each part of the LCL and MCL. The Lachman, anterior drawer, and posterior drawer tests evaluate the ACL and PCL.

If the child's symptoms abate quickly and the knee exam is normal, he or she may return to play with close observation. Otherwise, the knee is placed in an immobilizer and the patient referred for orthopedic evaluation.

The definitive orthopedic evaluation includes a thorough physical examination, in which the child's baseline ligament laxity is assessed (13). This is done by checking for the Steinberg sign (protrusion of the flexed thumb beyond the ulnar border of the hand), using the thumb-to-forearm test, and checking for finger and elbow hyperextension and knee recurvatum (1,3).

Radiographic studies are performed as needed. Plain radiographs including anteroposterior, lateral, tunnel, and skyline views, and, in some instances, a computed tomographic scan, are needed to rule out fracture. Stress radiographs are ordered if a nondisplaced physeal separation is suspected. Magnetic resonance imaging (MRI) can be used to evaluate the soft tissues including ligaments and cartilage.

Joint aspiration that reveals hemarthrosis with fat globules suggests osteochondral fracture.

Treatment Options

The choice of treatment depends on whether the injury is an avulsion fracture or an intrasubstance tear (figure 4: not shown). ACL injury in children presents a difficult management problem. Left untreated, the injury may often result in the same long term disability as seen in adults. With eventual stretching of the secondary restraints to anterior tibial translation, instability may result in meniscus damage and secondary degenerative changes (14). However, the decision to treat often raises difficult issues: Treatment of avulsion fractures may not always restore original function, and for intrasubstance tears, the method will depend on the patient's skeletal age.

Avulsion fractures. Avulsion fractures involving either the tibial or femoral insertion of the ACL must be anatomically reduced and held until they are healed. Nondisplaced type 1 fractures require immobilization in a long-leg cast for 4 to 6 weeks. Displaced type 2 and 3 fractures require closed or open reduction and internal fixation and cast immobilization for 4 to 6 weeks. For the patient described in the case study, we preferred arthroscopy over open reduction because arthroscopy creates less surgical trauma and enables an easier rehabilitation with less morbidity.

Even with anatomic reduction, about 50% of patients have measurable ACL laxity (14,15) that is secondary to the interstitial ligament damage that occurs before ligament failure or avulsion (16). Based on a 3- to 10-year follow-up of 45 young patients who had tibial eminence fractures, Wiley and Baxter (15) recommended open anatomic reduction and internal fixation for displaced fractures, but warned that the technique may not prevent ACL laxity or guarantee full knee extension. Anatomic reduction, however, is still the best option for treating these fractures.

Intrasubstance tears. Without treatment, the torn ACL has no better healing potential in children than in adults (5). The injury therefore warrants treatment. Angel and Hall (4) studied the natural history of untreated intrasubstance ACL injuries. Twenty-seven patients ages 8 to 18 years were followed for 26 to 87 months. In this group there were 15 complaints of instability episodes, 12 complaints of pain with activity, 10 complaints of swelling, and 4 complaints of locking. Only 11 of 27 patients returned to their previous level of activity. This is similar to what is known about the natural history of ACL deficiency in the adult population.

Treatment of intrasubstance ACL tears includes both nonsurgical and surgical options. The appropriate choice is based on the patient's skeletal age. Younger children with open growth plates are best treated nonoperatively. Older children who are nearing skeletal maturity may be candidates for surgical ACL reconstruction. For both groups, accompanying meniscus tears should be repaired arthroscopically.

Nonsurgical treatment includes aggressive rehabilitation, bracing, and elimination of jumping and cutting sports, which are most likely to cause knee instability (2). Nonsurgical treatment is continued until the child reaches skeletal maturity and can undergo an intra-articular reconstruction without injury to the growth plates. Persistent instability with activities of daily living warrants consideration of surgery in a patient who is not skeletally mature.

Surgical options include primary repair of the ligament, extraarticular tenodesis, and intra-articular reconstruction. A primary repair may be attempted when the ligament has been avulsed from its femoral or tibial insertions. Such repairs may heal and provide some stability to the knee. The results of primary repairs of interstitial ligament tears, however, have been poor (14).

For patients who have open growth plates, a lateral extra-articular tenodesis can be performed in an attempt to stabilize the knee. The procedure may provide anterior tibial stability and correct the anterolateral rotatory instability that accompanies ACL failure (17). The procedure will eliminate the pivot shift episodes that occur with cutting maneuvers; however, it is not an anatomic reconstruction, and there are concerns that the overloaded lateral joint compartment may undergo premature degenerative changes.

An adult type of intra-articular reconstruction can be performed if the child is near skeletal maturity. Allograft tissue, autogenous patella tendon, or semimembranosus and gracilis tendon is used to replace the torn ACL. The procedure involves drilling intra-articular femoral and tibial tunnels, 10 mm in diameter, through the growth plates. If the child is not near skeletal maturity at the time of the procedure, the devastating complication of physeal injury and growth arrest can occur. However, Andrews et al (18) recently reported 6 excellent, 1 good, and 1 fair outcome in a series of 8 such intra-articular reconstructions performed on skeletally immature patients. The growth disturbances that occurred were not clinically significant in this group. Still, we would be cautious about using such procedures until more experience is at hand.

A viable surgical option in the face of open growth plates has been presented by Parker et al, (19) who describe an intra-articular reconstruction that avoids the growth plates. They report excellent clinical stability and no growth plate injuries in six patients. This technique may prove useful in managing the select group of skeletally immature patients who continue to experience instability despite adequate conservative treatment.

Despite reports of new surgical options in patients who have open growth plates, it is our recommendation that intrasubstance ACL tears be managed nonoperatively until the child reaches skeletal maturity. We believe the patient should be offered the surgical procedure with the greatest chance of success (intra-articular arthroscopic reconstruction) when this surgery can be performed with acceptable risks. The downside of bracing and activity modification is minimal when compared to the surgical complication of physeal injury and growth arrest if surgery is performed at a time of skeletal immaturity. We feel that this conservative approach offers the best and most predictable outcome for pediatric patients who have ACL tears.

Optimizing ACL Outcomes

ACL injury is part of the differential diagnosis any time a child presents with a knee injury, especially when hemarthrosis is present. The goal of the examination is to determine whether the injury is an intrasubstance tear or the more common avulsion fracture.

Understanding the special issues involved in treating children's ACL injuries will help physicians preserve knee function and the leg's growth potential so that young people can develop healthful, active habits that last a lifetime.


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Dr Lastihenos is assistant attending orthopedic surgeon at Good Samaritan Medical Center in West Islip, New York, and at Southside Hospital in Bay Shore, New York. Dr Nicholas is associate director of the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital in New York City. He is also associate team physician for the New York Jets of the National Football League and a team physician for Hofstra University in Hempstead, New York. Dr Goldberg is director of sports medicine at Yale University Health Services and a clinical professor of pediatrics at Yale University School of Medicine in New Haven, Connecticut. Dr Hershman is assistant director of orthopedic surgery at Lenox Hill Hospital. Dr Goldberg is an editorial board member of The Physician and Sportsmedicine. Address correspondence to Stephen J. Nicholas, MD, 130 E 77th St, New York, NY 10021.