History

A tear of the ACL can result from an impact to the knee or, more commonly, a noncontact twisting or landing injury. The timing of injury, either acute or chronic, should be noted. Knee effusion, pain, and ability to bear weight are important factors in diagnosing an ACL tear. An audible pop heard at the time of injury may be reported. An acute hemarthrosis, particularly in the first 6 to 12 hours after injury, should raise concern for ACL injury. Stanitski and coworkers⁴² found that 47% of preadolescents with a knee effusion had an ACL injury.

Children with congenital limb deficiencies, such as tibial and fibular hemimelia, congenital short femur, or proximal femoral focal deficiencies are other subsets of patients with ACL insufficiency. These children may develop instability at a much younger age and without any history of trauma to the knee. These cases are more complex and must be evaluated on an individual basis.

Physical Examination

The most important component in diagnosing pediatric knee injuries is the physical examination.⁴¹ The presence of an effusion should be noted. Palpation of the joint line and physeal plates should be performed. Active and passive motion should be documented. Varus and valgus laxity should be checked in full extension and at 30° of flexion. Lachman testing should be assessed for magnitude. Pivot shifting may be quite uncomfortable in the acute setting and is not recommended. If the Lachman examination is positive acutely, the pivot shift test can be deferred until the examination under anesthesia if surgical intervention is chosen. Findings should always be compared with those in the contralateral knee. The patient should be assessed for generalized laxity with the degree of knee hyperextension noted.

Diagnostic Tests

A routine four-view radiographic series should be obtained. The formation of the tibial spine and femoral notch should be assessed. Children with congenital limb deficiencies often have a deficient tibial spine and lateral femoral condyle. Comparison views and stress views may be selectively needed if physeal injury is suspected. Magnetic resonance imaging (MRI) can assist in detecting ACL tears as well as associated meniscal pathology and chondral injury in those individuals who are difficult to examine. However, physical examination has been found to be more sensitive and specific than MRI in the evaluation of these patients. In reality, MRI can localize areas of injury but cannot determine degrees of laxity. MRI may be helpful in assessing other causes of anterior knee instability in the young patient, including tibial eminence fractures, periarticular (physeal) fractures, and congenital absence of the ACL. As in adults, arthrometric measurements can be done to support the diagnosis.

Skeletal Maturity

The patient’s level of skeletal maturity should be defined preoperatively. It is generally assumed that girls grow until age 14 ± 1 years and boys until age 16 ± 1 years²; however, age may not be the best indicator of potential growth. Peak growth velocity occurs between the ages of 10 to 11 years for girls and 13 to 14 years for boys. Closure of the triradiate cartilage, which can be seen on a standard radiograph of the pelvis, typically marks the end of peak growth velocity.²⁶ The patient can be assessed physiologically for signs of development, as noted by Tanner and Davies.⁴³ Age at onset of menses can be useful in females. After menarche, girls enter a deceleration phase of growth and typically reach skeletal maturity 18 months later. Family height can be used as an approximate estimate of growth potential as well. The patient can be assessed radiographically to determine skeletal maturity using the Risser sign on the pelvis.³⁷ The Risser sign is a radiographic measurement based on ossification of the iliac apophysis, beginning on the lateral aspect and progressing medially. Divided into four quadrants, the Risser sign proceeds from 0 (no ossification) to Risser 4, in which all four quadrants show ossification of the apophysis. Patients with Risser 0 or 1 have a significant amount of growth remaining, and the Risser 4 patient is skeletally mature. Bone age is another method to determine skeletal maturity by obtaining a radiograph of the hand and wrist and comparing it with the standards in the Gruelich and Pyle atlas.¹² The “rule of thirds” suggests that the distal femur and proximal tibia grow an average of 0.9 cm and 0.6 cm, respectively, per year of growth remaining.³² Limb lengths and bilateral lower extremity alignment should be measured and any differences noted.

Associated Intra-articular Pathology

Previous studies have shown that 20% to 100% of pediatric patients who sustain ACL injuries have a concomitant meniscal injury.^11,34 Millett and associates³⁴ found that the incidence of medial meniscus tears increases significantly with chronic ACL insufficiency. Of the 22 patients who underwent surgery more than 6 weeks after injury, 72% had associated meniscal tears. If unstable meniscus tears exist, aggressive management is indicated. Every attempt should be made to salvage the meniscus in children and adolescents. Meniscectomy in this age group carries an even more ominous prognosis.¹⁸ Manzione and colleagues²⁸ evaluated the results of partial and total meniscectomy in 20 patients with a mean age of 15 years (range, 5–15 yr). At 6-year follow-up, 16 knees had grade I osteoarthritis and 4 had grade II or III changes. Osteochondral injuries may require débridement, drilling, and/or stabilization at the time of ACL reconstruction.

Primary Repair

DeLee and Curtis⁷ reported on three patients who underwent primary ACL repair through sutures tied across the physis. At 21 months follow-up, all had clinical laxity and two of the three had episodes of giving-way. Engebretsen and coworkers¹⁰ reviewed eight patients 3 to 8 years after primary repair and found that all experienced a decrease in activity level and five of the eight demonstrated instability on clinical examination. Grontvedt and associates¹³ also noted that primary repair of the ACL in the skeletally immature patient had poor results, similar to those found in adults.

Physeal-Sparing Techniques

Early reports of physeal-sparing intra-articular reconstruction describe using a hamstring autograft left attached distally, passed into the knee under the anterior portion of the medial meniscus, and fixed to the lateral femoral condyle with staples in the over- the-top position on the femur⁶ (Fig. 11-1). This technique is nonanatomic and does not reproduce the normal knee ligament kinematics. In a report of nine patients at 36.5 years follow-up, all had a 1+ Lachman and 1+ anterior drawer test. Six of nine patients returned to sports, but with bracing and precautions. No growth disturbances were reported.⁶

FIGURE 11-1 Cross-section of the left knee shows the trajectory of the graft. The inset shows the tibial plateau with the graft coursing under the anterior horn of the medial meniscus.

(Modified from Brief, L. P.: Anterior cruciate ligament reconstruction without drill holes. Arthroscopy 7:350–357, 1991. Used with permission from Elsevier.)

More recently, Kocher and colleagues²¹ described Micheli and coworkers’ technique,³³