Injuries to the anterior cruciate ligament (ACL) in the pediatric population are predominantly in the form of tibial spine avulsion fractures and ACL tears. Tibial spine avulsion fractures are one of the most common knee injuries in children, usually resulting in avulsions of the anterior intercondylar eminence from the pull of ACL, with posterior intercondylar eminence avulsions being much less common. ACL tears are classified as partial- or full-thickness tears, depending on the degree of disruption to the ligament. Tibial spine avulsion fractures and partial ACL tears constitute a greater percentage of ACL injuries in preadolescents when compared to complete tears due to the ability of the immature skeleton to absorb force. As children mature, the risk of a complete ACL tear increases secondary to increased skeletal rigidity.¹ The two basic treatment options available for ACL injuries are conservative nonoperative management and surgical reconstruction. The management of ACL injuries in the pediatric population continues to be controversial, as there is low methodologic quality of published studies on the outcomes of each treatment.² Regardless of the modality, treatment is directed at restoring the stability of the knee in order to maintain the integrity and long-term durability of the remaining knee structures. The degree of skeletal maturity is an important factor in deciding which treatment modality is most appropriate. The skeletally immature patient is one in whom the growth plates are open and significant axial growth is expected. Historically, a tibial spine avulsion fracture and a midsubstance injury to the ACL in a patient with significant growth remaining were treated with a nonoperative regimen aimed at restoring stability through bracing, active rehabilitation, and modification of activity. As time has progressed, there has been a shift toward reconstructive surgery of the ACL in the pediatric population, particularly in adolescents who have reached skeletal maturity.³ This chapter discusses the nonoperative approach to treating an injury to the ACL in the preadolescent and adolescent patient and the indications for doing so.

The management of an ACL injury in patients with open growth plates presents a challenge as physicians and patients must weigh the risks of nonoperative treatment with the risks of early surgical treatment. In addition, there is the option of delaying surgical reconstruction in a skeletally immature child until the physes have fused. The management remains controversial as nonoperative and operative treatment both have the potential for serious risks. Nonoperative treatment can result in increased meniscal and articular cartilage damage from chronic instability, leading to a greater risk of early degenerative disease. Early surgical intervention on an immature skeleton carries the risk of growth arrest and angular deformities from disruption of the tibial and femoral growth plates. The chief concern in this growing population is the potential for iatrogenic injury to the physes, as the distal femoral physes and proximal tibial physes contribute 70% and 55% to the growth of their respective bones.⁴ Damage to the physis can result in limb length inequality and angular joint deformity. Due to the potential for long-term complications resulting from either of the available treatment options, it is essential to determine which patients are potential candidates for nonoperative management and which patients are better suited for surgical reconstruction.

The nonoperative treatment algorithm involves a structured and supervised rehabilitation program, usually broken into three distinct phases. The patient must progress through the phases based on specific functional milestones before returning to their preferred activities. Discussion of the first phase includes modes of decreasing swelling, the use of a custom-fit knee brace, the use of crutches, and the duration of activity modification and limitation. The second phase details the specifics of the rehabilitation program, including strength, balance, and plyometric exercises. The final phase is a secondary prevention program composed of neuromuscular and functional muscle strengthening exercises that should be continued indefinitely to maintain strength and stability of the knee joint.⁵ All three phases are integral components of the nonoperative treatment approach. Historically, some individuals who have been managed nonoperatively have required subsequent reconstructive surgery after reaching skeletal maturity. The indications for adolescent ACL reconstruction in a patient who has maximized nonoperative care are also discussed in this chapter.

The treatment approach for a skeletally immature or mature pediatric patient with an ACL injury is different for each patient, depending on their unique traits and the specifics of their injury. Regardless of how the ACL is torn, an experienced physician will work with each patient to determine a personalized
course of treatment. It is important to recognize which young patients are potential candidates for nonoperative treatment. The initial assessment, obtained through the history, physical examination, and a magnetic resonance imaging (MRI), should include sexual maturity, skeletal age, associated injuries, location and extent of the ACL injury, and the predicted level of compliance of the child.

Although chronologic age can provide a rough estimate of the patient’s maturity, it is important to determine their physiologic and skeletal age, which can vary significantly from the chronologic age of the child. The maturity assessment allows patients to be classified as either prepubescent or pubescent. Tanner staging of sexual maturity is the most commonly used method of assessing physiologic maturity⁶ (Table 5.1). Tanner staging takes into account the secondary sex characteristics in both males and females and the menarche history in females. Skeletal age, another measure of determining maturity, can be evaluated by a variety of different methods. The Hospital for Special Surgery (HSS) shorthand bone age assessment tool facilitates evaluation of the bone age without the use of an atlas (Table 5.2). This tool has been validated and shown to be equally as accurate as the Greulich and Pyle method used at other institutions.⁷ The prepubescent child has physiologic characteristics defined by Tanner stages 1 and 2 and a skeletal age of less than 12 years in boys and less than 11 years in girls. The pubescent child has physiologic characteristics defined by Tanner stages 3 and 4 and a bone age of 13 to 16 years in boys and 12 to 14 years in girls. The management of a tibial spine avulsion fracture is not dependent on the sexual and skeletal maturity of the patient. Conversely, physiologic and skeletal maturity, in combination with the features discussed in the following text, play a large role in which patients are candidates for nonoperative management of a torn ACL.

The extent of the ACL injury is an important determinant of which children can be considered for nonoperative management. In a tibial spine avulsion injury, the fracture of the intercondylar eminence is classified by severity of the displacement and angulation, which guides management. A nondisplaced or minimally displaced tibial spine avulsion injury can be treated nonoperatively with positive results, whereas more severely displaced and angulated avulsion injuries require arthroscopic reduction and internal fixation regardless of the child’s age or skeletal maturity.⁸ Similarly, the location of the ACL tear and the amount of ligament torn play a large role in differentiating which patients are candidates for nonoperative therapy. Patients with partial tears of the ACL, particularly those compromising less than 50% of the diameter of the ligament, have been shown to be promising candidates for nonsurgical management. Kocher et al.⁹ performed a prospective cohort study on 45 skeletally mature and immature patients 17 years of age or younger to assess the functional outcome after partial ACL tears in children and adolescents treated nonoperatively. Of the 45 patients treated with a nonoperative structured rehabilitation program and followed for at least 2 years, only 14 of the patients (31%) underwent subsequent reconstruction due to symptoms of instability or episodes of reinjury. The study found that the need for reconstruction after initial nonoperative treatment was significantly associated with tears greater than 50% of the thickness of the ligament, tears that were predominantly posterolateral in location, and patients older in chronologic and skeletal age. Therefore, the research advocates for consideration of nonoperative management for ACL tears in children and adolescents 14 years of skeletal age or less with less than 50% tear of the ligament.⁹ While assessing the degree of the ACL tear through the physical examination and MRI studies, it is important to evaluate the knee joint as a whole to determine if there has been damage to any other structures. Many studies have evaluated skeletally immature patients with ACL tears and concomitant tears to the meniscus and have found poor outcomes with nonoperative treatment.¹⁰ Therefore, the non-operative approach is best suited for those with isolated injuries to the ACL with no other ligamentous or cartilage involvement.

Compliance with both the rehabilitation program and willingness to modify activity is essential for a patient to be successful with nonoperative treatment. Many children and adolescents with ACL injuries are competitive athletes who desire to pursue sports that involve cutting and pivoting movements for a lifetime. The modification and limitation of certain activities is temporary, with the hope that proper rehabilitation can nurture the patient back into their desired activities without hindrance. However, every patient should know that both nonoperative and operative treatment carry the risk of not returning to high-risk activities, such as cutting and pivoting sports. The benefit of each treatment far outweighs the risk, as the patient would be unable to engage in such activities without one treatment or the other. A prospective cohort study by Moksnes et al.¹¹ investigated changes in functional performance following a nonoperative treatment algorithm for ACL injuries in skeletally immature children 12 years and younger. A majority (78%) of the 36 children treated nonoperatively remained ACL deficient with adequate knee function.
Ninety-one percent of the ACL-deficient children reported consistent participation in pivoting sports and/or physical education classes in school.¹¹ These patients did also report changing their primary sport to one that does not pose a risk to the ACL, which can be attributed to apprehension of reinjury.

The nonsurgical approach is most effective in a highly compliant patient with a partial ACL tear and no additional intraarticular injury who is willing and able to decrease their activity level during a given period of time. Despite these generalizations, every young patient should be well informed about the nonoperative treatment option and the pros and cons of this management program if faced with an ACL injury.