The question of remaining endochondral growth after growth plate injuries has been of great interest for orthopedic surgeons for more than 150 years [6, 61]. Based on the first clinical experiences with epiphysiodesis [7, 63] in the first half of the twentieth century, many experimental studies were published with the goal to develop treatments regulating longitudinal growth like temporary epiphysiodesis, epiphysiolysis capitis femoris, and their respective fixation principles [5, 9, 17, 18, 23–26, 42, 43, 58, 76]. With the development of ACL reconstruction techniques and the identification of the problem of ACL injuries in children, several specific surgical-experimental studies analyzing pediatric ACL replacements were published during the last three decades. They were conducted in rabbits, pigs, sheep, and dogs with open growth plates [13, 14, 22, 29, 47–50, 57, 62, 71, 77]. They allowed recognizing the risks related to specific surgical techniques and especially the fact that a technically correct anterior cruciate ligament surgery in a pediatric patient bears little risk of a clinically relevant secondary growth change. From these experimental studies on the growth plate as well as clinical experiences from the past, a certain number of surgical principles can be applied either directly or indirectly to ACL reconstruction with open growth plates. They have been recently summarized in a review article [72] and are represented in Table 8.1.

Many surgical techniques have been described in order to perform the best possible ACL replacement in children and at the same time to reduce the surgically induced complication potential to a minimum. On the contrary to an adult knee, an anatomic graft placement is difficult to obtain in children with the currently available techniques [45]. This is due to the presence of the growth plates, especially on the femoral side. According to the localization of the tibial and femoral tunnels, the surgical techniques can be divided into three categories (Fig. 8.2): (a) transphyseal procedures, where the tunnels are drilled through the growth plates; (b) epiphyseal techniques, where the tunnels are located in the tibial and femoral epiphyses, not injuring the growth plate; and (c) extraepiphyseal techniques, where the graft is placed around the growth plate. Finally, different types of graft placements can be used on the tibial side and the femoral side. Every surgical technique bears its own, specific complication potential. General surgical guidelines have been established to make the surgical procedure as safe as possible with respect to continuity of normal growth (Table 8.1).

The different graft types, which are used in adults, may also be used with some modifications in children. Hamstring grafts are probably the most popular. In some rare cases, they can be too thin and may be reinforced with other tendon material, i.e., by a quadriceps or iliotibial band strip. It is important not to harm the periosteal attachment of the hamstrings [72, 75]. As opposed to the adult harvesting technique, the tibial attachment site is left intact, and the hamstrings are cut proximal to their bony insertion site. This avoids an injury and potential growth arrest of the tibial tuberosity apophysis, which may cause a later development of a recurvatum knee. Quadriceps and patellar tendon grafts can be used as well, in which case they should be harvested without a bone block. If a bone block is part of the technique, care should be taken never to place it through the growth plate in order to avoid an early growth plate fusion. The iliotibial band may be used as a graft material as well, especially if an extraepiphyseal, extra-articular technique is performed [51]. Care should be taken to inform the patient on potential cosmetic (large incision) and harvesting site problems (pain). In Europe, there is limited experience with allografts in immature children. A new approach is the use of living donor hamstring tendon allografts. This allows for a more predictable graft size and for preservation of the child’s own tendons for potential use in later life. First reports of parents donating their hamstring tendons to their children have recently been published and showed good results, both for the outcome of the child’s and parent’s knees [21]. The permanent use of synthetic graft material is prohibited as it may cause significant growth arrest as well as the need for complex, three-dimensional corrective surgeries for malalignment or leg length discrepancies. Newly developed ACL repair techniques [15] must be critically evaluated before pediatric use in order to avoid large growth plate injuries and the need for extended revision surgery in case of failures (Fig. 8.3).

Some authors differentiate their specific pediatric ACL reconstruction technique according to the amount of knee growth remaining [16]. In order to minimize the risk of growth disturbance, Kocher [33, 34] advocated a physeal-sparing combined intra-articular and extra-articular reconstruction with an autogenous iliotibial band in prepubescent (Tanner stage 1 or 2) children with a large amount of growth remaining. In pubescent adolescents with growth remaining (Tanner stage 3), they recommend a transphyseal hamstring graft technique with extracortical fixation [34]. This technique is similar to the one used by the first author of the present article on a routine basis, both in prepubescent children and adolescents [79] (Fig. 8.4). This arthroscopic single-bundle technique differs only minimally from the adult technique. Graft diameter generally varies between 6 and 8 mm. In prepubescent children under the age of 10, the femoral tunnel is drilled in a transtibial fashion. This allows for a more perpendicular positioning of the femoral tunnel in relation to the distal femoral physis in order to keep the drill injury as small as possible. After the age of 10 and with still significant knee growth remaining, the femoral tunnel is drilled through the anteromedial portal in deep knee flexion. This causes a larger drill injury but allows for a more anatomic femoral graft placement [72]. An injury of the perichondral structures should be avoided by all means [71]. Preventing a blowout of the posterior cortex can be achieved by using a femoral drill guide with a 5 or even a 7 mm offset. On the tibial side, care must be taken to position the tunnel entrance more medially as it is done in adults in order to protect the apophysis of the tibial tuberosity and avoid subsequent development of a varus knee and/or a recurvatum knee [74].

Anderson [1–3] uses a transphyseal technique with cortical fixation. The semitendinosus and gracilis tendons are harvested with a standard tendon stripper and detached distally. The tendons are prepared in a quadrupled manner with Endobutton for the femoral attachment. The femoral guidewire is drilled under fluoroscopic guidance in both antero-posterior (AP) and coronal plane with arthroscopic visualization of the intercondylar notch. The tibial guidewire is inserted to the anteromedial aspect of the tibia through the epiphysis with the aid of tibial drill guide. The graft is measured, and the smallest appropriate drill is used for the femoral and tibial tunnels to get a tight as possible fit. The graft is pulled to its place through the tunnels. A washer is placed to the femoral side to secure the Endobutton fixation. The tibial fixation is done in 10 degree knee flexion by tying the No. 2 FiberWire sutures over a tibial screw that is placed medial to the tibial tubercle apophysis and distal to the proximal tibial physis.

Chotel [10, 27] uses an arthroscopically assisted transphyseal technique on the tibial side and an intraepiphyseal technique on the femoral side (Fig. 8.5). The quadriceps tendon is harvested with a trapezoidal bone block from the patella. A femoral pin is inserted under fluoroscopic guidance in order to be parallel and at the same time at a safe distance from the physis. After validating the femoral pin placement, an outside-in technique is used for femoral tunnel drilling. The graft is introduced from outside-in and from the femur to the tibia. The bone block is impacted press-fit in the femoral tunnel. An extracortical staple and a biodegradable screw in the tunnel, which is placed distal to the tibial physis, achieve double tibial fixation.

An example of a nonanatomic, extraphyseal technique is the so-called Clocheville technique [8, 68] using the mid-third of the patella tendon without bone blocks. Instead of bone plugs, a periosteal flap is harvested at the patellar and the tibial insertion sites. The femoral tunnel is positioned proximally to the growth plate. On the tibial side, the graft is fastened at the epiphysis in a 1 cm deep bone trough. This procedure is technically more demanding than the arthroscopic single-tunnel technique. It has been used for many years, especially in very young, prepubertal children.

The tremendous evolution of arthroscopic ACL surgery has led to the recent development of an intraepiphyseal all-inside technique [44]. Both the femoral and tibial tunnels are drilled in a retrograde fashion and do not cross the physeal plate, hence allowing for a minimally invasive and anatomic reconstruction technique. It requires the intraoperative use of fluoroscopy in order to prevent physeal injuries. The soft tissue graft is deployed into the tunnels from the inside of the joint, and graft fixation is achieved over soft tissue fixation buttons. This technique is very promising but technically demanding. It can be considered to be in the pioneering phase of surgical development [73].

Rehabilitation is similar to all the techniques, although more carefully handled than in adults. There is no universally accepted rehabilitation protocol. Children are allowed to bear weight on the operated leg in an extension brace over a period of 6 weeks; motion must be started early on to avoid arthrofibrosis [59]; sports activities can be resumed after 6 months at the earliest, in many cases only after 9–12 months.

The risks related to different techniques of pediatric ACL reconstruction are increasingly recognized, and scientific research in the field is growing. In the last decade, it has been shown that a technically correct pediatric ACL reconstruction has little risk in creating growth abnormalities [19]. Nevertheless, they do occur [11, 32, 35, 36, 67, Shifflett 2013], and the understanding of the pathophysiologic changes of an iatrogenic injury to the growing cartilaginous structures in the knee is still incomplete. Growth disturbances can be described from different perspectives, depending on their pathophysiological explanation, their anatomic location, and their clinical relevance. An attempt to classify these different aspects and the respective treatment options is presented in Table 8.2.

From a pathophysiological point of view, reported growth disturbances after ACL reconstruction were classified into three categories [11] (Fig. 8.6). The process of growth arrest (A) is caused by a localized growth plate injury, which generates the formation of a transphyseal bone bridge. Spontaneous breakage of the bone bridge may occur in very young children whose growth plate can create large distraction forces. Bone bridge formation can be prevented with a soft tissue graft at the height of the injured growth plate. A transphyseal bone block, i.e., with a quadriceps or a bone-patellar tendon-bone graft, a transphyseal hardware placement, or even a transphyseal synthetic ligament placement can cause such a sudden growth arrest as well. It is important for the surgeon to understand that a growth disturbance evolves throughout the remaining growth process. The amount of deformity is proportional to the localization and the size of the initial growth plate injury. A growth arrest can lead to axial deformities if it is located at the periphery of the physis or to symmetrical leg length discrepancies if it is located in the center of the growth plate. On the distal femur, peripheral growth plate injuries can be caused either by a tunnel with a too large diameter or a posterior blowout with an injury of the perichondral structures of the growth plate (Ranvier zone and perichondral ring of LaCroix) if a transphyseal technique is employed. If an epiphyseal tunnel is drilled (which should always be performed under fluoroscopy), the femoral tunnel is located distal to the growth plate. If a growth plate injury occurs with this technique, it will cause the development of a femoral valgus deformity. The growth disturbance will be much larger in comparison with the transphyseal technique, and asymmetric growth may be much more severe in comparison with an arrest would be caused by transphyseal drilling. Finally, if the surgeon chooses an extraepiphyseal technique (over the top technique), caution must be paid to avoid an excessive rasping of the over-the-top position for a better graft adherence. This surgical maneuver may injure the perichondral structures and lead to axial malalignment as well [71]. Due to its posterolateral position, a growth arrest at the femoral tunnel will lead to a deformity in valgus and flexion. In such cases, anticipating the remaining growth allows to predict the amount of deformity. On the tibial side, peripheral injuries may be caused by damaging the tibial tuberosity apophysis, either during harvesting of the hamstring tendons or through a too anterior positioning of the tibial tunnel entrance. In this case, the growth arrest will cause a recurvatum of the proximal tibia [75].