2018 International Olympic Committee consensus statement on prevention, diagnosis and management of paediatric anterior cruciate ligament (ACL) injuries

Rehabilitation focus

Dynamic, multi-joint neuromuscular control is the primary focus of ACL rehabilitation in children. For the youngest patients (with markedly open physes, < 12 years), there is less emphasis on the development of muscular strength and hypertrophy. During maturation, and throughout the onset of puberty, rehabilitation strategies that more closely resemble those used with adult patients are appropriate, due to the increase in androgenic hormones [15]. These strategies must include heavier and externally loaded strength training.

Following surgical treatment, the graft type used for ACL reconstruction, and associated injury or surgery to other ligaments, menisci or articular cartilage, necessitate specific adjustments to the rehabilitation program. Rehabilitation programs should be designed to allow the child to participate in his or her team training sessions to maintain the social benefits of staying within the team. Parents or guardians should be active participants in the daily rehabilitation [101]. This may include assisting the child in technical and functional exercises during team training (e.g., short passes in football/soccer).

Rehabilitation phases

Rehabilitation for the child with an ACL injury is organised into four phases (Summary Box 2, Supplementary file 2), with an additional prehabilitation phase for those who choose ACL reconstruction. Specific clinical and functional milestones should be met before progressing from one phase to the next [128]. Throughout the first two phases, the child should be guarded from cutting and pivoting activities during sport, free play and physical education classes in school.

Rehabilitation progression

The framework for progression through functional milestones is similar for ACL reconstruction and non-surgical treatment. However, there are different expectations for progression and time to return to full participation in sport. For all patients, rehabilitation progression must be guided by clinical and functional milestones (Summary Box 2), and return to full participation [7] is dependent on successfully achieving the return to sport criteria (Summary Box 2). Non-surgical treatment should last for at least 3–6 months [49]. Post-operative rehabilitation should last for a minimum of 9 months before return to full participation in preferred physical activities [50].

Data from international registries suggest that young athletes are at high-risk for a second ACL injury following an ACL reconstruction [76], and the risk is highest in the first 12 post-operative months [28, 50]. Therefore, consider advising the child athlete not to return to pivoting sport until at least 12 months following ACL reconstruction. Rehabilitation is also an excellent opportunity to train the uninjured leg, which might be important considering the risk of contralateral injury [28]. Once the child returns to sport, a comprehensive injury prevention program, emphasising biomechanical alignment and landing/cutting technique should be integrated with usual training.

Five considerations when designing rehabilitation programs for the prepubescent child

Children who are close to skeletal maturity may follow rehabilitation [128] and RTS guidelines [50, 77] intended for adults. There are five important considerations for the prepubescent child:

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Bracing

Many clinicians involved in non-surgical treatment of skeletally immature children recommend the child wear a protective brace during strenuous physical activities [92]. The child who has had surgical treatment typically wears a brace during the prehabilitation phase, until ACL reconstruction is performed. Following surgery, it is recommended that the child wears a protective knee brace through the successful completion of the functional milestones in rehabilitation phase 1 (usually 2–6 weeks post-operative, depending on concomitant surgical procedures). However, the effectiveness of bracing following ACL injuries or reconstruction in paediatric patients is unknown. Other considerations related to the use of a brace might be to prevent knee hyperextension or knee valgus/varus, to enhance the child’s awareness of his or her injury, and as a protective signal to others the child might encounter (e.g., at school).

Key indications for ACL reconstruction

There are three indications for paediatric ACL reconstruction:

There are three possible techniques for paediatric ACL reconstruction:

Graft choice and fixation

Only soft tissue grafts (not allografts) should be used for ACL reconstruction in paediatric patients with open physes. The quadrupled hamstring graft is most common [25, 38, 55, 71, 114]. A quadriceps tendon graft may be used [53]. The patella tendon should not be harvested in paediatric patients with open growth plates to avoid damage to the tibial tubercle apophysis. Allografts are not indicated in paediatric patients in most cases, since the use of allografts in paediatric ACL reconstruction has poor clinical outcomes [61, 108, 123]. A novel technique involving the use of living-donor hamstring tendon allograft has been reported [47, 55] to avoid the varied sterilisation techniques used in cadaveric soft-tissue allografts, and preserve of the neuromuscular unit of the growing patient [139, 140]. However, long-term clinical outcomes are yet to be assessed.

Extracortical fixation of soft tissue grafts may be performed with a cortical button, suture, post or staple. Aperture fixation may be performed with interference screws, provided the screws do not cross the physis.

Graft incorporation

Data regarding ACL graft incorporation in children are scarce. Paediatric soft tissues have a greater biological growth potential compared to adults [40, 94], and cell migration and proliferation of ACL-fibroblasts slows as the person grows older [83]. The clinical relevance of the growth potential to paediatric ACL reconstruction is still unclear [102], although there is a rationale from animal models that the paediatric ACL graft may remodel faster than the adult ACL graft [89].

Adaptations and remodelling in the growing child

The ACL graft must adapt as the child grows. The graft may increase in length as the bone grows, and the bone tunnels may reduce in relative size [16, 73]. It is uncertain whether the diameter of the intraarticular part of the graft becomes longer and thinner [11], or not [16], as the child grows. The graft does not increase diameter as the child grows, but may increase in length [10].

With longitudinal bone growth after transphyseal ACL reconstruction, the graft may become more vertically oriented. This observation might be explained by the movement of the femoral fixation site with physeal growth or because the tibial tunnel aperture becomes relatively more posterior due to greater anterior growth of the proximal tibia. Other changes occurring as the child grows are secondary intercondylar notch narrowing, distal migration of the tibial and/or proximal migration of the femoral extracortical fixations, and verticalisation of the Blumensaat line [110]. However, the long-term clinical significance of these growth-related changes is unclear.

Risk 1: growth disturbance

Growth disturbances are a rare (approximately 2%) [41], but serious risk of ACL reconstruction. Growth disturbances may be a result of hardware, bone plugs at the physis, extra-articular tenodesis, or use of over-the-top femoral position. Most of the growth in the child’s lower extremities occurs from the physes of the distal femur and proximal tibia. Any surgical procedures, where tunnels are drilled through or near the physis are associated with a risk of growth arrest, and associated angular deformity and/or leg length discrepancy. Transphyseal techniques have a higher rate of graft rupture and a lower rate of lower limb deformity or axis deviation. Physeal-sparing techniques have a lower rate of graft rupture, and a higher rate of lower limb deformity or axis deviation.

Highly tensioned soft tissue grafts placed across femoral physes have been associated with limb length discrepancy and angular deformity [34]. Metaphyseal fixation techniques may pose an increased risk of femoral angulation and rotation relative to other techniques. Epiphyseal techniques may increase the risk of rotational deformity and decrease the risk of angular deformity [23]. Excessive growth may also be a problem, including symmetrical and asymmetrical overgrowth [22].

Most patients with ACL rupture requiring surgical treatment are approaching skeletal maturity, and do not have substantial growth remaining. This means that angular deformities and limb length discrepancies are likely of relatively low clinical significance. Therefore, it may be reasonable to perform transphyseal procedures when the child has minimal growth remaining.

Regularly monitor the patient until skeletal maturity

Routine clinical and radiological follow-up within the first 12 post-operative months can help the surgeon detect early clinical and radiographic evidence of leg length discrepancy, angular deformity or and physeal injury. For the child with markedly open physes, appropriate follow-up evaluation of leg length discrepancy might include annual clinical assessment and knee radiographs with long-leg alignment views until skeletal maturity and physeal closure. Height should be monitored, and if growth exceeds 6 cm in 6 months, or if clinical findings warrant, the annual assessment should be brought forward.

Classifying growth disturbances

Growth disturbances can occur in several different forms (Fig. 9). The growth arrest may be due to:

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Risk 2: secondary ACL rupture

Young age, returning to pivoting sport and receiving an allograft are important predictors of new ACL injury after index ACL reconstruction [2, 61]. One in four patients under 25 years who returned to pivoting sports after ACL reconstruction can be expected to sustain a new ACL injury (the pooled ipsilateral reinjury rate is approximately 10%; the pooled contralateral reinjury rate is approximately 12%) [135].

High rates of reinjury among young people with ACL reconstruction are concerning, although data regarding reinjuries among children with ACL reconstruction are sparse in comparison to data from skeletally mature patients. The best available evidence suggests a graft rupture rate in children and adolescents (age range 6–19 years) of 13%, and a contralateral ACL injury rate of 14% [63]. It is reasonable to hypothesise that high-quality rehabilitation with high adherence is likely an important step in reducing reinjury risk. The principles of rehabilitation for the skeletally immature patient are addressed in “Section 3: treatment of ACL injuries in children”. The ACL graft is also affected by the status of the other ligaments, menisci, cartilage surfaces, limb alignment, rotation and the dynamic muscle control of these structures—all factors that must be considered during treatment decision-making.

Risk 3: poor long-term knee-health

Meniscectomy is associated with an increased risk for osteoarthritis [24, 103, 137]. Therefore, wherever possible, treatment of ACL injuries must emphasise preservation of the meniscus. Prior meniscectomy at the time of ACL reconstruction is associated with higher likelihood of chondral lesions, while prior meniscal repair is not associated with a higher likelihood of chondral lesions [19]. Because of the technical nature of performing ACL and concurrent meniscal surgery in smaller, younger patients with open physes, patients in whom meniscus repair is indicated should be treated by surgeons who (1) are experienced in treating patients with open physes, and (2) perform a high volume of meniscal repairs.

Risk 4: knee stiffness

Knee stiffness may be due to the degree of injury to the ACL, disruption of the joint capsule, and injury to structures other than the ACL. Knee stiffness may also be related to surgical interventions or inadequate rehabilitation. Knee stiffness is rare in children aged 13 years and younger, and less common in males and in those having surgery with an iliotibial band or hamstring autograft [98]. Patients who have knee stiffness following ACL injury should aim for full active knee extension range of motion prior to undergoing ACL reconstruction. If the knee extension deficit persists beyond 3 months post-operative, MRI to assess for anterior impingement (cyclops lesion), and subsequent arthroscopy (should the deficit continue to be unresolved despite focused rehabilitation attention) may be warranted.

Risk 5: infection

Data related to infection risks for paediatric patients are extrapolated from literature that combines paediatric and adult patients. Infection rates in adult patients are generally low for ACL reconstruction. The rate of deep infections after ACL reconstruction with autograft is 0.19% [13].

Associated meniscus and cartilage injuries in children with ACL injuries

The degree of vascular penetration of the menisci declines with age to between 10 and 30% of the menisci receiving vascular inflow in adults [104]. The more robust vascular distribution in the paediatric menisci is reflected by increased intrameniscal signal intensity on MRI. Globular and intrameniscal signal may be observed in children and may appear to be an intrasubstance meniscal tear. However, these findings are benign, and usually reflect the abundant vascularity of the paediatric menisci (Fig. 10) [26].

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It is important to evaluate the MRI characteristics of the paediatric menisci to rule out meniscal injuries. In cases where the diagnosis is difficult, a diagnostic arthroscopy may be performed to clarify the diagnosis and ascertain the state of the meniscus. The clinician should also assess for a posterior medial meniscocapsular tear (ramp lesion). Ramp lesions may be present in 1 in 6 adult patients with ACL injury, and the prevalence of ramp lesions in children with an ACL injury is similar to adults [84]. The surgeon should be vigilant to verify the presence or absence of a medial meniscal ramp tear by visualising the posteromedial compartment. Use a posteromedial knee arthroscopic portal, if necessary, to probe the posteromedial meniscocapsular junction. Ramp lesions may place more stress on an ACL reconstruction if the lesion is not concurrently repaired [30].

Meniscal repair should be performed whenever possible in the paediatric patient because of the deleterious effects of meniscectomy and the positive outcomes of meniscal repair (i.e., the improved healing potential of the meniscus) [4, 74, 113]. This is especially important for bucket-handle, root and radial meniscal tears, and ramp lesions. If the surgeon does not have the skills or equipment to repair the meniscus tear, he or she should consider referring to a surgeon who has the expertise and equipment. Early diagnosis and appropriate treatment of ACL injuries and meniscus tears is needed to provide the best chance of preserving meniscal tissue.

Articular cartilage injuries in combination with ACL injury are less common than meniscal tears [4]. However, the clinician should have a higher degree of suspicion of articular cartilage injury in patients with combined ACL and meniscal injuries [33]. The medial femoral condyle may be particularly vulnerable [33]. Factors that may be associated with more severe chondral lesions are recurrent instability episodes and increased time between ACL injury and reconstruction [33, 51, 81]. It is unclear whether non-surgical management of ACL injuries is associated with a higher incidence of new chondral and meniscal lesions than ACL reconstruction [91].

Associated ligament injuries in children with ACL injuries

There is limited research on multiligament knee injuries and treatment in paediatric patients, and these injuries are less common in children than in adults [87]. Therefore, consider referral to a specialist centre.

Specific surgical treatment considerations

Combined ACL and fibular collateral ligament injuries Use fluoroscopy prior to placing suture anchors for a repair, or for tunnel reaming for a concurrent ligament reconstruction, to evaluate tunnel position in relation to the physes [136].

Combined ACL and posterior cruciate ligament (PCL) injuries Non-surgical treatment may be appropriate for partial PCL tears or non-displaced avulsion injuries. PCL reconstruction is a relatively safe and viable treatment option in patients with multiligament injuries [69]. Using a tibial inlay technique with a modified femoral tunnel location avoids transphyseal drilling [132]. Although, there are no high-quality studies of this technique in children.

True knee dislocation Perform a reduction by manipulating the tibia relative to the femur. Avoid forceful hypertension or rotation, to minimise the risk for damage to cartilaginous and/or neurovascular structures. Following reduction, a dynamic knee brace can be applied (for at least 12 weeks) to prevent further intraarticular damage and to help hold the knee reduced [79] while further treatment is planned. Ultimately, reconstruction of the ACL and PCL in combination with repair/reconstruction of additional ligaments (as needed) is the appropriate treatment.