Paediatric ACL Injuries

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Original Editor - Wanda van Niekerk

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Over the past few years there has been a rise in paediatric Anterior Cruciate Ligament (ACL) injuries. (ref: Werner et al, Shaw et al) This is of great concern to clinicians seeing and treating these patients. Various questions arise when faced with a paediatric ACL injury, such as: Do children with ACL injuries mature similarly as their uninjured peers? Should they continue with sport or rather focus on their education and other interests? Is an ACL rupture a life changing event for these children? (ref Ardern et al) Children with ACL injuries face an array of challenges, such as having to cope with their knee problem for the rest of their life, and this in turn may compromise their quality of life. Furthermore, it may increase their risk of further injury, as well as the risk for meniscal tears and early onset osteoarthritis (ref Whittaker et al). Adding to all these issues, is the limited high-quality evidence available to guide decision-making in the treatment of paediatric ACL injuries. (ref Moksnes et al)

Children are a vulnerable population and clinicians in contact with this population has the responsibility to provide accurate information as well as effective treatment. The long-term prognosis after an ACL injury in childhood is still uncertain and there is a need for evidence-based studies to aid and strengthen confidence in clinical decision-making(ref Ardern et al). It is important to note that "long-term outcomes after ACL injury in childhood, including the development of osteoarthritis, have not been studied." (ref (Ardern et al)

In the current scope of clinical uncertainty and the limited evidence-based scientific knowledge, it is therefor challenging to manage these type of injuries in children. Other compounding factors are the intricacies involved in shared decision-making with children and the potential long-term and life-changing effect of such injuries. (ref Ardern et al).

Prevention of Paediatric ACL Injuries

Anterior cruciate ligament (ACL) injuries in childhood has serious potential long-term consequences (Ardent et al) as well as an increased risk of re-injury to either knee (ref Paterno et al). It is therefore essential to prevent ACL injuries in children as well as incorporate the principles of injury prevention into the treatment of the child with an ACL injury.(Ardern et al).

Research has shown great advances in the development and application of ACL injury prevention programs, specifically in pivoting sports such as football.(Walden et al). A reduction in the number of athletes sustaining an primary ACL injury and a reduction in the number of new ACL injuries among athletes who return to sport after primary ACL injury, have been reported. (Soligard et al, Mandelbaum et al, Sugimoto et al, Myklebust et al, Silvers-Granelli et al)

A modifiable risk factor for injury is the athlete's biomechanical movement patterns.(Ardern et al) These biomechanical movement patterns are targeted by specific Injury Prevention Programs (IPP). These injury prevention programs aim to incorporate strength training, plyometrics as well as sport-specific agility training (Emery et al; Lauersen et al). Another key component of the programs is the education of the coach and athlete, specifically on cutting and landing techniques (eg, wide foot position when cutting or flexed knee when landing). These specific methods avoid high-risk knee positions and are fundamental in the aim to prevent paediatric ACL injuries.

Advantages of Injury Prevention Programs

  • straightforward to implement (ref)
  • require little or no equipment (ref)
  • can be performed as part of regular team training or physical education 2-3 times per week (ref)

It is advised that children be introduced to injury prevention programs at an early age or developmental process. This provides the child with the best opportunity to develop and maintain strong and favorable movement strategies (Ardern et al).

The FIFA 11 and 11+Kids is an injury prevention program that reduce football-related lower limb injuries by over 50%. (Thorborg et al, Rossler et al_2016 and 2017). Children who take part and complete these programs show improved motor control as well as an improvement in balance and agility, when compared with children not completing the program (Rossler 2016).

Although these injury prevention programs have successful outcomes such as a reduced injury rate and injury time loss (Thorborg et al; Attwood et al), the effect thereof can be influenced by how frequent athletes perform the training. (Hagglund et al; Soligard et al_2010, Steffen et al) For these injury prevention programs to be successful it needs to be consistently implemented and utilised, as well as adhered to across all levels of competitive play (Ardern et al). These factors are the biggest challenges that clinicians face. It is also paramount that clinicians involved in youth sports and treating paediatric athletes with ACL injuries, advocate strongly for injury prevention methods in all settings. (Ardern et al)

Diagnosis of Paediatric ACL Injuries

As mentioned before, injury prevention programs are the first line of defense against the possible effects of an ACL injury. Should these prevention strategies fail, it is incumbent that a timely and accurate diagnosis be made. (Ardern et al). Accurate diagnosis is the starting point for effective management planning as well as shared decision-making. (Ardern et al). Clinicians make use of their specific skills and gather knowledge from:

  • patient history
  • examination
  • clinical tests
  • imaging

With this combined information clinicians can build a clear clinical picture that will enable diagnosis and assist in the treatment plan.(Ardern et al)

Clinical pearls to consider with the diagnosis of paediatric ACL injuries

  1. Haemarthrosis (acute swelling in the knee within 24 hours after trauma due to intra-articular bleeding) following an acute knee injury is suggestive of a structural knee injury.(Ardern et al)
  2. Diagnosis is more challenging with children, as they may be poor historians, have greater physiological joint laxity (examine both knees!) and MRI interpretation is difficult as a result of developmental variants in children.(Kaplan et al, Thapa et al)
  3. Children have an immature skeleton and this predisposes them to different knee injuries (eg. sleeve fracture of patella, epiphysiolysis) than adults (Ardern et al)


Key points with regards to imaging

  • Consider starting assessment with plain knee radiographs for all paediatric patients with a haemarthrosis or suspected structural knee injury
    • Tibial eminence fractures and ACL tear may have similar history and clinicial examination findings
    • Vital to rule out any other possible paediatric fractures such as sleeve fracture of the patella or an epiphyseal fracture
  • MRI can be performed to confirm diagnosis of an ACL injury and to evaluate other soft tissue structures (Kocher et al)
  • MRI may show other relevant injuries such as meniscal tears, osteochondral lesions and other ligament injury
    • In paediatric patients presenting with a locked knee, MRI is needed to assess the possibility of a displaced bucket handle meniscal tear or an osteochondral lesion

Special tests

Clinicians should be aware that "no isolated question, test or image can accurately identify an ACL injury, every time." (Ardern et al)

Management of Paediatric ACL Injuries

It is important for clinicians to be familiar with the available treatment options for children with ACL injuries. The various options should be discussed with the child and the child's parents/guardian in order to facilitate and enable a the process of shared decision-making on how to manage the knee injury. (Ref)

Treatment goals

  • Restore a stable, well-functioning knee that allows a healthy, active lifestyle across the lifespan
  • Reduce the impact of existing and the risk of further meniscal or chondral pathology, degenerative joint changes and the need for future surgical intervention (ref)
  • Minimise the risk of growth arrest and femur and tibia deformity (ref)

Treatment options

  • High-quality rehabilitation alone (non-surgical treatment)
  • ACL reconstruction plus high-quality rehabilitation

High-quality rehabilitation

Rehabilitation is essential in the management of ACL injuries. The principles of rehabilitation stay the same, whether the child has had surgery or has selected non-surgical treatment. It remains uncertain whether adult principles apply to children (ref Yellin et al, 2016). "Children are not small adults" (ref)Therefore, rehabilitation exercises and functional goals should be modified and not just copied from adult-orientated rehabilitation protocols. (ref) One cannot expect children to perform rehabilitation exercises with immaculate technique under no supervision! Qualified experienced clinicians should supervise rehabilitation for the child with an ACL injury. Furthermore, rehabilitation must be performed in close collaboration with the child's parents/guardian.(ref).

Rehabilitation focus

Dynamic, multijoint neuromuscular control is the most important area to focus on. In young patients with an open physis and younger than 12 years, less importance is placed on muscular strength development and hypertrophy. Later on during maturation, and through the onset of puberty, rehabilitation protocols more resembling of the adult-orientated protocols are appropriate and can be implemented. These protocols can include heavier and externally loaded strength training (ref)

  • Rehabilitation must be thorough
  • Rehabilitation must be individualised to the child's physiological and psychological maturity
  • Focus on exercises that facilitate dynamic lower limb alignment
  • Focus on biomechanically sound movement patterns
  • Gradual progression through phases II and III of the paediatric ACL rehabilitation protocol
  • Be aware of re-injury anxiety as well as the child's confidence in his/her injured knee
  • After surgery, ensure that the rehabilitation program is adapted accordingly
  • Design rehabilitation programs that allows the child to participate in his/her team training sessions to maintain the social benefits of being part of a team
  • Parents or guardians should be actively involved in rehabilitation on a daily basis
Rehabilitation phases

Ardern et al advocate that the rehabilitation for the child with an ACL injury be divided into four phases. There is an additional prehabilitation phase for children undergoing surgery. It is of the utmost importance that specific clinical and functional goals be reached before progressing to the next phase of rehabilitation. Children should avoid any cutting and pivoting actions during their sport, free play and physical education classes during phases I and II.

Recommended functional tests and return to sport criteria for the child and adolescent with ACL injury (From Ardern et al)
For patients who choose ACL reconstruction


  • Full active extension and at least 120 degrees active knee flexion
  • Little to no effusion
  • Ability to hold terminal knee extension during single leg standing
  • For adolescents: 90% limb symmetry on muscle strength tests
For patients who choose ACL reconstruction OR non-surgical treatment

Phase I to phase II

  • Full active knee extension and 120 degrees active knee flexion
  • Little to no effusion
  • Ability to hold terminal knee extension during single leg standing

Phase II to phase III

  • Full knee range of motion
  • 80% limb symmetry on single-leg hop tests, with adequate landing strategies
  • Ability to jog for 10 min with good form and no subsequent effusion
  • For adolescents: 80% limb symmetry on muscle strength tests

Phase III to phase IV: sport participation (return to sport criteria), and continued injury prevention

  • Single-leg hop tests: >90% of the contralateral limb (with adequate strategy and movement quality)
  • Performed gradual increase in sport-specific training without pain and effusion
  • Confident in knee function
  • Knowledge of high injury-risk knee positioning, and ability to maintain low-risk knee positioning in advanced sport-specific actions
  • Mentally ready to return to sport
  • For adolescents: 90% limb symmetry on muscle strength tests

Muscle strength testing should be performed using isokinetic dynamometry or handheld dynamometry/one repetition maximum. The type of test and experience of the tester are highly likely to influence the results. If using handheld dynamometry/one repetition maximum, consider increasing the limb symmetry criterion cut-off by 10% (ie, 90% limb symmetry becomes 100% limb symmetry). Clinicians who do not have access to appropriate strength assessment equipment should consider referring the patient elsewhere for strength evaluation

Exercise examples for each phase of paediatric ACL rehabilitation
Phase I
Stationary bike
Active knee extension
Single leg balance
Other exercise examples for phase I:
  • Quads setting
  • Closed chain hip and pelvis control exercises
Phase II
Single leg squat
Lunge onto Bosu
Squat on Bosu
Other examples of exercises for Phase II;
  • Step-ups (front and lateral)
  • Single leg standing control of dynamic terminal knee extension
Phase III
Split squat with dumbbells
Leg press
Other exercise samples for Phase III;
  • Stair jumps
  • Hopping and landing
  • Agility exercises
  • Running direction change exercises
  • Injury prevention programs such as FIFA 11+

Rehabilitation progression

Whether the child is undergoing an ACL reconstruction or opting for non-surgical treatment, the progression through the functional milestones are similar. There are different expectations for progression and return to sport, though. Full return to sport is dependent on the child managing to successfully achieve the return to sports criteria (ref 34).

Guidelines for time to return to sport
  • Non-surgical - treatment should last for at least 3 - 6 months (ref 35)
  • Surgery - post-operative treatment should last for a mimimum of 9 months (ref 36
    • Young athletes are at a higher risk for a second ACL injury following ACL reconstruction and the risk is highest in the first 12 month after surgery. (REF 36) Consider advising the child not to return to any pivoting sports until at least 12 months following ACL reconstruction.ref
  • Use the rehabilitation period and train the uninjured leg as well as there is a risk of contralateral injury (ref 38)
  • Once the child is back at sport, a detailed and sport specific injury prevention program should be part of usual training.

Considerations when designing rehabilitation programs for young children

  • Avoid boredom - design a home-based program with emphasis on play and a variation of exercises
  • Be wise about what tests to use - tests like single-leg hop and isokinetic strength tests have large measurement errors in young children (ref 40)
  • Concentrate on the quality of movement instead of symmetry in tests like single-leg hop
  • Be a responsible clinician - movement quality tests still needs validation - make sure that you have the skill and experience to use these tests, if not....refer!
  • Current return to sport criteria is designed and tested in skeletally mature athletes, it is still unsure if the same criteria can be used in the prepubescent child.

Outcome Measures

  • Child Health Questionnaire
  • PedsQL
  • Paediatric PROMIS
  • Pedi - IKDC
  • KOOS - Child
  • Paediatric Functional Activity Brief Scale


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