In general, regarding the field of pediatric ACL injuries, there is a need for well-planned, high-quality studies with prospective follow-up from time of injury and until skeletal maturity. These studies should address key topics such as management, diagnosis, treatment and prevention. Also, multicenter collaborations are necessary to increase numbers and thus statistical power and impact.
Examples of key topics that should be addressed in future studies:
Identifying predictors for non-coping, and consequently indication for ACL-reconstruction, is important for clinical decision making. This knowledge may facilitate earlier intervention for predisposed patients and may therefore protect their short-and long-term knee health by saving the meniscus. Larger data sets such as the PAMI and PLUTO collaborations may contribute to this in the future. PLUTO stands for Pediatric ACL: Understanding Treatment Outcomes and is an American prospective multicenter cohort study which started to enroll patients in 2016. PAMI stands for Pediatric ACL Monitoring Initiative and is a pan-European registry of pediatric ACL injuries.
Furthermore, there is a need for high quality diagnostic tests to determine decompensation over time and support decision making. Can radiological methods help detect progression of knee instability? Standing monopod x-rays (mimics Lachman test) and changes in the PCL angle on sagittal MRI images based on annual knee MRI evaluations have been promising in Luxembourg (unpublished data; Lecture on Pediatric ACL injuries, Roman Seil, Kleivstua May 2019). Systematic evaluation of the measuring properties of these tests and other potential diagnostic tests are warranted.
Also, there is a need for evaluation of the measuring properties of tools and tests used to describe outcome in pediatric ACL patients. The measuring tools used in clinic and research should be reliable, responsive and valid in the pediatric population. For instance, ACL-RSI (ACL-Return to Sport after Injury) scale is not validated in children, but is used and has been reported in the literature. Other tests that are not validated in children are strength testing, hop performance and evaluation of movement patterns.
Evaluation of long-standing rays are challenging. How should we interpret long-standing x-rays at baseline and at follow-up? What are normative values regarding leg length and alignment? How do we diagnose leg length deficiency and malalignment in clinic, and what is the appropriate way to report this in research? Should functional deficits or cut-offs for leg length deficiency or malalignment determine the diagnosis?
We require better evidence regarding what is the optimal treatment approach for pediatric ACL injuries. Only a randomized controlled trial (RCT) is designed to appropriately answer this question. However, a RCT may not be feasible nor justified ethically because it may be problematic to intervene with early ACL reconstruction in a non-symptomatic pediatric ACL deficient patient. On the other hand, not to perform ACL reconstruction and meniscal repair in a patient with an initial bucket handle injury cannot be justified. Those who need early surgery can obviously be excluded, but this will affect the external validity of the study.
Furthermore, the non-operative study arm is likely to allocate in a non-operative group and a delayed surgery group depending on coping abilities and probably also preferences.
According to our results we should expect approximately 50% cross-over to ACL
reconstruction in the operated study arm. This large number of “cross overs” from non-operative treatment to surgery need to be accounted for in power analysis and may
complicate the assessment.
As we have different surgical traditions as well as different patient expectations, a matched case-control study may be an option to compare treatment outcomes. A healthy control group may also be included to allow for examining normal fluctuations in PROMs, functional tests, trends in activity level and changes in leg length, alignment and PCL angle over time.
Nested studies within the PAMI and PLUTO studies could be designed.
We would benefit from continued research on outcomes following both ACL reconstruction and non-operative treatment. Also, we need to investigate current surgical techniques and choice of ACL grafts as well as rehabilitation and prevention. We require effective and time
efficient protocols for rehabilitation and prevention. Studies on how to implement
prevention effectively in pediatric sports is also relevant as adherence is fundamental to the effect.
The biological aspect in the pediatric knee is an import area to explore. There are ongoing trials investigating ACL repair augmented with scaffold in young adults197. Children have favorable healing potential. Thus, we need better understanding regarding the healing potential of the ACL in pediatric patients, and how to trigger this process. Furthermore, continued research is necessary to study biomarkers to better understand the post-injury degenerative process and hopefully block or slow this process down.
Researchers should also investigate the patient perspective and be aware that there may be social and psychological implications for children who sustain an ACL injury. This has not been investigated in the pediatric population. Also, no pediatric ACL study has previously included user involvement strategies. Inviting patients and their caretakers to contribute in the planning phase of a study may be valuable in directing research toward topics and perspectives that are important for the patients.
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