Activity level is a key factor in management of ACL injuries in children and adults. High activity level and participation in pivoting sports are risk factors for knee re-injury35 36. However, the treatment decision may be influenced by activity level. High pre-injury activity level especially in pivoting sports is likely to increase the probability of ACL reconstruction as these patients are traditionally advised to undergo ACL reconstruction. Consequently,
activity level is an important confounder for new meniscal tears or graft ruptures. In our, systematic review we considered activity level as the most important confounder for new meniscal tears. However, very few studies adjusted for activity level.
In our clinical studies the activity level was reported at baseline, 1 and 2-years follow-up and at final follow-up. The high rate of sports participation (91%) at final follow-up in our clinical studies is in line with several pediatric studies101 133 134 which report very high short-term activity levels (91-96%). Interestingly, we found that 2 out of 3 patients in our studies did no longer participate in pivoting sports at final follow-up, but the majority participated in other sports without pivoting- regardless of final treatment.
In a systematic review, the pooled estimate of return to any sport after ACL injury in children and adolescents was 92%, but the return to sport rate was not stratified by level of
pivoting135. In adult elite athletes, return to sport rate was 85%, and for athletes playing pivoting sports such as American football, basketball and soccer return to sport rates were 78-85%136. However, the drive to continue sports activities may be higher in athletes compared to children. The patients in our study were not selected athletes. Multicenter initiatives have concluded that an elite sporting career is unlikely following a pediatric ACL injury137. However, two of the patients in our series are competing at a national level (alpine skiing n=1 (ACL reconstructed) and cross-country skiing (not ACL reconstructed)). A national level in cross-country skiing in Norway is considered elite level as national level matches international level.
A recent randomized controlled trail (RCT) from Norway where adults with ACL injury were allocated to receive single or double bundle ACL reconstruction had a return to sport rate of 44% and 53% respectively138. Before ACL injury, 64% of these patients participated in
pivoting sports. Just like in our study, patients were informed about the re-injury risk following pivoting sport and this may explain the relatively low rate of return to sport138. A cross-sectional study from Sweden reported that only 40% of patients had returned to pre-injury activity level 1-7 years after ACL pre-injury. The most common factors for not returning to sports was inability to trust the injured knee, fear of re-injury and poor knee-related
function139. About half of the patients who dropped out from pivoting sports in our study reported that the drop of activity was knee related either because their knee did not function adequately or because they were afraid of re-injury. The remaining patients, reported lost interest or change in priorities (i.e. education) as the main reason for quitting pivoting sport.
The patients included in Project 2 (Article 2 and 3) are no longer children, but young adults, and similar studies that we can compare to do not exist. An interesting detail that may help to illustrate post-injury activity level in this group is the normal trends in sports participation.
In Norway, national surveillance data show that in high school there is a drop in organized sports participation i.e. soccer and team handball (3 out of 4 have dropped out)140. Our study population may follow the same trends as the rest of the population and this may affect the activity level outcomes. The reasons why we experienced a drop in activity level is therefore very multifaceted. Investigating this was not our main objective and our design is not
optimal to detect certain evidence regarding this.
In general, there are some important challenges with post-injury activity level as an outcome, especially if this outcome is a measure of success which is common in many
articles25. There are multiple reasons patients do not return to their previous activity level139. Reduced function, fear of re-injury or trust issues are problems for some patients, while other choose to participate in other sports and activities which actually may be a wise
decision for long-term knee health35 36. We know that return to high activity levels35 36 101 and especially early return100, is a predictor of re-injury. As a result, clinicians should not
encourage early return to high load activities. Changing a sporting career may in certain instances be a better alternative. The normal trends in the adolescent population is also important to consider. These trends may differ from one country to another because they are likely to depend on school and educational system. For instance, in Norway organized sports are normally conducted outside the school or university, whereas college sports are part of the norm for instance in the United States and some other countries. We can also speculate whether these normal trends and common changes in activity level from childhood to maturity may affect PROMs.