The number of ACL reconstructions (ACLR) being performed in Australia, particularly in young people, has risen significantly in recent years. One study has shown that the number of ACLRs being performed in under 25yr-olds has increased by 74% (Zbrojkiewicz, Vertullo, & Grayson, 2018). This increasing trend has also been recently observed in New Zealand (Sutherland, Clatworthy, Fulcher, Chang, & Young, 2019).
ACLR is a very common recommendation for ACL injury, with one study showing that 98% of paediatric patients in Australia were recommended ACLR (Shaw & Finch, 2017). However, not all ACLR are the same. Depending on the age of the patient and the number of previous ACLRs the patient has had; the surgeon may perform an autograft ACLR (using the patient’s own tissue - bone-patella tendon-bone, hamstring or quadriceps) or an allograft ACLR (using donor or cadaver tissue; most common Achilles tendon).
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While these two types of ACLR are both treatment options for the ACL injured athlete, they can both fail, with allografts more likely to fail than autografts in younger athletes. In a prospective, randomised controlled trial (RCT) on highly active military personnel (mean age 26yrs) Bottoni et al., (2015) reported an allograft failure rate of 26% versus autograft failure rate of 8% at 10-year follow-up. Wasserstein, Sheth, Cabrera, & Spindler (2015) found similar numbers in their systematic review on autograft and allograft failure rates in athletes aged under 25yrs. When looking at these ACLR treatment options, autografts have been shown to be more cost-effective than allografts (Mistry et al., 2019).
Despite ACLR being a very common treatment for ACL injury, it is not the only treatment option. A prospective RCT by Frobell et al (2013) - the only one of its kind published to date – found that exercise rehabilitation-alone was equally as effective as ACLR at 2-year and 5-year follow-up in a cohort of ACL injured adults in many outcome measures (to be discussed in more detail throughout this paper).
A common goal for the ACL injured patient is to return to their pre-injury level of sport, and there is a widely held belief that the patient requires an ACLR to do so. Unfortunately, ACLR does not guarantee a return to pre-injury level of sport, with Ardern, Taylor, Feller, & Webster (2014) showing that only 65% of non-elite ACLR athletes will return to pre-injury level of sport (time taken to return to pre-injury level of sport unclear). This is in contrast to professional athletes, with 83% returning to pre-injury level of sport no later than 13 months post-op ACLR (Lai, Ardern, Feller, & Webster, 2018).
There is also an assumption that an ACLR is required to preserve the articular cartilage and meniscus from further injury upon return to sport and to prevent osteoarthritis (OA) changes over time. This assumption has not been shown to be entirely true, as observed by the outcomes in the studies from Frobell et al (2013) and Hurd, Axe, & Snyder-Mackler (2008). Poulsen et al (2019) show that OA change is 4-6x more likely to happen over at least 10 years following ACL injury regardless of treatment choice. There is some evidence however that does show worsening meniscus and cartilage lesions with delayed ACLR (Sanders et al., 2016), but as Filbay (2019) points out in her recent review, high-quality strengthening and neuromuscular training is not accounted for in these studies.
These two pertinent topics to the ACL injured patient (return to pre-injury level of sport and OA risk) will be discussed in more detail.
Return to pre-injury sport
Frobell et al (2013) randomly allocated 120 ACL injured patients (mean age 26 years) to two separate groups; Group One was offered an early ACLR (either hamstring or bone-patella tendon-bone autografts), whilst Group Two was offered structured rehabilitation with the option of having a delayed ACLR whenever they chose to do so. The authors then followed both groups for 2 years and 5 years, and at these 2 time points they had a sub-group of participants from Group Two who were managing well with rehabilitation-alone (these participants formed Group Three).
The authors found that after 2 years, 38% of delayed ACLR group (Group Two) had elected to have a delayed ACLR. At 5 years, 51% of Group Two had elected to have a delayed ACLR, leaving 49% of Group Two still managing without an ACLR (including returning back to pre-injury levels of activity). This remaining 49% were considered Group Three (rehabilitation-alone).
At 5 year follow-up, there was no statistically significant differences between groups in regards to pain, symptoms, function in ADLs, function in sports, knee-related QOL, general physical/mental health, current physical activity level, return to pre-injury activity level, radiographic OA or the number of meniscus surgeries performed between those treated with early ACLR and those given the option of having a delayed ACLR or those performing rehabilitation-alone.
Despite showing no differences between groups with returning to pre-injury levels of sport, the authors did show that only 20% of the participants in each of the treatment groups were still participating in their pre-injury levels of sport at 5-year follow-up. Considering the average age of the participants at the time of injury was 26, and 5 years later being 31 years of age, it’s possible that personal circumstance at this stage of life (focus on career and family rather than sport), may have influenced this decline in pre-injury levels of sport. Another RCT of this type in a younger population would be interesting to see if this trend is different between the three treatment groups.
Nevertheless, the assumption that one must have an ACLR to ensure a return to pre-injury level of sport was not supported in this well conducted trial. Nor was it observed in a case study of elite European handball players, where it was shown that 82% of a group of ACL injured patients successfully return to pre-injury levels with rehabilitation alone. These athletes also went on to participate at their pre-injury level of sport for a further 4.1years. This is in contrast to 58% of a group of players who returned to pre-injury levels of sport following ACLR, who went on to play for a further 3.8 years at pre-injury level of sport (Myklebust, Holm, Maehlum, Engebretsen, & Bahr, 2003). Similar to Frobell et al (2013), Myklebust et al (2003) showed no significant differences between either ACLR and rehab-alone groups when looking at radiographic OA changes and patient reported outcome measures at long term follow-up. Furthermore, a professional English Premier League soccer player was observed to make a successful return to pre-injury level of sport without ACLR, just 8 weeks after rupturing his ACL injury in a game, and was able to manage a further 2 years at EPL standard of play without re-injury (Weiler, Monte-Colombo, Mitchell, & Haddad, 2015).
Both of these examples are not as strong as the evidence provided in the Frobell et al (2013) paper, but it does further highlight that ACLR is not the only treatment choice for ACL injured athletes, even elite athletes.
Given the above evidence that ACL injuries can be managed successfully with rehabilitation-alone, it should be acknowledged that the ACL injured patients from the Frobel et al (2013) study were excluded from the RCT if they had high grade concomitant injuries to the knee (full PCL, MCL, LCL ruptures, posterior-lateral corner injuries, full thickness chondral lesions and complex meniscus injuries). Therefore, care must be taken when discussing the findings of this paper with patients, and applying these findings in a clinical environment.
The challenge for the clinician is to identify those who can potentially cope without an ACL, including returning to pre-injury levels of sport. Hurd et al (2008) used a screening test to identify “potential copers” that could be considered by clinicians. The screening test consisted of the KOS-ADLs, the Global Rating of Knee Scale (GRS), 6m timed hop test and the number of instability episodes the patient has had since injury. To be considered a “potential coper” one must pass ALL of the following criteria:
Hurd et al (2008) screened 345 ACL injured athletes (mean age 27) and identified 42% as “potential copers”. 72% of the “potential copers” returned to pre-injury levels of sport without ACLR. Furthermore, none of the 72% sustained further chondral or meniscal injuries during the 10-year follow-up period, and none of those who elected to have a delayed ACLR due to instability worsened their knee. At 10-year follow-up, 40% of the original “potential copers” were still classified as such, whilst 57% elected to have a delayed ACLR at some time point during the 10 years. Extending on this, Thoma et al., (2019) showed that 45% of ACL-injured patients identified early after their injury as a “non-copers” can change their coping status to “potential coper” in as little as 10 sessions of strengthening and neuromuscular training over 5 weeks. This work from both of these authors demonstrate the ability for ACL injured patients to change coping status over time; emphasising the importance of strengthening and neuromuscular control training once the knee has become “quiet” following ACL injury.
This information strengthens the argument to not rush in to early ACLR, and we should encourage the ACL injured patient into structured exercise rehabilitation as the first line of treatment for at least 5 weeks before a decision is made (Eitzen et al 2010). The positive is that if the patient chooses to have a delayed ACLR, this period of rehabilitation has been shown to improve post-op outcomes (KOOS, IKDC scores and chances of returning to pre-injury level of sport) for at least 2 years after ACLR (Failla et al., 2016).
In regards to exercise rehabilitation following ACL injury, the only exercise protocol that has been consistently used in ACL studies (Eitzen et al 2010) has been shown to be highly effective by various authors including Thoma et al., (2019) and Failla et al., (2016). Eitzen et al., (2010) developed an exercise program for a group of ACL injured patients based on the recommendations by the American College of Sports Medicine for resistance training in healthy adults. In addition to commonly prescribed closed chain and open chain exercises in a gymnasium setting, the authors also added in plyometric and perturbation exercises to enhance neuromuscular development and co-ordination.
The program ran for 10 sessions over 5 weeks, once the knee had settled following injury, and the authors assessed a variety of physical outcomes, functional outcomes and patient reported outcome measures at the start of the rehab program, at the end of the rehab program (where a decision was made whether or not to have an ACLR or continue non-operative management) and 6 months after the program had ceased.
The results showed that the program significantly improved outcomes at the end of the rehab period and at 6 months follow-up in all outcome measures. The program was also very well tolerated with only 4% of the group experiencing mild adverse events (pain and swelling) during the rehabilitation period. Without a control or comparison group, it is difficult to say that this exercise program is superior to other exercise programs; however, clinicians can be confident that clinically important improvements in both strength and function is possible in 5 weeks of rehab following ACL injury with this program.
For those who are coping well with non-operative management and wishing to return to pre-injury level of sport, Filbay & Grindem, (2019) suggest that the non-operative ACL patient gradually expose themselves back to sport and perform the same return to sport test battery as ACLR patients; >90% limb symmetry on quadriceps and hamstring isokinetic strength tests, >90% on hop test battery, >90% on patient reported outcome measures such as KOS-ADLs and GRS, and be psychologically ready (assessed via ACL-RSI).
Knee OA risk
With regards to knee OA risk over one’s lifetime following ACL injury, strong evidence shows that it is the ACL injury itself, rather than the treatment choice, that results in the person developing OA (Poulsen et al., 2019).
Poulsen and colleagues showed in their systematic review and meta-analysis of OA risk after knee injury, which included over 185,000 isolated ACL injured patients and over 750,000 patients with combined ACL and meniscus injury, that when compared to an uninjured knee and regardless of treatment choice, the risk of developing OA over at least a 10 year period was 4.2x greater and 6.4x greater respectively. Similar findings of knee OA risk over 10 years following ACLR have been found by Chen et al., (2019) and knee OA risk after ACL injury regardless of treatment choice (Ajuied et al., 2014).
In their systematic review and meta-analysis, Ajuied et al (2014) report that the risk of developing any type of knee OA (mild, moderate, severe) at least 10 years after ACL injury was significantly higher in non-operatively treated patients (4.98x greater risk) than ACLR treated patients (3.62x greater risk). However, the opposite was true regarding the risk of developing moderate to severe OA, which was significantly higher in ACLR patients than non-operative patients; 4.7x greater and 2.4x greater respectively.
In a prospective cohort study of 100 ACL injured patients, who were all encouraged into high quality rehabilitation for between 5-8 months following ACL rupture, Neuman and colleagues looked at radiographic changes over 15 years in regards to tibio-femoral OA (TFOA) (Neuman et al., 2008) and patella-femoral OA (PFOA) (Neuman et al., 2009). They found that 15% had TFOA at 15 years, all of whom had menisectomy surgery at some point during the 15-year study. They also reported that 23% had a delayed ACLR (all had bone-patella tendon-bone ACLR) on average 4 years post injury. When PFOA prevalence was observed at 15-year follow-up, 46% of the ACLR group had radiographic PFOA whereas only 8% of those continuing non-operative management had radiographic PFOA.
These two studies have two limitations that needs to be acknowledged; lack of comparison group from baseline and 25% of the original cohort were not accounted for at 15-year follow-up. The results however indicate that when high-quality rehabilitation is taken into account, and performed regularly during the first 6 months following ACL injury, a very favourable outcome in regards to knee OA changes can be achieved for the patient pursuing a non-operative ACL treatment plan.
In summary, there are consistent findings across several cohort studies show that nonoperative ACL patients (even elite athletes) do just as well, and in some cases, better than ACLR patients in short-term and long-term outcome measures, including function, quality of life and return to pre-injury levels of sport.
A patient-centred and shared decision making approach needs to be undertaken for the ACL injured patient following ACL injury and the decision to pursue a non-operative pathway or undergo early ACLR needs to be carefully considered based on a number of factors including, but not limited to; age, sex, level of sport competition that the person wishes to return to.
Regardless of treatment choice, and in the absence of high-grade concomitant injuries to the knee, exercise rehabilitation for at least 10 sessions should be considered the first-line of treatment once the knee has settled, as this has been shown to improve short-term and long-term outcomes in both non-operative ACL patients and ACLR patients.
The patient should also be counselled that a delayed ACLR can be performed at any time they wish, with high quality evidence showing that it is unlikely that delaying ACLR will result in further deterioration or damage to the meniscus and/or cartilage.
Unfortunately for the patient, radiographic OA changes are likely to occur slowly over time regardless of treatment option; however it needs to be reinforced that exercise therapy is an important treatment strategy for those with symptomatic knee OA with at least 2 supervised sessions per week for 6 weeks showing a clinically meaningful benefit (Skou & Roos, 2019).
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