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[Physio Explained] Is there an optimal time to return to sport post ACL reconstruction? With Dr Enda King

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In this episode with Dr Enda King, we discuss a recent paper looking at time to return to sport post ACL reconstruction. We discuss:

  • Is there an optimal time to return to sport? 
  • How important is time as an indicator post ACL reconstruction? 
  • Role of different graft types in timing of return to sport
  • Other implicating factors which may contribute to re-injury
  • Testing for return to sport

Enda King PhD MSc is a sports physiotherapist, strength and conditioning coach, researcher, and educator who works with elite athletes and teams across various sports. As Head of Performance at the Sports Surgery Clinic in Dublin, he developed and led advanced clinical and research pathways for ACL and Athletic Groin Pain rehabilitation, serving athletes from top global leagues including the Premier League, NFL, NBA, and UFC. He has authored over 40 peer-reviewed publications and book chapters focused on groin pain, ACL recovery, and biomechanics in performance and rehab. King is also a respected international educator and consultant, especially in lower limb injury rehabilitation.

Reference to article -  Kotsifaki R, King E, Bahr R, Whiteley R (2025) Is 9 months the sweet spot for male athletes to return to sport after anterior cruciate ligament reconstruction? British Journal of Sports Medicine Published Online First: 26 February 2025. 

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Our host is @James_Armstrong_Physio from Physio Network

SPEAKER_02:

And so the paper compares or contrasts re-injury rate between those that returned before nine months and those that returned afterwards and found there was no difference in re-rupture rates between the two. It also found that those that completed their rehabilitation to pass their return to play tests or discharge physical criteria were far more likely to return to pivoting sports than those that didn't.

SPEAKER_01:

Welcome to the Physioexplained podcast. In today's episode, Dr. Enda King joins us to discuss a recent paper he co-authored titled, Is Nine Months the Sweet Spot for Male Athletes to Return to Sport after Anterior Crucial Ligament Reconstruction? Led by Rula Kotsufaki, the study examines the importance of timing in return to sport post-ACL surgery and its clinical implications. We'll dive into what the paper found, the key factors that determine when an athlete is ready to return, and how we can better assess their readiness. Dr. Ender King is a leading sports physiotherapist, strength and conditioning coach and researcher specialising in ACL reconstruction and returned sport decisions. He is currently the head of elite performance and development in Asparta. Ender has worked with athletes from Premier League players, NBA, NFL, NHL, UFC and more, providing cutting edge rehabilitation strategies for these athletes. He is recognised internationally for his expertise in injury prevention and rehabilitation in elite sport. So stick around as we break down the key takeaways from this important study and explore what it means for your clinical practice and how the future of ACL rehabilitation is shaping up. I'm James Armstrong, and this is Physio Explained. Endo, welcome back to the Physio Explained podcast. It's been a while, but it's good to have you back on. Thank you, James. Pleasure to be involved. So we instigated this recording due to a recent paper that you've been involved with, with some other authors, which I'm sure we'll mention, around this return to sport after an anterior cruciate ligament reconstruction. And I wanted to dive into this paper and really use it, I suppose, to challenge what some clinicians may be thinking they should be doing with their patients after reconstruction and getting them back to sport. So let's start with the important stuff. Can you talk us through this paper and the authors and what the background of it is?

SPEAKER_02:

Yeah, absolutely. So I'm actually about three years in Aspartame now and was very lucky to jump on the bandwagon of much of the work that has been done primarily by Rula Katsafaki, who's the lead author in this paper and has done a huge amount on jump testing and other things in relation to ACL rehabilitation and assistant director Rod Whiteley, who's done Massive amount of research across several areas. And of course, Roald Baar is Roald Baar, so it's hard to ignore or forget his credentials. So I was fortunate enough to be involved in this paper. They have a large prospective cohort ongoing that they're collecting in Aspatar. And one of the questions very much was around, as you said, and I wouldn't say almost the mantra or the punchline that it has to be at least nine months. And indeed, there's another paper, I think it's by Tim Hewitt and Kate Webster, where, you know, should it be two years? So you get variations of that. And obviously, every case is individualized, but it certainly wasn't reflecting our practice. It certainly wasn't reflecting What you see in higher level or elite sport where many athletes are able to make a very successful return in a timeframe shorter than that and not go on to second injury. And so the paper compares or contrasts the ability to a re-injury rate between those that returned before nine months and those that returned afterwards and found there was no difference. in re-rupture rates between the two. I also found that those that completed their rehabilitation to pass their return to play tests or discharge physical criteria were far more likely to return to pivoting sports than those that didn't. So they were the two main punchlines from the paper. There has been some work to support some of this. When I was in sports surgery clinic in Dublin, we looked at the difference in re-injury rate between 6 and 9, 9 and 12 and 12 and 15 months and found no difference in re-injury rate across that cohort again in pivoting sports and Francesco Della Villa has another in European football looking at risk factors for re-injury and found that time from surgery was not a risk factor didn't increase your odds of injury so I think a lot of that would consistently highlight that probably after a minimum threshold so let's say after six months is a minimum the time from surgery is not an indicator of whether you're going to re-injure or not. That doesn't mean you should or shouldn't wait. That's a separate conversation. But this notion that you can take a nominal time point and then that will clear you or make it safe is a bit naive, I would say, but also for a number of different reasons. Number one is there are a number of studies that show that different grafts do not mature at the same rate. So generally speaking, hamstring grafts mature a little slower than patellar tendon grafts both in terms of how they heal within the tunnel and the rate of maturation of the 10 of the graph itself. So if you're going purely on a timeline based, you know, is an umbrella term really appropriate to compare for both patella and hamstring grafts? And second of all, them same studies would show the graft maturation can take, you know, I can go back to those reference that it can take up to two years. And we know that many athletes have returned long before that and had no issues in re-injury afterwards. So you clearly don't need a fully mature or whatever the hell that is ACL graft. in order to make a safe return to pivoting sports. And part of that might be in that original BSM paper that flagged the nine months. One, which is no fault of the authors, one misconception or one misconstruence is that it talks about re-injuries as ACL re-ruptures, but actually there was a relatively small number of re-ruptures within that cohort. It was almost any knee issue of which anterior knee pain or meniscus or antidepressant could be done. So very often people will look at the punchline and as usual, will not read the paper. So when you're talking about re-injury specific to graft re-injury, That's not what that study looks at in isolation where these other studies have and tend to show that it makes no difference.

SPEAKER_01:

So we're really getting from this paper that we don't have a timeframe that we need to wait for that automatically makes a patient or an athlete safe to return. How do you feel it correlates to sort of your general population of amateur recreational enthusiasts, your weekend warriors who are maybe playing netball just the weekend, maybe training once a week? Do you think there's any crossover? Do you think we could apply this quite reasonably to that population as well?

SPEAKER_02:

Yeah, I think the biggest challenge with your more recreational populations is that the time to physically recover or regain function is longer, either because of the level of treatment they're getting, the frequency of treatment, their ability to train and commit in isolation to that project versus having work and family commitments, etc. So it's not inappropriate to suggest that they should take a bit longer only that the longer you take in theory could be a surrogate for your functional recovery and physical recovery and insufficient physical recovery and those physical deficits undoubtedly are likely to play a role in knee overloading or offloading and how that will influence either acute knee overload not just ACL but in terms of meniscus and chondral surface and stuff like that as well so never mind other soft tissue injuries outside of that so it's very fair to say that those cohorts are at no greater or lesser risk of returning compared to professional athletes. At least in my experience, the difference is that it takes them longer to physically recover. And that was, again, one of the things from Rule's paper here was that if you passed your criteria, regardless of when you passed them, you're much more likely to return to pivoting sports. So I think for all practitioners, regardless of where you work or what facilities you have, I think it's important to highlight to your athletes, recreational and higher level, what the top of the mountain looks like functionally or physically and guide them to the top and try and not let them get off the bus before they get up there and get their chance of returning and maintaining a safe return will be greatly increased, independent of what time they return from.

SPEAKER_00:

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SPEAKER_01:

assessing and monitoring athletes' physical readiness.

SPEAKER_02:

Yeah, absolutely. For a number of reasons, I suppose. Number one is you get to chart their progress, but having worked the last 15 or more years with a biomechanics lab and a strength testing facility, it's very humbling to have your work reviewed periodically and see that, well, maybe I didn't make the improvement that I thought I did with making with this athlete either because obviously, or compliance, because my programs are obviously outstanding all the time, but picking the wrong exercises for that athlete, not periodizing them, not manipulating the exercise to get the adaptation you're looking for. So, The testing not only tells us where we are in the mountain, but the rate of progress we've made over the last block. And that can be really useful in modifying your practice and learning. Because ultimately, the graft is going to remodel. The knee will settle down. People move on with their lives. And that's often our problem or our challenge is that we have a window of opportunity, albeit a long one in ACL, to make a very positive impact with these athletes. But you don't find the time in the weeks going by and then they'll say, right, it's been nine months, it's been a year. it's time to go back. So if you don't have those tests there to chart the progress for both of you, but also give them an idea of when they're good enough. And again, that's not to say that if you pass physical criteria tests, of which this has been shown repeatedly, you won't re-injure either, but at least the job of rehabilitation is to restore function. So at least you can put them back to either normal or good, whatever you want to set those thresholds at, and then work from there, the chance of success are going to be increased.

SPEAKER_01:

Absolutely, yeah. With certain mechanisms of injury, an ACL rupture can occur whether you've had a reconstruction or not, can't it? So we have to bear that in mind and not just blame the reconstruction every time someone re-ruptures. No, sort of like,

SPEAKER_02:

I mean, family histogenetics are shown to come into it and also... If your first injury has been a pivoting and non-contact injury, obviously you have a susceptibility there different than if you are getting a contact injury or some other injury mechanism. So I think that those factors, the difficulty with the ACL prediction studies is like there's so few re-injuries relative to, it's so difficult to build up a large database. And then there's so many factors that can contribute to re-injury that you really need an incredibly large database, which probably, any one unit or institution would struggle to collect. And then if they were getting a multi-centre trial, trying to get everyone to collect the data with the same quality and same precision, it's quite the challenge. So I think we'll be making projections on some of those for a long time to come.

SPEAKER_01:

Absolutely. And it just goes to show in research, I mean, I think ACL research is probably There's a lot of it. So it just goes to show in terms of how hard to get the research to show us the information we want. So even with this, where we've got lots and lots of research going on, it's still difficult to make those prediction studies work for us. Yeah,

SPEAKER_02:

and as you said, it's one of the most publicised areas. But actually, probably in the last couple of years, many of those studies are actually changing in practice. They're just different ways of looking at the same thing and big questions that we want answered in terms of what's most important and when am I good enough. I wouldn't say they're impossible to answer, but certainly they're very challenging studies to not overestimate or overstate your findings based on your sample size and the number of things that you looked at. Absolutely.

SPEAKER_01:

When it comes to testing, and I mean, you might not be an answer for this, but is there any sort of go-to things that you advise you've got for clinicians when they are testing? Any tests that you think are really useful? Obviously, it's going to be athlete, patient-centred, but is there anything that you can advise people listening to this utilize or look at when it comes to enhancing their testing of these athletes?

SPEAKER_02:

Yeah, I think most tests add value. It's when we over-interpret what one test means into others or have too narrow a field. So certainly the simplest things will be performance tests like strength, jump height, drop jump performance, etc. Particularly isolated strengthening testing of the quadriceps and hamstrings are always shown to be, depending on your graft, quite indicative. And as Rula has highlighted already, horizontal jump performance will improve before vertical jump performance and counter movement jump will improve before drop jumps. There's almost like a hierarchy there of progressions over time. We do know, though, if you look at the movement, whether that's your knee valgus, your knee flexion, that will add additional information in on top of what you're getting from your performance. And we know that thirdly, if you look at the forces across the knee or at the ground or whatever, that will add even more information again. So obviously, there's a certain amount of technology required for all of these, carrying out some strength tests, carrying out some jump tests, especially vertical tests, especially drop jumps and video on people when they do them. Even if it's with your iPhone, you can pick up a huge amount of information in a relatively modest setup that will look after the big fish and then obviously if you have the benefit of 3D biomechanics the level of detail you can get is much higher and if I'm honest the standard of your rehab improves because you see what you look for and you look for what you know so if you never see the residual deficits you don't recognise the gaps in your systems and then how you can evolve from there.

SPEAKER_01:

Absolutely. This has been really useful. I think I'd advise anyone listening to this to have a look at this paper and also have a look at some of the previous studies by all of the authors that are listed, because I think it can really build up a good picture of how you should be aiming to rehabilitate your patients and athletes and how to incorporate testing. And I know Aspartar's got some great guides on that as well.

SPEAKER_02:

Yeah. So certainly, as I said, we're standing on the shoulder of Rulikot-Savarsky and our incredibly applied block of work she's done over the last while and how that's evolved in everyone's practice, but also on the Ascotar website and general social channels. You'll find our current ACL rehabilitation protocol, the tests we use, the kind of KPI and progressions we use that work in our environment. And then you can reflect your own practice again, see what works for you and what you do differently, and then evolve your own protocol from there.

SPEAKER_01:

Definitely. So those listening who are rehabbing their ACL, reconstructive patients can take away something from this in terms of that actually the timeframes again are being shown. They're not necessarily as important and it's more about what you do with your patients to see whether they're physiologically, psychologically ready to return is far more important. Really, yeah. Brilliant. Thank you so much, Ender. And no doubt, I'm sure we will have you on the podcast again. Let's maybe not leave it so long for next time. I look forward. Thanks a million, James. Cheers, Ender. Bye-bye.