Re-injury risk and how to reduce it
One of the most important goals for an athlete following ACL reconstruction, and one of the main markers of a successful Return to Sport is prevention of reinjury. But how good are we at helping our patients achieve this goal? And how do we know when a player is at a suitably low risk to RTS?
To answer this question we first need to understand the stats regarding reinjury risk and how this differs between populations.
What is the risk of reinjury?
Overall risk
-4.5% sustained graft rupture and 7.5% of entire cohort sustained a contralateral ACL injury at 3-5years follow up (Webster et al)
-5.8% pooled autograft re-rupture rate (minimum 5 years follow up) and 11.8% pooled contralateral ACL rupture (Wright et al, 2011)
Age
-Odds of sustaining an ACL graft rupture increased 6 fold for patients under the age of 20 (Webster et al 2014) compared to age >20y.
-29% risk of either ACL graft rupture or contralateral ACL rupture at minimum 3-5years follow up in athletes aged <20y…….. ie 1 in every 3.4 young athletes (Webster et al)
-29.5% reinjury rate in the first 2y RTP in athletes aged <20y. This comprised 20.9% contralateral ACL injury, and 9.0% ipsilateral graft rupture (Paterno et al, 2014)
-Second ACL injury in youth athletes most commonly occurs within first 2years post-op (Wright et al)
-Is age a direct factor in ACL injury risk eg. neuromuscular maturation or a proxy for other factors such as exposure? 88% of people age <20 returned to cut/pivot sports compared to 53% of people aged >20y (Webster et al)
Gender
-While Webster et al found nil link between gender and reinjury rate…
-Paterno et al found that 23.7% of young female athletes (aged <20y) sustained a contralateral ACL injury compared with 10.5% of males in the same age group (p=0.18). Whereas 8.5% females suffered an ipsilateral graft re-tear compared to 10.5% males (aged <20y) when adjusted for athletic exposures.
-Paterno et al also found that young female athletes (age <20y) were twice as likely to sustain a contralateral injury in first 2y RTS than an ipsilateral graft tear when adjusted for athletic exposures
Other surgical or injury factors
-Webster et al found no link between ACL re-injury and graft diameter or meniscal/chondral injury at time of ACLR.
-29.5% of the ACLR group and 8.5% of the control group in Paterno et al’s study sustained non-contact or indirect contact ACL injuries, whereas nil contact injuries occurred in their cohort. However a contact mechanism of original injury led to a 3 fold increased reinjury rate compared to non-contact mechanism in Webster et al’s study
Family History
Positive family ACL injury history doubled the odds of an ACL graft rupture or contralateral ACL injury compared with nil family ACL history (Webster et al 2014), though this raises the question over genetic vs active family lifestyle as contributing factors
Generalised hypermobility
Significantly increased risk of knee injury in people with generalized joint hypermobility compared to those without generalized hypermobility playing contact sports (Pacey et al)
Time to Return to Sport
-Reinjury rate was significantly reduced by 51% for each month RTS was delayed until 9months post-op, after which no further risk reduction was observed (Grindem et al, note- Grindem ‘reinjury’ doesn’t necessarily mean ACL reinjury, but knee injury in general).
- Return to Level 1 (cutting and pivoting) sports <9months post-op = 39.5% reinjury compared to 19.4% reinjury rate in those RTS >9months (Grindem et al)
- All patients (n=4) returning to level 1 sports before 5months post op sustained a reinjury within 2months of RTS (Grindem et al)
- Paterno et al found a 15 fold increase in further ACL injury in athletes aged <20y returning to sport within 12months post ACLR compared to age matched controls
Type of Sport
-Grindem et al found patients returning to Level 1 sports (jumping/pivoting/hard cutting sports) had a 4.32 times higher reinjury rate than those that didn’t return to Level 1 sports at 2 years (p= 0.048)
-Returning to cutting/pivoting sport increased the odds of graft rupture by a factor of 3.9 and increased contralateral ACL rupture by a factor of 5 (Webster et al) compared to returning to less pivoting type sport
Revision ACL reconstruction
Webster et al (2018) found a very high rate (27%) of 3rd ACL injury ie graft re-rupture or contralateral ACL injury in people following revision ACL reconstruction. There was a significant link between those with medial meniscal pathology at time of revision ACL reconstruction having higher rates of reinjury (p=0.03), and those returning to pre-injury sports (p=0.02).
Objective physical testing
-Not meeting all 6 discharge criteria (isokinetic quads deficit <10% at 60°/sec; running T-test <11sec; LSI >90% for 3 hop tests; on-field sports specific rehab) before returning to team training had a 4.1 times increased risk of ACL graft rupture, p< 0.001 (Kyritsis et al, professional male cohort)
-For every 10% decrease in hamstring:quadriceps strength ratio there was a 10.6 times higher risk of sustaining an ACL graft rupture, p=0.005 (Kyritsis et al, 2017).
-These results are mirrored by Grindem et al (mixed gender cohort, non-elite): 38.2% of athletes who failed the formalized RTS criteria (>90% LSI quads strength along with >90% LSI hop tests) suffered reinjury compared with 5.6% who passed, ie. an 84% lower reinjury risk though not statistically significant
-More symmetrical quads strength on RTS significantly reduced reinjury risk (Grindem et al), 3% reduced reinjury rate for every 1% point increase in strength symmetry; 33.3% reinjuries vs 12.5% reinjuries with RTP quad LSI < 90% vs >90%
So, what does this tell us about re-injury risk following ACL reconstruction?
In a nutshell, it’s individual. Though in several population groups the stats aren’t reflecting successful outcomes, there are some strong trends to keep in mind when calculating an individual athlete’s risk.
Eg. A 17year old female, with strong family history of ACL injury, generalized hypermobility, keen to return to soccer; vs a 30year old male with nil family history, nil hypermobility, and aiming to return to rowing.
However, if you follow the advice of Nagelli et al, they advocate most people delay return to Level 1 sports until 2 years post-ACLR as they have correlate the timeframe of highest reinjury risk upon RTP with evidence that a reconstructed knee hasn’t fully recovered structurally and functionally until 2 years ie…
-It can take 2 years for tibial bone mineral density to return to normal levels, and for bone bruising and markers of chondral injury to resolve, indicating an extended time period for recovery of joint homeostasis
-Evidence that it may take at least a year for joint proprioception to be restored after losing the sensory input from the native ACL
-ACL graft remodeling, ligamentization and vascularization can take 24months to optimize, especially in hamstring tendon grafts
-More likelihood of full recovery of adequate neuromuscular control and symmetrical strength which usually is lacking at varying isokinetic speeds until 2years post op, and resolution of kinematic and kinetic alterations (though this can persist for 5years post-op)
That said, I find it very hard trying to tell a promising young athlete to delay their RTP until 2 years post-op. Hence, this is where objective testing comes into play.
RTS testing, our process:
An athlete can be assessed for their readiness to undertake functional objective RTS tests once:
- They are bare minimum 9 months post-op (preferably 12 months, and ideally 18 months in those aged <20y)
- They have completed a comprehensive rehab program incorporating neuromuscular control, strength, power, full return to running and progressive sport skill training, hopping and jumping
- Passed an isokinetic test with <10% difference in quad and hamstring LSI and good hamstring:quad ratios
- They have passed clinical assessment of their knee including ROM, swelling, graft integrity
- They have good in rooms dynamic single leg control
Our RTS tests assess whether the required physical goals which need to be achieved (signifying satisfactory physical rehabilitation and lowest risk of re-injury) have been met. From the functional test outcomes and an assessment of other non-modifiable factors it’s then a shared decision around where the individual sits on the risk of re-injury spectrum i.e.. Should progression to unrestricted training and RTP be allowed versus potentially lowering reinjury risk further with more time and specific rehab? I think full disclosure and discussion with the individual, their family their surgeon/doctor, and coaching staff is essential in coming to a final decision. Even then, despite best rehab and testing practice there’s still no guarantee of a successful injury free return to play due to other potential variables and the unpredictable nature of sport.
-Grindem H, Snyder- Mackler L, Moksnes H, et al. Br J Sports Med 2016;50:804–808.
-Kyritsis P, Bahr R, Landreau P, et al. Br J Sports Med 2016;50: 946–951.
-Nagelli and Hewett (2016). Should Return to Sport be Delayed Until 2 Years After Anterior Cruciate Ligament Reconstruction? Biological and Functional Considerations. Sports med, July
-Pacey, V., Nicholson, L.L., Adams, R.D. et al (2010). Generalized Joint Hypermobility and Risk of Lower Limb Joint Injury During Sport, A Systematic Review With Meta-Analysis. American Journal of Sports Medicine 38(7)
-Paterno MV, Rauh MJ, Schmitt LC, et al. Incidence of con- tralateral and ipsilateral anterior cruciate ligament (ACL) injury after primary ACL reconstruction and return to sport. Clin J Sport Med. 2012;22(2):116–21.
-Webster, K.E., Feller, J.A., Kimp, A.J., and Whitehead, T.S. (2018). Revision Anterior Cruciate Ligament Reconstruction outcomes in younger patients- Medial meniscal pathology and high rate of return to sport are associated with third ACL injuries. AJSM DOI: 10.1177/0363546517751141
-Webster KE, Feller, JA, Leigh WB and Richmond AK. (2014) American Journal of Sports Medicine. 42 (3) 641-647
-Wright RW, Magnussen RA, Dunn WR, et al. Ipsilateral graft and contralateral ACL rupture at five years or more following ACL reconstruction a systematic review. J Bone Joint Surg Am. 2011;93A(12):1159–65.