A typical knee flexion, internal rotation and valgus ACL injury.
Anterior Cruciate Ligament (ACL) injuries of the knee are devastating for an athlete. They have major effects on an athlete physically, psychologically and financially. These effects are both short and long term across athletes of all standards and sports. Primary prevention of these injuries is paramount and some excellent evidence-based programs such as the FIFA 11+ are available to help sporting teams reduce incidence. For those athletes who sustain an ACL injury, what are the long-term outcomes? How can they rehab their knee for the best outcome? And finally the big question, when can they return to sport?
Post ACL reconstruction, one in three athletes will develop symptomatic Osteoarthritis of the knee within 10-15 years (Lie et al 2019). Further, one in two athletes will show radiographic changes consistent with Osteoarthritis. A recent study of athletes by Patterson et al (2019) at 1 year post ACL reconstruction assessed four functional tasks – 3 hop tests and 1 single leg rise test – all common assessment tools toward end stage rehab. Passing required 90% symmetry compared to their non-operative leg. Of the 78 athletes tested, only 18% passed. These athletes were followed up at 5 years post op and performing poorly on all four tests was associated with 3.66 times increased risk of worsening Patellofemoral Osteoarthritis. (Patterson et al 2019). Research regarding functional test performance and development of Tibiofemoral Osteoarthritis shows more mixed results at this stage.
Interestingly, for the 80% of athletes who failed these functional tests, there was no correlation between poor knee function and self-report of decreased functional capacity. Whilst the athletes felt their knee didn’t restrict sports-skill and functional tasks, their inability to complete the tests adequately may suggest they learnt ways to work around their biomechanical deficits. This supports further research showing the majority of ACL reconstruction athletes develop altered movement patterns which allow them to complete sports specific tasks but at a much higher injury risk.
The change in mechanics most frequently seen post ACL reconstruction include:
· Running biomechanics: Decreased knee flexion motion and internal knee extension moments are seen (Pairot-de-Fontenay et al 2019). These changes continued to be evident 5 years post-surgery. Specific targeted strengthening and neuromuscular training are required to improve running biomechanics post ACL reconstruction.
· Jump tests: Single leg hop test for distance shows decreased knee extension moment and/or shifting of the centre of mass closer to the knee to decrease demand on the knee extensors (King et al 2018). This is achieved via increased trunk, pelvis or hip flexion or maintenance of greater knee extension angle throughout the task. Single leg drop jumps show decreased hip and knee extension angles during latter part of push off to also offload the Quadriceps. A greater proportion of power may also be generated at the ankle (O’Malley et al 2018). Such altered kinematics may still be present even if performance of the task (ie equal jump distance or height) is achieved on both legs in testing.
· Neurophysiological dysfunction: Neural excitability is altered post ACL reconstruction. This is proposed to be one of the drivers behind the “stiffened knee strategy” displayed by athletes and resulting in impaired energy attenuation at the knee (Pietrosimone et al 2015). The ACL contains mechanoreceptors and therefore directly influences the neuromuscular control of the knee. Rupture of the ACL causes interference in this communication pathway and affects the motor control of the lower limb. ACL injury can therefore be considered a neurophysiological dysfunction and not a simple peripheral musculoskeletal injury (Van Melick 2015).
· Increased Motor Unit Recruitment: True muscle asymmetries may be accounted for with the athlete creating the same peak torque by increasing neural recruitment within the muscle. (King 2020). This means more of the muscle motor units are contributing to the movement to compensate for the decreased true strength in the muscle. This effect is lost very quickly if athlete takes a break of as little as a week from strength training.
A further study by Kyritsis et al (2016) examined male professional athletes at ~ 8 months post-surgery with a battery of 6 tests – isokinetic strength testing of the Quadriceps, single and triple hop, Triple crossover hop, running T test and completion of full sports specific on-field rehabilitation. Results were definitive that athletes must build strength and power:
-> For every 10% difference in Quadriceps to Hamstring strength ratio, risk of ACL reinjury increased 10.6 times.
-> Athletes who passed all criteria had only a 10% reinjury rate compared to 33% on return to sport.
-> Athletes failing to pass the testing criteria had 4 times increased risk of reinjury.
It is worth noting as this study included only professional male athletes, it is reasonable to expect the failure rate on testing and reinjury rate would be higher in females and recreational athletes.
Studies on ACL reinjury rates show 30% of athletes suffer a second ACL injury within 2 years, with greater frequency in the contralateral knee. For the younger athlete, one in four who are under the age of 25 and return to pivoting sports will suffer a reinjury (Wiggins et al 2016). Reviews on longevity in sport post injury found 35% of professional male soccer players retired within 3 years of sustaining an ACL injury (Walden et al 2016).
How can I rehab my knee for the best outcome?
Australia has an alarming trend of ACL reconstruction patients being undertreated in their rehabilitation phase (Grindem et al 2018). 45% of patients do not see a clinician after 3 months post-operatively and 70% never progress through a graduated agility or landing exercise program as per evidence based Clinical Practice Guidelines. Accordingly our patients also have poor outcomes on functional outcome tests with only 30-50% passing key tests compared to 80-90% of patients in the USA and Norway. When you consider the kinematic changes, reinjury rates and long-term injury sequelae even in professional athletes, we need to do better.
It must be acknowledged that ACL rehab is time consuming as well as physically, mentally and emotionally demanding. Patient motivation with such a long journey can be variable and the Therapist must act as a continual source of motivation for the patient through education, goal setting and repeated functional testing for feedback and rehab direction. A structured and progressive supervised pre-operative and post-operative program with close follow up increases the likelihood of Return to Sport (Grindem et al 2015). For most recreational athletes it is a journey of well over over 12 months from injury to end point with ongoing hard work and maintenance to follow. For elite athletes this can be faster as there are less “life distractions” along the way and more immediate medical management initially.
The Melbourne ACL Rehab Guide 2.0 outlines the following typical stages and focus points of an ACL Rehab program:
· Pre-Op Phase
Recovery from original injury, preparing for surgery with range of motion exercises, swelling management, regaining quads and hamstring strength.
· Phase One – Recovery from Surgery
Achieve knee extension, minimal swelling and activation of quads.
· Phase Two – Strength and Neuromuscular Control
Regain most of single leg balance, muscle strength and work on Single leg squat control.
· Phase Three – Running, Agility and Landings
Excellent hopping performance, graduated agility program and modified game play, full strength and balance.
· Phase Four – Return to Sport
Full functional screening passed, Psychologically ready and confident in returning to sport, ongoing strength maintenance
· Phase Five – Maintenance and Injury Prevention
Ongoing strength work, adherence to Injury Prevention Protocols.
The early stages of rehab follow more stereotypical physio programs with lower load and less time-consuming exercise programs. Often the pathway is straight forward until Phase Three, when some recreational athletes may waiver in motivation and effort. Concurrently the knee is also more symptomatic up until Phase Three and therefore a constant reminder of rehab needs. The introduction of running sessions, straight line and progressing to change of direction, in conjunction with heavy full body weights programs becomes time consuming. For athletes this phase is more enjoyable but can sometimes result in “cherry picking” and performing exercises or activities they like and neglecting others. Phase Three is also (to quote ACL guru Enda King) when an athlete "makes some money” with each session of building muscle, fitness and movement patterns resulting in increasing athleticism, minimizing injury risk and improving performance.
A hyperextension ACL injury preceded by overstriding and initiation of trunk extension in transition from dribbling to preparing to shoot.
A significant portion of Phase 3 should be spent improving cutting or change of direction time. In change of direction sports, reduced cutting time is often used to identify high performance athletes. Biomechanical analysis has shown the keys to performance are peak ankle power, peak ankle plantar flexor moment, range of pelvis lateral tilt, maximum thorax lateral rotation angle and total ground contact time (King et al 2018). To improve or rehabilitate cutting time, training should focus on gastrocnemius, soleus and hip abductor strength and plyometric exercises. In addition the coaching of correct technique is vital to ensure restoration of skill post injury rather than adaptive technique. Development of athletic physical qualities (concentric, reactive, isometric and eccentric strength; rate of force development) and the ability to rapidly produce and accept force across the whole force velocity spectrum improves change of direction speed and agility performance, as well as decreases injury risk and improves mechanics (Dos Santos 2019).
When can I return to sport?
Clinical decision-making regarding return to sport post ACL reconstruction is a complex process. The Strategic Assessment of Risk and Risk Tolerance (StARRT) framework highlights the individual considerations for each athlete (Shrier 2015). The basic premise is: the load tissues can absorb prior to injury is identified; the expected cumulative load that will occur is identified; factors which may shift the level of acceptable risk are considered and a decision is made. Accordingly, the return to sport decision for an International Hockey player in their last Olympic campaign is very different to that of a 15 year old female recreational netball player. It is important to note that Psychological testing regarding readiness to return to play can also influence decision making.
Discussions with athletes regarding return to sport also need to cover the return to participation versus return to performance continuum. Returning to sport for many athletes may be considered the end point for rehab goals, particularly for recreational athletes. Education of athletes is vital to help them understand this is not the end of their rehab journey. Statistics from the NFL, NBA and European soccer show that whilst at least 80% of athletes return to sport, performance ratings decrease 30 – 45% post injury. Returning to sport should therefore be celebrated as a great milestone, but akin to the player receiving their probationary driver’s licence. Good enough to join in but not yet considered great at their sport of choice. Continued hard work will benefit both their sporting performance and the long-term health of their knee.
The aim is return to performance not return to sport. (Ardern et al 2016)
Can I play now?
Having worked through the final stage of rehab developing power, reactive strength, plyometric ability, linear and multidirectional running, sport specificity and fatiguability the athlete should be primed. Based on research findings our physical parameters for a fully rehabilitated athlete are:
· Strength testing – Quads 260% bodyweight, Hamstrings 160% bodyweight
· No asymmetry on Single Leg Counter Movement Jump, Drop Jump and Catch
· Running – no asymmetry in push off or midstance with maximal speed
· Change of direction running – no asymmetry especially unplanned cutting
· Completed graduated return to training with 4 full weeks of unrestricted training
· Appropriate level of Conditioning
· Maintenance of Strength and Power whilst completing full training load
· Psychologically ready to return to sport
Objective testing is required to ensure athletes have reached these goals before returning to sport to minimize the risks of reinjury, optimize long term joint health and maximize performance. Maintenance of these athletic qualities through specific training is paramount however the motivator for this should be performance not rehabilitation. This training can take the form of ongoing gym work for strength, specific agility/change of direction exercises and implementation of any of the ACL Injury Prevention Programs that are available. These ACL programs must be performed for at least 15 minutes prior to each training session and game to be effective. Our aim is to continue to maintain or increase that “bank balance” of athletic properties we established during all those months of rehab.
The rehab journey of an ACL reconstruction is a long and arduous one requiring extreme dedication and hard work. Frequent objective reviews are required to ensure specific, measurable athletic goals are established with targeted intervention plans to achieve the best outcome. The reward for the athlete is optimal knee health and a return to performance in a superior physical state than prior to the injury.
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