Anterior Cruciate Ligament Rehabilitation: Is it a Software or Hardware problem? PART 1

04 March 2018

Anterior cruciate ligament (ACL) tears are relatively common in sports such as football, basketball, netball and skiing. Anatomically, The ACL is purported to prevent the tibia from moving forward during weight bearing and help to prevent internal rotation of the knee joint. Injury most often occurs when an athlete is pivoting, decelerating suddenly or landing from a jump.

Although evidence supports neuromuscular training for effective injury prevention and rehabilitation, the typical rehabilitation plan for ACL injuries involve biomechanical factors such as knee valgus angle, hamstrings to quadriceps strength ratio, trunk stability, single leg hopping, balance and plyometric function with less consideration for cognitive and neurological components.

With all this in mind there hasn’t been a significant decline in the reoccurrence of ACL injuries. Are biomechanical and fitness parameters sufficient to drive positive outcomes?

The most significant study by Kyritsis et al (2016) addressed 6 discharge criteria for return to play after an ACL reconstruction. These include:

  1. Single leg hop – Limb symmetry index > 90%
  2. Triple hop – Limb symmetry index > 90 %
  3. Triple crossover hop – Limb symmetry index > 90%
  4. Running T-test - <11 seconds
  5. On-field sports-specific rehabilitation
  6. Hamstrings deficit < 10% at 60 degrees/sec

These criteria bring about confidence in my ability to appropriately discharge athletes onto the sporting field. However, I believe unresolved neuroplastic changes after ACL injury and reconstruction should be utilized more practically in private practice and on the sporting field.

As stated by Grooms & Myer (2016), a vast majority of literature has placed too much emphasis on surgical outcomes related to graft type. A hamstring tendon autograft anterior cruciate ligament reconstruction (ACLR) does not prevent the development of patellofemoral osteoarthritis (OA). Patellofemoral OA severity after ACLR is associated with worse symptoms and function, independent of tibiofemoral OA.

Emerging evidence indicates that ACL injury induces a mild neurological insult to the central nervous system (CNS), causing neuroplastic changes due to the lost mechanoreceptors, pain and developed motor compensations. In my private practice I would also integrate a neurocognitive approach during rehabilitation alongside the 6 discharge criteria as stated above for return to play after an ACL reconstruction. This involves a visual– spatial–cognitive–motor rehabilitation approach to support neuromuscular optimisation.

An excellent paper by Grooms et al (2015) expresses a viewpoint contrary to what is currently being administered in rehabilitation programs today. They state that “Sport and activities require an external focus of control where attention is directed to the environment and the body naturally self-selects the most appropriate motor control pattern to maintain joint to joint integrity.”

Unfortunately, most ACL rehabilitative programs demonstrate a considerable amount of internal rather than external focus. For example, an internal focus strategy applied to an exercise might be for that client to: “avoid the knee bowing inwards” or avoid excessive knee bend”. An internal focus however might provide positive benefits early in rehabilitation when there is a need to develop conscious awareness of an injured joint and its movement as opposed to attention to the external environment. Whilst this might be beneficial in the short term to support protective mechanisms, it certainly must be addressed once tissue healing has occurred. Prior to returning to sport, the athlete must incorporate programs which focus on external cueing involving a highly complex, dynamic visual and auditory environment, movement planning, rapid decision making and unanticipated perturbations.

A neuro-imaging investigation in those with ACL injury performed on the brain during knee flexion and extension showed increased activation of the pre-supplementary motor area of the brain. Although this task was relatively simple, those with ACL injury needed to engage in high level movement planning. This means that the attentional capacity in those with a previous ACL injury is much more limited than those without ACL injury. Therefore, it would make sense to gradually improve one’s attentional capacity, as we do with progressing the load or any other typical fitness parameter employed in ACL rehabilitation programs.

My approach to ACL rehabilitation would be to:

  1. Improve somatosensory input and awareness of sensory-motor planning
  2. Reduce reliance on visual information to plan movement and maintain neuromuscular control
  3. Increase cortical top-down movement strategies rather than prescribe exercises that work on a simplistic biomechanical model of progression.

We cannot underestimate the brains role in driving a successful rehabilitative outcome. The majority of research investigating the effects on ACL rehabilitation has largely focused on biomechanical parameters. However, we must not forget that the visual or objective alterations in biomechanical movement are an end-product of a neurological network that hasn’t been updated!

Stay tuned for PART 2 where we will be discussing the key rehab exercises that are administered today.


Benjaminse A, Gokeler A, Dowling A V, Faigenbaum A, Frd K, Hewett T E, Onate J A O, Otten B & Myer G D, Optimisation of the Anterior Cruciate Ligament Injury: Prevention Paradigm, Novel Feedback Techniques to Enhance Motor Learning and Reduce Injury Risk (2015) Journal of Orthopaedic & Sports Physical Therapy, Vol 45, No.3 170

Culvenor A G, Lai C C, Gabbe B J, Makdissi M, Collins N J, Vicenzino, Morris H G, Crossley K M, Patellofemoral osteoarthritis is prevalent and associated with worse symptoms and function after hamstring tendon autograft ACL reconstruction (2013) British Journal of Sports Medicine

De Stasi S, Myer G D & Hewett T E, Neuromuscular Training to Target Deficits Associated With Second Anterior Cruciate Ligament Injury (2013) Journal of Orthopaedic & Sports Physical Therapy

Grooms D R, Myer G D, Upgraded hardware─What about the software? Brain updates for return toplay following ACL reconstruction (2016) British Journal of Sports Medicine

Grooms D R, Neuroplasticity Following Anterior Cruciate Ligament Injury: A Framework for Visual-Motor Training Approaches in Rehabilitation (2015) Journal of Orthopaedic & Sports Physical Therapy

Grooms D R, Page S J, Nichols-Larsen D S, Chaudhari A M W, White S E, Onate J A, Neuroplasticity Associated with Anterior Cruciate Ligament Reconstruction (2016) Journal of Orthopaedic & Sports Physical Therapy

Kyritsis P, Bahr R, Landreau P, Miladi R, Witvrouw E, Infographic. Avoid ACL Graft Rupture. Meet Discharge Criteria. (2016) British Journal of Sports Medicine, 50:952