Early phase of ACL rehabilition

Contents of Article

  1. Aim
  2. Introduction
  3. Functional anatomy
  4. Mechanism
  5. Clinical examination
  6. Rehabilitation plan after anterior cruciate ligament reconstruction
  7. Pre-surgery / pre-op / pre-rehabilitation
  8. Post op ‘Early phase’
  9. References
  10. About the Author and disclaimer


The aim with this blog series is to share some thoughts about rehabilitation, reconditioning and return to sport and performance following an Anterior Cruciate Ligament (ACL) injury.

We hope that it will inspire both health professionals and athletes recovering from ACL injuries. 


An ACL injury is a devastating injury for athletes of all levels and often sidelines them from their sport. When the ACL ruptures, the knee often becomes unstable with impaired limb function and decreased quality of life (QoL). The goal for the rehabilitation process is to allow the athlete to return to their pre-injury strength and function, while also minimizing the risk of re-injury and possible early onset of osteoarthritis. Luckily, ACL injuries are NOT a common injury in sports, with an overall incidence rate 1.52 per 10.000 athletic exposure (AE) across different sports (Montalvo et al., 2018).

An ACL injury commonly requires extensive rehab before returning to their pre-injury strength level. Having a plan and following a roadmap can optimize the rehabilitation process, which is crucial for a successful long-term return to their sport.

Athletes with ACL injuries tend to have very high expectations prior to ACLR, which do not match average outcomes. In a study by Feucht et al. in 2014, all of the athletes expected to return to normal knee function within 12 months of surgery, 91% expected to return to sport within one year of surgery and 98% expected little to no increased risk of knee osteoarthritis after ACLR.

Even though ACL reconstruction (ACLR) is the most common treatment for ACL injuries, surgery does not always result in a return to pre-level activity. A study published by Ardern et al. (2014) showed that only 63% of athletes returned to pre-injury level, 44% returned to competitive sports and approximately 65% did not return to pre-injury level after 12 months. However, 80% of the ACL patients in this study returned to some form of sport within 1 to 2 years post-op (Ardern et al., 2014). Among elite athletes, return to sport (RTS) rates are much higher with 83% returning to pre-level sport within 13 months post-op ACLR (Lai et al., 2018), and 94% of elite footballers (Ekstrand, 2010).

With the low numbers of RTS in mind, ACLR is not always the right treatment for ACL injuries, and RTS depends on many multifactorial contextual factors.

In fact, one prospective RCT by Frobell et al. (2013) found that by delaying the ACLR at least 10 weeks, 50% of the athletes did not need a ACLR at all. After 5 years, no difference was found between ACLR or those treated conservatively with rehabilitation alone. This has been further investigated by Grindem (2018) who proposed a prediction model for a more accurate two year prognosis for those who were treated with the non-surgical method. Athletes who were older, women, and individuals with better knee function early after ACL rupture were more likely to have successful two-year outcomes. These RTS numbers drop further if the athlete has a revision ACLR (Grassi, 2015).

Therefore, clearing the athlete for RTS is not a straight forward procedure, which has also been highlighted in a consensus statement on RTS (Ardern, 2016) which explains how its multifactorial, biological, psychological and social factors might influence treatment and outcomes (Ardern, 2016). RTS criteria will be discussed in a future blog post.

This information should be delivered in a way that is comprehensible to the patient to make informed, shared decisions before deciding to pursue ACLR or conservative rehabilitation (Feucht, 2014).

Functional anatomy

The ACL is located in the center of the middle of the knee and runs between femoral condyle and into the tibial bone. The ACL is the primary restraint to anterior translation of the tibia relative to the femur and secondary to internal rotation. The restraints from the ACL help with controlling the glide in the knee joint throughout the movement in various range of motions. Damage to the ACL can disrupt this system, resulting in aberrant movement during activities and causing a general feeling of instability.


The fairly common description of an ACL injury involves a ‘non-contact’ episode where the athlete typically describes a twisting sensation occurring during change of direction (pivoting) or landing from a jump. The athlete often reports a ‘popping’ or ‘snapping’ sound associated with pain and swelling shortly after the injury.

A common injury pattern has been observed during multidirectional activities (football, soccer, rugby, basketball) with up to 85% of the ACL injuries being non-contact injuries (Walden, 2015). The injury typically appears during 1) change-of-direction maneuvers such as jumping, cutting and pivoting movements, 2) re-gaining balance after kicking or 3) landing with hyperextended knee. 

The ACL will typically rupture during a forceful valgus moment at 5-30 degrees of knee flexion, where the knee is closer to the midline of the body than the ankle. While the tibia is moving forward and rotating internally, the forces from the foot-contact to the ground is compressing the tibia against the femur and elongating the ACL more than tolerated. The rupture occurs in approximately 17 to 50 milliseconds after this initial ground contact (Walden et al., 2015; Jordan et al., 2017).

An injury to the ACL often occurs concomitantly with damage to other knee joint structures such as the meniscus, articular cartilage and medial and collateral ligament which can influence the rehabilitation time and surgical procedure.

Clinical examination

  • History: An ACL rupture should always be suspected if the patient reports the previously mentioned injury mechanism combined with hearing or feeling a “pop” in addition to knee swelling and if the athlete has a perception of an “unstable” knee.
  • Test: Several clinical tests can be used to detect an ACL rupture. The Lachman test is the most accurate clinical diagnostic test with a pooled reported sensitivity of 85% and specificity of 94%. A positive result with the pivot shift test is a very clear indication of an ACL rupture (98% specificity). A negative test, however, is not sufficient to rule out possible injury (24% sensitivity). The anterior drawer test has high sensitivity and specificity for chronic ACL ruptures (92% sensitivity and 91% specificity), but lower accuracy for acute cases. (Filbay, 2019). All of the above tests measure a form of knee laxity.
  • Magnetic resonance imaging (MRI): If the above history and clinical test indicate an ACL injury, MRI can be used to determine if the ACL is ruptured. ACL ruptures often occur with concomitant ligament sprains, meniscus tears, bone marrow lesions, articular cartilage injuries, and intra-articular fractures with a prevalence of 30% and 42%, respectively for medial collateral ligament (MCL) injuries and meniscal tears. The rates of concomitant lateral collateral ligament (LCL) and posterior cruciate ligament (PCL) injuries are generally lower (Frobell, 2006).

Rehabilitation plan after anterior cruciate ligament reconstruction

Over the past few decades, rehabilitation protocols after ACL injuries have moved away from strict time-based protocols to more criteria-based guidelines. Programs are often individualized to the person’s injury, training status/experience and expectation for the rehab. Progressing from one phase to the next only occurs when the patient meets specific clinical milestones. One of the first milestones is to regain full range of motion (knee extension and flexion) pain-free, optimizing muscular strength and function and being familiar with basic post-operative exercises and expectations (patient education). However, creating a long-term rehabilitation plan can be challenging, therefore short-term milestones built on a combination of time-frame and criteria-based decision-making are advisable for building up a plan for your athlete. These time-frames are often called early phase, intermediate phase, late/advanced phase (Filbay, 2019), sports specific, return to participation, return to sport and return to performance (Ardern, 2016).

Timeline and criteria-based road map 

The figure below is an example of what a simple roadmap can look like:

Range of motionMotor controlMuscle strength
Early phaseDaily/weekly measurable skills and task: E.g. pain, swelling, range of motion. Early phase exercises
Milestone / CriteriaMilestone / CriteriaMilestone / Criteria
Intermediate phaseFunctional test, intermediate level exercises, preparing for return to run and jump
Milestone / CriteriaMilestone / CriteriaMilestone / Criteria
Advance/late phaseFunctional test, advanced level exercises, return to running, jumping and preparing for sport.
Milestone / CriteriaMilestone / CriteriaMilestone / Criteria
Main goal – Return to Sport

Pre-surgery / pre-op / pre-rehabilitation

The rehabilitation process prior to the ACL surgery is termed “preoperative rehabilitation” or just pre-op. 

In the first days and weeks after the injury, the focus is to restore full range of motion, control swelling and pain, and good quadriceps activation. Later in the pre-op, the goal is to either prepare the athlete for surgery or nonoperative management.

After the injury, the athlete can be subclassified into:

  1. coper (athlete that can resume previous recreational activities without reconstruction)
  2. non-coper (athlete that requires ACLR because of recurrent give-away episodes in activities of daily living)
  3. adaptors (athletes that can manage without reconstruction by modifying/lowering their activity level).

Thoma et al. (2019) showed that almost half (45%) of initial potential noncopers became potential copers after a 5 week pre-op neuromuscular strength training program, while only 13% of initial potential copers became noncopers after the training program.

The program consisted of progressive strengthening, plyometric, and neuromuscular exercises (Eitzen, 2010).

Stationary cycleContinuous warm-up at your preferred resistance10 min
TreadmillContinuous warm-up at your preferred speed. Walking or running10 min
Elliptical trainerContinuous warm-up at your preferred resistance10 min
Single-limb squatMaintain knee-over-toe position3 × 8
Step upMaintain knee-over-toe position2 x 10
Squat on BOSUMaintain knee alignment and core stability. Squat quickly down and up2 x 20
Single-limb leg pressStart in 90° knee flexion3 x 6 (+2)
Single-limb knee extensionStart in 90° knee flexion4 x 6 (+2)
SquatSquat slowly down to 90° knee flexion, stop, lift quickly up again3 × 8 (+2)
Leg curlLift quickly up, stop, and then slowly down to full extension3 × 8 (+2)
Hamstring on FitballOne foot on top of the ball, lift back and pelvis up, pull ball towards you3 × 6
Single-leg hopHop up on step, stop, continue down and directly 1 hop forward with a soft controlled landing1 × 15
Progressively perturbation trainingIncludes balance and stability exercises on custom-made roller board, rocker board, and platform, and involved perturbation of the support surface that allowed altered forces and torques to be applied to the injured limb in multiple directions in a controlled manner 

Eitzen et al. (2009) have also shown that quadriceps strength limb symmetry with a deficit below 20% is a significant predictor of knee function two years after an ACL injury. Similarly, another systematic review from Ashewaiver et al. (2016) analyzed 451 patients (15-57 years), showing that a 3-14 weeks pre-op period with an average training of three times per week improved the outcomes of patients with ACLR.

A part of getting the athlete ready for surgery could be obtaining a list of objective and subjective data that can be used to guide the rehabilitation. These test could involve: muscle testing (with hand held dynamometer (HHD), nordbord/physiometer or isokinetic device), jump testing (using force platform, mobile app like MyJump2 or use measuring tape and stopwatch to record limb symmetry in distance- or numbers for single leg jump for distance, 6-m jump test, triple cross-over test, cross-hop for distance, side hop, countermovement jump, functional testing a numbers of single leg squat, % of RM in back squat, deadlift etc. 

My recommendation is to choose a handful of tests that are available, time-saving and fit in our facilities. Furthermore, questionnaires like Tegner scale, IKDC2000, KOOS. ACL-RSI, Tampa Scale of Kinesiophobia (TSK-11) can be useful to track the rehabilitation.

In study by Ardern et al. (2013), it was suggested that a score of ≥ 56 points on the ACL-RSI scale increased the odds by four of RTS, which may help to identify at-risk athletes with lower points.

Post op ‘Early phase’

Following ACL surgery, a period of protected loading is recommended due to the graft healing, pain, swelling, limit range of motion and muscle control in order to limit muscle atrophy and avoid arthrogenic muscle inhibition. Acute management should adhere to the general principles of POLICE (Protection, Optimal Loading, Ice, Compression and Elevation) to ensure joint protection, removal of pain and swelling, meanwhile maintaining a gradual restoration of function.  

The athletes are presented with a set of surgical restrictions set by the surgeon depending on the surgical procedure and the surgeon clinical experience. These restrictions are often based on graft-type where bone-to-bone (BTB) and hamstring tendon is among the most common for first choice ACLR. Comorbidities of knee joint structures may involve meniscus meniscectomy, meniscus repair, lateral tenodesis (ALL), cartilage damage and in rare cases high tibial osteotomy. Each surgery is slightly different and can influence the progression in the first phase of rehabilitation and therefore it is important to fully understand the surgical procedure.

In the early phase rehab, training should focus on patient education, pain/swelling, range of motion (ROM), motor control and muscle strength to minimize the loss of muscle strength and volume. The goals through the early phase can be visualized as below.

Range of motionMotor controlMuscle strength
Early phaseDaily/weekly measurable skills and task: E.g. pain, swelling, range of motion. Early phase exercises
Criteria based rehab (Ardern, 2018, Wilk 2018)Milestone: Have minimal/trace effusion or zero swelling. (Measure with stroke test and knee circumference). Have minimal or no pain (0-2 NRS). Full active extension, 120 degrees active knee flexion.Walking without crutches, walking on stairs. Stationary bike. Drive car.Full quadriceps activation without quadriceps lag in single leg raise. Restore balance and perform mini squat weight shift. Ability to hold terminal knee extension during single leg standing without support 10 sec. 
Intermediate phaseFunctional test, intermediate level exercises, preparing for return to run and jump
Milestone / CriteriaMilestone / CriteriaMilestone / Criteria
Advance/late phaseFunctional test, advanced level exercises, return to running, jumping and preparing for sport.
Milestone / CriteriaMilestone / CriteriaMilestone / Criteria
Main goal

In the early phase we recommend beginning training with low to moderate intensity (e.g. 12-20 RM in multiple set) and slowly progressing to support more optimized muscle hypertrophy and strength.

In addition, a focus on non-weightbearing exercises such as lumbopelvic hip exercise, upper body and cardio can be used to stimulate the exercise program. In addition, modalities such neuromuscular electrical stimulation (NMES) or blood flow restriction can be used to enhance muscle activation and growth. Furthermore, cross-education training with heavy strength training of the non-injured leg, shortly after ACLR has demonstrated improvement in quadriceps muscle strength at 8 weeks when perform 3 or 5 days per week compared with control which did not receive cross-educational training (Papandreou et. al. 2012). Similar result has been reported after 24 weeks when trained 3 times per week (Harput, 2019), however Zult et al. did not got these results. One explanation could be that the intervention group only performed cross-education training group twice a week. This illustrate, that there might be a dose-response relationship in cross-education training, recommend at least 3 times per week. Although further research should be conducted to investigate the long-term effects of cross-education training in ACLR rehabilitation.

Post op ‘Early phase’ exercises

Before beginning rehabilitation consider following restriction.

  • Follow surgical advice
  • ACLR: Full weightbearing, no brace
  • ACL + lateral tenodesis: Full weight-bearing + brace 0-90° for 4-6 weeks. Be careful with lateral weighted exercises.
  • ACL + Meniscus repair: Protected weight-bearing + brace 0-90° for 4-6 weeks (different protocols).
  • POLICE protocol for management of pain and swelling.

0-2 weeks


  • Control pain, swelling, range of motion (0-105°+ (Wilk, 2018)), restore balance, minimize loss of muscle strength.
  • Criteria to phase 2 includes: closed wound, full active knee extension, 120°+ knee flexion, little to no effusion, active dynamic gait pattern without crutches, ability to hold terminal knee extension during single leg (Arderen, 2018, Gokeler, 2017).
Patella mobilizationPatella mobilization (Superior/inferior and medial/lateral directions).1-2 min
Knee flexionTowel slide, sitting on a chair and passive flexion and extension assisted by the “good” leg, wall slide3 set x 15 reps+. multiple times per day
Static Quads-activationContract m. quadriceps in several seconds (see if you can lift the heel from the surface)3 set x 15 reps+. multiple times per day
Straight leg raisesLift up your leg without lag of extension3 set x 15 reps+. multiple times per day
Supermanprone straight leg raise extension3 set x 15 reps per day
Prone assisted hamstring curlsProne position and flex your assisted by the opposite foot under the ankle3 set x 15 reps per day
Side lying hip abduction/clamsBe careful if the patient has undergo meniscus repair3 set x 15 reps per day
Side lying hip adductionStart in week 2-3 if not pain.3 set x 15 reps per day
Calf: Seated calf raisesBed based/seated plantar flexor strengthening.3 set x 15 reps+. multiple times per day
Balance exercisesChallenge the oculomotor, vestibular and proprioceptive system. Single leg balance with open, close eyes, rotational head movement eg. other body part.3 set x 15 reps+. multiple times per day
Terminal Knee Extension 3 set x 15 reps per day
Squat 3 set x 15 reps per day
Step up 3 set x 15 reps per day
LungesACL in front starting week 23 set x 15 reps per day
Upper body driven core exercises  
Gait re-education (March walk, hurdle walk, side walk)  
Cardio: SkiErg, Concept2 Rowing  
Neuromuscular Electrical Stimulation (NMES)  


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  21. Thoma, L. M., Grindem, H., Logerstedt, D., Axe, M., Engebretsen, L., Risberg, M. A., & Snyder-Mackler, L. (2019). Coper Classification Early After Anterior Cruciate Ligament Rupture Changes With Progressive Neuromuscular and Strength Training and Is Associated With 2-Year Success: The Delaware-Oslo ACL Cohort Study. The American Journal of Sports Medicine, 036354651982550. doi:10.1177/0363546519825500
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  24. Zult T, Gokeler A, van Raay JJAM, et al. Cross-education does not accelerate the rehabilitation of neuromuscular functions after ACL reconstruction: a randomized controlled clinical trial. Eur J Appl Physiol. 2018;118(8):1609–1623. doi:10.1007/s00421-018-3892-1

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