The Anterior Cruciate Ligament (ACL) knee tear is very common in contact and pivoting sports such as soccer, basket, handball or ski. It is considered one of the most severe injuries in sport as it usually requires surgery and a long recovery process. 

There is a high percentage of athletes who are not able to return to their pre-injury level or even finish their sport careers after suffering this injury. It is therefore paramount to develop an adequate rehabilitation program. 


The ACL is a broad ligament that originates from the posterolateral aspect of the intercondylar notch and inserts into the anterior tibial plateau, just lateral to the tibial spine. It is composed of 2 primary functional bundles: 

  • The anteromedial (AM) bundle: It is the primary restraint to anterior tibial translation in the flexed knee. It is generally composed of isometric fibers with increased tightens in flexion. The AM-bundle tightens is reduced from 0 to 30º, and increase from 30 to 130º.
  • The posterolateral (PL) bundle: provides additional rotational stability to the knee. It is generally composed of anisometric fibers that wrap the AM-bundle during knee flexion forming an arch. The PL-bundle tightens in extension: it gradually decreases from 0 to 90º of flexion and increase from 90º onwards.

Figure 1. Role of AM and PL bundles during knee flexion (retrieved from Sonnery-Connet & Colombet, 2016).

Function of ACL

The ACL is the major stabilizing structure of the knee-joint:

  • Avoid anterior tibial translation over the femur (main function).
  • Restrain internal rotation of the tibia.
  • Resist varus and valgus forces at the knee.

Main injury mechanisms

Figure 2. Distinctive body position in ACL injury (retrieved from LaBella, Hennrikus & Hewett, 2014)

The ACL is commonly injured via a non-contact mechanism during sports participation (70%), particularly in sports involving jumping, pivoting and cutting maneuvers. There is a distinctive body position that is related to non-contact ACL-injury (1) (Figure 2):

  • Internal rotation of the hip.
  • Semi-flexion of the knee, close to full extension.
  • Foot planted into the ground.
  • The body is decelerating, resulting in a dynamic knee valgus.

In the systematic review and meta-analysis of Pappas et al. (2), 4 theories are proposed as to the causes that significantly increase the risk of ACL injury in athletes:

  1. Ligament dominance theory: athletes at high ACL injury risk perform landing and cutting maneuvers with excessive dynamic knee valgus, hip adduction and hip internal rotation. 
  2. Trunk dominance theory: deficits in trunk control lead to increased risk for ACL injury. 
  3. Quadriceps dominance theory: excessive quadriceps forces relative to posterior chain recruitment place the ACL at high risk for injury.
  4. Leg dominance theory: large leg-to-leg asymmetries.

In soccer, this injury is usually occurred in the following situations:

  • Internal turns with the knee semi-flexed and the foot planted on the ground. 
  • On jumps when the athlete lands with the knee extended. 
  • Aggressive actions that cause a dynamic knee valgus (e.g., after an opponent’s thrust).

Injury incidence

Relevant data regarding the injury incidence for the management of ACL tear are shown below (3–5):

  • RTP rate: 82%
  • Rate of preinjury level: 63%
  • 35-45% of athletes do not return to competitive sport (RTS). 
  • Even at elite-level, 20-25% of athletes are incapable to RTS.
  • In professional soccer, RTS is very high (>90%) one year after injury. However, only 65% of players are still competing at the top level 3 years after ACL reconstruction (ACLR).
  • Risk of ACL reinjury in the following two years: 15% (all ages). 
    • Young athletes (<25 years): 30% in the following two years.
  • The risk of reinjury is x30-40 higher in matches than in training.
  • The risk of ACL tear is higher in women than in men.

In addition, athletes with a follow-up ≥ 24 months reported a much higher rate of RTS than those with a follow-up < 24 months (65% and 38%, respectively) (3). However, these values may vary according to the type of sport analysed.

Partial-tear vs total-tear of ACL

Among ACL injuries in sports, total ligament tear is the most common. Partial tears accounts for only 10-28% of all ACL tears, being more prevalent in men and young athletes (6). The injury incidence is higher in the PL-bundle as it receives greater stress. Also, partial tears progress to total tears in 50% of cases (7).

On the other hand, when an athlete is injured with an ACL-tear, it is very common that other structures of the knee, such as meniscus, are also affected (8). These authors found in their review that approximately 50% of acute ACL injuries also involved meniscal tears. In addition, the risk of osteoarthritis is higher in patients who have had a concomitant meniscal injury compared to an isolated ACL injury (48% vs 13%, respectively). The risk of concomitant meniscal injury is lower with partial tears (24%) than total tears (42%) of ACL. Accordingly, ACLR is warranted in those patients to reduce the risk of future osteoarthritis. 

The recovery period for partial tears is 5 to 7 months, while for total tears is 9 to 12 months.

Clinical evaluation and tests

Manual tests to evaluate and diagnose an ACL tear: 

  • Lachman test (for anterior knee instability)
  • Anterior drawer test (for anterior knee instability)
  • Pivot-shift test (rotatory knee instability)

Test to assess the damage on Associated structures:

  • Valgus/varus stress test (for collateral ligaments)
  • McMurray’s test (for menisci)
  • Posterior drawer test (for PCL
  • Reverse pivot shift test (for posterolateral complex)

*Either way, magnetic resonance imaging (MRI) is the gold standard test to confirm an ACL tear.

ACLR vs conservative treatment

ACL reconstruction is the most common surgical procedure after an ACL tear, and is especially recommended for young athletes. However, some authors have argued that conservative treatment for ACL tears may provide sufficient knee stability for patients who do not have the desire to engage in ‘high-risk’ activities, such as the practice of sports like soccer, basket or ski. It should be noted also that the risk of reinjury with conservative treatment is 50% (7).

For developing the conservative treatment, it is very important that the athlete must be a coper. According to the revision of Secrist et al. (8), non-copers show several properties different from copers, such as worse balance and gait patterns that cause excessive internal rotation of the tibia, among others. Some characteristics that potential copers must have in order to perform conservative treatment are: 

  • No concomitant injuries
  • LSI ≥ 80% (for all hop tests)
  • > 80% KOS-ADLS
  • > 60% IKDC 1000 (self-report of knee function)
  • ≤ 1% subjective report of knee giving way

In patients with isolated ACL-tears, there is also the option of delaying ACLR for up to 6 months and performing perturbation exercises during this period to develop dynamic mechanisms while the final decision of surgery is determined. Either way, ACLR must be addressed when there is concomitant meniscal injury or symptomatic instability in order to reduce the risk of additional knee injuries. According to the current literature, all ACL tears in sport should be treated with ACLRs as soon as possible. 

Rehabilitation program after ACLR

In high-level sport, the period of time between the athlete performing ACLR and RTS is usually between 6 and 9 months. However, most authors consider a short period of time to adequately recover this injury (3,5,7,9–11). Van Melick et al. (11) recommend a minimum recovery of 12 months after an ACLR in soccer to return to competition with lower risks. Nonetheless, several authors have found no differences between an accelerated rehabilitation program (≤ 6 months) compared to a ‘common’ program (12). In this sense, the rehabilitation program is highly affected by the individual characteristics of the athlete, such as the injury history, age or gender, among others.

Before-surgery phase

Several authors recommend starting the rehabilitation program before ACLR for the following reasons (11):

  • Full knee extension deficit before surgery is the main risk factor for extension deficit after ACLR. 
  • Quadriceps strength deficit > 20% prior to surgery may negatively affect the athlete during the two years after ACLR.
  • Starting rehabilitation properly before ACLR ensures better knee function for two years after ACLR.  

Early phase (4-6 weeks post-surgery)

  • The rehabilitation process should begin 24 hours after the ACLR with assisted mobility exercises.
  • Controlling pain and swelling is one of the most important goals in the early postoperative rehabilitation stage.
  • Light-WB immediately after surgery does not affect knee laxity and reduces anterior knee pain. However, it should only be performed if the movement pattern is adequate and there is no pain (11).
  • Cryotherapy is recommended to reduce swelling.
  • Neuromuscular electrical stimulation (NMES) can be useful to improve the quadriceps strength during this phase when movement is limited, in addition to promote the activation and re-education of voluntary contraction.

Goals (13,14):

  • Minimize pain and swelling.
  • Protect the healing graft.
  • Minimize the effect of immobilization.
  • Establish a normal gait pattern.
  • Eventually discontinue crutch use.
  • Achieve 90-120º of flexion and full extension.
  • Promote quadriceps function and good quadriceps control (neuromuscular control).
  • Restore the ability to perform a straight-leg raise (SLR) without a quadriceps lag.
  • Progression to full weight bearing (WB).

Criteria for progressing to the next phase:

  • Walk normally without crutches or gait deviation
  • Full passive knee extension symmetric to the non-involved knee.
  • 100-120º of knee flexion.
  • No evidence of an extensor lag.
  • Minimal effusion or other signs of active inflammation.

Strengthening phase (4-6 weeks to 6 months post-surgery)

  • Progression of WB in closed kinetic chain (CKC) and non-WB in open kinetic chain (OKC).
  • First 3 months after surgery:
    • Limited ROM between 90-60º (for non-WB knee extensions).
    • ROM 0-60º for WB exercises.
  • >3-4 months: 
    • OKC knee-extensions through full arc of motion. 
    • Initiating OCK knee-flexions to increase the strength of hamstrings (> 6 weeks).
    • CKC progression of ROM 75-90º (WB exercises). 


  • Proper technique.
  • Avoiding compensatory mechanisms.
  • Continuing progression of strengthening.
  • Neuromuscular control. 
  • Train the balance and proprioception.
  • Core stability training.
  • Jogging. 
  • Preparation for the return to activity and sports stage.

Criteria for progressing to RTP phase

  • Appropriate strength: Limb Symmetry Index (LSI) (3,4,9,11,15): 
    • LSI≥90% 
    • Specific for pivoting sports: LSI ≥100%
  • Achieve good balance.
  • No pain or gait difficulties.
  • *Gathering the criteria for progressing to RTP phase before starting reduce the risk of reinjury by 75-84% (4).

Return to play (RTP)

In the RTP phase the athlete should be progressively incorporated into the team’s training while continuing his specific rehabilitation program.


  • Complete the entire functional rehabilitation spectrum.
  • Full return to the patient’s previous level of daily, occupational, and athletic activity, and sports participation.
  • Gradual increase in specific function.
  • Strengthening exercises through the full ROM and 
  • Enhance NM control.
  • Progression to full-effort sprinting, cutting and plyometric activities.
  • Quadriceps index ≥85%, appropriate ROM, strength, proprioception and cardiovascular capacity.
  • Progressive incorporation to team training until completing the full session normally. 

Criteria to return to competition (RTS):

  • LSI strength index of the Knee flexors and extensors:
    • Pivoting sports: LSI = 100%
    • Other sports: LSI ≥ 90%
  • LSI-index hop tests: LSI > 90% (all sports)
  • Subjective perception of having an appropriate level readiness for competition (ACL-RSI scale): no fear, good sensations.
  • Adequate subjective self-perception of function and symptoms (IKDC 1000 or IKDC 2000).
  • Risk factors for ACL reinjury: increased valgus, low hip internal rotation with asymmetry in knee extension at initial contact during a vertical jump at landing, and postural stability deficits during single leg stance.
  • Athletes with ACLR show impaired hip-ankle coordination in dynamic 1-leg activities.

At high-level sport, the RTS is usually after 6 months of ACLR. However, there is a high risk reinjury from 6 to 12 months. Accordingly, biological and functional deficits last up to 2 years after ACLR (5). Most authors recommend a recovery process of 12 months before returning to competition. In addition, environments should be as realistic and context-specific as possible when evaluating the ability to RTS: under fatigue and reactive situations. Finally, it is paramount to take into account the athlete’s self-perceived symptoms/function and psychological readiness for RTS due to the increased percentage of athletes with a fear of reinjury after an ACL tear.


  • The implementation of specific prevention programs will reduce the risk of ACL injury in sport. These programs must emphasize correction of biomechanical technics individually in order to improve neuromuscular control. 
  • The specific exercises’ program and follow-up of the rehabilitation process after ACLR should be at least 24 months, despite starting to compete 9-12 months after surgery.
  • Currently an elevated number of tests and clinical evaluations are performed for RTS in sport. However, the literature shows adverse results in the recovery of this injury in sport. Webster & Feller (16) consider that more focus should be placed on identifying a smaller number of tests that are more predictive.
  • The hop performance tests are the most consistent predictors of a subsequent RTS.
  • It is paramount to take into account self-perceived symptoms/function and psychological readiness of the athletes in the decision of RTS.  
  • The risk of ACL tears and reinjury is greater in young athletes < 25 years.
  • The RTS should be 9 to 12 months after ACLR.
  • ACLR is recommended after ACL tear among athletes, especially in contact and pivoting sports.
  • The conservative treatment, if applied, may only be performed by copers.
  • If applied, only copers may perform conservative treatment. 
  • Although is essential in the rehabilitation programs after ACLR to optimize and attain proper gait and quality patterns, it should be noted that ACL injuries in sport do not usually occur under pre-planned movements. Therefore, athletes should simulate competitive conditions in training prior to RTS: under fatigue and reactive situations.
  • It is essential to have load management strategies during the RTP-phase to ensure optimal recovery and adaptation.

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Dr. Berni Guerrero-Calderón

S&C Coach | Rehab Therapist |Sport Scientist

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This article has been made based on the references showed, other studies reviewed but not showed and according to the experience and knowledge of the author. In this way, it may include subjective ideas and opinions not contrasted in the research.

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