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ACL Tear (Anterior Cruciate Ligament Tear)

Causes and treatment of anterior cruciate ligament tears

Cruciate ligament tear (十字韌帶撕裂) is a common sports-related injury of the knee joint. There are front (anterior) and back (posterior) cruciate ligaments, and the mechanisms of injury are also different. According to an article by the Faculty of Medicine of CUHK, there are an average of about 2,000 cases of anterior cruciate ligament tears in Hong Kong every year, while posterior cruciate ligament tears are less common. 


What are the anterior (ACL) and posterior (PCL) cruciate ligaments?  

The anterior and posterior cruciate (“cross-shaped”) ligaments are bands of strong connective tissue crossing the middle of the knee joint fastening the femur (thigh bone) and tibia (shin bone). Together with the lateral (LCL) and medial collateral (MCL) ligaments, they serve to stabilize the knee during passive and active motion. 


The anterior cruciate ligament (ACL) limits the forward displacement of the tibia, and controls the rotation, varus, valgus, and bending of the knee joint.  It is most commonly injured through a sudden stop, change of direction or pivoting while the foot is firmly planted such as in the sports of football, rugby and basketball. 


The posterior cruciate ligament (PCL), on the other hand, has the opposite function as the ACL, limiting the posterior displacement of the tibia and maintaining the joint's stability with the opposite action. The chance of tearing the posterior cruciate ligament is lower than that of the anterior cruciate ligament. It is usually caused by a violent impact on the tibia anteriorly due to traffic or motor vehicular accidents (“dashboard injury”), falling on the knees and may also be encountered in football, rugby and skiing accidents. 


Causes of ACL Tear 

Among all sports injuries, 40% of injuries involve torn cruciate ligaments. Generally speaking, there are two main factors that lead to ACL tears: 

  • Excessive extension of the calf forward 
  • Knee and calf rotation 

The following are common actions that can cause ACL tears: 

  • Improper landing after a high jump 
  • Sudden stop or deceleration 
  • Sudden turns or pivots 
  • Collision with another person, such as a football tackle 

Symptoms of ACL Tear 

Common symptoms of an anterior cruciate ligament tear: 

  • Feeling or hearing a "pop" in the knee  
  • Knee pain and swelling 
  • Bruises around the knee joint 
  • Reduced range of motion or inability to walk
Common symptoms of posterior cruciate ligament tear: 
  • Knee joint instability when going up and down stairs 
  • Pain in the knee joints when walking for long periods 


Diagnosis of ACL tear

Determination of the mechanism involved in the injury is among the first investigations made. After which, physical examination that includes assessment of joint stability and mobility is performed. The Lachman Test (most sensitive), anterior drawer test, pivot shift test and lever sign test are the common provocative procedures that are done. The KT-1000 is a more quantitative test for ACL injury. 

In addition to the above, - imaging techniques such as X-rays and MRI’s (most sensitive and specific for ACL injury) are employed to further assess not just the ACL itself but other structures that may be involved such as the meniscus, the other ligaments and the adjoining bones themselves. 

Grading of ACL Tear: 

  • Grade 1: the ligament is damaged microscopically but is grossly intact; adequate stability is still provided 
  • Grade 2: the ligament is partially torn and loosened but still connected 
  • Grade 3: the ligament is almost completely or completely torn apart; no stability provided 


Treatment for ACL Tear 

Management of ACL tears usually is an individualized plan that takes into consideration the patient’s age and demands, activity level, sports engagement and condition of other structures in the knee joint. Depending on these factors, treatment methods are broadly divided into conservative and -surgical treatments: 


  • Conservative treatment: for most Grade 1 tears; Grade 2 tears for non-athletes and individuals with less demanding lifestyle. 

Acute Treatment after injury includes R.I.C.E.: 

  • Rest  
  • Immobilization  
  • Compression – of the affected knee joint 
  • Elevation – of the affected leg 


  • Physiotherapy: A physical therapist will tailor a treatment plan (such as leg lifting, etc.) according to the patient's degree of injury to help them regain their original mobility. 
  • Medication:  Analgesics and anti-inflammatory drugs are prescribed as assessed by the physician. 
  • Surgical treatment: Done through either repair or reconstruction; most surgeries now employ the minimally invasive approach using an arthroscope inserted through a small incision which allows day procedures or earlier hospital discharge for patients. 
  • ACL repair: Approximating and suturing the torn pieced together; currently preferred treatment of choice in pediatric patients and isolated AM/PL bundle tears; advantages include less invasive, retains native anatomy, avoids graft complications, relatively faster recovery 
  • ACL reconstruction surgery: Currently the gold standard for treatment of Grade 3 injuries and qualified Grade 2 tears; uses tissues (graft) harvested from either the hamstring or patellar tendon to anatomically reconstruct the torn ligaments; advantages include improved stability and faster return to sports activity. 


How long does it take for an ACL Tear to heal? When can I resume my normal activities? 

Recovery time from a torn cruciate ligament depends on various factors, including the severity of the tear, the individual's health, the body's natural ability to recover, and the effectiveness of rehabilitation exercises performed during recovery.  

For mild tears that require only non-surgical treatment, recovery to a point where you can resume normal activities may require weeks to months of physical therapy and rehabilitation. 

The recovery process may take longer if the tear is more severe and requires surgery. Initial recovery after surgery, including reducing pain and swelling and restoring knee mobility, usually takes several weeks to months. Typically, it takes about six to twelve months from surgery to full recovery and return to original activities. During the rehabilitation phase, patients need targeted physical therapy to strengthen leg muscles and improve the stability and function of the knee joint, which may take several months to a year. For athletes returning to high-intensity sports, it may take a year or more as some studies have shown that it can take up to 18 months for grafts to become fully functional and integrated. An early resumption of demanding activities can cause graft failure and/or re-injury. 


OT&P Medical Advice 

Whether it is the anterior or posterior cruciate ligament, a torn cruciate ligament can be a major or minor problem. If the cruciate ligament is accidentally ruptured, you need to closely track the progress with your doctor and physical therapist to achieve the best recovery results. If you don't know whether you need surgery or have any questions about physical therapy, talk to your family doctor or physical therapist. 

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Please note that all medical articles featured on our website have been reviewed by qualified healthcare doctors. The articles are for general information only and are not medical opinions nor should the contents be used to replace the need for a personal consultation with a qualified medical professional on the reader's medical condition.

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