Damage to the anterior cruciate ligament (ACL) is a commonly encountered sports medicine condition. The ACL is one of four major ligamentous stabilizers of the knee. The main purpose of the knee is to prevent forward movement of the tibia (shin bone) on the femur (thigh bone). The ACL also helps to prevent excessive rotation through the knee. The dual function of the ACL is explained by two different bundles of fibers within the ACL: anteriormedial and posterolateral.

Although ACL tears can occur in many ways, the most common mechanism is a twisting force through the knee with the foot planted (the so-called non-contact pivot). Immediate pain, a ‘popping’ sensation, swelling and inability to continue participating in sport or activity are common symptoms. People are often able to walk with extreme difficulty. Following injury, they are often seen in the emergency room or urgently in their family physicians office. X-rays are commonly normal for any major fracture but a careful look will often identify a small fleck of bone pulled off the outside of the front of the tibia. This so-called Segond fracture represents a failure of the anterolateral ligament (ALL), another stabilizing structure of the knee.

ACL injuries commonly occur along with other injuries. For example, the so-called ‘Terrible Triad of the Knee’ includes an ACL tear along with a lateral meniscal tear and a Medical Collateral Ligament Tear. The chance of additional injury is often predicted by the severity of the initial injury.

Once a tear occurs your body is often unable to heal it on its own. However, the pain associated with many tears recover with time and therapy. For that reason, the presence of an ACL tear on MRI does not absolutely mean you need an operation! We operate on ACL tears in people that have feelings of instability despite an attempt at physical therapy.


ACL Tears and Arthritis

We as a profession have likely not done a good enough job advertising two facts which have been consistently shown to be true across multiple studies:

  1. ACL Tears greatly increase the chance that an injured knee will develop arthritis in the decades to come. The chance of developing arthritis likely depends on multiple factors, including muscle strength, obesity, presence of meniscal tears, and/or high-impact activity. I quote a 90% chance of developing arthritis over the next 3 decades, although recent data suggests rates may in fact be higher.
  2. ACL Surgery does not decrease risk of developing arthritis.

Despite evolution of technique, reconstructing torn ACLs has not shown to decrease development of arthritis – even in young patients. Although ACL reconstructive surgery is successful at improving sensations of instability and allowing many people to return to sport, no therapy to date has been proven to decrease the chance of developing arthritis.



Patients are often seen first in either the emergency room or their family physician’s office. For any patient with knee pain where a fracture has been ruled out, clinical exam will dictate how quickly an MRI should be considered. If a clinical exam is very highly suggestive of an ACL injury, an MRI can be arranged on a non-urgent fashion.  Regardless, we recommend having your family physician refer you to a formal physical therapy program to regain quads strength and maintain range of motion.

The diagnosis of an ACL tear on MRI inevitably prompts a referral to an Orthopaedic surgeon.  It is important that you continue performing physical therapy until assessed by a surgeon. We cringe when we hear ‘I did not want to do any exercises until I saw you Doc’, as this represents a missed opportunity to maintain or improve the condition of your knee.



If time and therapy do not resolve symptoms of knee instability, additional treatments may be entertained:

  • Ongoing Physical Therapy: Not all therapists are alike. We favor ones that encourage movement and strengthening of the quadriceps, core and hip muscles over less proven ‘adjuvant’ modalities (i.e. ultrasound or laser). The best therapy makes you move, sweat and helps build muscle. Ensuring the proper therapy is performed is key to your recovery.
  • Injections: There are multiple injections around the knee that may be considered. All seek to provide pain relief. Newer injections, such as Platelet Rich Plasma, may have regenerative properties for other conditions around the knee but have limited evidence supporting their use in ACL tears.
  • Weight Loss: Obesity can place great strain on knees, exacerbating pain associated with ACL tears. Achieving and maintaining a healthy weight is an important consideration in helping rehabilitate a knee from any injury or arthritis.
  • Bracing: Bracing can take many forms, from an over the counter knee sleeve to a custom fitted ACL brace. Some braces can be very expensive and may not be required in all patients. We recommend extensive physical therapy before considering bracing. If the mutual decision is made to brace a knee, the brace should be fit by an experienced individual who will be available to service the brace in the future.

If the above recommended options are not successful in relieving pain, or in specific unique circumstances (i.e. a bucket handle tear with a locked knee), surgery will be discussed. Surgery may not be advisable in several circumstances, such as in older individuals or in knees with pre-existing arthritis. It is important to know that surgery is not designed to stitch the ACL back together again. Instead, the surgery focuses on ‘reconstructing’ the ACL by replacing the old ACL with different tissue. Most surgical procedures are arthroscopically assisted, meaning the size of incisions can be decreased.

If surgery is felt to be indicated, your surgeon should inform you of the type of graft that they prefer. There are several graft choices, each with unique sets of pros and cons. An important factor is also surgeon preference, as some surgeons exclusively utilize one graft and refer to other surgeons should another graft be chosen.

Common Graft Choices Include:

  • Bone Patellar Tendon Bone: The center of the patellar tendon is harvested, along with bone from the patella (knee cap) and tibia (shin bone). This tendon will then be weaved into the knee and secured. This surgery is technically demanding and comes with a larger scar over the knee when compared to other techniques, but it is largely considered the ‘gold standard’ graft and is thought to have the lowest chance of re-rupture. Because of its strength, it is our graft of choice in younger athletes or those participating in contact sports. Because of how the graft is harvested, this graft has a higher chance of pain under the knee-cap, stiffness and has a low risk of a patella fracture.
  • Hamstrings Tendon: Two of the three hamstrings tendons are harvested from the inside of the knee/thigh and are doubled-up on one another to create a 4 strand graft. The hamstring is then weaved through the knee and secured. This technique comes with less scars around the knee and has an excellent track record, but has been found to have a slightly higher risk of surgical failure when compared to the graft mentioned above. As no bone is harvested, the recovery is felt to be easier and as such we prefer this graft in older individuals that are more likely to be affected by post-operative stiffness. One significant consideration with this graft is the hamstrings muscles will not work to the same degree they did before surgery. There is thus a concern that knee functional kinematics will be disrupted and in turn predispose an athlete to re injury. This is one of the most common grafts used.
  • Allograft Tissue: Allograft refers to tissue obtained from another organism. Relating to ACL surgery, cadaver tissue is used. This tissue is sterilized to decrease risk of disease transmission, and is used to reconstruct the ACL by weaving it through the knee and securing it. The recovery with this graft is the easiest, as no other tissue needs to be harvested as part of the surgery. The most notable draw-back with this surgery is the allograft tissue is simply not as strong as tissue harvested at time of surgery from your own body. For that reason, risk of failure or graft rupture is much higher than with other graft choices. We consider this graft choice in revision surgery settings or in older individuals where the risk of recovering from a graft harvest may be significant.


Expected Follow-up and Recovery

Recovery can be unique to each patient depending on multiple factors (presence of meniscal tears, other ligaments injured, pre-existing knee strength, presence of osteoarthritis, etc.). The following is a common recovery pathway experienced by most patients, but may be modified depending on graft choice and the presence of other injuries within the knee:

  1. No Surgery: Most ACL injuries should be initially treated with physical therapy and avoidance of aggravating activity. As symptoms resolve, the goal is to regain and maintain strength followed by a return to activity. Ideally, a patient continues at their place of work as part of their rehabilitation program. Return to work or sport depends on the nature of the injury and the demands of the activity and may range from 1-12 weeks.
  2. Surgical Reconstruction: Patients are placed in a knee immobilizer post-operatively. Ability to walk immediately after surgery depends on individual surgical post-operative protocols and the type of graft used. Therapy can start immediately in the brace and with protected active range of motion via heel drags. At 6 weeks more aggressive range of motion is instituted and light quads strengthening is encouraged. More intense strengthening starts at 3 months post-operatively. Running is allowed 4 months post-operatively. Return to contact sport is allowed at 6 months post-operatively. Office workers can return to work within 1-2 weeks while taking time off for ongoing physical therapy. Extremely physical jobs may require 12 weeks before returning to work on progressive hours and duties.


General Information

  • See our Knee Arthroscopy Patient Handout for specific post-operative recommendations on wound care.
  • The presence of arthritis is thought to delay recovery by 1-2 weeks depending on severity.
  • Surgery is designed to improve the stability of the knee but will not address arthritis symptoms arthritis symptoms (i.e. stiffness, activity related ache) nor will it prevent the development of arthritis.
  • ACL surgery involves drilling holes into bones within the knee. Due to this, swelling for 6-10 weeks following an operation is to be expected.
  • Sudden chest pain or shortness of breath is not normal and should prompt immediate assessment at the most local emergency room to rule out a blood clot.


General Therapy Instructions

Please note: this alone does not constitute as a formal referral to a physical therapy. As each injury is unique, the below may not apply to everyone.

 Post-operative rehabilitation should be guided by the procedure performed. Obtain your surgeons post-operative protocol, in advance if possible, so that you and your therapist fully understand any rehabilitation required following surgery.

The general non-operative rehabilitation protocol is as follows

  • 0-4 weeks: A brief period of rest, ice, compression and elevation can be useful for a few days but detrimental in the long run if range of motion is not started ASAP. Come out of the knee immobilizer to start heel drags from 0-90o in the first two weeks, and progress to 120o between week 2-4. The short-term goal should be to regain extension of the knee. In the knee immobilizer, leg lifts may be started to encourage quads strengthening. Patients may be either toe touch weight bearing or full weight bearing in a knee immobilizer depending on a surgeons post-operative protocol.
  • 4-6 weeks: Full active range of motion is allowed within tolerance of pain. Care is taken to avoid passive manipulation of the knee. Straight leg raises out of the knee immobilizer may be considered, if able.
  • 6-12 weeks: Focus is on achieving full range of motion while progressively strengthening the knee. The knee immobilizer is weaned.
  • 12-24 weeks: Progressive strengthening continues, with a gradual shift in sport-specific conditioning.
  • 4 months: Running is allowed
  • 6 months: Return to sport is allowed


Expected Outcomes

ACL injuries can be expected to have an excellent result in the majority of people, regardless of what treatment is required. The more associated injuries around the knee, the slower the recovery and the greater the chance of developing arthritis later in life. An active lifestyle with maintenance of a healthy weight can decrease those risks as much as possible.

It is important to consider that return to sport rates may not be as high as previously thought. Many non-professional athletes choose to avoid the sport that led to the ACL injury given the length of recovery required and the knowledge that they are at a higher risk of arthritis. Psychological factors should also be considered, as many athletes struggle with concerns of re injury that impact performance. Each person is unique, and it is important to explore your future goals with your surgeon and your therapist so a realistic timeline can be set.


Notable Challenges

  • Knee Stiffness: May develop due to post-injury or post-surgical. Follow-up with your surgeon to discuss management options.
  • Knee Swelling: Swelling is expected for several weeks post injury or surgery. Persistent swelling may impede rehabilitation or necessitate more aggressive therapies to manage. Follow-up with your family physician or surgeon to discuss management options.
  • Blood Clot: Sudden onset calf swelling, shortness of breath or chest pain may represent a blood clot and should prompt a visit to a local emergency room.
  • Arthritis: an ACL tear may be the cause of development of post-traumatic arthritis as detailed above.


Summary of Common Treatment/Rehabilitation Pathway