Anatomy of the knee

Your knee is made up of bones and soft tissue which hold the joint in place and allow it to function properly, moving through the various motions of the knee smoothly and with stability. Ligaments are bundles of dense connective tissue which connect bone to bone and help keep the bones in the proper alignment. There are four strong ligaments connecting the upper leg bone (the femur) to the primary lower leg bone (the tibia). One of these ligaments is the anterior cruciate ligament (ACL) which runs through the middle of the knee joint, attaching the femur to the tibia. It is a ligament which is crucial to join stability by preventing forward movement of the tibia in relation to the femur and by preventing rotational movements of the knee joint. Both of these actions help to reduce stresses on the knee joint and give the knee stability, particularly during jumping and landing, pivoting motions and rapid decelerations.

ACL injuries

The ACL is a commonly injured ligament. These injuries often occur by a twisting movement of the knee, a rapid stop or direction change, or an awkward landing from a jump. This frequently occurs in jumping or pivoting sports, such as basketball or soccer, and in contact sports, such as football. A “pop” is sometimes felt or heard during an ACL injury, and the knee may feel like it gives out. ACL tears can be either partial or complete. In partial tears, some of the ligament fibers tear, but some don’t. This could result in varying levels of instability and discomfort in the knee. In a complete tear, all of the ACL fibers connecting the femur to the tibia are torn, or the ligament may tear completely off the bone. As well, sometimes other structures in the knee (e.g. other ligaments or meniscus) are damaged during an ACL injury, or may be damaged during physical activity following an ACL injury due to increased stresses on the joint.

The particular symptoms of an ACL tear depend on the individual. Some people experience large amounts of pain and swelling immediately following injury, others experience very little. Some people are able to walk immediately following injury, or even to continue to participate in sports, others require the use of crutches for several days. The long-term impact of an ACL injury on activities of daily life also depends on the individual, and depends a lot on the individual’s desired level of physical activity. Some people experience very little difficulty living with an ACL tear. For these people, exercises and physiotherapy designed to strengthen the leg can often provide adequate stability. Braces may also be used to increase knee stability or to protect other injured tissue in the knee. In other patients, a significant amount of instability, pain, or the sensation of “giving out” may be experienced following an ACL injury; either in everyday activities or during athletic pursuits.  In these patients, a surgical ACL reconstruction may be beneficial to improve the function of the knee and to alleviate symptoms. The decision about whether or not to operate will be made jointly between you and your healthcare team and will be based on a number of factors including age, activity level, amount of instability in the knee, and associated injury.

How are ACL injuries diagnosed

ACL injuries are diagnosed in several ways. Firstly, the doctor will take a history of any knee injury sustained, the mechanism of the injury, and any knee instability or pain. This will allow the doctor to determine whether your injury fits the picture of an ACL tear. The doctor will also physically examine your knee to feel for any instability, specifically any anterior-posterior or rotational instability. These two pieces of information should give the doctor a good idea about whether or not the ACL is torn. Finally, an MRI scan will most likely be ordered to confirm the diagnosis. Unlike x-rays, MRI’s show soft tissue, allowing damage to the ACL to be visualized. X-rays may also be taken to rule out any fractures or bone injuries to the knee.

Surgical ACL reconstruction

The ACL does not heal on its own, nor can it simply be sewn back together. For these reasons, the surgical approach to an ACL tear involves an ACL reconstruction, in which the torn ligament is replaced. In this procedure one or two tendons from the region of your knee are removed and formed into a graft ligament to replace the old ACL. This graft is passed through a bone tunnel drilled in your tibia and femur, replicating the ACL. The graft is then secured to your tibia and femur using screws and other devices. Over time, the bony tunnel will begin to grow closed, and the graft will fuse to the bone, securing it in place just like a normal ligament. Associated injuries may also be addressed at the time of surgery.

The surgery takes approximately 1.5 hours and is performed mostly arthroscopically. This means that specialized instruments will be inserted through small incisions around the knee, and a video camera will be used to visualize the inside of the knee. Arthroscopic surgery has many benefits over open surgery including a quicker recovery because it’s less invasive, much smaller scars, and a minimized risk of blood loss and infection. The surgery will be a day procedure, which means that you will come in to the hospital in the morning and will go home that same afternoon. It will be performed under general anesthetic, meaning that you will be asleep for the procedure, and a nerve block may also be used to numb the leg and reduce post-operative pain. See the “Day of Surgery” section for more details regarding the day of surgery.

Risks of ACL reconstruction

As with any surgery, an ACL reconstruction does carry some risks. These risks include, but are not limited to, pain, stiffness, scarring, infection and nerve damage. In the majority of cases, these complications are not permanent and should resolve over time, or are reversible with appropriate treatment. Your surgeons will make every effort to minimize these risks.

Recovery and outcome

Recovery after ACL reconstruction takes months of hard work to rehabilitate the leg in order to achieve a full range of motion and adequate strength for a high level of physical activity. It takes at least 6 months of rehab before returning to high intensity physical activity. Following surgery, your knee will never feel exactly the same as it did prior to the injury, but the goal is to end up with a knee that feels strong, stable, pain free, and which gives you the confidence to pursue all of your physical activity goals and to return to your pre-injury level of sports. Although this goal is achieved in most patients, some will find that although their knee is improved, they are unable to return to their pre-injury level of activity following surgery.  Following ACL reconstruction you have a re-rupture rate of approximately 7% which is less than the risk of rupturing your ACL on the opposite knee.

Recovery timeline

Recovery is a process that will be different for everyone. It depends on a number of factors including the work and motivation the individual puts into rehab, the individual’s pre- and post-injury levels of physical activity, and the particular injuries sustained. Recovery should be a steady improvement in the long-run, however there will be bumps along the way.  A successful recovery depends on the patient putting in the work to increase strength and mobility, while still protecting the graft.

The following outlines a timeline of what is typically expected post-op, but once again, this will differ from person to person. Dr. Murnaghan and your physiotherapist will monitor your progress and may recommend modifying the timeline slightly if necessary. However, do note that the milestones for returning to activity are minimums, not averages; you have to give your body the time to heal no matter how much rehab you do.

Post-op 0–2 weeks

See the “FAQ” section for some frequently asked questions regarding the first two weeks after surgery.

What to expect during this period:

During this time it is not uncommon to experience some pain, discomfort, swelling and discolouration in your knee and calf.

Pain medication, ice, and elevation can be used to minimize this discomfort. Ankle pumps are also useful in reducing swelling.

You will probably notice some areas of numbness around your knee – this is normal – some of the numbness will resolve over time, some, such as numbness around the incision, may be permanent.

Activity level during this time:

You should limit your activity during the first 72 hours post-op. During the first week your activity will likely be limited to moving around the house plus trips to physiotherapy.

You should use crutches during this time, but can start weight-bearing as tolerated immediately following surgery with the crutches.

You should begin physiotherapy during this time.

Prior to starting physiotherapy, you can begin some home exercises to minimize the effects of immobilization including:

1. Gently bending and straightening the knee ten times, three times a day.

2. Straight leg raises, ten times, three times a day.

Goals for this period:

The goals during this time are to protect the graft, to minimize immobilization, to control swelling, and to begin physiotherapy.

You should also begin to work on regaining full straightening (extension) of the knee.

When we’ll see you:

You will come back for a follow-up appointment at about the 2 week mark and you will likely be sent for x-rays at this appointment. Dr. Murnaghan will check your incisions, swelling, and progress so far. You should have started physiotherapy BEFORE this appointment.

Post-op 2–6 weeks
What to expect during this period:

During this time, the pain in your knee should decrease greatly, although you will likely still notice some pain and swelling during or after exercise and range of motion activities.

As your knee begins to feel better, you may develop some pain and swelling in your shin or calf when standing upright. This is normal and will resolve.

You may notice that you still have difficulty with certain daily activities such as going up or down stairs.

Activity level during this time:

Most patients are ready to get rid of their crutches at or around the 2 week mark. Your physiotherapist will let you know when your leg is strong enough for you to begin to wean the use of the crutches.

You should be attending physiotherapy regularly during this period to work on exercises which increase strength and range of motion. “Closed-chain” strengthening exercises (those which keep the foot planted on the ground, such as squats and lunges) are the best form of exercise because they better imitate the types of stresses that will be placed on your knee during sports, and do not cause unnecessary stresses on the joint or graft. The stationary bike is also useful for improving strength and range of motion. Your physiotherapist will assist you with these activities.

Goals for this period:

The goals during this time are to protect the graft, to minimize immobilization, and to control swelling.

By the end of this period your goals are to have achieved full leg extension (straightening the knee), and to be walking without a noticeable limp on level surfaces.

When we’ll see you:

You will come in for a follow-up appointment at about 6 weeks post-op.

Post-op 6–12 weeks
Where you should be by this point:

By this point, you should have achieved full leg straightening, near full bending, good quadriceps strength, minimal swelling and a normal walking gait on level surfaces.

What to expect during this period:

Although your leg may feel very strong at this point, your graft is still healing and it is extremely important to continue to protect it.

Activity level during this time:

During this time you should continue the activities you were working on during the first 6 weeks, and your physiotherapist will direct you on how to increase their intensity.

You may also begin using the Stairmaster and elliptical trainer.

Running is still not allowed at this time, but you may begin waist deep pool running if desired.

Don’t forget to protect your graft even as your leg begins to feel strong!

Goals for this period:

Your goals for this period are to continue to protect the graft, to maintain full extension and progress towards full flexion (bending), to restore normal gait with stair climbing, and to increase leg strength and balance.

When we’ll see you:

You will come in for a follow-up appointment at about 3 months post-op, at which point Dr. Murnaghan will assess your leg strength. If you demonstrate sufficient strength and balance, you may begin running at the 3 month point.

Post-op 3–4 months
Where you should be by this point:

By this point you should have minimal pain and swelling. You should also have close to complete range of motion.

What to expect during this period:

Although your range of motion should be close to full, you may notice some inertia in the knee, meaning that it tends to be stiff after being either straight or bent for long periods of time.

You will probably notice that your body and knee become tired quickly with physical activity. As long as you keep working hard on your rehab, this will improve over time.

Activity level during this period:

At your 3 month appointment, Dr. Murnaghan will assess your leg strength. If you demonstrate sufficient strength and balance, you may begin running at the 3 month point.

When you first begin running, you should start with short runs (~5mins) which are best accomplished on a treadmill, or else on a straight, level surface. Because you will likely get tired quickly, you want to run in a way that will not leave you far from where you started!

You should continue with your strength and range of motion exercises and can also progress to endurance training on the Stairmaster, elliptical or bike.

You can begin swimming if desired.

Goals for this period:

By the end of this period you should have achieved full range of motion, you should continue to improve strength, endurance and balance to prepare for sports, you should develop normal running mechanics, and should aim for strength of approximately 70% that on the uninvolved leg.

You should continue to protect the graft and joint.

When we’ll see you:

We will not see you between 3 and 4 months unless there is a problem.

Post-op 4–5 months
Where you should be by this point:

By this point you should have no significant swelling/inflammation with full, pain-free range of motion and no joint irritation.

You should also have strength of approximately 70% of the uninvolved leg as well as normal running gait and sufficient strength and balance to begin agility activities.

What to expect during this period:

Remember to begin sport specific training in a very controlled and safe manner to allow your knee time to develop the necessary strength.

Activity level during this period:

During this period you may begin agility drills and begin sport specific drills.

You should also continue flexibility and strengthening work.

You can increase your running distance.

Goals for this period:

Your goal for this period is to begin sport specific agility drills.

By the end of this period, you should be able to demonstrate symmetric performance on both legs for these drills and should have approximately 85% the strength of the uninvolved leg.

When we’ll see you:

We will not see you between 4 and 5 months unless there are problems.

Post op 5–6 months

You will come in for a follow-up appointment just before 6 months, at which point Dr. Murnaghan will evaluate your range of motion, strength, endurance and proprioception, and will determine whether or not you are ready to resume partial or full activity. You may then safely and gradually return to pre-surgery activities. You have to remember to continue your strength and endurance work, and it’s important to realize that it is likely that this knee will require more work, in terms of additional exercises and stretching, than it did prior to surgery.

Many patients continue to see improvements well past the 6 month point. Your knee will never feel exactly the same as it did prior to the injury, but the goal is to end up with a knee that feels strong, stable, pain free, and which gives you the confidence to pursue all of your physical activity goals. You may find that this knee swells up slightly with large amounts of exercise, and may require more stretching before or after exercise. There will be certain activities that some people may find take more than 6 months to return to normal, such as kneeling, deep squats or running long distances on concrete.