The Complete Guide
to ACL Injuries

What is the Anterior Cruciate Ligament?

The Anterior Cruciate Ligament (ACL) is a rope-like structure that connects the femur (thigh bone) to the tibia (shin bone).  It is an important stabilizer of the knee and when it is injured patients can experience knee instability or giving way.

Who is at risk for ACL injury?

ACL tears are a common injury among individuals in their teens or early adulthood. They most often occur as a result of a non-contact pivoting or twisting injury. When the injury happens it is usually very apparent. Patients will feel or hear a ‘pop’ inside their knee and this will be accompanied by a rapid onset of swelling or fluid buildup. In fact, the number one cause of knee swelling (i.e. hematoma) after a sports injury is an ACL tear.  After the initial injury, most patients will have an encounter with the healthcare system where individuals are told to start some physiotherapy and see a surgeon for a consultation.

When does an ACL tear need physiotherapy vs surgery?

Initially, all patients with an ACL tear need physiotherapy. Even if surgery is a possible downstream scenario, patients will only be considered eligible for surgery once the swelling in the knee has been minimized, the muscles around the knee (i.e. the quadriceps) have been strengthened and/or re-activited, and there is full range of motion. In the absence of more complex injuries (like displaced meniscus tears or other associated ligamentous injuries), this can take anywhere from 3-6 weeks.

After this initial period of recovery and rehabilitation following ACL injury, the decision making process of whether or not surgery is needed comes into play. If patients can modify their activities and rehabilitate to an extent (usually after 3-6 months) where their knee does not give way, then ongoing nonoperative care is suitable. This may involve the use of a custom ACL brace for pivoting and twisting activities. When patients have persistent knee instability despite appropriate neuromuscular rehabilitation or if their work/sports/recreational activities necessitate pivoting, twisting, acceleration and deceleration movement patterns, then surgery can be considered.

Based on the above, it is clear that surgery is required for patients who are symptomatic (with instability) despite an initial period of rehab. For patients who are competitive athletes, early surgical management is often suggested to obviate the risk of knee instability and secondary damage to other structures in the knee.

What are the long term consequences of an ACL tear?

It is well known that a proportion patients with ACL tears develop osteoarthritis. Some estimates say upto 50% of people can develop xray signs of arthritis within 10 years. Surgery does not in and of itself change this risk. The key element is that ongoing knee instability that can cause secondary damage to meniscus and cartilage. Reinjury becomes the main culprit and the risk of this needs to be minimized. So whether physiotherapy alone can prevent this or surgery is required, the important part is that patients should be able to pursue a life of activity and meaningful endeavours without symptoms.

How is ACL reconstruction surgery performed?

ACL reconstruction is one of the most common surgeries performed by orthopaedic surgeons. Please watch the video here, for a technical overview of how ACL surgery is performed.

Overall, there is general agreement among surgeons that an ‘anatomic reconstruction’ with accurate placement of femoral and tibial sockets is the most important technique related factor to ensure success.  The technique to accomplish an anatomic reconstruction has evolved over time and the specific details of how this is achieved may vary across different surgeons.

What type of graft can be used to reconstruct the ACL?

The first decision that is make is whether an allograft (donor graft) or autograft (from the patients own body) is utilized.  The clear trend that is evidence based is to use autograft since many studies have demonstrated higher failure rates with the use of allograft (especially in younger patients).  The commonly used autograft options include patellar tendon, quadriceps tendon, and hamstring autograft.  While all of these grafts have particular advantages and disadvantages, the most important factor is whether a surgeon is comfortable with the particular technique selected.

Physiotherapy following ACL Reconstruction

Physiotherapy after anterior cruciate ligament (ACL) reconstruction is crucial to achieving a successful outcome. The following video outlines the philosophy for rehabilitation following ACL surgery.

Principles of ACL Rehabilitation

The phases outlined below for ACL physiotherapy are for patients undergoing an autograft ACL reconstruction.  Progression and specific exercises and milestone may change if concomitant procedures such as meniscus repair or cartilage repair are performed.

Phase I

During the first six weeks, the priority is to decrease swelling, obtain full extension of the knee, and achieve full flexion.  Patellar mobilization is important to minimize scar tissue formation and encourage pain free range of motion.  Quadriceps stimulation and isometric exercises are necessary to prevent atrophy and to improve ambulation. Working on core strength with side-lying exercises is also encouraged.

Phase II

Upon achieving full range of motion and minimizing knee swelling, more attention is devoted to quadriceps strengthening using closed chain kinetic exercises, balance exercises, hamstring curls, stationary bike, and advanced hip/core exercises.

Phase III

After 12 weeks, progressive work on core muscles, advanced closed chain kinetic strengthening, proprioception training is encouraged. Elliptical use can commence at approximately 10 weeks and running straight ahead commences at 12 weeks.

Phase IV

After 4-5 months, patients can commence jumping, sprinting, backward running, cutting activity, and plyometric exercises that are sports specific

Phase V

Sports Specific training commences at six months. Full return to competition is permitted at 9 months postoperatively.  Generally agreed upon criteria to return to sports include full motion, absence of swelling, quadriceps strength >80% compared with the normal leg, and the absence of subjective pain and instability.

What are the most important rehabilitation principles to remember following surgery?

The most important things to do for rehab after ACL surgery include:

  1. Early quadriceps activation.  To watch a video demonstration, click here
  2. Regain knee extension early.  To watch a video demonstration, click here
  3. Obtain full range of motion in the first six weeks
  4. Have a goal-oriented rehab plan and work with a physiotherapist
  5. Return to play based on the absence of swelling/pain/instability and the successful performance of function/strength based tasks.

When is is safe to return to sports after ACLR?

In a research study (British Journal of Sports Medicine) between the University of Delaware and Norwegian School of Sports Sciences, investigators looked at the relationship between re-injury following ACL surgery, determination of the timing for return to sports, and knee function.  There were 106 patients who were followed for two years after their ACL was reconstructed.

The authors determined that in order to minimize the rate of re-injury, participants should (i) wait at least nine months from surgery until participation in sports that involve jumping, pivoting and hard cutting; and (ii) have symmetrical quadriceps (thigh muscle) strength. Furthermore, return to sports that involve cutting and pivoting had a four-fold higher risk of knee re-injury compared to lower demand activities. The implications of this research are massive. Preventing secondary injury can minimize the rate of simultaneous cartilage and meniscus pathology and as a result limit the progression of osteoarthritis in the future.

From a practical standpoint, this research suggests that return to sports decision-making should be time based and function based.  Working with a physiotherapist to improve core strength, quadriceps strength, and eliminate swelling are essential to optimizing function and sport-specific readiness, especially in the context of pivoting and cutting activities.

The Final Word

While ACL tears are common and the road to recovery can be fraught with challenges, the combination of a motivated patient and qualified care team (orthopaedic surgeon, physiotherapist, athletic therapist ,etc), a milestone-based rehabilitation program, and an understanding of the pearls and pitfalls of the recovery process can allow patient to regain function and quality of life, as well as, return to sport in a predictable manner.