A PT’s Guide to Rehabilitation After ACL Surgery

People of all ages, physical conditions, and abilities can tear an ACL.

A complex set of tendons and ligaments help stabilize and support the knee joint with its every movement, from a simple walking step to a cheerleader jump. Unfortunately, these tissues are vulnerable to injury. One of the most common knee injuries is an anterior cruciate ligament (ACL) sprain, or tear, which must often be treated with surgery. What should physical therapists know about rehabilitation after ACL surgery?

Recommended course: ACL Injury, Surgery, and Rehabilitation: A Science-Based and Evidence-Informed Approach

What is the ACL and what does it do?

The anterior cruciate ligament (ACL) is one of four major ligaments in the knee joint. The other ligaments are the Posterior Cruciate Ligament (PCL), the Medical Collateral Ligament (MCL), and the Lateral Collateral Ligament (LCL). The ACL helps maintain the knee's rotational stability and prevents the tibia (shinbone) from slipping in front of the femur (thighbone). Many people hear a pop or feel a "popping" sensation in the knee when an ACL injury occurs. The knee may swell, feel unstable and become too painful to bear weight.

Athletes who participate in high demand sports like soccer, football, and basketball are more likely to injure their ACL. All these sports involve sudden stops or changes in direction, jumping and landing, which can cause ACL injuries. Injuries can be contact injuries, where some fall on the leg: think football. Many injuries, however, are non-contact in nature.

Common ACL injuries

Often, when someone injures their ACL, they also have other injuries that commonly go along with ACL injuries. Orthopedic surgeons have known about the association between injuries to the anterior cruciate ligament, medial collateral ligament, and medial meniscus (MM) since 1936. O'Donoghue first used the term "unhappy triad" of the knee to describe this condition in 1950.

Who experiences ACL tears and injuries?

People of all ages, physical conditions and abilities can tear an ACL. Active women experience a higher incidence of ACL injuries than men because their biomechanics tend to put more stress on their knees. ACL injuries are also becoming more common in children, especially as youth sports become increasingly competitive.

Diagnosing and evaluating an ACL injury

A doctor can usually diagnose a torn ACL from a physical exam, although magnetic resonance imaging (MRI) is helpful. Getting an MRI is also important to find out if other parts of the knee have been injured. Injured ligaments are considered sprains and are graded on a severity scale.

• Grade 1 sprains. The ligament is mildly damaged in a Grade 1 sprain. It has been slightly stretched but is still able to help keep the knee joint stable.
• Grade 2 sprains. A Grade 2 sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament. Partial tears are not as common as complete tears.
• Grade 3 sprains. This type of sprain is commonly called a complete ligament tear. The ligament has been torn in half or pulled directly off the bone, and the knee joint is unstable.

The prognosis for a partially torn ACL is often good, with the recovery and rehabilitation period usually lasting at least 3 months. Surgery is usually not needed, unless the patient does not progress well with Physical Therapy. Complete ACL tears have a much less positive outcome without surgery.

Nonsurgical treatment for ACL injuries

A doctor may recommend nonsurgical management of isolated ACL tears for:

• Patients with partial tears and no instability symptoms.
• Patients with complete tears who don't experience symptoms of knee instability during low-demand sports and are willing to give up high-demand sports.

Progressive physical therapy and rehabilitation can restore the knee to a condition close to its pre-injury state and teach the patient how to prevent instability. Exercises include strengthening exercises of the quads, the hamstrings, and the glutes. Emphasize close-kinetic chain (CKC) exercises, as these exercises cause less shearing of the knee joint.

The doctor may also recommend wearing a hinged knee brace for added support. However, many people who choose not to have surgery for the ACL injury suffer an injury to another part of the knee due to instability in the joint.

Surgical treatment for ACL injuries

Surgical treatment is usually recommended for combined injuries, or ACL tears that occur along with other injuries in the knee. The torn ACL is generally replaced by a substitute graft made of tendon. These tendons can be “autografts” from the patient themselves, or “allografts” from a tissue donor. Commonly used tendons are the patellar tendon, hamstring tendon, or the gracilis.

The potential drawbacks of the patellar tendon autograft include post-operative pain behind the kneecap and pain with kneeling. Using a hamstring tendon usually has a faster recovery time and needs a smaller incision, but drawbacks include more limited post-operative function and larger risk of increased laxity (looseness) in the knee.

Physical therapy, rehabilitation, and ACL surgery

Before any surgical treatment, doctors will often send the patient to physical therapy. Historically, surgery was done much quicker after the injury, but in the last decade patients typically wait several weeks, or even up to six months to have the surgery.

Patients who have a stiff, swollen knee lacking full range of motion at the time of ACL surgery may have significant problems regaining motion after surgery. Therefore, it’s better to have knee rehabilitation before the surgery. It may take several weeks, or sometimes months, from the time of injury for the swelling and stiffness to subside enough to proceed with surgery.

Rehabilitation after ACL surgery

After surgery to repair the ACL, patients usually attend physical therapy for 3-6 months. Most surgeons have specific protocols and guidelines on how to treat their patients after surgery. Early weight bearing and early rehabilitation intervention vary for allograft and hamstring autograft. Expectations are that the “early return to sport”-phase will be delayed. For patients that also had surgery for concomitant injuries (for example a meniscus repair), the protocols are usually more conservative as well.

The first phase focuses on protecting the graft, reducing pain/swelling, improving Range of Motion (ROM). A physical therapist may start with early ambulation with assistive devices as indicated. When the patient can fully extend their knee, has good quadriceps control and strength, and can perform a Straight Leg Raise (SLR) with any extension-lag, they usually get progressed to the next phase.

Later stages of rehabilitation after ACL surgery

During the second phase, the goal of physical therapy is to still protect the graft and maintain full extension ROM. At this point, the patient is starting to regain full flexion of their knee. Another goal is to normalize gait without assistive devices. Patients typically still use a brace during the second phase, depending on the specific surgeon’s protocol. When the swelling has been mostly resolved and ROM is close to the mobility of the other knee, the patient can progress to Phase 3.

Phase 3 starts with more strengthening exercises and may include weight machines and weight-bearing exercises like partial squats and deadlifts. In this phase, closely monitor pain and swelling. Adapt exercise intensity based on how the patient responds with pain and swelling. Phase 3 typically starts around 6-8 weeks after surgery.

At 9-12 weeks after surgery, patients typically progress to more functional activities, but do not return to sports activities yet. Plyometric exercises may be added during this phase. Swelling and pain should still be monitored and should be used to determine exercise intensity. Early return-to-sport phase usually starts at 4-6 months post-op. This is usually when a patient’s doctor will clear them to start running.

Most surgeons have very specific and detailed protocols for rehabilitation after ACL surgery. It’s important for physical therapists to follow these protocols and ensure good communication with the surgeon when unexpected symptoms occur.

This article was written by Dr. Pieter L. de Smidt, PT, DPT, Cert. MDT, MTC.