ACL Reconstruction

ACL reconstruction is an arthroscopic knee operation that replaces a torn anterior cruciate ligament with a tendon graft. The goal is to restore rotational and forward-backward stability of the knee so that patients can walk, work, exercise and, when appropriate, return safely to activities that involve running, jumping, cutting or pivoting.

The anterior cruciate ligament, usually shortened to ACL, runs diagonally through the center of the knee between the femur and tibia. Together with the posterior cruciate ligament and the collateral ligaments, it helps control the movement of the knee. The ACL is especially important when the body changes direction while the foot is planted.

An ACL can tear during football, soccer, basketball, skiing, rugby, handball and other sports that involve sudden deceleration, landing or pivoting. Many ACL tears occur without another person striking the knee. AAOS describes the ACL as an important restraint against the tibia moving too far forward relative to the femur and as an important contributor to rotational stability.

Not every ACL tear requires surgery. Some people can function well after structured physiotherapy, particularly if they have a partial tear, do not experience repeated episodes of the knee giving way and do not need to return to high-demand pivoting activities. Other patients continue to feel instability despite rehabilitation. For them, ACL reconstruction surgery may provide a more stable platform for work, daily life or sport.

The word reconstruction matters. In conventional ACL reconstruction, the torn ligament is not simply sewn together. A new ligament is created from a tendon graft. That graft may come from the patient's own patellar tendon, hamstring tendons or quadriceps tendon. In selected circumstances, donor tissue may be used instead.

During arthroscopic ACL reconstruction, a small camera is introduced into the knee through a portal. The surgeon examines the joint, confirms the ligament injury and assesses the menisci and articular cartilage. Additional portals allow small instruments to enter the knee. The surgeon prepares the chosen graft, creates accurately positioned bone tunnels or sockets in the femur and tibia, passes the graft through them and secures it using fixation devices.

Associated injuries are important. ACL tears may occur with meniscus tears, cartilage damage, medial collateral ligament injury or other structural damage. AAOS notes that roughly half of ACL injuries are associated with other knee injuries.

For this reason, ACL surgery is not identical for every patient. One person may need an isolated ACL reconstruction. Another may undergo ACL reconstruction together with meniscus repair. A third may require additional treatment for cartilage or another ligament.

These differences affect operating time, weight-bearing, rehabilitation and return-to-sport timing.

The goal of the procedure is functional stability, not simply creating an MRI image that looks normal. A technically successful graft still requires months of biological healing, muscle strengthening, neuromuscular retraining and progressive sports-specific rehabilitation.

Patients sometimes ask whether they will receive a “new ACL.” Biologically, the answer is more nuanced. The graft begins as tendon tissue. After implantation, it gradually remodels and adapts to its new role inside the knee. The process continues long after the surgical wounds have healed.

That is why an athlete can feel relatively normal several months after ACL reconstruction while the graft and entire lower limb are still adapting.

The rehabilitation phase therefore has the same importance as the operation itself.

Preparing properly for ACL reconstruction surgery can affect both the early postoperative experience and the quality of rehabilitation.

Confirming the diagnosis

The process usually starts with a detailed history and knee examination. The surgeon asks how the injury happened, whether a pop was heard or felt, how quickly the knee swelled and whether the knee now gives way.

Clinical tests assess ACL stability and other knee structures.

MRI is commonly used to confirm the ACL injury and evaluate the menisci, cartilage, collateral ligaments and other structures. Plain X-rays may also be performed to assess the bones and exclude fracture or significant arthritis.

The decision to reconstruct the ACL should not be based on MRI alone. Symptoms, activity level, instability, associated damage and patient goals need to be considered together.

Prehabilitation before ACL surgery

Prehabilitation can begin before the operation.

Typical goals include reducing swelling, restoring full knee extension, improving flexion, normalizing walking and rebuilding quadriceps control.

Entering surgery with a stiff or significantly swollen knee can make the initial postoperative period more difficult. For that reason, some patients benefit from several weeks of physiotherapy before the operation.

Common preoperative exercises may include quadriceps activation, straight-leg raises, stationary cycling when tolerated, heel slides and progressive strengthening.

The exact programme should be prescribed by the treating physiotherapist or surgeon because associated meniscus or cartilage injuries can change what is safe.

Timing of ACL reconstruction

There is no single correct number of days between an ACL tear and surgery for every patient.

The knee needs to be ready, but unnecessary prolonged instability can expose the menisci and cartilage to additional injury.

AAOS's current clinical practice guideline states that when surgery is indicated for an acute isolated ACL tear, earlier reconstruction is preferred because the risk of additional meniscal and cartilage injury begins to increase within approximately three months.

This does not mean every ACL tear should be operated on immediately.

A severely swollen, painful knee with limited movement may need rehabilitation first. Associated injuries can also alter timing. The surgeon balances joint recovery against the risk created by ongoing instability.

Choosing the ACL graft

One of the most important discussions before surgery concerns the graft.

Common choices are:

The AAOS guideline recommends that surgeons consider autograft over allograft, particularly in young or active patients, because of better outcomes and a lower graft-failure risk.

When comparing patellar tendon with hamstring autograft in skeletally mature patients, AAOS states that patellar tendon graft may be favored when reducing graft failure is particularly important, whereas hamstring graft may be favored when minimizing anterior or kneeling pain is a priority.

Quadriceps tendon graft has become increasingly common and may be especially useful in certain primary and revision reconstructions. Graft selection should still be individualized according to age, sport, occupation, anatomy, previous surgery and surgeon experience.

Medical assessment

Before the operation, the hospital may arrange:

• blood tests;

• anaesthetic assessment;

• medication review;

• electrocardiogram when clinically indicated;

• pregnancy testing when appropriate;

• additional medical clearance for significant health conditions.

Patients taking anticoagulants, antiplatelet medication, diabetes medication or other important prescription drugs should receive individualized instructions. They should never stop these medications without medical advice.

Smoking and nicotine

Smoking and nicotine can interfere with tissue healing.

Patients who smoke or use nicotine products should discuss cessation with their healthcare team. Stopping before surgery and remaining nicotine-free during recovery is generally encouraged.

Planning the first postoperative week

International and local patients should plan the practical aspects of recovery before travelling to hospital.

Arrange:

• transport home;

• help with shopping or household responsibilities;

• a comfortable place to elevate the leg;

• prescribed medications;

• ice or approved cold-therapy equipment;

• crutches if recommended;

• physiotherapy appointments;

• a follow-up appointment;

• wound-care supplies when required.

A patient travelling internationally should also know how to contact the treating team after leaving the hospital.

How is ACL reconstruction done?

ACL reconstruction is usually performed arthroscopically. The surgeon inspects the knee with a small camera, prepares a tendon graft, creates precisely positioned tunnels or sockets in the femur and tibia, passes the graft into the anatomical position of the torn ACL and fixes it securely to the bone.

NHS describes ACL surgery as keyhole surgery in which an arthroscope is introduced through a small incision, the damaged ACL is assessed, a graft is positioned in place of the torn ligament and fixation devices are used to secure it.

Step 1 — Anaesthesia and positioning

ACL reconstruction may be performed under general anaesthesia or spinal/regional anaesthesia.

A peripheral nerve block may also be offered to reduce postoperative pain.

The patient is positioned so that the surgeon can move the knee freely during the operation. A tourniquet may be used depending on surgeon preference.

Step 2 — Arthroscopic examination

The surgeon inserts the arthroscope into the knee.

Saline solution expands the joint and improves visibility.

The surgeon examines:

• the torn ACL;

• posterior cruciate ligament;

• medial meniscus;

• lateral meniscus;

• articular cartilage;

• patellofemoral joint;

• other structures visible arthroscopically.

This examination is important because an MRI does not always identify every clinically relevant lesion.

If a meniscus tear is found, the surgeon may repair or selectively trim it depending on tear pattern, tissue quality and location.

Meniscus preservation is generally desirable whenever a repairable tear is present because the menisci play an important role in load distribution and joint stability.

Step 3 — Graft harvest and preparation

When an autograft is used, the selected tendon is harvested through an additional incision.

The graft is then prepared on a sterile table.

Its diameter and length are measured.

Strong sutures are placed through the ends of the graft so it can later be passed into the bone tunnels.

The graft choice determines exactly how this part is performed.

A bone–patellar tendon–bone graft includes small bone blocks.

A hamstring graft is commonly folded to form multiple strands.

A quadriceps graft may be used with or without a bone block.

Step 4 — Preparing the original ACL footprint

The damaged ACL tissue is assessed.

Enough tissue is removed to allow anatomical tunnel positioning while preserving useful landmarks when possible.

The objective is not simply to create “a ligament” inside the joint. The graft needs to reproduce the orientation and function of the native ACL as closely as possible.

Tunnel position is one of the important technical factors in ACL reconstruction.

Poorly positioned tunnels can alter graft tension and knee mechanics and are a recognized cause of reconstruction failure.

Step 5 — Femoral tunnel or socket

Using arthroscopic guides, the surgeon identifies the ACL attachment area on the femur.

A guidewire is placed.

A drill or reamer creates a tunnel or socket matched to the graft.

Different drilling techniques can be used.

The exact technique is less important to the patient than accurate anatomical positioning and secure graft fixation.

Step 6 — Tibial tunnel

A tibial guide is used to identify the native tibial ACL attachment.

A guidewire is passed through the tibia.

The tunnel is drilled to the planned size.

The position is checked arthroscopically to ensure the graft will not impinge on surrounding structures as the knee moves.

Step 7 — Passing the ACL graft

The prepared graft is passed through the tibial and femoral tunnels or sockets.

The surgeon checks its position and tension.

The knee may be moved repeatedly through flexion and extension to ensure the graft tracks correctly.

Step 8 — Fixation

Different fixation systems are available.

They include interference screws, cortical buttons, suspensory fixation and other orthopedic implants.

Some fixation devices remain inside the bone permanently.

The choice depends on the graft, bone quality, tunnel technique and surgeon preference.

Step 9 — Tensioning the graft

The graft is tensioned with the knee positioned according to the surgical technique.

The surgeon assesses stability and range of motion.

A correctly positioned ACL graft should control abnormal translation and rotational instability without preventing normal knee motion.

Step 10 — Associated procedures

If the patient also has a meniscus tear, cartilage lesion or another ligament injury, treatment may be performed in the same operation.

This is one reason why ACL reconstruction operating times differ substantially between patients.

An isolated ACL reconstruction may be relatively straightforward.

ACL reconstruction combined with meniscal root repair, multiple meniscus repairs or complex multiligament surgery can take longer and may require a more restrictive rehabilitation programme.

Step 11 — Closing the incisions

The arthroscopy portals and graft-harvest incision are closed.

Sterile dressings are applied.

A brace may be placed if required.

The patient then goes to the recovery area.

Single-bundle versus double-bundle ACL reconstruction

The normal ACL has functional bundles that behave differently as the knee moves.

This led surgeons to develop double-bundle reconstruction techniques intended to reproduce more of the native ligament anatomy.

However, AAOS reviewed the evidence and concluded that both single-bundle and double-bundle ACL reconstruction can be considered because measured clinical outcomes are broadly similar.

Single-bundle reconstruction remains widely performed.

The most appropriate technique depends on the surgeon's experience and individual anatomy.

ACL reconstruction versus ACL repair

These procedures are different.

ACL reconstruction replaces the torn ligament with graft tissue.

ACL repair attempts to preserve and reattach the original ACL.

Traditional repair has historically had a higher failure rate than reconstruction because the ACL has limited intrinsic healing capacity in the intra-articular environment. AAOS therefore describes reconstruction as the usual surgical treatment for most ACL tears.

Modern repair techniques and biologic approaches are being studied and may be reasonable in highly selected injury patterns, particularly some proximal tears with good-quality tissue.

They should not be presented as interchangeable with standard ACL reconstruction.

Most patients having an uncomplicated primary ACL reconstruction can leave the hospital on the same day.

After surgery, the patient is transferred to a recovery area while the effects of anaesthesia wear off.

Nurses monitor blood pressure, pulse, pain control, wound dressings and circulation in the leg.

Pain is treated using a multimodal approach that may include local anaesthetic, a nerve block, acetaminophen/paracetamol, anti-inflammatory medication when appropriate and stronger pain medication for a limited period.

A physiotherapist or trained clinical team member may help the patient stand and walk.

NHS guidance states that most patients begin mobilizing soon after surgery and can usually return home on the day of the operation.

Crutches may be used initially.

Weight-bearing instructions depend on what was performed.

After an isolated ACL reconstruction, patients are often permitted to bear weight relatively early.

However, rehabilitation may be more protective when ACL reconstruction is combined with a meniscus root repair, complex meniscus repair, cartilage procedure or additional ligament reconstruction.

A knee brace is not required for every ACL reconstruction.

Some surgeons use one routinely in the early phase, while others use it selectively.

Before discharge, the patient should understand:

• how much weight can be placed through the leg;

• how to use crutches;

• whether a brace is required;

• wound-care instructions;

• medication dosing;

• exercises to begin immediately;

• warning signs requiring medical attention;

• the date of follow-up.

Patients should not drive themselves home after anaesthesia.

International patients should remain within practical reach of the treating team during the initial postoperative period according to the surgeon's travel protocol.

ACL reconstruction recovery time

ACL reconstruction recovery is a gradual process that usually takes many months. Walking and basic daily activity return much earlier than competitive sport. Many patients are functioning independently within weeks, but running, cutting, pivoting and unrestricted sport require progressive rehabilitation and objective clearance.

NHS notes that patients may resume many activities within a few months but that returning to sport can take up to a year.

AAOS describes return to full sports participation as commonly occurring within approximately 6–12 months, depending on strength, mechanics, symptoms and individual progress.

Those ranges should not be interpreted as a guarantee.

A professional athlete, recreational skier and office worker have very different functional endpoints.

Why recovery takes so long

The wounds heal relatively quickly.

The deeper recovery is slower.

Three processes occur at the same time:

The graft must biologically remodel.
The tendon graft adapts to its ligament-like role inside the knee.

Muscles must recover.
Quadriceps weakness is common after ACL injury and surgery.

Movement patterns must be retrained.
Strength alone does not ensure safe cutting, landing or pivoting.

Return-to-sport planning therefore considers both biology and function.

ACL reconstruction is generally effective at restoring mechanical knee stability and improving function in appropriately selected patients.

Long-term observational research from the MOON cohort has shown meaningful improvements in validated knee outcome scores after ACL reconstruction that were maintained through approximately 10 years, although activity level may decline over time and outcomes vary between patients.

“Success,” however, can mean several different things.

A stable knee is one outcome.

Returning to jogging is another.

Returning to competitive football at the same level is much more demanding.

For this reason, a single ACL reconstruction success-rate percentage can be misleading.

Return to sport after ACL reconstruction

Return-to-sport rates vary according to age, sport, competition level, associated injuries, rehabilitation and how “return” is defined.

A 2026 systematic review and meta-analysis of elite and professional athletes reported that approximately 85.8% returned to play, with a pooled average return time of approximately 292 days. The population was highly selected elite/professional athletes, so these figures should not be presented as the expected outcome for every ACL patient.

The same study estimated graft failure at about 7% in that athlete population, again emphasizing that failure rates depend strongly on population and activity exposure.

Will the knee be exactly the same as before injury?

Not necessarily.

Many patients regain high levels of function, but reconstruction cannot recreate a completely untouched knee.

The original injury may already have damaged the meniscus, cartilage or bone.

The graft is not biologically identical to the original ACL.

Some patients also experience persistent weakness, stiffness, altered sensation, kneeling pain or reduced confidence.

The realistic objective is a stable, functional knee—not a promise that the injury never happened.

Does ACL reconstruction prevent arthritis?

ACL reconstruction is performed primarily to restore stability and function.

It should not be promoted as a guaranteed method of preventing osteoarthritis.

ACL injury itself can initiate changes inside the knee, particularly when the meniscus or cartilage is also damaged.

Preventing repeated instability and preserving repairable meniscal tissue may be beneficial, but reconstructed knees can still develop degenerative changes later in life.

ACL fixation technology includes:

• interference screws;

• cortical buttons;

• suspensory devices;

• adjustable-loop systems;

• fixed-loop systems;

• staples in selected techniques;

• bioabsorbable or biocomposite fixation in some systems;

• metallic fixation.

The “best” implant cannot be determined independently of the graft and surgical technique.

Correct tunnel position, graft preparation, fixation, tensioning and rehabilitation generally matter more than marketing language around a specific implant.

Computer navigation and robotic technology

Navigation and robotic assistance are increasingly visible across orthopaedic surgery.

ACL reconstruction may use digital planning, intraoperative measurement or navigation systems in selected centers, but conventional arthroscopic reconstruction remains established practice.

Technology should support anatomical accuracy rather than replace surgical expertise.

Patients should therefore ask what clinical benefit a proposed technology offers for their specific knee rather than choosing a surgeon solely because a robotic or computer system is advertised.