Acl surgery Risks & Side Effects Explained by Surgeons

You have torn your ACL, surgery has been mentioned, and the first question in your head is probably the honest one: what could go wrong?

The usual answers are pain, swelling, stiffness, infection, blood clots and nerve irritation. Less often, the graft fails or the knee is injured again. Most people come through safely, provided the surgical assessment is right, they are watched closely early on and they follow a structured rehabilitation plan. But your own outcome depends on the injury pattern, the graft chosen, what you want to get back to, and how much you commit to physiotherapy.

Overview: What Are the Risks of ACL Surgery?

ACL surgery risks range from expected short-term effects, such as pain, swelling and limited movement, to less common complications including infection, blood clots, persistent stiffness and failure of the reconstructed ligament. The operation is widely performed, and serious complications are uncommon, but no surgery is risk-free. A surgeon can explain how an individual’s health, knee injury and activity goals affect the balance of benefits and risks.

The anterior cruciate ligament (ACL) is one of the main ligaments that stabilizes the knee, especially during twisting, cutting and landing movements. When it tears, some people can manage well with rehabilitation alone, while others experience repeated giving-way episodes or have associated damage to the meniscus, cartilage or other ligaments. Here we focus on weighing up the risks; if you want a fuller explanation of the operation itself, read our page on ACL surgery.

ACL reconstruction usually replaces the torn ligament with a graft rather than sewing the original ligament together. The graft may come from the patient’s own tendon, a donor, or, in selected situations, another material. The choice can influence recovery considerations and potential side effects, so it should be discussed individually with an orthopedic surgeon.

Who May Benefit From ACL Reconstruction?

Not every ACL tear requires surgery. A person may be a candidate for reconstruction when the knee repeatedly feels unstable despite rehabilitation, when they want to return to pivoting or contact sports, or when their job requires reliable knee stability. Surgery may also be recommended when an ACL tear occurs alongside repairable meniscal damage, injuries to other ligaments, or certain cartilage injuries.

Age alone does not decide whether surgery is appropriate. Surgeons consider the person’s overall health, activity level, knee symptoms, imaging findings, occupation, sport goals and ability to take part in rehabilitation. Children and adolescents require particular planning because growth plates may still be open, while older adults may benefit from either surgery or non-operative care depending on knee function and goals.

Before proceeding, swelling and inflammation are often allowed to settle, and the person may complete prehabilitation exercises to restore knee extension, improve muscle control and prepare for recovery. Operating on a very stiff or swollen knee can increase the chance of post-operative movement problems. A shared decision with an orthopedic specialist helps clarify whether the likely benefits outweigh the possible ACL surgery risks.

How the Procedure Works: Step by Step

ACL reconstruction is commonly performed using arthroscopy, a minimally invasive technique involving a camera and small instruments inserted through small incisions around the knee. The operation is carried out under anesthesia. Before reconstruction, the surgeon examines the inside of the knee and may treat associated meniscal or cartilage injuries when appropriate.

The surgeon prepares the selected graft and creates carefully positioned tunnels in the femur and tibia, the upper and lower leg bones that form the knee joint. The graft is passed through these tunnels in the position of the ACL and secured with fixation devices. Over time, the body incorporates the graft into the knee, a biological process that is supported by progressive rehabilitation.

After surgery, patients usually begin guided movement and muscle-activation exercises early, unless another repair changes the plan. Some people go home the same day, while others may require short observation depending on their procedure, pain control and medical needs. Crutches, a brace or activity restrictions may be advised for a period, particularly if the meniscus was repaired.

Anesthesia carries its own considerations, as it does with any operation. You may have nausea, a temporary sore throat or an allergic reaction, and rarely more serious heart or breathing events. The anesthesia team reviews medical history, medicines, allergies and fasting instructions before surgery to reduce avoidable risks.

Expected Side Effects and Possible Complications

Short-term side effects after ACL reconstruction commonly include pain, swelling, bruising, tiredness and difficulty bending or fully straightening the knee. The area around the incision or graft-harvest site may feel numb, tingly or sensitive. These effects usually improve during the early healing phase, although swelling can fluctuate as activity increases.

Less common complications include infection in the wound or joint, bleeding, a blood clot in the leg, delayed wound healing and troublesome scar tissue. Arthrofibrosis is excessive scar formation that causes significant stiffness or loss of movement; it may need intensive rehabilitation and occasionally an additional procedure. Nerve irritation can cause altered sensation, while major injury to nerves or blood vessels is rare.

Longer-term concerns can include ongoing pain, kneeling discomfort related to certain graft choices, weakness of the thigh or hamstring muscles, and anterior knee pain. The graft may stretch, tear or fail to provide adequate stability, particularly after a new injury or an early return to high-risk activity. A tear can also occur in the ACL of the other knee. Rehabilitation reduces risk but cannot remove it completely.

ACL reconstruction does not guarantee prevention of future osteoarthritis. The original injury, especially when accompanied by meniscal or cartilage damage, may contribute to later joint changes regardless of treatment. Maintaining strength, healthy movement patterns and an appropriate body weight can support long-term knee health.

• Risk may be higher with smoking, poorly controlled diabetes, obesity, prior knee surgery, active infection, clotting disorders or difficulty following rehabilitation guidance.
• Risk may be lower when swelling is controlled before surgery, medical conditions are optimized, prevention measures for clots and infection are followed, and return to sport is based on functional testing rather than time alone.

Benefits, Recovery and Return to Activity

The main potential benefit of ACL reconstruction is improved knee stability. This may help reduce giving-way episodes, support return to selected sports or physical work, and protect other structures from repeated instability events. Results vary, however, and surgery cannot fully restore the knee to its pre-injury state in every person.

Recovery is gradual. During the first days and weeks, priorities include controlling swelling, protecting the graft and any repaired tissues, regaining full knee extension, and reactivating the quadriceps muscle. Walking mechanics and knee bending are then progressed under the guidance of a physiotherapist. Recovery plans differ when meniscal repair or additional ligament reconstruction has been performed.

Over subsequent months, rehabilitation develops strength, balance, landing technique, agility and sport-specific control. Running, jumping, pivoting and contact activity are introduced only when the knee is ready. Return to sport often takes many months and should be guided by symptoms, examination, strength and functional assessments rather than a calendar date alone.

Expect good weeks and flat weeks, particularly after you step up your activity. That is normal. Persistent swelling, instability, locking or inability to regain movement should be discussed with the surgical team or physiotherapist rather than ignored.

Reducing Risk Before and After Surgery

Much of the work happens before you reach the operating room. Patients should tell the care team about all medicines, supplements, allergies, smoking or nicotine use, past blood clots, bleeding problems and health conditions. A clinician may advise changes to certain medicines before surgery; patients should not stop prescribed medication without medical guidance.

After surgery, stick to the wound-care, mobility and medication instructions you are given. Early prescribed movement, ankle exercises and walking when cleared can help circulation, while the surgical team may recommend additional clot-prevention measures for some people. Keeping the wound clean and dry as instructed, attending follow-up visits and reporting concerning symptoms promptly can support early treatment if a problem develops.

Rehabilitation should be progressive rather than rushed. Pain or swelling that becomes worse after exercise may mean the knee needs activity adjustment. Adequate sleep, balanced nutrition, avoiding tobacco and nicotine, and maintaining communication with the rehabilitation team all support healing.

If you are travelling from abroad, our orthopedic teams at Acıbadem Health Point work across specialties in JCI-accredited hospitals to assess ACL injuries and plan treatment, with surgery and rehabilitation coordinated together.

When to Seek Medical Care

Patients should contact their surgeon or healthcare team promptly if pain, redness, swelling or warmth around the wound is worsening; if there is drainage from the incision; or if fever or chills develop. New or increasing difficulty moving the knee, sudden locking, a fall, or a new feeling that the knee is giving way also deserves medical advice.

Urgent medical assessment is needed for calf pain or swelling, unexplained shortness of breath, chest pain, coughing blood, fainting, or severe leg swelling. These symptoms can have several causes, but they may indicate a blood clot or another serious condition and should not be managed at home.

Before surgery, a person with a newly injured knee should seek assessment if there is severe swelling, inability to bear weight, deformity, numbness, a cold foot, or a locked knee. Early evaluation can identify injuries that need timely treatment and help develop an appropriate plan for safe recovery.

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