ACL reconstruction is a commonly performed procedure for restoring stability after an anterior cruciate ligament (ACL) tear. Like any surgery, however, it carries potential risks and complications. Understanding these possibilities can help you know what to expect during recovery and which symptoms should be discussed with your medical team.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
If you are considering ACL reconstruction, your individual risks depend on factors such as the extent of the knee injury, the type of graft used, associated meniscus or cartilage damage, general health, surgical technique, and rehabilitation.
How Common Are Complications After ACL Reconstruction?
Most people recover without a major complication, but problems can occur during the early recovery period or later. Some complications are related to the surgery itself, while others involve graft healing, knee movement, stability, or the return to physical activity.
Having a potential complication listed does not mean that it will happen to you. Your surgeon can explain which risks are particularly relevant to your procedure and medical circumstances.
Common Risks After ACL Reconstruction
Pain and swelling
Pain and swelling are expected during the early stages of recovery. They generally improve as healing progresses and rehabilitation begins. Persistent or worsening symptoms should be assessed rather than assumed to be a normal part of recovery.
Knee stiffness
Some people develop difficulty fully straightening or bending the knee after surgery. Regaining knee movement is an important early rehabilitation goal because prolonged stiffness can interfere with normal function.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Temporary muscle weakness
Weakness, particularly in the quadriceps, is common after ACL reconstruction. Muscle strength may take considerable time to return, which is why progressive rehabilitation is an important part of recovery.
Infection
Infection is an uncommon but potentially serious complication of ACL reconstruction. It can involve the surgical wound or, more rarely, the knee joint itself.
Symptoms that may require prompt medical assessment include increasing redness or warmth around the incision, worsening swelling, drainage from the wound, fever, or pain that is becoming more severe rather than improving.
Blood Clots
Blood clots in the leg, known as deep vein thrombosis (DVT), are another possible complication after surgery. A clot can occasionally travel to the lungs and cause a pulmonary embolism, which is a medical emergency.
Seek urgent medical attention if you develop sudden shortness of breath, chest pain, coughing with blood, or significant difficulty breathing. New or unexplained swelling, warmth, or pain in one leg should also be reported promptly to your medical team.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Graft Failure or Re-Tear
The reconstructed ACL can stretch, partially fail, or tear again. This may occur because of a new injury, inadequate biological healing, excessive loading before adequate recovery, or other factors.
A new ACL injury can happen during sports involving pivoting, cutting, jumping, or sudden changes in direction. Returning to these activities before adequate strength and functional control have been restored may increase the risk of injury.
Graft failure does not necessarily mean that the original surgery was unsuccessful. Some failures occur because of a subsequent traumatic event or other factors that develop after reconstruction.
Knee Instability After Surgery
One of the main purposes of ACL reconstruction is to restore knee stability. If the reconstructed knee continues to feel unstable or repeatedly gives way, further assessment may be necessary.
Persistent instability can be associated with graft problems, inadequate rehabilitation, additional knee injuries, or other factors affecting knee mechanics.
Arthrofibrosis and Loss of Motion
Arthrofibrosis refers to excessive scar tissue formation that can restrict knee movement. It is an uncommon complication but can significantly affect recovery when it develops.
Early attention to swelling, restoration of knee extension, appropriate movement, and rehabilitation can help address factors associated with postoperative stiffness. Persistent loss of motion should be evaluated by the treating team.
Problems at the Graft Harvest Site
The risk of donor-site symptoms depends partly on which graft is used.
- Patellar tendon graft: May be associated with anterior knee pain or discomfort when kneeling.
- Hamstring graft: Can be associated with temporary or persistent hamstring weakness or discomfort.
- Quadriceps tendon graft: May temporarily affect quadriceps strength and cause discomfort around the harvest site.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Nerve or Blood Vessel Injury
Nerves and blood vessels around the knee can rarely be injured during surgery. Nerve irritation or injury may cause numbness, tingling, altered sensation, or weakness. Significant vascular injury is uncommon but can be serious.
Any new or worsening loss of sensation, unusual weakness, or changes in circulation should be promptly reported to your medical team.
Meniscus and Cartilage Problems
ACL injuries can occur alongside meniscus or cartilage damage. If these injuries are present, they may influence both treatment and recovery.
Even after successful ACL reconstruction, some patients can develop further meniscal or cartilage problems, particularly if the knee sustains another injury. Repeated instability may also place additional stress on structures inside the knee.
Anterior Knee Pain
Some people experience pain around the front of the knee after ACL reconstruction. This may be related to the graft harvest site, particularly when a patellar tendon graft has been used, but anterior knee symptoms can have other causes as well.
Pain during kneeling, stairs, squatting, or other activities should be discussed with your rehabilitation team if it persists or interferes with recovery.
What Increases the Risk of Complications?
Complications can occur even when surgery and rehabilitation are appropriately managed. However, certain factors may influence the risk or recovery process.
- Additional meniscus, cartilage, or ligament injuries
- Previous surgery on the knee
- Limited knee movement before surgery
- Difficulty following postoperative rehabilitation restrictions
- Returning to demanding activities too early
- A new traumatic injury after reconstruction
- Individual medical or healing factors
Can ACL Reconstruction Complications Be Prevented?
Not every complication can be prevented, but following the postoperative plan can help support recovery and reduce avoidable risks.
This includes following instructions about wound care, medication, weight-bearing, exercises, brace or crutch use, and progression of physical activity. Attending follow-up appointments also allows your medical team to identify problems early.
Rehabilitation should progress gradually. Even when pain has improved, the knee may not yet have recovered enough strength and control for running, jumping, pivoting, or competitive sports.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
The Bottom Line
ACL reconstruction can successfully restore knee stability for many patients, but recovery involves potential risks ranging from temporary pain and weakness to less common complications such as infection, blood clots, significant stiffness, or graft failure.
Understanding these risks does not mean that complications are expected. Following the postoperative instructions, progressing through rehabilitation appropriately, attending follow-up appointments, and reporting concerning symptoms promptly can help support a safe recovery.
Your individual risk profile depends on your knee injury, graft choice, associated injuries, surgical procedure, and personal health factors, so these considerations should be discussed with your orthopedic team before and after surgery.
