Knee replacement surgery is generally considered a safe and successful procedure for people with severe knee damage, particularly when pain, stiffness, and reduced mobility are no longer adequately controlled with non-surgical treatment. Like any major operation, however, it carries some risks.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Most people recover without a major complication, but understanding the possible problems can help you recognise warning signs early and have a realistic idea of recovery. Some complications occur shortly after surgery, while others may develop months or years later. Learn more about the procedure itself in our Knee Replacement Surgery guide.
What Are the Risks of Knee Replacement Surgery?
The risks can broadly be divided into complications related to the operation and anaesthesia, early postoperative problems, and issues that may affect the artificial knee over time. Possible complications include:
- Blood clots in the leg or lungs
- Wound or deep joint infection
- Bleeding or blood collection around the wound
- Persistent pain or swelling
- Knee stiffness or reduced movement
- Nerve, blood vessel, or surrounding tissue injury
- Knee instability
- Problems with the position, wear, or loosening of the implant
- Fracture around the artificial joint
- The need for additional surgery or revision knee replacement
Short-Term Complications After Knee Replacement
Blood Clots
A deep vein thrombosis (DVT) can develop in the veins of the leg after surgery. In some cases, part of the clot can travel to the lungs, causing a pulmonary embolism (PE), which can be serious.
Because knee replacement temporarily reduces mobility, measures to lower clot risk are an important part of recovery. Depending on your individual risk, these may include early movement, exercises, compression devices or stockings, and blood-thinning medication.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Infection
An infection can develop around the surgical wound or, less commonly, deeper around the artificial joint. A superficial wound infection may respond to antibiotics, while a deep infection involving the implant can require additional surgery as well as prolonged antibiotic treatment.
Infection can occur soon after surgery, but an artificial joint can also become infected later in life. Increasing pain, redness, swelling, wound drainage, fever, or feeling generally unwell should be assessed promptly.
Bleeding and Haematoma
Some bleeding is expected during and after knee replacement surgery. Occasionally, blood can collect under the skin or around the surgical area, forming a haematoma. Most cases can be managed without major intervention, but significant bleeding may occasionally require further treatment.
Swelling and Bruising
Swelling around the knee and leg is common during the early recovery period. It can fluctuate with activity and may take weeks or months to gradually settle. Elevation, appropriate exercises, walking, and following the rehabilitation plan can help manage postoperative swelling.
Problems That Can Affect Knee Movement and Comfort
Knee Stiffness
Some stiffness is expected after surgery, but excessive or persistent stiffness can interfere with everyday activities. Rehabilitation and regular exercises are important for restoring movement.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
In a small number of patients, significant stiffness may continue despite physiotherapy and may require additional treatment. The likelihood of achieving good movement also depends partly on the condition and movement of the knee before surgery.
Persistent Pain
Pain is normal during the early stages of recovery, but it should gradually improve. A small proportion of patients may continue to experience pain after the initial healing period.
Persistent pain does not always mean that the implant has failed. Doctors may need to investigate several possible causes, including infection, implant loosening, instability, alignment problems, or other conditions affecting the knee or surrounding tissues.
Knee Instability
The artificial knee is designed to provide stability during standing and walking. In some patients, however, the knee may feel unstable or give way.
This can be related to the soft tissues around the knee, implant positioning, ligament balance, or changes that develop over time. Depending on the cause and severity, treatment may range from physiotherapy and observation to further surgery.
Nerve, Blood Vessel and Surrounding Tissue Injury
Nerves, blood vessels, ligaments, and other tissues are located around the knee. Although injury to these structures during knee replacement is uncommon, it is a recognised surgical risk.
Nerve irritation or injury may cause numbness, altered sensation, weakness, or other symptoms. Some numbness around the surgical scar can also persist even when the operation itself has been successful. Significant blood vessel injury is uncommon but requires prompt medical attention if it occurs.
What Can Happen to a Knee Replacement Over Time?
A knee replacement is designed to provide long-term pain relief and improved function, but the artificial components are not immune to wear or other mechanical problems.
Implant Wear
The materials used in the artificial joint can gradually wear with use. Small particles produced by wear may contribute to inflammation and changes around the implant.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Loosening of the Implant
Over time, an implant may become loose from the bone. This can cause increasing pain or reduced function and may eventually require revision surgery.
Fracture Around the Implant
A fracture can occasionally occur in the bone surrounding a knee replacement, particularly after significant trauma. Treatment depends on the location and severity of the fracture and the stability of the implant.
Instability or Implant Position Problems
Changes in the soft tissues or mechanical relationship between the implant components can sometimes cause instability or difficulty using the knee comfortably. Some cases can be managed conservatively, while others may require revision surgery.
When Might Revision Knee Replacement Be Needed?
Revision surgery means removing and replacing some or all of the existing knee replacement components. It is not routinely required simply because a person has had a knee replacement for many years. Revision may become necessary when there is a significant problem such as:
- Deep infection
- Significant implant loosening
- Severe wear
- Persistent instability
- Fracture around the implant
- Other mechanical failure of the artificial joint
Modern knee replacements can last for many years, but their longevity varies between individuals. Activity level, implant factors, bone quality, age, and other medical considerations can all influence how long a replacement remains functional.
Who May Have a Higher Risk of Complications?
Knee replacement complications cannot always be predicted, but certain health and lifestyle factors may increase risk. These can include:
- Poorly controlled diabetes
- Smoking
- Significant excess body weight
- Existing heart, lung, kidney, or circulation problems
- Previous blood clots
- Reduced mobility before surgery
- Previous surgery around the knee
- Other conditions that affect wound healing or infection risk
How Are Knee Replacement Complications Reduced?
Risk reduction begins before the operation rather than only after it. Your medical team may review existing health conditions, medications, mobility, blood tests, and other factors that could affect surgery or recovery.
After surgery, early movement and prescribed physiotherapy help restore mobility and can reduce complications associated with prolonged inactivity. Measures to prevent blood clots, appropriate wound care, pain management, and follow-up are also important parts of recovery.
Following the rehabilitation plan does not guarantee that complications will not occur, but it can support safe recovery and help identify problems when they arise.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
The Bottom Line
Knee replacement surgery can significantly reduce pain and improve mobility, but it is still a major operation with potential complications. Most patients recover without a major problem, while issues such as temporary swelling, pain, and stiffness are part of the normal healing process.
The more important complications—such as deep infection, blood clots, significant nerve or blood vessel injury, implant loosening, instability, or fracture—are less common but can require additional treatment. Knowing the warning signs and following the recommended rehabilitation and follow-up plan can help support a safer recovery.
Your own risk profile matters more than a general list of complications. Before surgery, your orthopaedic and medical teams can assess your health, identify factors that may increase risk, and explain which precautions are appropriate for you.
