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Can you injure a knee replacement? You can. A replaced knee is strong, but it is not immune to injury. Falls, fractures, infection, loosening, or joint instability can still cause problems. These issues may appear soon after surgery or many years later.
A fracture near a knee implant is called a periprosthetic fracture. It may involve the thigh bone, shin bone, or kneecap. Risk is higher in people with weak bones, osteoporosis, or a history of falls.
This type of fracture affects the thigh bone near the implant. Doctors look at the break itself and check whether the knee replacement is still secure.
A stable fracture may heal with a brace and limited weight-bearing. More severe breaks often need plates, screws, or a rod. Revision surgery may be needed if the implant has come loose.
A tibial periprosthetic fracture affects the shin bone below the knee replacement. Bone strength, fracture location, and implant stability all affect treatment.
Some stable breaks can be managed with bracing. More serious fractures may need surgery to repair the bone or replace part of the implant.
Kneecap fractures after knee replacement are uncommon. They may happen after a fall or develop when the bone becomes weak.
Some can heal with a brace. Surgery may be needed if the implant is loose or the knee cannot straighten as it should.
Problems can still develop after a knee replacement has healed. Pain, swelling, warmth, stiffness, weakness, or a knee that gives way are signs to take seriously.
Clicking or popping does not always mean something is wrong. Some people hear these sounds as the metal and plastic parts move.
Noise without pain is often less concerning. Painful clicking, locking, or a knee that feels unstable should be checked.
A certain amount of pain is expected after surgery. For many patients, the biggest improvements happen over the first few months.
Pain becomes more concerning when it gets worse, returns after improving, or limits daily movement. Infection, loosening, fracture, or instability may be behind it.
Stiffness is common early in recovery. Regular movement and physical therapy usually help improve flexibility.
If stiffness lasts or gets worse, there may be another cause. Scar tissue, swelling, infection, or implant position can all affect motion.
Nerve injury after knee replacement is uncommon. It may cause numbness, tingling, weakness, or trouble lifting the foot.
Recovery is not the same for everyone. Some people improve within months, while others need more time.
Knee surgery can sometimes stretch or put pressure on nearby nerves. New weakness or lasting numbness should be reported to the surgeon.
Most knee replacements reduce pain and make movement easier. Still, problems can happen after surgery, and some may require another procedure.
| Problem | Possible warning signs |
| Infection | Redness, warmth, drainage, fever, worsening pain |
| Loosening | Pain while walking, swelling, reduced function |
| Instability | Buckling, shifting, or giving way |
| Fracture | Sudden pain after a fall or injury |
Infection may develop soon after surgery or much later. The American Association of Hip and Knee Surgeons reports infection in about 1% to 2% of first-time joint replacements.
Treatment depends on how long the infection has been present and whether the implant is secure. Some patients need surgical cleaning. Others need part or all of the knee replacement changed.
A knee implant can loosen over time. Wear, bone loss, infection, or poor fixation may all contribute.
Pain with standing or walking is one possible warning sign. Doctors usually begin with knee X-rays.
CT or MRI may be used when more detail is needed. Blood tests and joint fluid testing can also help rule out infection.
Instability means the knee no longer feels steady. It may buckle, shift, or feel as though it might give way.
Ligament problems, implant position, or wear can cause this. Treatment may include therapy, bracing, or revision surgery.
A fracture can happen during surgery or years later. Falls are a common cause, especially when bones have become weak.
Treatment depends on the location of the break and whether the implant is still stable. Some fractures can be repaired, while others need revision surgery.
The phrase “implant rejection” can be misleading. Knee implants are not rejected in the same way as transplanted organs.
The better term is metal hypersensitivity. It is rare, and doctors usually rule out infection, loosening, and instability first.
A knee replacement can develop trouble long after the first recovery period. Wear, loosening, infection, fractures, and instability are all possible.
New pain should not be brushed off just because the implant is old. An orthopedic exam and imaging can help show what is happening.
Revision surgery may replace one part of the implant or the full knee replacement. Physical therapy often starts soon after surgery and can continue for several months. Swelling may also last for three to six months.
Revision surgery removes and replaces part or all of the old implant. The surgeon may also repair damaged tissue or areas of weak bone. Some patients need bone grafts, stems, or metal supports.
Treatment depends on where the bone broke and whether the implant stayed secure. Stable fractures may heal with bracing and limited weight-bearing. Others need plates, screws, rods, or revision surgery.
The American Association of Hip and Knee Surgeons reports infection in about 1% to 2% of first-time joint replacements. The risk is higher after revision surgery. Health conditions and past infections can also affect a person’s risk.
There is no single recovery timeline. Some patients need physical therapy for around three months, while swelling may last three to six months. More complex revision surgery can take longer to recover from.
Doctors usually start with a physical exam and X-rays. CT or MRI may be added if the cause of pain is unclear. Blood tests or joint fluid tests may also be used to check for infection.
Yes. Wear, falls, infection, loosening, and instability can cause problems years after the original surgery. New pain, swelling, or trouble using the knee should be checked.
Knee replacements often work well for many years, but new problems can still come up. Pain, swelling, warmth, instability, or trouble walking deserve medical attention. Sunnyvale Sports Medicine and Orthopedic Center can examine your knee and explain the next steps. Schedule an appointment today to learn more.
