After knee replacement surgery, many older adults get a fright the first time they bend and straighten the leg, and the family members caring for them become anxious too. The knee gives a "click" with the slightest movement, and sometimes a "clunk" when standing up from a chair. Is the new joint badly fitted, or has it been damaged? This worry is especially common during the swelling phase.
To answer the family's concern directly: clicks and clunks from the knee after replacement are, in the great majority of cases, normal mechanical sounds. They come mainly from metal contacting plastic components and from scar tissue sliding, and they fade as swelling settles and strength returns. If the noise comes with pain, swelling, instability, catching or giving way, an orthopaedic review should be arranged promptly (Cozzarelli 2023; Taniguchi 2020). The sections below explain which noises are normal and which situations need attention.
Are noises from an artificial knee normal?
Hearing grinding, popping, clicking or clunking after surgery is quite common and is not a rare abnormality. A large cohort study compared robotic-arm-assisted surgery with conventional surgery and found that nearly 40% of patients in both groups reported noises, with no significant difference between them. This suggests that noise has little to do with the surgical method and is more a built-in feature of artificial joints (Cozzarelli 2023).
A noisy joint does not mean a problem.Research shows that these noises have little effect on joint awareness and on self-rated recovery. Even when the joint makes noise, satisfaction stays high as long as the older adult's range of movement and daily function are good, so noise and satisfaction are only weakly related (Taniguchi 2020). The family should therefore watch for whether there is also pain, swelling, catching or instability, and not for whether there is a noise.
Why an artificial knee makes noise
Once the family understands where the noise comes from, there is no need to worry too much. Noises from an artificial knee come mainly from three harmless factors, all of which are normal as the new joint and the surrounding soft tissues adapt to each other (Conrad 2014; Sequeira 2020).
These noises are mostly a mechanical effect of the "interface plus soft tissue" and do not indicate a loose implant. If the family also wants to check whether swelling, pain and numbness around the wound are normal, they can go back to the parent article on swelling, pain and the wound after knee replacement.
Telling three common noises apart: clicking, crepitus and clunking
When an older adult says the knee "makes a noise", this covers several different kinds of sound. Clinically they fall broadly into two types. One is an even, mild mechanical sound that comes with movement. The other is a "clunk" that pops suddenly at a particular angle. Once the family can tell them apart, they know whether any action is needed (Conrad 2014; Yau 2003).
- Clicking: a single crisp sound on bending or straightening, from the component interface
- Crepitus (crunching): a continuous, mild rubbing feeling, from the patellofemoral groove
- Mostly painless, with no catching, and reducing as swelling settles and strength returns
- Patellofemoral crunching is more common than a clunk, and a good proportion improves with conservative treatment
- Clunk (a pop): a sudden "clunk" as the knee straightens to a certain angle
- Seen mostly in posterior-stabilised (PS) knee replacements, from a scar nodule (Yau 2003)
- A clunk that is painless and without catching can still just be watched
- Further assessment is needed only if there is pain, catching or loss of function
Understanding patellar clunk (patellar clunk syndrome)
Of all the noises, "patellar clunk" (patellar clunk syndrome) is the one most often mentioned on its own. The mechanism is that a small fibrous nodule forms under the quadriceps tendon, near the upper pole of the kneecap. When the knee bends, the nodule catches in the intercondylar box of a posterior-stabilised (PS) femoral component. When the knee straightens to about 30 to 45 degrees, the nodule suddenly pops out and makes a "clunk" (Sequeira 2020). Research also points to implant design as one of the main factors. When the intercondylar box is made narrow enough, the rate of clunk is reduced significantly (Sequeira 2020).
Families can be reassured that this clunk is well known but not common. A systematic review covering 39,018 operations found an overall rate of patellar clunk syndrome of about 2.59%, ranging from 0% to 20% across studies. The wide range is due to differences in implant design and surgical factors (Hedeman 2026). Local data from Hong Kong agree with this. The orthopaedic team at the University of Hong Kong (Queen Mary Hospital) identified 27 patellar clunks (in 25 patients) among 236 consecutive PS total knee replacements, and found an association with a low-lying kneecap after surgery and with forward placement of the tibial tray (Yau 2003). This is also a reliable local peer-reviewed reference. A simple clunk that is painless and without catching usually needs only observation, and may not need special treatment.
How the noise changes over time
The most reassuring point for patients and families is that noise symptoms tend to fade with time, as swelling settles and strength returns, and do not get worse the longer they are left. Comparing patients at different times after surgery shows that time itself is an improving factor (Cozzarelli 2025; Conrad 2014).
In other words, even when an older adult has a noisy knee in the first year after surgery, if there is no pain and the range of movement is good, the noise is likely to fade gradually as recovery progresses. Patients and families do not need to panic or stop daily activities because of the noise.
Warning symptoms that need medical attention
The mechanical noises above are mostly part of a normal recovery path, but there is one situation that is the opposite. The family must treat it as a warning and take the older adult to an orthopaedic doctor for review promptly. What matters is whether the noise comes together with the following symptoms (Taniguchi 2020; Costanzo 2014).
- Clear or persistent pain at the time of the noise
- Repeated swelling in the same place that does not go down for a long time
- The joint feels caught, locked or unable to move
- The knee suddenly gives way when walking, with a feeling of being unable to stand steadily
- A noise that was not there before suddenly appears many years after surgery
- If it is only an ordinary mechanical noise, painless and without catching, the family can observe first and let the older adult continue the exercises as usual.
If a clunk comes with pain or catching, it needs further examination. Once patellar clunk causes pain or catching, or affects daily life, it should not be left to improve by itself. The medical literature describes ways of managing this situation (Costanzo 2014). Whether treatment is actually needed, and what kind, should be decided by the orthopaedic doctor. Patients and families should not just put up with it, and should report it to the doctor early.
How physiotherapy improves joint tracking and noise
For mechanical noises without red-flag symptoms, physiotherapy works on how smoothly the joint moves, and does not try to silence the noise directly. Once the older adult's strength returns, the kneecap tracks better and compensating movements while walking reduce, many of the clicks heard on walking fade by themselves (Conrad 2014).
- Quadriceps training—Straight leg raises, seated knee extensions and small wall squats help the patient rebuild the quadriceps at the front of the thigh. With stronger thigh muscles the kneecap slides more steadily in the groove, and there is less crunching from uneven sliding.
- Restoring range of movement—Gradually restoring knee bending and straightening softens scar tissue and the surrounding soft tissue. When the tissues slide more smoothly, there is less rubbing and popping on bending and straightening.
- Gait re-education—Some older adults, from fear of pain or lack of strength, unconsciously favour the operated leg when walking. Physiotherapy corrects these walking patterns so that weight goes evenly through both legs, and abnormal noises when walking reduce as well.
Rebuilding quadriceps strength is the main thread of the whole recovery process. If the patient is still in the swelling phase, and the family wants to know how to help rebuild strength step by step, see the page on numbness around the wound and recovery of sensation, which covers the pace of recovery of both sensation and strength. For the overall progress from surgery to returning to daily activities, see returning to daily activities after knee replacement.
How home physiotherapy in Hong Kong follows up knee noises after knee replacement
In Hong Kong, home recovery after knee replacement in older adults has its own environmental needs. When a therapist providing home physiotherapyvisits, the therapist observes at the patient's home at which moment the knee makes noise when moving from sitting to standing and when going up and down stairs. The therapist can then sort on the spot whether it is a bending mechanical noise, a patellar tracking noise, or a red-flag warning with pain or catching. This kind of professional sorting during real daily movements is far more accurate than the patient and family guessing from phone videos.
For home training, the therapist demonstrates straight leg raises, small wall squats and seated knee extensions to train the quadriceps and range of movement, to reduce noise that comes from abnormal kneecap tracking and compensated walking during the swelling phase. The therapist also advises the family to add handrails and non-slip mats in the bathroom and by the bed, so that the older adult does not move less out of fear of joint noise. Moving less leads to weaker muscles and more noticeable noise, which becomes a vicious circle. At the first home assessment after knee replacement, the patient and family often worry most about "noise when the knee moves". Explaining clearly which noises need attention is more effective in reducing anxiety than a general word of comfort.
The registered physiotherapists at Nova Health visit patients at home to sort knee noises after replacement. If the noise is a painless click or crunch that appears during the swelling phase and reduces with activity, the therapist explains to the patient and family that it is a normal mechanical sound and teaches them how to monitor it themselves. If the noise comes with pain, swelling, catching or giving way, or is a new noise that appears many years after surgery, the therapist recommends an orthopaedic review straight away. For local resources, families can also refer to the Chinese entries on total knee replacement on the public information platform of the Hong Kong College of Orthopaedic Surgeons (香港骨科醫學院) (www.orthoinfo-hkcos.org) and the Hospital Authority's information on total joint replacement (www.ha.org.hk) as a reference for care after surgery.