What are signs that a knee replacement is wearing out or failing?
Executive summary
Persistent or worsening pain, swelling or warmth, instability or a new limp, limited range of motion (stiffness), and new grinding/clicking are the most commonly reported signs that a knee replacement may be failing (see University of Utah Health; HSS; Colorado Advanced Orthopedics) [1] [2] [3]. Causes commonly cited across sources include infection (early failure), aseptic loosening and wear of components (later failure), and mechanical problems such as malalignment or broken parts — each requiring clinical assessment and imaging to confirm [4] [1] [5].
1. What patients report first: pain, swelling and loss of function
Doctors and clinics list persistent or worsening pain as the most frequent early complaint — pain that doesn’t follow the expected recovery pattern or returns after a period of improvement — often accompanied by swelling or reduced ability to walk or perform daily tasks [2] [3] [5]. University of Utah Health specifically groups worsening knee function, pain, swelling and weakness/instability as common symptoms of loosening or instability [1].
2. Signs that point to infection versus mechanical failure
Redness, warmth and increasing swelling around the joint suggest infection and are emphasized repeatedly as urgent warning signs that need rapid evaluation [6] [3]. By contrast, sensations of instability (knee “giving way”), grinding, clicking, new or worsening limp, and a progressive loss of range of motion more commonly point to mechanical problems: loosening of components, wear of the plastic spacer, malalignment, or a fractured implant [7] [5] [8].
3. Imaging and exams: how clinicians confirm problems
Clinical examination looking for instability, decreased motion or focal tenderness is the first step; imaging (X‑rays, CT, sometimes advanced imaging) is vital to find loosening, wear, malposition or broken components and to plan revision surgery if needed [5] [9]. The literature and specialist sources stress that some failures show clear radiographic signs (loosening, component migration), while others — especially chronic unexplained pain — may have normal images and still lead to revision [4].
4. Timing matters: early vs late failures and likely causes
Prosthetic joint infection is the most common reason for early failure (noted as a major cause of early revisions in registry data cited in the surgical-review literature), while aseptic loosening and wear become dominant reasons for revision later on [4]. Sources note that implants generally last many years, but younger or more active patients, high body weight, malalignment, or recalled/defective devices can accelerate failure [1] [10] [8].
5. When symptoms are subtle: persistent pain without clear cause
Clinical reviews document that a meaningful proportion of revisions are performed for persistent, unexplained pain even when X‑rays and other tests show no obvious mechanical failure; between 12% and 18% of revised total knee replacements list pain as a reason in registry summaries cited by the surgical literature [4]. That means normal imaging does not rule out an important problem — specialist assessment matters.
6. Device issues and recalls: a separate signal to monitor
Reporting from legal/advocacy and clinic sites highlights that defective implants or packaging (for example, certain recalled devices) can prompt premature loosening, cracking or early wear; patients with known recalled prostheses are often advised to be monitored more closely [11] [10]. Sources recommend seeing a provider promptly if symptoms appear, especially for patients with known problematic devices [10].
7. What to do: practical next steps and limits of available reporting
If you have new or worsening pain, swelling, warmth, instability, stiffness, or a new limp after a knee replacement, seek orthopedic assessment; clinicians will perform a physical exam, order imaging and, if infection is suspected, laboratory tests — and may recommend revision surgery depending on findings [2] [5]. Available sources do not provide a single diagnostic checklist that guarantees a failing implant; they emphasize variable presentations and the need for individualized evaluation [4].
Limitations and competing perspectives: sources agree on core warning signs but differ in emphasis — some clinics emphasize warmth/redness (infection) while registries and surgical reviews underline that aseptic loosening and unexplained pain are major reasons for revision later on [6] [4]. All sources stress that definitive diagnosis requires clinical assessment and imaging; none in the provided set gives a sole, definitive symptom or time threshold that proves failure [1] [5] [2].