Two people can describe the same pain and have completely different problems. One may have infection. Another may have an unstable knee, a stiff joint, referred pain from the hip or a tendon problem. That is why revision planning begins with the story of the knee.
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When did the knee become painful?
A knee that never felt right after surgery raises different questions from one that worked well for ten years and then deteriorated. Pain from the beginning can relate to infection, alignment, instability, stiffness, nerve sensitivity or an unrecognised source outside the knee. A later change may point towards infection, loosening, wear, fracture or ligament failure.
Timing narrows the possibilities, but does not diagnose them. The location of pain, swelling, clicking, giving way, wound history and effect of walking all matter.
Infection must be considered
Joint-replacement infection is sometimes obvious, with fever, drainage or a hot swollen joint. It can also be quiet. Low-grade infection may present as persistent pain without dramatic illness.
Assessment commonly begins with examination, weight-bearing X-rays and inflammatory blood tests such as ESR and CRP. If infection remains possible, aspiration may be needed for cell count, differential and cultures. Results are interpreted together. Patients should not start, stop or time antibiotics for a planned aspiration without instructions from their treating clinician. [2]
Loosening and implant wear
A component can lose its stable bond to bone. The plastic bearing may wear, and the body's reaction to wear particles can contribute to bone loss. Serial X-rays are valuable because change over time is often more informative than a single recent film.
Not every line around an implant means loosening. The pattern, symptoms, earlier images and sometimes further imaging are needed before that label is used. [1],[3]
Instability, stiffness and alignment
An unstable knee may feel unreliable on stairs or when rising from a chair. The problem can appear only in a particular part of the movement. Examination helps the surgeon understand which ligaments and gaps are involved.
Stiffness may result from scar tissue, infection, component position, pain or several factors together. Alignment and rotation can also affect movement, tracking and balance. CT or other targeted imaging is requested only when it answers a specific question. [1],[3]
Clicking and swelling need context
A replaced knee is mechanical, and some clicking can occur as the components and soft tissues move. Noise without pain, swelling or loss of function is different from a new clunk with giving way. The examination determines whether the sound represents ordinary implant mechanics, tendon movement or instability.
Swelling can persist after an uncomplicated operation, but its timing and direction matter. A knee that is slowly becoming calmer is different from one that becomes newly hot and tense. Swelling may arise from the joint, soft tissues, infection, bleeding or a problem elsewhere in the leg.
Not every cause is inside the implant
Hip arthritis, spinal nerve irritation, vascular disease, tendon pain and regional pain conditions can all be felt near a replaced knee. Repeating surgery without finding the source may leave the original problem untouched.
Weakness and poor walking mechanics can also overload tissues around an otherwise stable replacement. A diagnostic injection or targeted local assessment may occasionally help separate competing causes, but no single test should be treated as a shortcut.
| Pattern | Questions it raises | Usual next step |
|---|---|---|
| Never comfortable | Infection, stiffness, balance, position or pain outside the knee | Full history, examination, standing X-rays and screening tests |
| New pain after a good period | Loosening, infection, wear, instability or fracture | Compare serial images and investigate the suspected cause |
| Giving way | Ligament or gap instability, weakness or neurological cause | Hands-on stability and strength assessment |
| Fever or drainage | Possible infection | Urgent local clinical assessment |
This table helps organise questions. It cannot diagnose the cause. [1]
What treatment might involve
Treatment follows the diagnosis. It may involve physiotherapy, pain management or care for a problem outside the knee. A defined implant problem may require a targeted component revision, full revision or a staged pathway when infection is present. Bone loss or instability can require stems, cones, augments or a more constrained implant.
Stiffness soon after primary surgery may be handled differently from stiffness that has existed for years. Infection treatment depends on timing, organism, fixation, tissues and medical health. A fracture may need fixation, revision components or both. This range is why “change the implant” is not a diagnosis. [1],[2]
What the common tests actually contribute
- Standing X-rays: show alignment, fixation, wear, fracture and the position of the components under load.
- Earlier X-rays: reveal change that a single image cannot show.
- ESR and CRP: help screen for inflammation but do not prove or exclude infection alone.
- Aspiration: may provide joint-fluid cell counts and cultures when infection is a concern.
- CT: can answer selected questions about component rotation, position or bone.
More tests are not automatically better. Each should be ordered because it can change the diagnosis or plan. [2],[3]
How pain location helps, and where it can mislead
Pain at the front of the knee can raise questions about kneecap tracking, tendon loading or stiffness. Pain at the side may come from a prominent component or irritated soft tissue. Pain on first standing can occur with loosening, but the same description can have other causes. Night pain and rest pain deserve attention, yet they do not prove infection.
These patterns guide the examination. They should not be used as a home diagnostic chart. The surgeon still needs to reproduce the symptom, assess stability and compare the findings with imaging and laboratory results.
Why the old operation record matters
The operation note and implant stickers identify the component design, size, fixation and bearing. That information can show whether a limited component exchange is mechanically possible and which extraction tools may be required. It also helps the surgeon interpret an X-ray that looks unfamiliar.
If records are missing, the reviewing team should help identify whether the original hospital, surgeon or implant supplier can provide them. Implant identification should not be guessed from a photograph.
A revision decision should answer four questions
- What is the most likely cause of the pain or failure?
- What evidence supports that diagnosis, and has infection been addressed?
- Which part of the proposed operation corrects that cause?
- What are the reasonable alternatives if the findings remain uncertain?
If those answers are unclear, another operation may be premature. A careful explanation is more valuable than a quick promise to replace the implant.
Patients seeking an overseas opinion should also ask whether the proposed treatment can be completed in one trip, what could turn it into a staged pathway and who will provide urgent examination after return. These practical answers belong beside the surgical explanation.
For a planned overseas opinion, the records guide explains what helps and how to handle gaps. Acute problems need local treatment first.
