A patellar clunk is an uncomfortable clunk noise (and feeling) around the patella, usually associated with certain types of knee replacement, and due to scarring above the patella.
Page updated July 2023 by Dr Sheila Strover (Clinical Editor)
What actually makes the clunk?
A clunk may be associated particularly with a posterior stabilised knee replacement. The sound (and symptom) may first appear about 7 months after the surgery and the noise usually happens when the knee extends. It is caused by a nodule of scar tissue which may develop at the back of the lower part of the quadriceps tendon, and which gets trapped as the patella engages the 'box' of the implant (which encloses the stabilising 'cam and post') - and then releases with a painful clunk.
Patients with pre-existing patella baja are at particular risk of developing patellar clunk syndrome after knee replacement.
Minimising the risk during initial surgery
The most important factor in this syndrome is the patellar tendon length, particularly if there is pre-existing patella baja. The surgeon is likely to try to remove less of the femur during surgery to tension the extension gap and minimise the risk of patellar tendon shortening. Also the patellar height seems to be important, and the surgeon will try to maintain adequate patellar height. Both of these measures may reduce the contact between the quadriceps tendon and the top of the intercondylar notch.
How is patellar clunk syndrome managed?
Surgery is generally required to fix the problem, although the patient may be sent to physiotherapy before surgery to strenthen the quadriceps and hamstrings muscles. Surgery is usually arthroscopic, during which the nodule of scar tissue is debrided and removed, resolving the problem.
Quick links
Peer-reviewed papers
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Quote:
"Patellar clunk syndrome....occasionally occurs after posterior stabilized total knee replacement....and is characterized by a painful palpable audible clunk of the patella when the knee moves from flexion to extension....[it] usually occurs between three and 12 months....[and is commonly due] to a prominent fibrous nodule formation at the junction of the proximal patellar pole and the articular aspect of the quadriceps tendon....[due to]....impingement of the undersurface of the tendon into the sharp anterosuperior edge of the intercondylar notch of the femoral component....Treatment....consists of non-operative measures, including physiotherapy and injections, and operative measures corresponding to either arthroscopic or open excision of the nodule...."
Citation: Chamseddine AH, Haidar I, Rahal MJ, Asfour A, Boushnak MO. < href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7732733/">Patellar Clunk Syndrome Following Posterior Stabilized Total Knee Replacement: Report of Two Cases. Cureus. 2020 Nov 11;12(11):e11435. doi: 10.7759/cureus.11435. PMID: 33324518; PMCID: PMC7732733.