My favorite emails to write are the ones where I explain what I thought was wrong.
In this case, I thought a patellar clunk (in the context of TKA) happened when you increased the Q angle and created patellar maltracking. But apparently nah, it’s a whole other thing.
What I learned today
Patellar clunk syndrome (PCS) is a complication of posterior-stabilized TKA wherein patients develop a fibrous nodule at the proximal pole of the patella. This scar tissue catches on the box of the femoral component, causing a “clunk.”
The clunk typically occurs at ~30-40° from full extension. Symptoms are noted when climbing stairs or rising from a chair and typically present 7-12 months after TKA.
→ What are some identified [component] risk factors for PCS?
shortened patellar length
smaller patellar or femoral component
decreased patellar composite thickness
increased posterior femoral offset
flexed femoral component
thicker tibial polyethylene insert
→ What are some patient-specific risk factors for PCS?
preop patella baja
valgus alignment
decreased patella thickness and/or length
Treatment consists of arthroscopic (vs. open) resection of the fibrous nodule.
In the article by Costanzo et al, 75 knees (68 patients) out of 2713 primary TKAs were diagnosed and treated arthroscopically for PCS (incidence of 2.76%). The post-op WOMAC and SF-12 scores of the clunk patients were not statistically different from controls after arthroscopic resection.
So yeah, now we both know.
Sources
Costanzo JA, Aynardi MC, Peters JD, Kopolovich DM, Purtill JJ. Patellar clunk syndrome after total knee arthroplasty; risk factors and functional outcomes of arthroscopic treatment. J Arthroplasty. 2014 Sep;29(9 Suppl):201-4. doi: 10.1016/j.arth.2014.03.045. Epub 2014 May 24. PMID: 25034884.
Orthobullets Patellar Clunk Syndrome