Systematic review of the etiology behind patellar clunk syndrome

Total knee arthroplasty is one of the most successful operations performed worldwide today. Patellar clunk syndrome (PCS) is a postoperative complication that arises due to the development of a fibrous nodule along the undersurface of the quadriceps tendon. The current literature on PCS has not yet come to a consensus regarding its etiology. To date, this is the first study that analyzes the existing literature on PCS in order to generate a conclusion regarding its etiology. It is hypothesized that prosthesis design is the main component behind the development of PCS.

To determine the etiology of PCS and its association with pre and post-operative characteristics of the prosthesis and native knee.

We conducted a systematic review according to the PRISMA guidelines by searching through PubMed, Cochrane, and Google Scholar from May-July 2018 for cases of PCS using search MeSH terms "patella OR patellar" AND "clunk" OR "catch" OR "crepitus". The search included case series and clinical trials and excluded review articles, yielding 30 articles from the original search and 3 additional articles from reference lists. We extracted data upon the outcomes in patients afflicted with PCS to determine the etiology of PCS. We performed additional bias assessments to validate our search algorithm and results.

Prosthesis design was the metric most frequently implicated in the incidence of PCS, though several other metrics were contributory toward its pathogenesis. Later prosthetic designs incorporate a reduced intercondylar box ratio and box width to reduce contact between the proximal patellar pole and the intercondylar box, thereby reducing incidence of PCS.

The etiology of PCS is multifactorial, owing to the growing metrics that have associations with its incidence. This conclusion is validated by the significance of prosthesis design as the most likely parameter involved in developing PCS since different prosthesis designs are often the result of different parameters. Future studies should be directed at isolating individual prosthetic parameters of prosthesis designs in order to determine what permutation of parameters is most closely associated with the development of PCS.