Patellar Clunk Syndrome: A Systematic Review of Risk Factors and Treatment.

Background: Patellar Clunk Syndrome (PCS) is a known complication of total knee arthroplasty (TKA). Prior studies have identified multiple risk factors for PCS, including male sex, patellar size, and implant design. Previous literature suggests surgical intervention as the preferred treatment for PCS. No review to date has systematically assessed risk factors and treatment outcomes of PCS. Methods: Following PRISMA protocol, 4 online databases were searched for English language studies published during or after the year 2000 that reported PCS as a primary outcome of TKA and identified (1) risk factors for developing PCS and/or (2) outcomes following treatment. The methodological quality of studies was assessed using the Newcastle-Ottawa Scale (NOS). The following outcomes were collected and reported: demographic information, overall PCS complication rate, risk factors, treatment plans, and treatment outcomes. Results: The initial search yielded 699 articles. A total of 316 articles underwent full-text review; 24 articles were ultimately included and analyzed. Nineteen articles assessed risk factors, 2 assessed treatment outcomes, and 3 assessed both. Of the articles assessing risk factors, 9 (41%) reported specific implants, 3 (16%) reported mobile-bearing design, and 2 (9%) reported posterior stabilized (PS) design. Additional risk factors identified include retained patella, smaller patellar thickness, and higher postoperative knee flexion. Five articles assessed arthroscopic treatment for PCS, and all demonstrated satisfactory outcomes. Conclusions: Risk factors for developing PCS include implant design, implant type, retained patella, patellar thickness, and higher postoperative flexion. Other risk factors were not supported by multiple studies. Arthroscopic treatment has strong evidence for improving functional outcomes in patients with symptomatic PCS.