Overlooked and underestimated: the prevalence and impact of mechanical cement-related complications in unicompartmental knee arthroplasty

BACKGROUND: This study aims to elucidate the prevalence, clinical manifestations, and potential risk factors of residual bone cement following unicompartmental knee arthroplasty (UKA) to inform effective diagnostic and therapeutic strategies. METHODS: This retrospective analysis included 321 patients from a single centre who underwent UKA. Residual bone cement was diagnosed using postoperative imaging and classified as residual cement extrusion (RCE) or free cement fragmentation (FCF). Patient data, including clinical records, laboratory findings, and selected management strategies, were collected to analyse risk factors for residual bone cement. The primary outcomes were the prevalence and clinical features of residual bone cement; secondary outcomes included risk factor identification and management outcomes. RESULTS: Residual bone cement occurred in 84 patients (26.16%), 66 (20.56%) of whom had RCE, and 18 patients (5.61%) had FCF. All RCE patients were asymptomatic or experienced only mild discomfort (66 in 66, 100%). Six patients with FCF required additional surgical intervention due to pain and/or impaired mobility. The thinner polyethylene insert emerged as a risk factor for postoperative residual bone cement (OR 2.59, 95% CI 1.38-4.98, p = 0.005). CONCLUSIONS: The prevalence of residual bone cement following UKA is notably higher than previously recognized. Residual bone cement occurred in 84 patients (26.16%) in our study. As CT was performed only in symptomatic patients, this figure likely represents a lower-bound estimate of the true prevalence. Although most patients with residual cement are asymptomatic, further surgery is needed when FCF causes consistent pain and affects joint function. Arthroscopic removal appears effective for fragments in symptomatic patients. A thinner insert is a risk factor for residual bone cement.