Extremes of cement mantle thickness associated with increased incidence of radiolucent lines in total knee arthroplasty

Introduction The optimal thickness of the cement mantle in cemented total knee arthroplasty (TKA) has been proposed to be 3–5 mm. This study aims to assess the association between cement mantle thickness in TKA and radiolucent lines (RLLs). A secondary objective was to investigate the significance of cement penetration into the anterior tibial pin tracks. Methods 100 primary TKA performed by five surgeons in the total joint replacement team were included from 2017–2018. Initial postoperative radiographs were assessed to measure the cement penetration at the tibial component at different zones according to the Knee Society Scoring System and the presence of cement penetration into pin tracks. Postoperative radiographs at 2 years were evaluated for RLLs at each zone. Results TKA were grouped by cement mantle thickness into <3 mm, 3–5 mm and >5 mm. There was a significantly higher incidence of RLLs at the implant–cement junction from the <3 mm cement thickness group at the anteroposterior Zone 6, corresponding to the distal end of the tibial keel/stem. Five out of 12 patients (41.7%) had RLL in the <3 mm group, compared to 7 out of 64 (10.9%) in the 3–5 mm group and 2 out of 24 (8.3%) in the >5 mm group ( p = .003). At the other zones, there was no difference in RLL around the tibial tray in the different cement thickness groups. In the different cement thickness groups, there were no significant differences in the incidence of pin track cement penetration. Conclusion Below the tibial tray, there were no differences in RLLs between the cement thickness groups, which may challenge the importance placed on the accepted optimal cement thickness of 3–5 mm. However, at the tip of the tibial keel/stem, a cement thickness of >3 mm for TKA is suggested, which was associated with less RLL.