Cement mantle thickness in total knee arthroplasty more closely associated with tibial bone density than cement viscosity : findings from a randomized controlled trial.

Aims: The aims were to assess the influence of tibial bone mineral density (BMD) and cement viscosity on cement mantle thickness in total knee arthroplasty (TKA), and to determine whether BMD is a more dominant factor than cement viscosity in achieving optimal cement penetration.

Methods: A prospective, randomized controlled trial involving 117 knees from 130 patients undergoing primary TKA was conducted. Patients were allocated to receive either medium-viscosity cement (Group M) or high-viscosity cement (Group H). Cement mantle thickness was measured radiologically at predefined tibial zones using the Modern Knee Society Radiographic Evaluation System. Preoperative tibial BMD was assessed via CT-based quantification. Correlations between tibial BMD and mantle thickness were analyzed, and a cutoff tibial BMD value for achieving ≥ 2.1 mm mantle thickness was determined. This threshold was based on previous findings suggesting that a cement mantle thickness of at least 2.1 mm may help reduce the incidence of radiolucent lines around the tibial component.

Results: No significant differences in mantle thickness were observed between groups at peripheral zones. However, Group H showed significantly greater thickness at central zones (Zone 3 medial (M) (p = 0.001); Zone 3 lateral (L) (p = 0.001); Zone 3 anterior (A) (p=0.001); and Zone 3 posterior (P) ( p = 0.001). Strong negative correlations were found between tibial BMD and mantle thickness in both groups (r = -0.64 to -0.70). The cutoff tibial BMD value to achieve ≥ 2.1 mm mantle thickness was 78.4 HA/cm³. The intra- and inter-rater reliability of the radiological measurements were acceptable (interclass correlation coefficient 0.77 and 0.68, respectively).

Conclusion: Cement penetration beneath the tibial tray is more closely associated with tibial BMD than with cement viscosity. In patients with extremely dense bone, alternative fixation strategies such as cementless fixation or enhanced drilling should be considered.