Central Bone Mineral Density Is Not a Useful Tool to Predict Bone Strength of the Distal Femur for Cementless Total Knee Arthroplasty

Background: The increasing prevalence of cementless total knee arthroplasty (TKA) necessitates a reliable assessment of bone quality. Central bone mineral density (BMD), measured by dual-energy x-ray absorptiometry (DEXA) in the lumbar spine and hip, is conventionally used to estimate bone quality. However, its effectiveness in predicting the actual bone strength at the knee, which is crucial for cementless TKA, is under scrutiny. This study investigated the relationship between central BMD and actual bone strength at the knee. Methods: This prospective study included 191 knees undergoing standard posterior-stabilized TKA between November 2021 and March 2023. Central BMD was assessed 3 months before TKA, and the failure load of bone fragments collected during box preparation was directly measured using an indentation test. Relationships between central BMD and failure load as a measure of the actual bone strength at the knee were analyzed. Results: Linear regression analysis revealed a weak correlation between central BMD and the actual bone strength at the knee (R² = 0.146 in all patients; < 0.001 in osteoporosis group; 0.126 in non-osteoporosis group). The correlation suggested by the regression models was particularly insignificant in the osteoporosis subgroup, showing that central BMD is not a reliable predictor of bone strength for cementless TKA. Conclusions: Central BMD measurements have limited utility in accurately predicting the real bone strength at the knee for cementless TKA. This study highlights the need for more specific and direct methods of assessing bone quality at the knee to ensure the success of cementless TKA.