Aim

This study aimed to investigate the short-term clinical results after the cementless total knee arthroplasty (TKA) and assess whether there was any relationship between the changes of the bone mineral density (BMD) around the TKA components and clinical results.

Materials And Methods

This study included 17 patients (14 women and 3 men) who were diagnosed with osteoarthritis (16 patients) or rheumatoid arthritis (1 patient), and subsequently underwent Attune cementless CR mobile-bearing TKA. The postoperative anteroposterior radiographs of the knee joint were converted into the 256-level grayscale images in which the density value of the air around the knee was 0 and that of the center of the femoral components was 255. The five regions of interest were defined around the tibial component (proximal medial (M1), distal medial (M2), proximal lateral (L1), distal lateral (L2), diaphysis (D)), and the average density of each ROI was obtained using image analysis software as a substitute for the BMD measurement. Then, the relative densities based on the density immediately after surgery were calculated for each ROI at 6,12 months after surgery. This measurement was performed twice with an interval of 2 weeks or more, and the average values were used for the analysis. Furthermore, the intraclass correlation coefficients (ICC) were evaluated for each ROI. The pre-operative and post-operative hip-knee-ankle (HKA) angle was measured from anteroposterior radiographs. The range of motion (ROM) of the operated knee and the 2011 Knee Society Score (2011 KSS) were used for the clinical evaluation. Friedman’s test was performed to analyze the BMD changes of each ROI. Spearman’s test was performed to analyze the correlations between relative density values and 2011 KSS scores. Paired t-test was used to compare the pre-and post-operative HKA angle. Statistical significance was set at p<0.05.

Results

There was no complication, and the ROM and 2011 KSS were significantly improved at 12 months after surgery, respectively (p<0.05). The HKA angle was significantly changed after surgery from -10.1 to -0.85 degrees(p<0.001). The ICCs of the relative density of each ROI were 0.99, 0.97, 0.94, 0.96, and 0.94 for M1, M2, L1, L2, and D, respectively. The largest change in relative density was seen at M1, decreasing by 13% and 10% at 6,12 months after surgery (p=0.012, 0.017). A similar change was seen at M2, decreasing by 8.8% at 6 months (p<0.001), but significantly improved toward 12 months (p=0.04). The relative densities at L1, L2 showed significant negative correlations with the 2011 KSS subscale “symptoms” at 12 months after surgery (L1:r=-0.30, p=0.014, L2:r=-0.36, p=0.023)

Conclusion

The short-term clinical result was good after cementless CR mobile-bearing TKA. It was suggested that the BMD around the tibial component was associated with postoperative pain.