Summary

The posterior tibial plateau offset shows high preoperative variability, significant pre- to postoperative change and is strongly correlated with sagittal tibial component malposition in patients undergoing total knee arthroplasty.

Abstract

Background

Sagittal boney knee morphology has a proven impact on knee biomechanics. Yet its variability and, consequently, its reconstruction in total knee arthroplasty (TKA) is underreported. The posterior tibial plateau offset (PTPO) is defined as the offset of the midpoint of the tibial plateau from the anatomical tibial axis in the sagittal plane. It is an important factor in when using stemmed tibial implants and avoiding posterior (popliteal) impingement. However, the variability of PTPO, its reconstruction, and its association with sagittal tibial component malposition among patients undergoing TKA is unclear.

Purpose

The purpose of this study was to report on the variability of the PTPO among patients undergoing TKA, its reconstruction, and its correlation with sagittal tibial component malposition.

Methods

Pre- and postoperative radiographs of 98 patients undergoing primary conventional TKA using mechanical alignment technique were analyzed. The PTPO and posterior or anterior tibial component over- (TCO) or underhang (TCU) were measured on lateral radiographs. Descriptive statistics were performed, and the pre- to postoperative difference in PTPO was tested for statistical significance using a Student's t-test. The correlations between TCO, TCU, and PTPO were assessed using Pearson correlation coefficients. Furthermore, patients were grouped based on their sagittal component position as anatomical (no TCO or TCU), mild malposition (1-3 mm TCO or TCU), or severe malposition (> 3mm TCO or TCU). Differences in PTPO between these groups were tested for statistical significance using student’s t-test, and Bonferroni correction was applied to correct for multiple testing.

Results

The mean preoperative PTPO was reported as 6.89 mm (standard deviation (SD) 5.69 mm; interquartile range 2.46 – 9.67; coefficient of variance 53.27; confidence interval 6.16 – 7.62). The mean postoperative PTPO was reported as 5.89 mm (SD 3.44 mm), resulting in a mean change in PTPO of -1.06 mm (SD 3.45 mm; p < 0.01). A pre- to postoperative change in PTPO of more than 10 mm was found in 18 cases (18.37 %). Anterior or posterior TCO was observed in 6 (6.12%) and 9 (9.18%) of patients, respectively. Anterior or posterior TCU was observed in 21 (21.43%) and 33 (33.67%) of patients, respectively. Overall, 56 (57.14%) patients had anatomical implant positioning, 30 (30.61%) had mild malposition, and 12 (12.24%) had severe malposition. Patients with mild or severe malposition had significantly higher preoperative PTPO values compared to those in the anatomical sagittal tibial component position group (p < 0.01). A moderate positive correlation (r = 0.59) between preoperative PTPO and anterior TCO/TCU and a strong positive correlation (r = 0.71) between preoperative PTPO and posterior TCO/TCU was found.

Conclusion

The posterior tibial plateau offset shows high variability among patients and is significantly reduced in patients undergoing TKA. Increased posterior tibial plateau offset is associated with sagittal tibial component malposition.