Rosa Berndt

Purpose: The posterior tibial plateau offset (PTPO) is a parameter of sagittal plane bony tibia morphology with high variability and clinical relevance, particularly in cases involving stemmed tibial implants, where posterior tibial cortex interference may occur. However, its change during total knee arthroplasty (TKA), and its relationship to tibial component positioning remain unknown. Methods: Pre- and postoperative sagittal radiographs of 98 patients undergoing primary, mechanically aligned TKA using a single implant system were retrospectively analyzed. PTPO was measured as the distance between the tibial anatomical axis and the center of the tibial plateau or tibial component. Tibial component placement (TCP) was assessed anteriorly and posteriorly and categorized as anatomical (0–1 mm), mild (1–3 mm), or moderate (>3 mm) underhang (TCU) or overhang (TCO). Pre- and postoperative changes in PTPO were analyzed, preoperative PTPO was compared across TCP categories. Correlations with absolute anterior and posterior deviation from anatomical component placements were calculated. Results: PTPO showed high preoperative variability (mean 6.89 ± 3.69 mm) and was significantly reduced after TKA (5.89 ± 3.44 mm; mean change −1.06 ± 3.44 mm; p < 0.001). Higher preoperative PTPO was associated with anterior (p = 0.01) and posterior TCU (p = 0.02). PTPO showed a moderate correlation with anterior (r = 0.53, p < 0.01) and a strong correlation with posterior implant deviation (r = 0.68, p < 0.01). Conclusions: PTPO shows high variability among patients undergoing TKA, is significantly altered through surgery and correlates with tibial component malposition, particularly TCU. Surgeons should consider PTPO during preoperative planning to optimize tibial component positioning and reduce the risk of implant-to-bone conflict, especially when using stemmed implants. In patients with a high preoperative PTPO, accuracy-enhancing techniques such as computer navigation or robotic assistance may be considered.

Purpose: To compare patellar height measurement (PHM) using the Caton‐Deschamps Index (CDI) on malrotated versus properly positioned lateral knee radiographs within the same patients. It was hypothesised that malrotation would significantly alter CDI values. A secondary aim was to establish an anterior–posterior distance (APD) cut‐off for malrotation corresponding to a minimally clinically important difference (MCID) of 0.1 in ΔCDI. Methods: This retrospective analysis included patients with lateral knee radiographs between January 2020 and March 2023 at a single academic institution. Patients were included if at least two radiographs were available: one with malrotation (APD ≥ 1 mm) and one properly aligned (APD < 1 mm). Radiographs with tilt, prior osseous surgery, or fractures were excluded. Patellar height was measured using the CDI. Inter and intrarater reliability were assessed via intraclass correlation coefficients (ICC). Paired t ‐tests compared CDI values. Cases with a ΔCDI exceeding the MCID of ≥0.1 were identified. The APD cut‐off corresponding to a ΔCDI of 0.1 was determined by regression of ΔCDI on APD. Results: A total of 126 lateral knee radiographs from 63 patients (57% female) were analysed. Inter and intrarater reliability was excellent (ICC > 0.8 for all comparisons). The mean CDI was 0.96 ± 0.06 on properly aligned and 1.03 ± 0.08 on malrotated radiographs, with a significant mean difference of 0.07 ± 0.05 ( p < 0.001). In 34.9% of patients, CDI differed by ≥0.1 between imaging conditions. Linear regression of ΔCDI on APD showed a slope of 0.016 per mm ( R ² = 0.57). The APD cut‐off corresponding to a ΔCDI of 0.1 was 6.3 mm (95% CI, 5.7–6.9 mm). Conclusions: Malrotation significantly alters PHM using the CDI on lateral knee radiographs. A clinically relevant difference of ≥0.1 in ΔCDI occurred in over one‐third of patients. Malrotated radiographs should be used with caution, and repeat imaging should be considered when CDI values approach clinical decision thresholds. Level of Evidence: Level III, diagnostic study.