Aseptic varus tibial baseplate subsidence (VTBS) is a serious complication following total knee arthroplasty (TKA), often necessitating complex revision surgeries with substantial morbidity, mortality, and economic impact. Identified risk factors for VTBS include varus malalignment of tibial components, younger age, higher BMI, preoperative limb alignment, osteoporosis, and uneven joint balancing. The Coronal Plane Alignment of the Knee (CPAK) classification, a novel classification system that defines nine distinct knee phenotypes, offers valuable insights into knee alignment patterns. This study aims to investigate whether certain pre- and post-operative CPAK classifications and combinations are associated with increased VTBS rates, alongside evaluating other relevant risk factors. We conducted a retrospective chart review examining the potential causative factors for primary TKAs in VTBS requiring revision TKA. Eight hundred and thirty-eight patients with aseptic loosening were identified at 2 tertiary centers between April 2013 to March 2023. Seven hundred and twenty patients were excluded based on our exclusion criteria: 1) cases not in VTBS following primary TKA; 2) septic loosening; 3) trauma outside of medial tibial baseplate collapse. A total of 120 patients were included and were compared against a control group of 52 patients for analysis (Figure 1). Factors such as patient demographics, surgical data and comorbidities were included. Radiographic features were extracted from radiographs, including assignment of pre- and postoperative CPAK classifications. Both demographic data and comorbidity data were compared to determine the difference between groups. Either Fisher's exact test or Student's t-test were employed, depending on the variable. Significant differences noted in the VTBS group compared to control group included younger patient age (P=<0.001), increased BMI (P=0.003), larger proportion of patients with tibial component oversize or undersizing (P=<0.001), less tibial stem extensions used (P <0.001), higher Charlson Comorbidity Index (P<0.001), and a higher proportion of patients classified post-operatively in CPAK group 2 (neutral arithmetic hip-knee-ankle angle, apex distal joint line obliquity; P=0.044; Figure 2). This study highlights key factors associated with aseptic VTBS following primary TKA, including younger age, higher BMI, undersized/oversized tibial component, absence of tibial stem extensions, and higher Charlson Comorbidity Index. Notably, we propose that post-operative classification in CPAK 2, characterized by a neutral arithmetic hip-knee-ankle angle and apex distal joint line obliquity, may be a risk factor for developing aseptic VTBS. These findings underscore the importance of a thorough preoperative assessment and careful selection of prosthetic components in certain patient populations. Future research with larger, more diverse cohorts and standardized protocols is necessary to validate these results and improve TKA outcomes. For any figures or tables, please contact the authors directly.
Zhao et al. (Wed,) studied this question.