Variability and influencing factors of posterior condylar offset in posterior-stabilized total knee arthroplasty

Background Posterior condylar offset (PCO) is a crucial knee anatomic parameter closely linked with joint function. Its restoration during posterior-stabilized total knee arthroplasty (TKA) draws wide research attention. Most studies focus on the impact of the PCO alterations on soft tissue balance and postoperative function, while relevant contributing factors remain poorly investigated. Objective To explore PCO variation after posterior-stabilized TKA and analyze potential influencing factors contributing to such changes. Methods From November 2020 to November 2021, 146 consecutive participants with a diagnosis of severe knee osteoarthritis were enrolled for this prospective study. All participants underwent primary posterior-stabilized TKA utilizing 3D-printed patient-specific instrumentation. Perioperative clinical variables and radiographic parameters were assessed, and the osteotomy thickness in the posterior femoral condyle was quantified during the TKA procedure. Results A total of 134 participants (17 males and 117 females) were recruited in this prospective study, including 72 patients (53.7%) with changes of PCO after TKA < 3 mm in group 1, and 62 patients (46.3%) with changes of PCO after TKA ≥ 3 mm in group 2. The demographic characteristics, clinical scores, and radiographic measurements of the two groups were comparable before TKA. In general, postoperative PCO was considerably reduced compared with preoperative PCO (29.77 ± 3.52 mm vs. 27.67 ± 2.99 mm, p < 0.001). Postoperative PCO reduction was noted in 99 patients (73.9%). The correlation analysis indicated a relatively weak positive relationship between PCO variation and the osteotomy of posterior lateral femoral condyle ( r = 0.282, p = 0.004). Moreover, radiographic evaluation revealed that patients in group 1 had a smaller preoperative posterior tibial slope (PTS, p < 0.001) and a smaller PTS change ( p = 0.002) after TKA. Conclusion PCO tends to decrease after posterior-stabilized TKA. The osteotomy in posterior lateral femoral condyle may potentially serve as a direct influencing factor for such reduction. The preoperative PTS and a greater PTS change were found to be indirect influencing factors associated with PCO variability in posterior-stabilized TKA. These imply that the anatomical morphology in posterior femoral condyle should not be sacrificed for the pursuit of uniform femoral and tibial osteotomy concepts.