Sagittal parameters after primary TKA affecting knee joint function: a correlative analysis and predictive model construction

Abstract Background The accuracy of prosthesis placement was crucial to the clinical efficacy after primary total knee arthroplasty (TKA). Some patients’ X-ray after TKA showed that the coronal and patellar axial parameters of the prosthesis position were within the acceptable range, but the clinical efficacy was still not as expected, which may be correlated to the abnormal sagittal parameters of postoperative prosthesis placement. Therefore, this study was designed to analyze the relevant factors of sagittal parameters on clinical efficacy after TKA and build a clinical prediction model. Method A retrospective analysis was conducted to collect patients who underwent primary TKA with osteoarthritis of knee joint from the First Affiliated Hospital of Kunming Medical University from September 2017 to September 2024. X-ray imaging and PACS imaging system were used to collect the coronal, patella axial and sagittal parameters from the anteroposterior, lateral and axial radiographs of the knee joint. According to the inclusion criteria, coronal parameters [Hip–Knee–Ankle HKA (177.8° ± 0.8°)] and patellar parameters [sulcus angle SA (135° ± 10°)], patellar tilt angle (11° ± 2.5°) within the normal range were collected. Sagittal parameters including femoral parameters [lateral femoral component angle (LFCA), femoral prosthesis flexion angle (FPFA), posterior condylar offset (PCO), Anterior–posteior dimension (ACP), posterior condylar offset ratio (PCOR), anterior femoral notching (AFN)], tibial parameters [lateral tibial component angle (LTCA), posterior tibial slope (PTS)] and patellar parameters [blackburne–peel index (B–P index), patella thickness, patella length)]. Furthermore, Forgotten Joint Score (FJS-12), Kujala patellofemoral score (KPS) and Hospital for Special Surgery Knee Score (HSS) were used to evaluate the prognosis of patients. Spearman coefficient was used to analyze the correlation between sagittal knee parameters with HSS and Kujala score. Univariate and multivariate logistic regression methods were used to investigate the risk and protect factors of Forgotten Joint Score (FJS-12) and build a clinical predictive model by R language. Result A total of 188 patients were collected, including 25 males and 163 females, with an average age of 64.8 years. PTS (P < 0.05, OR = 0.2), PCO (P < 0.05, OR = 0.2) and PCOR (P < 0.05, OR = 0.2) were considered positively correlated with HSS, but patellar thickness (P < 0.05, OR = − 0.2) and B–P index (P < 0.05, OR = − 0.2) was negatively correlated with HSS. However, only B–P index was negative with KPS. In addition, PTS (P < 0.05), PCO (P < 0.05), PCOR (P < 0.05), B–P index (P < 0.01) and patella thickness (P < 0.05) were independently associated with FJS-12. Moreover, clinical prediction model showed that PTS ≥ 5.5°, PCO ≥ 31.2 mm, B–P index < 1 and patella thickness < 16.6 mm were the optimal parameter for patients to achieve satisfactory postoperative status after TKA. Conclusions The prognosis of patients after TKA was influenced by sagittal parameters, including PCO, PCOR, PTS, B–P index and patellar thickness, which should be paid close attention by clinicians when placing prostheses.