Preoperative Factors Predicting the Preservation of the Posterior Cruciate Ligament in Total Knee Arthroplasty

Abstract

Objective: Predicting the successful preservation of posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) is an important step for preoperative planning to secure the satisfactory outcomes. We aimed to examine the preoperative factors predicting the successful preservation of the PCL in cruciate-retaining TKA and the outcome of sacrificing the PCL.

Methods: In this retrospective study, we analyzed TKAs consecutively performed by a single surgeon between January 2019 and August 2021 who had been preoperatively planned to undergo implantation of cruciate-retaining (CR) prostheses. The outcome of the current study was whether the PCL was retained or sacrificed. Anterior-stabilized (AS) tibial bearings when the PCL was sacrificed as needed were used intraoperatively. Age, sex, body mass index (BMI), and preoperative diagnosis from the patients' medical records were obtained. The medial-lateral width of epicondyle (MLW), the medial posterior condyle height (MPCH), the lateral posterior condyle height (LPCH), the ratio of MLW and MPCH, the ratio of MLW and LPCH, the Insall-Salvati index, and the severity of the varus or valgus deformity were measured using preoperative radiographs. Univariate and multivariate regression were fitted to assess the association of these factors with the successful retention of PCL. To examine the influence of sacrifice of the PCL on the surgical procedure, the size of the tibial and femoral components, the thickness of the polyethylene insert, and the rate of patella replacement between the CR group and AS group were also compared using t tests or chi-square tests.

Results: Among 307 TKAs included, PCL was sacrificed with concurrent use of AS prostheses in 89 (29.0%) procedures. Knees with rheumatoid arthritis (P < 0.01), lower Insall-Salvati index (P < 0.01), and more severe varus deformity (P = 0.011) were at a higher risk of sacrificing the PCL intraoperatively. There was no significant difference in age, sex, BMI, MLW, MPCH, LPCH, ratio of MLW and MPCH, ratio of MLW and LPCH, size of the tibial and femoral components, or replacement of the patella between the CR and AS groups. Converting from CR to AS was associated with a higher risk of using a thicker polyethylene insert (P < 0.01).

Conclusion: Rheumatoid arthritis, lower Insall-Salvati index, and more severe varus deformity were associated with an increased risk of sacrificing the PCL in TKAs planned to undergo implantation CR prostheses. Converting to AS tibial bearing may result in a thicker polyethylene insert. These factors should be carefully considered for the appropriate selection of prosthesis type preoperatively.

Keywords: Knee geometrics; Posterior cruciate ligament; Predictor; Total knee arthroplasty.

Fig. 1

Measurement of the radiograph factors. (A) The mechanical axis was defined as the center of the plateau to the center of the plafond, and the anatomic axis was defined as the center of the tibial diaphysis. (B) MLW: medial‐lateral width of epicondyle. The MLW was defined as the distance between the lateral epicondyle and the medial epicondyles. (C) MPCH: medial posterior condyle height, LPCH: lateral posterior condyle height. The longitudinal posterior condylar line was determined on the cut with the largest anterior–posterior dimension at the lateral and medial femoral condyle. The distance between the anterior femoral cortex line and the posterior condylar line of the lateral and medial femoral condyle was defined as LPCH or MPCH. (D) Insall–Salvati index: The Insall–Salvati index was defined as the Patellar length compared to the patellar tendon length