PCA Calculation Based on Multiplane Two-Dimensional Computed Tomography Sliding Measurement in Preoperative Total Knee Arthroplasty Planning.

Abstract

Background: Various osteotomy measurement techniques to assess the posterior condylar angle (PCA) are utilized in total knee arthroplasty (TKA). However, the most accurate method remains unclear. This study made use of preoperative two-dimensional (2D) computed tomography (CT) images to measure the PCA and integrated three-dimensional (3D) printing technology for in vitro verification and to improve preoperative planning of osteotomy measurement techniques in TKA.

Patients and methods: A retrospective study was conducted involving a limited cohort of 10 patients diagnosed with knee osteoarthritis. These patients underwent three-dimensional CT reconstruction of the knee joint using a medical 3D model. This study employed three distinct methodologies to measure the PCA. The first method involved single-plane 2D CT measurement, which provides a clear assessment of the posterior femoral condyle axis line (PCAL) and the surgical epicondylar axis (sTEA) of the femur. The second method utilized multiplane 2D CT with continuous plane sliding positioning to identify both the PCAL and sTEA when measuring PCA. The third method incorporated a 3D printing model whereby a solid model of the patient's distal femur was fabricated using 3D printing technology. In this approach, the PCAL and sTEA were marked using in vitro Kirschner wires, followed by CT scans of the marked femur. The PCA was subsequently measured based on the positioning of the Kirschner wires, with the PCA obtained from the 3D printed model considered the reference standard. The accuracy and consistency of PCA measurements obtained from different CT planes were evaluated using paired sample t-tests and intraclass correlation coefficients (ICC).

Results: In the single-plane 2D CT measurement group, the PCA value was 1.33 ± 0.50° (0.83-2.1°, 95% CI: 0.97-1.69°) with a measurement error of -0.84 ± 1.12° (-3.24-0.87°, 95% CI: -1.64--0.04°) and an outlier rate of 10%. In the multiplane 2D CT sliding measurement group, the PCA value was 1.61 ± 0.38° (1.13-2.32°, 95% CI: 1.34-1.88°) with a measurement error of -0.56 ± 1.09° (-2-1.6°, 95% CI: -1.34-0.22°) and no abnormal values were detected. The PCA measurement value for the 3D printed model group was 2.17 ± 1.16° (0.23-4.01°, 95% CI: 1.34-3.00°). The PCA measurement values in the single-plane 2D CT group were significantly lower than those in both the multiplane 2D CT sliding measurement group and the 3D printed model group, with no significant difference observed between the latter two groups. Moreover, the measurement error and outlier rates in the multiplane 2D CT sliding measurement group were significantly lower than those in the single-plane 2D CT group. The PCA measurements in the single-plane 2D CT group exhibited moderate repeatability (ICC: 0.507-0.641) while those in the multiplane 2D CT sliding group demonstrated high consistency (ICC: 0.840-0.940).

Conclusions: The utilization of multiplane 2D CT sliding measurements to assess the PCA during preoperative measurement and osteotomy planning for TKA demonstrates high accuracy and repeatability. We recommend employing this method prior to surgery to determine the rotational positioning of the femoral prosthesis during osteotomy and improve the precision of the rotational alignment of the femoral prosthesis.