Influence of the femoral entry point for intramedullary alignment in total knee arthroplasty: A computer-aided design approach

Abstract

Objectives The aim of this study was to simulate different entry points and investigate potential angulation errors of the intramedullary device and resulting changes in the distal femoral cut using a computer-aided design (CAD) approach. Materials and methods We used a CAD approach to simulate various distal femoral entry points for intramedullary instrumentation. Simulations were performed on (i) a commercially available three-dimensional (3D) CAD model of a human femur (DigitalFemur) and (ii) a digital 3D model of an analogue large femur model produced using a coordinate measuring machine (FaroFemur). Divergent insertion points medial, lateral, anterior and posterior to the ideal position were simulated. Angulation deviations of the resulting positions of the intramedullary rod were measured and changes in the anatomical-mechanical axis angle were calculated. Differences between the two simulation models were quantified. Results The ideal entry point in the FaroFemur was 9.9 mm anterior and 4.3 mm medial to the apex of the intercondylar notch, and 9.2 mm anterior and 3.6 mm medial in the DigitalFemur. A medial entry point increased the angle between the anatomical femoral axis and the alignment rod in the FaroFemur and DigitalFemur (with 5 mm displacement 2.510° and 2.363°, respectively; with 10 mm displacement 3.239° and 3.283°, respectively). In contrast, a lateral entry point decreased the angle between the anatomical femoral axis and the alignment rod (with 5 mm displacement 2.267° and 2.262°, respectively; with 10 mm displacement 3.158° and 3.731°, respectively). An anterior entry point changed the angle between the anatomical femoral axis and the alignment rod towards extension (1.802° in the FaroFemur; 2.142° in the DigitalFemur), while a posterior entry point generated a deviation toward flexion (2.045° in the FaroFemur; 2.055° in the DigitalFemur). The mean difference between the two models was 0.108±0.121° with the highest difference for anterior displacement. Conclusion Minor deviations of the entry point for intramedullary instrumentation during total knee arthroplasty can result in malalignment of several degrees.

Phenotyping of the Turkish population according to Coronal Plane Alignment of the Knee classification: A retrospective cross-sectional study

“…Total knee arthroplasty is one of the widely performed orthopedic surgeries worldwide; achieving a pain-free and functional joint, along with high patient satisfaction, are among the goals of this surgery. [ 1 ] Patient, surgeon, and implantrelated factors influence the outcomes. One of the patient-related factors is the morphological changes of the distal femur and proximal tibia, which contribute to the formation of the knee joint surface.…”

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“…1 Some studies may vary 9.2mm anterior to and 3.6mm medial to Anterior Intercondylar notch. 4 Literature review shows no clear research work comparing long and short alignment rod for femur and its impact on alpha angle.…”

Gerdy’s tubercle as a novel anatomical landmark for the proximal tibial cut in total knee arthroplasty

“…It is known that improper prosthesis placement and positioning would affect clinical outcomes by causing aseptic prosthesis failure, instability, and premature wear of polyethylene. [ 3 ] Studies have shown that proper alignment of these components is essential for better postoperative outcomes and the long-term survival of TKAs. [ 4 ] Numerous instruments have been developed for the correct implantation and execution of surgery.…”