Abstract
Introduction
For preoperative planning of Total Hip Arthroplasty (THA) it is paramount to choose the correct implant size to avoid subsidence with too small a component or fracture with too large a component. This planning can be done either in 2D or 3D. 2D templating from X-rays frontal images remains the gold standard technique in THA preoperative planning despite the lower accuracy with uncemented components. 3D planning techniques require a CT-Scan examination overexposing patients to radiation. Biplanar EOS® radiographs are an alternative to obtain bone 3D reconstructions with a very low dose of radiation. The objective of this study was to evaluate the accuracy and reproducibility a novel 3D technique for THA preoperative planning based on biplanar low-dose radiographs.
Materials and methods
31 patients (20 women, 11 men, average age 66.1 y/o) who underwent a primary THA (Hardinge anterolateral approach) were included. Two senior orthopedic surgeons (Op_1 and Op_2) performed the pre-operative planning: (1) In 2D superimposing templates of the cup and the stem on CR radiographs. The CR images had a magnification coefficient of 1.15. (2) In 3D using dedicated hipEOS (EOS Imaging, France) software. 2D planning was performed once by each operator, 3D planning twice.
3D planning with hipEOS [Figure 1] was performed by importing 3D models of the stem and cup and superimposing them on frontal-lateral EOS® radiographs. This software proposes an initial estimate of the components size and position. If necessary, the user can correct the size of the stem and perform translations and rotations of the 3D models in order to correct the position, while clinical parameters such as the cup anteversion and inclination, as well as the femoral offset and leg length are automatically recalculated.
To evaluate the accuracy, we have compared the 2D and 3D planning with respect to the actual size implanted during the surgery. To evaluate reproducibility we have calculated the Intra-class Correlation Coefficient (ICC) of both techniques.
Results
In 2D, the stem size was planned in 69% of cases within ± 1 size with respect to the actual size, compared to 83% in 3D [Table 1]. The ICC [table 2] for stem planning was 0.91 in 2D, and 0.88 in 3D.
In 2D, the cup size was planned in 87% of cases within ± 1 size, compared to 92% in 3D. The ICC for cup planning was 0.71 in 2D, and 0.84 in 3D.
Discussion
The 3D planning technique proposed is accurate and reproducible. 3D planning based on biplanar EOS® radiographs can become an alternative to 2D techniques which require calibration devices. The method proposed is a novel concept of 3D THA planning with a very low radiation dose, if compared to CR and CT [Delin, Eur J Radiol 2013; Deschênes, Spine 2010].
Conclusion
The 3D preoperative planning of THA based on EOS® biplanar radiographs proved to be accurate and reproducible if compared to the ‘gold standard’ technique. A prospective study to evaluate clinically relevant parameters of THA surgeries such as the leg length and the femoral offset with hipEOS is in progress.
