A cementless total hip arthroplasty successfully treated damaged hip joint by removing pain from patient and recovering function of the joint. During the operation of the hip arthroplasty, surgeon should enlarge a femoral canal as the shape of the implant for insertion. Inaccurate femoral cavity increases the possibility of post-operative complications, as well as intra-operative problems include bone breakage. Also, in the minimal invasive surgery the manual surgery is more challenging than the conventional surgery because the viewing site of the femur is limited. Thus several methods including robotic surgery were introduced in the clinical scene to enhance the accuracy and reliability of the femoral shaping during hip arthroplasty. But robotic surgery is not widely used yet because it requires additional time and cost. Moreover, quantitative analysis method of the femoral canal shaping accuracy is not standardized yet. Clinical effect of the canal shaping is not known, as follow-up study is not reported. Thus, identification of the reason of inaccurate femoral canal shaping and its elimination with minimum cost expect to improve clinical output of the hip arthroplasty, if its effect on the more clinically proven indexes is evaluated.
In this paper, author hypothesized that the rotation of the broach during the femoral canal machining increases the possibility of stem malpositioning and bone breakage, as well as inaccurate femoral canal shape. Thus to ensure the alignment of the broach to the femoral axis before and during the broaching process, a guided broach system using a femoral canal guide is proposed. Proposed system was compared with the conventional broach system in the alignment of the installed stem, fill of the femoral canal, fit to the cortical bone and the amount of the interfacial gap by installing stem to the composite bone by each method. Result showed that the proposed system installed the stem to the same position with the conventional system, with significantly less interfacial gap. In other words, by the conventional method only 66.1% of the stem surface have contacted to the bone in the less than 0.3mm distance but it improved to 81.5% by the proposed method(p＜0.035). Also, rotation of the broach during the preparation of the femoral canal reduced to the 47.6% compared to that of the conventional method by the proposed method (p＜0.075). Primary stability of the implant also improved by the proposed method; migration of the stem under 1000 cycles of the walking and stair climbing reduced significantly by the proposed method(p＜0.05). Also, micromotion tends to decreased in the proposed method. FE models which simulated the micromotions showed that the less interfacial gaps in the proposed method attributed to decrease the micromotion. Additional FE study showed that the existence of the interfacial gaps in the Gruen zone 7(proximal medial surface) and the Gruen zone 8(proximal anterior surface) affected the micromotion most significantly. Also, micromotion increased with wider interfacial gaps. Until the gaps covered 70% of stem surface, micromotion increased linearly (0.24μm/%, r2=0.99). But the micromotion nonlinearly increased with more than 70% of interfacial gaps. Moreover, comparison in the strain energy density in the proximal spongeous bone of the FE models showed that the possibility of the stress-shielding of the spongeous bone increases with less contact ratio.
In conclusion, we have showed that the rotation of the broach could be effectively reduced by the proposed method which resulted in less interfacial gaps between the femur and the cementless implant. Improved femoral canal shape reduced relative motion of the stem to the bone, which expect to lessen the possibilities of the post-operative complications.
