Abstract
Introduction
Planning of the stem antetorsion angle (SAA) is difficult with radiograph before THA. 3D THA planning software with CT is useful for planning the cup and the stem implantation angles before THA. However, even using the 3D planning software, we sometimes experience the different SAA during surgery compare to the planned SAA. The purpose of this study was to compare the implanted SAA with the preoperative planned SAA, which was planned by using 3D THA planning software.
Materials and Methods
CT evaluation was performed in 44 patients (5 males) who underwent primary THA. The mean age at surgery was 67 years (range 26–85 years). The mean BMI at surgery was 24.1kg/m2 (15.6–31.7kg/m2). Forty-one patients had osteoarthrosis, 2 patients had osteonecrosis, and 1 patient had femoral neck fracture. All surgeries were performed in the supine position with the direct anterior approach. The OrthoPilot imageless navigation system (BBraun/Aesculap) was used during surgery. Excia stem was used in 34 patients and Bicontact stem was used in 10 patients. Planning of the surgery was performed using 3D THA planning software (ZedHip, Lexi). After surgery, SAA was measured with CT by the same 3D THA planning software. SAA was evaluated by comparison of the planned values before surgery with the CT measured values. Also, the shape of the femur and the stem were evaluated.
Results
The mean SAA of the preoperative planning was 29.6±5.6 degrees (mean±sd) [range 20.4–42.8 degrees]. The mean SAA after surgery was 29.8±5.6 degrees [10.7–49.7]. The mean difference between postoperative SAA and planned SAA (post. minus pre.) was 0.2±7.6 degrees [−16.0–24.9]. The mean SAA of the Bicontact stem was 25.9±8.8 degrees and the Excia stem was 30.9±9.1 degrees. The difference between postoperative SAA and planned SAA of the Bicontact stem was −1.8±6.2 degrees and the Excia stem were 0.8±8.0 degrees. Ten patients showed more than 5 degrees of antetorsion after surgery compared to the planned SAA. Among them, Excia stem was used in nine patients. There were 11 cases of champaigne-flute type, 29 cases of normal type, and 4 cases of steovepipe type femurs. The mean difference between postoperative SAA and planned SAA with champaigne-flute type, normal type, and stovepipe type were 3.8±7.7 degrees, −0.5±7.6 degrees, and −4.7±3.9 degrees, respectively.
Discussion
In this study, the mean difference of SAA between postoperative values and preoperative planned values were very small. 3D planning software is useful for predicting SAA before surgery. The Excia stem showed greater difference of SAA and greater antetorsion compare to the Bicontact stem. Also, Champaign-flute cases tend to show greater difference of antetorsion compare to the other types of femur. The shape of the stem and the shape of the femur affected the antetorsion angle of the stem. When choosing an implant before surgery, surgeon better to consider the characteristic of the stem and the shape of the patients’ femur.
