Background and Objectives: Intraoperative fluoroscopy can be used to increase the accuracy of the acetabular component positioning during total hip arthroplasty. However, given the three-dimensional nature of cup positioning, it can be difficult to accurately assess inclination and anteversion angles based on two-dimensional imaging. The purpose of this study is to validate a novel method for calculating the 3D orientation of the acetabular cup from 2D fluoroscopic imaging. Materials and Methods: An acetabular cup was implanted into a radio-opaque pelvis model in nine positions sequentially, and the inclination and anteversion angles were collected in each position using two methods: (1) a coordinate measurement machine (CMM) was used to establish a digitalized anatomical coordinate frame based on pelvic landmarks of the cadaveric specimen, and the 3D position of the cup was then expressed with respect to the anatomical planes; (2) AP radiographic images were collected, and a mathematical formula was utilized to calculate the 3D inclination and anteversion based on the 2D images. The results of each method were compared, and interrater and intrarater reliably of the 2D method were calculated. Results: Interrater reliability was excellent, with an interclass correlation coefficient (ICC) of 0.988 (95% CI 0.975–0.994) for anteversion and 0.997 (95% CI 0.991–0.999) for inclination, as was intrarater reliability, with an ICC of 0.995 (95% CI 0.985–0.998) for anteversion and 0.998 (95% CI 0.994–0.999) for inclination. Intermethod accuracy was excellent with an ICC of 0.986 (95% CI: 0.972–0.993) for anteversion and 0.993 (95% CI: 0.989–0.995) for inclination. The Bland–Altman limit of agreement, which represents the error between the 2D and 3D methods, was found to range between 2 to 5 degrees. Conclusions: This data validates the proposed methodology to calculate 3D anteversion and inclination angles based on 2D fluoroscopic images to within five degrees. This method can be utilized to improve acetabular component placing intraoperatively and to check component placement postoperatively.

To establish and validate a novel method for aligning femoral rotation to accurately measure femoral offset for preoperative templating and component sizing, and to identify the physical location of two radiographic lines utilized in the described method. Cadaveric proximal femurs were skeletonized and mounted to a biaxial load frame. Two radiographic lines along the greater trochanter were identified fluoroscopically. The femurs were rotated, and images were taken when the lines appeared superimposed, then in 2-degree increments to 10° of internal and external rotation, and at 30°. Radiographic femoral offset was calculated at each angle, and the maximum and aligned offsets were compared. Bone was removed until the radiographic lines disappeared, then a metal wire was inserted in place of the bone to confirm that the lines reappeared. The physical locations of the radiographic landmarks were on the anterior and posterior aspects of the greater trochanter. The mean true femoral offset was 38.2 mm (range, 30.5–46.3 mm). The mean aligned femoral offset was 37.3 mm (range, 29.3–46.3 mm), a 2.4% underestimation. The mean angle between aligned and true offset was 3.6° of external rotation (range, 10°ER-8°IR). Intra-rater intraclass correlation coefficient was 0.991. Alignment of the radiographic lines created by the anterior and posterior aspects of the greater trochanter is a reliable and accurate rotational positioning method for measuring true femoral offset when using plain films or fluoroscopy, which can aid surgeons with preoperative templating and intraoperative component placement for total hip arthroplasty.

Developmental dysplasia of the hip is associated with inferior clinical outcomes when treating concomitant intra-articular pathologies. Shelf acetabuloplasty has been proposed as a less invasive alternative to periacetabular osteotomy for developmental dysplasia of the hip; however, there is a lack of biomechanical studies regarding its efficacy. We hypothesized that a cadaveric dysplasia model would cause increased range of motion and lateral femoral head translation compared to native, and that shelf acetabuloplasty would restore native biomechanics. Ten cadaveric hips were dissected down to the capsule and mounted to a six-degree-of-freedom robotic arm. Each specimen was tested sequentially in 4 states: 1) Native, 2) Capsular repair, 3) Acetabular dysplasia model created by acetabular rim resection to achieve a lateral center-edge angle (LCEA) of 15-20° under fluoroscopic guidance, and 4) Shelf acetabuloplasty restoring LCEA of 35-40° utilizing a bone graft harvested from the iliac crest. Robotic testing included: 1) 5- Newton Meter (Nm) abduction, 2) 5-Nm internal rotation (IR) at 75° flexion, 3) 5-Nm flexion, and 4) 88-N lateral drawer. Range of motion under standardized torque was used as a surrogate measure of rotational stability. The effect of specimen state was determined using analysis of variance, and post hoc pairwise comparisons were made using Tukey's method. Capsular repair did not statistically significantly differ from the native state. Compared to native, the acetabular dysplasia model showed increased abduction (+2.3°, p = 0.004) and IR at 75° flexion (+0.9°, p = 0.017) without statistically significant changes in flexion or lateral translation. Shelf acetabuloplasty restored native abduction and IR at 75° flexion but reduced hip flexion (-1.7°, p = 0.003). This study demonstrated that acetabular rim resection increased rotational motion under applied torque, while shelf acetabuloplasty restored rotational motion to native levels. However, shelf acetabuloplasty resulted in a statistically significant reduction in hip flexion (-1.7°, p = 0.003), suggesting potential over-constraint depending on graft positioning. Not Applicable, Controlled Laboratory Study.