Fluoroscopy assessment during anterior minimally invasive hip replacement is more accurate than with the posterior approach.

PURPOSE: Acetabular component position is important for stability and wear. Fluoroscopy can improve the accuracy of acetabular component placement in the posterior approach and the direct anterior approach (DAA). The purpose of this study was to determine if the direct anterior approach in the supine position facilitates the accurate use of fluoroscopy and improves acetabular component position.

METHODS: This retrospective, comparative study of 60 THAs with fluoroscopic guidance (30 in posterior approach group and 30 in DAA group) was performed by one surgeon from 2012 to 2014 at a single institution. Demographic and perioperative data were compared using the Kolmogorov-Smirnov test to determine if they were statistically different. The difference between the measured intra-operative and postoperative values for both inclination and anteversion were analysed respectively.

RESULTS: In the posterior approach group we found an average inclination on intra-operative fluoroscopy (IFluoro) of 36.8° ± 3.72°, an average anteversion on intra-operative fluoroscopy (AFluoro) of 25.6° ± 3.64°, an average inclination on postoperative standing AP pelvis X-ray (IAP X-ray) of 39.29° ± 4.58° and an average anteversion on postoperative standing AP pelvis X-ray (AAP X-ray) of 21.31° ± 4.04°. In the DAA group we found an average DAA IFluoro of 42.32° ± 1.91°, an average DAA AFluoro of 22.3° ± 1.41°, an average DAA IAP X-ray of 42.98° ± 1.81° and an average DAA AAP X-ray of 22.88° ± 1.38°. A difference was seen in variability using Kolmogorov-Smirnov test for inclination and anteversion with significant higher variation of measurements in the posterior approach group (p = 0.022 and p < 0.001 respectively). No statistically significant difference was seen in the DAA group using the fluoroscopy for inclination and anteversion.

CONCLUSION: Using fluoroscopy in the direct anterior approach, we achieved better intra-operative assessment of cup orientation resulting in decreased variability of acetabular cup anteversion than when used in the posterior approach. At least some of the improvement was due to the fact that the fluoroscopic image in the supine position was more accurate as measured against the postoperative standing AP pelvis. This study may influence the choice of approach in total hip replacement.