Intraoperative measurement of cup inclination using fluoroscopy: do we need a different correction factor when using a different C-arm model.

INTRODUCTION

The direct anterior approach (DAA) in THA allows for intraoperative fluoroscopy imaging (IF). A previous study has shown that the intraoperative determination of radiographic cup inclination (RI) using IF during DAA THA is reliable and reproducible. However, a 5° correction factor should be applied to intraoperative measurements to adjust for parallax when using a standard 12-inch GE 9900 elite C-arm (GE Healthcare, Chicago, IL). The current study evaluates if the use of a flat panel C-arm requires a different correction factor.

MATERIALS AND

METHODS

The current study included 112 patients who underwent primary THA utilizing DAA with IF for cup placement. RI was measured using intraoperative fluoroscopy images of two different C-arm models (12-inch GE 9900 elite C-arm and OEC Elite flat panel and compared to postoperative AP pelvis radiographs.

RESULTS

Using the 12-inch GE 9900 elite C-arm (n = 76) mean intraoperative RI measurements (35.5°, range 28-42°) were on average 6.4° lower compared to mean postoperative measurements (41.9°, range 36-49°). Using the OEC Elite flat panel C-arm (n = 36) mean intraoperative RI measurements (36.1°, range 29-40°) were on average 5.6° lower compared to mean postoperative measurements (41.7°, range 37-48°).

CONCLUSION

The current study confirms that a correction factor needs to be applied to intraoperative measurements of cup inclination to adjust for parallax regardless of the type of C-arm.