[Conventional cup navigation with 2D fluoroscopy in THA: accurate cup positioning respecting pelvic tilt]

The objective of this study was to asses the accuracy of conventional cup navigation with 2D-fluoroscopy compared to free-hand positioning in total hip arthroplasty.

A test of the procedure in a plastic bone model of the pelvis was undertaken: the implantation of 28 cups respecting the individual pelvic tilt was evaluated. The intraoperative determination of a reference plane for navigation by fluoroscopic matching of the anterior pelvic ring with the pre-operative X-ray of the pelvis was performed. The target zone was a radiological inclination 40 ± 10° and a radiological anteversion 15 ± 10°. Measurement of cup position was done with 3D-CT respecting the pelvic tilt and additionally with conventional X-ray images. CLINICAL APPLICATION IN PATIENTS: A comparison was made of 80 consecutive, in 2008 operated patients (navigation group) with 80 consecutive in 2006 operated patients (free-hand group). Measurement of cup position in both groups was made with conventional X-ray of the pelvis (mean value and standard deviation of radiological inclination and anteversion, the number of outliers of the target zone in navigation group and free-hand group).

In plastic bone models all cups were positioned in the target zone. Measurement of radiological inclination and anteversion with 3D-CT and X-ray demonstrated a good concordance (mean difference CT versus X-ray for inclination 0.625°, max. 2°, for anteversion 0.75°, max. 3°). In patients, conventional cup navigation was significantly superior to free-hand positioning in anteversion (SD 2.9° nav, SD 8.1° free, outliers of target zone: n = 2 nav, n = 18 free). No significant differences were detected in inclination.

The coronal plane of the patient was found to be a valid plane for cup navigation that can be determined by intraoperative fluoroscopy. The method allows for a safe positioning of the cup in the target zone for inclination and anteversion. Conventional cup navigation with 2D-fluoroscopy is simple and safe with limited investment in time, manpower and material.