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

Area of Science:

• Orthopedic Surgery
• Surgical Imaging Technology
• Arthroplasty Biomechanics

Background:

• Direct anterior approach (DAA) total hip arthroplasty (THA) utilizes intraoperative fluoroscopy (IF) for cup placement.
• Previous research established the reliability of IF for measuring radiographic cup inclination (RI) in DAA THA.
• A 5° correction factor was previously recommended for parallax adjustment with a standard 12-inch GE C-arm.

Purpose of the Study:

• To evaluate if a different correction factor is required for intraoperative parallax adjustment when using a flat-panel C-arm compared to a standard C-arm during DAA THA.
• To compare intraoperative RI measurements with postoperative measurements across different C-arm technologies.

Main Methods:

• A cohort of 112 patients undergoing primary THA via DAA with IF was analyzed.
• Radiographic cup inclination (RI) was measured intraoperatively using two C-arm models: a 12-inch GE 9900 elite and an OEC Elite flat panel.
• Intraoperative measurements were compared to postoperative AP pelvis radiographs.

Main Results:

• With the 12-inch GE 9900 elite C-arm (n=76), mean intraoperative RI (35.5°) was 6.4° lower than postoperative measurements (41.9°).
• With the OEC Elite flat panel C-arm (n=36), mean intraoperative RI (36.1°) was 5.6° lower than postoperative measurements (41.7°).
• Both C-arm types demonstrated a consistent underestimation of RI intraoperatively due to parallax.

Conclusions:

• A correction factor is necessary for intraoperative RI measurements in DAA THA to compensate for parallax.
• The type of C-arm used (standard 12-inch or flat-panel) does not alter the need for a parallax correction factor.
• Consistent application of a correction factor ensures accurate cup positioning in DAA THA regardless of imaging equipment.