Accuracy of Posterior Wall Acetabular Fracture Lag Screw Placement: Correlation Between Intraoperative Fluoroscopy and Postoperative Computer Tomography.

OBJECTIVE

Compare intraoperative "on end" fluoroscopy lag screw position to postoperative computer tomography.

DESIGN

Retrospective review.

CLINICAL SETTING

Level 1 trauma center.

PATIENTS

One hundred sixteen patients sustaining operative acetabular fractures with posterior wall components.

INTERVENTION

Posterior wall lag screws placed using "on end" fluoroscopic imaging.

MAIN OUTCOME MEASUREMENTS

The primary outcome was determining correlation between lag screw position, in relation to the acetabular articular margin, using intraoperative fluoroscopy and postoperative computer tomography. Analysis was performed based on location around the acetabulum, including posterior (P), superoposterior (SP), and superior (S) regions, and screws 0-5, 5-10, and >10 mm from the joint.

RESULTS

Two hundred forty-four lag screws were identified as follows: 51.6% in the P group, 25.4% in SP, and 23.0% in the S group with excellent correlation noted in all groups. For screws pooled based on fluoroscopic distance from the joint, 28.3% were 0-5 mm, 52.9% 5.01-10 mm, and 18.4% >10 mm. Correlation coefficients were 0.60 for 0-5 mm and 0.68 for both groups >5 mm. Subdividing screws based on anatomic region and fluoroscopic location found increasing correlation as screws moved further from the joint in the P region. In the SP group, excellent correlation was noted for screws 0-5 mm with decreasing correlation further from the joint. Within the S group, correlation for screws 0-5 mm did not reach significance, but good correlation was noted for screws >5 mm. Overall incidence of intraarticular screws was 1.2%.

CONCLUSIONS

Intraoperative axial fluoroscopy for posterior wall lag screw placement correlates closely with postoperative computer tomography allowing for reliable posterior wall lag screw placement in all regions around the acetabulum. Care should be taken while placing lag screws within 5 mm of the articular surface, particularly within the posterior region.