The direct anterior approach for THA offers some advantages, but is associated with a significant learning curve. Some of the technical difficulties can be addressed by the use of intraoperative fluoroscopy which may improve the accuracy of acetabular component placement.Questions/purposes
The purposes of this study were to determine if (1) there is decreased variability of acetabular cup inclination and anteversion with the direct anterior approach using fluoroscopic guidance as compared with the posterior approach THA without radiographic guidance; (2) if there is a learning curve associated with achieving accuracy with the direct anterior approach THA. We also wanted (3) to assess the frequency of complications including dislocation with the anterior approach, which initially had a learning curve, and the posterior approach.Methods
This retrospective, comparative study of 825 THAs (372 posterior THAs without fluoroscopic guidance and 453 direct anterior THAs, performed by one surgeon, focused on a radiographic analysis to determine cup inclination and anteversion on standardized pelvic radiographs using specialized software. The first 100 direct anterior THAs performed while transitioning from the posterior approach to the direct anterior approach were included in the learning curve group. During this learning curve period, the direct anterior approach was used for all patients except those with conversion of previously fixed intertrochanteric or femoral neck fractures to THAs, gluteus medius tears, and obese patients with an immobile abdominal pannus (100 of 127 THAs). Variability of the acetabular component was compared among the posterior group, learning curve group, and direct anterior group.Results
Variances for cup inclination and anteversion were significantly lower in the direct anterior group (19 and 16 respectively, p < 0.01) as compared with the posterior group (50 and 79 respectively).Target inclination and anteversion were achieved better in the direct anterior group (98% and 97% respectively) as compared with the posterior group (86% and 77% respectively) (p < 0.01, OR for inclination = 9.1, 95% CI, 3.5 to 23.4; OR for anteversion = 8, 95% CI, 4 to 16). In the learning curve group, target anteversion achieved (91% of cases) was marginally lower than that of the direct anterior group (p = 0.03; OR = 2.9, 95% CI, 1.1 to 7.3) and target inclination (95%) was similar (p = 0.13). There was one posterior dislocation in the posterior group, two anterior dislocations in the learning curve group, and none in the direct anterior group.Conclusions
Use of fluoroscopy with the patient in the supine position during direct anterior THA enables intraoperative assessment of cup orientation resulting in decreased variability of acetabular cup anteversion. However, there is a learning curve associated with achieving this accuracy. We could not discern whether this difference was the result of the approach or the use of fluoroscopy in the direct anterior group.Level of Evidence
Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.