Is Dislocation Risk due to Posterior Pelvic Tilt Reduced With Direct Anterior Approach Total Hip Arthroplasty?

Pelvic tilt affects acetabular anteversion, and thus total hip arthroplasty (THA) dislocation risk. The pubic symphysis-sacrococcygeal distance (PSCD) is an indicator of pelvic tilt, and a PSCD < 0 mm (ie, excessive posterior pelvic tilt) is associated with a 3.7-fold increase in postoperative dislocation rate. However, it is not known if the direct anterior (DA) approach might reduce this dislocation rate, specifically in high-risk populations such as negative PSCD.

Standing anteroposterior radiographs were reviewed for 510 consecutive DA THAs to determine PSCD. Patients were separated into 2 groups: (1) PSCD > 0 mm (PSCD[+]) and (2) PSCD < 0 mm (PSCD[−]). Incidence of dislocation was determined. We recorded if patients had spinal deformity or lumbar fusion. Continuous variables were analyzed using Student’s t-test, categorical variables were analyzed using Fisher’s exact test, and a sample size calculation was performed.

Three hundred fifty-eight hips (70.2%) were PSCD[+], while 152 hips (29.8%) were PSCD[−]. Three dislocations (3/510 hips, 0.6%) occurred. Two dislocators were in the PSCD[−] group (2/152 hips, 1.3%) and 1 dislocator was in the PSCD[+] group (1/358 hips, 0.3%) (P = .21). Twenty-four patients had degenerative scoliosis (24/510, 4.7%), of which 1 had a dislocation (1/24, 4.2%); 2 dislocations occurred in nonscoliosis patients (2/486, 0.4%) (P = .134). Twenty-seven patients had lumbar spinal fusion (27/510, 5.3%), of which there were no dislocations (0/27, 0.0%); all dislocations were in nonfusion patients (3/483, 0.6%) (P = 1.0).

We demonstrate no increased risk for THA dislocation in patients with a PSCD < 0 mm who have undergone a DA approach. These data would suggest a protective effect of the DA approach against dislocation, even in historically high-risk populations.