Background: 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.
Methods: 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.
Results: 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).
Conclusion: 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.
Keywords: direct anterior approach; dislocation; pelvic tilt; spinopelvic; total hip arthroplasty.
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