Prosthetic Hip Dislocations in Direct Anterior versus Posterior Approach in Patients with Instrumented Lumbar Fusion.

BACKGROUND: Instrumented Posterior Lumbar Spinal Fusion (IPLSF) has been demonstrated to contribute to instability following Total Hip Arthroplasty (THA). It is unclear whether a supine Direct Anterior (DA) approach reduces the risk of instability.

METHODS: A retrospective review of 1,773 patients who underwent THA through either a DA approach or a posterior approach at our institution over a 7-year period. Radiographic and chart review were then used to identify our primary group of interest comprised of 111 patients with previous IPLSF. Radiographic review, chart review, and phone survey was performed. Dislocation rates in each approach group were then compared within this cohort of patients with IPLSF.

RESULTS: Within the group of patients with IPLSF, 33.3% (n=37) received a DA approach while 66.6% (n=74) received a posterior approach. None of the 9 total dislocations in the DA group had IPLSF, whereas 4 of the 16 total dislocations in the posterior approach group had IPLSF (p=0.78). When examining the larger group of patients, including those without IPLSF, patients undergoing a DA approach had a lower BMI and were likely have a smaller head size implanted (p<0.001 for both). Using Fischer's exact test, fusion was associated with dislocation in the posterior approach group (p<0.01), whereas fusion was not associated with dislocation in the anterior approach group (p=1.0).

CONCLUSIONS: While there was no significant difference in dislocation rates between posterior and anterior approach groups, in patients with IPLSF, the anterior approach had a lower percentage of dislocation events compared to the posterior approach.