Review Question - QID 463

Degenerative joint disease due ankylosing spondylitis (AS) with a concomitant hip flexion contracture increases post-operative rates of anterior hip dislocations. Correction of hip flexion contracture with THA can restore sagittal balance. However, when positioning the acetabular component in a patient with AS, one must account for the relationship of the pelvis to the lumbar spine in the sagittal plane in order to avoid an excessively hyperextended hip once the patient resumes an upright position.

Tang el al followed 95 primary THA's in patients with AS for over 10 years. Their series had 3 dislocations, 2 of which were anterior. They noted that, because of the presence of relative hyperextension of the hips after THA, AS patients are more prone to anterior dislocation when acetabular components are placed in their normal position relative to the pelvis.

In a more recent study, Bhan et al retrospectively reviewed 54 patients (92 hips) who underwent cementless total hip arthroplasty for bony ankylosis in AS via a posterior surgical approach. At an average of 8.5 years follow-up, they noted that anterior dislocation occurred in 4 (4.3%) of the hips and that there were no posterior dislocations.