Figure 4.

Lateral standing (A) and deep-seated (B) spinopelvic views of a 61 year old patient with Bechterew’s disease prior to his left total hip replacement, having undergone right total hip replacement earlier. The radiographs show all measurements that can be performed as part of pre- and post-op assessments. In this patient the change in LL between positions was 4° and his PI-LL value was 15° indicating that he is at a higher risk of instability post-THA due to a lumbar spine flat-back deformity and stiff lumbar spine. LL, lumbar lordosis angle; PI, pelvic incidence; PT, pelvic tilt; PFA, pelvic femoral angle as a measure of hip flexion; AI, ante-inclination