The significant relationship among the factors of pelvic incidence, standing lumbar lordosis, and lumbar flexibility in Japanese patients with hip osteoarthritis: A descriptive radiographic study.

Abstract Introduction: Spine stiffness is known to increase the risk of total hip replacement (THR) instability. The sagittal posture and lumbo-pelvic kinematics have therefore become parameters of interest when planning THR. We conducted this study to investigate (1) the distribution and characteristics of the spino-pelvic standing alignment, (2) the relationship between pelvic incidence (PI) and standing lumbar lordosis (LL) and lumbar flexibility, in Japanese hip osteoarthritis patients. Hypothesis: (1) Japanese hip osteoarthritis patients with different sagittal spino-pelvic alignments do not differ markedly in their demographics, PI, or lumbar flexibility; and (2) there is no significant relationship between PI, standing LL, and lumbar flexibility in a population of Japanese hip osteoarthritis patients. Material and Methods: A retrospective study of radiographs from 945 Japanese patients who consecutively received THR for the treatment of hip osteoarthritis. All patients pre-operatively underwent lateral standing and deep-seated lumbo-pelvic radiography on which the spino-pelvic parameters were measured. The difference between the standing and deep-seated LL angles defined the lumbar flexibility and was calculated as the delta (Δ) LL. Individual spino-pelvic standing alignment was stratified based on the difference between the PI and standing LL (‘PI-LL mismatch’). ‘PI-LL mismatch’ of 10° was defined as hyperlordosis, normolordosis, and flatback, respectively. Results: In the present study, the spinal alignment of 115/945 (12.2%), 559/945 (59.2%), and 271/945 (28.6%) patients were classified as hyperlordosis, normolordosis, and flatback, respectively. Hyperlordotic patients had significantly lower PI (47.6° ± 7.8° vs. 52.7° ± 10.5°, p Discussion: A large proportion of Japanese hip osteoarthritis patients have abnormal PI-LL mismatch (12% and 29% have hyperlordosis and flatback, respectively). The PI was a determinant of the standing LL, and the standing LL was a strong determinant of the lumbar flexibility, especially in the normolordotic and lyperlordotic individuals. Level of Evidence: III; retrospective diagnostic radiographic study.