WHAT PATIENT PARAMETERS INFLUENCE LUMBAR FLEXION AND RELATIVE HIP USE?

Reduced lumbar spine flexion, leads to a greater dependence on the hip to achieve the sagittal flexion required for tasks of daily living and thus, increased instability risk post-THA. Although huge variability in lumbar spine flexion has been described, what innate parameters contribute remain unknown. This study aims to determine what parameters (demographic and anatomical) influence lumbar flexion and relative hip use amongst patients presenting to a hip clinic. This is a retrospective, consecutive case series from an academic center. All patients (n=651) presenting to a hip clinic underwent dynamic spinopelvic views in the standing and deep-seated positions. Of those 90 had a spinal MRI and formed the study cohort. Spinopelvic parameters of interest included standing pelvic tilt (PT), lumbar- lordosis (LL) and flexion (ΔLL) (stiffness: ΔLL degenerative-disc-disease (DDD) was quantified radiographically (facet arthrosis; disc height; endplate proliferative changes). Lumbar facet orientation and muscle atrophy as measured by fat infiltration for both flexors (psoas) and extensors (multifidus) determined from Spinal-MRIs. Mean ΔLL was 45°±16 and 8 patients had spinal stiffness. Extend of DDD (number of levels involved) was associated with increasing age (rho=0.42, p lordosis (rho=−0.51, pp DDD (p and psoas integrity (No atrophy: 54°±11 vs. Atrophy: 47°±11; p=0.03) and standing LL was dependent on multifidus integrity (No Atrophy: 55°±9 vs. Atrophy: 64°±9; p=0.02) and facet orientation at L4/5 (rho=0.37, p < 0 .001). Lumbar flexion is dependent on modifiable (psoas integrity, lumbar lordosis and thus multifidus integrity) and nonmodifiable (extend of DDD) factors. Such knowledge is of value for non-operative management of hip pathology, emphasizing the relevance of core muscle rehabilitation in improving posture and spinal flexion. Identification of 3 or more levels with DDD should alert hip surgeons of the 20x increased risk of spinal stiffness and instability risk post-THA.