Pelvic incidence: a fundamental pelvic parameter for three-dimensional regulation of spinal sagittal curves

Abstract

IntroductionSagittal spinal morphology varies from one individual to the another and is specific to each person. Classifications proposed in the literature are based on the measurements of curvatures, angulations or other parameters, chiefly for a normal population [1-3, 7, 11, 13, 15-17]. They are purely descriptive rather than in any way analytic.Modifications of sagittal spinal curvatures have been connected with changes in pelvic orientation [7,11,12,16,17]. Nevertheless, the role of pelvic anatomy in this positioning has never been investigated. A pelvic anatomic parameter named pelvic incidence is proposed in this study as the key factor for this sagittal balance regulation. Spinal balance is conceived as the result of an optimal lordotic positioning of the vertebrae above a correctly oriented pelvis. "Optimal lordotic positioning" and "correctly oriented pelvis" values are defined in this study, performed on a normal and a scoliotic population. Materials and methods MaterialsThe data of two population groups were analysed. The first group comprised a normal population of 49 adults free of vertebral disease. There were 21 women and 28 men, with a mean age of 24 years (SD 5.8 years; range 19-50 years). Mean height was 173 cm (SD 8 cm): 177 cm (SD 7 cm) for the men and 161 cm (SD 8 cm) for the women). Mean weight was 65.8 kg (SD 10 kg): 71 kg (SD 8.6 kg) for the men and 59.2 kg (SD 7.7 kg) for the women. These 49 adults constituted the control group for assessing the relationship between spine and pelvis for a normal population. They consisted of volunteer medical and physical therapy students.The second group comprised 66 adult scoliotic women, with a mean age of 33 years (SD 19.8 years; range 10-84 years), and a mean height of 161 cm (SD 8 cm) and a mean weight of 55 kg (SD 8 kg). The frontal curves were lumbar in 24 cases and thoracolumbar in 42 cases. MethodsThe anatomical parameters (vertebral curvatures and pelvic parameters) were measured on orthogonal plain radiographs in standAbstract This paper proposes an anatomical parameter, the pelvic incidence, as the key factor for managing the spinal balance. Pelvic and spinal sagittal parameters were investigated for normal and scoliotic adult subjects. The relation between pelvic orientation, and spinal sagittal balance was examined by statistical analysis. A close relationship was observed, for both normal and scoliotic subjects, between the anatomical parameter of pelvic incidence and the sacral slope, which strongly determines lumbar lordosis. Taking into account the Cobb angle and the apical vertebral rotation confers a three-dimensional aspect to this chain of relations between pelvis and spine. A predictive equation of lordosis is postulated. The pelvic incidence appears to be the main axis of the sagittal balance of the spine. It controls spinal curves in accordance with the adaptability of the other parameters.

Does Degenerative Lumbar Spine Disease Influence Femoroacetabular Flexion in Patients Undergoing Total Hip Arthroplasty?

“…Our study is the first, to our knowledge, to stratify patients undergoing THA into those with or without lumbar DDD, and we found that most patients with DDD had flattened backs (mean 7°less lumbar lordosis) and more posterior pelvic tilt (mean 5°more sacral slope) in standing. Decreasing values in lumbar lordosis and sacral slope angles in patients with DDD are consistent with the spine literature, where these sagittal parameters are used to evaluate individual sagittal balance [4,5,28]. Interestingly, similar to a previous study evaluating sagittal balance during standing in patients undergoing THA [24], some patients with DDD in our study had such excessive posterior pelvic tilt and lack of lumbar lordosis that they required knee flexion to adapt, because hip extension was insufficient.…”

Intra- and inter-observer reliability of determining radiographic sagittal parameters of the spine and pelvis using a manual and a computer-assisted methods

“…Pelvic incidence Angle subtended by a line which is drawn from the center of the femoral head to the midpoint of the sacral endplate and a line perpendicular to the sacral endplate [16]. Sacral slope The angle subtended by a horizontal reference line and the sacral endplate line.…”

Compensatory mechanisms contributing to keep the sagittal balance of the spine

“…It is essential to have an optimal congruence between pelvic and spinal parameters to achieve an economic posture placing the axis of gravity in a physiologic position [3,5,14,17].…”