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.

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

Study design A prospective radiographic study of 160 volunteers without symptoms of spinal disease was conducted. Objectives The objective of this study was to describe, quantify, and classify common variations in the sagittal alignment of the spine, sacrum, and pelvis. Summary of background data Previous publications have documented the high degree of variability in the sagittal alignment of the spine. Other studies have suggested that specific changes in alignment and the characteristics of the lumbar lordosis are responsible for degenerative changes and symptomatic back pain. Methods In the course of this study, anteroposterior and lateral radiographs of 160 volunteers in a standardized standing position were taken. A custom computer application was used to analyze the alignment of the spine and pelvis on the lateral radiographs. A four-part classification scheme of sagittal morphology was used to classify each patient. Results Reciprocal relationships between the orientation of the sacrum, the sacral slope, the pelvic incidence, and the characteristics of the lumbar lordosis were evident. The global lordotic curvature, lordosis tilt angle, position of the apex, and number or lordotic vertebrae were determined by the angle of the superior endplate of S1 with respect to the horizontal axis. Conclusions Understanding the patterns of variation in sagittal alignment may help to discover the association between spinal balance and the development of degenerative changes in the spine.

Classification of the normal variation in the sagittal alignment of the human lumbar spine and pelvis in the standing position.

STUDY DESIGN Prospective radiographic and clinical analysis. OBJECTIVE Investigate the relationship between spino-pelvic parameters and patient self reported outcomes on adult subjects with spinal deformities. SUMMARY OF BACKGROUND DATA It is becoming increasingly recognized that the study of spinal alignment should include pelvic position. While pelvic incidence determines lumbar lordosis, pelvic tilt (PT) is a positional parameter reflecting compensation to spinal deformity. Correlation between plumbline offset (sagittal vertical axis [SVA]) and Health Related Quality of Life (HRQOL) measures has been demonstrated, but such a study is lacking for PT. METHODS This prospective study was carried out on 125 adult patients suffering from spinal deformity (mean age: 57 years). Full-length free-standing radiographs including the spine and pelvis were available for all patients. HRQOL instruments included: Oswestry Disability Index, Short Form-12, Scoliosis Research Society. Correlation analysis between radiographic spinopelvic parameters and HRQOL measures was pursued. RESULTS Correlation analysis revealed no significance pertaining to coronal plane parameters. Significant sagittal plane correlations were identified. SVA and truncal inclination measured by T1 spinopelvic inclination (T1-SPI) (angle between T1-hip axis and vertical) correlated with: Scoliosis Research Society (appearance, activity, total score), Oswestry Disability Index, and Short Form-12 (physical component score). Correlation coefficients ranged from 0.42 < r < 0.55 (P < 0.0001). T1-SPI revealed greater correlation with HRQOL compared to SVA. PT showed correlation with HRQOL (0.28 < r < 0.42) and with SVA (r = 0.64, P < 0.0001). CONCLUSION This study confirms that pelvic position measured via PT correlates with HRQOL in the setting of adult deformity. High values of PT express compensatory pelvic retroversion for sagittal spinal malalignment. This study also demonstrates significant T1-SPI correlation with HRQOL measures and outperforms SVA. This parameter carries the advantage of being an angular measurement which avoids the error inherent in measuring offsets in noncalibrated radiographs.

Pelvic tilt and truncal inclination: two key radiographic parameters in the setting of adults with spinal deformity.

Background: There is an increasing recognition of the clinical importance of the sagittal plane alignment of the spine. A prospective study of several radiographic parameters of the sagittal profile of the spine was conducted to determine the physiological values of these parameters, to calculate th

Radiographic analysis of the sagittal alignment and balance of the spine in asymptomatic subjects.

Study design Current concepts review. Objective Outline the basic principles in the evaluation and treatment of adult spinal deformity patients with a focus on goals to achieve during surgical realignment surgery. Summary of background data Proper global alignment of the spine is critical in maintaining standing posture and balance in an efficient and pain-free manner. Outcomes data demonstrate the clinical effect of spinopelvic malalignment and form a basis for realignment strategies. Methods Correlation between certain radiographic parameters and patient self-reported pain and disability has been established. Using normative values for several important spinopelvic parameters (including sagittal vertical axis, pelvic tilt, and lumbar lordosis), spinopelvic radiographic realignment objectives were identified as a tool for clinical application. Because of the complex relationship between the spine and the pelvis in maintaining posture and the wide range of "normal" values for the associated parameters, a focus on global alignment, with proportionality of individual parameters to each other, was pursued to provide clinical relevance to planning realignment for deformity across a range of clinical cases. Conclusion Good clinical outcome requires achieving proper spinopelvic alignment in the treatment of adult spinal deformity. Although variations in pelvic morphology exist, a framework has been established to determine ideal values for regional and global parameter in an individualized patient approach. When planning realignment surgery for adult spinal deformity, restoring low sagittal vertical axis and pelvic tilt values are critical goals, and should be combined with proportional lumbar lordosis to pelvic incidence.

Adult spinal deformity-postoperative standing imbalance: how much can you tolerate? An overview of key parameters in assessing alignment and planning corrective surgery.

Pelvis and spinal curves were studied with an angular parameter typical of pelvis morphology: pelvic incidence. A significant chain of correlations between positional pelvic and spinal parameters and incidence is known. This study investigated standards of incidence and a predictive equation of lordosis from selective pelvic and spinal individual parameters. One hundred and forty nine (78 men and 71 women) healthy adults, aged 19–50 years, with no spinal disorders, were included and had a full-spine lateral X-ray in a standardised upright position. Computerised technology was used for the measurement of angular parameters. Mean-deviation section of each parameter and Pearson correlation test were calculated. A multivariate selection algorithm was running with the lordosis (predicted variable) and the other spinal and pelvic parameters (predictor variables), to determine the best sets of predictors to include in the model. A low incidence ( 62°) increased sacral-slope and the lordosis is more pronounced. Lordosis predictive equation is based on incidence, kyphosis, sacral-slope and ±T9 tilt. The confidence limits and the residuals (the difference between measured and predicted lordosis) assessed the predicted lordosis accuracy of the model: respectively, ±1.65 and 2.41° with the 4-item model; ±1.73 and 3.62° with the 3-item model. The ability of the functional spine-pelvis unit to search for a sagittal balance depended both on the incidence and on the variation section of the other positional parameters. Incidence gave an adaptation potential at two levels of positional compensation: overlying state (kyphosis, T9 tilt), underlying state (sacral slope, pelvic tilt). The biomechanical and clinical conditions of the standing posture (as in scoliosis, low back pain, spondylisthesis, spine surgery, obesity and postural impairments) can be studied by comparing the measured lordosis with the predicted lordosis.

Sagittal alignment of spine and pelvis regulated by pelvic incidence: standard values and prediction of lordosis

The anatomic pelvic parameter "incidence" – the angle between the line perpendicular to the middle of the sacral plate and the line joining the middle of the sacral plate to the center of the bicoxo-femoral axis – has been shown to be strongly correlated with the sacral slope and lumbar lordosis, and ensures the individual an economical standing position. It is important for determining the sagittal curve of the spine. The angle of incidence has also been shown to depend partly on the sagittal anatomy of sacrum, which is established in childhood while learning to stand and walk. The purpose of this study was (1) to define the relationship between the sacrum and the angle of incidence, and (2) to compare these parameters in three populations: young adults, infants before walking, and patients with spondylolisthesis. Forty-four normal young adults, 32 infants not yet walking and 39 patients with spondylolisthesis due to isthmic spondylolysis underwent a sagittal full-spine radiography. A graphic table and the software for bidimensional study of the sacrum developed by J. Hecquet were used to determine various anatomic and positional parameters. Comparison tests of means, and multiple and partial correlation tests were used. A study of the reliability of the measurements using factorial plan methods was performed. The sagittal anatomic parameters of the sacrum were found to have a close relationship with the pelvic parameter of incidence angle, and therefore with the sagittal balance of the spine. The anatomy of the sacrum in spondylolisthesis patients is particular in that some features are much like those of young infants, but it is more curved and the incidence angle is significantly larger. There is a close relationship between angle of incidence and the slip of spondylolisthesis. All the parameters of young infants are significantly smaller than those of adults. It can be concluded that the sagittal anatomy of the sacrum plays a key role in spinal sagittal balance. The sacral bone is an integral a part of the pelvis and constitutes the undistorted part of the spinal curves. Organization of sagittal curves during growth can be followed up by looking at the sacrum. The sacrum in the spondylolisthesis group differs from the normal, and the greater angle of incidence and sacral slope in this group could predispose to vertebral slip.

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The sagittal anatomy of the sacrum among young adults, infants, and spondylolisthesis patients

Analysis of the sagittal balance of the spine includes the study of the spinal curves and of the pelvis in the sagittal plane. It therefore requires full-spine lateral radiographs. The sagittal balance of the spine was studied in forty-nine young adults. Strong correlations were observed between parameters related to the pelvis ("pelvic incidence angle", "sacral slope" and "pelvic tilting"), and the sagittal spinal curves ("lordosis" and "kyphosis"). We therefore propose to begin the evaluation of the sagittal plane alignment of the spine in clinical practice with measurement of the pelvic incidence angle. The relationship between the pelvic incidence angle and the sacral slope, as well as between the sacral slope and lordosis, is then assessed, and these are related to each other. The use of a graphic abacus facilitates assessment of the physiological comparison of the measured values and of the relationship between pelvic and spinal parameters, within their range of physiological variability. This analysis of the sagittal alignment of the spine also considers its dynamic aspect and the importance of gravity load and of muscular contraction on the lumbar structures. These data have been published previously and are recalled here. Three basic patterns of disruption of the relations between parameters may be encountered: a sacral slope angle exceeding the value expected considering the measured pelvic incidence angle (owing to fixed flexion contracture of the hips), excessive lordosis with regard to the observed sacral slope angle (with hyperkyphosis at the thoracic level) and stiff hypolordosis with pelvic retroversion. These three conditions are analysed in the light of the repercussions of the gravity load on the lumbar structures. A convenient method is thus available for functional analysis of the sagittal balance of the spine.

Sagittal plane alignment of the spine and gravity: a radiological and clinical evaluation.

L'utilisation combinee des programmes de releve tridimensionnel du rachis de J. Hecquet et du barycentremetre a permis, pour une serie de sujets normaux, de mettre en relation la position du centre de gravite du segment corporel supporte par les tetes femorales avec des parametres rachidiens (lordose, cyphose, gite rachidienne sagittale) et des parametres pelviens morphologiques (incidence et epaisseur) et positionnels (pente sacree, version pelvienne et porte-a- faux). Une chaine de correlation significative relie ces parametres et demontre le role primordial du parametre anatomique pelvien «incidence» dans les variations individuelles des courbures rachidiennes sagittales qui assurent le caractere economique de l'equilibre rachis-pelvis

Jean Legaye

Papers

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

Sagittal alignment of spine and pelvis regulated by pelvic incidence: standard values and prediction of lordosis

The sagittal anatomy of the sacrum among young adults, infants, and spondylolisthesis patients

Sagittal plane alignment of the spine and gravity: a radiological and clinical evaluation.

Equilibre sagittal du rachis. Relations entre bassin et courbures rachidiennes sagittales en position debout