Analysis of balance is emerging as an important parameter in spinal deformity. Force plate technology permits a quantitative study of balance through centre of pressure (COP) measurement. COP measurements obtained from the force plate approximate the projected centre of gravity. In a standing subject the COP reflects the projected centre of gravity however repeatability and reliability of such analysis is lacking.

COP measurements were obtained from eight asymptomatic volunteers (mean age 32) with no history of back pain or previous spinal surgery. Each subject stood on a Zebris force plate platform for 30 seconds daily. 15 sets of data were acquired for each subject. For one subject, an additional 15 sets of data were collected on one day for comparison to the longitudinal data.

Intra- versus inter-subject reliability analysis revealed a Cronbach’s alpha value > 0.9 for the following COP movement parameters: distance travelled over 30 seconds, distance travelled in the first and last five seconds, and average speed. Comparison of the mean intra- versus inter-subject coefficients of variation revealed significant differences for all parameters (p< 0.004).

COP movement parameters are reliable in terms of intra-subject repeatability and can detect significant individual subject movement patterns. This suggests that COP movement patterns over time are idiosyncratic for each individual. While the repeatability of COP measurement has been established, the sensitivity to change with pathology and in response to treatment for spinal pathology remains to be evaluated.

Précis: A recently developed Classification of adult scoliosis was utilised to study surgical treatment in 339 patients. At 12 month follow up after surgery for thoracolumbar/lumbar scoliosis greatest improvement in outcome scores were noted in the following patients: lost lumbar lordosis, treatment with osteotomies, fusion to the sacrum for marked sagittal imbalance. Complication rates were greatest for: fusion to the sacrum, sagittal imbalance greater than 4cm.

Introduction: A recently proposed radiographic Classification of adult scoliosis offers a useful system with high clinical impact and reliability. Continued work is required to apply this system in the development of treatment guidelines. The purpose of this study was to anal surgical treatment outcomes, and complications, by Classification subtype at 12 months post-operative follow up.

Material and Method: This study included 339 patients: Type IV (thoracolumbar major) and Type V (lumbar major) adult scoliosis (Spinal Deformity Study Group). All patients had complete full-length spine radiographs and outcomes questionnaires (SRS, ODI and SF-12). An analysis of classification subtypes (modifiers) included outcome scores by surgical treatment. The latter included approach (anterior, posterior, both), use of osteotomies, and extension to the sacrum (or not).

Results: Lordosis modifier was strongly correlated with baseline disability and post-operative improvement. Type C (loss of lordosis) patients had the lowest baseline outcome but also greatest improvement with surgery (p< 0.05). Subluxation modifier had impact on preoperative but not on postoperative outcomes measures. Marked sagittal balance had the worst outcomes of all groups if fusion fell short of the sacrum. Patients with osteotomies saw greater improvement than those without (p< 0.05). Anterior, posterior or combined procedures showed no significant difference in outcomes. Peri- and post-operative complications did not vary by lordosis modifier, subluxation modifier but were elevated for fusion to the sacrum (p< 0.05).

Conclusion: At 12 month follow up for surgical treatment of adult thoracolumbar/lumbar scoliosis greatest improvement in outcome scores were noted in the following patients: lost lumbar lordosis, treatment with osteotomies, fusion to the sacrum for marked sagittal imbalance. Complication rates were greatest for: fusion to the sacrum, sagittal imbalance greater than 4cm. Further longitudinal follow up will permit validation of optimal treatment by Classification type of adult spinal deformity and refine patient and surgeon expectations of operative care.

Précis: A multi-centre prospective effort focused on analysis of a previously reported Classification of adult scoliosis. 809 thoracolumbar/lumbar deformities were studied. Radiographic analysis (deformity apex, lumbar lordosis, intervertebral subluxation), outcomes measures (ODI, SRS instruments) and surgical rates were examined. The Classification into Types, based on deformity apex location, and addition of modifiers (lordosis, subluxation) established clinically significant groups (disability, pain). In addition to high clinical impact, the Classification was also able to predict surgical rates.

Introduction: A recently proposed radiographic classification of adult scoliosis offers a reliable method of categorizing patients. Continued work on this classification is expected to develop treatment guidelines. This investigation anald treatment patterns of a large patient population of thoracolumbar and lumbar adult scoliosis, emphasizing surgical rates and approaches by classification subtypes.

Methods: This investigation anald 809 Type IV (thoracolumbar major) and Type V (lumbar major) curves from the Spinal Deformity Study Group database. Enrolled patients had complete SRS, ODI and SF-12 outcomes questionnaires and free standing full-length spine radiographs. Analysis compared non-operative versus surgical treatment (no imposed protocol) with surgical treatment assessed by approach (anterior, posterior, both), +/− osteotomies.

Results: Of 809 patients, 348 were treated surgically (43%) and classified as lordosis type A (n=422), B (n=313), C (n=74). Surgical rates were greater for B vs. A (51% vs. 37%, p< 0.05)), trend for A vs. C (46%). Subluxation modifier scores: 0 (n=360), + (n=159), ++ (n=290). Surgical rates were greater for ++ vs. 0 (52% vs. 36 %, p< 0.05), trend vs. + (42 %). Greater sagittal imbalance was more likely to receive surgical treatment. Loss of lumbar lordosis (modifier B, C) was associated with increased osteotomy rates and posterior or circumferential treatment versus anterior only procedures (most common in modifier A). Greater subluxation (modifier ++) was associated with more circumferential surgery. Greater sagittal imbalance was associated with higher rate of posterior only surgery.

Discussion: In this analysis, greater lordosis or subluxation modifier score was associated with higher surgical rates. Loss of lordosis and greater subluxation grade was associated with higher rates of circumferential surgery than lordotic spines or those without significant subluxation. This information suggests the ability of this classification system to predict treatment. Longitudinal follow up will permit validation of optimal treatment by classification of adult spinal deformity.

Précis: Using full length x-rays and force plate technology, the purpose was first to investigate the relationship between the gravity line and spino-pelvic parameters on asymptomatic adult volunteers and then to analyse age related changes. Trunk inclination and pelvic parameters appears as the two key-factors of the GL location; with age the GL location regarding the heels does not change but trunk global inclination shifts forward, pelvic tilt increases, and the pelvis shifts toward the heels.

Introduction: Although work by several authors has placed emphasis on global balance in the setting of spinal deformity, the relationship of spino-pelvic parameters related to this concept remains poorly defined. Using the force plate device and radiographic measurement, this study aimed to define the relationship between these parameters and the location of the gravity line (GL) in asymptomatic adult population.

Materials and Methods: 75 asymptomatic adult volunteers were recruited and subdivided by age (18–40, 41–60, > 61). Full-length free-standing AP and lateral radiographs were obtained with simultaneous assessment of the force plate gravity line (GL) location. The latter was projected on each x-ray to compute distance between anatomical components and GL and correlate its location with radiological parameters. Age related changes were investigated using ANOVA with Bonfer-roni-Dunn Post-Hoc test.

Results: Radiographic measurements revealed strong correlations between trunk global inclination and distance from S1 to the GL (r=0.7), sacral slope and pelvic incidence (r=0.78), distance from the bi-femoral head axis to the GL and S1 to the GL (r=0.73), and sacral slope and lordosis (r=0.89). With advancing age, the GL location with respect to the heels does not change and a global spino-pelvic regulatory mechanism appears to maintain this posture: trunk global inclination shifts forward, pelvic tilt increases, and the pelvis shifts toward the heels, increasing its distance from the GL.

Discussion: his study demonstrates the importance of pelvic parameters and trunk inclination in the regulation of the GL location. The relationship between the gravity line, pelvic parameters, and overall spinal alignment may emerge as essential in the evaluation of spinal deformity. Further investigation in this field may lead to a formula of balance that can assist in optimal planning of corrective procedures for spinal deformity.

Précis: Gravity Line (GL) measurement by forceplate offers key information on standing balance. In this study x-ray measurements and GL offsets were calculated in two adult: volunteer controls, sagittal plane deformity patients. The deformity group revealed significant pelvic retroversion and posterior sacral displacement regarding GL and heels. However, GL-heel and GL-femoral head offsets were similar indicating that sagittal plane deformity may induce posterior pelvic translation and retroversion in order to maintain an inherent ideal/fixed GL-heel relationship.

Introduction: Sagittal spinal imbalance in the adult remains poorly understood and challenging. Limitations of radiographic analysis have lead researchers to apply forceplate technology to enhance the study of spinal balance through evaluation of the gravity line (GL). The aim of this study was to investigate differences between asymptomatic adults and patients with sagittal spinal deformities, with a hypothesis that imbalance would lead to changes in the GL – spinal relationship.

Material and Method: This prospective study included 44 asymptomatic subjects (mean 57yo) and 40 patients with sagittal deformities (mean 65yo, inclusion criteria: L1-S1 lordosis< 258, Pelvic Tilt> 208, C7 plumbline> 5 cm). Coronal plane deformities were excluded. Full-length free-standing sagittal radiographs were obtained with simultaneous acquisition of the GL and heel position (by forceplate). Spino-pelvic radiographic parameters were calculated and distances (offsets) from the GL analysed. Group differences were evaluated by independent sample t-tests.

Results: Groups did not differ in age, thoracic kyphosis, offsets from femoral heads to heels, femoral heads to GL, and GL to heels. As per inclusion criteria the sagittal deformity group had greater mean C7 plumbline (8cm vs 0cm), increased pelvic tilt (27° vs 13°) and loss of lordosis (46° vs 58°). The sagittal deformity group also had greater pelvic incidence (60° vs 51°), anterior trunk inclination (−3° vs −11°), S1 displacement toward the heels (distance decreased, 87 vs. 46mm). All differences p< 0.001.

Discussion: The sagittal spinal deformity group revealed marked differences; the sacrum has a more posterior position in relation to the GL and heels. However, the GL to femoral head offset was not markedly influenced. The additional finding of no change in the GL to heel offset and rather fixed GL-femoral head offset appears to indicate that sagittal spinal deformity induces a posterior sacral translation and pelvic retroversion in order to maintain a fixed GL-heel relationship.