The effect of Luque-rod instrumentation on the sagittal contour of the lumbosacral spine in adolescent idiopathic scoliosis and the preservation of a physiologic lumbar lordosis.

The changes in the sagittal alignment of the lumbar spine were investigated in 28 patients with adolescent idiopathic scoliosis undergoing long posterior spinal fusion to L4 or L5 with contoured Luque rods and segmental sublaminar wiring. The lumbar lordosis over the instrumented levels was preserved, and there was no compensatory hyperlordosis of vertebral segments distal to the fusion. In situations where long posterior spinal fusions are indicated, instrumentation with contoured Luque rods and segmental sublaminar wiring can preserve the normal sagittal alignment of the lumbosacral spine.     

Proximal kyphosis after short posterior fusion for thoracolumbar scoliosis

Thoracolumbar idiopathic scoliosis usually is treated by anterior spinal fusion. However, short posterior spinal fusion that includes only the structural curve has been tried in a limited number of patients. The fusion may end cranially in the lower thoracic region and cause an increase in sagittal decompensation at the proximal junction. From July 1989 to July 1998, 14 patients were treated with thoracolumbar idiopathic scoliosis by short posterior spinal fusion. The lateral radiographs were evaluated preoperatively, immediately postoperative, and during followup. The focal kyphotic angle was used to examine the changes in focal sagittal alignment. A 10 degrees progression was defined as the radiographic criterion for the development of junctional kyphosis. Proximal junctional kyphosis occurred in six of the 14 patients, in which one patient needed revision surgery. In all six patients, the average preoperative lumbar lordosis was greater than 35 degrees, and decreased more than 10 degrees during surgery. In the five patients with a focal kyphotic angle larger than 10 degrees, four had proximal junctional kyphosis develop. According to the current findings, short posterior spinal fusion can be done only if the focal kyphotic angle proximal to the fusion is less than 10 degrees, and the lumbar lordosis must be preserved carefully during surgery.     

Biomechanics of scoliosis]

Scoliosis is defined as a three-dimensional deformity of the spine. The most pronounced component of scoliosis is in the frontal plane, comprising the lateral bending of the spine. Rotation of vertebra takes place in the transverse plane. In most cases of idiopathic scoliosis a decrease of thoracic kyphosis in the sagittal plane occurs. A more rare event is the appearance of a junctional kyphosis between the primary and secondary curve. The instrumentation introduced by Harrington dealt mainly with balancing the bending forces in the frontal plane (distraction of the concavity of the curve), along with fusion of the instrumented area. The multisegmental CD instrumentation allowed for the diminution of the lateral curve in the frontal plane, while at the same time "forcing" an increase of thoracic kyphosis in single curves, and restoration of physiological sagittal curves (thoracic kyphosis lumbar lordosis) in double curve scoliosis. The CD method achieved this good by a 90 degrees rotation of the rod towards the concavity of the curve, "changing" the lateral curve into kyphotic curve. In the AO USS (Universal Spine System) correction is achieved by pulling the hooks towards the rod. The procedure ends with the linking of two rods with transverse connectors forming this way a stable framework. The degree of correction achieved with this method is based on the biomechanic inter relation between the spine and the instrumentation system (application of distraction forces, compensatory forces and translocation of the instrumented segment). Post-op decompensation of the spine is usually the result of incorrect hook fixation, inadequate application of forces (distraction and compression) and use of a standard hook pattern for thoracic curves (type III) in other types of scoliosis.     

Differences in early sagittal plane alignment between thoracic and lumbar adolescent idiopathic scoliosis

Background contextIt has previously been shown that rotational stability of spinal segments is reduced by posteriorly directed shear loads that are the result of gravity and muscle tone. Posterior shear loads act on those segments of the spine that are posteriorly inclined, as determined by each individual's inherited sagittal spinal profile. Accordingly, it can be inferred that certain sagittal spinal profiles are more prone to develop a rotational deformity that may lead to idiopathic scoliosis; and lumbar scoliosis, on one end of the spectrum, develops from a different sagittal spinal profile than thoracic scoliosis on the other end.PurposeTo examine the role of sagittal spinopelvic alignment in the etiopathogenesis of different types of idiopathic scoliosis.Study design/settingMulticenter retrospective analysis of lateral radiographs of patients with small thoracic and lumbar adolescent idiopathic scoliotic curves.Patients sampleWe included 192 adolescent idiopathic scoliosis patients with either a thoracic (n=128) or lumbar (n=64) structural curve with a Cobb angle of less than 20° were studied. Children with other spinal pathology or with more severe idiopathic scoliosis were excluded, because this disturbs their original sagittal profile. Subjects who underwent scoliosis screening and had a normal spine were included in the control cohort (n=95).Outcome measuresThoracic kyphosis, lumbar lordosis, T9 sagittal offset, C7 and T4 sagittal plumb lines, pelvic incidence, pelvic tilt, and sacral slope, as well as parameters describing orientation in space of each individual vertebra between C7 and L5 and length of the posteriorly inclined segment.MethodsOn standardized lateral radiographs of the spine, a systematic, semi-automatic measurement of the different sagittal spinopelvic parameters was performed for each subject using in-house developed computer software.ResultsEarly thoracic scoliosis showed a significantly different sagittal plane from lumbar scoliosis. Furthermore, both scoliotic curve patterns were different from controls, but in a different sense. Thoracic kyphosis was significantly decreased in thoracic scoliosis compared with both lumbar scoliosis patients and controls. For thoracic scoliosis, a significantly longer posteriorly inclined segment, and steeper posterior inclination of C7–T8 was observed compared with both lumbar scoliosis and controls. In lumbar scoliosis, the posteriorly inclined segment was shorter and located lower in the spine, and T12–L4 was more posteriorly inclined than in the thoracic group. The lumbar scoliosis cohort had a posteriorly inclined segment of the same length as controls, but T12–L2 showed steeper posterior inclination. Lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope, however, were similar for the two scoliotic subgroups as well as the controls.ConclusionsThis study demonstrates that even at an early stage in the condition, the sagittal profile of thoracic adolescent idiopathic scoliosis differs significantly from lumbar scoliosis, and both types of scoliosis differ from controls, but in different aspects. This supports the theory that differences in underlying sagittal profile play a role in the development of different types of idiopathic scoliosis.     

Segmental analysis of the sagittal plane alignment of the normal thoracic and lumbar spines and thoracolumbar junction

Recent advances in spinal instrumentation have brought about a new emphasis on the three-dimensional spinal deformity of scoliosis and especially on the restoration of normal sagittal plane contours. Normal alignment in the coronal and transverse planes is easily defined; however, normal sagittal plane alignment is not so simple. This retrospective study was undertaken to increase the understanding of the normal alignment of the spine in the sagittal plane, with a special emphasis on the thoracolumbar junction. Measurements were made from the lateral radiographs of 102 subjects with clinically and radiographically normal spines. Cobb measurements of the thoracic kyphosis (T3-T12), the thoracolumbar junction (T10-T12 and T12-L2), and the lumbar lordosis (L1-L5) were determined. The spices of the thoracic kyphosis and lumbar lordosis also were determined. Using a computerized digitalizing table, the segmental angulation was determined at each level from T1-2 to L5-S1. In conclusion, there is a wide range of normal sagittal alignment of the thoracic and lumbar spines. When using composite measurements of the combined frontal and sagittal plane deformity of scoliosis, this wide range of sagittal variance should be taken into consideration. Using norms established here for segmental alignment, areas of hypokyphosis and hypolordosis commonly seen in scoliosis can be more objectively evaluated. The thoracolumbar junction is for all practical purposes straight; lumbar lordosis usually starts at L1-2 and gradually increases at each level caudally to the sacrum.     

The role of Harrington instrumentation and posterior spine fusion in the management of adolescent idiopathic scoliosis

The Harrington instrumentation system was the first widely used, internationally accepted internal fixation system for the correction of idiopathic scoliosis when combined with a spinal arthrodesis. It has been generally available to the orthopedic surgeon for more than 25 years, and therefore its capabilities and limitations have been identified through this long experience. Its implantation requires minimal invasion of the spinal canal and is associated with a low (less than 0.5 per cent) incidence of neurologic complications. It provides predictable correction of spinal deformity with little subsequent loss of correction. When compared with other newer, more complex internal fixation systems for spinal deformities, the Harrington system has a shorter, less difficult "learning curve"; requires less operating time and blood loss to insert; implants a smaller mass of metal; and in some cases costs substantially less for the implant system. The Harrington system has an extremely low incidence of hook dislodgment and pseudoarthrosis formation in single thoracic curves, being reported as near zero for these curves in two recently published series. Conversely, there are some disadvantages to the Harrington system when compared with other types of fixation. It has limited ability to provide sagittal plane control. It does not effectively and predictably derotate the spine. A recent study showed that at an average of 4 years postoperatively, nearly two thirds of the patients had an actual increase in their rib prominence. The pseudoarthrosis rate is high, up to 4 per cent, in the thoracolumbar and lumbar spine. Hook dislodgment approaches 3 per cent when used below the thoracic region. Another disadvantage is the necessity for postoperative external support. As a result, the Harrington system remains an excellent means of treating single and double thoracic idiopathic curves in a safe and predictable manner, while admittedly having limited derotation and sagittal plane control. Other systems that are more sophisticated at segmental fixation of the spine appear to be more appropriate for scoliotic deformities requiring fusion of the thoracolumbar or lumbar spine and those associated with significant sagittal plane deformities.     

Loss of lumbar lordosis. A complication of spinal fusion for scoliosis

Symptomatic loss of lumbar lordosis is a disabling complication of scoliosis surgery. This so-called "flat-back syndrome" is characterized by an inability to stand erect and by upper back pain. Distraction instrumentation extending into the lower lumbar spine or sacrum is the most frequently identified etiologic factor responsible for loss of lordosis. The more distal the level of instrumentation, the severer the loss of lumbar lordosis. Other factors that may aggravate the loss of lordosis include thoracolumbar kyphosis, fixed thoracic kyphosis, hip flexion contractures, and pseudoarthrosis. Because of the wide range of values for kyphosis and lordosis in normal individuals, there is no absolute value that can be considered "normal." It is the overall sagittal plane balance that is most important. The most useful radiographic measurement to evaluate this sagittal plane balance is the full-length standing lateral radiograph with the knees extended. On this view, the C7-S1 measurement should fall within 2 cm of the anterior aspect of the sacrum. Surgical treatment for symptomatic loss of lumbar lordosis consists of closing wedge osteotomies through the fusion mass. This should generally be preceded by an anterior release and interbody fusion. Correction should be obtained at the site of the deformity with particular attention paid to the thoracolumbar junction. The surgery is difficult and the risk of complication is high. The most important aspect of this postural disorder is prevention. Avoid distraction instrumentation that extends into the lumbar spine if possible. When distraction instrumentation is used, the techniques described will help preserve lumbar lordosis. When performing a fusion to the sacrum, distraction instrumentation should not be used.     

腰椎退行性疾患接受腰椎融合术后发生下腰痛和腰椎矢状位序列的相关性研究

目的探讨分析腰椎退行性疾患接受腰椎融合术后发生下腰痛和腰椎矢状位序列的相关性。方法回顾性分析我院于2010年2月~2011年6月收治的38例接受腰椎融合术的腰椎退行性疾病且术后发生下腰痛患者的临床资料,于所有患者出院后进行为期24个月的随访。在手术前及随访期间收集所有患者站立位X线片腰椎前凸的Cobb角,并分析其与患者下腰痛程度之间的相关性。结果术后12个月及24个月与手术前的腰椎矢状位Cobb角比较,均无统计学意义(分别为t=0.042,P=0.967及t=0.268,P=0.789);术后12个月及24个月的腰椎矢状位Cobb角与正常角度的差值与手术前比较均无统计学意义(分别为t=0.450,P=0.900及t=0.174,P=0.862)。术后12个月及24个月的VAS评分与手术前相比,有明显改善(分别为t=2.838,P=0.006及t=3.251,P=0.002),而术后12个月及24个月的ODI评分与手术前相比也有明显改善(分别为t=2.300,P=0.024及t=3.320,P=0.001)。术后12个月及24个月所有患者的腰椎前凸丢失与VAS评分及ODI评分均呈正相关(P0.05)。结论腰椎前凸角度的丢失与腰椎退行性疾患腰椎融合术后的腰痛关系密切,手术过程中腰椎前凸的重建十分重要。     

Selective posterior thoracic fusion by means of direct vertebral derotation in adolescent idiopathic scoliosis: effects on the sagittal alignment

The objectives of this retrospective study were to evaluate the effect of direct vertebral derotation on the sagittal alignment of the spine after selective posterior thoracic fusion for Lenke Type I adolescent idiopathic scoliosis (AIS). Preservation of the sagittal alignment has become critical in the management of spinal deformity. Better coronal and rotational corrections in posterior selective thoracic fusion for AIS have been reported with direct vertebral derotation as compared with the simple rod rotation technique. A greater lordogenic effect has been anticipated with direct vertebral derotation; however, data comparing those two techniques in terms of correction in the sagittal plane are still lacking. Standing full-spine PA and standard lateral serial X-rays of a total of 30 consecutive patients with adolescent idiopathic scoliosis treated between 2002 and 2008 at a single institution were evaluated. All the patients had Lenke Type I curves and underwent selective posterior thoracic fusion with pedicle screw instrumentation. Patients who were treated with additional osteotomies and concave or convex thoracoplasty or concomitant anterior releases were excluded. Minimum follow-up period was 24 months. Preoperative and postoperative coronal and sagittal spinal alignments in both the groups were compared. In 13 patients, the correction was achieved by means of a simple rod rotation (SRR). In 17 patients, the technique of direct vertebral derotation (DVD) was used. Scoliosis correction averaged 67 and 69%, respectively, and was similar in both groups (p > 0.05). Thoracic kyphosis and lumbar lordosis remained unchanged in the SRR group (p > 0.1). In the direct vertebral derotation group, a significant decrease of both thoracic kyphosis and lumbar lordosis of 8.1° and 11.8°, respectively, was observed (p < 0.0001). Global sagittal balance remained within normal limits in all the patients at the latest follow-up. Decrease in thoracic kyphosis and lumbar lordosis should be taken into account when using direct vertebral derotation for selective posterior thoracic fusion in AIS. In order to preserve sagittal alignment in these patients, ultra hard rods or maneuvers that pull posteriorly the concave side of the spine, thus avoiding the application of additional flattening forces should be considered.     

Excessive thoracic lordosis and loss of pulmonary function in patients with idiopathic scoliosis.

Idiopathic thoracic lordoscoliosis is more common and more productive of respiratory compromise than is kyphoscoliosis. In some patients with idiopathic scoliosis, thoracic lordosis is the predominant component of the disease. Five such patients, all of whom had idiopathic scoliosis with excessive thoracic lordosis, progressive deformity despite Milwaukee brace treatment, and significant compromise of pulmonary function, are presented. Harrington instrumentation (distraction rod only) and spine fusion improved the deformity and respiratory function. The recommended treatment for this type of idiopathic scoliosis is early recognition and prompt surgical correction. The Milwaukee brace should be avoided. Postoperative management must include early ambulation combined with vigorous breathing exercises.     

特发性胸椎侧凸患者的胸椎后凸状态对腰骶椎矢状面形态的影响

目的 探讨特发性胸椎侧凸患者的胸椎矢状面形态对腰骶椎矢状面形态的影响. 方法 研究对象包括胸弯犁青少年特发性脊柱侧凸(AIS)患者55例.所有研究对象均摄站立位脊柱全长正位片,并在上肢抱胸体位下摄站立位脊柱全长侧位片.按胸椎后凸(TK)的测量值分为:第一组TK<10°和第二组10°≤TK≤40°,测量的参数指标包括:腰椎前凸(LL)、上腰椎前凸、下腰椎前凸、骶骨后上缘与C,铅垂线的距离、骨盆倾斜角(PT)、骶骨倾斜角(SS)、骨盆投射角(PI).将第一组及第二组就参数的测量结果进行t检验比较(P<0.05),并对相关参数指标进行相关分析(P<0.01). 结果 第一组的LL和上腰椎前凸小于第二组的LL和上腰椎前凸,且具有统计学意义(P<0.05).胸弯型MS患者相邻节段的脊柱在矢状位形态上存在相关性,其中TK与LL、上腰椎前凸存在明显的线性相关.PT、SS及PI也存在明显的线性相关. 结论 胸弯型AIS患者的胸椎矢状面形态对患者的腰椎前凸有明显影响,并通过上腰椎对整个腰椎产生影响,在对主弯为胸椎的脊柱侧凸在进行选择性胸椎融合时必须考虑这种相互影响.     

Prevention and management of iatrogenic flatback deformity

The most common cause of iatrogenic flatback syndrome is Harrington distraction instrumentation extending into the lower lumbar spine. Other common causes and exacerbating factors include failure to enhance regional lordosis during lumbar fusion for degenerative spondylosis, development of pseudarthrosis or postoperative loss of correction, development of kyphosis at the thoracolumbar junction, development of degeneration and decompensation cephalad or caudad to a prior fusion, and hip flexion contractures. Prevention of flatback syndrome involves preoperative assessment of sagittal balance, avoidance of distraction instrumentation and extension of long fusions into the lower lumbar spine, enhancement of physiologic lordosis during lumbar fusions, and intraoperative positioning with the hips extended. Treatment of flatback syndrome involves corrective pedicle subtraction or Smith-Petersen osteotomies with segmental instrumentation. Polysegmental osteotomies and vertebral column resection may be utilized in cases of sloping global sagittal imbalance and related severe coronal imbalance, respectively. Following surgical treatment, sagittal balance is generally improved with fair-to-good clinical outcomes, high patient satisfaction, and moderately high perioperative complication rates.     

Lumbosacral fusions with Harrington rods and intersegmental wiring

Harrington rods are a valuable adjunct for fusion of the lumbosacral spine. Major limits of distractions are achieved with these rods. Greater amounts of decompression are possible. Decompression, alignment, and stability are maintained. Intersegmental wiring increases security and eliminates the problem of hook and rod displacement and loss of lumbar lordosis. A variety of methods are available for sacral fixation to avoid neurologic complications from the distal hooks. Three- and four-level Harrington rod distraction lumbosacral fusions have proven to be successful in returning severely-disabled spinal stenotic, obese, and osteoporotic patients to normal activities.     

The effect of Harrington rod contouring on lumbar lordosis

The effect of Harrington rod sagittal plane contouring, or lack of it, on total lumbar, segmental lumbar, and lumbosacral lordosis was studied retrospectively in a series of 36 patients operated on for idiopathic scoliosis. Regardless of contouring, there was a decrease in total lumbar lordosis and lordosis above L4, with an increase in lordosis below L5. Although not statistically significant, patients with contoured rods had less loss of segmental (L1-4) lordosis and less increase in segmental lumbosacral lordosis (L4-S1) than the noncontoured group. Although helpful, additional steps beyond concave rod contouring appear to be necessary to consistently preserve lumbar lordosis.     

Longitudinal changes in trunkal balance after selective fusion of King II curves in adolescent idiopathic scoliosis

STUDY DESIGN: A retrospective study was performed on the longitudinal changes of the trunkal balance in King II curves treated with selective posterior fusion of the thoracic curve. OBJECTIVES: To determine the effect of selective fusion on the coronal and sagittal plane balance in King II adolescent idiopathic scoliosis by analyzing the changes in shoulder level, pelvic tilt, trunk shift, centering of fusion mass, changes in the T11-L1 sagittal angle, and behavior of the unfused lumbar curve and its correlation with the end level of fusion. SUMMARY OF BACKGROUND DATA: It has been shown that selective fusion of the thoracic curve in a King II curve is associated with good results and arrest of lumbar curve progression in selected cases. Detailed quantitative analysis of the longitudinal changes and correlation between various clinical and radiologic parameters was not readily available in the literature. METHODS: This study investigated 24 patients with King II adolescent idiopathic scoliosis treated with Harrington rod and segmental spinous processes wiring in a 10-year period with follow-up periods of 3 to 8 years. Clinical and radiologic parameters were analyzed longitudinally during the preoperative and immediate postoperative period, then at 6 months, 1 year, 3 years, and final follow-up assessment. RESULTS: Progressive improvement in the trunk shift to within 2 cm of the center sacral line together with progressive leveling and stabilization of the shoulder and pelvic tilt was noted during the first year after surgery. Gradual movement of the Harrington rod toward the center sacral line assuming a "straight rod sign" with a rod to center line distance of less than 1 cm was found in 90% of the cases. Improvement of the sagittal alignment with no significant residual junctional kyphosis also was found. The unfused lumbar curve improved in both the coronal and sagittal plane and did not show any further progression. Patients whose lower end level of fusion was at T12 had a better percentage of lumbar curve correction than those that ended at L1. CONCLUSIONS: Selective thoracic fusion for King II idiopathic scoliosis curve can achieve acceptable coronal and sagittal plane balance of the spine. The rod to centersacral line distance is a helpful parameter in assessing the results and prognosis of surgically treated patients.     

3-D study of the immediate effect of the Boston brace on the scoliotic lumbar spine]

In order to study the immediate 3-D effect of the Boston brace on lumbar scoliosis, 31 adolescents with idiopathic scoliosis King type I or II had a 3-D computerised reconstruction of their deformity with and without the brace. Results demonstrate that the brace produces a distraction of the lumbar spine similar to that produced by the Harrington instrumentation by correcting the frontal deformity at the expense of a significant reduction of the physiological lumbar lordosis. No significant effect on rotation of the apical vertebra or "detorsion" of the spine could be measured. We feel that a orthosis that provides a real 3-D correction of the deformity has yet to be developed.     

The influence of lumbar lordosis on spinal fusion and functional outcome after posterolateral spinal fusion with and without pedicle screw instrumentation

The aim of the current study was to examine the correlation between lumbar lordosis, spinal fusion, and functional outcome in patients suffering from severe low back pain, treated by posterolateral spinal fusion with or without pedicle screw instrumentation. One hundred thirty patients were randomly allocated to posterolateral lumbar fusion with or without Cotrel-Dubousset instrumentation. Functional outcome was assessed preoperatively, and 1 and 2 years postoperatively. Lordosis angles of the lumbar spine and fusion rates were assessed at the 1- and 2-year follow-up. No difference in lordosis angle was found between the two groups at any time. Lordosis was unchanged at 2 years compared with preoperative status in both groups. In the instrumented group, nonunion (23%) was followed by a decrease in lordosis at follow-up (p < 0.05). However, in the noninstrumented group, nonunion (14%) resulted in increased lordosis (p < 0.05). No correlation was found between functional outcome and lordosis angle. The current study showed no correlation between functional outcome and lordosis angle either before or after posterolateral spinal fusion. Use of instrumentation did not influence lumbar spinal alignment compared with noninstrumented fusions. The sagittal alignment was stable both 1 and 2 years after solid fusion. The failure mode of instrumented fusions was a reduced degree of lordosis in contrast to an increased degree of lordosis in patients with noninstrumented fusion.     

The lumbar lordosis below Harrington instrumentation for scoliosis

This retrospective study evaluates lumbar lordosis in 43 patients before and after Harrington instrumentation into the lumbar spine. The authors measured overall lumbar lordosis, lordosis of unfused lumbar levels, and sagittal vertical axis. Lordosis decreased progressively in lower levels of fusion. The increase in lordosis below the fusion did not compensate for the overall loss of lordosis. The sagittal vertical axis moved forward, producing a subtle, asymptomatic form of flat back syndrome.     

Sagittal plane analysis in idiopathic scoliosis patients treated with Cotrel-Dubousset instrumentation

One hundred sixty patients with idiopathic scoliosis underwent preoperative and postoperative sagittal plane analysis of the thoracic spine, thoracolumbar junction, and lumbar spine. The data suggest that mild to moderate improvements in thoracic hypokyphosis are possible. When crossing the thoracolumbar junction, reversal of rod bend and reversal of hooks on the derotation rod appears to provide the most physiologic sagittal contour. Cotrel-Dubousset instrumentation to the mid and distal lumbar spine can preserve and, at times, enhance lumbar lordosis.     

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

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.