Sagittal Alignment in the Degenerative Lumbar Spine

Abstract

• ➤Sagittal alignment of the spine has gained attention in the field of spinal deformity surgery for decades. However, emerging data support the importance of restoring segmental lumbar lordosis and lumbar spinal shape according to the pelvic morphology when surgically addressing degenerative lumbar pathologies such as degenerative disc disease and spondylolisthesis.
• ➤The distribution of caudal lordosis (L4-S1) and cranial lordosis (L1-L4) as a percentage of global lordosis varies by pelvic incidence (PI), with cephalad lordosis increasing its contribution to total lordosis as PI increases.
• ➤Spinal fusion may lead to iatrogenic deformity if performed without attention to lordosis magnitude and location in the lumbar spine.
• ➤A solid foundation of knowledge with regard to optimal spinal sagittal alignment is beneficial when performing lumbar spinal surgery, and thoughtful planning and execution of lumbar fusions with a focus on alignment may improve patient outcomes.

The concept of spinopelvic alignment was described by Jean Dubousset as a “cone of economy” where the axial skeleton balances in line above the pelvis, lower limbs, and feet¹. From this idea, an understanding of multiple important sagittal alignment parameters (Fig. 1) emerged in the spinal deformity literature over the past few decades, and the importance of a harmonious spine is now well established². However, in the degenerative spine realm, careful consideration of the sagittal plane was not widely considered when planning operations for degenerative pathology. Recently, this paradigm has begun to shift, and the importance of sagittal alignment in assessment and treatment of patients with degenerative spinal conditions is becoming increasingly recognized. With the increased volume of lumbar fusions, and the need for better short-term and long-term patient outcomes, alignment concepts are emerging to possibly provide solutions to improve the outcomes and longevity of short construct fusions^3-5. This review will discuss the importance of sagittal plane alignment in the setting of degenerative lumbar disease based on recent literature, with the aim of assisting surgeons in improving outcomes following surgical management of degenerative spinal pathology.

Fig. 1.

Schematic representation of radiographic parameters used for sagittal alignment assessment. TPA = T1-pelvic angle, SVA = sagittal vertical axis, T1-T12 = thoracic kyphosis, T10-L2 = thoracolumbar junction, L1-S1 = LL, and L4-S1 = distal LL or lower LL.

Sagittal Alignment and Degenerative Lumbar Pathologies

The implications of abnormal spinopelvic alignment in degenerative lumbar pathologies have been recently investigated^6-10. Patients with higher pelvic incidence (PI) are more prone to experiencing lumbar spondylolisthesis, and those with extremely high PI values have a greater likelihood of developing 2-level disease^10-20. Although the literature has been conflicting with regard to the impact of degenerative spondylolisthesis on global lumbar lordosis (LL), a nuanced evaluation found that patients with degenerative spondylolisthesis have decreased LL in the caudal L4-S1 levels and increased LL in the cranial L1-L3 levels^11,13,16,18.

Sagittal alignment is also a factor in the clinical presentation of patients with spinal stenosis. However, in comparison with degenerative spondylolisthesis, where the anatomy exacerbates the clinical symptoms, the opposite appears to be the case in spinal stenosis. The loss of LL and increased sagittal vertical axis in patients with spinal stenosis are, in some cases, a compensatory mechanism in the flexible spine in order to open the neural foramen, although it should be noted that spinal stenosis occurs at different rates in patients depending on spinopelvic morphology^8,21. As malalignment progresses in spinal stenosis, these patients maintain their pelvic tilt (PT) and compensate by shifting the pelvis posteriorly, with pelvic retroversion considered a late finding in this cohort of patients²². This differs from patients with primary adult spinal deformity, who use pelvic retroversion as an earlier means of compensation²². For patients with lumbar spinal stenosis, simple lumbar decompression can potentially improve spinopelvic alignment, with Ham et al. demonstrating improvement in relative spinopelvic measures in patients with preoperative pain within 10 minutes of standing²³. The application of sagittal alignment principles to lumbar degenerative disease may help to improve outcomes because one of the main issues facing degenerative spine surgery is the increased prevalence of overcorrected and undercorrected lordosis in patients with short-segment fusions²⁴. This is partly due to the ambiguity in defining lordosis targets for any given lumbar disc-vertebral segment. Evaluating the contribution to lordosis from each segment is important, as it varies from one subject to another, even in the non-pathologic spine. The following sections will delve deeper into the normal lordosis and shape of the lumbar spine and the impact of age and degeneration on both.

LL, the Body, and the Disc

LL, a critical component of the sagittal plane for maintaining an upright posture, is primarily formed by a combination of wedging of the lumbar vertebral bodies and intervertebral discs^25-28. Vaz et al. demonstrated that more lordosis is achieved by intervertebral disc wedging than by vertebral body wedging²⁷. Been et al. confirmed these results and noted a progression from increased dorsal (lordotic) wedging of the vertebral bodies in the lower lumbar spine to slight ventral (kyphotic) wedging of the upper lumbar spine as LL transitions to thoracic kyphosis²⁸. This transition usually occurs at the L2 vertebra, although this is influenced by normal variations in sagittal alignment among humans. Additionally, variations in sagittal alignment also influence the relative proportions of lordosis generated from the body and the disc.

Roussouly et al. was the first to describe different lumbar spinal shapes based on normal variations in sacral slope (SS)²⁵. In this work, Roussouly et al.²⁵ redemonstrated an earlier finding from Legaye et al.²⁹, showing global LL to significantly correlate with SS and PI, although a weaker correlation was demonstrated with PI. PI describes the orientation of the sacrum within the ilium. PI increases throughout skeletal maturation, with anterior-posterior growth of the pelvis, before becoming fixed in adulthood, with a range from 20° to >80° in normative data³⁰. PI is thought to remain unchanged in adulthood, even with degeneration^31-33. However, recent data revealed that PI actually may change over time via increased stress over the sacroiliac joints and subsequent remodeling of these joints and the sacral end plate, a process evident in patients with long fusions involving S1 as the lower instrumented vertebra^34,35. Nevertheless, given the relative stability of PI compared with SS, LL is often evaluated relative to PI²⁵. In asymptomatic subjects, PI affects the magnitude and distribution of LL; subjects with a larger PI have a more horizontal sacrum, a higher SS, and a larger LL with a more proximal apex compared with those with a low PI^34,36,37. LL is also correlated with thoracic kyphosis; in particular, the upper arch of the lordosis is often equal to the lower arch of the thoracic kyphosis^38,39. Therefore, it is favorable to evaluate LL based on its relationship with PI and thoracic kyphosis.

Defining Normal Global, Regional, and Segmental LL

Defining surgical targets for LL has evolved over the years. The historical target was “as much lordosis as possible.” This continued until several authors, including Schwab et al. and Lafage et al., proposed matching PI to LL within 10°, which has been shown to improve outcomes even in surgical procedures for degenerative pathology^35,40-51. It has been suggested to correct LL to PI + 10° if the PI is low and to PI − 10° if the PI is high⁵². Since then, this simple concept of PI–LL has progressed into targeting the ideal lumbar apex and distribution of lordosis between the cephalad and caudal segments^36,53. Those measurements are of particular importance in the degenerative lumbar spine because patients may have a poor distribution of LL even though global lordosis may appear normal. In one formative study, Pesenti et al. helped to define the regional distribution of lordosis in normal subjects³⁴. The distribution of caudal lordosis (L4-S1) and cephalad lordosis (L1-L4) as a percentage of global lordosis varies by PI, with cephalad lordosis increasing its contribution to total lordosis as PI increases³⁴. Their study also built on the work by Roussouly et al.²⁵ and redemonstrated that, as PI increases, the apex of lordosis migrates to a more cephalad location, with a concomitant increase in the magnitude of proximal lordosis. Therefore, lordosis of the lumbar segments above and below the apex became better appreciated. It is important to note that authors have differed in their definitions of caudal and cephalad lordosis. Roussouly et al. defined cephalad lordosis as the lordosis proximal to the apex, which varies by PI²⁵. However, to simplify the concept, Pesenti et al. analyzed lordosis within fixed boundaries of L1-L4 and L4-S1 (Fig. 2)³⁴. The application of these measurements in degenerative spine diseases has been shown to reduce the risk of postoperative malalignment, adjacent segment disease, and revision surgery^24,54-56. Recent studies have furthered the understanding of a harmonious sagittal plane, reporting the mean segmental lordosis values based on PI^34,35. Table I includes the mean segmental lordosis per PI category; these values were extrapolated from recent normative segmental lordosis publications^34,35. The table provides a general reference for surgical planning; however, surgical planning should be personalized for each patient’s spinopelvic anatomy. For example, in cases of low PI, it can be normal for the proximal lumbar vertebrae to be kyphotic, and aiming for a neutral T10-L2 alignment would be appropriate for most patients.

Fig. 2.

Evaluating global LL (left), regional LL (middle), and segmental LL (right).

TABLE I.

Mean Segmental Sagittal Alignment Values for the Lumbar and Thoracolumbar Spinal Regions^*

PI Category	T10-L2	L1-L2	L2-L3	L3-L4	L4-L5	L5-S1
40°	−6.9°	1.7°	4.4°	9.5°	15°	17.5°
50°	−4.3°	1.7°	6.2°	10.1°	15°	20°
60°	−4.3°	3.1°	7.9°	11.2°	15°	20°
70°	2.1°	4.9°	9.2°	15.4°	15°	20°
80°	2.1°	5.5°	11.9°	17°	19°	20°
90°	2.1°	7.3°	14.6°	12.9°	22°	20°

^*These data should be interpreted with caution, as the values are means and thus may not be prescriptive for every patient.

Impact of Age and Degeneration on LL

Prost et al. examined the correlation between age and sagittal alignment of the spine in asymptomatic volunteers⁵⁷. They found that, in individuals with low PI, there was a global decrease in LL in both cephalad and caudal segments; in contrast, in individuals with high PI, more prominent loss of caudal lordosis was associated with increased PT and more prominent loss of cephalad lordosis was associated with increasing kyphosis and positive sagittal malalignment⁵⁷. These findings have important implications and call for thorough assessment of PI and caudal and cephalad lordosis, with a surgical plan that aims to restore appropriate segmental lordosis based on spinopelvic anatomy⁵⁸.

In the degenerative setting, decreased global LL (or flattening of the lumbar spine) can occur by squaring of the intervertebral discs from their previous dorsal wedging and degeneration of the intervertebral discs to a more kyphotic alignment, leading to alteration of segmental lordosis^59-62. Thus, measurement of vertebral body wedging and intervertebral disc lordosis of the segment of interest will inform decisions with regard to the type of interbody device required in terms of magnitude of lordosis, height, location of the end-plate contact, and need for posterior compression of that segment²⁵. For example, in isthmic spondylolisthesis, as the L5 vertebra translates anteriorly, the vertebral body has been shown to become more trapezoidal, the sacral dome becomes more dysplastic, and relative kyphosis develops at the intervertebral disc and lower lumbar segments⁵⁹. Therefore, careful assessment of the L5 body and L5-S1 segmental alignment is important in surgical decision-making and choices of implants and techniques (Fig. 3). Overall, when performing a short-segment lumbar fusion, one should always be aware of the magnitude of lordosis in the level of interest, as well as in adjacent segments. Degenerative changes altering the magnitude of lordosis in 1 segment induce compensatory changes in other segments to maintain sagittal alignment. Thus, global lordosis may appear normal, but focused analysis will reveal the suboptimal lumbar distribution between cephalad and caudal segments^63,64. The implications of this concept may explain some biomechanical failures in short lumbar fusions that include both pathologic segments and those in compensated positions; however, there have been no data yet to support this hypothesis. Similarly, fusion might be indicated for a hyperlordotic-compensated segment with resultant stenosis; recognizing this phenomenon enables surgeons to fuse in a proper segmental lordosis. In this scenario, the alignment goal might be to reduce (rather than increase) lordosis in that segment.

Fig. 3.

Two examples of L5 vertebral body shapes that could factor into restoring segmental lordosis. The yellow lines indicate L5 vertebral end plates.

Although the prior argument emphasizes the importance of sagittal alignment in the degenerative spine, alignment itself is not an indication for surgical intervention. Patients’ physical examination, symptomology, and clinical correlation of radiographic findings to patient-reported outcome measures remain the first line to indicate patients for a surgical procedure. Therefore, it is imperative to note that we do not encourage fusing additional segments to optimize the sagittal plane, but rather encourage a critical analysis of segmental lordosis throughout the lumbar spine and an aim of restoring the surgically indicated levels to the normative targets. Figure 4 illustrates 3 types of degenerative spine conditions; note the associated loss of segmental lordosis, cephalad or caudal, and hyperlordotic compensation in adjacent segments^65-67.

Fig. 4.

Three types of degenerative lumbar disease from a sagittal alignment standpoint: loss of lordosis in caudal segments (Fig. 4-A), cephalad segments (Fig. 4-B), and globally throughout the lumbar spine (Fig. 4-C). L2-L3 and L3-L4 compensatory hyperlordosis is noted in Figure 4-A, L2-L3 decompensation (rotational failure) and L5-S1 compensatory hyperlordosis are noted in Figure 4-B, and no compensation due to regional degeneration (red oval) is noted in Figure 4-C.

Why Should Surgeons Preserve or Restore the Sagittal Plane in Degenerative Lumbar Surgery?

The decision to fuse the lumbar spine for degenerative pathology can be challenging. We believe that there are 3 important concepts to which to adhere (Table II).

TABLE II.

Recommendations for Restoring the Sagittal Plane in Degenerative Lumbar Surgery

Benefits of Ideal Segmental Lordosis	Grade of Recommendation*
No creation of lumbar segmental malalignment during spinal fusion surgery	B
Prevention of adjacent segment disease	B
Reduction of the incidence of low back pain	B

^*According to Wright¹¹², grade A indicates good evidence (Level-I studies with consistent findings) for or against recommending intervention; grade B, fair evidence (Level-II or III studies with consistent findings) for or against recommending intervention; grade C, poor-quality evidence (Level-IV or V studies with consistent findings) for or against recommending intervention; and grade I, insufficient or conflicting evidence not allowing a recommendation for or against intervention.

The first concept is to not create malalignment. The spinal surgery community remains poor at restoring alignment, with 1 study showing that 28% of patients remained malaligned following short-segment fusion for degenerative lumbar pathologies⁶⁸. Despite advances in segmental fixation and the power of newer interbody devices, there remains a high prevalence of iatrogenic sagittal plane deformity following short-segment fusions^69-72. Subsequent management of these patients can include the need for invasive procedures such as pedicle subtraction osteotomies, with complication rates as high as 60%. This indicates the importance of careful preoperative planning at the index surgical procedure⁶⁸.

Specific approaches to the spine and the use of selected interbody devices can profoundly impact spinopelvic parameters and regional alignment. Anterior lumbar interbody fusion (ALIF) is a reliable procedure that can provide powerful correction exceeding 30° of segmental lordosis; this may be vital at the L5-S1 segment. However, moving cranially in the spine can make the approach for ALIF cage placement challenging. Lateral approach techniques such as lateral lumbar interbody fusion (LLIF) and oblique lumbar interbody fusion (OLIF) can provide access to upper lumbar disc spaces and provide a substantial increase in segmental lordosis when combined with an anterior column realignment approach, compared with posterior-based approaches^73-77. LLIF and OLIF can be combined with a posterior approach for posterior-column osteotomies to further improve segmental and global alignment^78,79. Posterior-based approaches include transforaminal lumbar interbody fusion (TLIF) and posterior lumbar interbody fusion (PLIF). Multiple studies have shown that surgeons and implants vary in their ability to achieve lordosis at an individual segmental level utilizing TLIF^44,80,81. Successful restoration (or retention) of segmental lordosis can be challenging via TLIF, but may be achieved with the aid of dedicated spinal tables, anteriorly placed TLIF cages, posterior column osteotomies, and compression posteriorly before the final tightening of the set screws^82,83. Therefore, after the ideal segmental lordosis and the overall lumbar shape and apex have been chosen, choosing the proper surgical technique and implant may optimize achievement of alignment goals for the individual lumbar segments⁸⁴.

In vertebral levels that already have substantial disc height and segmental lordosis, it can be challenging to further increase lordosis, and interbody device placement may induce kyphosis without appropriate attention to technical detail⁸⁵. Bilateral facetectomy, anterior cage placement with compression across the posterior pedicle screws, and the use of expandable cages have been shown to mitigate these risks, although surgeons should be aware of the increased risk of subsidence with expandable cage placement^86,87. Furthermore, iatrogenic foraminal stenosis and inadequate restoration of foraminal height are potential issues with lordosis restoration that need to be carefully considered. In general, and regardless of the approach and type of interbody device utilized, targeting segmental lordosis ideals should be the goal from an alignment perspective. It is important to note that restoring the segmental lordosis or achieving ideal alignment does not mean fusing an additional level, but rather ensuring that the indicated segment has adequate lordosis by increasing it, maintaining it, or sometimes decreasing it (Table I).

The second concept is to aim to prevent the development of adjacent segment disease. Sagittal malalignment may be a risk factor for developing adjacent segment disease, even following short-segment lumbar fusion for degenerative pathology. This is likely due to altered spinal biomechanics and stress concentration at the adjacent disc segments. This point was exemplified by Herrington et al., who showed that surgically reducing lordosis at L4-L5 led to increased focal lordosis at L3-L4 and a higher reoperation rate for adjacent segment disease at that location⁵⁵. Similarly, Bari et al.²⁴ and Zheng et al.⁵⁶ demonstrated that, postoperatively, patients in whom <50% of the total lordosis was generated at L4-S1 experienced higher revision rates compared with patients with an adequate distribution of lordosis. Other studies have corroborated these findings, demonstrating the importance of sagittal alignment in lowering the risk of adjacent segment disease after lumbar fusion for degenerative pathology^88-93. Although multiple studies have found an association between adjacent segment disease and sagittal alignment, Toivonen et al. found no association in their study with 10-year clinical outcome follow-up but only 3-month postoperative radiographic follow-up⁹⁴. Hsieh et al. reported similar findings in a smaller study sample without a control group⁹⁵. Furthermore, Hsieh et al. focused on global LL using PI–LL, instead of assessing segmental lordosis, which may have misclassified patients with compensatory changes adjacent to the indicated levels⁹⁵.

The goal should not simply be to obtain as much disc height or segmental lordosis as possible, but to follow segmental lordosis targets⁹⁶. Thus, harmonious restoration of level-specific sagittal parameters may help to reduce the risk of adjacent segment disease after lumbar fusion. Other factors that may contribute to the development of adjacent segment disease include preexisting facet degeneration cranial to the fusion, increased preoperative PT that does not correct after fusion, inadequate restoration of lordosis, advanced age, osteoporosis, higher body mass index, and longer fusion length^97-102.

The third concept is to decrease the incidence of low back pain and spine-related disability by improving spinopelvic alignment parameters. In cases where spinopelvic alignment improves after isolated decompression, the associated back pain experienced by patients also improves¹⁰³. This finding has carried over into cases of fusion, where restoration of both segmental lordosis and PT has resulted in decreased low back pain¹⁰⁴. More globally, the correction of PI–LL as well as a positive sagittal vertical axis have also been shown to aid in the reduction of back pain for degenerative pathologies¹⁰⁵. Back pain and fatigue in patients with spinopelvic malalignment may be driven by compensatory changes that occur outside of the fusion construct due to flattening of the thoracic kyphosis, elevated PT and posterior shift, knee flexion, cervical alignment compensation, and muscle fatigue due to increased energy expenditure^106-108.

Case Example

Brief History

A 73-year-old patient presented with progressive low back pain, unresponsive to conservative measures, and bilateral lower-extremity radiculopathy. Magnetic resonance imaging (MRI) scans revealed moderate central and neuroforaminal stenosis bilaterally at the L4-L5 and L5-S1 levels. The preoperative patient-reported outcome measures were an Oswestry Disability Index (ODI) of 40, EuroQol Index Score (estimated health utility) of 0.60, Patient-Reported Outcomes Measurement Information System (PROMIS) Global Mental Health (GMH) of 50.80 and Global Physical Health (GPH) of 37.40, and Moderate to Vigorous Physical Activity (MVPA), determined from the Exercise Vital Sign (EVS), of 90.00.

Preoperative Radiographic Alignment

Obtaining imaging that captures the entire spine and the lower extremities is preferred to assess any compensatory changes that have occurred. Lumbar and full-body lateral free-standing radiographs revealed L4-L5 and L5-S1 grade-2 spondylolisthesis, dynamic in nature when compared between flexion and extension radiographs. In addition, compensatory L3-L4 lordosis and L2-L3 hyperlordosis were noted. The patient had an L1-L4 lordosis of 38.1° and an L4-S1 lordosis of 18.3°, indicating a maldistribution of lordosis (Fig. 5). The PT was 28°, indicating compensatory pelvic retroversion.

Fig. 5.

Preoperative sagittal alignment, with spinopelvic parameters. CT = computed tomography.

Surgical Planning

Preoperatively

To obtain 20° of lordosis at L5-S1, an ALIF device with 18° of lordosis was provisionally planned, pending confirmation of a preserved shape rather than plastic deformation of the L5 body intraoperatively (the preoperative L5 body lordosis was approximately 10°, but it was mostly driven by the concavity of the inferior end plate). A 12° ALIF device was planned at L4-L5 to obtain the segmental goal of 15°, pending intraoperative assessment of end-plate contact, as L4 vertebral body lordosis was only 7°. Finally, the baseline height difference between the L4-L5 and L5-S1 foramina was expected to factor into the heights of the cages (a 14-mm cage at L5-S1 compared with a 12-mm cage at L4-L5). We perform intraoperative measurements to ensure the achievement of segmental lordosis targets. Interbody device plans can be modified according to end-plate contact, reduction of spondylolisthesis, the impact on segmental lordosis, and lordosis gained from the cage. The decision was made to perform posterior instrumentation and fusion from L4 to the pelvis, and the plan was simulated via dedicated software; 5.5-mm titanium rods that could be prebent were requested.

Intraoperatively

During the anterior stage of the operation, the anterior edge of the inferior end plate of the L5 body had plastically deformed, necessitating an 18° L5-S1 ALIF cage, whereas the L4-L5 plan remained a 12° cage. During the second stage, and in a prone position, intraoperative fluoroscopy revealed that 39° of L4-S1 lordosis was achieved, which was the ideal target based on the PI that the patient had. Following instrumentation, L4-S1 increased to 42°, which remained within an acceptable range of the target. To achieve better end-plate contact of the ALIF cages, the decision was made to compress the screws posteriorly by the final tightening of the L4 pedicle screws and the compression of the L5 and S1 screws (our preferred method of compression), which migrated the apex from the L4 body to the L4-L5 disc. Subsequently, S2-alar-iliac fixation was performed because of the magnitude of spondylolisthesis and lordosis correction (Fig. 6).

Fig. 6.

Intraoperative fluoroscopy during the anterior stage (Figs. 6-A and 6-B) and the posterior stage (Figs. 6-C, 6-D, and 6-E) of the surgical procedure.

Postoperatively

Full-body standing EOS radiographs (EOS Imaging) revealed restoration of caudal and cephalad lordosis and relaxation of adjacent segment compensation at L2-L3 and L3-L4. Imaging also revealed relaxation of the PT. At the 1-year follow-up (Fig. 7), the patient was satisfied with the surgical procedure, and the postoperative patient-reported outcome measures were an ODI of 3, a EuroQol Index Score of 0.81, a GMH of 62.50, a GPH of 50.80, and an MVPA of 210.00.

Fig. 7.

Postoperative sagittal alignment, with spinopelvic parameters.

Future Directions

Sagittal alignment in degenerative spine disease will probably be the focus of numerous future studies. Future research could explore the impact of PI-adjusted relative spinopelvic measurements on outcomes following short-segment lumbar fusion, given their demonstrated benefits in adult spinal deformity correction^109-111. Specifically, and more tailored to patients with spinal degeneration, there remains the need to investigate the impact of segmental lordosis surgical targets on patient-reported outcomes and rates of long-term complications and revision surgery. Restoring the shape of the lumbar spine requires carefully planning each lumbar fusion operation and tailoring interbody selection, rod contouring, and segmental correction to the patient’s need, primarily driven by the morphology of the pelvis.

Summary

Sagittal alignment of the degenerative lumbar spine is important for spinal surgeons to measure and assess prior to the surgical procedure. A detailed examination of segmental (level-specific) lordosis is likely more important in degenerative conditions than in spinal deformity, due to the performance of short fusions for degenerative conditions rather than long-segment deformity fusion crossing the spinal junctions. Importantly, sagittal realignment, in itself, is not an indication for longer fusions. Our preferred approach is foundational and focuses on proper LL distribution in the indicated levels, which may include maintenance, restoration, or even reduction of lordosis. The subtle deterioration of the sagittal profile in revision surgery is often overlooked. Chasing adjacent segment failure without analyzing the sagittal plane can lead to avoidable revisions. Thus, optimizing caudal lordosis, avoiding fusing cephalad segments with too much lordosis, and ensuring a proper thoracolumbar inflection point are integral concepts in realignment of the degenerative lumbar spine.