Calculation of the Target Lumbar Lordosis Angle for

SPINE Volume 41, Number 4, pp E211–E217

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DIAGNOSTICS

Calculation of the Target Lumbar Lordosis Anglefor Restoring an Optimal Pelvic Tilt in ElderlyPatients With Adult Spinal Deformity

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Yu Yamato, MD, PhD,� Tomohiko Hasegawa, MD, PhD,� Sho Kobayashi, MD, PhD,� Tatsuya Yasuda, MD,�

Daisuke Togawa, MD, PhD,� Hideyuki Arima, MD,� Shin Oe, MD,� Takahiro Iida, MD, PhD,y

Akira Matsumura, MD, PhD,z Naobumi Hosogane, MD, PhD,§ Morio Matsumoto, MD, PhD,{

and Yukihiro Matsuyama, MD, PhD�

Results. In the cross-sectional study, the linear regression
Study Design. This investigation consisted of a cross-sectional
study and a retrospective multicenter case series.Objective. This investigation sought to identify the ideal lumbar

lordosis (LL) angle for restoring an optimal pelvic tilt (PT) in

patients with adult spinal deformity (ASD).Summary of Background Data. To achieve successful cor-

rective fusion in ASD patients with sagittal imbalance, it is

essential to correct the sagittal spinal alignment and obtain a

suitable pelvic inclination. We determined the LL angle that

would restore the optimal PT following ASD surgery.Methods. The cross-sectional study included 184 elderly volun-

teers (mean age 64 years) with an Oswestry Disability Index

score less than 20%. The relationship between PT or LL and the

pelvic incidence (PI) in normal individuals was investigated. The

second study included 116 ASD patients (mean age 66 years)

who underwent thoracolumbar corrective fusion at 1 of 4 spine

centers. The postoperative PT values were calculated using the

parameters measured. On the basis of these studies, an ideal

LL angle was determined.

right © 2016 Wolters Kluwer Health, Inc. Unau

the �Department of Orthopaedic Surgery, Hamamatsu Universityof Medicine, Shizuoka Prefecture, Japan; yDepartment of Ortho-Surgery, Dokkyo Medical University Koshigaya Hospital, Saitama

ure, Japan; zDepartment of Orthopaedic Surgery, Osaka City Generalal, Osaka Prefecture, Japan; §Department of Orthopedic Surgery,al Defense Medical College Hospital, Saitama Prefecture, Japan; andrtment of Orthopaedic Surgery, School of Medicine Keio University,to, Japan.

wledgment date: May 13, 2015. First revision date: July 23, 2015.tance date: August 20, 2015.

anuscript submitted does not contain information about medical(s)/drug(s). No funds were received in support of this work. Relevantal activities outside the submitted work: consultancy, grants, pay-or lectures, royalties.

s correspondence and reprint requests to Yu Yamato, MD, PhD,ment of Orthopaedic Surgery, Hamamatsu University School ofine, 1-20-1, Handayama, Higashi-ku, Hamamatsu-city, Shizuoka92, Japan; E-mail: [email protected]

0.1097/BRS.0000000000001209

equation for the optimal PT as a function of PI was ‘‘optimal

PT¼0.47� PI – 7.5.’’ In the second study, the postoperative PT

was determined as a function of PI and corrected LL, using the

equation ‘‘postoperative PT ¼0.7 �PI – 0.5 � corrected

LLþ8.1.’’ The target LL angle was determined by mathemat-

ically equalizing the PTs of these 2 equations: ‘‘target

LL¼0.45�PIþ31.8.’’Conclusion. The ideal LL angle can be determined using the

equation ‘‘LL¼ 0.45�PIþ 31.8,’’ which can be used as a

reference during surgical planning in ASD cases.Key words: adult spinal deformity, elderly patients, elderlyvolunteers, pelvic tilt, posterior corrective fusion, posteriorsurgery, sagittal plane balance formula, spino-pelvic alignment,spino-pelvic parameters, surgical planningLevel of Evidence: 4.Spine 2016;41:E211–E217

t is well known that sagittal spino-pelvic alignment,

I including pelvic position, is important for maintaining ahigh health-related quality of life (HRQOL) in patients

with adult spinal deformity (ASD). ASD includes manypathologies such as kyphosis after osteoporotic vertebralfractures, degenerative kyphosis or de novo kyphoscoliosis,adult scoliosis with degeneration, and iatrogenic spinaldeformity. Spinal sagittal malalignment has been correlatedwith pain, physical disability, and mental disability,1–10

despite differences in the pathologies of these conditions.Takemitsu et al1 found that most patients with degenerativelumbar kyphosis have low back pain, and most cases show amarked loss of sacral inclination. Itoi2 revealed the relation-ship between spinal deformity and low back pain in patientswith osteoporosis, observing lower lumbar lordosis (LL)and pelvic retroversion in patients with low back pain. Morerecently, Glassman et al3,4 established that global sagittalalignment correlated with HRQOL in patients with scoliosisgreater than 30 degrees or other significant spinal

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DIAGNOSTICS Calculation of the Target Lumbar Lordosis Angle � Yamato et al

deformities, including a primary deformity in the sagittalplane. Lafage et al5 reported high correlations of pelvicretroversion, measured by the pelvic tilt (PT), and thesagittal vertical axis (SVA) with HRQOL scores, under-scoring the role of sagittal spino-pelvic parameters as themain drivers of disability for patients with ASD. Schwabet al6,7 recently established thresholds for key radiographicparameters [SVA, PT, and pelvic incidence-LL (PI-LL)] onthe basis of their linear regression with Oswestry DisabilityIndex (ODI) measures. Many authors have hypothesizedthat HRQOL is affected by not only global sagittal align-ment but also the appropriate pelvic inclination.

The contribution of pelvic inclination to sagittal spinalalignment has also been emphasized.11 Considering thecompensatory mechanisms, the concept of global spino-pelvic alignment is important for maintaining an uprightposture and a high HRQOL.3–8 In terms of surgical treat-ment for elderly ASD patients, long fusion that includes thepelvis is frequently necessary to restore the optimal globalspino-pelvic alignment. Patients with a fused pelvis cannotcompensate for an improper spino-pelvic alignment usingpelvic retroversion after surgery. A compensated spino-pelvic alignment should not be reconstructed during ASDcorrective surgery in elderly patients.

The PT depends on the patient’s PI, age, and ethnicity.11–13

Many studies have explored the normal range of variousradiographic spino-pelvic parameters in asymptomaticparticipants.14–17 The spino-pelvic alignment of elderly indi-viduals and the effect of aging are unknown, because previousstudies enrolled young participants.

The prediction of postoperative alignment is necessaryfor optimal surgical planning for the treatment of spinaldeformity. Several mathematical prediction formulas thatestimate the sagittal alignment after corrective surgery havebeen reported.18–22 Lafage et al23,24 determined anequation to predict PT after surgery using multilinearregression analysis with key parameters. Although thealignment of the lumbar spine can be corrected via surgery,the ideal LL angle remains unknown. In the present set ofstudies, we aimed to determine the ideal LL angle thatwould restore the optimal pelvic inclination followingASD surgery. First, in a cross-sectional study to determinethe normal PT as a function of the PI, we assessed theradiographic spino-pelvic parameters of normal elderlyJapanese people. Second, we evaluated the postoperativepelvic inclination among patients to determine a model thatcan identify the PT using corrected parameters. On the basisof the results of these studies, an ideal correction target LLangle was determined.

MATERIALS AND METHODSBecause this study had two distinct aims, two differentgroups of subjects were investigated. In order to determinethe ideal LL, we investigated the optimal PT of healthyelderly Japanese volunteers. Next, the postoperative pre-dicted PT of elderly ASD patients who underwent surgerywas determined through a multicenter investigation.

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E212 www.spinejournal.com

Cross-Sectional Study: Determination of theOptimal Sagittal Alignment in Elderly IndividualsThis cross-sectional study was conducted in the town ofToei in the Aichi prefecture of Japan. A total of 690 adults(aged 50–94 years) who participate in an athletic healthscreening program in Toei were assessed for inclusion in thisstudy. The spino-pelvic radiographic parameters of an entirespine standing X-ray were measured. The ODI was utilizedfor the HRQOL evaluation. Spino-pelvic alignments inelderly volunteers over age 70 significantly deterioratedue to a degenerative change. Therefore, individuals agedbetween 50 and 70 years with an ODI score less than 20%were included in this study. Individuals with an obviousradiographic abnormality such as spondylolysis, spondylo-listhesis, scoliosis, or hip joint disease were excluded fromthis study, to ensure that the normative alignment is deter-mined. Radiographic data collection consisted of full-lengthstanding sagittal radiographs obtained in a free-standingposture with the fingers on the clavicles.25 All images weredigitized and analyzed using the validated dedicated spinesoftware Surgimap (Nemaris Inc., NY). Radiographicmeasurements were conducted by 7 orthopedic surgeons.Spino-pelvic measurements included thoracic kyphosis(TK), LL, SVA, PI, PT, and sacral slope (SS). All parameterswere measured 2 times by 2 of 7 orthopedic surgeons, andresults were averaged. The inter-observer reliability wascalculated using reliability statistics by intraclass correlation(ICC) of initial 150 subjects. This study was approved by theinstitutional review board of Toei hospital.

Postoperative PT Study: Predicted PTThe second study was a retrospective, multicenter caseseries. The second group of patients included consecutiveASD patients who underwent thoraco-lumbar correctivesurgery in 2013. Patients with a neurologic deficit, neuro-muscular disease, or hip joint disease that affects pelvicinclination were excluded from this study. We examinedthe standing radiographs as previously described, obtainedbetween 2 and 6 weeks after the operation. Spino-pelvicparameters were measured in these X-ray images using themethod described in the cross-sectional study. The post-operative PT value was predicted from the corrected spino-pelvic parameters using a multiple regression analysis. Apredictive model of PT was based on the PI and surgicallycontrollable parameters. Values of the PT predictive modelwere compared with actual postoperative values to verifyand improve the precision of the model. This study wasapproved by the institutional review board of HamamatsuUniversity School of Medicine.

Statistical AnalysisIn the cross-sectional study, the relationship between the PI,LL, and PT values was investigated using Pearson’s corre-lation coefficient tests and linear regression analysis. In thepredictive postoperative PT study, multiple regressionanalysis was used to create the predictive PT model. Therelationship between the predicted and measured PT was


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Figure 1. The relationship between pelvic tilt (PT) and pelvic inci-dence (PI) in elderly volunteers with an Oswestry Disability Index(ODI) under 20%.


investigated using a Pearson’s correlation coefficient test. Adifference with P value less than 0.05 was consideredsignificant. All statistical computations were processedusing the Statistical Package for the Social Science (SPSS)software (version 21.0; SPSS INC, Chicago, IL).

RESULTS

Cross-Sectional StudyThe cross-sectional study included 184 healthy elderlyvolunteers with an ODI score under 20%. The mean ageof the sample was 64, and it consisted of 86 females and 74males. The reliability statistics by ICC of SVA, PT, PI for theinter-observer reliability were 0.996, 0.990, and 0.966,respectively. The average values of the spino-pelvicparameters are summarized in Table 1. The PT values ofthe healthy elderly volunteers were significantly correlatedwith PI (r¼0.55, P<0.001). When the PT values wereconsidered response variables, the linear regression equationfor the optimal PT as a function of PI was ‘‘optimalPT¼0.47�PI – 7.5’’ (Figure 1). The linear regressionequation for the optimal LL as a function of PI was ‘‘optimalLL¼0.57�PIþ16.2’’ (Figure 2).

Predicted Postoperative PT StudyIn the second study, the predicted value of PT after anoperation was determined using data from 116 ASD patients(aged 37–84 years; mean 66 years) who underwent thoraco-lumbar corrective fusion in 4 hospitals. Table 2 summarizesthe pre- and postoperative spino-pelvic parameters of thesubjects. In order to control the postoperative PT, we couldonly consider the PI and LL during the operation. Thus, thepostoperative PT was determined as a function of the PI andcorrected LL using multiple regression analysis. The post-operative PT was determined using the equation ‘‘predictedPT¼0.69�PI – 0.49�LLþ8.1.’’ The postoperative PTvalues calculated using this equation were strongly corre-lated with the PT values measured on the postoperativeradiographs (r¼0.82, P<0.001) (Figure 3).


TABLE 1. Radiographic Parameters in 184Elderly Volunteers With an OswestryDisability Index (ODI) Under 20%

Parameter Mean SD

PT (8) 14.2 7.8

SS (8) 31.7 8.1

PI (8) 46.4 9.1

LL (8) 42.8 12.6

TK (8) 31.6 11.1

SVA (mm) 27.6 31.0

PI – LL (8) 3.6 4.7

LL indicates lumbar lordosis; PI, pelvic incidence; PT, pelvic tilt; SS, sacralslope; SVA, sagittal vertical axis; TK, thoracic kyphosis.

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Computation of the Ideal LLIn order to restore the optimal PT after surgery, we math-ematically equalized the predicted PT and optimal PT. Wedefined an ideal LL as a solution of the simultaneousequations. As a result, the ideal LL angle necessary to recon-struct the optimal PT was ‘‘ideal LL¼0.45�PIþ31.8’’(Figure 4). This equation reveals that the ideal LL is approxi-mately 10 degrees larger than the optimal LL determinedfrom volunteers. Using this formula, a corrected LL of 54.3degrees is required to obtain an optimal pelvic inclination in apatient with a PI of 50 degrees.

Illustrative Case

Case 1: A 71-Year-Old WomanThe whole standing X-ray showed spinal sagittal malalign-ment with lumbar steep kyphosis (Figure 5). The patient hada wedge vertebral deformity at L3 due to a vertebral frac-ture, which caused sagittal imbalance and pelvic retrover-sion. According to the preoperative X-ray measurement, thesagittal spino-pelvic parameters were LL: 7, TK: 19, PT: 41,and PI: 55 (Table 3). During the surgical planning process,the desired postoperative alignment values were determined


Figure 2. The relationship between lumbar lordosis (LL) and pelvicincidence (PI) in elderly volunteers with an Oswestry DisabilityIndex (ODI) under 20%.


0

10

20

30

40

50

60

70

20 30 40 50 60 70 PI (˚)

LL (˚)

ideal LL = 0.45 × PI + 31.8

optimal LL = 0.57 × PI + 16.2

Figure 4. The linear relationship between the ideal lumbar lordosis(LL) and pelvic incidence (PI) is shown in this graph. For reference,the linear regression equation between the optimal LL and PI inelderly volunteers is also shown. �A simultaneous equation wasmade to equalized the predicted PT and optimal PT as ‘‘0.47�PI –7.5¼0.69�PI – 0.49� LLþ8.1.’’ The solution of simultaneousequation was ‘‘LL¼0.45 x PIþ31.8.’’

TABLE 2. Pre- and Postoperative RadiographicParameters From the MultiCenterOperation Study

Parameter Pre Op Post Op

PT (8) 31.9� 10.7 21.4�9.3

SS (8) 16.4� 10.9 26.7�9.4

PI (8) 49.3� 10.6 48.1�10.0

LL (8) 10.6� 20.2 40.0�12.5

TK (8) 19.6� 15.4 31.4�12.1

SVA (mm) 90.5� 68.5 30.4�36.2

PI – LL (8) 29.6� 26.1 8.1�13.3

Mean� SD.



by using following values: Optimal PT¼0.47�55 –7.5¼18.4 degrees, and ideal LL¼0.45�55þ31.8¼56degrees. Preoperative CT sagittal reconstruction imagingshowed local severe kyphosis of 32 degrees between theupper endplate of the L3 and the lower endplate of the L4vertebra (Figure 6). We planned posterior corrective fusion(from the T10 vertebra to the ilium) with a grade 4 osteot-omy, using the Schwab spinal osteotomy classification,26 atL4 to achieve an LL of 56 degrees. The local lordosis anglebetween the upper endplate of L5 and S1 was 26 degrees,and 20 degrees of lordosis at the L4 vertebra osteotomy siteand approximately 10 degrees of lordosis at the interverte-bral fusion with cages at L1/2 and L2/3, respectively, wereneeded to restore an LL of 56 degrees. Postoperative X-rayrevealed an LL of 55 degrees, which was almost equivalentto the ideal LL (Figure 7). We restored the optimal PT of17 degrees on the postoperative X-ray (Figure 8).

DISCUSSIONMany studies have indicated that spinal sagittal alignmentand global balance are essential for maintaining a highHRQOL.1–10 Pelvic retroversion also correlates withHRQOL. To correct improper spinal sagittal alignment,thoraco-pelvic fusion is a standard operation method for


Figure 3. The scatterplot of predicted pelvic tilt (PT) and measuredPT values.


elderly ASD patients. Pelvic retroversion is the main com-pensatory mechanism used to react against spinal deformityin elderly ASD patients. In the postoperative unphysiolog-ical spine, this compensatory reaction does not occurbecause of the lack of motion in the spino-pelvic junction.Spino-pelvic fusion in the retroverted pelvic position shouldbe avoided in elderly patients. Schwab et al6,27 showed thatthe concrete threshold values for SVA, PT, and PI-LL are 45,20, and under 10, respectively. However, it is difficult to


Figure 5. Illustrative case: A71-year-old woman. Preoperative wholespine radiographs in a standing position.

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TABLE 3. Radiographic Parameters in theIllustrative Case

Pre-Op Post-Op

PI (8) 55 56

SS (8) 14 39

PT (8) 41 17

LL (8) 7 55

TK (8) 19 33

SVA (mm) 150 27

Optimal PT¼0.47 �56 – 7.5¼18.4.

Ideal LL¼0.45 �55þ31.8¼56.


Figure 7. Illustrative case: A 71-year-old woman. Postoperativewhole spine radiographs in a standing position.


control all parameters during a spinal surgery, because thestandard fusion area extends from the lower thoracicvertebrae to the ilium in elderly ASD patients. The onlyparameter that is possible to reconstruct directly in athoraco-pelvic corrective fusion surgery is the LL. It isnecessary to determine a target LL angle when planningcorrective fusion surgery for ASD patients. However, thebest way to determine the target correction value of LL iscontroversial.18–22,28 Thus, we have determined the idealtarget LL for restoring normal pelvic inclination in elderlyASD patients.

To determine the normative spino-pelvic alignment, it isimportant to investigate the radiographic parameters ofasymptomatic volunteers. Many studies have reported14–17

spino-pelvic parameters in healthy volunteers and ASDpatients. A sagittal profile of elderly participants wasreported only by Hammerberg and Wood.17 Spino-pelvicalignment varies by age, with degeneration or decreasingmuscle strength occurring as part of natural aging. Thenatural course of spino-pelvic alignment in elderly patientsis still unknown.29,30 Our cross-sectional investigationrevealed that spino-pelvic parameters were worse in


Figure 6. Illustrative case: A 71-year-old woman. Preoperative com-puted tomography reconstruction sagittal image.

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asymptomatic Japanese individuals who were over 70 thanin those who were in their 50s or 60s. We determined thetarget alignment on the basis of the individuals between 50and 70 years of age. In this cross-sectional study, the linearregression equations for the optimal PT and LL as a functionof PI in 50 to 70-year-old participants were ‘‘optimalPT¼0.47�PI – 7.5’’ and ‘‘optimal LL¼0.57�PIþ16.2.’’

Lafage et al23 developed formulas to predict the PTresulting from a single-level pedicle subtraction osteotomy(PSO). Multiple linear regression analysis with a stepwise


Figure 8. Illustrative case: A 71-year-old woman. Pelvic lateralradiograph in a standing position. (A) Preoperative and (B)postoperative.



condition was applied to obtain the prediction model. Themodel containing PI, maximal LL, and TK explained 84%of the variation in PT. In this study, 67% of variation in thepredicted PT was explained by the PI and LL. Sufficientaccuracy was only obtained with the parameters PI andcorrected LL, because the coefficient of TK was small andLL correlated with TK. Thus, we determined that the post-operative PT is best predicted using the equation ‘‘predictedPT¼0.69�PI – 0.49�LLþ8.1,’’ with only controllableparameters in the operation.

Some reports have suggested a target value for the sagittalparameters in ASD surgery. Kim et al18 recommended thatthe sagittal Cobb angle difference between LL and TK be aminimum of 20 degrees and proposed the formula LL �TKþ20 degrees to achieve optimal postoperative sagittalalignment. Rose et al19 reported that PI and TK can predictthe LL necessary to correct sagittal imbalance in patientsundergoing PSO and recommended the formulaPIþLLþTK � 45 degrees. Recently, Schwab et al20

reported the formula PI – LL � 9 degrees, determined usingdata from 452 ASD patients. Smith et al28 demonstrate thatmany formulas designed to aid in preoperative PSO plan-ning poorly predict the optimal sagittal alignment aftersingle-level PSO. A high PT is a risk factor for incompletecorrection and residual sagittal spinal malalignment. Theseformulas did not include the pelvic inclination and pelviccompensation against spinal sagittal imbalance. Thus, wepropose the set point for restoring an anteverted pelvis andeconomical spino-pelvic sagittal alignment.

In this study, the ideal LL angle was determined on thebasis of mathematically equalizing the PTs of 2 equations, toobtain the formula ‘‘ideal LL¼0.45�PIþ31.8.’’ Thisequation reveals that the ideal LL is approximately10 degrees larger than the optimal LL, which was deter-mined from healthy elderly volunteers as follows: ‘‘optimalLL¼0.57�PIþ16.2.’’ Also, compared with Schwab’srecommendation of PI-LL less than 10 degrees,27 muchmore LL is necessary to restore the optimal PT after surgeryin elderly patients. Determining the optimal corrected LLangle necessary to improve postoperative HR-QOL isimportant for elderly patients with sagittal imbalance.

A limitation of this study is that we did not considerupper and middle thoracic alignment. Our essential oper-ative range extends from the lower thoracic segments to theilium in elderly patients with sagittal imbalance, andoccasionally extends to the upper thoracic vertebra. Achange of thoracic sagittal alignment after surgery is anunforeseeable factor when the operation is performed on thelower thoracic vertebrae.

CONCLUSIONSOn the basis of our findings, we suggest that the ideal LLangle for restoring a normative PT without any compen-sation can be obtained using the equation LL¼0.45�PIþ31.8. This equation reveals that the ideal LL is approxi-mately 10 degrees larger than the optimal LL determinedfrom elderly volunteers. We can use the ideal LL angle as a



reference during surgical planning for correcting the lumbarspine in elderly patients with ASD.

th

Key Points

or

The optimal PT was determined from 184 elderlyvolunteers who had an ODI score less than 20%.The linear regression equation for the optimalPT as a function of PI was ‘‘optimal PT¼ 0.47�PI – 7.5.’’

The ideal LL angle to obtain the optimal pelvicinclination can be determined using the formula0.45�PIþ 31.8, which can be used as a referenceduring surgical planning for ASD.

The ideal LL is approximately 10 degrees largerthan the optimal LL determined using data fromhealthy elderly volunteers.

ize

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