The demand for spinal fusion is increasing, with concurrent reports of iatrogenic adult spinal deformity (flatback deformity) possibly due to inappropriate lordosis distribution. This distribution is assessed using the lordosis distribution index (LDI) which describes the upper and lower arc lordosis ratio. Maldistributed LDI has been associated to adjacent segment disease following interbody fusion, although correlation to later-stage deformity is yet to be assessed. We therefore aimed to investigate if hypolordotic lordosis maldistribution was associated to radiographic deformity-surrogates or revision surgery following instrumented lumbar fusion.
All patients undergoing fusion surgery (≤ 4 vertebra) for degenerative lumbar diseases were retrospectively included at a single center. Patients were categorized according to their postoperative LDI as: “normal” (LDI 50–80), “hypolordotic” (LDI<50), or “hyperlordotic” (LDI>80).
We included 149 patients who were followed for 21±14 months. Most attained a normally distributed lordosis (62%). The hypolordotic group had increased postoperative pelvic tilt (PT) (p<0.001), pelvic incidence minus lumbar lordosis (PI–LL) mismatch (p<0.001) and decreased global lordosis (p=0.007) compared to the normal group. Survival analyses revealed a significant difference in revision surgery (p=0.03), and subsequent multivariable logistic regression showed increased odds of 1-year revision in the hypolordotic group (p=0.04). There was also a negative, linear correlation between preoperative pelvic incidence (PI) and postoperative LDI (p<0.001).
In patients undergoing instrumented lumbar fusion surgery, hypolordotic lordosis maldistribution (LDI<50) was associated to increased risk of revision surgery, increased postoperative PT and PI–LL mismatch. Lordosis distribution should be considered prior to spinal fusion, especially in high PI patients.
Degenerative lumbar spine diseases are common and related to pain and disability. These conditions are among the most important causes of decreased health-related quality of life, and often treated using spinal fusion [
Optimal lordosis is also well established as a cornerstone in treating patients with adult spinal deformity and should reflect pelvic incidence (PI). A PI minus lumbar lordosis (PI–LL) mismatch has been associated with poor postoperative outcome [
We retrospectively screened all patients undergoing short-segment instrumented spine surgery for degenerative lumbar pathologies in a 2-year period from January 1st, 2015 through December 31st, 2016 at a single tertiary institution. Short-segment fusion was defined as instrumented fusion of ≤ 4 vertebrae. Only adult patients (≥ 18 years) were eligible for inclusion. Exclusion criteria were: a history of previous instrumented fusion. Inclusion criteria were sufficient preoperative or postoperative radiographs including both femoral heads, sacral endplate, and all lumbar vertebras up until the inflection point to the thoracic kyphosis. This study was retrospective, noninterventional and LDI was therefore not considered at the time of surgery. This study was approved by the National Health and Medical authority and The National Data Protection Agency.
Patients screened for inclusion underwent surgical treatment for degenerative lumbar spine pathologies including spondylolisthesis (< grade 3), spinal stenosis, disc herniation, degenerative disc disease, or a combination. Surgical treatment included posterior instrumented fusion of 2–4 vertebral levels. Decompression or interbody fusion was performed when deemed necessary. Patient characteristics, medical history, and surgical data were obtained using electronic medical records. Follow-up consisted of clinical and radiographic assessment at 3 months and 1-year following surgery. Radiographic measurements were performed using the online imaging system KEOPS (SMAIO, Lyon, France) [
We performed all statistical analyses using the language and environment R (R Core Team 2020, Vienna, Austria) version 4.01 [
We identified 249 adult patients undergoing instrumented fusion of which 75 (30%) were excluded due to history of previous fusion. Out of 174 eligible patients, 23 (13%) were excluded due to insufficient preoperative radiographs and 2 (1%) due to insufficient postoperative radiographs leaving 149 for final analyses (eligibility ratio: 86%).
Differences between preoperative and postoperative radiographic measurements were assessed and found with significant increase in pelvic tilt (PT) (18°±9° vs. 20°±9°, p<0.001) and PI–LL (4°±14° vs. 7°±14°, p<0.001). These remained significant at 1-year follow-up (p<0.001). A modest, although significant, decrease was seen in sacral slope (37°±11° vs. 35°±11°, p<0.001) and without significant difference at 1-year follow-up (p=0.072). Global lordosis decreased from 53°±14° preoperatively to 49°±13° postoperatively (p<0.001) and remained decreased at 1-year follow-up (50°±15°, p<0.001). Long-standing radiographs were only available in select patients, as deemed by the surgeon, although analyses were performed when available and without significant differences between groups.
Mean±SD postoperative LDI was 59%±22% and without significant difference when compared to preoperative (62%±23%) and 1-year measurements (59%±22%). Patients were further subcategorized according to their postoperative LDI: 93 (62%) were classified as normal (LDI 50–80), 36 (24%) as hypolordotic (LDI<50) and 20 (13%) as hyperlordotic (LDI>80).
Linear regression analysis (
We found no differences in complications across LDI groups (
The main outcome of this study was revision due to other causes than infection, hematoma or wound dehiscence and rates were assessed across LDI groups (
The demand for spinal fusion is increasing, with concurrent reports of iatrogenic causes of adult spinal deformity. The role of lordosis maldistribution following short-segment fusion is not fully understood. Therefore, we aimed to assess postoperative LDI after short-segment fusion for degenerative lumbar disease resulting in 3 main findings. Firstly, most patients had adequate postoperative distribution of their lordosis. Secondly, radiographic parameters related to poor outcome in adult spinal deformity were more frequent in patients with maldistributed postoperative LDI. Thirdly, LDI maldistribution was associated to increased risks of revision surgery. In addition, postoperative LDI was inversely, and significantly, correlated to PI.
Overall, surgical alteration in radiographic parameters related to poor outcome was found in several analyzed measurements, including increased PT suggesting compensated sagittal imbalance and inadequate attention to lordosis [
The ideal lordosis can be estimated as roughly equal to the PI (PI–LL mismatch) [
Recently, Zheng et al. [
Sagittal spine shape is not only complex but also varying between individuals. Using asymptomatic individuals, Roussouly et al. [
The results of the present study should be evaluated in light of several limitations. The current cohort consisted of patients with various spinal pathologies, complicating interpretation. However, the aim was to assess LDI as a viable concept and we acknowledge that further detailed estimates are required in different etiologies as effects may vary. The retrospective nature both reduces external validity and increases risks of selection and sampling bias. Although, the fully disclosed inclusion process and the short enrollment period add to reducing these risks. Further, the short minimum follow-up is unsatisfactory as previous studies have suggested up to 5-year follow-up in efforts to appropriately detect postoperative complications [
Most patients undergoing short-segment fusion for lumbar degenerative spine disease had adequate postoperative lordosis distribution. Patients with postoperative maldistributed LDI had increased PT, increased PI–LL mismatch and an overall reduced global lordosis following surgery. Revision surgery was most frequent in patients with postoperative hypolordotic maldistribution (LDI<50). Our results suggest that inadequate lordosis distribution may predispose iatrogenic deformity and should be considered in short-segment spinal fusion. Special care should be allocated to high PI patients as LDI maldistribution and PI were linearly correlated.
BD (consulting fees from Stryker outside of the submitted work), MG (institutional grants from K2M and Medtronic outside of the submitted work), the remaining authors report no conflicts of interest.
Lordosis distribution index (LDI). The LDI is calculated as a ratio between the lower lordosis (L4–S1) and the global lordosis. The LDI should reflect the increasing lordosis towards the lower spinal segments.
Linear regression model of postoperative lordosis distribution index (LDI) and preoperative pelvic incidence (PI). We found a negative linear correlation between PI and postoperative LDI illustrating the complexity of achieving adequate lower arc lordosis in high PI patients. OR, odds ratio; CI, confidence interval.
Revision surgery according to postoperative lordosis distribution index (LDI). Revision surgery excluding hematoma, infection, and wound dehiscence according to postoperative LDI. Revision rates were lowest in patients with “normal” postoperative LDI (LDI 50–80). LDI ratios refer to the following LDI groups: 50–80, normal distribution; < 50, hypolordotic maldistribution; > 80, hyperlordotic maldistribution.
Incidence of revision surgery according to postoperative lordosis distribution index (LDI). Cumulative incidence of revision surgery, using 1-Kaplan Meier survival analyses, according to postoperative LDI groups showed a significant difference in revision between groups. The lowest incidence of revision was found in patients with “normal” postoperative LDI (LDI 50–80). Revision surgery was defined as revision for any reason except hematoma, infection, or wound dehiscence. The provided p-value is derived from an unweighted log-rank test (p=0.030). Fleming-Harington weighted log-rank test: p=0.036. LDI ratios refer to the following LDI groups: 50–80, normal distribution; < 50, hypolordotic maldistribution; > 80, hyperlordotic maldistribution.
Weibull regression model for revision surgery according to LDI groups. The Weibull regression model for accelerated, and proportional, relative event rates and relative extension survival time showed lowest incidence of revision surgery in patients with “normal” postoperative lordosis distribution index (LDI) defined as LDI of 50–80. Revision surgery was defined as revision for any reason except hematoma, infection, or wound dehiscence. LDI ratios refer to the following LDI groups: 50–80, normal distribution; < 50, hypolordotic maldistribution; > 80, hyperlordotic maldistribution.
Patient characteristics and surgical data (n=149)
Characteristic | Value |
---|---|
Age (yr) | 59 ± 13 |
Female sex | 98 (66) |
Etiology | |
Multiple | 51 (34) |
Listhesis | 32 (22) |
Disc herniation | 21 (14) |
Degenerative disc disease | 18 (12) |
Stenosis | 16 (11) |
Other | 11 (7) |
Carlson Comorbidity Index | 2± 2 |
ASA PS classification | 2± 1 |
Surgery time (min) | 177 ± 51 |
Interbody cage | 118 (79) |
Minimal invasive | 4 (3) |
Instrumented vertebra | 3 (3–4) |
Length of stay | 4 (4–6) |
Follow-up (mo) | 21 ± 14 |
Previous spine surgery | 64 (43) |
Values are presented as mean±standard deviation, number (%), or median (interquartile range).
ASA PS, American Society of Anesthesiologists physical status.
Radiographic parameters and complications according to lordosis distribution index (LDI) groups
Variable | Normal (LDI: 50–80) (n = 93) | Hypolordosis (LDI < 50) (n = 36) | Hyperlordosis (LDI > 80) (n = 20) | Total (n = 149) | p-value† | p-value‡ | |
---|---|---|---|---|---|---|---|
Preoperative radiographic measurements | |||||||
Pelvic incidence (°) | 54.5 ± 13.7 | 58.8 ± 13.5 | 47.1 ± 11.2 | 54.6 ± 13.7 | 0.007 |
0.112 | |
Pelvic tilt (°) | 16.5 ± 8.1 | 22.3 ± 10.1 | 18 ± 6 | 18.1 ± 8.7 | 0.002 |
0.003 |
|
Pelvic tilt > 20° | 27 (29.0) | 18 (50.0) | 7 (35.0) | 52 (34.9) | 0.081 | 0.039 |
|
Sacral slope (°) | 38 (11.4) | 36.6 (8.2) | 29.1 (10.9) | 36.5 (11) | 0.003 |
0.426 | |
Global lordosis (°) | 55.7 ± 14.7 | 50.8 ± 13.2 | 43.9 ± 10.9 | 53 ± 14.4 | 0.001 |
0.069 | |
SVA (mm) |
34.5 ± 49 | 61.1 ± 51.5 | 47.3 ± 32.6 | 43.3 ± 47.8 | 0.111 | 0.064 | |
SVA > 40 mm |
15 (33.3) | 11 (57.9) | 7 (46.7) | 33 (41.8) | 0.174 | 0.096 | |
PI–LL (°) | 0.1 ± 11.5 | 11.7 ± 17.2 | 8 ± 11.7 | 4 ± 14 | < 0.001 |
< 0.001 |
|
PI–LL ≥ 10° | 12 (12.9) | 16 (44.4) | 7 (35.0) | 35 (23.5) | < 0.001 |
< 0.001 |
|
LDI | 65.2 ± 14.4 | 38.5 ± 24.8 | 85.8 ± 15.7 | 61.5 ± 22.9 | < 0.001 |
< 0.001 |
|
LDI groups | < 0.001 |
< 0.001 |
|||||
50–80 | 69 (74.2) | 9 (25.7) | 5 (25.0) | 83 (56.1) | |||
< 50 | 12 (12.9) | 25 (71.4) | 0 (0.0) | 37 (25.0) | |||
> 80 | 12 (12.9) | 1 (2.9) | 15 (75.0) | 28 (18.9) | |||
Postoperative radiographic measurements | |||||||
Pelvic incidence (°) | 54.6 ± 14.1 | 58.5 ± 13.5 | 47 ± 10.8 | 54.5 ± 13.9 | 0.009 |
0.145 | |
Pelvic tilt (°) | 17.8 ± 7.9 | 25.1 ± 11.2 | 20.8 ± 5.5 | 20 ± 9 | < 0.001 |
< 0.001 |
|
Pelvic tilt > 20° | 38 (40.9) | 22 (61.1) | 12 (60.0) | 72 (48.3) | 0.063 | 0.049 |
|
Sacra slope (°) | 36.9 ± 10.1 | 33.5 ± 8.9 | 26.2 ± 9.7 | 34.6 ± 10.4 | < 0.001 |
0.065 | |
Global lordosis (°) | 52.2 ± 12 | 45.3 ± 12.6 | 40.6 ± 11.3 | 48.9 ± 12.8 | < 0.001 |
0.007 |
|
SVA (mm) |
68.8 ± 54.4 | 127.5 ± 41.9 | 88.7 ± 51.8 | 91.4 ± 53.1 | 0.195 | 0.092 | |
SVA > 40 mm |
4 (66.7) | 4 (100.0) | 3 (100.0) | 11 (84.6) | 0.252 | 0.467 | |
PI–LL (°) | 3.2 ± 11.1 | 16.1 ± 16.9 | 11 ± 11.4 | 7.4 ± 13.9 | < 0.001 |
< 0.001 |
|
PI–LL ≥ 10° | 21 (22.6) | 19 (52.8) | 11 (55.0) | 51 (34.2) | < 0.001 |
0.001 |
|
LDI | 63 ± 8.6 | 32.8 ± 22.3 | 90.6 ± 8.5 | 59.4 ± 22 | < 0.001 |
< 0.001 |
Values are presented as mean±standard deviation or number (%).
SVA, sagittal vertical axis; PI–LL, pelvic incidence minus lumbar lordosis.
A p-value was derived using †analysis of variance comparing all 3 LDI groups, followed by pairwise comparison of the ‡“normal” and “low (LDI<50)” LDI groups using either Student t-test or Fisher exact test.
p<0.05.
SVA was available in n=79 preoperatively and n=13 postoperatively.
Complications and revision surgery according to lordosis distribution index (LDI) groups
Variable | Normal (LDI: 50–80) (n = 93) | Hypolordosis (LDI < 50) (n = 36) | Hyperlordosis (LDI > 80) (n = 20) | Total (n = 149) | p-value† | p-value‡ | |
---|---|---|---|---|---|---|---|
Complications | |||||||
Early (< 3 mo) | 33 (35.5) | 16 (44.4) | 7 (35.0) | 56 (37.6) | 0.621 | 0.419 | |
Late (> 3 mo) | 43 (46.2) | 13 (36.1) | 8 (40.0) | 64 (43.0) | 0.558 | 0.328 | |
Minor | 45 (48.4) | 16 (44.4) | 7 (35.0) | 68 (45.6) | 0.544 | 0.700 | |
Major | 36 (38.7) | 16 (44.4) | 10 (50.0) | 62 (41.6) | 0.600 | 0.556 | |
Mechanical complications | |||||||
Major | 5 (5.4) | 5 (13.9) | 3 (15.0) | 13 (8.7) | 0.126 | 0.140 | |
Minor | 2 (2.2) | 1 (2.8) | 0 (0) | 3 (2.0) | 1.00 | 1.00 | |
Any | 7 (7.5) | 6 (16.7) | 3 (15) | 16 (10.7) | 0.229 | 0.188 | |
Adjacent segment disease | |||||||
Major | 8 (8.6) | 3 (8.3) | 0 (0) | 11 (7.4) | 0.587 | 1.00 | |
Minor | 1 (1.1) | 0 (0.0) | 0 (0) | 1 (0.7) | 1.00 | 1.00 | |
Any | 9 (9.7) | 3 (8.3) | 0 (0) | 12 (8.1) | 0.550 | 1.00 | |
Any complication | 57 (61.3) | 25 (69.4) | 12 (60.0) | 94 (63.1) | 0.659 | 0.422 | |
Revision |
|||||||
Revision 1 yr | 6 (6.5) | 7 (19.4) | 3 (15.0) | 16 (10.7) | 0.082 | 0.046 |
|
Revision 2 yr | 15 (16.1) | 10 (27.8) | 7 (35.0) | 32 (21.5) | 0.100 | 0.143 | |
Revision any time | 27 (29) | 12 (33.3) | 9 (45.0) | 48 (32.0) | 0.378 | 0.672 |
Values are presented as number (%).
A p-value was derived using †analysis of variance comparing all 3 LDI groups, followed by pairwise comparison of the ‡“normal” and “low (LDI<50)” LDI groups using either Student t-test or Fisher exact test.
p<0.05.
Revision surgery due to infection, hematoma, or wound complications was not included.
Logistic regression analyses of 1-year revision
Variable | Univariable |
Multivariable |
|||
---|---|---|---|---|---|
OR (95% CI) | p-value | OR (95% CI) | p-value | ||
Age (yr) | 1.04 (0.99–1.09) | 0.140 | - | - | |
Male sex | 1.57 (0.53–4.50) | 0.398 | - | - | |
CCI | 1.06 (0.78–1.38) | 0.688 | - | - | |
ASA PS classification | 1.27 (0.52–3.08) | 0.590 | - | - | |
Surgery time (min) | 1.00 (0.99–1.01) | 0.784 | - | - | |
Interbody cage | 0.53 (0.18–1.82) | 0.282 | - | - | |
Instrumented vertebra (per 1 increase) | 0.71 (0.28–1.26) | 0.374 | 0.71 (0.27–1.33) | 0.398 | |
Sacral fusion | 0.75 (0.07–8.55) | 0.820 | |||
Previous spine surgery | 1.37 (0.48–3.95) | 0.548 | - | - | |
Length of hospital stay | 1.10 (1.02–1.18) | 0.010 |
- | - | |
Preoperative radiographic measurements | |||||
Pelvic incidence | 1.01 (0.97–1.04) | 0.752 | 1.00 (0.96–1.04) | 0.906 | |
Pelvic tilt | 1.05 (0.99–1.11) | 0.108 | - | - | |
Pelvic tilt ≥ 20 | 2.69 (0.94–7.99) | 0.065 | - | - | |
Sacral Slope | 0.97 (0.92–1.02) | 0.263 | - | - | |
Global lordosis | 0.97 (0.93–1.00) | 0.065 | - | - | |
SVA (mm) | 1.01 (1.00–1.03) | 0.024 |
- | - | |
SVA ≥ 40 | 3.94 (1.15–15.82) | 0.036 |
- | - | |
PI–LL | 1.04 (1.00–1.07) | 0.029 |
- | - | |
PI–LL ≥ 10 | 1.56 (0.46–4.66) | 0.441 | - | - | |
LDI | 0.98 (0.96–1.00) | 0.104 | - | - | |
LDI groups (reference: 50-80) | - | - | - | - | |
LDI < 50 | 2.10 (0.63–6.82) | 0.213 | - | - | |
LDI > 80 | 0.84 (0.12–3.72) | 0.829 | - | - | |
Postoperative radiographic measurements | |||||
Pelvic incidence | 1.00 (0.97–1.04) | 0.853 | - | - | |
Pelvic tilt | 1.05 (1.00–1.11) | 0.058 | - | - | |
Pelvic tilt ≥ 20 | 3.65 (1.20–13.59) | 0.032 |
- | - | |
Sacral Slope | 0.96 (0.91–1.01) | 0.144 | - | - | |
Global lordosis | 0.95 (0.91–0.99) | 0.024 |
- | - | |
SVA (mm) | 1.01 (0.98–1.03) | 0.574 | - | - | |
SVA ≥ 40 | NA | 0.997 | - | - | |
PI–LL | 1.03 (1.00–1.07) | 0.076 | - | - | |
PI–LL ≥ 10 | 3.74 (1.30–11.64) | 0.016 |
- | - | |
LDI | 0.99 (0.97–1.02) | 0.596 | - | - | |
LDI groups (reference: 50–80) | - | - | - | - | |
LDI < 50 | 3.50 (1.08–11.70) | 0.036 |
3.37 (1.03–11.39) | 0.043 |
|
LDI > 80 | 2.56 (0.50–10.75) | 0.213 | 2.72 (0.52–11.98) | 0.198 |
OR, odds ratio; CI, confidence interval; CCI, Carlson Comorbidity Index; ASA PS, American Society of Anesthesiologists physical status; SVA, sagittal vertical axis; PI–LL, pelvic incidence minus lumbar lordosis; LDI, lordosis distribution index. NA, upper or lower CI=infinity.
p<0.05.
Revision surgery due to infection, hematoma, or wound complications were not included.