Criteria for Severe Dynamic Sagittal Imbalance in Adult Spinal Deformity and its Importance

doi:10.21203/rs.3.rs-3239036/v1

Download PDF

Research Article

Criteria for Severe Dynamic Sagittal Imbalance in Adult Spinal Deformity and its Importance

https://doi.org/10.21203/rs.3.rs-3239036/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 09 Feb, 2024

Read the published version in BMC Musculoskeletal Disorders →

You are reading this latest preprint version

Background

To analyze the characteristics of “severe” dynamic sagittal imbalance (DSI) in patients with adult spinal deformity (ASD) and establish criteria for them.

Methods

In total, 102 ASD patients with four cardinal signs of lumbar degenerative kyphosis were retrospectively analyzed. All patients underwent deformity corrective surgery and were divided into three groups according to the diagnostic criteria. The criteria were based on the Oswestry disability index scores and dynamic features (△Time_walk: time until C7 sagittal vertical axis [C7SVA] reaches ≥ 20 cm after the start of walking) of sagittal imbalance. The paravertebral back muscles were analyzed and compared using T2-weighted axial images. We performed a statistically time-dependent spinopelvic sagittal parameter analysis on full standing lateral lumbar radiographs. Lumbar flexibility was analyzed based on dynamic lateral lumbar radiographs

Results

Based on the diagnostic criteria, the 102 patients were classified into three groups: mild (△Time_walk ≥ 180 s, 35 patients), moderate (180 s > △Time_walk ≥ 30 s, 38 patients), and severe (△Time_walk < 30 s, 29 patients). There was a significantly higher signal intensity (533.4 ± 237.5, P < 0.05) and larger area of fat infiltration (35.2 ± 5.4, P < 0.05) in the back muscles of the severe group than in the mild (223.8 ± 67.6/22.9 ± 11.9) and moderate groups (294.4 ± 214.7/21.6 ± 10.6). The analysis of lumbar flexibility revealed significantly lower values in the severe group (5.8° ± 2.5°, P < 0.05) than in the mild and moderate groups (14.2° ± 12.4° and 11.4° ± 8.7°, respectively). The severe group had significantly lower lumbar lordosis (LL, 25.1° ± 22.7°, P < 0.05) and Pelvic incidence (PI)-LL mismatch (PI-LL, 81.5° ± 26.6°, P < 0.001) than the mild (8.2 ° ± 16.3°/58.7° ± 18.8°) and moderate (14.3° ± 28.6°/66.8° ± 13.4°) groups. In ROC curve analysis, PI-LL was statistically significant with AUC of 0.810 (95% confidence interval) when the baseline was set at 75.3°. The severe group showed more postoperative complications than the other groups.

Conclusions

We suggest the following criteria for severe DSI: C7SVA > 20 cm within 30 s after walking or standing, rigid lumbar curve < 10° on dynamic lateral radiographs, and PI-LL mismatch > 75.3°.

adult spinal deformity

degenerative flat back

dynamic sagittal imbalance

diagnostic criteria

severity

With aging of the global population, the prevalence of adult spinal deformities (ASD) has increased. The management of ASD can be classified as surgical or nonsurgical. Since surgical treatment of patients with ASD can provide recovery of spinal alignment and significant improvement of clinical outcomes, it can be a good treatment option. However, surgical treatment can lead to several complications. The first is related to the surgical outcomes. Depending on the degree of correction after surgical treatment, under-correction or over-correction may adversely affect patients. The second is various complications related to surgery[1]. There are early and late complications, according to the time of onset. Lonergan et al.[2] reported early postoperative complications after ASD surgery in patients aged 70 years. These were mainly medical complications, including postoperative anemia, gastrointestinal problems, such as constipation or ileus, or urinary retention. Lapp et al.[3], in their retrospective review of patients undergoing combined adult spinal deformity surgery, reported late postoperative complications, such as pseudarthrosis, loss of correction, or radiographic degenerative changes proximal or distal to the fusion level. Therefore, further studies are needed to reduce the surgical complications as much as possible.

Degenerative flat back characterized by sagittal imbalance is a specific type of ASD and is more common in Asian people[4]. Most patients with degenerative flat back have severe degeneration of the lumbar extensor muscles, causing a stooping posture[5]. Although a series of compensatory mechanisms, starting with pelvic retroversion, work to overcome the sagittal imbalance, they have limitations, and they are more challenging while walking than while standing. Lee et al.[6] explained the dynamic feature of sagittal imbalance in degenerative flat backs, which is generally called dynamic sagittal imbalance (DSI). Yin et al.[7] proposed that changes in the C7 sagittal vertical axis (C7SVA) during walking can be a convenient way to detect the severity of patients with DSI and their characteristics and treatment strategies. We have experienced relatively poor surgical outcomes and more complications during the postoperative period in many patients with severe DSI. Although the need for diagnosis of severe DSI is increasing, there are few studies on the diagnostic criteria for severe DSI that require more surgical correction. Therefore, the purpose of this study was to analyze the characteristics of ASD in patients with severe DSI and establish diagnostic criteria for severe DSI.

Study design

Between 2016 and 2019, a selected group of 196 patients with ASD and DSI was assessed at our center. The enrollment criteria included: a severe sagittal imbalance with dynamic feature (after start of walking, the C7SVA gradually increases and becomes larger than 20 cm) and four cardinal signs of lumbar degenerative kyphosis (LDK)[8]. Patients with gait disturbances due to leg-length discrepancy or a history of lower extremity surgery below the hip joint were excluded.

The 196 patients with DSI were classified into eight subgroups according to evenly divided time until C7SVA reached 20 cm or more after the start of walking (△Time_walk). To use the minimum clinically important difference (MCID), we calculated the diff_domain (MCID deviation of each patient from normative values) of the preoperative Oswestry disability index (ODI) in our patient subgroups[9] (Table 1). We determined the threshold values of DSI[10, 11] and divided them into three groups based on severity (Table 2)[12]: mild(△Time_walk ≥ 180 s), moderate (180 s > △Time_walk ≥ 30 s), and severe (30 s > △Time_walk) (Fig. 1).


Table 1 Preoperative ODI and diff_domain of each △Time_walk subgroup
	△Time_walk Subgroup
	≥ 180 sec*	≥ 180 sec	150–180 sec	120–150 sec	90–120 sec	60–90 sec	30–60 sec	0–30 sec
Cases	50	35	26	18	12	15	9	31
Proportion	25.6%	17.8%	13.3%	9.2%	6.1%	7.6%	4.6%	15.8%
ODI_preop	16.8 ± 10.5	20.7 ± 18.2	26.1 ± 13.5	29.4 ± 20.1	31.7 ± 17.9	35.8 ± 11.7	39.8 ± 14.5	50.5 ± 12.8
Diff_domain	0.972	1.452	2.126	2.539	2.825	3.348	3.848	5.182
ODI = Oswestry Disability Index; △Time_walk = time until C7SVA reaches 20cm or more after starting walking; ODI_preop = preoperative ODI; 180s* = nonoperative group in more than 180s Diff_domain = MCID deviation of each patient from normative values. = (ODI_{patient domain} – ODI_{normative domain})/MCID_ODI * The normative ODI score used in our study was 9.05 points obtained from Tonosu et al. * The MCID value of ODI used in our study was − 8 points

Of the 196 patients, only 102 underwent deformity correction surgery. The proportion of each group was as following: mild, 34% (35/102); moderate, 37% (38/102); and severe, 29% (29/102). Finally, the medical records of the 102 consecutive patients with ASD who underwent spinal surgery for deformity correction at a single institution between 2016 and 2019 were retrospectively reviewed. The final follow-up period was 2 years.

Data collection

△Time_walk measurements were recorded under the supervision of a well-trained physician assistant (PA) at our center. Patients who decided to undergo corrective deformity surgery were asked to undergo radiography to obtain two sets of anterior-posterior and lateral entire-spine radiographs. The first set of radiographs was obtained prior to walking. The patients were then immediately asked to walk at their usual speed for 10 min without rest. According to a previous study[6], a 10 min walk was considered to be sufficient for checking a patient’s posture change in an out-patient clinic. The PA supervised each patient for the entire 10 min walk. The second radiograph was obtained immediately after walking for 10 min. Patients who were unable to walk for 10 min due to a stooping posture were examined immediately after the termination of walking, and the time was recorded. For accurate time recording, patients with a C7SVA of 20 cm or more on the postgait radiograph underwent △Time_walk measurement again when admitted to the hospital.

Demographic and clinical data included patient age, sex, body mass index (BMI), bone mineral density (BMD: L1–4, T-score), diagnosis, including combined pathologies of the lumbar spine, comorbidities, upper instrumented vertebra (UIV), lower instrumented vertebra, operation time (defined as the start to end of anesthesia), blood loss (measured through estimated blood loss), and postoperative complications, including intensive care unit (ICU) stay and proximal junctional kyphosis.

To evaluate back muscle degeneration in each patient, we used a software available with the picture archiving and communication system of our institution. The back muscles included the multifidus and erector spinae in the lumbar region. Using lumbar spine magnetic resonance imaging (MRI), three T2-wighted axial images at each disc level were obtained and evaluated from the midpoint of each level as a reference point. In each MRI data, we evaluated the mean signal intensity, standard deviation (SD) of signal intensity, and fatty infiltration percentage at multiple levels (L1–2, L2–3, L3–4, and L4–5) in the lumbar back muscles[5]. Unlike Lee et al.'s study[5], we measured the cross-sectional area (CSA) of the back muscle compartment on both sides. Two independent orthopedic spinal surgeons performed all the measurements.

Radiologic spinopelvic parameters included C7SVA, thoracic kyphosis (TK, sagittal Cobb angle from the superior endplate of T5 to the inferior endplate of T12), thoracolumbar kyphosis (TLK, sagittal Cobb angle from the superior endplate of T10 to the inferior endplate of L2), lumbar lordosis (LL, sagittal Cobb angle from the inferior endplate of T12 to the superior endplate of S1), pelvic tilt (PT, angle made between lines originating at the bicoxofemoral axis and extending vertically and to the middle of the superior endplate of S1), sacral slope (SS, angle between the superior endplate of S1 and the horizontal line), pelvic incidence (PI, angle between a line perpendicular to the superior endplate of S1 and the line connecting the superior endplate of S1 to the bicoxofemoral axis), proximal junctional angle (PJA: sagittal Cobb angle between the UIV and the UIV plus 2 levels), PI-LL mismatch (PI-LL, mismatch between PI and LL), and lumbar flexibility. In particular, we established a receiver operating characteristic (ROC) curve analysis to determine the severe group in patients with DSI using PI-LL mismatch values. Lumbar flexibility was defined as the difference in LL between flexion and extension on lateral radiographs: rigid, < 10°; not rigid, ≥ 10°.

Statistical analysis

Continuous variables were presented as mean ± SD. Frequency analysis was used to analyze the categorical variables. Analysis of variance and chi-square or Fisher’s exact test was used as appropriate for group comparisons. Statistical significance was set at p value < 0.05. All statistical analyses were performed using SPSS for Windows (IBM SPSS 21.0, IBM Corp., Armonk, NY, USA). ROC curve analysis was performed using MedCalc software (version 20.1) to assess the specificity, sensitivity, and area under the ROC curve (AUC), and to select the optimal critical value for PI-LL mismatch.

Demographic data

Among the 102 patients who underwent surgery, the mean age of patients in the severe group was 72.0 years, which was more than that in the mild (68.8 years) and moderate (68.2 years) groups. There were no significant differences between the groups in terms of the sex ratio and BMI. Regarding BMD, the T-score (L1–4) was − 1.87 ± 0.6 in the severe group, which was significantly lower than those in the mild (-1.02 ± 0.7) and moderate (-1.25 ± 1.3) groups. Comorbidities of the patients, including hypertension or diabetes mellitus, were similar among the three groups. In all three groups, UIV was greater than T10 in most cases, and in particular, the proportion of patients with UIV greater than T10 was significantly higher in the severe group (100%) than those in the other two groups (80% and 94.7%, respectively). In patients in the severe group, the operation time (392.3 ± 57.2 min) was significantly longer than those in the other two groups (mild, 342.2 ± 54.7 min; moderate, 351.6 ± 61.5 min). The blood loss was also larger in patients of the severe group (2,526.7 ± 924.3 mL) than that in the other two groups (mild, 2,213.3 ± 760.5 mL; moderate, 2,253.3 ± 777.2 mL) (Table 3).

**Table 2** Determination of threshold values of DSI
	△Time_walk Subgroup
	≥ 180 sec*	≥ 180 sec (Mild group)	30–180 sec (Moderate group)	0–30 sec (Severe group)
Diff_domain (MCID)	0.972	1.452	2.126–3.848	≥ 5.182
Criteria (MCID)	< 1	1–2	2–4	> 4
MCID = minimum clinically importance difference; Diff_domain = MCID deviation of each patient from normative value

In the comparison of the preoperative diagnosis of patients in each group, LDK, a typical form of degenerative flat back, was rare in all three groups. Most of the patients had one or more pathologies simultaneously. In particular, the number of patients with spinal stenosis in the mild group (68.6%) and history of vertebral column fracture in the severe group (62.1%) were significantly higher than those in the other groups (Table 3).

Back muscle degeneration at lumbar levels

The mean signal intensities of the back muscles in the severe group were significantly higher than those in the other two groups at all levels (L1–L2, L2–L3, L3–L4, and L4–L5). The mean signal intensities through the L1–5 levels were significantly higher in the severe group (533.4 ± 237.5) than that in the other two groups (mild, 223.8 ± 67.6; moderate, 294.4 ± 214.7). The SDs of the signal intensity in the back muscles of the patients in the severe group were significantly larger than those in the other two groups at all levels (L1–L2, L2–L3, L3–L4, and L4–L5). The mean SD of the signal intensities through the L1–L5 levels was significantly higher in the severe group (312.5 ± 142.4) than that in the other two groups (mild, 131.9 ± 41.3; moderate, 179.9 ± 124.8). Overall, the fat infiltration area in the back muscles in the severe group was higher than that in the other two groups. The percentage of the fat infiltrated area in the back muscle compartment through L1–L5 levels was significantly higher in the severe group (35.2 ± 5.4%) than that in the other two groups (mild, 22.9 ± 11.9%; moderate, 21.6 ± 10.6%). Relative muscle compartment volume was calculated by dividing the CSA of the muscle compartment on the right side by the intervertebral disc area at the same level (muscle CSA/disc CSA). The differences in muscle-disc ratios among the patients in the three groups at all levels were not statistically significant (Table 4).

**Table 3** Baseline characteristics of patients in each group
		Mild (n = 35)	Moderate (n = 38)	Severe (n = 29)	P value
Age (year)		68.8 ± 3.99	68.2 ± 4.54	72.0 ± 5.29	0.065
Gender(female/male)		32:3	38:0	29:0	0.318
BMI (kg/m²)		23.49 ± 3.12	23.48 ± 2.19	22.04 ± 3.51	0.229
BMD (L1-4, T-score)		-1.02 ± 1.69	-1.25 ± 1.27	-1.87 ± 0.58	0.038*
Preop. diagnosis	LDK	2	4	4	0.762
	Combined state
	Spinal stenosis	24 (68.6%)	15 (39.5%)	10 (34.5%)	0.034*
	Spondylolisthesis	1 (2.9%)	1 (2.6%)	2 (6.9%)	0.675
	Old vertebral column fracture	8 (8.6%)	11 (28.9%)	18 (62.1%)	0.025*
	Scoliosis	4 (11.4%)	6 (15.8%)	5 (17.2%)	0.714
	Previous surgery	2 (5.7%)	2 (5.3%)	4 (13.8%)	0.383
No. of comorbidities	HTN	14 (40%)	12 (31.6%)	12 (41.4%)	0.726
	Angina	0 (0%)	2 (5.3%)	4 (13.8%)	0.463
	DM	2 (5.7%)	2 (5.3%)	6 (20.9%)	0.154
	CKD	2 (5.7%)	0 (0%)	1 (3.4%)	0.051
	Old CVA	2 (5.7%)	2 (5.3%)	0 (0%)	0.512
	RA	1 (2.9%)	0 (0%)	2 (6.9%)	0.481
	Parkinson’s disease	0 (0%)	2 (5.3%)	0 (0%)	0.714
	COPD	0 (0%)	0 (0%)	2 (6.9%)	0.081
UIV (n, %)	≥ T10	28 (80%)	36 (94.7%)	29 (100%)	0.043*
UIV (n, %)	≤ T11	7 (20%)	2 (5.3%)	0 (0%)	0.043*
LIV (n, %)	S1	35 (100%)	38 (100%)	29 (100%)
Operation time (min)		342.2 ± 54.7	351.6 ± 61.5	392.3 ± 57.2	0.041*
Blood loss (ml)		2213.33 ± 760.51	2253.33 ± 777.24	2526.67 ± 924.32	0.035*
BMI = body mass index; BMD = bone mineral density; Preop. = preoperative; LDK = lumbar degenerative kyphosis; HTN = hypertension; DM = diabetes mellitus; CKD = chronic kidney disease; CVA = cerebrovascular accident; RA = rheumatoid arthritis; COPD = chronic obstructive pulmonary disease; UIV = upper instrumented vertebra; LIV = lower instrumented vertebra; min = minutes.

Radiologic parameters and lumbar flexibility

The severe group (12.68° ± 15.23°) had a significantly larger preoperative TLK than the other groups (mild, 4.87° ± 7.54°; moderate 6.25° ± 8.65°). The severe group (25.09° ± 22.73°) also had significantly larger preoperative lumbar kyphosis than the other groups (mild, 8.21° ± 16.34°; moderate, 14.26° ± 28.58°). In the severe group, pelvic tilt tended to increase, and the pelvic tilt in the severe group (40.22° ± 11.91°) was significantly larger than that in the other two groups (mild, 28.64° ± 9.90°; moderate, 32.13° ± 9.03°). Conversely, the preoperative SS in the severe group was lower than that in the other two groups. The PI-LL mismatch was greater preoperatively in the severe group (81.49° ± 26.59°) than in the mild (58.71° ± 18.84°) and moderate (66.77° ± 13.38°) groups. Preoperative TK and PI were not significantly different among the three groups. The lumbar flexibility of patients in the severe group (5.83° ± 2.54°) was significantly lower than that of the patients in the other two groups (mild, 14.23° ± 12.38°; moderate, 11.36° ± 8.72°) (Table 5).

**Table 4** Signal intensity and fatty infiltration in back muscle
	Mild (n = 35)	Moderate (n = 38)	Severe (n = 29)	P value
	Mild (n = 35)	Moderate (n = 38)	Severe (n = 29)	I vs II	I vs III	II vs III
Mean of signal intensity
L1-L2	204.7 ± 60.9	276.5 ± 205.6	538.2 ± 280.5	0.631	< 0.001*	0.004*
L2-L3	228.0 ± 75.7	299.7 ± 215.3	547.9 ± 289.9	0.657	< 0.001*	0.010*
L3-L4	233.8 ± 75.1	297.4 ± 238.0	499.1 ± 234.8	0.681	0.003*	0.028*
L4-L5	228.9 ± 77.6	303.9 ± 213.9	521.9 ± 233.6	0.556	< 0.001*	0.011*
Mean L1-L5	223.8 ± 67.6	294.4 ± 214.7	533.4 ± 237.5	0.609	0.002*	0.008*
SD of signal intensity
L1-L2	109.1 ± 31.1	168.9 ± 115.9	311.5 ± 158.1	0.369	< 0.001*	0.014*
L2-L3	130.4 ± 45.5	181.8 ± 121.9	316.8 ± 157.2	0.495	0.002*	0.018*
L3-L4	147.2 ± 50.5	185.5 ± 139.8	315.5 ± 138.7	0.673	< 0.001*	0.012*
L4-L5	141.0 ± 43.5	183.3 ± 127.6	306.3 ± 133.7	0.576	< 0.001*	0.014*
Mean L1-L5	131.9 ± 41.3	179.9 ± 124.8	312.5 ± 142.4	0.581	0.003*	0.028*
Percentage of fat infiltration (%)
L1-L2	21.54 ± 15.4	19.3 ± 10.0	31.0 ± 7.1	0.913	0.041*	0.027*
L2-L3	21.0 ± 12.8	21.9 ± 12.2	31.6 ± 6.5	0.972	0.038*	0.043*
L3-L4	25.0 ± 12.0	21.9 ± 13.5	37.1 ± 8.2	0.765	0.022*	0.003*
L4-L5	24.5 ± 12.1	23.3 ± 11.3	41.3 ± 7.2	0.851	0.003*	0.002*
Mean L1-L5	22.9 ± 11.9	21.6 ± 10.6	35.2 ± 5.4	0.873	0.005*	0.002*
Relative cross-sectional area
L1-L2	1.04 ± 0.17	0.95 ± 0.22	0.84 ± 0.30	0.570	0.337	0.440
L2-L3	0.99 ± 0.19	0.92 ± 0.19	0.80 ± 0.27	0.640	0.293	0.315
L3-L4	0.93 ± 0.24	0.83 ± 0.17	0.85 ± 0.26	0.454	0.472	0.955
L4-L5	0.97 ± 0.26	0.77 ± 0.24	0.78 ± 0.15	0.370	0.381	0.932
Mean L1-L5	0.98 ± 0.16	0.87 ± 0.15	0.81 ± 0.23	0.454	0.363	0.560
L = lumbar; SD = standard deviation

In comparison of the degree of correction of LL immediately after surgery, the severe group (50.28° ± 19.18°) had significantly less correction than the other two groups (mild, 59.90° ± 7.47°; moderate, 62.01° ± 9.41°) (Table 5).

ROC curve analysis

The AUC of PI-LL mismatch value, cut-point, sensitivity, and specificity in the patients of the severe group were 0.810, 75.3°, 66.7%, and 90%, respectively (Figs. 2 and Table 6).

**Table** 5 Radiologic parameters & Lumbar flexibility
	Mild (n = 35)	Moderate (n = 38)	Severe (n = 29)	P value
	Mild (n = 35)	Moderate (n = 38)	Severe (n = 29)	I vs II	I vs III	II vs III
Preoperative sagittal spinopelvic parameters
Thoracic kyphosis (°)	6.36 ± 16.31	5.59 ± 9.73	7.37 ± 11.24	0.884	0.645	0.323
Thoracolumbar kyphosis (°)	4.87 ± 7.54	6.25 ± 8.65	12.68 ± 15.23	0.592	0.007*	0.019*
Lumbar lordosis (°)	8.21 ± 16.34	14.26 ± 28.58	25.09 ± 22.73	0.069	< 0.001*	0.017*
Pelvic tilt (°)	28.64 ± 9.90	32.13 ± 9.03	40.22 ± 11.91	0.213	0.032*	0.061
Sacral slope (°)	22.13 ± 9.77	20.21 ± 14.48	16.05 ± 11.66	0.437	0.021*	0.043*
Pelvic incidence (°)	50.41 ± 13.21	52.47 ± 12.36	56.18 ± 10.68	0.576	0.071	0.281
PI-LL mismatch (°)	58.71 ± 18.84	66.77 ± 13.38	81.49 ± 26.59	0.024*	< 0.001*	< 0.001*
Immed. LL correction (°)	59.90 ± 7.47	62.01 ± 9.41	50.28 ± 19.18	0.785	0.031*	0.027*
Lumbar flexibility (°)	14.23 ± 12.38	11.36 ± 8.72	5.83 ± 2.54	0.372	< 0.001*	0.032*

Immed. = immediate; LL = lumbar lordosis

Postoperative complications

After surgery, various complications, such as pseudarthrosis or pneumonia, were observed. Among them, neurologic complications and deep vein thrombosis (DVT) occurred significantly more in the severe group (13.8% and 13.8%, respectively) than in the other two groups (mild, 0% and 2.6%, respectively; moderate, 0% and 2.6%, respectively). Additional data on complications are presented in Table 7. Additionally, patients in the severe group (17.2%) experienced more ICU admittance than those in the other two groups (mild, 2.9%; moderate, 2.6%) (Table 7).

**Table 6** Receiver Operating Characteristic Analysis of PI-LL mismatch
Parameter	Cut-point	AUROC	Sensitivity	Specificity
PI-LL mismatch (°)	75.3°	0.810 (0.666–0.954)	66.67%	90.00%
AUROC = area under the receiver operating characteristic curve

Table 7 Postoperative complications in each group

		Mild (n = 35)	Moderate (n = 38)	Severe (n = 29)	P value
Complications (n, %)	PJK	6 (17.1%)	7 (18.4%)	6 (20.7%)	0.129
	Pseudarthrosis	5 (14.3%)	4 (10.5%)	5 (17.2%)	0.621
	Neurological	0 (0%)	1 (2.6%)	4 (13.8%)	0.042*
	Deep vein thrombosis	0 (0%)	1 (2.6%)	4 (13.8%)	0.031*
	Pneumonia	1 (2.9%)	1 (2.6%)	3 (10.3%)	0.077
	Surgical site infection	0 (0%)	2 (5.3%)	0 (0%)	0.745
	Cholecystitis	0 (0%)	1 (2.6%)	3 (10.3%)	0.071
ICU stay (n, %)		1 (2.9%)	1 (2.6%)	5 (17.2%)	0.017*
PJK = proximal junctional kyphosis; ICU = intensive care unit

Lee et al.[6] reported sagittal imbalance and its dynamic characteristics in a study of patients with degenerative flatback. The study suggested that the dynamic features of stooping posture were due to the degeneration of the lumbar extensor muscles and their association with the pelvis and lower extremities. Kim et al.[13] attempted to explain the relationship between dynamic features and pelvic compensation in patients with severe DSI by using motion analysis. However, none of the studies so far have clearly stated the criteria or severity of DSI. Yin et al.[7] classified severity according to the change in C7SVA and the resulting ODI value after walking in patients with DSI and presented their own diagnostic criteria. Because the study was conducted on out-patients, there were few patients who showed significant changes in C7SVA after walking, and they also showed a good outcome with nonoperative treatment. However, the patients in the group with a large C7SVA change after walking, the so-called severe DSI group, did not feel symptom relief with the nonoperative treatment, and most of them underwent surgical treatment. We were interested in the severe group of patients. In fact, we have experienced many patients with severe DSI who find it impossible to walk for more than 30 s due to stooping, which is aggravated by walking. The patients visited our hospital for surgical treatment. Therefore, we proposed the idea of applying walking time to distinguish the severity of DSI.

In the comparison of demographic data among the groups, there was a significant difference in BMD and posterior fusion segments. No studies have directly explained the relationship between BMD and severity of sagittal imbalance. In several previous studies, such as that by Zhang et al.[14], osteoporotic compression fracture was reported as a risk factor for sagittal imbalance, and we think our results were in the same context. In addition, it is possible that the fact that the patients in the severe group were relatively older than those in the other groups may have affected the results. The patients in the severe group had relatively higher UIV levels than those in the other groups because they needed more correction than the other two groups. Operation time and blood loss were significantly higher in the severe group than in the other two groups. This can be inferred from the diagnoses in Table 3 and the pathologies contributing to the sagittal imbalance in each group of patients. Patients in the mild group mainly had spinal stenosis, which required multi-segment decompression during the surgical procedure. Relatively, since the patients in the severe group required larger correction, aggressive surgical techniques, such as pedicle subtraction osteotomy (PSO), were required, which could have resulted in longer operation times and larger amounts of blood loss.

Takemitsu et al.[15] suggested that the main pathology of LDK, which is characterized by severe sagittal imbalance, is marked atrophy of the paravertebral muscles, accompanied by fatty infiltration. Yagi et al.[4] reported drop body syndrome as a distinct form of ASD. The criteria included a multifidus CSA < 300 mm², a fatty infiltration area > 80%, and normal muscle volume in other areas of body. Lee et al.[6] also emphasized that the dynamic feature of sagittal imbalance is not a direct effect of skeletal deformity, but a secondary phenomenon following weakness of the paravertebral muscles. In addition to these studies, many previous studies have reported that degeneration of the paraspinal back muscle is related to a stooping posture. It is noteworthy that, in our study, paraspinal muscle degeneration was more pronounced in patients in the severe group than in the other groups. This implies that degeneration of the back muscles not only causes sagittal imbalance but also affects its severity.

Although our study dealt with sagittal imbalance, we did not compare preoperative C7SVA as a sagittal spinopelvic parameter (Table 5). This was because most of our patients had severe stooping and C7 was not visible on the lateral-entire-spine radiograph; therefore, it could not be accurately measured and compared. There was no significant difference in PI among the three groups, the PT increased from the mild to the severe group, and the SS showed the opposite trend. In all three groups, the lumbar spine showed kyphosis on average, which was most prominent in the severe group. As the loss of LL worsened, a compensatory mechanism using the pelvis for an upright posture worked, and the SS decreased in patients in the severe group. This increase in the lumbar kyphosis angle among the groups led to a distinct difference in the PI-LL mismatch. Schwab et al. selected the PI-LL mismatch as one of the sagittal modifiers, set the threshold to less than 10°, and reported that this has a great correlation with the health-related quality of life (HRQOL) in patients with ASD[16, 17]. Therefore, it could be possible that all groups, especially the severe group, would have a lot of discomfort in their daily life, which explained the situations in which patients decided to undergo corrective surgery without hesitation. In addition, based on the result that the PI-LL mismatch showed more differences than the other two groups compared to other parameters, ROC analysis was performed by separating the PI-LL mismatch values of patients in the mild and moderate groups and the values of patients in the severe group. As a result, a cut-off value of 75.3° was obtained, which established one of the criteria for the severe group (Table 6). Understanding the degree of spinal flexibility in patients with sagittal imbalance is very important for planning surgery because patients with rigid or fixed deformities require more aggressive surgical procedures, such as osteotomy. Karikari et al.[18] reported that in patients with rigid deformities, satisfactory results were not obtained in radiologic and clinical outcomes when osteotomy was not performed. Sharma et al.[19] compared LL measured on a standing radiograph with LL measured on MRI performed in the supine position and classified it as flexible if the difference was more than 10°. However, there is no widely accepted cut-off value for the formula to determine if the deformity is flexible. We used a difference in LL between flexion and extension in lateral radiographs to evaluate the flexibility of the lumbar spine, and the lumbar flexibility of patients in the severe group was significantly lower than that in the other two groups. These results are related to the preoperative diagnosis of our patients, as shown in Table 3. As explained earlier, patients in the mild group had relatively more spinal stenosis with multilevel degenerative disc disease, whereas the more severe group had fixed deformity due to bony changes, such as erosive change or compression fracture history, or previous operation history; hence, it is possible that there was a difference in flexibility[14]. Therefore, we judged that lumbar flexibility was reasonable as a criterion for the severe group, and the standard was set at 10°.

In patients with sagittal imbalance, changes in LL and C7SVA are more important than other radiological parameters after surgery. Among the three groups, the degree of correction of LL after surgery in the severe group was significantly smaller than that in the other two groups (Table 5). Regarding these results, we can consider problems related to “over-correction”. Aggressive procedures, such as PSO, are frequently used in patients with severe disease who require relatively more correction. Dorward et al.[20] reported many complications that may occur after osteotomy during corrective deformity surgery. In our experience, the ICU experience of patients due to a long operation time, large blood loss, or a long bed rest period after corrective surgery could affect the degree of correction. Second, there are problems related to patient flexibility. Patients in the mild or moderate group were relatively more flexible; therefore, if they took the prone position under general anesthesia, some correction occurred spontaneously. Therefore, the angle to be corrected may be reduced during the surgery. However, in the severe group, spontaneous correction rarely occurred during surgery. Therefore, the correction angle that must be obtained during surgery is large, so the correction angle may be relatively small compared to the other groups.

Patients in the severe group, with a higher probability, experienced more postoperative complications than patients in the other two groups (Table 7). In particular, neurological complications, DVT, and ICU stay were significantly higher in the severe group. In 2016, Smith et al.[21] reported that neurological complications occurred in 27.8% of all patients at a minimum 2-year follow-up during surgery for patients with ASD. In our study, 5 out of 102 patients, or approximately 5% patients experienced neurological complications, and 4 of them belonged to the severe group. All neurological complications were transient and minor and did not require reoperation. We believe that most of them were temporary events that occurred after overcorrection, but there were cases where the cause was difficult to predict. The incidence of DVT following spinal surgery ranged from 0.3–31%[22]. In the severe group, 4 out of 29 patients, or approximately 13.8%, experienced DVT. In patients in the severe group, staged operations were performed in almost all cases, and the bed rest period was relatively long compared to the other two groups because aggressive procedures, such as osteotomy, were performed to obtain a larger correction. Therefore, the incidence of DVT is thought to be high. Schwab et al.[23], through a multicenter review, reported a large estimated blood loss (EBL), long hospitalization period, and staged operation as risk factors for major perioperative complications in ASD. In the severe group, five patients experienced ICU admission. Three of them were transferred to the ICU for close observation immediately after surgery because vital signs, such as blood pressure, were temporarily unstable due to the large blood loss during surgery. The other two were transferred to the ICU to care for complications that occurred during hospitalization. One was admitted for pneumonia, and the other was admitted for DVT with pulmonary thromboembolism.

This study had several limitations. First, the number of patients in each group was relatively small, and recall bias could have occurred because this study was conducted at a single institution. In addition, patient-reported outcomes, such as the scoliosis research societ-22, were not compared between the groups. Comparing HRQOL outcomes of patients with DSI after surgery may provide a better understanding of the characteristics of patients with severe DSI.

We have suggested three criteria for severe DSI in adult spinal deformities: first, C7SVA > 20 cm within 30 s after walking or standing; second, the rigid lumbar curve < 10° on dynamic lateral radiographs; and third, the PI-LL mismatch > 75.3°.

DSI: Dynamic sagittal imbalance; ASD: Adult spinal deformity; C7SVA: C7 sagittal vertical axis; LL: Lumbar lordosis; PI: Pelvic incidence; LDK: Lumbar degenerative kyphosis; MCID: minimum clinically important difference; ODI: Oswestry disability index; PA: physician assistant; BMI: body mass index; BMD: bone mineral density; UIV: upper instrumented vertebra; ICU: intensive care unit; MRI: magnetic resonance imaging; SD: standard deviation; CSA: cross-sectional area; TK: thoracic kyphosis; TLK: thoracolumbar kyphosis; PT: pelvic tilt; SS: sacral slope; PJA: proximal junctional angle; ROC: receiver operating characteristic; AUC: area under the ROC curve; DVT: deep vein thrombosis; PSO:pedicle subtraction osteotomy; HRQOL: health-related quality of life; EBL: estimated blood loss;

Acknowledgements

Not applicable.

Author’s contributions

Conception and design: YCK and KYH. Acquisition of data: SMK, SIY and XJL. Analysis and interpretation of data: SMK and YCK. Critical revision of the manuscript: YCK and KYH. Drafting the article: SMK. All authors have read and approved the final manuscript.

Funding

Not applicable.

Availability of data and materials

The datasets generated and/or analyzed during the current study are not publicly available due to ethical concerns, but are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

This study was approved by the Institutional Review Board (IRB#2022-05-011) of the Kyung Hee University Hospital at Gangdong, Gandong-gu, Seoul, South Korea. The requirement for informed consent was waived by the IRB due to the retrospective nature of the study design. This study was performed in line with the principles of the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Disclosure

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper. There was no financial support for this study

Scheer JK, Lafage R, Schwab FJ, Liabaud B, Smith JS, Mundis GM, Hostin R, Shaffrey CI, Burton DC, Hart RA et al: Under Correction of Sagittal Deformities Based on Age-adjusted Alignment Thresholds Leads to Worse Health-related Quality of Life Whereas Over Correction Provides No Additional Benefit. Spine (Phila Pa 1976) 2018, 43(6):388-393.
Lonergan T, Place H, Taylor P: Acute Complications After Adult Spinal Deformity Surgery in Patients Aged 70 Years and Older. Clin Spine Surg 2016, 29(8):314-317.
Lapp MA, Bridwell KH, Lenke LG, Riew KD, Linville DA, Eck KR, Ungacta FF: Long-term complications in adult spinal deformity patients having combined surgery: a comparison of primary to revision patients. Spine 2001, 26(8):973-983.
Yagi M, Kaneko S, Yato Y, Asazuma T: Drop Body Syndrome: A Distinct Form of Adult Spinal Deformity. Spine (Phila Pa 1976) 2017, 42(16):E969-E977.
Lee JC, Cha JG, Kim Y, Kim YI, Shin BJ: Quantitative analysis of back muscle degeneration in the patients with the degenerative lumbar flat back using a digital image analysis: comparison with the normal controls. Spine (Phila Pa 1976) 2008, 33(3):318-325.
Lee CS, Lee CK, Kim YT, Hong YM, Yoo JH: Dynamic sagittal imbalance of the spine in degenerative flat back: significance of pelvic tilt in surgical treatment. Spine (Phila Pa 1976) 2001, 26(18):2029-2035.
Yin J, Ma X, Lin T, Gao R, Zhou X: Characteristics and treatment of dynamic sagittal imbalance in adult spinal deformity. Eur Spine J 2020, 29(9):2340-2353.
Lee C-H, Chung CK, Jang J-S, Kim S-M, Chin D-K, Lee J-K: Lumbar degenerative kyphosis’ is not byword for degenerative sagittal imbalance: time to replace a misconception. J Korean Neurosurg Soc 2017, 60(2):125-129.
Slobodyanyuk K, Poorman CE, Smith JS, Protopsaltis TS, Hostin R, Bess S, Mundis GM, Jr., Schwab FJ, Lafage V, International Spine Study G: Clinical improvement through nonoperative treatment of adult spinal deformity: who is likely to benefit? Neurosurg Focus 2014, 36(5):E2.
Acaroglu E, Yavuz AC, Guler UO, Yuksel S, Yavuz Y, Domingo-Sabat M, Pellise F, Alanay A, Perez Grueso FS, Kleinstuck F et al: A decision analysis to identify the ideal treatment for adult spinal deformity: is surgery better than non-surgical treatment in improving health-related quality of life and decreasing the disease burden? Eur Spine J 2016, 25(8):2390-2400.
Tonosu J, Takeshita K, Hara N, Matsudaira K, Kato S, Masuda K, Chikuda H: The normative score and the cut-off value of the Oswestry Disability Index (ODI). Eur Spine J 2012, 21(8):1596-1602.
Moal B, Lafage V, Smith JS, Ames CP, Mundis G, Terran JS, Klineberg E, Hart R, Boachie-Adjei O, Bess S et al: Clinical Improvement Through Surgery for Adult Spinal Deformity: What Can Be Expected and Who Is Likely to Benefit Most? Spine Deform 2015, 3(6):566-574.
Kim HJ, Chun HJ, Shen F, Kang KT, Chang BS, Lee CK, Yeom JS: Analysis of pelvic compensation for dynamic sagittal imbalance using motion analysis. Eur Spine J 2020, 29(3):428-437.
Zhang YL, Shi LT, Tang PF, Sun ZJ, Wang YH: Correlation analysis of osteoporotic vertebral compression fractures and spinal sagittal imbalance. Orthopade 2017, 46(3):249-255.
Takemitsu Y, Harada Y, Iwahara T, Miyamoto M, Miyatake Y: Lumbar degenerative kyphosis. Clinical, radiological and epidemiological studies. Spine 1988, 13(11):1317-1326.
Schwab F, Bess RS, Blondel B, Hostin R, Shaffrey C, Smith J, Boachie-Adjei O, Burton D, Akbarnia B, Mundis G: Combined assessment of pelvic tilt, lumbar lordosis/pelvic incidence mismatch and sagittal vertical axis predicts disability in adult spinal deformity: a prospective analysis. The Spine Journal 2011, 11(10):S158-S159.
Schwab F, Ungar B, Blondel B, Buchowski J, Coe J, Deinlein D, DeWald C, Mehdian H, Shaffrey C, Tribus C et al: Scoliosis Research Society-Schwab adult spinal deformity classification: a validation study. Spine (Phila Pa 1976) 2012, 37(12):1077-1082.
Karikari IO, Lenke LG, Bridwell KH, Tauchi R, Kelly MP, Sugrue PA, Bumpass DB, Elsamadicy AA, Adogwa O, Lalezari R et al: Key Role of Preoperative Recumbent Films in the Treatment of Severe Sagittal Malalignment. Spine Deform 2018, 6(5):568-575.
Sharma A, Pourtaheri S, Savage J, Kalfas I, Mroz TE, Benzel EC, Steinmetz MP: The Utility of Preoperative Magnetic Resonance Imaging for Determining the Flexibility of Sagittal Imbalance. Neurosurgery 2018, 83(3):465-470.
Dorward IG, Lenke LG, Stoker GE, Cho W, Koester LA, Sides BA: Radiographical and Clinical Outcomes of Posterior Column Osteotomies in Spinal Deformity Correction. Spine (Phila Pa 1976) 2014, 39(11):870-880.
Smith JS, Klineberg E, Lafage V, Shaffrey CI, Schwab F, Lafage R, Hostin R, Mundis GM, Jr., Errico TJ, Kim HJ et al: Prospective multicenter assessment of perioperative and minimum 2-year postoperative complication rates associated with adult spinal deformity surgery. J Neurosurg Spine 2016, 25(1):1-14.
Inoue H, Watanabe H, Okami H, Kimura A, Takeshita K: The Rate of Venous Thromboembolism Before and After Spine Surgery as Determined with Indirect Multidetector CT. JB JS Open Access 2018, 3(3):e0015.
Schwab FJ, Hawkinson N, Lafage V, Smith JS, Hart R, Mundis G, Burton DC, Line B, Akbarnia B, Boachie-Adjei O et al: Risk factors for major peri-operative complications in adult spinal deformity surgery: a multi-center review of 953 consecutive patients. Eur Spine J 2012, 21(12):2603-2610.

No competing interests reported.

Download PDF

Journal Publication

published 09 Feb, 2024

Read the published version in BMC Musculoskeletal Disorders →

Editorial decision: Revision requested
02 Dec, 2023
Reviews received at journal
01 Dec, 2023
Reviewers agreed at journal
19 Nov, 2023
Reviews received at journal
04 Sep, 2023
Reviewers agreed at journal
03 Sep, 2023
Reviewers invited by journal
03 Sep, 2023
Editor assigned by journal
03 Sep, 2023
Editor invited by journal
30 Aug, 2023
Submission checks completed at journal
30 Aug, 2023
First submitted to journal
06 Aug, 2023

You are reading this latest preprint version

Criteria for Severe Dynamic Sagittal Imbalance in Adult Spinal Deformity and its Importance

Status:

Journal Publication

Version 1

Abstract

Background

Methods

Results

Conclusions

Figures

Background

Methods

Study design

Data collection

Statistical analysis

Results

Demographic data

Back muscle degeneration at lumbar levels

Radiologic parameters and lumbar flexibility

ROC curve analysis

Postoperative complications

Discussion

Conclusions

Abbreviations

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1