Abstract
Purpose
Although the incidence of distal junctional problems (DJPs) following long construct‐based treatment for degenerative lumbar scoliosis (DLS) is lower, affected patients are more likely to require revision surgery when they occur. So the aim of this study is to identify risk factors associated with DJPs to avoid its occurrence by at least 1‐year follow‐up.
Methods
A total of 182 DLS patients undergoing long instrumented fusion surgery (≥4 levels) between February 2011 and March 2022 were retrospectively analyzed. Patients were placed into the DJP group if a DJP occurred at the final follow‐up; patients without mechanical complications were matched 1:2 according to age, sex and BMI as the control group. Patient characteristics, surgical variables, radiographic parameters, lumbar muscularity and fatty degeneration were analyzed statistically. The statistical differences in the results between the two groups (p values <0.05) and other variables selected by experts were entered into a multivariate logistic regression model, and the forwards likelihood ratio method was used to analyze the independent risk factors for DJPs.
Results
Twenty‐four (13.2%) patients suffered a DJP in the postoperative period and the reoperation rate was 8.8%. On univariate analysis, the lowest instrumented vertebra (LIV) CT value (p = 0.042); instrumented levels (p = 0.030); preoperative coronal vertical axis (CVA) (p = 0.046), thoracolumbar kyphosis (TLK) (p = 0.006), L4‐S1 lordosis (p = 0.013), sacral slop (SS) (p = 0.030), pelvic tilt (PT) classification (p = 0.004), and sagittal vertical axis (SVA) (p = 0.021); TLK correction (p = 0.049); post‐operative CVA (p = 0.029); Overall, There was no significant difference in the paraspinal muscle parameters between the two groups. On multivariate analysis, instrumented levels (OR = 1.595; p = 0.035), preoperative SVA (OR = 1.016; p = 0.022) and preoperative PT (OR = 0.873; p = 0.001) were identified as significant independent risk factors for DJP.
Conclusion
Longer instrumented levels, a greater preoperative SVA and a smaller PT were found to be strongly associated with the presence of DJPs in patients treated for DLS. The degeneration of the paraspinal muscles may not be related to the occurrence of DJPs. For DLS patients, the occurrence of DJP can be reduced by selecting reasonable fusion segments and evaluating the patient's sagittal balance and spino‐pelvic parameters before operation.
Keywords: degenerative lumbar scoliosis, distal junctional problems, long instrumented fusion, paraspinal muscle, pelvic tilt, sagittal vertical axis
Decompression for neurological elements combined with long‐level instrumented fusion and fusion is a common method for the treatment of DLS. Although the incidence of DJPs is low, revision surgery is often required once it occurs. Our research found that selection of a longer fixed segment, larger preoperative SVA, and smaller PT were strongly associated with the presence of DJPs. Paraspinal muscle degeneration may not be related to the occurrence of DJPs.
Introduction
Degenerative lumbar scoliosis (DLS) is defined as a spinal deformity in a skeletally mature patient with a Cobb angle greater than 10° in the coronal plane, which can cause severe back and leg pain symptoms and result in a compromise in the health‐related quality of life of the patient. 1 The surgical management of DLS involves completely decompressing the nerve, stabilizing the spine, restoring the normal organization of the lumbar spine, and reshaping the spinal balance. Decompression for neurological elements combined with long‐level instrumented fusion is the typical surgical method, 2 , 3 but this process is a major surgical undertaking associated with considerable perioperative risks and a substantial complication profile. The natural history and risk factors associated with proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) have widely reported, 4 , 5 , 6 but distal junctional problems (DJPs), including distal junction kyphosis/failure (DJK/DJF), have rarely been reported in the literature. A systematic review of 12 studies showed that the incidence of DJF was only 3.6%, but it represented 27.3% of all revision surgeries. 7 This finding indicates that although the incidence of DJPs is lower than that of PJK/PJF, affected patients are more likely to require revision surgery when they occur. 8 , 9 The pathogenic mechanisms underlying DJPs are multifactorial, and older age, 7 large preoperative sagittal parameters, 10 fusion short of including the first lordotic disc, 11 selection of the incorrect lowest instrumented vertebra (LIV), 12 , 13 and inability to match the postoperative sagittal plane with the pelvic incidence (PI) 14 have been reported to be involved. Recently, lower muscularity and higher fatty degeneration have been reported as risk factors for PJK. 15 To the best of our knowledge, no studies have demonstrated the role of the condition of the lumbar paraspinal muscles on the incidence of DJPs following long instrumented posterior spinal fusion for DLS patients. The purpose of this study was to investigate the incidence of and risk factors for DJPs after long‐segment fusion for treating DLS.
So we put forward the following scientific points: (i) the long instrumented fusion segment may increase the incidence of DJPs (ii) The sagittal and spinopelvic parameters of patients may be related to the occurrence of DJPs (iii) Severe paraspinal muscle degeneration can lead to the occurrence of DJPs.
Materials and Methods
Study Design and Population
This retrospective study analyzed DLS patients undergoing posterior multilevel spinal fusion (PSF) from February 2011 to March 2022, with a minimum follow‐up of at least 1 year. The inclusion criteria were age ≥40 and a minimum of four fused levels. Patients with tumor, infections, traumatic spine pathology, revision surgery and secondary scoliosis due to other aetiologies (such as congenital scoliosis, neuromuscular scoliosis and so on) were excluded from the study. We placed patients with DJPs into the case group, and the remaining patients without mechanical complications were matched at a 1:2 according to age, sex and BMI as the control group.
DJP Definitions
A DJP was defined as the occurrence of DJK or DJF. DJK was defined as (a) an increase in the angle between the superior endplate of the LIV and the inferior endplate of the adjacent distal vertebra by 10° or (b) a change in the angle formed in the subsequent intervertebral space by the LIV causing a shift from lordosis preoperatively to median or kyphosis postoperatively. 11 , 16 Distal junctional failure was defined as (a) progressive loss of lumbar lordosis (LL) and loss of disk height with disk degeneration; (b) acute wedging in the disk below the instrumentation; (c) fracture of the most distal instrumented vertebra involving, in most cases, the inferior endplate; (d) failure of the instrumentation at the most distal level; and (e) spinal stenosis or segmental instability below the instrumentation. 17
Estimation of Bone Density
All patients underwent preoperative lumbar CT (SOMATOM Definition Flash, Siemens, Germany). The tube voltage of the CT scans was set at 120 kV. The average HU value of the region of interest (ROI) was calculated using a picture archiving and communications system (PACS). We chose the axial plane in the middle of the LIV to measure the vertebral HU. The ROI was chosen to include as much trabecular bone as possible and to avoid cortical bone and heterogeneous areas, such as the posterior venous plexus, bone islands, and compressed bone.
Surgical Procedure
In all cases included in this study, meticulous surgeries were performed by senior surgeons. Using the posterior midline approach, the spinous processes, lamina and facet joints were exposed. Pedicle screws were implanted by free‐hand technique, and neural decompression was performed with laminectomy and discectomy. The surgeons determined whether osteotomy and intervertebral fusion should be performed according to the patients' radiological and clinical findings. If needed, posterior column osteotomy (PCO) and pedicle subtraction osteotomy (PSO) were performed. Then, a cage with autogenous bone granule tamponade was placed into the appropriate intervertebral space. Posterolateral fusion was performed after the rods were assembled.
If one of the following occurred, we ended the fusion at the sacrum: (a) advanced degeneration of the L5/S1 intervertebral disk, (b) lumbosacral stenosis requiring decompression, (c) L5–S1 spondylolysis, or (d) oblique take‐off of L5 on the sacrum.
Data Collection
Demographic information collected included sex, age at surgery, body mass index, follow‐up time, comorbidities and American Society of Anaesthesiologists (ASA) classification. All patients underwent standing full spine X‐rays preoperatively and ≤6 weeks postoperatively. Radiographic evaluated parameters included the Cobb angle, apical vertebral translation (AVT), coronal vertical axis from the central sacrum vertical line (CSVL), apical vertebra rotation (Nash‐Moe classification), maximal lateral olisthesis, sagittal vertical axis (SVA), thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), difference between pelvic incidence and lumbar lordosis (PI‐LL) and T1 pelvic angle (TPA). A patient with a CVA between ‐30mm to 30mm was considered to have CVA balance. According to the Scoliosis Research Society (SRS) Schwab classification, 18 patients with a PI‐LL <10°, 10°–20°, and >20° were classified as 0/+/++; patients with an SVA < 4 cm, 4–9.5 cm, and >9.5 cm were classified as 0/+/++; and patients with a PT <20°, 20°–30°, and >30° were classified as 0/+/++.
Paraspinal Muscle Measurements
Magnetic resonance imaging (MRI) was performed for all enrolled patients on a 3.0 T system (Siemens, Germany or General Electric, USA) to measure muscle area and T2 signal intensity. Axial MRI images were aligned parallel to the middle of each disc at L2–L3, L3–L4, L4–L5 and L5–S1. The conditions of the psoas (PS), quadratus lumborum (QL) multifidus (MF) and erector spinae (ES) muscles were analyzed using the cross‐sectional area (CSA) and signal intensity (SI) on axial T2 weighted images. The area of the muscles was divided by the intervertebral disc area at the same level and multiplied by 100 (muscle CSA/disc CSA*100) to represent the lumbar muscularity of each individual. Similarly, the degree of fatty change was estimated as muscle–fat index at each level by muscle–subcutaneous fat SI ratio multiplied by 100. 19 A region of interest (ROI) covering the area of lean muscle tissue excluding fatty infiltration was drawn to determine the functional cross‐sectional area (FCSA), 20 and the muscle–fat index of the lean muscle within the ROI was defined as the lean muscle–fat index (LMFI). The gross cross‐sectional area (GCSA) was determined by drawing the outer perimeter of the muscle, including any areas of intramuscular fat, and the muscle–fat index of the GSCA was defined as the total muscle–fat index (TMFI). The GCSAs of the PS and QL were not measured since it was too difficult to distinguish their borders, so instead, the T2 signal intensities of the PS and QL were measured by using the FCSA instead. 15
Statistical Analysis
The data were analyzed by SPSS software version 24 (SPSS Inc., Chicago, IL). Continuous variables with an approximately normal distribution are expressed as the mean and standard deviation (SD) and as the median (interquartile range) otherwise. Categorical values are presented as frequencies and percentages. Simple comparisons of continuous data between groups were carried out with Student's t‐test or the Mann–Whitney U test, depending on whether the distribution was normal or nonnormal, respectively. Categorical variables were compared using the X 2 test or Fisher's exact test. Variables with p values <0.05 in the univariate analyses, as well as a number of variables selected by experts, were entered into a multivariate logistic regression model, and the forwards likelihood ratio method was used to analyze the independent risk factors for DJP. A p value <0.05 was considered statistically significant.
Ethics Approval
This retrospective study was carried out the case series of our hospital. The study was approved by the Peking University Third Hospital Medical Science Research Ethics Committee (IRB00006761‐M2020305) and was conducted in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was waived by our Institutional Review Board because of the retrospective nature of our study.
Results
The Basic Information between Two Groups and Incidence of DJPs
A total of 182 patients who met the inclusion and exclusion criteria were collected. Twenty‐four patients with DJPs were included in the case group, for a DJP incidence of 13.2%. Four patients had DJK, 4 had distal instrumented vertebra fracture, 5 had distal instrumented vertebra spinal stenosis or segmental instability, and 11 had implant failure at the site of distal segment fixation. Furthermore, 16 patients (8.8%) underwent reoperation (Figures 1 and 2). The control group included 48 patients who were matched 1:2 according to age, sex and BMI. There were no significant differences in age, sex, BMI, incidence of diabetes/hypertension, or ASA classification between the two groups. The CT HU value of the LIV was lower in the DJP group than in the control group (p = 0.042) (Table 1).
FIGURE 1.
A 64‐year‐old woman presented with low back pain and radiating pain in the right lower extremity for 4 years. (A, B) Preoperative spinal X‐ray showed Cobb Angle 42.5°, PT 42.2°, PI 79.2°, and SVA 96.24 mm. (C, D) The angle between L5‐S1 is 1.4° after T11‐L5 instrumented fusion. (E) CT showed that the L5‐S1 Angle changed to −10.1 at 13 months after operation (DJK). (F, G) X‐rays showed fusion with fixation to the iliac bone in revision surgery.
FIGURE 2.
A 66‐year‐old woman presented with low back pain for 15 years and radiating pain in the left lower extremity for 2 years. (A, B) Preoperative spinal X‐ray showed Cobb Angle 18.1°, PT 26.9°, PI 41.6°, and SVA 48.24 mm. (C, D) T9‐L5 instrumented fusion were performed. (E, F) Failure of the instrumentation occurred at the most distal level at 8 months after operation. (G, H) X‐rays showed fusion with fixation to the iliac bone in revision surgery.
Table 1.
Comparison of characteristics between the two groups.
| DJP group (n = 24) | Control group (n = 48) | p‐value | |
|---|---|---|---|
| Age at surgery (years) | 63.38 ± 4.64 | 63.40 ± 4.63 | 0.986 |
| Gender (Female/Male) | 20/4 | 40/8 | / |
| Follow‐up period (month) | 21.50 ± 19.15 | 24.42 ± 16.79 | 0.510 |
| BMI (kg/m2) | 25.18 ± 3.22 | 24.92 ± 2.95 | 0.733 |
| Hypertension | 11 (45.8%) | 18 (37.5%) | 0.497 |
| Diabetes mellitus | 6 (25%) | 7 (14.6%) | 0.279 |
| ASA classification | 3/21/0/0 | 7/41/0/0 | 0.811 |
| LIV CT value (Hu) | 112.06 ± 42.42 | 136.29 ± 54.03 | 0.042* |
Compared with the control group, p < 0.05.
Risk Factors Related to Surgery
The surgical data of the two groups are shown in Table 2. There was no significant difference in LIV distribution, interbody fusion, intraoperative blood loss or osteotomy grade (p > 0.05). Compared with those of the control group, the upper instrumented vertebra (UIV) segment was relatively higher (p = 0.002), and the operation time and fusion segment were longer (p = 0.030, 0.042) in the DJP group.
Table 2.
Comparison of surgical data between the two groups.
| DJP group (n = 24) | Control group (n = 48) | p‐value | |
|---|---|---|---|
| UIV at T10 and above | 6 (25%) | 1 (2.1%) | 0.002* |
| LIV at sacrum | 10 (41.7%) | 26 (54.2%) | 0.317 |
| Instrumented levels | 6.58 ± 2.34 | 5.42 ± 1.30 | 0.030* |
| Interbody fusion | 19 (79.2%) | 44 (91.7%) | 0.131 |
| Operative time (min) | 296.67 ± 102.53 | 248.40 ± 63.08 | 0.042* |
| Intraoperative blood loss (mL) | 1083.33 ± 621.83 | 849.38 ± 595.80 | 0.126 |
| Osteotomy classification | |||
| None | 4 (16.7%) | 11 22.9%) | 0.123 |
| Grade 1 | 8 (33.3%) | 20 (41.7%) | |
| Grade 2 | 5 (20.8%) | 13 (27.1%) | |
| Grade 3 | 7 (29.2%) | 4 (8.3%) | |
Compared with the control group, p < 0.05.
Risk Factors of Preoperative and Postoperative Imaging Parameters
The preoperative imaging parameters of the two groups are shown in Table 3. The DJP group had more obvious thoracolumbar kyphosis (p = 0.006), a larger sacral slope (p = 0.030), more obvious L4‐S1 lordosis (p = 0.013) and a higher SVA classification (p = 0.021). The PT classification according to the Schwab classification (p = 0.004) was lower in the DJP group than in the control group.
Table 3.
Comparison of preoperative radiographic parameters between the two groups.
| Parameters | DJP group | Control group | p‐value |
|---|---|---|---|
| Cobb angle (°) | 28.07 ± 11.11 | 25.32 ± 8.77 | 0.257 |
| AVT (mm) | 10.55 ± 23.21 | 20.07 ± 17.88 | 0.058 |
| Apical vertebra rotation (I/II/III/IV) | 10/12/2/0 | 25/22/1/0 | 0.304 |
| Maximal lateral olisthesis (mm) | 7.60 ± 2.82 | 7.24 ± 3.25 | 0.642 |
| CVA (mm) | 20.80 ± 21.55 | 18.33 ± 15.66 | 0.901 |
| Coronal imbalance | 3 (12.5%) | 8 (16.7%) | 0.215 |
| TK (°) | 20.13 ± 13.36 | 16.13 ± 13.69 | 0.243 |
| TLK (°) | 21.12 ± 16.05 | 9.54 ± 16.63 | 0.006* |
| LL (°) | 27.46 ± 17.66 | 20.62 ± 19.46 | 0.152 |
| L4‐S1 lordosis (°) | 32.57 ± 10.65 | 24.60 ± 13.40 | 0.013* |
| PI (°) | 50.79 ± 11.62 | 52.76 ± 9.88 | 0.455 |
| SS (°) | 27.05 ± 11.03 | 22.98 ± 9.75 | 0.030* |
| PT (°) | 24.40 ± 8.58 | 29.86 ± 10.39 | 0.115 |
| PT classification (0/+/++) | 8/13/3 | 7/19/22 | 0.004* |
| PI‐LL (°) | 23.33 ± 14.84 | 32.15 ± 20.18 | 0.062 |
| PI‐LL classification (0/+/++) | 5/4/15 | 7/7/34 | 0.455 |
| SVA (mm) | 73.63 ± 50.39 | 46.55 ± 43.54 | 0.021* |
| SVA classification (0/+/++) | 7/5/12 | 20/21/7 | 0.022* |
| TPA (°) | 24.55 ± 9.86 | 25.54 ± 10.60 | 0.705 |
Compared with the control group, p < 0.05.
Regarding the immediate postoperative radiographic parameters, there were no statistically significant differences between the two groups except coronal balance (p = 0.029). There was no significant difference in the changes in imaging parameters between the two groups before and after the operation except for ΔTLK (p = 0.049). (Table 4).
Table 4.
Comparison of immediate postoperative radiographic parameters between the two groups.
| Parameters | DJP group | Control group | p‐value |
|---|---|---|---|
| Cobb angle (°) | 11.28 ± 7.23 | 10.41 ± 5.60 | 0.576 |
| CVA (mm) | 16.25 ± 12.83 | 19.08 ± 11.88 | 0.016* |
| Coronal imbalance | 6 (25%) | 18 (37.5%) | 0.709 |
| TK (°) | 20.26 ± 11.62 | 21.54 ± 9.90 | 0.627 |
| TLK (°) | 9.60 ± 9.28 | 6.82 ± 11.13 | 0.296 |
| LL (°) | 33.41 ± 17.38 | 34.80 ± 11.34 | 0.725 |
| L4‐S1 lordosis (°) | 24.93 ± 15.63 | 24.90 ± 11.09 | 0.995 |
| PI (°) | 50.46 ± 12.62 | 53.12 ± 9.21 | 0.313 |
| SS (°) | 30.25 ± 9.73 | 28.65 ± 7.80 | 0.452 |
| PT (°) | 20.19 ± 7.78 | 24.78 ± 10.05 | 0.054 |
| PT classification (0/+/++) | 14/6/4 | 20/14/14 | 0.156 |
| PI‐LL (°) | 17.05 ± 15.94 | 18.32 ± 12.28 | 0.709 |
| PI‐LL classification (0/+/++) | 9/8/7 | 11/16/21 | 0.154 |
| SVA (mm) | 50.22 ± 72.79 | 33.15 ± 33.97 | 0.285 |
| SVA classification (0/+/++) | 10/7/7 | 25/22/1 | 0.078 |
| TPA (°) | 19.15 ± 11.06 | 20.61 ± 8.49 | 0.539 |
| ΔTLK | 14.38 ± 14.06 | 9.14 ± 8.16 | 0.049* |
Compared with the control group, p < 0.05.
Differences in Paraspinal Muscle Degeneration between the Two Groups
For the evaluation of the paraspinal muscle CSA and FI there was no significant difference between the two groups at most levels, but the muscle CSA in the DJP group tended to be larger than that in the control group. The FI of the DJP group was also higher than that of the control group (Tables 5 and 6). The convex to concave CSA and FI ratios were also compared, and there was no difference between the two groups.
Table 5.
Lumbar muscularity (muscle–disc CSA ratio × 100) of the paraspinal muscles of the two groups using MRI.
| Parameters | Levels | DJP group | Control group | p‐value |
|---|---|---|---|---|
| PS CSA | L2‐3 | 23.35 ± 7.00 | 22.77 ± 6.87 | 0.739 |
| L3‐4 | 32.53 ± 8.49 | 30.29 ± 8.00 | 0.276 | |
| L4‐5 | 42.20 ± 9.81 | 39.98 ± 11.49 | 0.421 | |
| L5‐S1 | 44.71 ± 10.82 | 41.29 ± 9.92 | 0.186 | |
| QL CSA | L2‐3 | 9.29 ± 3.15 | 10.15 ± 4.17 | 0.375 |
| L3‐4 | 14.76 ± 5.06 | 14.11 ± 3.96 | 0.552 | |
| L4‐5 | 15.58 ± 6.77 | 12.43 ± 5.62 | 0.056 | |
| L5‐S1 | / | / | / | |
| GCSA of MF | L2‐3 | 15.17 ± 5.34 | 17.31 ± 6.58 | 0.171 |
| L3‐4 | 24.52 ± 8.24 | 22.71 ± 769 | 0.363 | |
| L4‐5 | 39.06 ± 10.78 | 33.10 ± 11.26 | 0.035* | |
| L5‐S1 | 51.69 ± 11.91 | 46.88 ± 18.77 | 0.257 | |
| FCSA of MF | L2‐3 | 8.94 ± 4.66 | 11.42 ± 11.67 | 0.321 |
| L3‐4 | 13.86 ± 6.03 | 12.91 ± 4.28 | 0.497 | |
| L4‐5 | 20.91 ± 8.69 | 18.20 ± 6.92 | 0.190 | |
| L5‐S1 | 25.31 ± 10.88 | 23.65 ± 11.14 | 0.550 | |
| GCSA of ES | L2‐3 | 79.84 ± 15.10 | 88.93 ± 16.64 | 0.028* |
| L3‐4 | 76.12 ± 13.44 | 78.79 ± 15.81 | 0.481 | |
| L4‐5 | 74.21 ± 18.27 | 65.75 ± 16.88 | 0.055 | |
| L5‐S1 | 41.54 ± 23.05 | 38.78 ± 16.08 | 0.557 | |
| FCSA of ES | L2‐3 | 56.94 ± 18.84 | 64.43 ± 13.95 | 0.061 |
| L3‐4 | 51.67 ± 12.15 | 53.02 ± 12.27 | 0.659 | |
| L4‐5 | 44.81 ± 12.13 | 39.25 ± 11.31 | 0.059 | |
| L5‐S1 | 21.60 ± 14.04 | 20.01 ± 9.35 | 0.570 |
Abbreviations: CSA, cross‐sectional area; ES, erector spinae; FCSA, functional cross‐sectional area; GCSA, gross cross‐sectional area; MF, multifidus; PS psoas; QL, quadratus lumborum.
Compared with the control group, p < 0.05.
Table 6.
Degree of fatty change (muscle–subcutaneous fat mean signal intensity ratio × 100) of the paraspinal muscles of two groups using MRI.
| Parameters | Levels | DJP group | Control group | p‐value |
|---|---|---|---|---|
| LMFI of PS | L2‐3 | 14.67 ± 6.61 | 13.59 ± 5.28 | 0.456 |
| L3‐4 | 14.64 ± 7.11 | 13.42 ± 4.83 | 0.392 | |
| L4‐5 | 13.96 ± 6.60 | 11.65 ± 4.53 | 0.086 | |
| L5‐S1 | 13.06 ± 6.39 | 10.74 ± 4.30 | 0.118 | |
| LMFI of QL | L2‐3 | 17.63 ± 8.32 | 16.05 ± 5.40 | 0.402 |
| L3‐4 | 17.67 ± 9.49 | 16.48 ± 5.31 | 0.493 | |
| L4‐5 | 21.44 ± 7.86 | 17.19 ± 6.90 | 0.021* | |
| L5‐S1 | / | / | / | |
| TMFI of MF | L2‐3 | 38.25 ± 10.54 | 36.74 ± 10.39 | 0.567 |
| L3‐4 | 40.95 ± 16.37 | 37.88 ± 10.12 | 0.405 | |
| L4‐5 | 43.43 ± 13.75 | 37.24 ± 9.46 | 0.028* | |
| L5‐S1 | 46.26 ± 13.30 | 41.03 ± 10.49 | 0.073 | |
| LMFI of MF | L2‐3 | 26.27 ± 8.14 | 25.7 ± 7.10 | 0.768 |
| L3‐4 | 27.74 ± 10.39 | 26.18 ± 6.51 | 0.507 | |
| L4‐5 | 28.11 ± 9.28 | 24.90 ± 6.69 | 0.140 | |
| L5‐S1 | 27.96 ± 7.53 | 27.34 ± 8.10 | 0.754 | |
| TMFI of ES | L2‐3 | 34.26 ± 10.66 | 32.82 ± 8.92 | 0.547 |
| L3‐4 | 37.31 ± 12.37 | 35.92 ± 8.71 | 0.584 | |
| L4‐5 | 39.81 ± 11.11 | 36.43 ± 8.39 | 0.153 | |
| L5‐S1 | 42.74 ± 10.14 | 40.10 ± 9.07 | 0.265 | |
| LMFI of ES | L2‐3 | 23.27 ± 6.31 | 23.08 ± 6.27 | 0.903 |
| L3‐4 | 24.67 ± 8.45 | 23.97 ± 6.41 | 0.697 | |
| L4‐5 | 26.11 ± 9.34 | 23.59 ± 6.18 | 0.175 | |
| L5‐S1 | 29.37 ± 7.04 | 26.86 ± 6.38 | 0.132 |
Abbreviations: LMFI, lean muscle–fat index; TMFI, total muscle–fat index.
Compared with the control group, p < 0.05.
Logistic Regression Analysis of Risk Factors
Multivariate logistic regression analysis showed that a 1 mm increase in preoperative SVA was associated with a 1.6% increase in the probability of postoperative DJP. When the preoperative PT increased by 1°, the possibility of DJP decreased by 12.7%. The incidence of DJP which undergoing posterior long‐segment fusion (≥4 fusion levels) increased by 59.5% for each additional instrumented and fused level (Table 7).
Table 7.
Logistic regression analysis model for the independent risk factors associated with DJP.
| Odds ratio (95% confidence interval) | p | |
|---|---|---|
| Instrumented and fused levels (+1 level) | 1.595 (1.033–2.463) | 0.035* |
| Preoperative TLK (+1°) | 1.041 (0.993–1.092) | 0.096 |
| Preoperative PT (+1°) | 0.873 (0.802–0.949) | 0.001* |
| Preoperative SVA (+1 mm) | 1.016 (1.002–1.030) | 0.022* |
p < 0.05.
Discussion
There are few reports on DJK and DJF in the literature, and research on DJK has mainly focused on adolescent idiopathic scoliosis (AIS) and Scheuermann's disease. Different diseases and diagnostic criteria may lead to different incidences of DJK/DJF. For AIS and Scheuermann's disease, they often use a distal junction angle greater than 10° at follow‐up or an increase of 10° compared with that before surgery as the diagnostic criteria for DJK. 16 , 21 Because the LIV of long‐segment fusion in DLS patients is often at L5 or S1, the above diagnostic criteria could not be used. Therefore, in this study, a change in the angle of the next intervertebral space of the distal instrumented vertebra from preoperative lordosis to postoperative median or kyphosis, was also diagnosed as DJK. 22 , 23 For DJF, we adopted the DJF classification established by Arlet and Aebi. 17 Our study found that a longer instrumented level and a larger preoperative SVA were risk factors for DJP, and a larger preoperative PT value was a protective factor for DJP. Compared with the control group, patients with DJP were not found to have more severe paraspinal muscle atrophy and fat infiltration.
The Incidence of DJP
This study found that the incidence of DJP in DLS patients with long‐segment fusion was 13.2%, and the rate of secondary surgery after DJP was 8.8%. McDonnell et al. 24 reported a 40.2% incidence of DJK in patients with adjacent segment disease (ASD), but they selected all deformation patients with ASD rather than only DLS and used multiple surgical approaches. Another multicentre study on ASD patients found that the prevalence of DJK was 4.5% but did not calculate the prevalence of DJF. 25 The higher incidence of DJK/DJF in these two groups may be due to the higher complexity of deformity in their enrolled patients with respect to the present study. Recently, the CT HU value has become widely used for the evaluation of BMD and osteoporosis screening. 26 , 27 , 28 Tan et al. 29 reported two patients with DJF caused by L5 compression fractures and believed that increased bone fragility caused by osteoporosis was an important cause of L5 compression fracture. Kwon et al. 30 reviewed 13 patients who underwent revision due to progressive DJK after lumbar fusion. Among these patients, the majority (85%) had osteopenia or osteoporosis. We found that the bone mineral density (BMD) of the LIV was lower in the DJP group, which may have contributed to the distal implant failure.
Selection of Surgical Segments
There are many surgical risk factors for DJK/DJF. Long segment lumbar fusions may lead to junctional failures. 31 A long lever arm subjects the distal fixation to significant forces, which likely contributes to the failure of most caudal pedicle screws in many patients. The LIV selected in treating DLS is relatively consistent, so increasing the proximal fusion level will increase the possibility of DJP. Just as we assumed, we found that a UIV above T10 and longer instrumented and fused levels were risk factors for DJP. It is very important to clarify the segment responsible for the symptoms and whether the back pain is axial pain before the operation. Reserving spinal movement segments reasonably can reduce the occurrence of DJP.
Improper selection of the distal fixator is a known cause of DJK/DJF. In patients with AIS and Scheuermann's disease, recent studies have found that the selection of the distal fixed vertebra far beyond the stable vertebra in the sagittal plane can reduce the occurrence of DJK/DJF. 22 , 23 , 32 However, the choice of distal fusion level in DLS patients is still controversial, such as whether the normal L5/S1 segment should be fused and whether the fusion to S1 should involve routine fixation to the iliac bone. The range of the L5/S1 segment accounts for 15% of the total range of motion of the lumbar spine. 33 Establishing the LIV at L5 can preserve the L5/S1 motor segment, produce less surgical trauma and reduce the occurrence of postoperative pseud arthrosis. However, the disadvantage of choosing L5 as the LIV is that the incidence of L5/S1 segment degeneration and instability increases after surgery. Tan et al. 29 believed that establishing the LIV located at L5 is a risk factor for DJF, because compared with the upper lumbar vertebra, the L5 pedicle is shorter and contains more cancellous bone, and there is a risk of vertebral fracture or screw pullout at the end of fusion, which is a cause of DJK/DJF. Witiw et al. 34 reported 116 patients with ASD and found that DJF occurred in 6 patients after surgery, all of whom had the LIV located at L4/5 and underwent revision surgery. Taneichi H et al. 35 selected ASD patients with less severe disability and less complex deformity who underwent fusion to L5, but 50% of the patients required additional fusion to the pelvis. There were 14 patients for whom the LIV was established at L5 among 24 DJP patients, and 10 of them underwent revision surgery. It suggests that DJP is more likely to occur in DLS patients whose LIV is established at L5.
Sagittal Parameters and Spinopelvic Parameters
The preoperative TLK in the DJP group was larger, and ΔTLK was more obvious than that in the control group. In this study, most UIVs were located in the thoracolumbar segment, which increased stress at the thoracolumbar junction due to thoracolumbar kyphosis. If the angle of the thoracolumbar kyphosis changes greatly during correction, the proximal screw needs to bear a large tensile load to maintain the postoperative morphology, which will transmit the distal screws through the rods, resulting in implant‐related complication failure. Miller et al. 36 and Kawabata A et al. 25 also reach a similar conclusion. In terms of spinopelvic parameters, the PI values were similar between the two groups, but patients in the control group had higher PT, which means that for these patients, the impact of global sagittal malalignment could be reduced by increasing pelvic retroversion, 37 thus avoiding the occurrence of DJP. Therefore, for patients with a lower preoperative PT value, a more careful surgical plan should be developed to reduce the occurrence of DJP.
SVA is a reliable radiographic predictor of spinal sagittal balance. We found that a larger preoperative SVA increased the likelihood of DJP, which may be due to body compensation and the “leverage” effect of long‐segment fixation and fusion, resulting in increased stress in the distal junction area, which further leads to the failure of distal internal fixation and DJF. McDonnell JM et al. 24 found that the DJF had greater pre/postoperative SVA measurements. We found that the distribution of SVA classifications differed between the two groups; when we used a postoperative SVA ≥60mm as the criterion for SVA imbalance, there was significant difference between the two groups (10 [41.7%] vs. 9 [18.8%], p = 0.038). According to the theory proposed by Schwab, 38 an SVA ≥50mm can predict patient disability and provide a guideline for patient assessment for appropriate therapeutic decision making, but the age of the participants in this study was relatively young (51.9 ± 16.8). Under natural conditions, the SVA will increase with age, 39 and many elderly people have good mobility with increased forward sagittal tilt. Therefore, more liberal diagnostic criteria for sagittal imbalance may be needed for elderly patients with DLS.
Paraspinal Muscle Degeneration
Previous studies have reported that age and weight are risk factors for DJP 25 , 36 , 40 ; similarly, age and weight also affect the degree of paraspinal muscle degeneration. 41 To reduce their effect as confounding factors in the analysis of the relationship between paraspinal muscles and the occurrence of DJP, we performed 1:2 control matching with the case group. Many studies have shown that paraspinal muscle degeneration is closely related to PJK, 5 , 15 , 17 , 42 but to the best of our knowledge, this is the first study to investigate the relationship between the paraspinal muscles and DJPs. However, it is different from our hypothesis that we found that the DJP group did not have more significant muscle atrophy or more severe fat infiltration. This difference may be due to the following reasons. In PJK, proximal muscle degeneration will lead to a decrease in the effect of the posterior soft tissue as a “tension band,” 19 and ischaemia and intraoperative thermal injury may lead to paraspinal extensor muscle atrophy, 43 which will increase proximal instability. However, when the distal segment is L5/S1, the role of the distal muscles in stabilization is minimal. And in elderly individuals, the lower lumbar paraspinal muscles degenerate earlier than the upper segments, 41 which may be the reason why the degree of degeneration of the distal paraspinal muscles was similarly between the two groups. Overall, the DJP group had a larger CSA and more severe FI. This may be a compensatory hypertrophy of the muscles used to counter the imbalance in the sagittal alignment. 44 Previous studies have shown that the FI was significantly and positively correlated with the sagittal vertical axis (r = 0.488). 45 We believe that the differences in the paraspinal muscles are mainly caused by the differences in the SVA, rather than by the DJP itself.
Strengths and Limitations
This study has several limitations. First, we did not evaluate the effects of age, sex and BMI on the occurrence of DJP, which may have contributed to the results obtained. However, we also controlled for their confounding influence on paraspinal muscle degeneration. Second, we only measured parameters related to the paraspinal muscles in the preoperative period, and postoperative variations in the paraspinal muscles and their correlation with DJPs were not analyzed. Third, our study was retrospective in nature, introducing bias and lack of standardization into our results. Further studies with more appropriate study designs will be needed. Nevertheless, our study highlighted certain clinical and radiographic risk factors for DJF, and thus, we can optimize treatment strategies and reduce the incidence of postoperative DJF in long construct based treatment for DLS.
Conclusion
Longer instrumented and fused levels, a larger preoperative SVA, and a smaller preoperative PT were independent risk factors contributing to the occurrence of DJPs in DLS patients following long‐level posterior instrumented spinal fusion. LIV osteopenia, selection of L5 as the LIV, and large TLK correction may also increase the chance of DJP development. Degeneration of the paraspinal muscles not be related to the occurrence of DJPs. For DLS patients, the occurrence of DJP can be reduced by selecting reasonable fusion segments and evaluating the patient's sagittal balance and spino‐pelvic parameters before operation.
Author Contributions
All the authors have made appropriate contributions to this review. Yinhao Liu: data measurements, study design, and manuscript preparation. Lei Yuan: data measurements and study design. Yan Zeng: study design, surgery, and manuscript revision. Weishi Li: study design and surgery.
Funding Information
This work was supported by the National Natural Science Foundation of China (ID: 82272540).
Conflict of Interest Statement
The authors declare no competing interests.
References
- 1. Aebi M. The adult scoliosis. Eur Spine J. 2005;14:925–948. [DOI] [PubMed] [Google Scholar]
- 2. Ha KY, Jang WH, Kim YH, Park DC. Clinical relevance of the SRS‐Schwab classification for degenerative lumbar scoliosis. Spine. 2016;41:E282–E288. [DOI] [PubMed] [Google Scholar]
- 3. Koerner JD, Reitman CA, Arnold PM, Rihn J. Degenerative lumbar scoliosis. JBJS Rev. 2015;3:e1. [DOI] [PubMed] [Google Scholar]
- 4. Buell TJ, Chen CJ, Quinn JC, Buchholz AL, Mazur MD, Mullin JP, et al. Alignment risk factors for proximal junctional kyphosis and the effect of lower thoracic junctional tethers for adult spinal deformity. World Neurosurg. 2019;121:e96–e103. [DOI] [PubMed] [Google Scholar]
- 5. Kim DK, Kim JY, Kim DY, Rhim SC, Yoon SH. Risk factors of proximal junctional kyphosis after multilevel fusion surgery: more than 2 years follow‐up data. J Korean Neurosurg Soc. 2017;60:174–180. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6. Zhao J, Yang M, Yang Y, Yin X, Yang C, Li L, et al. Proximal junctional kyphosis in adult spinal deformity: a novel predictive index. Eur Spine J. 2018;27:2303–2311. [DOI] [PubMed] [Google Scholar]
- 7. McDonnell JM, Ahern DP, Wagner SC, et al. A systematic review of risk factors associated with distal junctional failure in adult spinal deformity surgery. Clin Spine Surg. 2021;34:347–354. [DOI] [PubMed] [Google Scholar]
- 8. Hosthota A, Govindasamy R, Rudrappa S. Distal junctional failure secondary to nontraumatic fracture of lower instrumented vertebra: our experience and review of literature. Int J Spine Surg. 2021;15:1031–1038. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9. Azzam MM, Guiroy AJ, Galgano MA. Surgical correction of distal junctional kyphosis. World Neurosurg. 2023;170:157. [DOI] [PubMed] [Google Scholar]
- 10. Kudo Y, Okano I, Toyone T, Kanzaki K, Segami K, Kawamura N, et al. Distal junctional failure after corrective surgery without pelvic fixation for thoracolumbar junctional kyphosis due to osteoporotic vertebral fracture. J Orthop Sci. 2023;15:S0949‐2658(23)00073‐8. 10.1016/j.jos.2023.03.002 [DOI] [PubMed] [Google Scholar]
- 11. Denis F, Sun EC, Winter RB. Incidence and risk factors for proximal and distal junctional kyphosis following surgical treatment for Scheuermann kyphosis: minimum five‐year follow‐up. Spine. 2009;34:E729–E734. [DOI] [PubMed] [Google Scholar]
- 12. Luzzi A, Sardar Z, Cerpa M, Ferrer X, Coury J, Crockatt W, et al. Risk of distal junctional kyphosis in scheuermann's kyphosis is decreased by selecting the LIV as two vertebrae distal to the first lordotic disc. Spine Deform. 2022;10:1437–1442. [DOI] [PubMed] [Google Scholar]
- 13. Lowe TG, Lenke L, Betz R, Newton P, Clements D, Haher T, et al. Distal junctional kyphosis of adolescent idiopathic thoracic curves following anterior or posterior instrumented fusion: incidence, risk factors, and prevention. Spine. 2006;31:299–302. [DOI] [PubMed] [Google Scholar]
- 14. Zhang H, Hai Y, Meng X, Zhang X, Jiang T, Xu G, et al. Validity of the Roussouly classification system for assessing distal junctional problems after long instrumented spinal fusion in degenerative scoliosis. Eur Spine J. 2022;31:258–266. [DOI] [PubMed] [Google Scholar]
- 15. Yuan L, Zeng Y, Chen Z, Li W, Zhang X, Mai S. Degenerative lumbar scoliosis patients with proximal junctional kyphosis have lower muscularity, fatty degeneration at the lumbar area. Eur Spine J. 2021;30:1133–1143. [DOI] [PubMed] [Google Scholar]
- 16. Ameri E, Behtash H, Mobini B, Ghandhari H, Vahid Tari H, Khakinahad M. The prevalence of distal junctional kyphosis following posterior instrumentation and arthrodesis for adolescent idiopathic scoliosis. Acta Med Iran. 2011;49:357–363. [PubMed] [Google Scholar]
- 17. Arlet V, Aebi M. Junctional spinal disorders in operated adult spinal deformities: present understanding and future perspectives. Eur Spine J. 2013;22:S276–S295. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18. Schwab F, Ungar B, Blondel B, Buchowski J, Coe J, Deinlein D, et al. Scoliosis Research Society‐Schwab adult spinal deformity classification: a validation study. Spine. 2012;37:1077–1082. [DOI] [PubMed] [Google Scholar]
- 19. Hyun SJ, Kim YJ, Rhim SC. Patients with proximal junctional kyphosis after stopping at thoracolumbar junction have lower muscularity, fatty degeneration at the thoracolumbar area. Spine J. 2016;16:1095–1101. [DOI] [PubMed] [Google Scholar]
- 20. Fortin M, Lazáry À, Varga PP, Battié MC. Association between paraspinal muscle morphology, clinical symptoms and functional status in patients with lumbar spinal stenosis. Eur Spine J. 2017;26:2543–2551. [DOI] [PubMed] [Google Scholar]
- 21. McDonnell JM, Ahern DP, Lui DF, et al. Two‐stage anterior and posterior fusion versus one‐stage posterior fusion in patients with Scheuermann's kyphosis. Bone Joint J. 2020;102‐B:1368–1374. [DOI] [PubMed] [Google Scholar]
- 22. Cho KJ, Lenke LG, Bridwell KH, Kamiya M, Sides B. Selection of the optimal distal fusion level in posterior instrumentation and fusion for thoracic hyperkyphosis: the sagittal stable vertebra concept. Spine. 2009;34:765–770. [DOI] [PubMed] [Google Scholar]
- 23. Kim HJ, Nemani V, Boachie‐Adjei O, Cunningham ME, Iorio JA, O'Neill K, et al. Distal fusion level selection in Scheuermann's kyphosis: a comparison of lordotic disc segment versus the sagittal stable vertebrae. Global Spine J. 2017;7:254–259. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24. McDonnell JM, Evans SR, Ahern DP, et al. Risk factors for distal junctional failure in long‐construct instrumentation for adult spinal deformity. Eur Spine J. 2022;31:3654–3661. [DOI] [PubMed] [Google Scholar]
- 25. Kawabata A, Yoshii T, Sakai K, Hirai T, Yuasa M, Inose H, et al. Identification of predictive factors for mechanical complications after adult spinal deformity surgery: a multi‐institutional retrospective study. Spine. 2020;45:1185–1192. [DOI] [PubMed] [Google Scholar]
- 26. Anderson PA, Polly DW, Binkley NC, Pickhardt PJ. Clinical use of opportunistic computed tomography screening for osteoporosis. J Bone Joint Surg Am. 2018;100:2073–2081. [DOI] [PubMed] [Google Scholar]
- 27. Hendrickson NR, Pickhardt PJ, Del Rio AM, et al. Bone mineral density T‐scores derived from CT attenuation numbers (Hounsfield units): clinical utility and correlation with dual‐energy X‐ray absorptiometry. Iowa Orthop J. 2018;38:25–31. [PMC free article] [PubMed] [Google Scholar]
- 28. Zou D, Li W, Deng C, du G, Xu N. The use of CT Hounsfield unit values to identify the undiagnosed spinal osteoporosis in patients with lumbar degenerative diseases. Eur Spine J. 2019;28:1758–1766. [DOI] [PubMed] [Google Scholar]
- 29. Tan JH, Tan KA, Hey HWD, Wong HK. Distal junctional failure secondary to L5 vertebral fracture‐a report of two rare cases. J Spine Surg. 2017;3:87–91. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30. Kwon BK, Elgafy H, Keynan O, Fisher CG, Boyd MC, Paquette SJ, et al. Progressive junctional kyphosis at the caudal end of lumbar instrumented fusion: etiology, predictors, and treatment. Spine. 2006;31:1943–1951. [DOI] [PubMed] [Google Scholar]
- 31. Lewis SJ, Abbas H, Chua S, Bacon S, Bronstein Y, Goldstein S, et al. Upper instrumented vertebral fractures in long lumbar fusions: what are the associated risk factors? Spine. 2012;37:1407–1414. [DOI] [PubMed] [Google Scholar]
- 32. Yang J, Andras LM, Broom AM, Gonsalves NR, Barrett KK, Georgiadis AG, et al. Preventing distal junctional kyphosis by applying the stable sagittal vertebra concept to selective thoracic fusion in adolescent idiopathic scoliosis. Spine Deform. 2018;6:38–42. [DOI] [PubMed] [Google Scholar]
- 33. Hey HWD, Lau ET, Tan KA, et al. Lumbar spine alignment in six common postures: an ROM analysis with implications for deformity correction. Spine. 2017;42:1447–1455. [DOI] [PubMed] [Google Scholar]
- 34. Witiw CD, Fessler RG, Nguyen S, Mummaneni P, Anand N, Blaskiewicz D, et al. Re‐operation after long‐segment fusions for adult spinal deformity: the impact of extending the construct below the lumbar spine. Neurosurgery. 2018;82:211–219. [DOI] [PubMed] [Google Scholar]
- 35. Taneichi H, Inami S, Moridaira H, Takeuchi D, Sorimachi T, Ueda H, et al. Can we stop the long fusion at L5 for selected adult spinal deformity patients with less severe disability and less complex deformity? Clin Neurol Neurosurg. 2020;194:105917. [DOI] [PubMed] [Google Scholar]
- 36. Miller DJ, Jameel O, Matsumoto H, Hyman JE, Schwab FJ, Roye Jr DP, et al. Factors affecting distal end & global decompensation in coronal/sagittal planes 2 years after fusion. Stud Health Technol Inform. 2010;158:141–146. [PubMed] [Google Scholar]
- 37. Lafage V, Schwab F, Patel A, Hawkinson N, Farcy JP. Pelvic tilt and truncal inclination: two key radiographic parameters in the setting of adults with spinal deformity. Spine. 2009;34:E599–E606. [DOI] [PubMed] [Google Scholar]
- 38. Schwab FJ, Blondel B, Bess S, Hostin R, Shaffrey CI, Smith JS, et al. Radiographical spinopelvic parameters and disability in the setting of adult spinal deformity: a prospective multicenter analysis. Spine. 2013;38:E803–E812. [DOI] [PubMed] [Google Scholar]
- 39. Jimbo S, Kobayashi T, Aono K, Atsuta Y, Matsuno T. Epidemiology of degenerative lumbar scoliosis: a community‐based cohort study. Spine. 2012;37:1763–1770. [DOI] [PubMed] [Google Scholar]
- 40. Ghasemi A, Stubig T, Nasto A, et al. Distal junctional kyphosis in patients with Scheuermann's disease: a retrospective radiographic analysis. Eur Spine J. 2017;26:913–920. [DOI] [PubMed] [Google Scholar]
- 41. Fortin M, Videman T, Gibbons LE, et al. Paraspinal muscle morphology and composition: a 15‐yr longitudinal magnetic resonance imaging study. Med Sci Sports Exerc. 2014;46:893–901. [DOI] [PubMed] [Google Scholar]
- 42. Pennington Z, Cottrill E, Ahmed AK, Passias P, Protopsaltis T, Neuman B, et al. Paraspinal muscle size as an independent risk factor for proximal junctional kyphosis in patients undergoing thoracolumbar fusion. J Neurosurg Spine. 2019;31:380–388. [DOI] [PubMed] [Google Scholar]
- 43. Pourtaheri S, Issa K, Lord E, Ajiboye R, Drysch A, Hwang K, et al. Paraspinal muscle atrophy after lumbar spine surgery. Orthopedics. 2016;39:e209–e214. [DOI] [PubMed] [Google Scholar]
- 44. Kim H, Lee CK, Yeom JS, Lee JH, Cho JH, Shin SI, et al. Asymmetry of the cross‐sectional area of paravertebral and psoas muscle in patients with degenerative scoliosis. Eur Spine J. 2013;22:1332–1338. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 45. Jun HS, Kim JH, Ahn JH, Chang IB, Song JH, Kim TH, et al. The effect of lumbar spinal muscle on spinal sagittal alignment: evaluating muscle quantity and quality. Neurosurgery. 2016;79:847–855. [DOI] [PubMed] [Google Scholar]