Orthopedics

Feature Article 

Characteristics of Osteoporotic Low Lumbar Vertebral Fracture and Related Lumbosacral Sagittal Imbalance

Junjie Niu, MD; Tao Feng, MD; Cheng Huang, MD, PhD; Qi Yan, MD; Dawei Song, MD; Minfeng Gan, MD, PhD; Huilin Yang, MD, PhD; Jun Zou, MD, PhD

Abstract

Osteoporotic vertebral fracture (OVF) usually occurs in the thoracolumbar region and rarely affects the low lumbar region. The characteristics of osteoporotic low lumbar fracture (OLLF) have not been reported. Lumbosacral sagittal balance plays an important role in preserving the normal physiologic function of the spine. However, it is unknown how lumbosacral parameters vary in patients with OLLF. The authors retrospectively analyzed the clinical and radiologic characteristics of patients with OLLF and osteoporotic thoracolumbar vertebral fracture (OTVF) who were treated at their institution. Vertebral height, local deformity angle, and visual analog scale and Oswestry Disability Index scores were assessed preoperatively and postoperatively for both groups. The changes in lumbosacral parameters were measured for patients with OLLF. The results showed that OLLF was more likely to occur at L3 (53.66%) and that the prevalence of severe trauma (29.27%) was higher among patients with OLLF (P<.05). The most common morphologic type of the vertebrae affected by OLLF was biconcave (58.54%, P<.05). Patients who had OLLF showed an apparent increase in pelvic tilt and a decrease in local lordosis and sacral slope. Postoperatively, vertebral height, local deformity angle, and visual analog scale and Oswestry Disability Index scores were significantly improved compared with preoperative values (P<.05). Among patients with OLLF, local lordosis and sacral slope increased significantly, whereas pelvic tilt decreased significantly after percutaneous kyphoplasty. Restoration of local lordosis had a mean value of 6.29°±4.80°. These results indicate that OLLF has unique characteristics compared with OTVF and that it results in lumbosacral sagittal imbalance. Percutaneous kyphoplasty is effective and safe for the treatment of OLLF and plays an important role in postoperative improvement of sagittal imbalance. [Orthopedics. 2021;44(1):e7–e12.]

Abstract

Osteoporotic vertebral fracture (OVF) usually occurs in the thoracolumbar region and rarely affects the low lumbar region. The characteristics of osteoporotic low lumbar fracture (OLLF) have not been reported. Lumbosacral sagittal balance plays an important role in preserving the normal physiologic function of the spine. However, it is unknown how lumbosacral parameters vary in patients with OLLF. The authors retrospectively analyzed the clinical and radiologic characteristics of patients with OLLF and osteoporotic thoracolumbar vertebral fracture (OTVF) who were treated at their institution. Vertebral height, local deformity angle, and visual analog scale and Oswestry Disability Index scores were assessed preoperatively and postoperatively for both groups. The changes in lumbosacral parameters were measured for patients with OLLF. The results showed that OLLF was more likely to occur at L3 (53.66%) and that the prevalence of severe trauma (29.27%) was higher among patients with OLLF (P<.05). The most common morphologic type of the vertebrae affected by OLLF was biconcave (58.54%, P<.05). Patients who had OLLF showed an apparent increase in pelvic tilt and a decrease in local lordosis and sacral slope. Postoperatively, vertebral height, local deformity angle, and visual analog scale and Oswestry Disability Index scores were significantly improved compared with preoperative values (P<.05). Among patients with OLLF, local lordosis and sacral slope increased significantly, whereas pelvic tilt decreased significantly after percutaneous kyphoplasty. Restoration of local lordosis had a mean value of 6.29°±4.80°. These results indicate that OLLF has unique characteristics compared with OTVF and that it results in lumbosacral sagittal imbalance. Percutaneous kyphoplasty is effective and safe for the treatment of OLLF and plays an important role in postoperative improvement of sagittal imbalance. [Orthopedics. 2021;44(1):e7–e12.]

Osteoporosis is a serious global public health issue. Osteoporotic fractures are the most severe complications of osteoporosis, and osteoporotic vertebral fracture (OVF) is the most common type. According to data from Medicare, the mortality rate for conservative treatment of OVF is as high as 50%.1 This type of fracture usually occurs in the thoracolumbar region (T11-L2) and rarely affects the low lumbar region (L3-L5).2 The characteristics of osteoporotic low lumbar fracture (OLLF) have not been reported.

Lumbosacral sagittal balance plays an important role in preserving the normal physiologic function of the spine.3,4 Normal sagittal alignment of the lumbosacral region is crucial to maintain stable posture and transfer normal axial stress. Researchers have reported that changes in lumbosacral sagittal alignment, especially the loss of lumbar lordosis, has a significant negative effect on quality of life.5 Lumbosacral sagittal alignment usually is measured as lumbar lordosis (LL), pelvic tilt (PT), sacral slope (SS), and pelvic incidence (PI).4 Spondylolisthesis, lumbar degenerative disease, and spinal deformity have been reported to disturb normal lumbosacral sagittal balance.3,6 However, how lumbosacral parameters vary in patients who have OLLF is unknown.

Percutaneous kyphoplasty (PKP) is widely used among patients with OVF because of its superior therapeutic effect compared with conservative treatment and percutaneous vertebroplasty.7 Immediate pain relief and early mobilization can be achieved after PKP.8 Further, by using an inflatable balloon, PKP can restore vertebral height and correct spinal kyphotic deformity to avoid long-term complications of spinal deformity. However, the clinical efficacy of PKP in treating OLLF is unknown. Kyphoplasty was designed to restore vertebral height and correct local kyphotic deformity; thus, its effect on restoring lumbosacral sagittal alignment is unknown.

This study was performed to evaluate the clinical characteristics of OLLF and the clinical and radiologic efficacy of PKP in treating OLLF.

Materials and Methods

Patients

The authors retrospectively analyzed patients with OVF who underwent single-level PKP surgery at their institution between January 2015 and December 2017. Patients were excluded for the following reasons: pathologic fracture as a result of vertebral infection or primary or metastatic spinal tumor; neurologic deficit caused by vertebral fracture; life-threatening systemic disease or coagulation disorder; loss to follow-up or incomplete clinical data; and subsequent vertebral refracture at the operated level or a new level during follow-up.

This study included 35 men and 107 women with a mean age of 67.07±6.69 years (range, 55–85 years). A total of 41 patients with OLLF (L3–L5) were enrolled as the OLLF group (group A), and 101 patients with osteoporotic thoracolumbar vertebral fracture (OTVF; T11-L2) were included as the control group (OTVF group; group B).

Percutaneous Kyphoplasty

Percutaneous kyphoplasty was performed according to the standard procedure reported previously.9 For fractured low lumbar vertebrae, the puncture channel should be mostly parallel to the inferior and superior end plates to reduce the height of the middle portion of the vertebral body. After the balloon was inflated, polymethyl methacrylate cement was injected into the vertebral body under fluoroscopic guidance to stabilize and strengthen the fractured vertebrae. Patients were allowed to get up and walk around with the help of a lumbar brace 1 day after surgery. Oral antiosteoporotic drugs were used during follow-up.

Evaluation of Therapeutic Outcomes

Radiologic Evaluation. Bone mineral density was assessed as T score in the lumbar spine with dual-energy x-ray absorptiometry. Findings of preoperative magnetic resonance imaging were evaluated to confirm the fractured vertebrae that caused intravertebral bone edema and to detect intravertebral osteonecrosis.10 For patients with OLLF, plain radiographs were obtained in the standing position preoperatively, 3 days after surgery, and at final follow-up. According to Genant et al,11 the shape of the fractured vertebrae was classified into 3 types based on the preoperative lateral radiograph: wedge, biconcave, or crush. Local spinal deformity angle and anterior and middle vertebral height were measured with lateral plain radiographs. Vertebral height was expressed as fractured vertebral body height/[(upper adjacent vertebral body height+lower adjacent vertebral body height)/2]. If the fractured vertebra was L5, then the vertebral height of L4 was used as a reference. The local deformity angle (LDA) was measured with the Cobb method, which defined the angle between the lines drawn parallel to the inferior and superior end plates of the fractured vertebra. All measurements were performed with Picture Archiving and Communication Systems imaging display software (Neusoft Inc).

The lumbosacral parameters of patients with OLLF were calculated as follows (Figure 1)4:

  1. LL, the angle between the lines drawn parallel to the superior end plate of S1 and the superior end plate of L1. The angle is recorded as a positive value when lordosis is present; otherwise, it is recorded as a negative value.

  2. SS, the angle between the lines drawn parallel to the sacral plate and the horizontal line.

  3. PI, the angle between the line perpendicular to the sacral plate at its midpoint and the line connecting the middle axis of the femoral heads to the midpoint of the sacral plate.

  4. PT, the angle between the vertical line and the line connecting the midpoint of the sacral plate and the middle axis of the femoral heads. The value is recorded as positive when the hip axis lies in front of the middle of the sacral plate; otherwise, it is negative.

A 67-year-old man had low back pain for 4 weeks after a slip on a rainy day. Preoperative short-time inversion recovery (a), T2-weighted (b), and T1-weighted (c) images showing L3 vertebral fracture. Preoperative (d) and postoperative (e) plain lateral radiographs showing that both local lordosis and sacral slope were significantly increased and pelvic tilt was slightly decreased postoperatively. Black circles indicate the profile of the femoral head.

Figure 1:

A 67-year-old man had low back pain for 4 weeks after a slip on a rainy day. Preoperative short-time inversion recovery (a), T2-weighted (b), and T1-weighted (c) images showing L3 vertebral fracture. Preoperative (d) and postoperative (e) plain lateral radiographs showing that both local lordosis and sacral slope were significantly increased and pelvic tilt was slightly decreased postoperatively. Black circles indicate the profile of the femoral head.

Clinical Evaluation and Complications. The visual analog scale was used to evaluate pain, and the Oswestry Disability Index was used to evaluate function. Cement leakage was detected on postoperative radiographs and computed tomography scans, and the location of leaked cement was recorded in detail.

Statistical Analysis

Statistical analysis was performed with SPSS, version 19.0, software (SPSS Inc). The differences between the 2 groups were compared with a t test or Mann–Whitney U test for continuous variables and a chi-square test for categorical variables. A paired t test or the Wilcoxon signed-rank test was used to compare the differences at different follow-up times. P<.05 was considered statistically significant.

Results

Characteristics of Osteoporotic Low Lumbar Fracture

The characteristics of the patients included in the study are shown in Table 1. The fracture level in group A was L3 for 22 patients (53.66%), L4 for 13 patients (31.71%), and L5 for 6 patients (14.63%). Based on the history, more patients in group A than in group B had severe trauma, and this difference was statistically significant (29.27% vs 9.90%, respectively; P<.01). The most common fracture type was biconcave in group A (58.54%) and wedge in group B (53.47%) (P=.03). The volume of injected cement was much greater in group A than in group B (8.12±0.60 mL vs 6.68±0.79 mL, P<.01). Intravertebral cleft, which was known as intravertebral osteo-necrosis, was more common in group B than in group A, but the difference was not statistically significant (4.88% vs 12.87%, respectively; P=.16).

Characteristics of Low Lumbar and Thoracolumbar Vertebral Fractures

Table 1:

Characteristics of Low Lumbar and Thoracolumbar Vertebral Fractures

Clinical Evaluation and Complications

All procedures were completed successfully without severe complications. One patient with OVTF had chest congestion and hypotension 6 hours after surgery, with relief of symptoms after dexamethasone injection and oxygen therapy.

Asymptomatic cement leakage was detected among 14 patients. In group A, 2 patients had paraspinal soft tissue leakage and 2 had intradiskal leakage. In group B, 2 patients had intravenous leakage, 3 patients had intradiskal leakage, 4 patients had paraspinal soft tissue leakage, and 1 patient had intravenous and paraspinal soft tissue leakage.

Patients had significant relief of pain after surgery. Both visual analog scale and Oswestry Disability Index scores decreased significantly, and these improvements were maintained at final follow-up (P<.01) (Table 2). No statistically significant differences between the groups were found at each follow-up time (P>.05).

Clinical and Radiologic Findings

Table 2:

Clinical and Radiologic Findings

Radiologic Evaluation

In group A, middle vertebral height was significantly lower compared with group B (60.08±10.14% vs 66.57±11.61%, P<.01) which was consistent with the previously mentioned finding that the biconcave type was most common in patients with OLLF. In both groups, anterior and middle vertebral height was significantly restored after surgery (P<.01) (Table 2). At final follow-up, vertebral height was maintained compared with preoperative values (P<.01). No statistically significant difference in vertebral restoration values was noted between the 2 groups (anterior: 21.87%±5.03% vs 21.54%±7.13%, P>.05; middle: 20.24%±6.63% vs 19.31%±6.36%, P>.05).

In group B, fractured vertebrae showed local kyphotic deformity. The LDA was 13.13°±6.64° preoperatively, decreased to 6.99°±4.87° after surgery, and was 7.39°±4.76° at final follow-up. In addition, postoperative LDA values showed statistically significant differences compared with preoperative values (P<.01). In group A, the fractured vertebrae showed an apparent lower value of local kyphotic deformity angle compared with group B (9.22°±4.85° vs 13.13°±6.64°, P<.01). The LDA in group A decreased significantly from 9.22°±4.85° preoperatively to 3.80°±2.67° 3 days after surgery (P<.01). The correction of LDA was 5.41°±3.50° and 6.14°±4.34° in the 2 groups, respectively (P>.05).

In group A, patients with fracture showed an apparent decrease in local lordosis. Considering the spinopelvic parameters, preoperative LL, SS, PT, and PI were 29.95°±7.75°, 25.66°±7.67°, 24.34°±4.72°, and 45.15°±8.65°, respectively (Figure 2). After PKP, LL and SS increased significantly to 36.24°±6.37° and 29.29°±7.46°, whereas PT decreased significantly to 20.85°±5.05°. Postoperative PI was 44.49°±8.34°, which showed no statistically significant difference compared with preoperative PI. Mean improvement of LL, SS, and PT was 6.29°±4.80°, 3.63°±1.84°, and 3.49°±1.66°, respectively.

Evaluation of lumbosacral parameters. Local lordosis (LL) and sacral slope (SS) significantly increased and pelvic tilt (PT) decreased after kyphoplasty. Abbreviations: F-U, follow-up; PI, pelvic incidence.

Figure 2:

Evaluation of lumbosacral parameters. Local lordosis (LL) and sacral slope (SS) significantly increased and pelvic tilt (PT) decreased after kyphoplasty. Abbreviations: F-U, follow-up; PI, pelvic incidence.

Discussion

An OVF most commonly occurs in the thoracolumbar region (T11-L2), where the spinal curve changes from thoracic kyphosis to lumbar lordosis and spinal axial stress is concentrated. Low lumbar verte-brae (L3–L5) rarely have fractures because of their peculiar location and anatomic structure. The strong iliolumbar ligament and paraspinal muscles, combined with the pelvic ring and iliac crest, protect the low lumbar vertebrae from trauma.12 Previous studies showed that traumatic low lumbar vertebral fractures most often occurred at L3, which is anatomically closer to the thoracolumbar region.12–14 The current study also showed that most cases of OLLF occurred at L3 (53.66%). The greater concentrated mechanical stress may make L3, which is adjacent to the thoracolumbar region, susceptible to fracture.

Because of the lower quantity and quality of bone, patients with OVF usually had slight trauma or even no trauma. The current authors found that more patients with OLLF (29.27%) had severe trauma compared with patients with OTVF (9.90%), and the difference was statistically significant. This finding suggests that osteoporotic low lumbar vertebrae are more difficult to fracture than thoracolumbar vertebrae and that more external force may be needed to cause OLLF. Radiologically, most fractured low lumbar vertebrae showed a biconcave shape rather than the wedge shape that was more common in OTVF (Table 1).11 The larger, thicker disk in the low lumbar region may compresses the adjacent osteoporotic vertebra, and the middle portion of the vertebra, which is made of fragile trabecular bones, is more easily compressed. If the goal of PKP is to restore vertebral height among patients with OLLF, the balloon should be placed in the middle portion and parallel to the inferior and superior end plates. However, greater elastic potential energy is stored in adjacent disks during balloon expansion among patients with OLLF, with larger, thicker disks, and more vertebral height loss occurs after balloon withdrawal because of preload in the prone position and viscoelastic creep of the adjacent disks.15 This occurrence is known as the deflation effect during balloon kyphoplasty. Several vertebral body stents are designed to resist existing preloads and can significantly decrease the deflation of secondary vertebral height and kyphotic angle loss compared with balloon kyphoplasty.15–18

Spinal sagittal balance has been recognized as among the most important factors in preserving normal physiologic function of the spine.3,4 Researchers have reported that spinal sagittal alignment was largely related to chronic back pain in adults.3,6 Further, imbalanced sagittal alignment has an undesirable effect on the knee and hip joints, and osteoarthritis can develop as a result of incorrect posture and unphysiologic axial loading.19 To date, no studies have reported the effect of OLLF on lumbosacral sagittal balance. Previous studies reported that healthy elderly people had LL, SS, PT, and PI of nearly 39° to 50°, 30° to 36°, 13°to 20°, and 43°to 56°, respectively.20,21 The current study showed that both LL and SS decreased significantly, whereas PT increased significantly after low lumbar fractures. These negative changes in lumbosacral parameters indicate imbalanced spinopelvic alignment.21 Low lumbar vertebral fractures lead to decreased vertebral height and an anterior shift of the center of gravity, resulting in a decrease in LL and local kyphotic deformity.19 Posterior rotation of the pelvis around the hip joint occurs and leads to a decrease in SS and an increase in PT to compensate for the decrease in LL.20,22 In addition, the effect of positional changes on lumbosacral parameters as a result of back pain caused by vertebral fractures cannot be ignored. Severe pain leads to protective paraspinal soft tissue tension and induces a crouched posture that contributes to a decrease in LL.

Research has reported that correction of spinal sagittal imbalance is associated with favorable clinical efficacy after lumbar surgery.23,24 Thus, a plan to restore lumbosacral sagittal alignment should be formulated preoperatively. Percutaneous kyphoplasty has been used widely for patients with OVF and has shown a superior therapeutic effect. Further, by using an inflatable balloon, kyphoplasty was designed to correct local spinal kyphotic deformity. However, it is unknown whether kyphoplasty can restore lumbar lordosis for patients with OLLF and decreased lumbar lordotic angles. Kanayama et al5 evaluated the effect of PKP on global spinal alignment among 56 patients with OVF (53 with thoracic and thoracolumbar fracture and 3 with low lumbar fracture). They reported that PKP did not improve global sagittal spinal alignment after OVF. Yokoyama et al20 reported that kyphoplasty played a role not only in reducing pain associated with OVF but also in improving total sagittal imbalance among 21 patients with painful OVF (18 with thoracic and thoracolumbar fracture and 3 with low lumbar fracture). The current authors found that LL and SS increased significantly after kyphoplasty among patients with OLLF. Pelvic tilt decreased from 24.34°±4.72° preoperatively to 20.85°±5.05° postoperatively, a statistically significant difference. These results indicate that, for patients with OLLF, kyphoplasty can, to a certain extent, correct imbalanced lumbosacral parameters, and especially restore lumbar lordosis. Restoration of LL is the most important factor contributing to the improvement of sagittal imbalance.5 Although the improvement of SS and PT (Figure 2) is slight, these values appear to improve further during long-term follow-up as a compensation for restoration of LL.

How does kyphoplasty affect the improvement of lumbosacral parameters? The authors suppose that, among patients with OLLF, after general anesthesia, the use of chest and pelvic bolsters extended the spine sufficiently to restore lumbar lordosis. Then the inflatable balloon was expanded under fluoroscopic guidance to further restore vertebral height and the lumbar lordotic angle. Finally, cement was injected into the fractured vertebra to stabilize and preserve the reduced vertebrae. The authors consider that kyphoplasty may not be able to improve global sagittal spinal alignment; however, it can correct OLLF-related lumbosacral sagittal imbalance by reducing intraoperative posture and balloon dilation.

This study had several limitations. First, the authors focused on lumbosacral parameters and did not obtain full-length spine radiographs, so measurement of thoracic and cervical spinal alignment was unavailable. Second, severe pain caused by vertebral fractures may affect the accuracy of measurement because of the larger error within radiographs for several patients. Third, because lateral radiographs showing the lateral femur heads were not obtained for patients with OTVF, the lumbosacral parameters could not be measured for these patients and the 2 groups could not be compared. Finally, this study had a relatively small sample and used a retrospective study design without a restrict control.

Conclusion

An OLLF has different clinical and radiologic characteristics compared with an OTVF and has a negative effect on lumbosacral sagittal balance. To a certain extent, kyphoplasty could correct the imbalanced lumbosacral parameters, and especially restore lumbar lordosis.

References

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Characteristics of Low Lumbar and Thoracolumbar Vertebral Fractures

CharacteristicLow lumbar vertebral fracture (L3–L5)Thoracolumbar vertebral fracture (T11-L2)P
Patients, No.41101
Age, mean±SD, y68.15±7.2166.63±6.45.22
Female, No.2978.42
Follow-up, mean±SD, mo26.41±5.0924.98±6.20.16
Bone mineral density, mean±SD, T value−2.66±0.29−2.75±0.28.08
Body mass index, mean±SD, kg/m225.18±3.7425.76±3.96.42
Symptom duration, mean±SD, wk3.90±1.463.77±1.38.63
Smoking, No.415.42
Daily alcohol consumption, No.212.21
Steroid use, No.516.58
Trauma history, No..02a
  None926
  Slight2065
  Severe1210
Medical history, No.
  Hypertension931.29
  Diabetes312.42
  Hyperlipidemia618.65
Fracture type, No..03a
  Wedge1454
  Biconcave2435
  Crush312
Intravertebral cleft213.16
Injected cement volume, mean±SD, mL8.12±0.606.68±0.79<.01a

Clinical and Radiologic Findings

ParameterLow lumbar vertebral fracture (L3–L5)Thoracolumbar vertebral fracture (T11-L2)


Preoperative3 days postoperativeLast follow-upImprovementPreoperative3 days postoperativeLast follow-upImprovement
AVH62.00%±11.62%83.87%±12.46%a81.74%±12.75%b21.87%±5.03%60.51%±12.99%82.06%±13.49%a77.67%±14.58%b21.54%±7.13%
MVH60.08%±10.14%80.32%±10.97%a77.51%±11.37%b20.24%±6.63%66.57%±11.61%85.89%±11.24%a81.11%±12.43%b19.31%±6.36%
LDA9.22°±4.85°3.80°±2.67°a4.05°±2.51°b5.41°±3.50°13.13°±6.64°6.99°±4.87°a7.39°±4.76°b6.14°±4.34°
VAS6.02±0.791.95±0.67a2.05±0.71b67.24±11.346.10±0.882.00±0.53a2.29±0.82b66.54±10.12
ODI63.76±7.8024.05±5.21a26.63±6.60b61.88±8.6065.54±8.2625.25±3.65a27.92±6.07b60.93±7.13
Authors

The authors are from the Department of Orthopaedic Surgery (JN, TF, QY, DS, MG, HY, JZ), the First Affiliated Hospital of Soochow University, Jiangsu, and the Department of Orthopaedic Surgery (CH), China-Japan Friendship Hospital, Beijing, China.

Drs Niu and Feng contributed equally to this work and should be considered as equal first authors.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Jun Zou, MD, PhD, Department of Orthopaedic Surgery, the First Affiliated Hospital of Soochow University, 188 Shizi St, Suzhou, Jiangsu, China 215006 ( jzou@suda.edu.cn).

Received: August 16, 2019
Accepted: November 07, 2019
Posted Online: November 03, 2020

10.3928/01477447-20201028-05

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