Correction loss following short-segment posterior fixation for traumatic thoracolumbar burst fractures related to endplate and intervertebral disc destruction

DOI: https://doi.org/10.21203/rs.3.rs-2208145/v1

Abstract

Background

Short-segment posterior fixation (SSPF) for traumatic thoracolumbar burst fractures has been widely used. Few studies have addressed the association between the destruction of the vertebral endplate and adjacent disc and postoperative correction loss. This study aimed to investigate the risk factors for correction loss after SSPF.

Methods

This study included 48 patients (mean age of 35.0 years) who underwent SSPF for thoracolumbar burst fracture. The mean postoperative follow-up period was 25.7 months (range, 12–98 months). Neurological status and postoperative back pain were assessed using medical records. The segmental kyphotic angle (SKA) and anterior vertebral body height ratio (AVBHR) were measured as radiographic parameters to evaluate the indirect reduction of the vertebral body and local kyphosis. The intervertebral disc and vertebral endplate injury severity were assessed using the preoperative Sander’s traumatic intervertebral disk lesions (TIDL) classification and AO classification. Correction loss was considered to be present if ΔSKA was ≥ 10°. Multivariate logistic regression analysis was performed to identify risk factors for postoperative correction loss.

Results

The distribution of fractures was as follows: 10 in T12, 17 in L1, 10 in L2, 9 in L3, and 2 in L4. Vertebral fractures were classified as follows: 13 patients had type A3, 11 had A4, 11 had B1, and 13 had B2. Union of the fractured vertebrae was achieved in 47 patients (98%). SKA and AVBH significantly improved after surgery from 11.6° to 3.5° and from 67.2–90.0%, respectively; however, correction loss at follow-up were 10.4° and 9.7%, respectively. Severe TIDL (Grade 3) was observed in 20 patients (42%). Patients with TIDL grade 3 showed significantly greater ΔSKA and ΔAVBHR after surgery than patients with TIDL grade 0–2. The multivariate logistic regression analysis revealed that the presence of cranial grade 3 TIDL and an older age were significant risk for ΔSKA ≥ 10°. All patients were able to walk at final follow-up. The postoperative severe back pain was associated with TIDL grade 3 and ΔSKA ≥ 10°.

Conclusion

Severe disc and endplate destruction at injury and older age are risk factors for correction loss following SSPF for thoracolumbar burst fractures.

Background

Thoracolumbar burst fractures are common spinal injuries usually caused by high-energy trauma, sometimes accompanied by neurological complications. Although various surgical procedures have been used to treat these spinal injuries, definitive treatment methods remain controversial [1–3]. Nevertheless, surgical treatment aims to improve neurological deficits, reduce the deformed spine, and prevent future kyphotic deformity.

Short-segment posterior fixation (SSPF) for traumatic thoracolumbar burst fractures has been widely used because of its minimally invasive technique and efficacy in reducing kyphotic deformity while preserving the motion segment [1, 2], however, postoperative correction loss remains a concern. Risk factors for correction loss after SSPF have been discussed [4–8]. Previous studies have demonstrated that most correction loss occurs at the intervertebral disc level and not in the vertebral body [4, 9], which may be supported by the report that endplate injuries are the leading cause of degeneration in damaged discs [10]. Therefore, assessing intervertebral disc and adjacent endplate damage is crucial for determining viable treatment methods and predicting delayed kyphotic deformity. If correction loss after surgery is highly suspected, anterior reconstruction surgery or long-segment posterior fixation (LSPF) could be preferred procedures. The assessment of traumatic intervertebral disk lesions (TIDLs) based on magnetic resonance imaging (MRI) has been proposed to evaluate damaged intervertebral discs [9–13]. However, few studies have addressed the association between intervertebral disc injury and postoperative delayed kyphotic deformity due to correction loss.

This study aimed to investigate risk factors for correction loss following SSPF for thoracolumbar burst fracture, especially concerning endplate damage of the fractured vertebrae and adjacent discs.

Materials And Methods

Patient demographics

This retrospective study using anonymized data with a general opt-out procedure was approved by the institutional review board (Approval number: zn210817). All procedures performed in this study were in accordance with the ethical standards of our institutional ethics committee, and with the 1964 Helsinki Declaration and later amendments or comparable ethical standards. The need for informed consent was waived due to the retrospective study design. Patients who underwent SSPF for traumatic thoracolumbar burst fracture between October 2011 and August 2020 were included. The exclusion criteria were as follows: osteoporotic fractures, multiple vertebral burst fractures, patients with less than 12 months of follow-up, and those treated with anterior reconstruction or LSPF. Ultimately, 48 patients were enrolled in this study.

Surgical technique

All surgical procedures were performed under general anesthesia. Patients were placed in the prone position. Using the Wiltse paraspinal approach [14], pedicle screws (CD Horizon Solera Sagittal Adjusting Screw®, Medtronic) were placed in the vertebrae below and above the fracture. After attaching the rod, indirect reduction via ligamentotaxis was performed to restore the vertebral body height and achieve posterior wall decompression. Seventeen patients underwent vertebroplasty by filling hydroxyapatite blocks through the trans-pedicular approach. Seven patients who showed severe canal compromise by the posterior wall fragment before surgery underwent additional posterior decompression.

Assessment of clinical outcomes

Neurological conditions were assessed using the American Spine Injury Association (ASIA) impairment scale [15]. In addition, postoperative low back pain was classified according to the Japanese Orthopaedics Association (JOA) scoring system as follows: no pain (3 points), occasional minor back pain (2 points), constant back pain or sometimes severe back pain (1 point), and constant severe back pain (0 points) [16]. In this study, postoperative severe back pain was defined as positive in patients with zero or one point.

Radiographic assessment

Plain radiographs and computed tomography (CT) scans were obtained before surgery, immediately after surgery, at the removal of the implants, and during the final follow-up. The segmental kyphotic angle (SKA) and anterior vertebral body height ratio (AVBHR) were measured as radiographic parameters to evaluate the indirect reduction of the vertebral body and local kyphosis. SKA was defined as the Cobb angle calculated between the cranial vertebra's upper endplate and the caudal vertebra's lower endplate. AVBHR was defined as the percentage of the anterior vertebral height of the fractured vertebra in relation to the average anterior height of the two adjacent vertebrae (Fig. 1) [17].

The indirect reduction of fractured vertebrae and correction loss during observation were evaluated using SKA and AVBHR. In this study, correction loss was considered to be present if the ΔSKA was ≥ 10° from immediately after surgery to the final examination [4, 6].

We evaluated the degree of vertebral body involvement using the load sharing classification (LSC) scoring system [18]. The vertebral fractures were classified according to the AO classification system [19]. The intervertebral disc and vertebral endplate injury severity were assessed using the preoperative Sander’s TIDL classification based on T2-weighted MRI (Table 1) [10, 13]. In this study, TIDL was considered grade 3 when CT showed an apparent fracture of the vertebral endplate (Fig. 2). If both the upper and lower discs were damaged, a more severe TIDL grade was adopted.

Table 1

Classification of TIDL

Grade

T2-weighted MRI

Endplate fracture

Characteristic finding

0

  

None

Intact

1

Hyperintense

None

Edema

2

Hypointense with perifocal hyperintense

None or mild

Disc rupture with intradiscal bleeding

3

Hypointense with perifocal hyperintense

Moderate or severe

Infraction of the disc into vertebral body, annular tears, or infraction without herniation into endplate
TIDL, traumatic intervertebral disc lesion

Statistical analysis

The Student’s t-test was performed for continuous normally distributed data, and the Mann-Whitney U test was performed for non-normally distributed data. Categorical data were compared using the chi-square test or Fisher-Freeman-Halton Exact test. Multivariate logistic regression analysis was performed to identify significant risk factors for postoperative correction loss. Statistical analyses were conducted in SPSS for Windows, Version 25 (SPSS Inc., Chicago, Illinois, USA). The level of significance was set at P < 0.05.

Results

Patient characteristics

In this retrospective study, 48 participants were enrolled, which included 26 men and 22 women. The mean age was 35.0 years (range, 13–63 years) and the mean body mass index (BMI) was 22.0 kg/m2 (range, 15.8–28.7 kg/m2) (Table 2). The distribution of fractures was as follows: 10 in T12, 17 in L1, 10 in L2, 9 in L3, and 2 in L4. The causes of injury were falls in 33 patients, motor vehicle accidents in 11, and blunt contusions caused by heavy falling objects in 4. Vertebral fractures were classified as follows: 13 patients had type A3, 11 had A4, 11 had B1, and 13 had B2. Implant removal was performed in 38 patients at a mean of 12.8 months after surgery. The mean postoperative follow-up period was 25.7 months (range, 12–98 months).

Table 2

Comparison of clinical data between patients with grades 0–2 and grade 3 TIDL.
 

Total (n = 48)

Grades 0, 1, and 2 TIDL (n = 28)

Grade 3 TIDL (n = 20)

P-value

Sex (male/female), n

27/21

16/12

11/9

0.883#

Age, years

35.0 (15.5), 30.5, 39.5

34.2 (15.0), 28.3, 40.2

36.1 (16.6), 29.1, 43.2

0.689*

Body mass index, kg/m2

22.0 (3.7), 20.9, 23.0

22.6 (3.8), 21.2, 24.0

21.1 (3.6), 19.5, 22.8

0.182**

Follow-up period, months

26.5 (21.9), 20.1, 32.8

26.3 (21.7), 17.9, 34.7

26.7 (22.7), 16.7, 36.7

0.866*

Fracture level (T12, L1/L2-4), n

27/21

19/9

8/12

0.055a

AO classification, n

        

B1/A3, A4, B2

11/37

11/17

0/20

0.001b

LSC score, n

        

<7 / ≥7

28/20

20/8

8/12

0.029a

Vertebroplasty, n

17

9

8

0.575a

Implant removal, n

38

21

17

0.488b

Severe back pain, n

11

1

10

< 0.001b
Continuous data are expressed as mean (SD), 95% confident intervals. P-values are calculated between the data of patients with TIDL grades 0–2 and grade 3 by Mann-Whitney test*, t-test**, chi-square testa, and Fisher’s exact testb. TIDL, traumatic intervertebral disc lesion; LSC, load sharing classification.

 

Radiographic outcomes

Overall, SKA and AVBHR significantly improved after surgery, from 11.6° to 3.5° and from 67.2–90.0%, respectively. However, the increase in SKA (ΔSKA) and decrease in AVBHR (ΔAVBHR) at follow-up were 10.4° and 9.7%, respectively (Table 3). Finally, union of the fractured vertebrae was achieved in 47 patients (98%).

Table 3

Comparison of radiological parameters between patients with grades 0–2 and grade 3 TIDL.
 

Total (n = 48)

Grades 0, 1, and 2 TIDL (n = 28)

Grade 3 TIDL (n = 20)

P-values

SKA (degrees)

        

Pre-operative

11.6 (11.5), 8.2, 14.9

14.5 (7.0), 10.3, 18.7

7.5 (15.0), 2.5, 12.5

0.037*

At surgery

3.5 (8.6), 1.0, 6.0

6.1 (6.8), 3.0, 9.2

-0.2 (9.6), -3.8, 3.5

0.018*

At follow-up

13.9 (13.1), 10.1, 17.7

13.4 (10.1), 8.4, 18.5

14.6 (16.8), 8.6, 20.5

0.859**

ΔSKA

10.4 (10.9), 7.2, 13.6

7.3 (6.3), 3.4, 11.3

14.7 (14.4), 10.0, 19.4

0.007**

ABVHR (%)

        

Pre-operative

67.2 (16.2), 62.5, 71.9

71.5 (14.8), 65.6, 77.4

61.1 (16.6), 54.1, 68.2

0.032*

At surgery

90.0 (11.4), 86.6, 93.3

90.9 (10.4), 86.6, 95.3

88.6 (12.8), 83.4, 93.8

0.507*

At follow-up

80.3, (16.4), 75.5, 85.0

83.4 (16.2), 77.2, 89.5

76.0 (16.1), 68.7, 83.2

0.105**

ΔABVHR

9.7 (11.0), 6.5, 12.9

7.6 (11.5), 3.5, 11.7

12.7 (9.7), 7.8, 17.5

0.018**
Data are expressed as mean (SD), 95% confident intervals. P-values are calculated between the data of patients with TIDL grades 0–2 and grade 3 by t-test* and Mann-Whitney test**. TIDL, traumatic intervertebral disc lesion; SKA, segmental kyphotic angle; AVBHR, anterior vertebral body height ratio

 

Comparison of clinical data between patients with grades 0–2 and grade 3 TIDL

Twenty patients (42%) showed severe traumatic disc lesions (TIDL grade 3) of the cranial and/or caudal discs. TIDL grade 3 was significantly more common on the cranial side than on the caudal side (20 vs. 2; P < 0.001), and two cases with TIDL grade 3 on the caudal side also showed cranial side lesions (Table 4). Comparing patients with either TIDL grades 0–2 or grade 3, there was no significant difference in gender, age, BMI, fracture level, and application of vertebroplasty (Table 2). Patients with TIDL grade 3 had a significantly higher LSC score (P = 0.029) and a predominance of AO type A3, A4, and B2 fractures compared to AO type B1 fractures (P = 0.001).

Table 4

Relationship of traumatic lesion grades between the intervertebral discs cranial and caudal to the fractured vertebra

Grade of traumatic intervertebral disc lesion

Caudal disc

0

1

2

3

Cranial disc

        

0

19

1

    

1

1

1

1

  

2

2

1

2

  

3

14

2

2

2

 

Comparison of radiological parameters between patients with grades 0–2 and grade 3 TIDL

Although pre- and postoperative SKA in patients with grades 0–2 TIDL were significantly higher than in patients with grade 3 TIDL (P = 0.037 and P = 0.018, respectively), ΔSKA during follow-up was significantly greater in patients with grade 3 TIDL (P = 0.007)(Table 3). Preoperative AVBHR was significantly higher in patients with grades 0–2 TIDL than in patients with grade 3 TIDL (P = 0.032), was maintained throughout the course of treatment, and tended to be higher at the final follow-up. ΔAVBHR during follow-up was significantly greater in patients with grade 3 TIDL (P = 0.018).

Risk factors for correction loss after surgery

To identify risk factors for correction loss, we compared clinical and radiological parameters between patients with ΔSKA < 10° and ≥ 10° (Table 5). ΔSKA ≥ 10° was significantly associated with greater ΔAVBHR (P < 0.001). ΔSKA ≥ 10° was significantly associated with an older age (P = 0.012), smaller preoperative AVBHR (P = 0.024), and grade 3 TIDL on the cranial side (P = 0.004). Patients with an endplate injury (AO types A3, A4, and B2) were more closely associated with ΔSKA ≥ 10° than were patients without an endplate injury (AO type B1) (P = 0.036) (Fig. 3). However, there was no significant difference in gender, fracture level, preoperative SKA, LSC score, and application of vertebroplasty.

Table 5

Comparison between patients with ΔSKA < 10° and ΔSKA ≥ 10°
 

ΔSKA < 10° (n = 26)

ΔSKA ≥ 10° (n = 22)

P-value

Preoperative SKA (degrees)

11.0 (10.1), 6.9, 15.1

12.2 (13.2), 6.4, 18.1

0.716**

Preoperative AVBHR (%)

72.0 (15.3), 65.8, 78.2

61.5 (15.8), 54.5, 68.5

0.024**

ΔSKA (degrees)

4.6 (3.8), 1.1, 8.2

17.2 (12.7), 13.4, 21.1

< 0.001*

ΔAVBHR (%)

4.2 (4.7), 2.3, 6.1

16.1 (12.7), 10.5, 21.8

< 0.001*

Age, years

30.3 (14.4), 24.5, 36.1

40.5 (15.3), 33.8, 47.3

0.012*

Sex (male/female), n

12/14

15/7

0.125a

Fracture level (T12, L1/L2-4), n

15/11

12/10

0.827a

AO classification, n

      

B1/A3, A4, B2

9/17

2/20

0.036a

LSC score, n

      

<7 / ≥7

17/9

11/11

0.281a

Vertebroplasty, n

11

6

0.278a

Implant removal, n

21

17

0.521b

Cranial TIDL, n

      

Grades 0–2/3

20/6

8/14

0.004a

Severe back pain, n

2

9

0.006b
Continuous data are expressed as mean (SD), 95% confident intervals. P-values are calculated by Mann-Whitney test*, t-test**, chi-square testa, and Fisher’s exact testb. SKA, segmental kyphotic angle; AVBHR, anterior vertebral body height ratio; LSC, load sharing classification; TIDL, traumatic intervertebral disc lesion.

 

Multivariate logistic regression analysis was used to calculate the adjusted odds ratio (OR) with 95% confidence interval (CI) for risks of ΔSKA ≥ 10° (Table 6). The presence of cranial grade 3 TIDL and an older age were significantly associated with correction loss.

Table 6

Multivariate logistic regression analysis for ΔSKA ≥ 10°

Step

Predictors

P-value

Odds ratio

95% CI

1

Cranial TIDL grade 3

0.006

5.83

1.66, 20.56

2

Age

0.026

1.05

1.01, 1.10
 

Cranial TIDL grade 3

0.007

6.81

1.71, 27.10
SKA, segmental kyphosis angle; CI, confidence interval; TIDL, traumatic intervertebral disc lesion.

 

Clinical outcomes

All patients were able to walk with or without assistance during follow-up. No neurological deterioration occurred, and 16 patients who were non-ASIA E preoperatively showed at least one grade of improvement (Fig. 4). The low back pain score was 0, 1, 2, and 3 points in 2, 9, 24, and 13 patients, respectively. Eleven patients (23%) had severe back pain during follow-up. The presence of postoperative severe back pain was significantly associated with grade 3 TIDL at injury (P < 0.001) and ΔSKA ≥ 10° (P = 0.006) (Tables 3, 5).

Complications

Eight patients underwent additional procedures. Two patients developed postoperative infections. One patient acquired iatrogenic radiculopathy due to nerve root compression by the leakage of hydroxyapatite blocks for vertebroplasty. Two patients underwent extension of the posterior fusion with instrumentation, and three patients underwent anterior reconstruction due to postoperative delayed kyphotic deformity or nonunion of the fractured vertebra.

Discussion

In this study, the correction loss in SKA was 10.4°, which agrees with previous reports (ranging from 1° to 13°) [1, 2, 4–9, 20]. Several risk factors associated with correction loss following SSPF have been reported. Aono et al. reported a mean correction loss of 9.1° in SKA for 76 patients. They identified a preoperative SKA greater than 15.4° and canal compromise greater than 52.8% as risk factors [4]. Jang et al. noted that an age greater than 43 years and a preoperative AVBHR less than 54% were risk factors [6]. In this study, the preoperative AVBHR was significantly smaller in patients with ΔSKA ≥ 10° and an older age was a significant risk for correction loss. These results indicate that severely collapsed vertebrae cannot remodel and that the repair capacity of the vertebral body and intervertebral discs is likely to decrease with age.

Previous report indicates that postoperative correction loss occurs at the disc level [4]. Schömig et al. reported that the vacuum disc phenomenon of the adjacent disc often occurred in burst fractures and found a significant correlation between AO A3 fractures and the vacuum disc phenomenon; this may lead to disc degeneration due to nutritional supply disturbances via the vertebral endplate [21]. Other reports have described the importance of reducing the damaged vertebral endplates to prevent progressive kyphotic deformity [22, 23]. Therefore, a preoperative assessment of the endplate and the adjacent disc may be crucial for choosing a treatment strategy and predicting correction loss. Several authors have reported methods for assessing traumatic intervertebral disc injuries [10–13]. Sander et al. classified TIDL according to MRI (Table 1) and reported that 40.7% of their cases were classified as grade 3 at injury [10, 13]. In this series, grade 3 TIDL was observed in 42% of patients, and all patients had cranial injuries. The presence of severe cranial endplate and disc injury (grade 3 TIDL) and an older age were significant risk factors for correction loss. Moreover, cases with AO type A3, A4, and B2 fractures, which accompany the destruction of the vertebral endplate, showed significantly worse correction loss than cases with an AO type B1, which has no endplate injury. Wang et al. reported that endplate fractures were strongly associated with disc degeneration [12]. Therefore, it is presumed that significant damage to the endplates will also cause considerable damage to the intervertebral discs, resulting in disc degeneration and correction loss at the disc level. Lee et al. showed an association between an intervertebral disc and endplate complex injury and postoperative correction loss [24]. However, their study only included patients younger than 45 years and did not assess the correction loss associated with both endplate injury and adjacent disc degeneration in older patients.

To our knowledge, this is the first study to investigate the association between the severity of an endplate and adjacent disc injury and correction loss following SPFF at all ages. Therefore, based on our findings, it can be presumed that the damage to either the vertebral endplate, adjacent disc, or both may cause disc degeneration leading to failure of the anterior support mechanism and severe kyphotic deformity. In addition, older patients are at a higher risk because of a reduced ability to repair the discs and endplates.

There is no consensus on whether residual kyphotic deformity is associated with worse clinical outcomes and back pain [6. 7, 20]. Our study demonstrates that severe postoperative back pain was significantly associated with grade 3 TIDL and ΔSKA ≥ 10°. Xu et al. noted that postoperative pain was associated with kyphotic deformity greater than 20° but not with the narrowing or degeneration of intervertebral disc [20]. Similarly, McLain et al. found that a progressive kyphotic deformity of more than 10° was associated with significant postoperative pain [7]. Together, these results demonstrate the association between residual kyphotic deformity and back pain; therefore, it is desirable to prevent excessive correction loss after surgery.

In younger patients or patients without severe TIDL and endplate injury, SSPF is an effective treatment because it can be expected to yield satisfactory results. In contrast, older patients or patients with severe TIDL and endplate injuries are at risk of progressive kyphotic deformity. They can be treated initially with SSPF; however, they require careful observation for correction loss. If severe correction loss occurs, additional surgery should be considered. In older patients with severe TIDL and endplate injury, LSPF or anterior reconstructive surgery may be an effective alternative for initial surgery.

This study had some limitations. First, the retrospective study design may have decreased the level of evidence. Second, the small number of patients evaluated limits the applicability of the study. Despite these limitations, we believe that this study is important. It demonstrated that severe damage to the vertebral endplates and adjacent discs are risk factors for postoperative correction loss and delayed kyphotic deformity.

Conclusion

Severe intervertebral disc and endplate destruction at injury and an older age are risk factors for correction loss following SSPF for thoracolumbar burst fractures. In younger patients or patients without severe disc and endplate injury, SSPF is an effective treatment. However, in older patients with severe destruction of disc and endplate, LSPF or anterior reconstructive surgery may be a preferred procedure for the initial surgery.

Abbreviations

SSPF: Short-segment posterior fixation; SKA: Segmental kyphotic angle; AVBHR: Anterior vertebral body height ratio; TIDL: Traumatic intervertebral disk lesions; LSPF: Long-segment posterior fixation; MRI: Magnetic resonance imaging; ASIA: the American Spine Injury Association; JOA: Japanese Orthopaedics Association; CT: Computed tomography; BMI: Body mass index

Declarations

Ethics approval and consent to participate

Approval for this study was received from the Ethics Committee of Kobe City Medical Center General Hospital (Approval Date: Aug 5, 2021; Approval Number: zn210817). This retrospective study using anonymized data with a general opt-out procedure was approved by the institutional review board. Informed consent was waived by the Ethics Committee of Kobe City Medical Center General Hospital due to the retrospective study design. All procedures performed in this study were in accordance with the ethical standards of our institutional ethics committee, and with the 1964 Helsinki Declaration and later amendments or comparable ethical standards.

Consent for publication

Not applicable.

Availability of data and materials

The datasets of this study are available from the corresponding author upon reasonable request.

Competing interests

The authors have no conflicts of interest to disclose.

Funding

No funding.

Authors' contributions

T.H, E.O. and T.Y. analyzed and interpreted the patient data. T. H and E.O. were major contributors in writing the manuscript. All authors read and approved the final manuscript.

Acknowledgements

Not applicable.

Informed consent

This retrospective study using anonymized data with a general opt-out procedure was approved by the institutional review board.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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