Preoperative planning of compact zone trajectory is necessary in treating osteoporotic vertebral compression fracture with endplate involvement: A prospective randomized controlled study

doi:10.21203/rs.3.rs-1991574/v1

Background

Treatment strategy focusing on osteoporotic vertebral body and endplate fracture is not emphasized. This prospective randomized controlled study aimed to compare the clinical and radiological outcomes between reduction methods with or without compact trabecular bone during percutaneous kyphoplasty in osteoporotic vertebral fractures.

Methods

100 patients who underwent percutaneous kyphoplasty were randomly divided into groups A (the guide pin and balloon were introduced into fracture site directly) and B (the guide pin and balloon were inserted away from the fracture site). Surgical duration, clinical and radiological outcomes at postoperative and follow-up, and complication of cement leakage and adjacent fracture were recorded. Patients were followed up for an average of 20.18 months. Clinical outcome was assessed using the Oswestry disability index and visual analogue scale (VAS).

Results

Both groups had similar patient demographics. Two groups had similar operation time and injected cement volume. The method of elevating the collapsed endplate indirectly had no significant influence on radiological outcomes, however, there was significant influence on decreasing intradiscal cement leakage and postoperative functional outcomes at 1-month and 12-month follow-up.

Conclusion

Elevating and reinforcing the collapsed endplate rather than just fulfilling the defect during percutaneous kyphoplasty is a safe and more effective way in pain and functional improvement with lower rates of further collapse in the osteoporotic vertebral fractures with endplate destruction.

percutaneous vertebroplasty

kyphoplasty

endplate fracture

osteoporotic vertebral compression fracture

Osteoporotic vertebral fracture (OVF) is one of the most common sequelae of osteoporosis. [1]The prevalence of OVF increases as proportion of aging people grows[2] It often leads to lower back pain and spinal deformity, which seriously affects the patients’ quality of life.[3] Percutaneous kyphoplasty (PKP) offers significant pain relief for patients who respond poorly to conservative treatment.[4]

However, the operation is focused mainly on the fractured vertebral body itself, ignoring the treatment of adjacent injured endplate-disc complex (EDC).[5] The EDC has important functions such as maintaining the stability and integrity of the spine, protecting the spinal nerves, absorbing shocks, and dispersing axial load.[6] When the trauma acts on the vertebral body, it often causes injury to the adjacent EDC at the same time.[7] Injuries to EDCs, which are the human body’s largest blood-free tissue, often accelerate disc degeneration, leading to chronic spinal instability and even secondary kyphosis.[8]

According to previous report, the incidence rate of EDC injury reached 67.0% among patients with OVF.[9] Endplate integrity is critical in treating vertebral compression fracture. [10] One recent study emphasized the importance of distribution pattern of cement distribution between upper and lower endplates in these patients. [11]

The treatment strategy varies as the advancement of bone cement and new implant design. Owing to the improving investigation of fracture mechanism and biomechanical property of vertebral body and endplate, the treating philosophy keep modifying for better patient outcome and less complication.[12] Recent study illustrated the impact of endplate fracture on postoperative vertebral height loss and aggravation of kyphosis. Vertebral compression fracture with concomitant endplate fracture is very common. Endplate fracture also contribute to higher rate of cement extravasation into disc, which lead to higher incidence of adjacent fracture and poor outcome.[13–15]

Furthermore, cement leakage through broken endplate may contribute to subsequent disc degeneration in dog and rabbit model.[16] The degree of intervertebral disc degeneration is correlative to the time after operation and the doses of bone cement.[17] In human model, the quantity of cement leaking into the disc space significantly influences the rate of progression of disc degeneration.[18]

However, treating strategy focusing on endplate fracture is not emphasized in previous studies. Thus, we compared the techniques of direct and indirect (through trabecular bone) reduction of endplate using balloon kyphoplasty to treat vertebral compression fracture with endplate deficit.

From January 2018 to August 2020, 100 patients who failed to conservative treatment with single level painful osteoporotic vertebral fracture and concomitant endplate fracture were enrolled prospectively after institutional review board approval. Pathological facture, multiple level fracture, endplate fracture with not enough trabecular bone layer for balloon to create the compact zone in the vertebral body, and fracture occurred more than 12 weeks were excluded. The fracture pattern and morphology were carefully investigated from preoperative CT or MRI. The fracture clefts were clearly identified. If the location of fracture clefts or the compact zone left remained uncertain, the case was excluded.

All patients were treated with Balloon kyphoplasty (BKP; Kyphon, Medtronic, Sunnyvale, CA, USA) followed by high-viscosity polymethyl methacrylate (PMMA) bone cement (Cohesion®, Vexim) injection.

Patients were allocated randomly to group A or group B. For patients in group A, the guide pin and balloon were introduced into fracture site directly under fluoroscopy. For patients in group B, the guide pin and balloon were inserted away from the fracture site, preserving more distance between balloon and fractured endplate without direct contact. The volume of injected cement depended on the bone defect and individual patient’s condition under fluoroscopy. Patient demography including age, gender, BMI, BMD, fracture pattern, fractured level, were assessed as Table 1.

Operative Techniques

CT or MR images were used for preoperative templating. The location of endplate fracture was identified. If the endplate fracture occurred unilaterally or centrally, unilateral transpedicular approach was used. Bilateral transpedicular approach was taken for bilateral endplate fractures. We located the fracture cleft and then decided the guide pin trajectory on sagittal view of CT or MR images.

For patients in group B, the guide pin was aimed below and away from the fracture cleft (Fig 1). Since the target plane we desired was away from the fracture plane, a compact trabecular zone with feeling of resistance would be perceived while introducing the guide pin. Guide pin trajectory would be adjusted if an empty space without resistance was achieved, on behalf of entry into the fracture plane.

During the procedure, we adjusted guide pin under fluoroscopy until optimal guide pin trajectory and position were achieved as preoperative templating in both A-P view and lateral view. Place the cannula over guide pin and remove guide pin. Introduce the bone drill to create a space in vertebral body to facilitate balloon insertion. The inflatable bone tamp (IBT) was inserted to adequate depth as templating. Inflate the IBT progressively in 0.25mL increments and verify the inflation progress in the lateral view and A-P view.

In group B, if the collapsed endplate realigned or there was compact bone zone between inflated balloon and the endplate (Fig 1c), the progress was terminated. The patients without the compact bone zone between the balloon and the endplate, too osteoporotic, were excluded.

On the contrary, for patients in group A the guide pin was aimed toward the fracture plane. An empty space without resistance was identified while introducing the guide pin (Fig 2).

Insert bone filler to the anterior portion of balloon cavity and start cement delivery until the cavity created by the balloon is filled. Stop filling immediately if any cement extravasation observed. Stop filling while cement leaking into intervertebral disc or reaching the posterior portion of the vertebral body

Outcome Analysis

Patients were followed at postoperative 1-month, 3-month, 6-month, and 12-month. Radiological outcomes and Clinical outcomes including VAS scores for pain and ODI for functional results were recorded preoperatively, and at postoperative 1-month, and 12-month if there had not been new symptom during the follow-up.

Radiographs included anteroposterior and lateral thoracolumbar spine views. Radiological outcomes included adjacent fracture, kyphosis correction, and further collapse. The degree of vertebral body compression was calculated from plain films including kyphotic angle, anterior vertebral body height (AVH), middle vertebral body height (MVH), and posterior vertebral body height (PVH). The anterior vertebral body height of the treated level was measured at 1-month and 12-month after treatment.

An additional computed tomography (CT) scan was done in cases of persistent, newly onset pain, and suspected new fractures on plain films. Adjacent level fracture which occurred within 3 months after treatment was noted. Further collapse was recognized if anterior vertebral body height loss more than 50% detected.

Clinical and radiographic assessments were performed by an independent blinded observer not involved in patient care (PHC). All patients were regularly followed up at our clinics. None of the patients dropped out of the study due to unknown reasons.

Statistical Analyses

The patients’ age, body mass index (BMI), preoperative VAS, preoperative ODI, and cement volume were analyzed with independent sample t test. The clinical outcomes (VAS and ODI) of each group after operation were analyzed using paired t test. Differences in sex, medical history and complications between groups were assessed using χ² test or Fisher’s exact test. Statistical significance was set at p<0.05. All statistical analyses were performed using SPSS version 20 (IBM, Chicago, IL, USA).

The mean age of the patients was 80.18 ± 6.74 years (range, 60–90 years) in group A and 79.76 ± 7.50 years (range, 63–91 years) in group B. Thirteen of 51 patients in group A are male, and 12 of 49 patients in group B are male. The mean BMI of the patients was 23.67 kg/m2 in group A and 23.06kg/m2 in group B. The mean DEXA T score was − 2.45 in group A and − 2.55 in group B.

Fracture vertebrae are most in the lumbar level in group A and in the thoracolumbar junction in group B, but there was no statistical significance. Most fractures are wedge shape, and some are biconcave shape, there was no significant difference, either. (Table 1.)

The preoperative VAS is 8.1 ± 0.70 in group A and 8.2 ± 0.77 in group B, and the preoperative ODI is 62.59 ± 12.28 in group A and 60.33 ± 9.15 in group B. There were no significant differences in preoperative VAS (p = 0.392) and ODI (p = 0.205) between two groups (Table 1).

In group A, the mean operative time was 36 minutes, and 35 minutes in group B, both groups are with intraoperative blood loss less than 30 mL. The cement volume injected is 3.85 ± 0.72 cc in group A and 4.05 ± 0.63 cc in group B. There was no significant difference in between each group. However, in the indirect reduction group, group B, there was only 1 complication of intradiscal leakage. And in group A, there was 39(76.5%) intradiscal leakage (Table 2).

The VAS score at postoperative 1-month was 3.65 in group A and 2.53 in group B, whereas the VAS score at 12-month was 2.27 in group A and 1.59 in group B (Table 2). The ODI score at postoperative 1-month was 30.43 in group A and 22.45 in group B, whereas the ODI score at 12- month was 24.16 in group A and 17.18 in group B. There were statistical significances in the 1-month and 12-month VAS and ODI scores between two groups

Radiological outcome measurements include anterior, middle, and posterior vertebral height and local kyphosis angle at preoperative, 1-month, and 12-month follow-up. All showed no significant difference in both groups (Table 3). However, the rate of further collapse was significantly lower in the indirect reduction group B.

We assumed that direct introduction of guide pin and subsequent balloon expansion into fracture site is responsible for cement leak through the fractured endplate. In most cases, the fracture line inside vertebral body often remains very close to endplate fracture site. The close proximity of fracture cleft makes endplate leakage so easy to occur during cement distribution. [19]

Our hypothesis is to create a layer of cancellous bone by balloon expansion, beneath the injured endplate, which may augment the endplate defect and prevent cement leakage. Therefore, we insert the guide pin away from the fracture site. As a result, the cancellous bone between fracture site and guide pin could be impacted while balloon expand. The eggshell created this way is thicker and acts as a shield between bone cement and fractured endplate. The fractured endplate could be partially reduced while the thicker cancellous layer was pushed upward by balloon expansion.[20]

In our theory, the principles of treating tibia plateau fracture could be applied when treating vertebral endplate fracture. Sufficient subchondral bone grafting is critical for articular fracture reconstruction. The cancellous bone which is elevated while balloon expand helps to support the fractured endplate, hence it prevents cement leakage into disc through the endplate defect.

Different strategies had been proposed to decrease the risk of cement extravasation into disc while treating vertebral compression fractures with fractured endplate, including the trochar position (away from the broken endplate, and unnoticed perforation of endplate by needle tip). However, the efficacy and safety of kyphoplasty in treating endplate fracture has seldom been discussed.

Poor prognosis was observed while endplate fracture occurs. Study showed postoperative vertebral height loss and aggravation of kyphosis may be associated with biomechanical changes in the vertebral body caused by endplate fracture.[5] Therefore, surgery should not only restore compressed vertebral body height and correct kyphosis, but also correct the deformity of endplate to achieve an effective treatment of OVCF patients with endplate fracture.

Our study had several limitations. First, the enrolled patients were too few to reach conclusions with adequate statistical power. We tried our best to contact asymptomatic patient to complete the follow-up examination. Second, cement augmentation and leakage prevention in every patient was performed by the surgeon’s experience under fluoroscopy as much as possible. Third, we did not routinely use postoperative CT to evaluate the radiological outcomes and cement leakage rates. Forth, not every patient has the compact bone layer enough in their vertebrae.

In conclusion, the indirect reduction method of this study was to reinforce the collapsed endplate rather than just fulfill the defect, which was a safe and more effective way to treat osteoporotic vertebral compression fractures with endplate fragmentation, and showed better pain improvement with less intradiscal leakage and lower rates of further body height collapse.

Acknowledgements

The study was supported by Division of Spine Surgery, Orthopaedic Department, Taipei Veterans General Hospital. We thank Hsin-Yi Huang from the Biostatistics Task Force, Taipei Veterans General Hospital, for the statistical assistance.

Ethics approval and consent to participate

To compare two surgical techniques that already exist, the need for approval was waived by IRB of Taipei City Hospital.

Consent for publication

Consent for publication have be obtained from every subjects.

Availability of data and materials

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

Competing interests

The authors declare that they have no competing interests

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Authors' contributions

PIH analyzed and interpreted the patient data regarding the procedure and was a major contributor in writing the manuscript. HHL performed the data analysis and methodology examination. All authors read and approved the final manuscript.

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Table 1 Patient demographics

	Group A (n=51)	Group B (n=49)	p
Age, years (±SD)	80.18±6.74	79.76±7.50	0.768
Gender (M:F)	13:38	12:37	0.908
BMI	23.67±4.51	23.06±3.73	0.460
BMD (DEXA)	-2.45±0.67	-2.55±0.86	0.507
Fracture Vertebra			0.376
T5-T10 (%)	6(11.8)	5 (10.6)
T12-L1 (%) L2-L5 (%)	19(37.3) 26(51.0)	25(51.0) 19(38.8)
Fracture type Wedge (%)	38(74.5)	35(71.5)	0.926
Biconcave	13(25.5)	14(28.6)
Pre-op VAS (±SD)	8.1±0.70	8.2±0.77	0.392
Pre-op ODI (±SD)	62.59±12.28	60.33±9.15	0.205

BMI, body mass index; DM, diabetes mellitus; Pre-op VAS, preoperative Visual Analogue Scale; Pre-op ODI, preoperative Oswestry disability index.

Table 2 Perioperative and clinical outcomes

	Group A (n=51)	Group B (n=49)	p
Operative time (minutes)	36	35	>0.999
Cement volume (cc)	3.85±0.72	4.05±0.63	0.144
Cement leakage disc (%) other (%)	39(76.5) 10(19.6)	1(2.0) 6(12.2)	<0.001 0.315
VAS
1 month	3.65±1.23	2.53±1.02	<0.001
12 months	2.27±1.04	1.59±0.84	<0.001
ODI
1 month	30.43±12.82	22.45±12.08	0.002
12 months	24.16±11.89	17.18±10.02	0.002
Mean follow-up (months) Revision surgery (%)	21.27±4.36 5(9.8)	19.10±3.02 5(10.2)	0.006 >0.999

VAS, Visual Analogue Scale; ODI, Oswestry disability index.

Table 3 Radiological outcomes

	Group A (n=51)	Group B (n=49)	p
Preoperative (mm) anterior vertebral height middle vertebral height posterior vertebral height	20.03±5.38 19.81±5.10 26.01±4.26	19.53±4.97 19.02±5.82 26.19±4.83	0.636 0.471 0.844
1-month follow-up (mm)
anterior vertebral height middle vertebral height posterior vertebral height 12-month follow-up (mm) anterior vertebral height middle vertebral height posterior vertebral height	23.52±5.34 23.65±4.40 28.43±3.74 20.12±5.27 20.75±4.30 26.59±3.80	24.32±4.64 24.56±4.80 29.92±4.54 21.55±4.50 22.04±4.78 28.14±4.57	0.426 0.322 0.076 0.150 0.158 0.068
Local kyphosis angle Preoperative 1-month 12-month Further collapse (%)	9.97±6.06 7.98±4.85 10.23±5.03 13(25.5)	11.45±3.87 8.31±4.57 10.76±5.22 4(8.2)	0.147 0.724 0.611 0.021
Adjacent fracture (%)	7(13.7)	7(14.3)	0.936
Mean follow-up (months)	21.27±4.36	19.10±3.02	0.006

VAS, Visual Analogue Scale; ODI, Oswestry disability index.

No competing interests reported.

Preoperative planning of compact zone trajectory is necessary in treating osteoporotic vertebral compression fracture with endplate involvement: A prospective randomized controlled study

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Abstract

Background

Methods

Results

Conclusion

Figures

Introduction

Materials And Methods

Results

Discussion

Declarations

References

Tables

Additional Declarations

Status:

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