Novel, safe, and easy spinal osteotomy for regional kyphotic deformities

Abstract

Objective

This study aimed to assess the efficacy and safety of a newly developed transpedicular, anterior open-wedge osteotomy procedure with lamina preservation to correct sagittal imbalance in regional kyphotic deformities following compression fractures.

Methods

All seven patients [four females and three males; mean (range) age, 67 (56–78) years] included in this study underwent surgery between May 2005 and May 2016 for symptomatic, rigid kyphosis secondary to compression fractures. Transpedicular, anterior open-wedge osteotomy with lamina preservation was performed in all patients using an osteotome to create a transverse fracture in the vertebral body through bilateral pedicles and an anterior open-wedge space filled with compacted bone graft to correct kyphosis. Pre- and post-operative kyphotic Cobb angles were evaluated, and the volume of intra-operative blood loss was measured.

Results

The pre- and post-operative kyphotic Cobb angle was 35.3° and 17.7°, respectively (p<0.01); mean angle correction was 17.6° (p<0.05). No patient developed any complication with neurologic injury. Mean blood loss was 771 mL. Callus formation viewed on plain film was evident in all patients and was accompanied by decreased thoracolumbar back pain.

Conclusion

Transpedicular, anterior open-wedge osteotomy with lamina preservation is an easy and safe spinal osteotomy procedure for the correction of regional, fixed kyphotic deformities.

Level of Evidence

Level IV, Therapeutic study

Introduction

In the sagittal plane, cervical and lumbar lordosis and thoracic kyphosis of the normal spine align and complement one another (1, 2). With age and disk degeneration, kyphosis becomes progressively pronounced, particularly in patients with a previous osteoporotic compression fracture and wedge-shaped collapse. Rigid kyphosis is usually accompanied by lower back pain and muscle fatigue. Eventually, sagittal imbalance interferes with ambulation and negatively affects quality of life. Surgical options for sagittal imbalance include spinal correction osteotomy plus instrumentation. Smith–Petersen osteotomy (SPO), pedicle subtraction osteotomy (PSO), and vertebral column resection (VCR) have been the most popular approaches for sagittal imbalance correction in recent decades (3–6). SPO yields 10°–15° correction, while PSO gradually yields 30° correction. Among these methods, VCR shows the greatest corrective power (3, 4, 6, 7).

Patient’s general medical status and surgeon’s experience are the other factors influencing treatment decision. SPO is less suitable in cases with the loss of anterior disc mobility (6). Although PSO is more effective, it is associated with high surgical risks including massive blood loss, durotomy, nonunion with pseudoarthrosis, and implant failure, particularly in elderly patients with comorbidities (3, 8–11).

In this context, we developed a novel spinal osteotomy technique termed transpedicular, anterior open-wedge osteotomy with lamina preservation.

Materials and Methods

Patients

From May 2005 to May 2016, we enrolled seven patients (four females and three males) with a mean (range) age of 67 (56–78) years. The inclusion criterion was a diagnosis of symptomatic rigid kyphotic deformity secondary to a compression fracture (Figure 1a). The etiology of compression fracture included fall from 2-meter height in one patient and fall while walking at the ground level in six patients. Compression fractures had been treated conservatively, and no patient had undergone prior spinal surgery. All patients underwent pre-operative radiography including serial imaging studies of the whole-spine kyphosis, flexion/extension views, and magnetic resonance imaging. A fixed deformity was diagnosed in case of rigid union over the fracture site with no mobile gap and bone edema (Figure 1. b, c). Exclusion criteria were presence of spinal stenosis or spondylolisthesis.

Figure 1. a–c.

Pre-operative imaging evaluation for the diagnosis of fixed kyphotic deformities. Kyphotic deformity of the thoracolumbar spine with a Cobb angle of 38.9° due to a T12 compression fracture with the loss of anterior vertebral body height. (a) Extension view, (b) flexion view. A dynamic plain film showed no mobile cleft in the compression fracture. (c) Iso-to-hypointensities in the T2-weighted phase of a magnetic resonance image signify improved bone edema, and no fluid accumulation in the T12 compression fracture was noted

This study was approved by Taichung Veterans General Hospital institutional review board (IRB TCVGH No: CE17136B) and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and ICH-GCP guidelines. All patients provided written informed consent to undergo surgery. Among the seven patients included, one, five, and one patients presented with injuries of T10, T12, and L1 level, respectively. Pre- and post-operative maximal kyphotic Cobb angle (i.e., Cobb angle in a sagittal plane) was evaluated, and the volume of intra-operative blood loss was measured. All measurements were performed by the same spine surgeon.

Surgical procedure

General anesthesia was administered, and patients were placed in the prone position with the abdomen hanging freely. Routine fluoroscopy was performed in the operating room to identify the collapsed vertebral body. Posterior pedicle screw instrumentation was performed at two levels above and below the collapsed vertebral body (Figure 2a). The bilateral pedicles of the target level were prepared and opened using the transpedicle screw technique to reach the anterior border of the vertebral body. The pedicle opening was dilated, and a half-inch osteotome was inserted through the pedicle opening. Under fluoroscopic guidance, a new fracture was created in the collapsed vertebral body using an osteotome (Figure 2b), and the transverse fracture was bilaterally expanded using cages of increasing sizes to create an anterior open-wedge space in the vertebral body (Figure 2c). Subsequently, gentle force was applied to the apex of kyphosis to enlarge the anterior open-wedge bilaterally (Figure 3. a–c). Kyphosis reduction was maintained using two straight rods. Compacted bone grafts such as allografts or demineralized bone matrix were used to fill the anterior open-wedge space of the vertebral body through the bilateral pedicular channels (Figure 3d).

Figure 2. a–d.

Intra-operative fluoroscopy of the transpedicular, anterior open-wedge osteotomy

Radiographs showing the surgical technique used to perform transpedicular, anterior open-wedge osteotomy with lamina preservation. (a) Following identification of the target level, posterior instrumentation was performed at two levels above and below the collapsed vertebral body. The pedicle screw technique was used to bilaterally probe a working channel. (b) An osteotome was used to break the anterior cortex, creating a new “vertebral fracture.” (c) Cages of increasing sizes were used to enlarge the anterior open-wedge space. (d) Transpedicular compacted bone grafting was applied bilaterally

Figure 3.

Transpedicular, anterior open-wedge osteotomy with lamina preservation. A transverse vertebral fracture was directly created using an osteotome through bilateral pedicles to produce an anterior open-wedge space to correct the kyphotic deformity

Post-operative rehabilitation

All patients were instructed to begin ambulation on post-operative day 3 and to wear a three-point back orthosis for 6 months. In addition, patients were asked to avoid forced bending motions and heavy work following osteotomy. All patients were regularly monitored at the outpatient department for a mean (range) follow-up duration of 24 (4–104) months.

Statistical analysis

Wilcoxon signed-rank test was used to analyze correction angles. The Z-value was −2.3664. However, the sample size (n=7) was insufficient for the Wilcoxon statistic “W” to form a normal distribution as the W-value was 0. The critical W-value for a sample size of seven at p≤0.05 is 2. Results with p≤0.05 were considered statistically significant. Calculations were performed using online statistical calculators in September 2016 (http://www.socscistatistics.com).

Results

Mean (range) pre-operative kyphotic Cobb angle was 35.3° (31°–40°) in patients with fixed kyphotic deformities due to a previous compression fracture. Mean (range) post-operative kyphotic Cobb angle was 17.7° (12°–25°) (Figure 4). Therefore, the difference between pre- and post-operative Cobb angles was 17.6° (p<0.05) (Table 1). Callus formation was evident on plain films in all patients and was accompanied by decreased thoracolumbar back pain. No patient in this study developed complications associated with neurologic injury either intra- or post-operatively, and no nerve-root impingement syndrome or spinal stenosis was reported. Mean (range) intra-operative blood loss was 771 (150–1.200) mL. By post-operative day 3, all patients could ambulate with the help of a back orthosis.

Figure 4. a, b.

Case presentation. A 77-year-old woman with a rigid kyphotic deformity due to a T12 compression fracture underwent transpedicular, anterior osteotomy. (a) Pre-operative examination showed a kyphotic deformity with a Cobb angle of 38.9°. (b) Post-operative evaluation with posterior instrumentation demonstrated a decrease in Cobb angle to 19.7° with a 19.2° angle of correction

Table 1.

Summary of correction angles achieved in seven patients using the novel procedure

Case no.	Age (years)	Apex of deformity	Pre-operative kyphotic Cobb angle (°)	Post-operative kyphotic Cobb angle* (°)	Degree of correction (°)
1	78	T12	3	20	19
2	68	T12	40	19	21
3	56	T10	33	12	21
4	76	T12	31	15	16
5	57	L1	37	25	12
6	72	T12	32	19	13
7	64	T12	35	14	21
Average	67.3		35.3	17.7*	17.6

^*p<0.05

Discussion

In this study, we developed transpedicular, anterior open-wedge osteotomy with lamina preservation, which is an effective and comparatively easy spinal osteotomy procedure for correcting regional fixed kyphotic deformities.

In elderly patients, fixed regional kyphotic deformities following compression fractures are a significant clinical problem, especially in our aging society. Patients may develop kyphosis in the thoracolumbar region even after a minor trauma (12). The most common etiology is an osteoporotic compression fracture. While sharp back pain usually improves with time, persistent kyphotic deformities influence sagittal balance, disrupt ambulation, and reduce quality of life. If a mobile intravertebral cleft is detected, percutaneous kyphoplasty may be considered for pain relief and kyphotic deformity reduction (13, 14). Corrective osteotomy is recommended for patients with rigid kyphosis due to a compression fracture. The aim of such a surgery is to restore physiological balance and maintain spinal stability. Different types of spinal osteotomy, classified as “anterior only,” “anterior and posterior combined,” and “posterior only,” have achieved successful outcomes in a number of studies (3, 5, 9, 15, 16). The anterior approach is the most efficient because the location of the disease is approached and addressed directly; moreover, the procedure achieves anterior column support, with a low incidence of instrumentation failure (17). Despite these benefits, however, the anterior approach usually requires prolonged operation time because the surgical technique is highly challenging. Therefore, this approach generally involves increased risk of damage to the internal organs including vessels injuries, vascular calcification, and pulmonary or gastrointestinal complications (18). In recent decades, the posterior-only approach has become the most popular. SPO and PSO have been applied via this approach to correct deformities with satisfactory results in numerous studies (4, 6, 9, 10, 19). SPO achieves an average angle correction of 10°–15°, whereas PSO is expected to achieve a correction of approximately 30° (3, 4, 6, 7). Moreover, SPO is less suitable for elderly patients because of the loss of anterior disc mobility resulting from disc degeneration and ossification of the anterior longitudinal ligament (5, 6). Thus, PSO is generally selected as the main osteotomy method in such cases. Zhang et al. described a modified transpedicular subtraction and disc osteotomy combined with long segment fixation, which involves creating a larger interspace and permitting a greater correction angle than regular PSO for kyphotic deformities (20). Although PSO yields satisfactory clinical and radiological results during long-term follow-up, it is technically challenging and associated with increased risk of complications such as blood loss, neurologic injury, and pseudoarthrosis (21–23). Kim et al. reported a series of 35 patients with kyphosis who underwent PSO. Although patient satisfaction (87%) and functional outcomes (69%) were good, pseudoarthrosis was identified in 10 cases (29%) within 5–8 years of follow-up (21). Buchowski et al. and Yang et al. reported 11.1% and 12% incidence rates of intra-operative and post-operative neurologic complications, respectively (22, 24).

Transpedicular, anterior open-wedge osteotomy with lamina preservation directly corrects the collapsed vertebral body, which is the main pathology of kyphosis, by creating a transverse, iatrogenic vertebral fracture and an anterior open-wedge space in the vertebral body. In the present case series, the mean correction angle of 17.6° for the developed osteotomy was equal or superior to that reported for SPO (3, 4). Conventional spinal osteotomy methods such as SPO or PSO require the removal of part of the lamina and pedicle, thereby increasing the risk of intra-operative bleeding and neurologic injury. In contrast, the novel procedure reported in this study does not require the removal of lamina and does not directly expose neurologic structures. Thus, this approach avoids damage to the spinal cord and epidural venous plexus and provides the possibility achieving outcomes free of iatrogenic and neurologic complications. In the present study, no iatrogenic or neurologic injuries were encountered, and the mean blood loss of 771 mL was less than mean blood loss of >2,000 mL reported for PSO and VCR (19). Theoretically, the anterior open-wedge technique does not shorten the middle column of the vertebra and does not result in ligamentum flavum redundancy. Furthermore, it reduces the risk of exacerbation of spinal stenosis. Preservation of the lamina provides further stability when combined with anterior vertebral bone grafting and posterior instrumentation, and this produces a rough surface to promote posterior lateral fusion. In addition, the technique described herein reduces the number of fusion levels. All patients also ambulated with a back brace by post-operative day 3, which reduced the duration of being bedridden as well as any complications related to a long recovery time.

This study has a few limitations that must be addressed. First, the small number of cases limited the statistical power of the results. Future studies should entail a larger patient cohort to remedy this shortcoming. Finally, no case of adjacent kyphosis or implant failure was detected during the study period. A longer follow-up duration is needed to determine the rates of adjacent kyphosis, screw loosening, and implant failure following this procedure.

In conclusion, transpedicular, anterior open-wedge osteotomy with lamina preservation is an easy and safe posterior-only approach to spinal osteotomy for correcting fixed kyphotic deformities even in the elderly. This technique results in fewer surgical complications than conventional approaches and provides patients and surgeons with a more effective alternative surgical option that merits further investigation.

MAIN POINTS.

• Use the pedicle screw technique to create an anterior open-wedge osteotomy for the correction of regional, fixed kyphotic deformities.

• Lamina preservation means do not directly expose neurologic structures and reduce iatrogenic injury.

• The mean correction angle of 17.6° was an amount equal or superior to SPO.