Key-words:
Anterior column reconstruction - bridwell criteria - frankel grade - kyphosis - thoracic spine - tuberculosis
Introduction
First described by Sir Percival Pott, Tuberculosis (TB) is an age-old problem affecting millions and millions worldwide. Developing countries are affected the most. TB in the past was considered to be a dead-end for the patient but with the advent of anti-tubercular chemotherapy and surgical advancements, millions of lives were saved. The thoracic spine is the most common site affected. Affects more commonly the anterior part of the vertebra and causes collapse leading to kyphotic deformity and neural compression. The goals of surgery in Pott's spine are adequate debridement and decompression, maintenance and reinforcement of stability, prevention, and correction of deformity if any.[[1]],[[2]],[[3]],[[4]],[[5]] The selection of whether anterior of the posterior approach for surgical treatment of thoracolumbar TB is still a matter of debate. Anterior approach was popularized by Hodgson in 1960. Throughout the past anterior-approach has always been favored because of involvement of the anterior part of the vertebra being more common and anterior-approach allows for thorough debridement of disease and decompression of cord. Reconstruction of the vertebral body by anterior approach looks far more promising and easy. But with time posterior-approach has gained more attention because of the complexity and morbidity associated with anterior-approach. Anterior reconstruction by posterior approach is now favored because of familiarity with the approach and ease of doing surgery. The anterior and posterior approach used for reconstruction have their own pros and cons. But are the results of reconstruction the same in both these approaches?? There are various studies showing variable results.[[6]],[[7]],[[8]],[[9]] The above study was conducted to see and compare the long-term outcome of reconstruction by direct anterior versus posterior approach using clinical and radiological methods and conclude so that it becomes a standard of care in the management of TB.
Aims and objectives
To retrospectively evaluate and compare the long-term outcome of anterior reconstruction of the vertebral body in TB of the dorsal spine by direct anterior versus posterolateral approach.
Materials and Methods
The above study was conducted over 245 patients of confirmed cases of TB of the thoracic spine who met the criteria for anterior vertebral body reconstruction and were operated by either direct anterior transthoracic approach or posterior approach. Patients are managed in our institute by the Middle path regimen of Tuli.[[10]] Patients with Frankel grade A and B are considered for immediate surgery whereas Frankel grade C, D, and E are put on bed rest and anti-TB chemotherapy. If no improvement is seen in 3–6 weeks then they are considered for surgical intervention. Of them, 118 patients were operated by anterior approach and 127 patients by posterior approach. Comparison was done between the two approaches using various factors like surgical time, blood loss, length of hospital stay, neurological recovery, correction of kyphosis, maintenance of correction, time for fusion, grading of fusion using Bridwell's grade and complications if any. All the patients were assessed clinically and their neurology was recorded using the Frankel grading system [[Figure 1]] preoperatively and were serially assessed at immediate postoperative, 1, 3, 6 months, and at 1 year. All the patients were assessed radiologically using X-ray, Magnetic Resonance Imaging, and computed tomography (CT) scan which were taken preoperatively and X-rays were repeated immediately postoperative, at 1, 3, 6 months, and at 1 year. CT scan was done in few patients to look for fusion in whom X-rays were not helpful. Radiological parameters taken into account were the number of vertebrae involved, level of instrumentation, correction, and maintenance of kyphosis as measured by Cobb's method [[Figure 2]], fusion grading as per Bridwell criteria. All patients were started on anti-tubercular therapy as per standard protocol immediately after surgery and was continued for a period as per the resistance of the organism. Patients with confirmed cases of TB of the dorsal spine with neurological deficit and vertebral body collapse with localized kyphosis were considered for surgery and anterior reconstruction was done in all of them. Patients with maintained records and with regular follow-up were selected for the study. Patients with vertebral body collapse due to causes other than TB, those with no maintained records and those lost to follow-up were excluded from the study. The above study has been conducted after attaining due consent from all patients and after approval from institutional ethics committee.
Figure 1: Frankel Grading of neurology
Figure 2: Cobb's method of measurement of kyphosis
Bridwell criteria: Anterior fusion grades
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Grade I: Fused with remodeling and trabeculae
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Grade II: Graft intact, not fully remodeled or incorporated, though no lucencies
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Grade III: Graft intact, but definite lucency at the top or bottom of the graft
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Grade IV: Definitely not fused with resorption of the graft and with collapse.
Surgical technique
Anterior approach
Patients operated by this technique were placed in the right or left lateral decubitus position based on the position of prevertebral abscess, the preferred approach was from left by placing the patient in the right lateral position. Transthoracic intrapleural approach was made via versatile approach technique [[Figure 3]] of Srivastava et al. Thorough debridement of pus and necrotic tissue until the healthy bleeding bone was reached. Neural decompression was carried out with subtotal or complete corpectomy of the involved vertebrae. Anterior reconstruction and kyphosis correction was done using either strut graft obtained from ribs or iliac crest or titanium mesh cage filled with morselized cancellous graft.[[11]],[[12]],[[13]] It is supplemented by posterior instrumented stabilization by pedicular screws or Hartshill rectangle and sublaminar wires in the same stage using the same incision.
Figure 3: (a) Preoperative X-ray showing dorsal Kochæs With collapse. (b) Versatile approach technique. (c) Thorough decompression and rib graft insertion. (d) Hartshill rectangle and sublaminar wire. (e) Immediate postoperative X-ray. (f) X-ray at 3 months postoperative
Posterior approach
Patients were operated on by using standard midline posterior incision. The posterolateral approach included transfacetal, transpedicular and costo-transversectomy routes as per the requirement of the case. The above approaches were used to reach the anterior aspect of the vertebrae. The transfacetal approach was considered in cases with single vertebral body collapse with Cobb's angle ≤30°. Transpedicular and costo-transversectomy approaches were considered in cases with ≥2 vertebral body collapse with severe kyphosis. The last two approaches are very helpful in the correction of rigid kyphosis. Debridement of all necrotic material was done until bleeding healthy bone was seen. Cord was decompressed, paraspinal abscess was drained and anterior vertebral body reconstruction was done using strut graft obtained by iliac crest or ribs or titanium cage filled with morselized cancellous graft. Pedicular screw and rod system was used to stabilize the spine[[14]],[[15]],[[16]],[[17]] [[Figure 4]]. Indications and summary regarding the two approaches have been mentioned in the table below [[Table 1]].
Figure 4: (a) X-ray AP view showing Tuberculosis of dorsal spine. (b) X-ray lateral view showing tuberculosis of dorsal spine. (c) Postoperative X-ray at 3 months. (d) Postoperative X-ray at 3 months
Table 1: Anteriror Vs Posterior Approach
Correction of rigid kyphosis
It is not uncommon to encounter rigid kyphosis in cases of TB spine. There are various techniques to correct rigid kyphosis, which can be done as a single or multi-stage procedure. Steps in any kyphosis correction involve thorough soft tissue release, anterior debridement and anterior column reconstruction, cord and root decompression, instrumented stabilization and posterior column shortening.[[18]] All of this can be done either by anterior or posterior approaches. Various techniques of kyphosis correction mentioned in the literature include transpedicular decancellation osteotomy by Bezer et al.,[[19]] pedicle subtraction osteotomy, direct internal kyphectomy, vertebral column resection, closing-opening wedge osteotomy by Rajasekaran.[[20]] Our preferred method of kyphosis correction in patients operated by posterior approach was closing-opening wedge osteotomy using extra-pleural costo-transversectomy approach and transthoracic intra-pleural route[[21]] for patients operated by anterior approach.
Results
Out of 245 patients, 118 were operated by anterior-approach via versatile approach technique and 127 by posterior-approach. The mean age in the anterior approach was 36.03 and 39.83 years in the posterior-approach. Anterior approach was preferred in younger patients and posterior approach preferred in older age group due to comorbidities which prevented the anterior approach. Anterior approach was preferred in patients with the higher number of vertebral body involvement. Out of 118 patients, 61% had involvement of two vertebral body, 22.9% had three or more vertebral body involvement and 16.1% had one body involvement. Out of 128 patients operated by posterior approach, 47.2% had involvement of two vertebral body, 16.5% had three or more vertebral body involvement and 36.3% had one body involvement. The mean operative time in the anterior approach was 6.11 and 5 h in the posterior approach. The mean blood loss in the anterior approach was 1.6 L which is higher compared to the posterior approach where mean blood loss is 1.1 L.
The mean preoperative kyphosis angle in the posterior approach was 34.803° and the mean postoperative kyphosis angle was 11.286° at 3 months. The correction achieved was 67.216% which is statistically significant (P < 0.001). However in subsequent follow-up it was noted that there was mean loss of 4.186° of correction when compared with kyphosis angle at 1 year. Fusion was graded as per Bridwell criteria and time for fusion was calculated only when fusion was noted to be of Grade1. Mean time taken for fusion was 6.34 months with values ranging from 5 to 9 months.
The mean preoperative kyphosis angle in the anterior approach was 41.154° and mean postoperative kyphosis angle at 3 months was 9.498° with a correction of 77.467% which was statistically significant (P < 0.001). In subsequent follow-ups, the loss of correction noted was 6.184° at 1 year. The meantime taken for fusion was 4.69 months with values ranging from 3 to 6 months.
The mean time taken for mobilization in the posterior approach was 1.18 weeks which is usually done after drain removal on day3 postoperative as per our protocol, whereas in the anterior approach the patients are mobilized after a mean duration of 2.51 weeks [[Table 2]].
Table 2: Results
Neurology was graded using the Frankel grading system. Among 127 patients operated by posterior approach, there were 8 patients with Frankel-A, 34 with Frankel-B, 57 with Frankel-C, 27 with Frankel-D, and 1 patient with Frankel-E. Postoperatively the neurology improved in most of the patients and by the end of 1 year there were 4 with Frankel-A, 10 with Frankel-B, 16 with Frankel-C, 30 with Frankel-D, and 67 patients with Frankel-E Significant improvement in neurology was noticed. Unfortunately, there were 7 patients in whom worsening of neurology was seen postoperative which slightly improved by the end of 1 year.
Among 118 patients operated by anterior approach, there were 28 patients with Frankel-A, 27 with Frankel-B, 39 with Frankel-C, 14 with Frankel-D, and 10 with Frankel-E. By the end of 1 year postoperative there were 7 patients with Frankel-A, 8 with Frankel-B, 6 with Frankel-C, 42 with Frankel-D, and 55 with Frankel-E. There was a significant improvement in neurology noticed by the end of 1 year. There was worsening of neurology in 3 patients which occurred postoperative and gradual improvement in neurology was noticed by the end of 1 year.
Out of 127 patients operated by posterior approach 35 patients had one or the other complications. Of 35 patients 11 had dural-tear, pseudoarthrosis, and implant failure was seen in 10 patients, 3 patients got operative site infection, 7 had suture complications, 4 had neurological deterioration with no subsequent improvement. Out of 118 patients operated by anterior approach 17 had complications. Of 17 patients 7 patients had suture site complications, 3 had pneumothorax, 2 had dural-tear, 3 had neurological deterioration, 1 had implant failure and 1 had graft slippage.
Discussion
TB of the spine has been a worldwide problem for ages and lot of research work has been done and continues to be done. There are some groundbreaking research articles which changed the course of management. After Oga et al.[[22]] in their study proved the safety of implants in regions with active TB, the treatment of TB of spine has drastically improved. Anterior approach was popularised by Hodgson in 1960[[23]] and since then it was commonly used in the anterior reconstruction of the vertebral body in TB and fractured spine. HodgsonandStock advocated anterior arthrodesis as the treatment of choice for TB of the spine. They also advocated posterior instrumentation to correct unfixed kyphus with the prior anterior release.[[23]] Direct approach to the pathology and the ability to thoroughly debride the diseased vertebra and place a large strut graft made the approach obviously favorably. Since transthoracic approach was hard to master on and due to the slightly higher risk involved, anterior approach started loosing its significance. Posterior approach via trans-facetal, trans-pedicular or costo-transversectomy slowly started gaining popularity and the results obtained were comparable to the anterior approach. Rajasekaran and Soundarapandian[[24]] suggested a strong correlation between the initial loss of the vertebral body and the final gibbus. They suggested the formula Y = a + bx which on calculation suggests that a loss of every whole vertebra, 30° ±3.58° of gibbus deformity occurred.
Louw[[25]] advocated the “Kalafong procedure” for the treatment of spinal TB with neurological deficit. Which consists of anterior debridement, cord decompression, and grafting followed by single or two-stage posterior osteotomies and instrumentation. They were able to achieve good results with this.
The mean age among the anterior group is 36 years as compared to 39.83 years in the posterior group as the anterior approach is slightly more morbid than the posterior approach and not preferred in the older age group with comorbidities which preclude its use. The mean blood loss in the anterior approach was 1.6 L as compared to 1.1 L in the posterior approach. The anterior approach allows for thorough debridement and since the area is highly vascular more blood loss was expected. There were no complications related to blood loss during surgery. Laheri et al.[[26]] in their study showed a mean operative blood loss of 850 ml (range 2000 ± 400 ml) in postero-lateral approach. Jain et al.[[27]] have shown a mean blood loss of 1170 ml via antero-lateral approach in their study.
Correction of kyphosis via anterior approach in our study was 77.467% as compared to 67.216% via posterior approach which turned out to be statistically significant (P < 0.001). This shows that anterior approach allows for better correction of kyphosis which is very essential to maintain spinal balance and for restoration of anterior weight-bearing column. Louw[[25]] in his study has shown an improvement in kyphosis angle form 56° to 27° via anterior approach. Yilmaz et al.[[28]] in their study showed a correction of 64% in kyphosis when operated via anterior approach. There are very few studies which actually compare correction of kyphosis by anterior and posterior approach. Laheri et al.[[26]] in their study showed a correction of 62.5% when operated through postero-lateral approach. Jain et al.[[27]] in their study have shown correction from 49.08° to 25°when operated via anterolateral approach.
The mean duration for fusion was 4–9 months. Mean time for fusion in the anterior approach group was 4.69 months as compared to posterior approach which was 6.34 months which is statistically significant (P < 0.01). The anterior approach group showed early fusion compared to the posterior group. Those operated by anterior approach had 100% fusion rate with few graft-related complications like graft slippage in 1 patient and implant failure in 1 patient. Those operated by posterior approach showed fusion rate of 93.7% with pseudoarthrosis in 8 patients and implant failure in 10 patients who were re-operated and subsequently fusion was seen. Ozdemir et al.[[29]] achieved a fusion rate of 96% via the anterior approach in their study. Ma et al.[[30]] in their study showed a fusion rate of 92.5% and 91% in anterior and posterior approach respectively. Laheri et al.[[26]] had shown a fusion rate of 100% in the posterior approach. Kemp et al.[[31]] reported 94.5% fusion rate of iliac crest grafting. The anterior approach allows for thorough debridement of necrotic tissue and use of large iliac crest and rib strut grafts which ensure high fusion rates. Debridement in posterior approach is limited by the anatomy and limited length of strut grafts can be used. Time to fusion depends on multiple factors starting from age of the patient to the technique of fusion.
The mean loss of correction in the posterior approach was 4.186° and in the anterior approach was 6.184° at 1-year postoperative. There is a higher loss of correction in the anterior approach. Laheri et al.[[26]] had a loss of 3.2° of correction in the posterior approach and Jain et al.[[27]] had a loss of 2.5° of correction in patients operated by anterior approach. Yilmaz et al.[[28]] had a loss of 3° of correction at 1 year. Ozdemir et al.[[29]] has showed a correction loss of 3° in the anterior approach. There are various studies showing results ranging from no loss of correction to loss of up to 30% of total correction achieved. It was noted in our study that the time taken to fusion and loss of correction are directly proportional. The longer the time for fusion, larger is the loss of correction.
Neurology was graded using the Frankel grading system. Among 127 patients operated by posterior approach, there were 8 patients with Frankel-A, 34 with Frankel-B, 57 with Frankel-C, 27 with Frankel-D and 1 with Frankel-E. Postoperatively, the neurology improved in most of the patients and by the end of 1 year, there were 4 with Frankel-A, 10 with Frankel-B, 16 with Frankel-C, 30 with Frankel-D, and 67 patients with Frankel-E. Significant improvement in neurology was noticed. Unfortunately, there were 7 patients in whom worsening of neurology was seen postoperative which slightly improved by the end of 1 year.
Among 118 patients operated by anterior approach, there were 28 patients with Frankel-A, 27 with Frankel-B, 39 with Frankel-C, 14 with Frankel-D and 10 with Frankel-E. By the end of 1-year postoperative there were 7 patients with Frankel-A, 8 with Frankel-B, 6 with Frankel-C, 42 with Frankel-D and 55 with Frankel-E. There was a significant improvement in neurology noticed by the end of 1 year. There was worsening of neurology in 3 patients which occurred postoperative and gradual improvement in neurology was noticed by the end of 1 year. The neurological improvement was slightly better in patients operated by the anterior approach. Laheri et al.[[26]] in their study had a 91.3% neurological recovery by the end of 15 months with worsening of neurology in 4.3%. Similar results were seen by Christodoulou et al.[[28]] in their study of anterior stabilization in TB spine. Garg et al.[[32]] in their study had results showing almost the same neurological improvement in anterior and posterior approaches.
Mobilization of patients was done as per our institutional protocol. Patients were mobilized after drain removal and after obtaining post-X-ray. Patients operated by posterior approach were mobilized after a mean duration of 1.18 weeks and those operated by anterior approach after 2.51 weeks. All patients were mobilized using suitable brace.[[33]]
Patients operated by posterior approach had a slightly higher rate of complications of some type as compared to anterior approach. Out of 127 patients operated by posterior approach 35 had one or the other complications. Of 35 patients, 11 had dural-tear, pseudoarthrosis and implant failure was seen in 10 patients, 3 patients got operative site infection, 7 patients had suture complications, 4 patients had neurological deterioration with no subsequent improvement. Out of 118 patients operated by anterior approach, 17 had complications. Of 17 patients, 7 patients had suture site complications, 3 had pneumothorax, 2 had dural tear, 3 had neurological deterioration, 1 had implant failure and 1 had graft slippage. The incidence of complications varies in different studies and is not comparable.
Single-stage anterior reconstruction and posterior stabilization via anterior approach allows reduction of longstanding rigid kyphosis. An important feature of the reduction of kyphosis is the restoration of normal spinal balance. The most feared complication of spinal cord damage is avoided by meticulous attention to the total release of all anterior and lateral adhesions allowing the spinal cord to move forward unhindered during reduction of kyphosis. Segmental instrumentation is preferred as it provides a very effective three-point fixation and immediate stability. Posterior instrumentation also helps to maintain correction of kyphosis till fusion is solid.
Conclusions
Decompression and deformity correction are the only answer to prevent the progression of neurological deficit, kyphosis, and late-onset paraplegia in these complex cases. Single-stage anterior reconstruction and posterior stabilization via anterior approach allow for thorough debridement, neural decompression, and much better anterior column reconstruction and deformity correction under direct vision than posterior approach. Direct visualization of the cord while correcting kyphosis reduces the chances of neurological complications significantly. Both approaches have their own unique advantages and limitations. The age-old saying of increased morbidity and poor results with the anterior approach have been proven wrong in this study. Though the posterior approach is easy to master, the results shown by the anterior approach cannot be overseen. We would like to conclude that better functional outcomes and significantly better kyphosis correction by the anterior approach are strong pointers favoring the anterior approach.
