10 Surgical Management of Spinal Tuberculosis
Introduction
Early diagnosis along with effective multidrug antituberculous chemotherapy has revolutionized the treatment of spinal tuberculosis (TB) and has obviated the need for surgery in the majority of patients. However, additional surgical intervention may be necessary in those who are diagnosed or present late, as chemotherapy alone may not be able to reverse the consequences of disk and vertebral destruction. Spinal TB primarily affects the anterior column of the spine, and progressive vertebral destruction with collapse may result in significant kyphosis and neurological deficit, thus necessitating surgery. The goals of surgery are to ensure adequate decompression, debridement, maintenance, and reinforcement of stability and correcting the deformity or halting the progress of deformity.
Historical Perspective and Evolution of Treatment
Historically, Hibbs in 1911 and Albee in 1913 advocated posterior fusion to prevent further progression of deformity with unpredictable results. Capener and later Wilkinson and Seddon demonstrated the efficacy of debridement by the costotransversectomy approach, which was termed anterolateral rachitomy. 1 Hodgson and Stock 2 in 1956 popularized the Hong Kong procedure, which not only revolutionized the surgical management of spinal TB but also paved the way for the anterior approach for other spinal pathologies, too. The Hong Kong procedure was considered the gold standard approach; it included radical debridement of the lesion and anterior interbody fusion with tricortical iliac or fibular strut grafts through an anterior approach. Severe neurologic deficit and significant kyphosis have always been considered as definitive indications for surgery.
To identify the role of surgery in patients without a neurologic deficit, the British Medical Research Council (MRC) conducted a series of prospective multicenter randomized clinical trials that compared the results of chemotherapy alone (an ambulatory regimen of rifampin and isoniazid) with debridement alone and with radical debridement and anterior spinal fusion together. Both short- and long-term findings indicated that all the three treatments achieved similarly favorable clinical results. 3 The favorable status was defined as no evidence of central nervous system involvement, no sinus or clinically evident abscess, no radiological evidence of disease activity, and no restriction of normal physical activity. The major shortcoming of the study was that it did not assess spinal deformity (kyphosis). However, careful evaluation of the short-term results revealed faster resolution of abscess and bony union with the Hong Kong procedure. This advantage was retained in the long-term results, with data showing minimal deformity and maintained sagittal alignment. In contrast, patients treated with chemotherapy and debridement showed relapse of sinuses and recurrence of cold abscesses and worsening of kyphotic deformity. In about 5% of the conservatively treated patients, there was a significant increase of kyphosis from 51 to 70 degrees. 4 The MRC trials also demonstrated resolution of cold abscesses with chemotherapy alone, and hence surgical drainage of cold abscesses is no longer recommended, unless they present with pressure effects.
The use of instrumentation became popular following the work of Oga et al, 5 who showed that tubercle bacilli, unlike pyogenic organisms, neither adhere to metal nor form any biofilm. With the advent of better instrumentation techniques, surgical treatment has yielded better results in terms of early ambulation, good disease clearance, and prevention of progression of deformity. The use of titanium implants enables healing of the disease to be assessed through postoperative imaging with computed tomography (CT) or magnetic resonance imaging (MRI). Although the anterior approach has been traditionally popular, the recent trend is for posterior approach–based spinal stabilization and decompression with or without global reconstruction, especially in the thoracic and lumbar spine. Modern posterior spinal instrumentation systems enable the safe correction of deformity, spinal fusion, and anterior reconstruction of vertebral defects without many complications. In the cervical spine, anterior debridement, reconstruction, and stabilization remain popular.
General Principles of Surgical Management
The advantages of surgical treatment are that it aids in histological confirmation of the diagnosis; decreases the disease burden; enhances the healing, correction, and prevention of spinal deformity; reduces the rate of recurrence; and promotes early neurologic recovery.
The five basic principles of surgical management of spinal TB are debridement, decompression of the spinal canal, correction of deformity, reconstruction of the anterior defect, and spinal stabilization. Depending on the severity of the bone destruction, kyphosis, and neurologic deficit, the surgery may include all or some of the five components. 6 Drainage of the cold abscess is rarely indicated, as anti-TB drugs can effectively resolve it in most cases. Notable indications for abscess drainage include respiratory distress or dysphagia due to a large cervical paravertebral abscess, and pseudo–hip flexion deformity due to a large psoas abscess or an abscess that has tracked into the subcutaneous plane with imminent rupture. Whenever feasible, drainage of the cold abscess by ultrasound guidance is preferred.
Tuberculosis of the spine can be classified based on the vertebral and disk space destruction as pauci-segment or multi-segment disease. Pauci-segment or pauci-level disease is considered to be present when the involvement is limited to two adjoining vertebrae and the intervening disk. Multisegment disease involves more than two vertebral bodies and intervertebral disks and is associated with significant instability and deformity. Multi-segment disease can be contiguous or non-contiguous. This classification can guide the surgical treatment with regard to approach, aggressiveness of debridement, and extent of instrumentation.
Debridement and Decompression
A typical surgical procedure for spinal tuberculosis involves debridement of the tuberculous focus—caseous material, granulation tissue, and sequestrated bone up to the posterior longitudinal ligament through an anterior approach. Debridement is extended proximally and distally until the bleeding cancellous bone is exposed from the cephalad and caudal vertebrae. In cases with destruction extending up to the upper or lower end plate, an extensive debridement involving removal of the disks above and below may be necessary. Experimental studies have shown that the concentrations of antitubercular drugs varied greatly in different tissues in spinal TB, and the least concentration and penetration of the drug was noted in the sclerotic focus, thus advocating its removal. 7
Debridement alone does not the prevent the progression of the deformity nor does it improve healing. Adequate debridement followed by interbody fusion and surgical stabilization relieves pain, improves neurologic function, and prevents deformity. It can be performed either by an anterior approach or by a posterior transfacetal, transpedicular, or costotransversectomy approach.
Reconstruction of the Anterior Defect
The reconstruction of the anterior defect can be performed with autografts, structural allografts, or titanium cages. Iliac crest grafts or ribs are preferred in smaller defects, whereas fibular grafts or tibial grafts are suitable options in larger defects. Autografts should be preferably tricortical autografts, as they provide structural support along with osteogenic potential. In larger defects, a high risk of graft failure has been reported in uninstrumented fusion as the bone tends to be invaded by the creeping substitution process, leading to collapse in the initial stage of remodeling of cortical bone. The use of only cancellous graft or a local autogenous graft along with transpedicular instrumentation could be an option in the lumbar spine. Recently, the trend is to use a titanium cage, as it provides strong mechanical support, enables packing with corticocancellous graft, and minimizes the risk of dislodgment. The use of cages avoids the morbidity of graft harvesting and the loss of strength of strut graft during its resorption phase. Titanium cages can be mesh cages, interbody cages, or expandable cages. 8 Titanium cages grab on to vertebral bone, and settling occurs on vertical loading, providing stability to the cage.
Deformity Correction
The development of kyphosis is the rule in spinal tuberculosis, and it is directly proportional to the destruction of the disk space and vertebral body. In patients treated conservatively, irrespective of the disease severity, it was ob served that there was a mean increase of spine deformity by 15 degrees, and at the end of treatment 3 to 5% of patients have a final deformity of more than 60 degrees. Hence, it is important to identify the risk factors leading to the development of severe kyphotic deformity and to surgically treat them in the active phase. 9 The kyphotic deformity during the active stages is usually flexible, and surgical correction of the deformity can be achieved by debridement, reconstruction of the defect, and instrumentation along with anti-TB chemotherapy.
Instrumentation
Spinal instrumentation helps to enhance stability, minimize graft dislodgment, correct deformity, and enable early mobilization and rehabilitation of patients. Additional benefits include providing immediate relief from the instability pain and enabling neurologic recovery. Lee et al 10 and Broner et al 11 reported that the immobilization effect achieved by the instrumentation might also suppress infection and provide a stable environment that can prevent TB recurrence. Mycobacterium tuberculosis has less affinity to adhere to biomaterial, and thus the use of titanium implants, which have an active oxide surface, renders less adherence compared with stainless steel implants, making their use safe in the presence of active infection. 5 The levels of instrumentation depend on the site of the lesion, the quality of the bone, and the surgical plan. Ideally, it is preferable to apply fixation at least two levels above and below the lesion. However, in the lumbar spine, in the presence of a rigid anterior interbody construct, one level of fixation above and below the lesion can be adequate. The extent of the spinal instrumentation can be minimized by introducing screws in the upper involved pedicle of the superior vertebral body in pauci-segment disease.
Indications of Surgery in Spinal Tuberculosis
Uncomplicated spinal TB is a medical disease, and it can be effectively managed by chemotherapy alone; surgical intervention may be needed in relatively few cases. However, in those cases complicated with TB (gross neurologic deficit, instability, deformity, unresponsive to medical therapy), it is advised that a combination of medical therapy and surgery be used to yield optimum results. Neurologic deficit, especially if it is severe or progressively worsening, and bowel and bladder incontinence are considered absolute indications for surgery. The presence of a stable, nonprogressive neurologic deficit is not an absolute indication for surgery in active spinal TB, as chemotherapy improves the neurologic outcome. 1 , 2 Tuli 1 introduced a middle-path regimen, wherein he treated neurologic deficit patients initially with bed rest and antituberculous chemotherapy. Surgery was considered only if there was further deterioration of a partial neurologic deficit or if there was no improvement after 3 to 4 weeks. Adding to this regimen, Jain and Kumar, 12 in an MRI-based study, found that cold abscesses causing neurologic deficit resolved with conservative treatment, and for those caused by bony compression and granulation tissue, surgical intervention was necessary. Conservative treatment of patients with a neurologic deficit, although successful, takes more time for neurologic recovery and for the patient to become ambulant. Hence, it would be prudent to consider early surgical decompression and fusion to enable more rapid resolution of the neurologic deficit and an earlier return to normal activity. Surgery is also indicated in multilevel contiguous or noncontiguous disease, pan-vertebral disease, kyphosis greater than 30 degrees, and junctional areas, as they are subjected to a high risk of biomechanical stress and instability.
Rajasekaran 13 described the radiographic “spine-at-risk” signs in pediatric patients that predict the likelihood of developing progressive deformity. These signs, which appear early in the disease, include facet dislocation, retropulsion of the diseased fragments, lateral vertebral translation, and toppling of the superior vertebra. Rajasekaran proposed calculating an instability score; a score of more than 2 indicated disruption of the posterior facet and is an indication for the surgery. These signs can help identify patients who are at risk for deformity progression of more than 30 degrees and a final deformity of over 60 degrees. Rajasekaran and Shanmugasundaram 14 advocated surgery for adults with loss of three fourths of a thoracic or thoracolumbar vertebra, or loss of one lumbar vertebra, aiming for a final kyphosis of no more than 30 degrees. In patients with a doubtful diagnosis, persistent pain, and no response to chemotherapy, surgery is indicated. The indications for surgery are summarized in Box 10.1 .
Box 10.1 Surgical Indications in Spinal Tuberculosis
Neurologic deficit
Severe neurologic deficit at presentation
Rapidly worsening deficits
New onset or deterioration of deficits during chemotherapy
Unimproved deficits after 6 to 8 weeks of chemotherapy
Spinal instability
Pan-vertebral disease
Loss of one vertebral body in the thoracic spine or 1.5 vertebral bodies in the lumbar spine
Initial kyphosis of 30 degrees
“Spine-at-risk” signs in a child
Posterior neural arch lesion with pedicular destruction
Axial pain due to instability
Response to chemotherapy
Lack of clinical response after 6 weeks of chemotherapy
Recurrence of disease despite chemotherapy
Late deformity
Severe kyphosis with late-onset neurologic deficits
Surgical Approach
A single surgical technique cannot be applied universally to all patients. Factors that are taken into consideration when deciding on the specific surgical approach are the age of the patient, the location of the bony lesion, the presence of medical comorbidities, the degree of kyphosis, the region of the spine involved, and the experience and preference of the surgeon. Although anterior approaches are preferred, as they enable thorough evacuation of all infected tissue, the recent trend is for an all-posterior global reconstruction, especially in the thoracic and lumbar spine. Irrespective of the approach used, it is mandatory that the tissue should be sent to the lab for a histopathology evaluation, culture sensitivity, and GeneXpert study.
Anterior Approach
The anterior approach provides direct access to the disease pathology and is ideal for debriding and reconstructing the defect. The anterior approach to the thoracic spine includes the anterolateral extrapleural approach and the transpleural anterior approach popularized by Hodgson et al. The anterior approach involves debridement of the tuberculous focus with removal of the diseased vertebrae, posterior longitudinal ligament (PLL), and adjacent disk spaces until bleeding healthy bone is reached, followed by performing an anterior fusion using a rib graft or a tricortical iliac crest graft. MRC trials have conclusively shown that the Hong Kong operation produced faster bony fusion, less kyphotic deformity, and decreased disease recurrence. The addition of anterior fixation devices has helped to enhance stability, minimize graft displacement, prevent loss of kyphosis, and facilitate early mobilization. In cases with large defects spanning over two or three vertebral bodies without instrumentation, increased risks of graft slippage, fracture, absorption, or subsidence of graft have been noted. Thus, in such a scenario, posterior stabilization is required to prevent complications. 15 , 16 The anterior procedure has limitations due to associated lung scarring secondary to old or active pulmonary tuberculosis, as well as such potential disadvantages as cage migration, major vessel injury, displacement of the screws, and injury to the viscera. Concomitant osteoporosis associated with infection renders the vertebrae structurally weak, and multiple segment fixation is technically difficult.
The current indication for anterior procedure is pauci-level disease with kyphosis of less than 30 to 40 degrees, which often entails less deformity and less instability. However, in TB of the subaxial cervical spine, the anterior approach remains the standard of care ( Fig. 10.1 ).
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