Neurological complications (paraplegia or quadriplegia) and spinal deformity especially kyphotic deformity are the most dreaded complications of tuberculosis of the spine.
The sequelae of these two complications affect the quality and span of life. Almost all tuberculosis of the spine, even if they are treated well, leave behind some amount of kyphosis in different segments of the spine. Persistent spinal deformity affects the biomechanics of all segments of the spine.
The advent of effective antituberculous chemotherapy has made uncomplicated spinal tuberculosis largely a medical disease. Attention has now turned to the problem of progressive deformity. In endemic regions, about 80% of patients with spinal involvement have some sort of detectable kyphosis at the time of presentation.
Patients treated conservatively have an average have of 15 degrees deformities and 3-5% develop deformity greater than 60 degrees.
Severe kyphosis is cosmetically and functionally disabling and can lead to late-onset paraplegia. Prevention of deformity should be an essential aspect of any treatment schedule in spinal tuberculosis as Correction of established deformity is difficult and hazardous, with a high complication rate.
Pathology of Kyphotic Deformity In Spinal Tuberculosis
In most of the cases, the tuberculous lesion starts as a paradisical inflammation. Gradually, as the disease progresses the vertebral endplates become structurally weak and intervertebral disc starts ballooning/herniating into the diseased vertebral body, visualized on x-ray as reduced disc space.
The vertebral body loses more anterior height than posterior as the line of weight transmission is anterior. The severity of kyphosis depends on the number of vertebral bodies affected, the severity of loss of anterior vertebral body height and segment of the spine affected.
A case of the dorsal spine or dorsolumbar spinal tuberculosis with three or more vertebral body affection is more likely to develop moderate to severe kyphotic deformity.
In the cervical and lumbar spine, the line of weight transmission is in the posterior half of vertebral bodies. Therefore, there is the first obliteration of natural cervical and/or lumbar lordosis and later on, kyphosis starts appearing.
In a usual scenario, in developing nations, about 95% patients show a clinically detectable kyphosis or reversal of normal lordosis, by the time patient seeks the consultation of a specialist.
Natural History of Kyphotic Deformity
Tuberculosis preferentially affects the anterior structures of the vertebral column in over 90% of cases. Although chemotherapy may inactivate the disease, vertebral collapse will continue until the healthy vertebral bodies in the region of the kyphosis meet anteriorly and consolidate.
In paradiscal lesions, the intervening discs are destroyed early, allowing the cancellous bone on either side to come into contact and achieve bony fusion, which is the hallmark of healing of spinal tuberculosis. When the disease is severe with the complete destruction of entire vertebral segments, the defect in the anterior column is too extensive for such a healing process to occur.
The severity of deformity depends on the extent of destruction, the age of the patient, and the level of the lesion.
The deformity progresses in two distinct phases
Phase I
The changes in the first 18 months during the period of activity of the disease.
Phase II
Changes that occurred after the disease was cured were termed Phase II or healed phase changes.
Adults had a lesser deformity at presentation, and lesser increase during Phase I, and virtually no change once disease cure,
Children had a higher deformity at presentation, a greater tendency for collapse during the active phase of the disease, and continued and variable progression even after the disease was cured and growth was completed
This could be due to
- Increased severity of destruction at presentation
- Increased flexibility of the spine in children
- Variable destruction of the growth plates interfering with future growth
- The suppressive effect of the mechanical forces of kyphosis
Types of Progression of Kyphosis
- Type 1
- Progression shows continued progress through the entire period of growth.
- Continuously after Phase I (Type 1 A)
- 3 to 6 years after the disease was cured (Type 1B).
- Type II
- Progression shows beneficial effects during growth with a decrease in deformity after healing of the disease.
- IIA – This can occur immediately after Phase 1
- IIB – after 3 to 6 years.
The Influence of the Level of Lesion
Patients with dorsal lesions have the greatest deformity at the time of presentation
Patients with dorsolumbar lesions have the worst prognosis because of a greater collapse during the active phase and a greater deterioration in children during the growth period. Patients with lumbar lesions have the best prognosis with the least deformity at presentation.
Behavior of Kyphosis in Adults
After the patient is put on chemotherapy, the kyphosis, if present, continues to grow despite being treated. This progression of kyphosis can be minimized by prescribing suitable braces. Patients treated nonoperatively have an average increase of 15 degrees in deformity.’Three to five percent end up with a deformity greater than 60 degrees.
If operated with surgical decompression and bone grafting, still the kyphosis may grow as the bone graft is most weak on the day it is implanted. Furthermore, graft slippage and breakage will give rise to the progression of kyphosis.
Once the osseous fusion has occurred, the kyphosis does not grow at an alarming rate in later life.
A lesion that heals with fibrous or fibro-osseous healing it may progress further.
Behavior of Kyphosis in Children
Due to the cartilaginous nature of vertebral bodies, the tubercular spine lesion causes more destruction. The kyphosis continues to increase with growth. The anterior growth potential of the vertebral body is either and unabated posterior growth may contribute to the increase in the kyphotic deformity.
During the growth spurt in a child
- 44% of cases show improvement in kyphosis
- 17% show no changes in kyphotic angle
- 39% of cases show the progression of kyphosis
- 10% will have an exponential progression of kyphosis to > 90°.
- The risk factors for the exponential increase are
- Age less than seven years at the time of disease
- Thoracolumbar involvement
- Loss of more than two vertebral bodies
- Presence of two or more spine at risk signs.
- Need strict observation and preventive surgery
Sequelae of Severe Kyphosis
In long-term kyphosis affects the biomechanics of the spine and body.
- The proximal and distal segments of the spine compensate by creating a reverse deformity
- Degenerative changes occur
- Back pain
- > 60° kyphosis
- Spinal cord changes occur due to repeated
- May develop clinical signs of upper motor neuron deficit
- Compensatory hyperlordosis proximally and distal to the healed lesion in the lumbodorsal region.
- Severe lumbar canal stenosis in prolonged follow-up
- Reduction in the capacity of the chest cavity and vital capacity
- Ventilatory failure
- Painful impingement of coastal margins over the iliac crest
Treatment of Kyphotic Deformity in Spinal Tuberculosis
Early diagnosis and treatment, preventive surgeries in patients who are likely to develop kyphosis and correction of angular kyphosis are mainstays of treatment.
Prevention of Deformity
If tubercular spine could be diagnosed in predestructive stage of disease and treated with chemotherapy, it may with no sequelae of kyphosis.
In patients who present late, the progression of kyphosis depends on the number of vertebral involvement, initial vertebral body loss and segment of the spine affected.
The kyphosis continues to increase on non-operative treatment and even after surgical decompression.
The radiological signs of the spine at risk are [These cases should undergo kyphosis correction.]
- Subluxation or dislocation of the facet joint at the apex of the kyphus
- Presence of retropulsion
- Translation of the vertebral column in the coronal plane
- Posterior toppling sign
- A line drawn along the anterior border of the distal healthy vertebra in an upward direction
- If that meets the upper half of the proximal healthy vertebra then it has chances of progressive kyphosis.
Kyphosis correction in an active disease
All kyphosis cases which report for the first time with moderate to severe kyphosis of 50° or more, may be taken up for kyphosis correction surgery.
MEthods of kyphosis correction
- Single stage transpedicular approach.
- Anterior decompression by posterior midline exposure through the pedicle of apex vertebra
- Posterior stabilization with two vertebrae on each side of the dorsal spine and one in the lumbar spine.
- Single or two-staged anterior decompression with bone grafting followed by correction of kyphosis and posterior instrumentation
- Single stage kyphosis correction by the extrapleural anterolateral approach.
Kyphosis correction in healed lesion
The hazard of deformity correction outweighs the gain hence it should not be carried out for cosmetic reasons only.
The patient should be warned about the risk of neural deterioration and life risk.
Corrective surgery for established deformity is difficult, has to be staged, and also is hazardous with a high complication rate. There also is a constant danger of paraplegia because of the need for meticulous debridement of the tissues all around the spinal cord before osteotomy. The patient must have prolonged postoperative immobilization in a halo-pelvic apparatus and a body cast until consolidation occurs.
References
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