Musculoskeletal tuberculosis (Tuberculosis of bone and joints or popularly known as bone TB) is found more in children, adolescents, and young adults, than in the elderly.
In the spine, the usual involvement is vertebral bodies and intervertebral disks in the dorsolumbar regions. Other regions of involvement are the cervical vertebrae, craniovertebral junction, sacrum and sacroiliac joints may be involved. Ribs, pelvic bones, small bones of the and foot, long bones, sternoclavicular joint, sternum, and bursae are also known to get infected.
Sometimes, more than one sites may be affected by musculoskeletal TB in the same patients and are termed as multifocal skeletal tuberculosis.
Pathology and Spread of Tuberculosis
Mycobacterium tuberculosis is the most common causative organism. The infection in musculoskeletal organs is always secondary to another focus, usually in the lungs or in the mediastinal lymph nodes.
The organisms spread through the bloodstream and settle in the bone usually near the epiphyseal cartilage in proximity to the synovial membrane. As they proliferate they form what is called ‘tubercle’, the microscopic pathological lesion with central necrosis surrounded by epithelioid cells, giant cells, and mononuclear cells.
Two types of microscopic lesions of musculoskeletal tuberculosis are known
- Caseating exudative type – caseating necrosis and cold abscess formation
- Proliferating type – cellular proliferation with minimal caseation e.g the tuberculous granuloma
The type of lesion formed would depend on how does body deal with bacteria or the immunity of the person.
Infection in bone and synovial tissue is secondary. The initial infection occurs in the lung (human type) or the intestine (bovine type).
The initial response is by polymorphonuclear cells which get rapidly replaced by mononuclear cells (macrophages and monocytes). These phagocytose the bacilli, the latter breakdown, and the lipid is dispersed throughout the cytoplasm, the mononuclear being transformed into the epithelioid cell. This cell, characteristic of the tuberculous reaction, is large and pale with a large vesicular nucleus, abundant cytoplasm, indistinct margins, and processes that seem to pass between the cells, forming an epithelioid reticulum.
The characteristic Langhans’ giant cells, with their peripherally placed nuclei, are probably formed by the fusion of a number of epithelioid cells. Their function is to digest and remove dead tissue. They occur in other chronic inflammations (syphilis, actinomycosis).
After a week, lymphocytes appear and form a ring about the periphery of the lesion. These are one of the sources of gamma globulin, the immune bodies. This mass of newly formed cells constitutes the translucent nodule known as the tubercle. Several small tubercles may fuse to form a larger one. Caseation necrosis, which is a coagulation necrosis formed by the liberation of the protein fraction of bacilli, begins at the second week.
The homogeneous center stains red with eosin, surrounded by pale epithelioid cells with one or more giant cells and ringed by a zone of dark blue lymphocytes. The caseous material softens and liquefies.
The future course of the tubercle varies:
- It may resolve completely.
- Fibrous tissue may encircle the lesion, and lime salts may be deposited in the central caseous substance.
- Infection may spread throughout the tissue with the formation of many more tubercles.
- When infection is virulent or massive, there may develop an acute inflammatory reaction.
- Skeletal and articular involvement occur by dissemination through the bloodstream. Implantations occur both in bone and synovial membrane.
Typically, an active focus is set up in a metaphysic (in a child) or in an epiphysis (in an adult), where the acute exudative reaction may cause local necrosis until caseation occurs. The intense hyperemia causes marked decalcification locally, a characteristic well seen in x-rays. Granulation tissue about the site constitutes the fibroblastic healing response.
The periosteum may react to a superficial cortical lesion by producing new periosteal bone. The exudates may penetrate outward through the soft tissue to exit through the skin as a fistula chronically draining caseous material, particles of bone, and partially liquefied, thick, grayish yellow substance.
Cartilage is resistant to tuberculous destruction. Therefore, the epiphyseal plate is not destroyed. However, the granulation tissue may invade the area of calcified cartilage and interfere with longitudinal growth.
The infected synovium may be swollen and congested with granulation tissue. The articular surface is studded with many translucent tubercles, and deposits of fibrin cover many areas. The joint fluid usually is moderately increased and clear. It contains rice bodies, which are small accumulations of fibrin, and pieces of articular cartilage.
Caseation necrosis of the synovium and the capsule is rare.
Abscesses in the soft tissues have a tendency to migrate along fascial planes and erupt at a distance from the original focus. This is seen best in the spine, where the infective material may enter the fascia enveloping the psoas muscle and erupt at the groin. [cold abscess]
The areas of predilection occur in the following order of frequency are the spine, hip, knee, ankle, tarsus, shoulder, and elbow.
The onset of the disease is insidious. The patient might have constitutional symptoms like low-grade fever, anorexia, and weight loss. If they usually precede local symptoms and signs such as pain, tenderness, and swelling of the affected part.
However, the absence of constitutional symptoms does not rule out the possibility of the disease as it is common for patients to present without any constitutional symptoms.
There might be muscle spasms and discharging sinuses. Discharging sinus is a hallmark of chronic infection.
The routine laboratory test may be inconclusive. A usual finding is a lymphocytosis, raised ESR and raised CRP. Mantoux test in a nonendemic region may indicate the presence of tubercular infection.
Aspiration of the joint fluid or cold abscess can be investigated to find the mycobacteria. Polymerase chain reaction is a very good test for this purpose. Acid-fast bacilli stain is rarely positive in musculoskeletal tuberculosis as the bacterial load is not much per se.
Xray of the affected part may show the destruction of the involved bone or joint. However, it is inconclusive in soft tissue affections or in cases where the disease is in the early stage and is yet to bring bony changes.
Computerized tomography and magnetic resonance imaging are helpful in defining the disease further. While CT is good for bony lesions, MRI defines soft tissues better.
MRI helps to catch the disease early before it is evident on x-rays. It may also pick the hidden lesions or lesions like granuloma in the spine. It also helps in assessing complications, assessing response to treatment, provides better delineation of vertebral lesions with adjoining soft tissue involvement and nerve compressions.
MRI is used more frequently than CT.
The biopsy may be needed in cases where a diagnosis could not be established otherwise. This can be done under the image guidance or by surgery. The material subjected to smear examination, PCR and culture, and histopathological examination.
Management of Musculoskeletal Tuberculosis
In medicine, early detection of the disease and treatment are key factors in the successful management of the disease. If osteoarticular tuberculosis is diagnosed and treated at an early stage, the large majority of patients are expected to achieve healing with near-normal function.
The goals of treatment are
- Contain and eradicate the infection
- Relieve pain
- Preserve and restore bone and joint function
- Preserve and restore neurological function (In cases of the spine)
The mainstay of treatment is multidrug antitubercular
- Traction or splint [whenever required]
- Active or assisted exercises of the involved joint throughout the period of healing
An initial period of rest is to be followed by supervised gradual mobilization.
Initial treatment is given under supervision and patient is hospitalized for that. This is done to take care of the affected part by traction or splint and to train the patient for modified self-care at home.
For example in cases of spinal tuberculosis with neurological deficit patient is advised rest for 12-16 weeks. The patient needs to stay in bed throughout that time. No sitting or standing is allowed. The patient is allowed and encouraged in bed turning. This needs to be monitored and his response to therapy needs to be monitored failing which he might undergo surgery. This would definitely require hospitalization.
Thus an initial period of hospitalization enables supervised treatment. Continuation treatment can be on a domiciliary basis. There had been various regimes of antitubercular drugs in vogue. But with the introduction of DOTS by WHO, most of the physicians follow it.
Operative intervention is required when the patient is not responding to an adequate trial of chemotherapy. Surgery aims at removing the diseased tissue and decreasing the bacterial load so as the response to drug increases.
Surgery may also be done if the therapeutic outcome is not satisfactory or an unacceptable deformity is left after the treatment. A loss of motion so severe that it hampers the activity of daily living is also an indication for surgery, if feasible.
It is also required for an unstable spine.
Most of the patients can be cured with first-line drugs of tuberculosis but few might develop multidrug resistance and require second-line drugs. Drugs are discussed separately.
Adequate nutritional support is also essential, as in all forms of tuberculosis.