Septic arthritis

Introduction to septic arthritis Intra-articular infection caused by purulent bacteria, called suppurative arthritis, is more common in children, often a complication of sepsis, but also due to surgical infection, joint traumatic infection, joint firearm injury. Intra-articular injection of drugs such as steroids is not easy to be sterilized. The most commonly affected parts are the knee and hip joints, followed by the elbow, shoulder and ankle joints. basic knowledge The proportion of illness: 0.003% Susceptible people: no specific population Mode of infection: non-infectious Complications: toxic shock syndrome sepsis

Cause of septic arthritis

Reduced body resistance (20%):

Suppurative arthritis is more common in children and the elderly because of their poor ability to resist bacteria, but also in patients with genetic defects or drugs that interfere with the body's defense mechanisms (such as glucocorticoids or immunosuppressants), chronic diseases. It is also complicated by septic arthritis, especially malignant tumors, chronic liver disease, diabetes and systemic lupus erythematosus. Patients with sickle cell disease tend to have arthritis and osteomyelitis of Salmonella, and Gram-positive and negative bacteria Infection, multiple myeloma is prone to pneumococcal infection, leukemia patients are prone to Gram-negative bacilli infection, chronic kidney disease is also a susceptible factor, but in kidney transplant patients, septic arthritis is rare.

Rheumatoid arthritis (18%):

It is an important susceptibility factor for septic arthritis. Most patients with septic arthritis have a long-term seropositive history. About 50% of patients with rheumatoid arthritis complicated with septic arthritis have been given oral or intra-articular injections. Glucocorticoids, and about 75% caused by Staphylococcus aureus, have poor therapeutic effects.

Intravenous medication is an important risk factor (8%):

Some infections are caused by Gram-negative bacilli, such as Pseudomonas aeruginosa, but in some parts, Staphylococcus aureus is common, often occurs in the ankle joint, sterno-lock joint and intervertebral joints, and catheter or hemodialysis is placed intravenously. It is also the same risk factor.

Iatrogenic septic arthritis (5%):

Joint cavity puncture, intra-articular injection of glucocorticoids or radiopharmaceuticals can cause septic arthritis.

(1) Causes of the disease

Joint synovial cells have the function of phagocytosis and clearance of invading bacteria, so not all patients with sepsis develop septic arthritis, but only under the following conditions:

Susceptibility factor

(1) Crystalline arthritis: gout patients and calcium pyrophosphate dihydrate (CPPD) crystallized arthritis are easily associated with septic arthritis, often a broad-spectrum infection, only 50% is Gram Positive bacteria, crystals in the synovial fluid, septic arthritis can reduce the pH of the synovial fluid, reduce the solubility of urate crystals, and proteolytic enzymes can also promote the exfoliation of cartilage crystals.

(2) joint degeneration: primary or secondary joint degeneration, are likely to cause septic arthritis.

(3) Severely traumatic joints and hemophilia patients are also prone factors: intra-articular hemorrhage with chronic synovitis, and destruction of the structure of bone and cartilage can become infected lesions, and the bloody synovial fluid extracted by puncture should be Conventional culture.

2. Common pathogens

Almost all pathogenic bacteria can cause septic arthritis, and non-specific bacteria that cause septic arthritis refer to almost all other pathogenic bacteria except for the specific bacteria such as Mycobacterium tuberculosis, pathogenic bacteria, and fungi. Or conditional pathogens, the most common is Staphylococcus aureus, accounting for more than 50%, followed by Streptococcus pyogenes, pneumococci, accounting for 15% to 20%, Pseudomonas aeruginosa and other Gram-negative bacilli, such as Escherichia coli, Salmonella cholera, Proteus, Haemophilus influenzae, Klebsiella, Anaerobic bacillus, Yersinia enterocolitica, Halophilic bacillus, Aeromonas and Titanium About 12%, penicillin-resistant staphylococci, such as Staphylococcus epidermidis, increased the number of cases of iatrogenic septic arthritis, and typhoid bacilli caused by septic arthritis.

Streptococcal septic arthritis usually originates from the blood-borne spread of the respiratory tract and skin. Gram-negative bacterial septic arthritis is often associated with urinary tract infections. In addition, approximately 10% of patients have typical infectious joints. Clinical manifestations of inflammation, but clinical evidence is difficult to obtain evidence of pathogens. About 19% of the infectious arthritis of unknown pathogens can be found by the special toxin test, and the pathogen of Clostridium genus is gonococcal. The most common foreign infectious arthritis is rare in China, but there is an increasing trend.

(two) pathogenesis

The synovial membrane is highly vascularized loose connective tissue. The inner surface is not lined with the basement membrane. The bacteria easily enter the joint with the blood flow through the synovial membrane. Therefore, sepsis is the most common cause of joint infection, and bacteria can also directly enter the joint. Joint infections occur during surgery, trauma, joint puncture, and drug injection, or by infection of the tissue near the joint or the spread of osteomyelitis.

Once the bacteria enter the joint, the synovial phagocytic cells and neutrophils begin to engulf the bacteria. However, this local defense mechanism can only eliminate Staphylococcus epidermidis in the joint, which is ineffective against Staphylococcus aureus. Synovial hyperplasia and agglomerated neutrophil infiltration occurred within 24 to 48 hours after injection of 103-105 Staphylococcus aureus. After 48 hours, chondrocyte necrosis, abscess and granulation tissue formation, synovial cells and hooliganism were observed. The granulocytes release protease, causing synovial membrane, cartilage and osteonecrosis. Protease degrades cartilage glycoprotein and cartilage destruction under the activation of synovial microzyme. Experiments show that the loss of chondroitin sulfate is earlier than collagen, Smith and Schurman will gold. Staphylococcus aureus was cultured with bone and found that Staphylococcus aureus produced a proteoglycan release factor, which increased the amount of proteoglycan released by cartilage within 48 hours by 3-4 times, thus confirming that the cartilage matrix was lost earlier in septic arthritis. The reason for the enzyme change, the inanimate bacteria have no effect on the release of proteoglycans, but there is evidence that the inanimate fine When present, synovitis and cartilage damage still progress, because the lipopolysaccharides of bacteria directly promote cartilage degradation release IL-1.

After the formation of the primary infection lesion, it usually takes several days for the blood to spread. During this period, the lymphocytes are activated to produce antibodies, and the antibody forms an immune complex with the bacteria or antigen fragments, which release histamine in the joint and produce chemotaxis. Factor, directly or indirectly promotes enzyme activation and phagocytosis. Therefore, the pathogenesis of septic arthritis can be divided into two stages: the inflammatory process produced by bacterial virulence factors and the aseptic inflammation produced by the patient's immune system. The virulence factors may exhibit different inflammatory symptoms in different patients; while the same patient may have different inflammatory manifestations at different times, due to the interaction of pathogenic bacteria or inactive antigens with the autoimmune system, the joints The sustained damage is not controlled by the infection, and the pathogen disappears and stops. Therefore, simply strengthening the early diagnosis and treatment of infectious arthritis does not reduce the disability rate of arthritis.

Synovitis occurs when bacteria enter the joint cavity, vital bacteria activate chondrocytes to release cartilage-degrading enzymes, synovial macrophages release metalloproteinases, neutrophils release elastase, destroy cartilage and bone, and granulation tissue resembles rheumatoid Arthritis, like vasospasm, affects articular cartilage to gain nutrients, erode cartilage and bone, and further damage joints.

The pathological process of inflammation can be divided into synovitis and arthritis. The former only affects the synovium, while the latter involves cartilage. It is actually a different stage of a disease course. According to the virulence of the bacteria, the reaction of the tissue and the time limit of infection. Different stages of inflammation have different joint exudates: 1 serous exudation period: synovial swelling, hyperemia, leukocyte infiltration, exudate is serous, at this time cartilage has not been destroyed, if it can control infection, cartilage matrix sugar The protein can be recovered, the joint function can be fully recovered, 2 serous fibrinous exudation period: the degree of synovitis is intensified, fibrin spots are formed on the synovial surface, the exudate is increased, the viscosity is thick, the cellular components are increased, and a large number of pus cells and fibrin The exudate covers the surface of the synovial membrane and the cartilage, and the intra-articular fiber adheres. Due to the synergistic action of the bacterial products, the glycoprotein composition changes, the mechanical pressure of the chondrocytes increases, the nutritional disorder, the ability to produce the matrix is lost, and the joint function after treatment is Different degrees of damage, 3 purulent exudation period: the most severe stage of inflammation, the synovial membrane is swollen, thickened, and begins to necrosis; Yellowish white pus; leukocyte autolysate destroys bone glial and residual glycoprotein; chondrocyte necrosis; synovial destruction, and invasion of bone; large granulation tissue formation in joint cavity; joint capsule and surrounding soft tissue infection, cellulite Inflammation and abscess formation, although after treatment, although it can control inflammation, joint function can not be completely restored, often with fibrous or bony rigidity, pathological dislocation and various joint deformities.

1. Pathways in which bacteria infect joints

Bacterial infection of the joints can be divided into hematogenous infections, direct contamination and surrounding infections extend to three types of joints.

(1) Hematogenous infection: Hematogenous infection refers to bacteria that enter the joint with the bloodstream through the synovial tissue, causing septic arthritis.

Bacteria are mainly derived from infectious lesions away from joints, such as bacterial contamination after skin damage, folliculitis, carbuncles, cellulitis, sputum, erysipelas, lymphadenitis, sepsis; respiratory tract, digestive tract, teeth, tonsils , genitourinary and other parts of the infection; intestinal typhoid, flu, scarlet fever and other acute infectious diseases; thrombophlebitis, cardiovascular implants, intravenous catheters, hemodialysis, and even common venipuncture, drug injection, infusion, etc. It can make bacteria directly enter the blood. The synovial membrane of the joint is a highly vascularized loose connective tissue. The inner surface of the joint is not covered with the basement membrane. The bacteria easily enter the joint with the blood passing through the synovial membrane.

Hematogenous infections occur mostly in susceptible joints. Susceptible persons mainly include infants, children, elderly and infirm; patients with genetic defects or drugs that interfere with the body's defense mechanisms, such as glucocorticoids, immunosuppressants; chronic Patients with diseases are also prone to septic arthritis, especially diabetes, chronic liver disease, malignant tumors, systemic lupus erythematosus, sickle cell disease, etc.; blood diseases that are resistant to bacterial decline, such as leukemia, myeloma patients, although chronic kidney disease It is a predisposing factor, and long-term use of immunosuppressive agents may be required after kidney transplantation, but septic arthritis rarely occurs in such patients for unknown reasons.

Joints with diseased joints are prone to purulent infections. For example, rheumatoid arthritis is easy to be infected, and 75% is caused by Staphylococcus aureus. Half of them have been orally and intra-articularly injected with glucocorticoids, which may be the cause of susceptibility. One of them, when gout combined with purulent infection, will lower the pH of the joint fluid and reduce the solubility of urate crystals. The proteolytic enzyme can promote the detachment of crystals on the cartilage and increase the intra-articular crystallization, primary or secondary to summer. Degenerative changes in the joints of the joints, and also easily lead to septic arthritis, severe joint trauma, hemophilic arthritis, blood accumulation in the joints, can become infected lesions, joint puncture fluid for such patients, Routine examination and training should be carried out to avoid missed diagnosis.

(2) Direct pollution: This infection pathway means that bacteria directly enter the joints in vitro and cause septic arthritis. This pathway is more common in joint open wounds, bacteria directly contaminate joints, and debridement is not timely or incomplete. The increase in accidents such as traffic accidents, mechanical injuries, etc., this type of septic arthritis has an increasing trend, in addition, septic arthritis has also increased due to medical behavior, such as joint puncture, joint closure treatment, intra-articular cavity Injection of drugs, especially intra-articular injection of prednisolone or glucocorticoid drugs such as Baosong; interventional or intra-articular surgery with arthroscopy; external fixation with percutaneous intra-articular fracture; artificial joint replacement Etc., these invasive examinations and treatments have increased the number of cases of exogenous articular purulent infections.

(3) Peripheral infection extends to the joint: This infection pathway refers to purulent infections around the joints, such as osteomyelitis, tendon, tendon sheath, synovial septic infection, cellulitis, deep abscess, etc., directly eroding the joint, Causes septic arthritis.

Osteomyelitis extends to the joints, causing joint infections in two ways: one is osteomyelitis in the joint bones, such as osteonecrosis of the femoral head and neck of infants and young children, which will develop into septic arthritis when inflammation cannot be effectively controlled; One case is osteoporosis of the metaphysis. When the inflammation breaks through the protection of the tarsal plate and the joint capsule to the joint, entering the joint, it will merge with septic arthritis, but the second situation does not necessarily occur. The metaphyseal osteomyelitis can cause joints. Sterile inflammatory exudation, joint effusion, misdiagnosis of osteomyelitis as septic arthritis at this time, in the treatment of osteomyelitis during joint puncture or surgery, care should be taken to avoid introducing inflammation into the joints, actively treating osteomyelitis, Prevent osteomyelitis from spreading to the joints.

The pus of septic arthritis can penetrate the joint capsule, cause cellulitis and abscess around the joint, and the abscess ruptures to form the sinus. It should be noted that: Do not misdiagnose the simple cellulitis and deep abscess around the joint as having occurred. Suppurative arthritis, which causes infection to be brought into the joint during treatment, releases interleukin-1, and causes synovial inflammation and cartilage destruction to continue to progress.

Septic arthritis prevention

The precautionary principle is early diagnosis, timely and correct treatment, preservation of life, preservation of joint function as much as possible, controlled joints and exercise function, and early initiation of muscle contraction exercise after local inflammation subsides. If there is no adverse reaction, automatic movement can be started to prevent Joint adhesions help to restore joint function, but attention should be paid to local inflammation.

Septic arthritis complications Complications toxic shock syndrome sepsis

The disease often occurs in the knee joint. The patient often places the knee joint in a semi-bend position, which relaxes the joint capsule to relieve the tension. For example, long-term flexion, joint flexion contracture will occur, joint pain will occur, protective muscles Hey, the patient is also at risk of concurrent sepsis. In severe cases, the lesion can be concealed. If the condition is delayed, metastatic lung abscess and toxic shock occur later.

Symptoms of septic arthritis Common symptoms High fever, loss of appetite, chills, joint swelling, joint pain, chills, aversion, severe pain, radiation pain, weakness

The patient may have other infected lesions, or a recent history of trauma, rapid onset, general malaise, loss of appetite, high fever, aversion to cold, body temperature of 38.5 ~ 40 ° C, sweating, rapid pulse, mostly single joint disease, Local joint pain, redness, increased skin temperature, tenderness in joints, increased pain during activity, muscle tension, limbs can not be weight-bearing, affected joints with spastic flexion, advanced joint deformity, pathological dislocation, sinus or joint rigidity Such sequelae, shallower joints such as knees, elbows, ankle joints, etc., local redness, swelling, tenderness, joint effusion is more obvious; deep joints such as hip joints, because of thick muscles around, early skin is not common To the obvious redness, but the local soft tissue is often swollen, the joint is in flexion and extension, abduction, external rotation, the joint capsule is looser to relieve pain, and there is often radioactive pain along the inner side of the thigh to the inside of the knee, shoulder joint purulence When infected, the affected limb is often in a semi-outer position and the shoulder is swollen.

Systemic symptoms

Mainly manifested as acute onset, chills, chills, high fever, general discomfort, loss of appetite and other systemic toxemia symptoms, bloodline infections may have the corresponding symptoms and signs of the primary lesion, but sometimes the primary lesion is not clear, directly People with joint infection caused by pollution generally have joint damage, history of joint puncture or joint surgery, peripheral infections extend to the joints, and lesions of tissue infection around the joints.

2. Local symptoms

Generally, it is a single joint disease, and the weight-bearing joint is easily affected, especially in the hip and knee joints. The second is the ankle, elbow, wrist, shoulder joint, small joints of the hand and foot. The clinical manifestations are severe pain in the affected joints and obvious joint activities. Restricted, mostly half-buckling passive position, refused to touch, if it is a baby patient or even a child who is afraid of the doctor touching and approaching the bed, the superficial joints have redness, swelling, heat, tenderness, and deep joint involvement. There is swelling, but red, heat is not obvious.

3. Atypical performance

Infants and young children, elderly debilitated patients and patients with immunosuppressive drugs and glucocorticoids, when the joint purulent infection occurs, the systemic and local symptoms may not be significant, but the joint damage is not slightly lighter, and the existing joints are complicated with suppuration. Sexual infection, suppurative inflammation symptoms, can be confused with the original joint disease caused by swelling, pain, dyskinesia and other symptoms, the ankle joints and other deep joint infection, clinical symptoms are easily concealed, in case In the case of the above-mentioned atypical septic arthritis, attention should be paid to distinguishing the subtle changes caused by suppurative infections. Through detailed examination, early diagnosis should be made to avoid delay in treatment and lead to severe joint destruction and loss of exercise.

Examination of septic arthritis

Laboratory inspection

1. As with general suppurative infections, 90% of patients with septic arthritis have a significant increase in the total number of white blood cells and neutrophils, but white blood cells are normal and cannot exclude purulent infections, especially in frail patients, ESR, C Both the reactive protein and serum precursor of amyloid protein AA (SAA) are elevated. Measurement of 1-acid glycoprotein in serum in response to concanavalin A may reflect infection, joints in patients with lupus erythematosus When infected, 1-acid glycoprotein increased significantly, synovial fluid was purulent, white blood cells were more than 50×109/L, even up to 200×109/L, 90% were neutrophils, and Gram staining can be found. Bacteria, 85% of synovial culture is positive, but lower than purulent osteomyelitis. When culture is negative, other special tests should be performed, such as checking the bacterial metabolites in synovial fluid. Generally, the results can be obtained within 4 hours, and the results are detected by immunoelectrophoresis. The bacterial antigen in the synovial fluid, even if the bacteria have been killed, the antigen is still positive. The lactic acid test helps to identify purulent or non-suppurative arthritis, and must be used for aerobic and anaerobic blood cultures. Bacteria Except for the contamination of the specimen, in addition to the suspicious entrance to the infection, secretion culture is required, and the erythrocyte sedimentation rate can be increased. In patients with delayed suppurative infection due to artificial joint replacement, the increase in erythrocyte sedimentation rate may be more meaningful than the change of white blood cell count. .

2. Bacteriology examination

The pathogenic bacteria can be found in the joint or in the puncture fluid, and the diagnosis of septic arthritis can be established. Therefore, bacteriological examination is of great significance for the diagnosis and treatment of septic arthritis. The routine examination includes: 1 smear examination: joint Liquid smear for Gram staining, Swiss dyeing, acid-fast staining and fungal staining, looking for pathogenic bacteria under the microscope, 2 bacterial culture: joint fluid and biopsy tissue specimens for bacterial culture, and drug sensitivity test, 3 blood culture: blood Culture and joint fluid culture to obtain the same bacteria, can also identify the cause of disease, 4 primary lesion secretion culture: This also has a reference value in diagnosis.

3. Microbial product inspection

The convective immunoelectrophoresis method can be applied to various body fluids, such as the identification of soluble bacterial antigens in joint fluids, and can quantitatively measure antigens, and use polymerase chain reaction technology to detect bacterial nucleic acid fragments in joint fluid.

4. Antibody testing

Detection of antibodies against specific pathogens contributes to the diagnosis of infectious arthritis. In general, IgM antibodies are positive, often means recent infections, compared with osteomyelitis, anti-staphylococcal acid antibodies, in septic arthritis The patient's seroprevalence rate is high, which can also be used as a reference for diagnosis.

Film degree exam

X-ray inspection

There was no significant change in the early X-ray, but the previous lesions could be confirmed. The degree of functional recovery can be assessed. The X-ray of the contralateral joint can be taken. Some small lesions can be found on both sides. Regular review of X-rays can help monitor treatment. As a result, the X-ray showed loose bone under the cartilage, bone erosion of the proximal joint, cartilage destruction, narrow joint space, trabecular bone hyperplasia of the articular surface, expansion of the joint cavity of the hip joint, increased soft tissue shadow, closed hole The positive internal muscle sign is more conducive to the diagnosis, that is, the edge of the myocutaneous tendon in the obturator adjacent to the hip joint capsule is widened and curved, and the air characteristic of the X-ray is relatively rare. This phenomenon is only in Clostridium perfringens. It can only be seen in the joints of the intervertebral space or septic arthritis of vertebral osteomyelitis produced by anaerobic bacteria and Gram-negative bacteria.

2. Arthrography

In addition to showing various structures within the joint, it can also show damage to the joint capsule and ligaments, often showing rupture of the rotator cuff and subluxation of the humeral head, as well as the location of the femoral head and its integrity and destruction. Intra-articular injection of contrast agent will not aggravate the infection, and will not interfere with the treatment of antibiotics. The sinus angiography can show the path of the sinus and the relationship with the joint, which can help the lesion removal surgery, and the contrast agent will not increase the damage of the infection. It does not increase the burden on the joints, but the joint fluid for staining and bacterial culture must be performed before the joint injection of the contrast agent.

3. CT examination

When the anatomical structure is complex (such as the spine) and the lesion is surrounded by bone tissue, the diagnostic value of CT examination is higher. However, in the neck or surrounding joints, the diagnostic value is small. CT can show bone destruction and cavity formation. , dead bones and paraspinal tissue abscesses, can also show deeper parts of the body, such as swelling and exudation of the ankle joint.

4. Magnetic resonance (MRI) examination

MRI can clearly and clearly distinguish and distinguish muscle, bone and soft tissue structures, and CT can hardly distinguish these structures. In addition, MRI can clearly show articular cartilage and children's growth cartilage, which can show the fibrous cartilage of the knee meniscus. A low-intensity structure that is significantly different from articular cartilage and clearly shows that the infection extends to the soft tissue adjacent to the joint, but MRI does not show CT and scan time for dead bones and calcifications. In addition, it has paramagnetic properties in vivo. Metals such as artificial joints, blood vessel clamps, pacemakers, etc., should not be examined by MRI.

5. Radionuclide scintillation

Scintillation with 99mTc and 67Ga citrate can show early infections, especially for deep joints such as the hip, shoulder and spine, but the positive results are not specific, some non-infectious inflammation, even joints Degenerative changes can also produce the same image, so it needs to be considered together with other data. For the specificity of bone and joint infection, the positive 67Ga citrate scintillation is more important than the positive 99mTc because 67Ga is concentrated in Protein and leukocyte exudation sites, and the absorption of 99mTc is more closely related to the increase of blood flow. In addition, 67Ga absorption is earlier in infected joints. Although this test is not specific, the abnormality of scanning is earlier than ordinary X-ray. The film is therefore an important aid to early diagnosis.

Diagnosis and differentiation of septic arthritis

diagnosis

Diagnosis is mainly based on medical history, clinical symptoms and signs. In patients with suspected blood-borne septic arthritis, blood and joint fluid bacterial culture and drug sensitivity test should be performed. X-ray examination does not help much in the early stage, only joint swelling is seen; There may be decalcification of the bone, joint space stenosis due to cartilage and bone destruction, joint bone or fiber toughness and deformity may occur in the late stage, and there is new bone hyperplasia, but less dead bone formation.

Differential diagnosis

Joint tuberculosis

The incidence is relatively slow, there is low fever, night sweats, rare high fever, local redness, acute inflammation is not obvious.

2. Rheumatoid arthritis

Often multiple, migratory, symmetrical joint swelling and pain, but also high fever, often accompanied by heart disease; joint extraction fluid clarification, no bacteria; no postoperative joint dysfunction.

3. Children with rheumatoid arthritis may have fever, but joint swelling and pain are multiple, often more than 3, and symmetry, some cases are single joint type, difficult to identify, rheumatoid factor for extract Determination, the positive rate is high.

4. Traumatic arthritis

No fever, withdrawal of liquid or bloody, less white blood cells.

5. Gout

Symptoms of the big toe and metatarsophalangeal joints are the most common. At night, there may be fever. According to the diseased part and blood uric acid, it can be identified. The sodium urate salt crystal is found in the joint extract, which has diagnostic value.

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