Hot and swollen joints: causes and examination algorithm

A hot and swollen joint is a clinical description of acute inflammation in or near a joint, characterized by pain, swelling, localized warmth, sometimes redness, and limited motion. In practice, this presentation most often corresponds to acute monoarthritis, that is, inflammation of a single joint, although some systemic diseases can also initially affect only one joint. This is why this complaint should not be assessed superficially: a similar external presentation can conceal both relatively benign causes and urgent conditions. [1]

The most dangerous cause is septic arthritis, which is an infection within the joint. Current guidelines emphasize that delays in diagnosis and treatment can quickly lead to cartilage destruction, damage to the underlying bone, persistent dysfunction, and even sepsis. Therefore, any acute, painful, hot, and swollen joint is considered with the understanding that "infection should be ruled out first, not last." [2]

However, a hot joint doesn't automatically indicate infection. This symptom is often caused by gout, calcium pyrophosphate crystal deposition disease, trauma, hemarthrosis, exacerbation of osteoarthritis, reactive arthritis, and the onset of chronic inflammatory joint diseases. The problem is that these conditions often overlap in terms of pain, redness, and swelling, and a clinical error in the first few hours can be especially costly. [3]

One practical characteristic is crucial for the initial examination: with a true intra-articular process, both active and passive motion are usually limited, whereas with periarticular conditions, such as bursitis or tendinitis, passive mobility may be better preserved. This criterion does not replace a full diagnosis, but it helps to distinguish between an "intra-joint problem" and "inflammation near the joint" early on. [4]

Another key point is that the absence of a fever is not reassuring. Current guidelines for septic arthritis clearly state that joint infection can occur without fever, especially in the elderly, immunocompromised patients, those receiving early antibiotics, and those with certain comorbidities. Therefore, relying solely on fever or elevated C-reactive protein is inappropriate. [5]

Table 1. Signs that a hot joint requires urgent evaluation

Sign	Why is this dangerous?
Acute 1 hot and painful joint without injury	Septic arthritis must be urgently ruled out.
Sharp pain with the slightest movement	Often occurs with intra-articular infection or severe crystalline arthritis
Prosthetic joint	Higher risk of periprosthetic infection and different treatment tactics
Immunosuppression, diabetes mellitus, rheumatoid arthritis	Increase the risk of septic arthritis
Recent surgery, joint injection, bacteremia, nearby skin infection	Increases the likelihood of infection
Fever, chills, confusion, severe weakness	Sepsis and rapid deterioration are possible.
Pain in the hip joint, sacroiliac region, sternoclavicular joint	These locations are often more difficult to evaluate clinically.

The table is compiled based on modern reviews and guidelines on septic arthritis and acute monoarthritis. [6]

Main causes and risk factors

The most common and most dangerous group of causes are infectious. In septic arthritis, the joint becomes infected hematogenously, that is, through the blood, or after an intervention, injury, bite, or adjacent soft tissue infection. In adults, the main pathogen remains Staphylococcus aureus, and among other common bacteria, streptococci are important; in the elderly, gram-negative bacteria also make up a significant proportion. The knee joint is most commonly affected, followed by the hip, shoulder, ankle, elbow, and wrist. [7]

The risk of septic arthritis is increased by age over 80, diabetes mellitus, rheumatoid arthritis, immunosuppressant therapy, recent joint surgery, the presence of a prosthesis, a contiguous skin infection, injection drug use, and bacteremia. A major pitfall in practice is that infection can also occur in a joint that has previously been affected by osteoarthritis or other arthritis, leading the physician to sometimes mistakenly attribute the infection to a "regular flare-up." [8]

The second very common group of causes is crystal-induced arthritis. Gout is caused by the deposition of monosodium urate crystals and typically presents with a rapid, often nocturnal, onset of pain, redness, and swelling, particularly in the first metatarsophalangeal joint, but also in the ankle, knee, elbow, and other joints. British guidelines recommend suspecting gout in the presence of sudden, severe pain, redness, and swelling, particularly in the area of the first metatarsophalangeal joint, but immediately stipulate that septic arthritis and pyrophosphate disease should be ruled out simultaneously. [9]

Calcium pyrophosphate crystal deposition disease, formerly often called pseudogout, is particularly common in older adults. It is closely associated with advancing age, prior joint trauma, osteoarthritis, and sometimes metabolic disorders, including hyperparathyroidism, hemochromatosis, hypomagnesemia, and hypophosphatasia. Clinically, it can present much like gout or septic arthritis, particularly when the knee, wrist, or ankle is affected.[10]

There are also non-crystalline, non-infectious causes: trauma, intra-articular fracture, meniscal tear, hemarthrosis due to anticoagulants or hemophilia, exacerbation of osteoarthritis, reactive arthritis, psoriatic arthritis, onset of rheumatoid arthritis, and Lyme disease in endemic regions. It is important for the physician to remember that even systemic inflammatory processes often initially appear as an isolated problem in one joint. [11]

Finally, there are conditions that mimic a "hot joint" but are actually localized outside the joint cavity. These primarily include bursitis, cellulitis, tendinitis, and other periarticular processes. This is why, during examination, it is so important to assess the depth of the effusion, the nature of pain with passive movement, and search for skin infection near the joint. [12]

Table 2. The most common causes of a hot and swollen joint

Cause	What is typical
Septic arthritis	Acute painful joint, severe limitation of motion, risk of systemic infection
Gout	Very rapid onset, severe pain, often in the 1st metatarsophalangeal joint, ankle or knee
Pyrophosphate disease	More often in older age, often the knee or wrist, can mimic an infection
Trauma or hemarthrosis	Association with trauma, anticoagulants, joint bleeding
Exacerbation of osteoarthritis	Pain and effusion, but usually fewer systemic signs of inflammation
Reactive or other inflammatory arthritis	There is often a history of infection, psoriasis, intestinal symptoms, uveitis, or other joint involvement
Bursitis, cellulite, tendinitis	Inflammation near the joint, not necessarily inside it

The table is compiled from reviews of acute monoarthritis, septic arthritis, gout and pyrophosphate disease. [13]

Table 3. How to distinguish an intra-articular process from a periarticular one

Sign	More often for intra-articular arthritis	More often for periarticular inflammation
Active movements	Limited	May be limited
Passive movements	Also limited	Often better preserved
Effusion	Often there is	It may not be
Pain with any small movement	More typical	Less typical
Localization of edema	Within the joint	More superficial or near the tendon, bursa
Example	Septic arthritis, gout, pyrophosphate arthritis	Bursitis, tendonitis, cellulite

The table is based on the clinical approach to acute monoarthritis in primary care. [14]

Diagnosis: What really needs to be done

Diagnosis begins with the correct clinical question: is it an infection, crystalline arthritis, trauma, or the onset of a systemic inflammatory disease. Initially, a medical history is collected, including the time of onset, rate of progression of pain, recent trauma, skin infection, fever, prosthesis, intra-articular injections, immunodeficiency, anticoagulants, previous gout, family history, and possible urogenital or intestinal infections. At this stage, the urgency and scope of the examination are determined. [15]

The key diagnostic test for suspected infectious or crystal-induced arthritis is joint aspiration, or arthrocentesis. Current guidelines for septic arthritis emphasize that, if clinically suspected, synovial fluid should be obtained as quickly as possible. An exception is patients with sepsis or septic shock, in which case systemic antibacterial therapy is initiated immediately according to the sepsis protocol. [16]

The synovial fluid is first examined for the pathogen, undergoing bacteriological examination, a white blood cell count with formula, and a search for crystals. If a synovial fluid infection is suspected, "just looking" is not enough: culture, Gram stain, cell count, and crystallography are required. An important modern rule is that crystals do not rule out septic arthritis, as infection and crystal-induced inflammation can coexist. [17]

Interpreting leukocytes in synovial fluid requires caution. For septic arthritis, a value of more than 50,000 cells per microliter is considered suspicious, but does not confirm the diagnosis. A value below 25,000 reduces the likelihood of infection, but does not rule it out. Therefore, any rigid formulas from old articles, where one digit supposedly "proves" or "excludes" a diagnosis, are considered erroneous in modern practice. [18]

Blood tests are helpful, but do not replace a biopsy. C-reactive protein, erythrocyte sedimentation rate, and complete blood count are useful as supportive information and for monitoring treatment response, but current guidelines clearly state that no single blood test is sensitive and specific enough to reliably confirm or exclude septic arthritis. If fever or bacteremia is suspected, at least two sets of blood cultures are obtained. [19]

Imaging techniques complement, but do not replace, clinical judgment. Radiography is essential as a baseline and for detecting fractures, osteoarthritis, osteomyelitis, chondrocalcinosis, and other structural changes. Ultrasound is particularly useful for detecting effusions and for guiding punctures of deep or hard-to-reach joints. Magnetic resonance imaging and computed tomography are helpful in difficult-to-locate areas, suspected abscesses, osteomyelitis, or axial lesions. [20]

If gout is suspected, British guidelines recommend measuring serum uric acid levels. A value of 360 micromol/L or higher supports a clinical diagnosis, but during an attack, the level may be normal. Therefore, if there is strong suspicion, the test should be repeated at least two weeks after the end of the attack. If the diagnosis remains unclear, a puncture with microscopy is recommended, and if aspiration is not possible, imaging studies, including ultrasound and dual-energy computed tomography, are recommended. [21]

Two factors are particularly important for pyrophosphate disease: detection of calcium pyrophosphate crystals in the synovial fluid and imaging. The current 2023 criteria of the American College of Rheumatology and the European League Against Rheumatism recognize the presence of calcium pyrophosphate crystals in the synovial fluid or crowned tooth syndrome as sufficient for classification. Additionally, radiography, ultrasound, and computed tomography play a significant role in clinical practice, especially in cases of axial involvement. [22]

Table 4. Practical algorithm for examining a hot joint

Step	What to do
1	Assess urgency: sepsis, instability, prosthesis, severe pain, immunosuppression
2	Determine whether this is an intra-articular or periarticular process
3	If septic or crystalline arthritis is suspected, perform arthrocentesis as soon as possible.
4	Send synovial fluid for culture, stain, cell count and crystals
5	Take blood tests, and if there is fever or suspected bacteremia, take blood cultures
6	Perform an X-ray, and if necessary, an ultrasound, magnetic resonance imaging, or computed tomography.
7	Don't rely solely on uric acid, C-reactive protein, or temperature

The table is compiled according to modern recommendations for septic arthritis, gout and acute monoarthritis. [23]

Table 5. How to interpret synovial fluid

Find	What does it mean?
Positive culture or identification of the pathogen	Confirms infectious arthritis
High leukocytosis in the synovial fluid	Supports infection or crystalline arthritis, but does not in itself make a diagnosis
More than 50,000 cells per microliter	Makes septic arthritis more likely, but does not automatically confirm it.
Less than 25,000 cells per microliter	Reduces the likelihood of infection, but does not eliminate it
Monourate crystals	Supports gout
Calcium pyrophosphate crystals	Supports pyrophosphate disease
Crystals in fluid when infection is suspected	Does not allow to exclude septic arthritis

The table is based on SANJO recommendations and crystal arthritis guidelines.[24]

Treatment, complications, prognosis and prevention

If septic arthritis is suspected, treatment is based on three pillars: rapid aspiration and microbiology, joint drainage, and antibiotic therapy. The SANJO guidelines recommend initiating empirical antibiotics after obtaining joint fluid and blood cultures, unless the patient is in a state of sepsis or septic shock. For large joints, arthroscopic debridement or surgical cleaning is more often required, as needle aspiration alone is often insufficient to reduce the bacterial load and intra-articular pressure. [25]

For empirical therapy in adults, Staphylococcus aureus and streptococci are initially treated, and the regimen is then refined based on microbiology results and the clinical context. The American Academy of Family Physicians notes that in many cases, after the initial phase, treatment may involve not only intravenous but also oral therapy, and the total duration is typically measured in weeks rather than days. Outcome depends not only on the antibiotic chosen but also on how quickly the joint is drained and how early treatment is initiated. [26]

In gout, treatment of an attack is focused on rapid inflammation relief. British guidelines recommend a nonsteroidal anti-inflammatory drug, colchicine, or a short course of oral glucocorticoid as first-line treatment, taking into account concomitant diseases and medications. If these options are contraindicated or ineffective, an injectable glucocorticoid can be considered, and cold applications can additionally reduce pain. An important practical point: high uric acid levels alone do not treat an attack, and urate-lowering strategies are discussed separately. [27]

Treatment for calcium pyrophosphate disease is also symptomatic, as there are currently no drugs that dissolve calcium pyrophosphate crystals. Current reviews indicate that nonsteroidal anti-inflammatory drugs, colchicine, and glucocorticoids are used for acute pyrophosphate arthritis; given the benefit-to-risk ratio, prednisolone may be a particularly convenient option for some older patients. For recurrent or chronic inflammation, prophylactic colchicine, hydroxychloroquine, methotrexate, and, in refractory cases, biologics are sometimes used, but the quality of evidence here is significantly weaker than for gout. [28]

If a hot joint is not caused by an infection or crystals, treatment depends on the underlying cause. In the case of hemarthrosis, consideration should be given to performing a puncture, discontinuing or adjusting anticoagulation, and ruling out intra-articular damage. During an exacerbation of osteoarthritis, unloading, pain relief, and identifying effusions are important. In the case of reactive arthritis or the onset of systemic inflammatory arthritis, the emphasis shifts to treating the underlying process and early referral to a rheumatologist. However, the general principle remains the same: until infection is ruled out, do not hastily administer glucocorticoids intra-articularly and attribute the diagnosis to "rheumatism" or "gout based on the analysis." [29]

Complications are primarily associated with missed or delayed infection: cartilage destruction, persistent limitation of mobility, osteomyelitis, sepsis, and death. The prognosis for gout and pyrophosphate disease is generally better if diagnosed correctly and early, but they can also seriously impair joint function and quality of life. Prevention includes control of gout risk factors, management of comorbidities, caution during intra-articular interventions, prompt treatment of skin infections, and avoidance of self-prescription of antibiotics or steroids before a puncture if infectious arthritis is suspected. [30]

Table 6. Treatment depending on the cause

Cause	Basic tactics
Septic arthritis	Urgent puncture, culture, blood cultures, antibiotics after collection of material, drainage or sanitation
Gout	Nonsteroidal anti-inflammatory drug, colchicine, or a short course of glucocorticoid
Pyrophosphate arthritis	Nonsteroidal anti-inflammatory drug, colchicine, glucocorticoid, sometimes therapy for relapses
Hemarthrosis	Assessment of trauma and anticoagulation, puncture as indicated, treatment of the cause
Exacerbation of osteoarthritis	Pain relief, unloading, assessment of effusion and mechanical causes
Reactive or other inflammatory arthritis	Confirmation of diagnosis and treatment of the underlying disease

The table is compiled based on recommendations for septic arthritis, gout, and modern reviews of pyrophosphate disease. [31]

FAQ

1. Is a hot joint always septic arthritis?
No. This can be a symptom of gout, pyrophosphate disease, trauma, hemarthrosis, bursitis, and inflammatory arthritis. However, septic arthritis is the most dangerous cause, so it is the first to be ruled out. [32]

2. Can infection be ruled out if there is no fever?
No. Current guidelines emphasize that septic arthritis can occur without fever, especially in elderly and immunocompromised patients. [33]

3. Is a C-reactive protein test and a complete blood count sufficient?
Not sufficient. These tests help assess inflammation, but they do not confirm or rule out septic arthritis. The main test is a synovial fluid analysis. [34]

4. Should antibiotics be started immediately if a joint infection is suspected?
If the patient is not septic, it is advisable to first obtain joint fluid and blood cultures and then start antibiotics. In sepsis, antibacterial therapy is started immediately. [35]

5. Can gout look as severe as an infection?
Yes. Gout can cause very severe pain, redness, and swelling, often with a nocturnal onset. This is why it cannot be reliably distinguished from an infection by eye alone. [36]

6. If crystals are found in the puncture, can infection be ruled out?
No. The presence of crystals does not rule out septic arthritis. Both processes can coexist in the same patient. [37]

7. Does a uric acid level confirm gout?
It supports, but does not alone resolve, the diagnosis. During an attack, the level may be normal, so if there is strong suspicion, it is repeated after the exacerbation subsides. [38]

8. When is pyrophosphate disease particularly likely?
More common in older people, especially when the knee or wrist is affected, due to osteoarthritis, previous injury, or certain metabolic disorders. [39]

9. What is the most important thing to remember at home before seeing a doctor? The following
should not be ignored: a combination of acute, hot joint with severe pain, inability to bear weight, fever, a prosthesis, immunosuppression, recent surgery, a bite, an injection into the joint, or a nearby skin infection. [40]

10. Is it possible to treat such a joint on your own with ointments and painkillers?
Until infection is ruled out, this is dangerous. Self-medication can blur the picture, delay the puncture, and worsen the outcome, especially in septic arthritis. [41]

Conclusion

A hot and swollen joint is not a diagnosis, but a clinical alarm signal. The doctor's most important task in the first few hours is not to "guess by appearance," but to quickly answer three questions: is there an infection, are there crystals, and is the inflammation truly located within the joint. The modern standard here is built around timely puncture, competent interpretation of synovial fluid, and early treatment of the underlying cause. [42]

In practice, the main principle can be formulated as follows: any acute, hot joint is considered potentially infectious until proven otherwise. This approach best reduces the risk of missing septic arthritis while simultaneously allowing for the rapid recognition of gout, pyrophosphate disease, trauma, or the onset of other arthritis. [43]