Causes of joint pain

Pain in the affected joint (arthralgia) occurs as a result of irritation of nerve endings in its various structures, excluding articular cartilage, which has no nerve endings and vessels. Polyarthralgia is understood as the presence of pain in 5 or more joints.

Joint pain is usually associated with signs of inflammation of the joints, soft tissues and/or tendon attachment sites to the bone (enthesitis), and is less often biomechanical or neurogenic. However, in many cases of rheumatic diseases, pain is associated with several mechanisms simultaneously. For example, in osteoarthritis, pain often has a biomechanical, inflammatory and vascular nature and can be associated with psychoemotional disorders.

When interviewing a patient, the doctor needs to get answers to a number of very important questions: it is imperative to clarify the location of the pain, its irradiation, prevalence and depth, determine the nature of the pain (stabbing, cutting, aching, burning, pulsating, etc.). It is also determined how long the pain syndrome has existed, the frequency of pain, its rhythm during the day (including the presence of so-called light intervals, that is, periods when there is no pain), the intensity of the pain syndrome is specified, whether the pain is constant or increasing. The doctor tries to find out what the patient associates the appearance of pain in the joint with. Risk factors for the development of damage to the musculoskeletal system are most often an infectious disease suffered the day before (acute respiratory viral infections, salmonellosis, etc.), exacerbation of chronic foci of infection (chronic tonsillitis, sinusitis, etc.), overload or damage to the joint, the use of glucocorticoids (bone osteonecrosis is possible against the background of their use). The appearance of joint syndrome after an infectious disease or allergic reaction allows the doctor to suspect the inflammatory nature of the joint damage - arthritis. The presence in the anamnesis of information about constant trauma, excessive and prolonged physical loads on the musculoskeletal system in the absence of inflammation (for example, in athletes) rather indicates the degenerative-dystrophic nature of the pathological process. The connection of the pain syndrome with certain movements, such as, for example, climbing or descending stairs, is also clarified. Pain in the bones (ossalgia) and joints can be associated with overtraining during sports, with a change in weather conditions, or with some other reason.

The doctor should not forget about the so-called arthralgia of non-organic etiology.

Family history and information about the patient's heredity contribute to the correct diagnosis of diseases of the musculoskeletal system, which can be either hereditary (generalized exostosis syndrome of long tubular bones, metaphyseal dysplasia, generalized chondrodystrophies, Ehlers-Danlos syndrome, Marfan syndrome, etc.) or have a hereditary predisposition (for example, rheumatoid arthritis).

As for the algorithm for making a diagnosis for joint syndrome, here we can take as a basis such an important symptom as pain in the joint:

1. Constant joint pain, increasing after exercise, with morning stiffness is characteristic of a number of diseases, such as rheumatoid arthritis, reactive arthritis, psoriatic arthropathy, i.e. for a group of inflammatory diseases. But it should be noted that morning stiffness characterizes not only inflammatory diseases, but also metabolic-dystrophic ones, therefore it occurs, including in osteoarthrosis - primary and secondary.
2. Starting (mechanical) joint pain is more common in osteoarthrosis. Pain syndrome occurs with a large load on the joint, or at the beginning of the load, or as the physical load increases towards the end of the day.
3. Pain, rapidly increasing in the joints of the first finger, with rapidly progressing swelling, and an increase in temperature very often occur at the onset of a gout attack. Oddly enough, despite this seemingly simplest and most striking characteristic of the pain syndrome, gout, nevertheless, of all the pathological conditions accompanying the joint syndrome, is the worst to diagnose.
4. Constant joint pain localized in the spine, intense, burning, without changing intensity, is most characteristic of the paraneoplastic process.

Thus, chronic pain syndrome in joints includes a whole group of nosological forms, which is represented, first of all, by diseases of the musculoskeletal system. These include inflammatory, metabolic-dystrophic diseases of joints, secondary joint lesions, joint lesions in non-rheumatic diseases.

Inflammatory joint diseases include rheumatoid arthritis, a large group of reactive arthritis, psoriatic arthropathy, spondyloarthritis and gouty arthritis.

Metabolic-dystrophic diseases of the joints include osteoarthrosis (osteoarthritis), gout (primary and secondary), osteoporosis, chondrocarcinosis (chondrocarcinosis), and hydroxyapatite arthropathy.

Secondary joint lesions include post-traumatic arthrosis and arthritis, osteoarthrosis against the background of primary arthritis, paracancerous arthritis, metastatic lesions of the spine in diseases of the blood system, joint lesions in vitamin deficiencies, lung diseases, amyloidosis.

It was once believed that the presence of rheumatoid arthritis does not provide for the addition of a second disease related to the group of secondary osteoarthrosis. But now it is known that it really often accompanies inflammatory diseases of the joints, therefore it is included in the group of osteoarthrosis against the background of primary arthritis.

Secondary arthropathies in non-rheumatic diseases are caused by allergic diseases (serum sickness, drug sickness and other allergic conditions), metabolic disorders (amyloidosis, ochronosis, hyperlipidemia, hemochromatosis), congenital defects of connective tissue metabolism (Marfan syndrome, Eders-Danlos syndrome, mucopolysaccharidosis), paraneoplastic diseases, endocrine diseases (diabetes mellitus, acromegaly, hyperparathyroidism, hyperthyroidism, hypothyroidism), leukemia and a group of lymphoproliferative diseases. Joint syndrome in this list of diseases occurs in the form of inflammatory joint damage or in the form of metabolic-dystrophic diseases.

Each of the listed nosological forms has its own characteristics of the course, but they are united by one and the most important symptom complex, which is represented, first of all, by arthralgia. Arthralgia is necessarily present in each of these diseases.

Joint pain may mimic fibromyalgia. Fibromyalgia is a syndrome of chronic (lasting more than 3 months), non-inflammatory and non-autoimmune diffuse pain of unknown etiology with characteristic pain points revealed during physical examination. Patients often complain of morning stiffness, fatigue, manifestations of Raynaud's phenomenon and other subjective signs characteristic of the inflammatory process. Physical examination and laboratory data do not reveal signs of inflammation or degenerative processes in the joints, bones and soft tissues. Microtrauma and lack of muscle training, increased production of substance P, and the phenomenon of increased alpha ₂ -adrenergic receptors in muscles, finger vessels, lacrimal and salivary glands, which manifests itself as muscle pain due to relative ischemia, Raynaud's phenomenon, etc. are important in its development. Fatigue and weakness in fibromyalgia are caused not by circulating cytokines, but by sleep disorders (alpha-delta sleep). Fatigue and generalized pain in fibromyalgia are nonspecific symptoms and occur in many conditions.

Bruises, sprains, less often dislocations and fractures, especially in people who regularly play sports, can be accompanied by symptoms "masked" as a true joint syndrome. The cause is stretching and inflammation of the muscle-tendon structures. Overtraining during sports (football, athletics) causes the development of patellofemoral stress syndrome. This condition develops when the process of extension of a repeatedly injured knee joint is disrupted and is characterized by chronic pain syndrome. It is necessary to differentiate this pathology from chondromalacia of the patella.

Complaints of a "pop" in the joint area during a knee injury may be a sign of such a pathology as meniscus injury, anterior cruciate ligament injury, or patellar subluxation.

Differential diagnostics of arthralgia of organic and non-organic etiology

Organic causes	Functional disorders
The pain occurs both during the day and at night The pain occurs on weekends and during vacations The pain is so severe that the patient is forced to stop working The pain is localized in the joint One-sided pain The patient limps or refuses to walk History: signs of systemic disease including weight loss, fever, night sweats, skin rash, diarrhea	The pain occurs only at night The pain occurs mainly on weekdays The patient continues to lead a normal life. The pain is localized between the joints Bilateral pain The gait does not change Anamnestic data: in all respects a healthy patient, the anamnestic data may include minimal neurotic disorders

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