INTRODUCTION — Joint pain and swelling are common manifestations of many musculoskeletal and rheumatologic diseases, as well as a wide range of nonrheumatic conditions. The differential diagnosis of childhood joint pain and swelling is large and includes both benign and serious conditions. The assessment of a child with joint pain and/or swelling should be conducted with some urgency, especially for those conditions with potentially serious consequences .
The evaluation of a child with joint pain or swelling is reviewed here. Although there is overlap among the causes of limping, hip pain, and joint swelling and pain, the causes and approaches to assessing a child with limp and/or hip pain are discussed separately. (See "Evaluation of limp in children" and "Overview of the causes of limp in children" and "Approach to hip pain in childhood".)
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of childhood joint pain or swelling is broad, ranging from benign to serious conditions, some of which can have devastating consequences (eg, septic arthritis and neoplastic conditions) (table 1). The categories of possible disease that may present with joint pain and/or swelling are included in the following mnemonic, ARTHRITIS:
●Avascular necrosis and epiphyseal disorders – (See "Approach to hip pain in childhood", section on 'Legg-Calvé-Perthes and secondary avascular necrosis' and "Evaluation and management of slipped capital femoral epiphysis (SCFE)", section on 'Osteonecrosis'.)
●Reactive and postinfectious arthritis – (See "Acute rheumatic fever: Clinical manifestations and diagnosis".)
●Trauma – Accidental and nonaccidental, including hypermobility associated with microtrauma and hemarthrosis with vascular and other congenital malformations .
●Hematologic disorders – Leukemia, bleeding diatheses, and hemoglobinopathies.
●Rickets, metabolic and endocrine disorders – (See "Overview of rickets in children".)
●Infection – Septic arthritis and osteomyelitis; adjacent soft-tissue infections including pyomyositis, abscess, and discitis; and other types of infections, such as Lyme arthritis and parvovirus-associated arthritis. (See "Bacterial arthritis: Clinical features and diagnosis in infants and children", section on 'Clinical features' and "Musculoskeletal manifestations of Lyme disease" and "Clinical manifestations and diagnosis of parvovirus B19 infection" and "Hematogenous osteomyelitis in children: Clinical features and complications", section on 'Clinical features'.)
●Tumors – Musculoskeletal neoplasia including nonmalignant tumors, such as osteoid osteoma, bone cyst, and pigmented villonodular synovitis, and malignant tumors, such as osteosarcoma, lymphoma, and neuroblastoma. (See "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)
●Idiopathic pain syndromes – These range from growing pains/benign nocturnal limb pains to complex regional pain syndrome (CRPS) type 1 and fibromyalgia. (See "Fibromyalgia in children and adolescents: Clinical manifestations and diagnosis" and "Complex regional pain syndrome in children".)
●Systemic rheumatic diseases – (See "Kawasaki disease: Clinical features and diagnosis" and "Childhood-onset systemic lupus erythematosus (SLE): Clinical manifestations and diagnosis" and "Chronic nonbacterial osteomyelitis (CNO)/chronic recurrent multifocal osteomyelitis (CRMO)".)
Note that the group of diseases incorporated under the grouping of juvenile idiopathic arthritis (JIA) does not appear on this differential diagnosis list. The diagnosis of JIA requires the exclusion of all of the above diagnoses.
INITIAL EVALUATION — A thorough history and detailed physical examination are the initial steps in determining the diagnosis of a child with joint pain and/or swelling. In particular, signs and symptoms that are cause for concern (ie, red flags or danger signs that suggest an underlying serious condition) should be sought.
Worrisome findings — There are certain signs and symptoms in the child who presents with joint pain and/or swelling that may indicate the presence of a more serious condition requiring urgent medical attention (table 2). These findings are typically uncovered during the initial history (see 'History' below) and physical exam. (See 'Physical examination' below.)
History — The history needs to differentiate between benign and pathologic conditions, especially those that require urgent medical attention, and helps provide a focus for the physical examination and diagnostic studies.
The important elements of the history include (table 3):
●Presence of fever.
●Pain characterization, including the site, number of joints involved, and the severity, frequency, duration, and pattern of pain. The characterization of swelling is also important and includes many of the same elements as those for pain, as well as the presence of associated findings of warmth and discoloration.
●Presence of precipitating factors, such as a history of trauma .
●Review of systems focusing on history of rash, weight loss, abdominal pain, and ocular abnormalities. Dietary deficiencies are rarely associated with periarticular or joint swelling .
●Other medical conditions associated with arthritis or arthralgias. These include celiac disease; inflammatory bowel disease; chronic lung or cardiac disease with hypoxia; uveitis; psoriasis; sickle cell disease; chronic inflammatory diseases (systemic lupus erythematosus [SLE], scleroderma, dermatomyositis, vasculitis, and juvenile idiopathic arthritis [JIA]); malignancy, including recurrence and osteonecrosis posttreatment (eg, leukemia); and cystic fibrosis.
●Family history. It is important to ask about the presence of psoriasis, hypermobility syndromes, inflammatory bowel disease, spondyloarthropathies, uveitis, and/or bony dysplasias in close relatives as these conditions have a genetic basis and may be associated with arthritis in the child. The likelihood that joint pain is due to an autoimmune condition is increased if a family member has suffered from an autoimmune disease and/or immune deficiency syndrome. This likelihood further increases if family members on both maternal and paternal sides are affected. The health and medical history of the patient's siblings may also be informative.
Fever — The presence of fever narrows the differential diagnosis significantly. If there is a history of fever, it is important to ascertain the timing and pattern of fever and the height of elevated temperature.
Fever may precede or present at the same time as joint symptoms in children whose disease is due to bacterial infection. High fever (temperature greater than 38°C) in a patient with monoarticular disease is typical of a bacterial infection of the joint or bone. However, subacute or partially treated infection may not be accompanied by significant fever. Fever also might have been present during an antecedent illness that preceded the development of reactive arthritis. (See 'Antecedent infection' below and "Reactive arthritis".)
Fever is also associated with noninfectious diseases including JIA, Kawasaki disease, vasculitis, and SLE. In some conditions, the pattern of fever is an important clue to the diagnosis, as demonstrated in the following examples:
●Systemic JIA is associated with a quotidian fever pattern: A daily spike of high fever often occurs in the afternoon or evening, with a return to normal or even subnormal temperature between fevers, typically in the early morning. (See "Systemic juvenile idiopathic arthritis: Clinical manifestations and diagnosis", section on 'Fever'.)
●Periodic fever syndromes, such as familial Mediterranean fever, have a characteristic pattern of irregular, intermittent episodes of fever. They last for a few days or longer, resolve spontaneously, and give way to weeks of normal temperature. During the febrile episodes, patients may have joint pain and swelling. (See "The autoinflammatory diseases: An overview".)
●The fever in patients with SLE has a gradual onset and is typically low grade and intermittent if present. (See "Childhood-onset systemic lupus erythematosus (SLE): Clinical manifestations and diagnosis".)
Pain, swelling, and stiffness characterization — Pain and swelling are characterized by their location, severity, frequency, duration, and factors that either exacerbate or relieve the finding (table 3). Joint stiffness is also a common feature but, like pain, is subjective and may be difficult to quantify, especially in children.
The following questions help to characterize the child's joint pain and swelling:
●How severe is the pain, swelling, or stiffness?
●Where is the location(s) of the pain, stiffness, or swelling?
●How many and which joints are involved?
●When and for how long have the joint(s) been painful, stiff, or swollen?
●How quickly did the pain, swelling, or stiffness appear?
●What makes the pain, swelling, or stiffness better or worse?
Severity — Although the severity or intensity of pain or stiffness should be assessed, one must be careful not to equate severity of pain or stiffness with severity of illness, because the perception of pain is subjective. However, pain severe enough to cause the child to refuse to put any weight on the affected limb is a "red flag" for serious illness, such as bacterial infection of the joint or bone (eg, septic arthritis and/or osteomyelitis) or malignancy (eg, leukemia and osteosarcoma). In contrast, JIA, Legg-Calvé-Perthes disease, slipped capital femoral epiphysis, Osgood-Schlatter disease, and transient synovitis are often associated with limping, but the pain is generally not severe enough for a child to refuse to bear weight. (See "Evaluation of limp in children".)
Young children and infants may have difficulty articulating the presence of pain and may not complain of joint pain even when there are obvious signs of joint inflammation and swelling . In cases that involve the lower extremities, the young child may manifest pain as a refusal to walk or walking with a limp, and, in those that involve the upper extremities, the patient may limit the movement and use of the involved arm.
In an adolescent who complains of excruciating pain often accompanied by inability to walk but does not seem to be particularly bothered by the problem ("la belle indifference"), a pain disorder such as complex regional pain syndrome (CRPS) type 1 or fibromyalgia may be the likely diagnosis. (See "Complex regional pain syndrome in children" and "Fibromyalgia in children and adolescents: Clinical manifestations and diagnosis".)
Pain that wakes a child in the middle of the night is generally severe and is a useful diagnostic clue as it is more commonly seen in patients with bony pain due to benign tumors, such as osteoid osteoma, or malignancies, such as leukemia. Although other benign conditions such as growing pains also occur typically at night, these children are always entirely well during the day. (See "Growing pains".)
Significant joint symptoms are likely to interfere with daily activities, such as walking long distances, participating in sports or physical education, and playing musical instruments. Involvement of the small joints of the hand may interfere with writing, buttoning clothes, and opening jars and bottles.
Location and number of involved joints — Determining the site(s) of the pain/swelling is important to develop a rational list of differential diagnoses and to direct subsequent evaluation and treatment. Involvement of a single joint is more concerning for an acute process and warrants more urgent evaluation than involvement of multiple joints.
It may be challenging to have children localize pain accurately, especially younger children. Children should be asked to tell or to point to the painful area(s). For the nonverbal child, family members are asked what led them to think that the child has a joint problem and whether they noted any unusual warmth or swelling of the joint(s).
There is overlap between causes of monoarticular and polyarticular pain and swelling (table 1). However, it is important to determine the number of involved joints because infection is a relatively common cause of acute pain and swelling in a single joint that can result in cartilage destruction within a few days if not treated. As a result, patients with monoarticular involvement need to be assessed urgently to ensure that therapy can be initiated as quickly as possible in those suspected of having a bacterial infection as the cause of their symptoms.
●Single joint involvement – Bacterial infections (eg, septic arthritis and osteomyelitis, adjacent soft-tissue infections such as abscess and pyomyositis, or part of more generalized infections such as parvovirus) and significant trauma (eg, fracture or hemarthroses) are important causes of pain in a single joint that must be considered without delay, as discussed above. Other common causes of monoarticular pain and/or swelling include osteonecrosis (ie, Legg-Calvé-Perthes disease), oligoarticular JIA, Lyme arthritis, and some cases of reactive arthritis. Anterior knee pain is a common presenting complaint in children, particularly in Osgood–Schlatter disease, patellar tendinitis, and patellofemoral instability . Rarer causes include osteoid osteoma, tumors, tumor-like lesions , and pigmented villonodular synovitis.
●Multiple joint involvement – As bacterial infection and significant trauma rarely affect multiple joints, there is less urgency to evaluate a child with polyarticular involvement . Causes of multiple joint pain and/or swelling include acute and chronic rheumatic diseases, such as reactive arthritis, viral arthritis, SLE, JIA, and inflammatory bowel disease-associated arthritis.
Frequency, duration, and pattern — Pain and swelling can be characterized based upon their frequency, duration, and pattern:
●Persistent, intermittent, and migratory pain/swelling – Persistent pain is characteristic of inflammation of the joint space commonly seen in patients with arthritis that is due to infection or a rheumatologic disorder or bony pain due to a neoplastic process.
Intermittent pain, particularly associated with activity, is more likely due to a mechanical problem (eg, patellofemoral pain, meniscal or ligamentous injuries of the knee, or rotator cuff impingement disorder in the shoulder). In addition, recurrent pain and swelling of one or two large joints followed by spontaneous resolution, particularly in the knees, is characteristic of Lyme arthritis.
Migratory joint pain is pain that lasts for several days in one or more joints and then completely resolves while other, previously unaffected joints become painful. It can be seen in patients with acute rheumatic fever (ARF) or poststreptococcal reactive arthritis, immunoglobulin A (IgA) vasculitis (Henoch-Schönlein purpura), and childhood leukemia or lymphoma. (See "Acute rheumatic fever: Clinical manifestations and diagnosis" and "IgA vasculitis (Henoch-Schönlein purpura): Clinical manifestations and diagnosis" and "Overview of the clinical presentation and diagnosis of acute lymphoblastic leukemia/lymphoma in children".)
●Time of day – Diurnal variation is an important distinguishing feature of many different causes of joint pain that aids in identifying the underlying diagnosis. Joint pain due to arthritis, such as JIA, is usually worse at the beginning of the day and improves throughout the day with movement and activity. In contrast, pain due to trauma or mechanical causes (eg, hypermobility, torn meniscus, patellofemoral pain, or Legg-Calvé-Perthes disease) is usually mild or nonexistent in the morning and worsens with activity or may only occur after increased physical activity. Growing pains typically occur in a well child, with pain that may affect the joint usually beginning at the end of the day and into the middle of the night, but not during the daytime . Although bone tumors can also cause nocturnal pain, the child also has pain during the day when a tumor is present. (See "Approach to hip pain in childhood", section on 'Legg-Calvé-Perthes and secondary avascular necrosis' and "Growing pains" and "Clinical presentation, staging, and prognostic factors of Ewing sarcoma" and "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)
●Acuity of onset – Rapid onset of findings within one or two days is often associated with septic arthritis, osteomyelitis, ARF, and vasculitis (such as IgA vasculitis), whereas many of the other causes of childhood joint pain and swelling are more insidious.
Other joint symptoms — The presence of a warm or red joint indicates inflammation of the joint (arthritis). These findings increase the concern for an infectious or inflammatory cause for joint pain and swelling. Locking or "giving way" of the joint are suggestive of a mechanical joint disorder.
Precipitating factors — The following factors may be associated with the initiation and/or worsening of joint symptoms. Their presence may be helpful in determining the possible cause of joint symptoms.
Antecedent trauma — Trauma may be the direct cause of joint pain, as with fractures or ligamentous injuries, or indirect, as with some cases of osteomyelitis. Judging the degree of trauma and determining the temporal relation between the trauma and the child's presentation are important in deciding whether trauma can be the cause or a contributing factor to a child's joint symptoms. In a significant traumatic injury, the precipitating event is usually associated with the immediate onset of pain, swelling, and sometimes bruising. In some cases, however, an episode of minor trauma may simply bring to attention a preexisting, but as yet undiagnosed and unrelated, condition.
Antecedent infection — Recent infections, especially with enteric pathogens (Salmonella, Shigella, Yersinia, and Campylobacter), viruses (eg, parvovirus B19 and varicella), Group A Streptococcus, and immunization (eg, rubella immunization), may be associated with reactive arthritis, a common cause of acute arthritis in children . As an example, the arthritis of ARF, a sequel of a group A streptococcal pharyngeal infection, typically occurs two weeks after the precipitating infection. (See "Acute rheumatic fever: Clinical manifestations and diagnosis".)
Reactive arthritis is broadly defined as an arthritis that develops soon after or during an infection elsewhere in the body but in which the microorganisms cannot be recovered from the joints. In the most restrictive definition, reactive arthritis has been used to refer to the triad of postinfectious arthritis, urethritis, and conjunctivitis, formerly called Reiter syndrome. (See "Reactive arthritis".)
Inactivity — Joint pain or stiffness that is worsened by periods of inactivity (called articular or inactivity gelling) is typical of chronic inflammatory arthritis, such as seen in some cases of JIA or SLE. An important question to ask is whether the child appears stiff in the morning with gradual resolution or improvement during the day's activity. Some parents/caregivers will volunteer that their child "looks like an old man" after getting up in the morning. Very young children may simply be irritable upon awakening and ask to be carried until they feel better. Affected children may have similar complaints/findings later in the day after a nap, a period of inactivity (such as a long car ride), or even sitting at a desk in class.
Increased physical activity — Children with mechanical causes of joint pain, such as hypermobility syndrome, patellofemoral pain, tarsal coalition (an abnormal connection between two tarsal bones) leading to foot pain, osteochondrosis, and spondylolisthesis, will often have pain that is significantly worse or only occurs after increased physical activity. Growing pains are also often reported to be more frequent after an active day. Repetitive stress injuries including tenosynovial disorders and fractures may occur in athletes. (See "Clinical manifestations and diagnosis of hypermobile Ehlers-Danlos syndrome and hypermobility spectrum disorder" and "Approach to chronic knee pain or injury in children or skeletally immature adolescents", section on 'Patellofemoral pain' and "Growing pains" and "Overview of the causes of limp in children", section on 'Osteochondrosis'.)
Review of systems — A thorough review of systems is critical as it can detect the presence of other symptoms and organ system involvement that may aid in the identification of the correct diagnosis. Clinical features, such as rash and other abnormalities in the skin, weight loss, abdominal pain, diarrhea, neurologic symptoms, and eye abnormalities, in combination with joint findings, suggest specific diseases based upon pattern recognition. Refer to the table for some examples (table 4).
Physical examination — Abnormalities detected by the physical examination are important clues to the diagnosis and help differentiate severe conditions requiring urgent medical intervention from more benign disorders (table 4).
In addition to a thorough general examination, a complete musculoskeletal examination includes:
●General appearance including measurement of growth parameters and vital signs.
●Special attention to the heart, lung, skin, and eyes since these organ systems are often affected in children with joint pain or swelling. In many cases, abnormalities of these organs may suggest an underlying etiology.
●Screen of the entire musculoskeletal system with a focused examination of the painful or swollen joint(s). Discovery of affected joints in previously unnoticed locations is not uncommon and may change the differential diagnosis. Referred pain is common in children; therefore, detailed examination of joints proximal and distal to the painful area should be included.
●Evaluation of motor strength (both proximal and distal) since neuromuscular conditions and inflammatory myopathies may be accompanied by joint symptoms.
Performing a meticulous pediatric musculoskeletal examination, especially in young children, requires a patient and persistent approach. It may even take more than one session to complete if the child is fractious. Without a thorough and systematic examination, however, subtle signs of critical importance to the diagnosis of the condition may be missed.
General appearance — A general inspection of the patient should determine whether the child is ill or well appearing. Height and weight measurements are compared with reference ranges and prior values. A change in the patient's growth curve or recent weight loss may be indicative of a serious or chronic disorder, such as systemic or polyarticular JIA, SLE, inflammatory bowel disease, celiac disease, or a malignancy (eg, leukemia ).
Vital signs include determination of blood pressure, which may be elevated in SLE or a primary vasculitis, and temperature. (See 'Fever' above.)
Musculoskeletal screening — The Pediatric Gait Arms Legs Spine (pGALS) examination is a simple screen for musculoskeletal abnormalities that can be performed in minutes (figure 1A and figure 1B and figure 1C and figure 1D) [12,13]. It is a screen that uses simple physical maneuvers, including observation of the gait, to assess for musculoskeletal abnormalities.
Focused joint examination — If an affected joint is extremely painful, its assessment should be reserved until the end to encourage cooperation with the rest of the evaluation.
The joint examination begins with inspection and proceeds to palpation and estimation of active and passive range of motion (ROM) (table 5).
Inspection — Observation is the first step in joint examination. If the joint pain location is asymmetrical or worse on one side than the other, compare both extremities, looking for differences in size and shape. Does the child hold an affected joint in a particular position of comfort? If a joint appears bigger than the corresponding contralateral articulation, further assessment will need to determine if joint effusion, synovial thickening, edema of the soft tissue overlying the joint, bony overgrowth, or some combination of these abnormalities has led to the increase in joint size. (See 'Palpation' below.)
Even if only a single joint is painful, the entire extremity should be examined to detect the presence of muscle atrophy, discrepancies of length, and/or generalized asymmetry. There are two commonly used clinical methods for measuring an apparent leg length discrepancy. The most accurate is to correct any pelvic tilt (observed from behind) by asking the child to stand with the foot of the shorter leg on an object of measurable height, such as a book, magazine, or even a specifically fashioned wooden block (a "lift"). Alternatively, each leg length can be compared after careful measurement from the anterior superior iliac spine to the medial malleolus, although this method is subject to considerable observer error.
The skin overlying the joint should be inspected for evidence of scars, bruises, and discoloration, which could be caused by a rash or inflammation.
Palpation — The first step is to assess any differences in the temperature of the skin overlying the affected joint. Increased warmth of the affected joint compared with the unaffected side can indicate inflammation due to infection or rheumatologic disorder. Extremities affected by CRPS type 1 can be either cooler or warmer than the unaffected side.
Palpation includes assessment for the presence and location of tenderness. Joint tenderness may be secondary to disorders of the bone, such as osteomyelitis, bone tumor, other causes of periostitis, or Osgood-Schlatter disease; synovial disease, such as arthritis; or abnormalities of the ligaments, tendons, and menisci. Palpation of the "entheses" (points of insertion of ligament, tendon, or joint capsule into bone) is of particular importance in determining the subtype of JIA (usually associated with enthesitis related arthritis or spondyloarthritis) and occasionally in other musculoskeletal and rheumatic diseases. Inflammation at these points of insertion is referred to as "enthesitis." Patients with CRPS type 1 usually have severe pain (allodynia) even with light stroking of the skin and complaints of tenderness with only minimal palpation or movement of the affected limb. (See "Complex regional pain syndrome in children", section on 'Pain'.)
If osteomyelitis is suspected, a careful palpation of the bone should be performed, and it should start away from the painful area and move towards it slowly. In a febrile child, severe pain in a localized area of bone ("point tenderness") is indicative of possible osteomyelitis. In a nonfebrile child, there is a wide differential diagnosis for bone point tenderness, including fracture, periostitis, benign or malignant neoplasia, and enthesitis. Subacute osteomyelitis is also possible in the afebrile child [14,15].
If swelling is present, palpation may help determine the nature of the enlargement. A cystic or fluctuant quality to the swelling suggests a fluid collection that may be indicative of a joint effusion, ganglion, meniscal cyst, bursal swelling, or abscess. A doughy or rubbery consistency suggests synovial thickening, whereas a hard, bony feel may indicate osseous overgrowth (eg, bone tumor or exostosis). (See "Nonmalignant bone lesions in children and adolescents", section on 'Examination'.)
Range of motion — ROM is an important part of the examination of a child with joint pain; however, if there is severe pain, particularly if there is a history of trauma and/or an obvious deformity, it is prudent to splint the involved joint and proceed to obtain radiographs to rule out a fracture or dislocation.
In the absence of severe pain, deformity, and/or a history of significant trauma, joint function is assessed with the following questions in mind:
●Is the ROM limited and, if so, to what degree? While most joints are limited in movement to flexion and extension, a few joints move in other planes, resulting in a greater ROM. These include the hips, shoulders, spine, wrists, and ankles. Active and passive ROM should be noted in abduction and with internal and external rotation of the hips and shoulders. A particularly valuable technique is to assess the degree of relaxed passive extension of the knees by raising both legs using the feet while the patient is supine and asking the patient to relax. The knees should have up to 10 degrees of recurvatum (hyperextension), and any asymmetry may indicate a subtle but significant loss of joint range.
Of note, one of the biggest mistakes that nonspecialists make when testing passive ROM is not pushing the joint to the limits of its ROM. Frequently in arthritis and other inflammatory conditions, there may be very subtle abnormalities that are missed when this is not done. As an example, in the knee, where loss of the normal few degrees of "relaxed passive extension" may be the only indication of knee pathology, a few degrees of motion may be the sole distinguishing feature between an arthritic joint and a normal one. To demonstrate this finding, while the child lies supine and relaxed with the legs extended, the feet are gently lifted off the bed by the examiner (as described in the preceding paragraph). If there is asymmetry of the expected 5 to 10 degrees hyperextension of the knees, pathology is generally found in the side that has "lost" relaxed passive extension.
●Is there excessive joint mobility ? Excessive mobility of the joint, which may be associated with joint pain, can be seen in benign hypermobility syndrome, which may be associated with increased musculoskeletal pain, and in pathologic joint laxity syndromes, such as Ehlers-Danlos or Marfan syndrome. (See "Clinical manifestations and diagnosis of hypermobile Ehlers-Danlos syndrome and hypermobility spectrum disorder" and "Genetics, clinical features, and diagnosis of Marfan syndrome and related disorders".)
●Is there pain with motion? If palpation and movement of the painful joint do not reproduce or exacerbate the pain, then referred pain should be suspected. As an example, knee pain may arise from a problem at the hip. If the hip and knee are normal on examination, consider an even more proximal site, such as the spine or retroperitoneum. For example, pyomyositis of the psoas (psoas abscess) typically presents with hip pain and flexion deformity .
●Is muscle strength normal? Muscle weakness, especially proximal weakness, may be an indication of myopathy, such as dermatomyositis or muscular dystrophy. The inflammatory myopathies in particular may be associated with joint symptoms, as well as muscle pain and weakness.
Specific joints — There are separate topics that review the pediatric evaluation of pain and/or injury of specific joints:
●Foot and ankle (see "Foot and ankle pain in the active child or skeletally immature adolescent: Evaluation")
●Back and spine (see "Back pain in children and adolescents: Evaluation")
REFERRAL — If the cause of a child's complaints remains elusive despite a comprehensive history and physical exam or if a disease or disorder requiring a specialist's expertise is discovered or suspected, referral to a pediatric rheumatologist or orthopedist is often a more efficient approach than performing numerous imaging and laboratory studies.
DIAGNOSTIC STUDIES — The addition of selective imaging and laboratory testing to a complete and thorough history and physical examination may help to establish the cause of joint abnormalities. Diagnostic studies should be done judiciously and chosen on the basis of likely diagnoses . In fact, most rheumatologic disorders affecting children are diagnosed based upon the history and physical examination, and imaging and laboratory studies are used to confirm or grade the pathology. Some of the most common systemic rheumatic diseases of children, such as juvenile idiopathic arthritis (JIA), may have few or no associated laboratory abnormalities. Diagnostic studies may help to exclude other conditions or support one's clinical impression, but rarely do they reveal a previously unsuspected diagnosis. A particular danger for the inexperienced clinician is finding and dealing with irrelevant or inconsequential "abnormalities" as a result of performing an overenthusiastic battery of investigations.
Joint aspiration — Joint aspiration and examination of the synovial fluid should be performed in any child with clinical features suggestive of septic arthritis (table 6) to either make the diagnosis or rule it out. Acute onset of fever with joint pain, swelling, and limited range of motion (ROM) in a single joint of the lower extremity is the classic presentation for bacterial arthritis. However, the presentation varies depending upon the age of the child, the site of infection, and the causative organism. As examples, the classical signs of sepsis may be missing in a child with tuberculous arthritis, an indolent condition that usually presents as monoarthritis, and with Kingella kingae infection, which is typically insidious, indolent, and with low-grade or no fever . (See "Bone and joint tuberculosis", section on 'Infectious' and "Bacterial arthritis: Clinical features and diagnosis in infants and children", section on 'Clinical features'.)
Joint aspiration is not necessary for most children with joint swelling and pain who lack features of sepsis (ie, fever, ill appearance, refusal to bear weight or use an extremity), since this investigation rarely adds useful information in this group of children. This is unlike the situation in adults, in whom other illnesses, such as gout, make arthrocentesis a more important diagnostic tool. In addition, the procedure is probably more painful and traumatic to a pediatric patient.
If it is necessary, older children usually can tolerate joint aspiration with the use of local anesthetics. Younger children and those requiring aspiration of a shoulder or hip may require procedural sedation or general anesthesia. Hip joint aspiration should be performed with ultrasonographic guidance by someone skilled in this procedure. (See "Joint aspiration or injection in children: Indications, technique, and complications".)
The following testing to assess the presence of septic arthritis is performed routinely on synovial fluid, although Gram stain and culture are undoubtedly the most useful:
●Cell count and differential – High white cell count is indicative of an inflammatory process such as JIA or septic arthritis.
●Microbiology (aerobic and anaerobic bacterial cultures) including mycobacterial stains and cultures.
●Polymerase chain reaction testing of unusual organisms such as K. kingae.
Examination of the joint fluid for crystals is rarely informative in children. Gouty arthritis is very rare before puberty, even in children with Lesch-Nyhan syndrome (hypoxanthine-guanine phosphoribosyltransferase deficiency) .
Imaging — Imaging is required for the investigation of virtually all musculoskeletal conditions. The primary imaging modality used, however, is evolving rapidly to reflect improvements in availability, technology, and experience in interpretation, especially for modalities such as magnetic resonance imaging (MRI) and ultrasound. Indications for these studies depend upon the diagnoses suspected and the joint(s) involved.
●Evaluation of conditions with presentations similar to JIA – Plain radiographs of the affected joint should almost universally be used, despite limitations in sensitivity. They have proved especially useful to identify the differential diagnoses of JIA, including fractures, periostitis, avascular necrosis, acro-osteolysis , hematologic malignancies, bone tumors, and bone dysplasias, and should be performed on every child in whom there is concern for one of these diseases. MRI has traditionally been reserved for instances when bone infection, traumatic joint injury, or tumor is of concern and computed tomography (CT) for fractures that are not evident on plain radiographs. However, there is increasing evidence that MRI is valuable for detecting pathology missed by plain radiographs and may have an important role in diagnosing undefined inflammatory conditions in children .
Decisions regarding more advanced imaging should be discussed with an experienced radiologist. Contrast-enhanced MRI and joint ultrasound scans to demonstrate joint effusions and synovitis are more commonly used than plain radiographs in the evaluation and management of JIA once the diagnosis is made. In cases of polyarticular JIA, the most severely affected joint(s) are typically imaged to monitor for evidence of chronic changes indicative of disease progression, such as cyst formation, cartilage thinning, or bony erosions.
Simultaneous plain radiographic imaging of the contralateral joint may be performed to allow for comparison of growth and development. Unilateral acceleration may be a sign of chronic inflammation associated with longstanding arthritis.
●Hip pain of unclear etiology – In patients with hip pain of unclear etiology, ultrasonography or MRI is particularly useful in detecting the presence or absence of a joint effusion, such as found in transient synovitis and septic arthritis, or a structural problem, such as avascular necrosis or slipped upper femoral epiphysis. Doppler flow ultrasound or vascular flow MRI may also prove useful in the early differential diagnosis of hip pain. An effusion associated with severe pain and/or fever suggests septic arthritis of the hip. (See 'Joint aspiration' above.)
●Suspected structural conditions (trauma, infections) – CT scans are generally reserved for evaluating possible structural bony conditions, such as traumatic bone and soft tissue injuries, back pain, tumors, and infections (osteomyelitis), and should be discussed with the appropriate radiologist prior to ordering the study. MRI may be useful in identifying the presence of infectious arthritis and especially osteomyelitis with bone and marrow involvement . However, inflammatory arthritis and septic arthritis without bone involvement may have similar MRI findings. Ultrasound evaluation is useful in specific musculoskeletal conditions such elbow trauma . Plain radiographs have limited sensitivity .
●Septic arthritis versus osteomyelitis – MRI scanning is recommended for the evaluation for musculoskeletal sepsis [25,26]. Technetium bone scans can be helpful in differentiating septic arthritis from osteomyelitis if MRI is not available. Osteomyelitis typically presents with isolated bone pain and fever, while septic arthritis presents with severe joint pain, highly restricted range of joint movement, and swelling as well as fever. However, osteomyelitis is occasionally associated with a sterile "sympathetic" effusion of the adjacent joint. The two conditions may coexist, particularly in joints where the metaphysis is within the joint capsule (such as the ankle in prepubertal children). Other conditions, such as pyomyositis and possibly noninfectious osteomyelitis (chronic recurrent multifocal osteomyelitis/chronic nonbacterial osteomyelitis [CRMO/CNO]), may be identified by MRI [21,27,28].
●Detection of skeletal tumors or trauma in patients with localized bone pain and no clear etiology – Plain radiographs are favored as first-line imaging in patients with localized joint pain and no concern for infection who may have unsuspected skeletal trauma or a tumor, such as osteoid osteoma, which may present with localized bone pain, especially at night. MRI is typically reserved for persistent symptoms. However, imaging is seldom as useful as the examination of an experienced practitioner. Bone scans, which primarily detect abnormal tracer uptake by osteoblasts, are no longer recommended as a primary imaging modality for musculoskeletal symptoms. Thus, referral to a pediatric rheumatologist or orthopedist prior to obtaining a bone scan in these patients is advised. (See "Nonmalignant bone lesions in children and adolescents", section on 'Radiologic evaluation' and "Imaging techniques for evaluation of the painful joint", section on 'Bone scan'.)
Laboratory testing — The following laboratory tests should be obtained in any child with acute or chronic joint pain without an immediately obvious cause or in whom one of the specific diagnoses listed for each laboratory test is suspected (table 1 and table 4):
●Complete blood count and differential to detect abnormalities of blood cell lines that may be associated with systemic lupus erythematosus (SLE), systemic JIA, bacterial and viral infections, and leukemia [29-32].
●Acute-phase reactants (erythrocyte sedimentation rate or C-reactive protein). When elevated, these relatively nonspecific markers of inflammation are suggestive of bacterial infection , rheumatic disease, or malignancy. However, children with inflammatory diseases, such as JIA, can have normal acute-phase reactants.
●Serum chemistries, especially liver and kidney function tests. Abnormal values may be indicative of a possible systemic disorder, such as SLE or vasculitis. Elevated levels of creatine kinase (CK) may be indicative of myositis. Of note, some biochemical tests may be higher in children than adults (eg, serum urate), although the relationship to disease in children (such as gout, which is rare in children) is unclear .
●Serum lactate dehydrogenase (LDH). Elevated levels may be indicative of the presence of malignant neoplasm [29-32,34].
●Urinalysis to detect urinary abnormalities that may be seen in some rheumatologic disorders such as SLE, vasculitis, and IgA vasculitis or to detect a urinary tract infection associated with septic arthritis in a younger child.
Further evaluation is dependent upon whether the joint symptoms are acute or chronic.
Acute joint pain — Acute joint pain, either as a solitary manifestation or when accompanied by systemic symptoms, may be directly or indirectly related to an infectious process. Thus, the following tests are indicated:
●Cultures of the throat, blood, stool, and/or urine in patients with localizing clinical findings and inflammation of multiple joints leading to suspicion for a reactive arthritis such as acute rheumatic fever (ARF)
●Antigen testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in children with multisystem inflammatory syndrome (MIS-C), including swelling of the hands and feet  (see "COVID-19: Multisystem inflammatory syndrome in children (MIS-C) clinical features, evaluation, and diagnosis", section on 'Testing for SARS-CoV-2')
●Serologic testing for Lyme disease for children who live in or have visited an endemic area since one of the most common late or chronic manifestations of Lyme disease is an acute pauciarthritis 
●Antistreptolysin-O (ASO) titer or similar studies looking for evidence of a recent streptococcal infection in a child suspected of having a reactive arthritis (eg, ARF or poststreptococcal reactive arthritis)
Chronic joint pain — Chronic joint pain is unlikely to be related to an infectious process, the primary exceptions being the arthritis of Lyme disease or tuberculosis.
The following tests are indicated in children with chronic joint pain and additional features that suggest specific diagnoses :
●Quantitative immunoglobulins to detect immune deficiencies in children with a history of unusually numerous or severe infections since immune deficiencies including hypogammaglobulinemia may be associated with a variety of autoimmune manifestations . Elevated levels of immunoglobulins similarly may be indicative of an autoimmune condition . (See "Autoimmunity in patients with inborn errors of immunity/primary immunodeficiency" and "Approach to the child with recurrent infections" and "Laboratory evaluation of the immune system".)
●Serologic testing for Lyme disease for children who live in or have visited an endemic area.
●Antinuclear antibody (ANA) testing is not a sensitive or specific enough test to use for general screening purposes. It is rarely helpful in the initial diagnosis of musculoskeletal symptoms and is usually reserved for the pediatric rheumatology team investigating a child suspected of having a multisystem inflammatory disease such as SLE. Higher ANA titers are more commonly seen in children with autoimmune disease [40,41]. Most children with JIA have negative autoantibody tests, and many healthy children have low titers of ANA not associated with pathology. Rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPA) are markers for potentially more severe disease and poor outcome in JIA but should only be performed in patients with an established diagnosis of JIA.
●Human leukocyte antigen (HLA) B27 testing is not a sensitive or specific enough test to use for general screening purposes. Its use is reserved for children already under the care of a pediatric rheumatology team. While the presence of this antigen is associated with an increased risk of enthesitis related arthritis, juvenile ankylosing spondylitis, psoriatic arthritis, arthritis associated with inflammatory bowel disease, and reactive arthritis, it is a poor general screening test. Approximately nine percent of patients from Asia, Europe, North America, and Latin America carry this gene, and almost all are healthy and never develop arthritis, while there are others (especially those from North Africa and the Middle East) who do not have HLA-B27 but still go on to develop ankylosing spondylitis and related conditions in association with different genetic markers .
SUMMARY AND RECOMMENDATIONS
●Differential diagnosis – The differential diagnosis for joint pain and swelling is broad, ranging from benign to serious conditions, some of which can have devastating consequences (table 1). (See 'Differential diagnosis' above.)
●Worrisome findings – A complete history may differentiate between benign and pathologic conditions, especially those that require immediate medical attention (table 2), and helps direct the physical examination and work-up. (See 'Initial evaluation' above and 'Worrisome findings' above.)
●History – The important elements of the history include characterization of the pain and/or swelling (ie, site, severity, frequency and duration of symptoms, and the number of joints involved) (table 3); presence of other joint findings (instability, warmth, and redness) and precipitating factors (antecedent infection or trauma and level of activity); review of other associated nonmusculoskeletal symptoms (eg, fever and rash) (table 4); and the presence of other medical conditions associated with arthritis (table 4). (See 'History' above.)
●Physical exam – Abnormalities detected by the physical examination may be important clues to the diagnosis and help differentiate severe conditions requiring urgent medical intervention from more benign disorders. A thorough physical examination and general inspection should be conducted, including measurement of growth parameters and vital signs, screening of the entire musculoskeletal system (figure 1A-D) as well as a focused examination of the affected joint(s) (table 5), and evaluation of motor strength to detect any neuromuscular conditions that may be accompanied by joint symptoms. (See 'Physical examination' above.)
●Diagnostic studies – Selective imaging and laboratory testing are directed by the history and physical examination. (See 'Diagnostic studies' above.)
●Referral – Referral to a pediatric rheumatologist or orthopedist is advised if the cause of joint pain or swelling remains elusive despite a comprehensive evaluation or if a disease or disorder requiring a specialist's expertise is discovered or suspected. (See 'Referral' above.)
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