What Causes Joint Pain?

Patient Presentation
A 9-year-old male came to clinic with a history of intermittent knee pain for several weeks. His mother was concerned because he usually was a happy active child who did not complain but had been complaining of knee pain around dinner time 2-3 days/week for a few weeks. She would tell him to lay down and rest and it usually would go away but a few times she had given him some acetaminophen but wasn’t sure if it was helpful. He would be normal in the morning and throughout the day. It never occurred while he was sleeping. She said she had not noticed any swelling, redness, or any problems with the joints themselves. They denied any trauma but he was a very active child and could have hurt himself when the parent wasn’t around. The past medical history was negative. The family history was negative for any malignancy, or rheumatological, or orthopaedic problems. There was hyperthyroidism in a maternal aunt and heart disease on both sides of the family. The review of systems was negative with both of them denying any rashes, diarrhea, fever, cough, recent illness, weight loss, night sweats, or problems with bruising or bleeding.

The pertinent physical exam showed a healthy boy with normal growth parameters with normal growth velocities since his last visit. His skin examination showed several bruises and scrapes on his knees and lower extremities and he was tanned. His general physical examination was normal. His musculoskeletal examination showed full range of motion in the hips, knees, ankles, forefoot and toes. There was no swelling or redness, nor pain elicited on movement or palpation. He had a normal neurological examination and did not have changes in muscle bulk and strength and tone were normal. Other joints showed full range of motion including his temporomandibular joint.

The diagnosis of of benign nocturnal leg pain was made. The physician explained the natural history to the parent and child but also recommended to monitor the patient and reviewed symptoms to contact him about immediately such as fever, rashes, increased bruising or bleeding, etc.

Discussion
Musculoskeletal problems are common problems in pediatric practice with up to 15% of acute care visits being for this problem.

Joint pain is a common concern for families but the differential diagnosis is extensive and needs thoughtful consideration. History is a key to discerning the potential diagnosis but also in guiding the physical examination and laboratory examination. Family history especially for systemic diseases should be considered. On physical examination all joints should be examined include sacroiliac and temporomandibular joints.

• Is this arthritis or arthralgia? Distinction between inflammatory and non-inflammatory joints is important. Joints with inflammation are painful or stiff after rest and improve with activity. Joints without inflammation are better after rest and get worse with more activity.
• What is the age of patient? The differential diagnosis will change with age. For example back pain is more likely to be due to overexertion or trauma in an adolescent. But true back pain in a child under age 6 may be due to malignancy or more serious problem.
• How long has the pain been occurring? Acute is generally < 6 weeks, and chronic is more.
• Single or multiple locations and are the locations consistent or migratory? This helps with classifying juvenile idiopathic arthritis, but also helps with other diagnoses as foreign body, trauma and septic joints are usually single joints. See the differential diagnosis below for additional information about various patterns.
• What is the joint involvement pattern? Small symmetric joints may point to JIA but large, migratory joints with fever may be rheumatic arthritis. See the differential diagnosis below for additional information about various patterns.
• Is there an enthesis involved? Soft tissue problems are common and insertion points can commonly be affected. “Entheses are sites of attachment of tendon and ligaments to bone and are typically inflammed in enthesitis-related arthritis.” Example of common sites for this are the patellar ligament on tibial tuberosity, Achilles tendon on the calcaneus or plantar fascia insertion on the metatarsal heads. See the differential diagnosis below for additional information about various patterns.
• Does the child have objective evidence of a “hot joint” or systemic illness such as redness, swelling, fever, weakness, weight loss, oral/genital ulcers, red eyes, rashes, nail changes, difficulty swallowing, shortness of breath, or diarrhea? Is there true night pain that awakens the patient? If so, then evaluation for malignancies, infections and rheumatological diseases should be carried out.

  
  Red flags for potentially more serious disease includes:

  • Pain, persistent and localized
  • Pain and/or stiffness after inactivity such as after resting or in the morning
  • Pain at night not relieved by analgesics
  • Joint swelling, redness or stiffness
  • Muscle weakness
  • Weight loss or decelerating growth parameters
  • Fever, malaise
  • Trauma history
  • Abnormal laboratory testing
• Is the problem affecting activities of daily living and functioning? Is the problem just bothersome or the child limps or refuses to walk or cannot eat, brush their teeth or write?
• Does the young child have non-specific symptoms? As young children cannot communicate verbally they may refuse to use a limb, adopt strange posture, be irritated, cry, whine or just act abnormally. This may indicate a joint problem.

Many but not all children do not require laboratory evaluation as history and physical examination will usually provide a likely cause. As with any test, one should ask “How will this test’s results alter the evaluation, treatment or outcome?” before ordering a test. Children with a history of suspected potential trauma, or persistent localized pain often will have plain radiographs of the area. Other radiological testing (e.g. magnetic resonance imaging) is usually a secondary test. Laboratory investigation is usually used when there is suspicion for infection, inflammation and malignant conditions and often include complete blood count with differential, lactate dehydrogenase, erythrocyte sedimentation rate and C-reactive protein and urinalysis. If these are completely normal, the probability of one of these rarer conditions is low. Autoimmune tests usually are not helpful in the initial evaluation for joint pain and can lead to false positives.

Learning Point
Many other cases involving rheumatological and orthopaedic problems can be reviewed here

The differential diagnosis of joint pain includes:

• Trauma
  • Fractures
  • Soft tissue injuries
  • Non-accidental trauma
  • Overuse injuries
• Orthopaedic
  • Osteochrondrosis
    • Kohler disease
    • Legg-Calve-Perthes disease
    • Osgood-Schlatter disease
• Miscellaneous
  • Clubfoot
  • Compartment syndrome
  • Developmental dysplasia of the hips
  • Leg length discrepancies
  • Osteochondritis dessicans
  • Slipped capital femoral epiphysis
  • Scheuermann’s disease
  • Synovitis
  • Spondylolisthesis/lysis
• Hypermobility
  • Benign hypermobility syndrome
  • Syndromes associated with hypermobility
  • Down syndrome
  • Ehlers-Danlos syndrome
  • Marfan syndrome
  • Noonan syndrome
• Infection
  • Discitis
  • Gonococcus
  • Osteomyelitis
  • Psoas abscess
  • Rubella
  • Septic arthritis
  • Soft tissue infections
  • Viral arthritis – is acute, involving small joints that are symmetrical and not involving the axial skeleton
• Rheumatological/inflammatory
  • Juvenile idiopathic arthritis (JIA)
  • Oligoarticular is chronic, mainly involving large joints that are asymmetric and usually does not involve the axial skeleton
  • Polyarticular is chronic, involves small and large joints that are symmetrical or asymetric and usually does not involve the axial skeleton
  • Systemic lupus erythematosus is chronic involving the small joints that is symmetrical and doesn’t involve the axial skeleton
  • Ankylosing spondylitis
  • Autoinflammatory syndrome
  • Chronic recurrent multifocal osteomyelitis
  • HLA-B27 arthropies
  • Inflammatory bowel disease
  • Juvenile dermatomyositis
  • Mixed connective tissue disease
  • Psoriatic arthritis is chronic and involves both large and small joints that is usually asymmetrical and may involve the axial skeleton
  • Sarcoidosis
  • Vasculitis
    • Henoch-Schonlein purpura
    • Multisystem inflammatory system disease in children due to novel Coronavirus 19
  • Post-infectious arthritis including mycoplasma, yersinia, meningococcus
  • Acute rheumatic fever is acute and may be migratory, involving large joints that are asymmetrical and usually not involving the axial skeleton
  • Lyme disease
  • Reactive arthritis including transient synovitis is acute involving large joints that are asymmetrical and may or may not involve the axial skeleton