Pain in a joint may be caused by a wide variety of conditions.  Below are fifteen of the more common causes of pain in or around a joint.

• Capsulitis   One of the most common (yet underdiagnosed) causes of acute pain in a joint is capsulitis.  Joint capsule is the covering that extends around a joint, so capsulitis is an inflammation of that joint covering.   Capsulitis is usually caused by small but repetitive trauma, like that caused from running or walking, but it can be caused by sudden, larger traumas like having something fall on the joint.  In cases caused by small, repetitive trauma, there is often a structural abnormality associated with those joints, such as a hammertoe, or if there is abnormal or excessive flattening of the feet, or pronation.  

• Synovitis   Synovitis is an inflammation of the cells within the joint fluid (the synovium).  Closely tied to the joint capsule, the synovium is actually produced by the joint capsule.  Some believe that if you have capsulitis, you also have synovitis. 

• Ligament damage  Ligaments holding the bones together are directly adjacent to the joint, and they may become strained or torn, giving the patient pain at the level of the joint.  Capsule may be considered as a specialized type of ligament.  

• Joint dislocation  In cases where the ligaments and/or capsule is compromised enough, the bones that comprise the joint may actually tear through the capsule, causing a dislocation of the joint.  
   
• Arthritis  Arthritis may develop in the joints in the area, frequently causing joint pain.  Some forms of arthritis tend to predispose particular joints in the body.  There are dozens of forms of arthritis, with the most common types being:     
  • Osteoarthritis, the "wear and tear" arthritis that may come from sudden, severe trauma or minor, low-grade repetitive trauma.  Affecting nearly 2 million Canadians, osteoarthritis is more common than all the other types of arthritis put together.
  • Rheumatoid Arthritis, or "RA" for short, is caused by an auto-immune response (where the body's defense system starts attacking the body, itself).   RA affects approximately 225,000 Canadians.  
  • Gouty Arthritis is caused by too much uric acid in the body, which can form crystals which get stuck in various joints and other tissues.  Gouty arthritis affects over 100,000 Canadians.
  • Ankylosing Spondylitis seems to have a genetic predisposition.  Primarily affecting the spine, Ankylosing Spondylitis affects approximately 40,000 Canadians.  
  • Juvenile Arthritis affects 25,000 children in Canada, despite the generally wide-held belief that arthritis primarily affects the elderly.  
  • Psoriatic Arthritis, a complication of psoriasis, affects approximately 20,000 Canadians.
  • Systemic Lupus Erythematosus (Lupus), a systemic disease, affects the joints in approximately 15,000 Canadians.  
    

• Bone bruise   The bones on the adjacent sides of the joint may become bruised.  Terms such as "metatarsalgia" (which literally means pain in the metatarsal bones) is an example of one form of bone bruise.      
  
• Periostitis  Periosteum is the thin, soft-tissue sheath surrounding the bones.   Periosteum may be thought of as a thinner version of joint capsule, and it may become inflamed.  Because of periosteum's close proximity to the bone itself, It may be difficult to differentiate periostitis from a bruise of the bone.      

• Stress Fractures   One step beyond metatarsalgia, stress fractures are small cracks in the metatarsals or toe bones that develop over time as a result of excessive strain or stress.  
  
• Foreign body  A foreign body (splinter, fragment of glass, etc) may cause severe pain in or around a joint.  This seems to be most common in patients with neuropathy, such as those with diabetes. 

• Neoplasms  There are several types of benign and malignant bone tumours, joint or soft tissue growths that may cause discomfort in the region of a joint.  
  
• Avascular necrosis   This is a degenerative condition where the constant stress to the metatarsal bones gets severe enough that a portion of the bone actually begins to die.  
  
• Tendinitis   There are a lot more tendons in the area of the classic neuroma location than you might think, any one of which may develop tendinitis.  Tendons to the Flexor Digitorum Longus, Flexor Digitorum Brevis, Extensor Digitorum Longus, Extensor Digitorum Brevis, the 3rd Dorsal Interosseus, the 2nd Plantar Interosseus and the 3rd Lumbrical muscles all attach in the area immediately adjacent to the classic neuroma location.      
  
• Crystal Deposition Disease  In addition to gout mentioned above, several other crystal deposition disorders may cause joint pain, including pseudogout, hydroxyapatite deposition disease, steroid crystal inflammation, and others.  
  
• Neuroma  Neuromas are basically pinched nerves.  The classic location is in the ball of the foot, between the third and fourth toes, something called a Morton's Neuroma.
  
• Infection  Infections may create pain in the area of a joint.  An infection may affect the soft tissues (the non-bony tissues), the bone itself, (a condition known as "osteomyeltis"), or the actual joint, (a condition known as "septic arthritis").