Osteoarthritis is traditionally separated into two main categories: primary and secondary. Primary osteoarthritis typically involves joints in characteristic locations and is likely to result mainly from genetic predisposition.
Typical symptoms of this include gradual onset of pain and stiffness in and around a joint with decreased function of that joint. Early in the disease process, the pain is typically mild, worsening with use of the affected joint and improving with rest. If present, morning stiffness rarely lasts more than 30 minutes. Stiffness is common after inactivity of the joint, usually resolving after a few minutes. Pain at rest or at night occurs in more severe disease.
Joints affected by osteoarthritis include knees; hips; cervical and lumbar spine; the first metatarsophalangeal joints of the feet; and distal interphalangeal (DIP), proximal interphalangeal (PIP), and first carpometacarpal (CMC) joints of the hand. Patients with knee osteoarthritis may complain of “buckling,” especially while descending stairs. Pain from hip osteoarthritis is usually felt in the groin but can radiate to the anterior thigh or knee. Osteophytes from osteoarthritis of the spine may cause radicular symptoms secondary to nerve root compression.
Multiple Heberden’s nodes (bony enlargement of distal interphalangeal joints of the hand) appear in middle age and are a strong marker for subsequent predisposition to knee osteoarthritis and osteoarthritis at other common target sites (nodal generalized osteoarthritis).
When osteoarthritis occurs in atypical joints, such as the ankle, the presentation alone should trigger consideration of secondary osteoarthritis. Typical aetiologies of secondary osteoarthritis include joint trauma, previous fracture and preceding inflammatory arthropathy such as gout.
Patients with osteoarthritis often have bony enlargement and tenderness of the joint. Periarticular muscle spasm may be present. Range of motion (ROM) is sometimes limited. Locking of a joint during ROM can occur from loose bodies or fragments of cartilage in the joint space. Signs of mild inflammation, such as warmth or swelling, may be present around an affected joint. Evidence of severe inflammation is suspicious for other disorders, such as septic arthritis, gout, or pseudogout.
Crepitus is commonly felt on passive ROM of the knee. It is caused by the irregularity of the opposing cartilage surfaces. A varus deformity of the knee is often seen from medial compartment degeneration, but a valgus deformity is possible with lateral compartment involvement.
Bony enlargements called Heberden’s nodes on the DIP joints and Bouchard’s nodes on the PIP joints are frequently present in osteoarthritis of the hand. These nodes may be painful, especially when they first develop, but are usually nontender after they are formed. Osteoarthritis does not typically involve the metacarpophalangeal joints as rheumatoid arthritis does. Rheumatoid arthritis involves multiple joints in a symmetrical pattern but spares the DIP and first CMC joints commonly affected by osteoarthritis.
Osteoarthritis is a clinical diagnosis. The main investigation that can help confirm osteoarthritis is plain X – ray, with demonstration of characteristic structural abnormalities:
- Focal joint space narrowing (due to cartilage loss)
- Marginal osteophytes or ‘spur’ formation
- Subchondral sclerosis of bone
It is important to note that majority of people with radiographic evidence of osteoarthritis have no symptoms of osteoarthritis. Biochemical abnormalities of the joint precede radiographic abnormalities by as much as decades. For this reason, much effort is currently being put into identifying more sensitive imaging modalities, such as magnetic resonance imaging, bone scintigraphy and ultrasound, along with biochemical indicators in blood, urine or synovial fluid, that might identify and quantify osteoarthritis more precisely and earlier than by X-ray.