Diagnostic Radiology/Musculoskeletal Imaging/Joint Disorders/Osteoarthritis

Etiology
The cause of OA is generally multifactorial. Joint integrity, local inflammation, mechanical forces, genetic predisposition, and cellular/biomechanical processes all play a role in the development of OA. Although the etiology cannot always be identified, in general it is caused by repetitive biomechanical stress on the articular cartilage and subchondral bone of the affected joint. This is often due to a preexisting deformity such as developmental dysplasia of the hip, or genu varus of the knee. Additionally, there are multiple risk factors that increase a patient’s predisposition for OA. These include:


 * 1) Advanced age
 * 2) Female sex
 * 3) Obesity
 * 4) Occupation
 * 5) Sports activities
 * 6) Previous injury to the affected joint
 * 7) Muscle weakness/imbalance around affected joint
 * 8) Acromegaly
 * 9) Calcium crystal deposition disease

Clinical Findings
Most often seen in patients over 40 year old. The most common complaint is pain worsened with activity and lessened with rest. Joint effusions and crepitus are often seen on clinical exam, and large osteophytes can be palplated at the affected joint.

The joints most commonly involved in primary OA include the knees, hips, hands, and spine, and less often the elbow, wrist, and ankle.

Symptoms in various joints:
 * Knees: Crepitus, joint effusion, osteophytes, pain, decreased ROM.
 * Hips: Pain in hip or referred to knee.
 * Hands: DIP (Heberden’s nodes), PIP (Bouchard’s nodes), and 1st CMC joint involvement which manifests as enlarged joints.
 * Spine: Most commonly seen at points of greatest spinal flexibility (C5, T8, and L3).
 * C-Spine: Uncovertebral and facet joint osteophytes can narrow the foramina and spinal canal.
 * L-spine: Apophyseal osteophytes can cause spinal stenosis.

Radiologic Findings
Plain films often do not correlate with physical exam findings in early disease. Findings consistent with OA include subchondral sclerosis, osteophytes, subchondral cysts, and joint space narrowing.

Prognosis
The most common course of OA is an intermittent, progressive worsening of symptoms over time, although in some patients the disease stabilizes. Prognosis also varies depending on which joint is involved.

Factors associated with progression of OA:
 * Knees: High body mass index, varus or valgus knee deformity.
 * Hips: Female gender, night pain, presence of femoral osteophytes and subchondral sclerosis.
 * Hands: Older age.