Osteoarthritis (OA) is a common form of arthritis, affecting up to 10% of the North American elderly population. In addition, the prevalence of radiographically established OA in the United States is estimated to be 33% among individuals over 63 years of age. This study was designed to determine whether ultrasound (US) can be effective in demonstrating a response to intra-articular corticosteroid injections to the knee.

Subjects included 35, consecutive subjects who met the American College of Rheumatology's radiologic criteria for OA. All subjects completed a symptom assessment and US examination at baseline, and returned for follow-up at 14 weeks. Of those, 19 participants were determined to be in need of a corticosteroid injection, and received 80 mg of methylprednisolone mixed with 2 mL of lidocaine one percent. The remaining subjects underwent no therapeutic intervention. All participants were asked to rate their knee pain on a visual analogue scale, and to complete the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC). The knee joints were assessed with US at baseline and at four weeks.

At follow-up US, synovial thickness was noted to have decreased in 16 of the 19 patients in the treatment group, and in two of the 14 patients in the control group (P=0.012). A reduction in synovial thickness was associated with a reduction in pain greater than or equal to the predetermined minimally clinically important improvement level (>20 mm on the VAS). With both groups combined, no substantial association was seen between changes in synovial thickness and changes in pain.

This pilot study suggests that US may be useful in detecting early changes in synovial pathology in response to intra-articular anti-inflammatory therapy.