What is the primary diagnosis for a patient experiencing evening joint stiffness and pain in weight-bearing joints?

The primary diagnosis for a patient experiencing evening joint stiffness and pain in weight-bearing joints is osteoarthritis. This condition is characterized by the degenerative changes in the joints, often resulting from wear and tear over time. Patients frequently report joint stiffness, especially after periods of inactivity, and this stiffness tends to improve with movement.

The fact that the symptoms occur significantly in the evening is particularly indicative of osteoarthritis, as individuals often feel greater discomfort after using their joints throughout the day. Weight-bearing joints, such as the knees and hips, are commonly affected, which aligns well with the symptoms described.

In contrast, rheumatoid arthritis typically presents with morning stiffness that lasts for more than an hour and affects multiple joints symmetrically. Gout would involve painful, swollen joints more acutely, often affecting a single joint usually starting at night. Tendinitis generally occurs due to overuse or injury, presenting with localized pain and tenderness, but not usually with the pattern of evening stiffness described. Overall, the characteristics of the patient's symptoms strongly point to osteoarthritis as the primary diagnosis.