Which condition is most consistent with medial knee pain in a 75-year-old patient worsened by stair climbing?

Medial knee pain in a 75-year-old patient that worsens with activities like stair climbing is highly suggestive of pes anserine bursitis. This condition involves inflammation of the bursae located beneath the pes anserinus, a structure formed by the tendons of three muscles (sartorius, gracilis, and semitendinosus) that insert onto the medial aspect of the tibia.

In older patients, pes anserine bursitis is often associated with factors like osteoarthritis, obesity, and overuse, which makes it particularly relevant in this demographic. The location of the pain, its aggravation during stair climbing (a movement that requires knee flexion and puts stress on the medial compartment), supports the diagnosis of pes anserine bursitis rather than other types of bursitis or knee conditions.

Pes anserine bursitis typically presents as localized tenderness and swelling on the medial aspect of the knee, and it is common in individuals who have underlying joint changes due to aging. Overall, the combination of age, specific knee pain location, and exacerbation with climbing stairs aligns well with this diagnosis.