Knee pain when bending and straightening, without swelling, is often not an emergency, but it should still be watched. Based on the source material, common possibilities include patellofemoral pain, tendon irritation, early osteoarthritis, or a meniscus problem, especially if the pain happens during stairs, squatting, running, or repeated knee movement.
The absence of swelling can be reassuring, but it does not rule out a knee problem. Some meniscus injuries or front-of-knee pain conditions can cause pain with movement and little or no visible swelling. A careful exam is usually the best way to check where the pain is coming from and whether imaging is needed.
Try reducing activities that clearly trigger the pain, such as deep squats, running, or repeated stairs, while keeping gentle movement as tolerated. Exercise-based rehab and strengthening around the hip and knee are commonly recommended in the source material for several non-urgent knee pain causes.
Seek care sooner if the knee locks, gives way, pain is worsening, or you cannot walk normally. Avoid self-medicating, especially with repeated painkiller use, and consider seeing a primary care doctor, orthopedist, or physical therapist for an exam and treatment plan.