Thank you for sharing your photos. Based on what you've described, the changes around your knees appear to be a combination of age-related skin laxity, thinning of the skin, and loss of collagen rather than simply a volume deficiency. This distinction is important because it influences which treatments are most likely to give you the improvement you're seeking. While fillers can be used around the knees, they are generally not my first choice for wrinkled or crepey knee skin. Fillers work best when there is a noticeable hollow or volume loss that needs to be restored. In lean individuals, adding filler can sometimes provide subtle smoothing, but it may not adequately address the loose, wrinkled skin itself. For knee rejuvenation, I often find that treatments focused on collagen stimulation tend to provide more natural-looking results. Options such as biostimulatory injectables (for example, Sculptra), radiofrequency microneedling, ultrasound-based skin tightening, or certain fractional laser treatments can help improve skin quality and firmness over time by encouraging your body to produce new collagen. If filler is used, the amount can vary significantly depending on the degree of volume loss and the desired result. It is not unusual for multiple syringes per knee to be needed, which can become costly, and even then, the improvement may be modest if the primary issue is skin laxity rather than lack of volume. In patients similar to you—lean, healthy, and in their 40s—I often see the best outcomes from treatments that focus on tightening and rebuilding collagen rather than simply adding volume. The goal is usually to improve the texture and quality of the skin while maintaining the natural contour of the knees. The good news is that the changes shown are relatively mild, and you have several non-surgical options that can help soften the wrinkled appearance and create a smoother, more youthful look without making the area appear overfilled.