Stretch marks (striae distensae) are a common form of dermal scarring resulting from the rapid stretching of the skin. These linear streaks frequently occur on the abdomen, thighs, and breasts. While less common than in other areas, stretch marks can appear on the knees. The skin around the knee joint is susceptible due to the high mechanical tension placed upon it during periods of rapid growth or significant changes in volume.
The Underlying Biological Mechanism
The formation of a stretch mark begins in the dermis, the layer beneath the epidermis that provides structure and elasticity. The dermis is rich in collagen and elastin, protein fibers responsible for the skin’s ability to stretch and snap back. When the skin expands faster than the fibroblasts can produce new supportive material, these fibers are overstretched and rupture. This mechanical failure disrupts the connective tissue, creating a tear beneath the surface. The resulting repair process leads to an abnormal formation of scar tissue, defining striae distensae.
Specific Triggers for Stretch Marks Near Joints
Stretch marks near the knees and other joints are linked to events causing a rapid change in skin tension. The most frequent cause is the rapid skeletal elongation experienced during adolescent growth spurts. As leg bones grow quickly, the skin must stretch suddenly, straining the dermis around the joint.
Significant weight gain or loss can also trigger knee stretch marks, especially if weight is carried in the legs. Rapid muscle hypertrophy, such as in bodybuilders focusing on quadriceps and hamstring development, can also stretch the skin past its limit. Elevated cortisol levels are a hormonal factor that can weaken the skin’s elastic fibers, increasing susceptibility to tearing.
How Striae Appear and Evolve
Stretch marks evolve through distinct phases, moving from an acute, inflammatory stage to a mature, scarred stage. Initially, they are known as striae rubrae, characterized by a pink, red, or purplish hue depending on skin tone. These early marks are often slightly raised, indicating active inflammation and a robust blood supply involved in healing. They may occasionally feel itchy or tender.
Over time, the marks mature into striae albae, appearing as hypopigmented, white, or silvery lines. This color change reflects the loss of blood vessels and the development of mature, flattened scar tissue. Striae albae represent permanent dermal atrophy where collagen has reorganized into a less flexible, linear structure.
Reducing the Appearance of Existing Marks
While stretch marks are a permanent form of scarring, their appearance can be significantly minimized through targeted treatments. Early intervention is most effective, particularly when the marks are still in the red or purple striae rubrae phase.
Topical Treatments
Topical retinoids (Vitamin A derivatives) are often prescribed because they encourage cell turnover and stimulate new collagen production within the dermis. Other beneficial topical ingredients include hyaluronic acid, which hydrates the skin and improves elasticity, and Centella asiatica, known for its skin-healing and collagen-boosting properties. These creams work best when applied consistently to newer marks.
Professional Procedures
For mature, white striae albae, professional procedures often yield better results. Pulsed dye laser therapy is effective for treating the redness of striae rubrae by targeting active blood vessels. For older, white marks, fractional laser treatments or microneedling are commonly used to create controlled micro-injuries in the dermis, prompting collagen remodeling. Microdermabrasion works by removing the outermost layer of skin to smooth texture and stimulate cell growth.