Achy knees are an inconvenience, especially when you have places to go and workouts to do. Both sexes experience knee pain, but women are more at risk for knee issues than men – but why? Are women unfortunate enough to have knees that are anatomically different? If not, what does account for the greater incidence of knee problems in females?
Osteoarthritis of the Knees
Osteoarthritis is one source of a knee problem that becomes more common in women after menopause. Osteoarthritis is marked by degenerative changes in the articular cartilage, the flexible connective tissue that acts as a cushion between the bones that make up the knee joint, the femur and the tibia. As the cartilage thins down, the joint space narrows and the bones thicken and form spurs. Eventually, the space between the bones shrinks to the point that the bones rub together, leading to pain, stiffness and reduced function. Unfortunately, the blood supply to cartilage is poor, making it hard for cartilage damage to be repaired.
Osteoarthritis is the most common form of arthritis men and women experience and the symptoms can vary from none to almost incapacitating. In healthy knees, the rate of cartilage synthesis is in equilibrium with cartilage breakdown, so there isn’t a net loss of cartilage. In osteoarthritis, this equilibrium is disrupted and shifted towards cartilage breakdown by enzymes called metalloproteinases. Osteoarthritis has an inflammatory component too, as evidenced by the fact that cytokines, proteins that regulate inflammation, are involved in joint cartilage breakdown.
Hormones May Play a Role in Knee Osteoarthritis
According to the American Academy of Orthopedic Surgeons, women are at greater risk for this common, degenerative form of arthritis than men. In fact, the incidence of osteoarthritis of the knees is 1.7 times greater in women relative to men. Why the higher incidence of osteoarthritis in females? One theory is that estrogen helps to maintain healthy knees and the drop in estrogen after menopause sets the stage for knee osteoarthritis. One study showed older women who used hormone replacement therapy experienced a slower progression of osteoarthritis of the knee. Estrogen seems to influence the metabolism of the cartilage components that cushion the knee.
Another theory is that insulin-like growth factor (IGF-1) made by the liver and involved in the maintenance of healthy bones and lean body mass plays a role in knee health. In one study, women who underwent a total knee replacement for osteoarthritis had lower levels of IGF-1 relative to women with healthy knees.
Other Knee Problems More Common in Women
Osteoarthritis isn’t the only knee condition that females have a higher incidence of. A condition called chondromalacia patellae marked by damage and “softening” of the cartilage that lies just underneath the kneecap is twice as common in women as opposed to men. Chondromalacia is a more frequent problem in athletes who run and jump or otherwise place excessive stress on their knees.
Weakness in the muscles that help stabilize the knees and kneecap injury is also a risk factor for chondromalacia of the knees. This is a condition that’s rampant among female runners, especially those with flat feet, which aren’t as effective at absorbing shock when feet hit the pavement. The pain of chondromalacia patellae is usually dull and aching and worsened by bending, squatting, and going up and down the stairs. It’s also more noticeable after sitting for a while and then standing.
Chondromalacia is most common among adolescents and teenage girls due to uneven pressure on the cartilage during the growth phase, but it can also show up during middle-age as the cartilage begins to break down. Muscle strength imbalances involving the vastus lateralis and vastus medialis parts of the quadriceps places a role too. The vastus lateralis is usually the stronger of the two components and places uneven pressure on the kneecap, leading to cartilage breakdown.
Why is chondromalacia more common in women? Again, hormones are thought to play a role. Female sex hormones, particularly estrogen, soften the cartilage beneath the knee cap, causing it to stretch and become more susceptible to damage. Combine this with muscle strength imbalances around the knee with uneven pressure on the kneecap and you have a recipe for knee pain.
Knee Injuries in Women
As if it’s bad enough that degenerative knee problems are more common, your risk for knee injury is higher if you’re a woman. Research shows females are at greater risk for tearing an ACL ligament in the knee, a serious injury that has ruined many an athletic career. Research has identified a number of reasons why women are at four times greater risk for ACL injury. These include different hormonal influences and the fact that women have smaller ACLs relative to men. Now a new study published in the Journal of Athletic Training points out another reason – when women jump they often land with their knees in a locked position, which stresses the ligaments more.
Women also have a greater “Q angle,” pertaining to the angle at which the tibia meets the femur. When women jump, the wider Q angle places more force on the ligaments, increasing the risk for injury. Plus, the channel through which the ACL ligament moves in women is narrower, boosting the chance that the ligament will “catch” and tear with sudden movements.
Keeping Your Knees Healthy
How can you prevent future knee problems? Vary your workouts so you’re not exposing your knees to repetitive stress. Include some low-impact workouts in your routine to give your knees a rest. Resistance training is an important part of the equation. Research shows building stronger quadriceps and hamstring muscles helps protect against osteoarthritis of the knee.
Include squats and lunges in your room with an emphasis on using good form. Even if you already have some arthritis in your knees, building stronger hams and quads helps slow down progression. Work on strengthening your core. Believe it or not, a strong core reduces stress on your knees and helps you land with better form when you jump.
Watch your weight. Being overweight or obese is a major risk factor for knee osteoarthritis since the added weight places greater pressure on your knees.
The Bottom Line
Women ARE at greater risk for knee problems, but there’s a lot you can do to prevent them. Cross-train, strengthen your quads, hamstrings, and core and maintain a healthy body weight.
American Academy of Orthopedic Surgeons. “How do sex and gender affect knee OA?”
Arthritis Res Ther. 2009; 11(5): 241.
Arthritis Rheum. 2006 Dec;54(12):3850-8.
PM R. 2012 May; 4(5 0): S45-S52.doi: 10.1016/j.pmrj.2012.01.019.
ACL Injuries in the Female Athlete 2012, pp 169-183.
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