Why do knee tendons rupture, sometimes from a small fall?

The mechanism

Healthy tendons are remarkably strong. Ruptures typically happen when the thigh muscle contracts hard while the knee is being forced to bend, such as catching yourself on a stair, landing awkwardly from a jump or slipping on a wet floor. If the tendon has been weakened over time, the force needed is much smaller.

Factors that weaken tendons

Common contributors include:

• Age-related change in the tendon, especially after about 40
• Previous tendon pain, such as long-standing jumper's knee
• Diabetes, chronic kidney disease, gout, rheumatoid arthritis and thyroid disease
• Long-term oral steroids, or repeated steroid injections close to the tendon
• Some antibiotics in the fluoroquinolone group, particularly in older adults or with steroids
• Anabolic steroid use in bodybuilding, which builds muscle faster than the tendon adapts
• Obesity, which increases the load on the extensor mechanism

In Qatar, diabetes and kidney disease are common enough that they are always worth checking when a tendon ruptures from a minor injury.

Why the cause matters

Understanding the cause changes care. Blood sugar control affects wound healing and infection risk after repair. Kidney disease may need coordination with your physician. Medicines that weaken tendons may be reviewed with the doctor who prescribed them. And if one tendon gave way from a small load, the opposite knee may need attention too.

Can it be prevented?

Not every rupture can be prevented, but treating tendon pain early, building quadriceps strength gradually, avoiding anabolic steroids, and discussing tendon risks before taking steroids or fluoroquinolones all help. Do not stop a prescribed medicine on your own; speak to your doctor first.