Many will remember the attack on U.S. ice skater Nancy Kerrigan when she was struck on the knee during a practice session by a hired assailant. The injury forced her to withdraw from the competition at that time. Most traumatic knee injuries are not that dramatic but can be very disabling just the same. In this review, orthopedic surgeons from the University of Colorado team up with experts from the New York University Hospital for Joint Diseases to review quadriceps tendon injuries. The assessment, diagnosis, and treatment of three problems are covered: quadriceps tendinosis, partial quadriceps tears, and complete quadriceps tendon ruptures.
The quadriceps muscle along the front of the thigh is made up of four muscles that attach to the quadriceps tendon: rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. Together, the quadriceps muscles, patellar tendon (where the quadriceps tendon attaches around and below the patella), and the patella (kneecap) form the extensor mechanism. The extensor mechanism is the motor that drives the knee joint and allows us to walk. It straightens the knee when the quadriceps muscle contracts making it possible to climb up stairs or get up from a sitting position.
Any injury to the quadriceps muscle or tendon affects the extensor mechanism causing pain, loss of knee extension, and loss of function. You've probably heard of tendinitis, an acute inflammatory process affecting tendons. But what is quadriceps tendinosis? The term tendinosis tells us that the injury is chronic (been there a long time). When examined under a microscope or with advanced imaging such as ultrasound or MRI, there is degeneration of the tissue but without any sign of inflammation.
A specific type of patellar tendinosis seen in athletes who repeatedly jump is known as peripatellar tendinosis or more commonly known as jumper's knee. At first there's an inflammatory response to overuse or repetitive motion. Acute inflammation occurs as tiny tears called microtears develop around the patellar tendon. These microtears can occur where the tendon inserts on the patella or on the tibial tuberosity, a bump on the lower leg bone just below the kneecap. The inflammatory process ends resulting in scar tissue that replaces the destroyed tendon tissue. That's when a tendinitis becomes a tendinosis.
Tendon tears are usually the result of an active injury either while engaged in a sports activity or from a fall. Less often, as in the case of the skater, trauma from a direct blow can cause the same kind of damage. Besides athletes, older adults are at risk for quadriceps tendon tears. For a long time, it was believed that a loss of balance and fall led to tendon ruptures. But more recent evidence has shown that weakness of the tendon from age-related degeneration causes tendon rupture first, then the fall. The fall is the result of the loss of knee joint stability from the torn tendon.
Older men, especially older black men seem to be affected most often. The injury doesn't just come out of the blue. Other risk factors include the use of certain antibiotics (fluoroquinolones) or steroids. Having a chronic, systemic health problem like diabetes, lupus, rheumatoid arthritis, gout, or kidney disease increases the risk of quadriceps tendon rupture considerably.