Knee extensor mechanism injuries

[Oralee]

Knee extensor mechanism injuries can involve the quadriceps tendon, patellar tendon, patella, or tibial tubercle. Surgical repair is usually required.
(See also Overview of Sprains and Other Soft-Tissue Injuries.)
Extension of the knee involves the quadriceps muscles, which are attached to the patella by the quadriceps tendon; the patella is connected to the tibial tubercle by the patellar tendon. Forced flexion at the knee with a contracted quadriceps muscle can damage these structures. Injuries include

Quadriceps tendon tears
Patellar tendon tears
Patellar fractures
Tibial tubercle fractures

In healthy people, significant force is required to injure these structures; normal tendons are strong enough that the patella often fractures transversely before a tendon tears. However, people with certain conditions are at risk of tendon tears. These conditions include

Older age
Osteoarthritis
Use of certain drugs (eg, fluoroquinolones, corticosteroids)
Diabetes mellitus
Obesity
Hyperparathyroidism
Polyneuropathy
Anabolic steroid abuse

In these at-risk people, the injury can result from minor trauma (eg, when descending stairs). The quadriceps tendon is injured more often than the patellar tendon, particularly in the elderly.