The kneecap, scientifically known as the patella, is a small, flat bone positioned at the front of the knee joint. Despite its modest size, it plays an important role in knee function, facilitating movement and protecting the joint.
Anatomy and Structure
The patella is unique among human bones because it is a sesamoid bone, meaning it is embedded within a tendon rather than directly articulating with other bones. It resides within the quadriceps tendon, which connects the large muscles on the front of the thigh to the lower leg. This bone typically has a triangular shape, with its pointed end, or apex, directed downwards.
The posterior surface of the patella is smooth and covered with articular cartilage, which allows it to glide efficiently over the lower end of the femur, or thigh bone. This cartilage can be quite thick, distributing forces across the joint. Its composition includes an outer layer of cortical bone and an inner core of cancellous bone.
Its Role in Movement and Protection
The primary function of the patella centers on facilitating knee extension, the straightening of the leg. It significantly improves the mechanical advantage of the quadriceps muscle, enabling more powerful and efficient leg extension. By acting as a natural pulley, the patella increases the leverage of the quadriceps tendon, enhancing the force the quadriceps can exert on the tibia.
Beyond its role in movement, the patella also provides a protective shield for the knee joint. It helps to minimize friction between the quadriceps tendon and the underlying femoral condyles, ensuring smooth motion during knee flexion and extension.
Common Issues and What They Mean
Several conditions can affect the patella, leading to pain and impaired knee function. One such issue is patellar dislocation, which occurs when the kneecap shifts out of its normal position within the groove on the femur. This displacement can be partial, known as subluxation, or a complete dislocation, often causing significant pain and instability.
Another common problem is a patellar fracture, a break in the kneecap. These fractures often result from a direct blow to the knee, such as a fall, or from a sudden, forceful contraction of the quadriceps muscle. Symptoms typically include pain, swelling, and difficulty or inability to straighten the leg.
Chondromalacia patellae involves the softening and breakdown of the articular cartilage on the underside of the kneecap. This condition, sometimes referred to as “runner’s knee,” can cause pain behind or around the kneecap, particularly during activities like climbing stairs, squatting, or prolonged sitting. A grinding or cracking sensation may also be felt with knee movement.