Patella
The patella (kneecap) is the largest sesamoid bone in the body, embedded within the quadriceps tendon. It protects the knee joint and improves the mechanical advantage of the quadriceps for knee extension.
Key Features
Articulations
- •Patellofemoral joint (with femoral trochlea) - plane synovial
Muscle Attachments
Clinical Relevance
Patella fractures result from direct trauma or forceful quadriceps contraction. Patellar dislocation typically occurs laterally. Chondromalacia patellae (runner's knee) involves softening of patellar cartilage. Bipartite patella is a normal variant.
Patella FAQs
Common questions about this bone
The patella increases the mechanical advantage of the quadriceps by holding the tendon away from the knee joint axis, increasing the moment arm for knee extension. It also protects the knee joint anteriorly.
The patellar reflex (knee jerk) is tested by tapping the patellar tendon, causing reflexive quadriceps contraction and knee extension. It tests the L3-L4 nerve roots and femoral nerve.
Chondromalacia patellae is softening and degeneration of the cartilage on the posterior surface of the patella. It causes anterior knee pain, especially with stairs, squatting, or prolonged sitting.
The patella tends to dislocate laterally because the quadriceps pulls it upward and laterally, and the lateral femoral condyle is less prominent. VMO weakness and ligament laxity increase risk.