Basic Stifle Joint Anatomy (Back Leg Knee Joint)

In order to better understand the various Dog Knee Stifle (ACL knee) braces OrthoPets provides for a torn ACL (cranial cruciate ligaments), MCL, LCL, and PCL ligament injury, it is important to understand the anatomy and function of the stifle (knee) joint. This section covers basic knee anatomy.

The Stifle (ACL knee) joint is made up of four bones, which are connected by muscles, ligaments, and tendons.

The femur is the large bone in the thigh. The tibia is the large shin bone. The fibula is the smaller shin bone, located next to the tibia. The patella, otherwise known as the knee cap, is the small bone in the front of the knee. It slides up and down in a groove in the femur (the femoral groove) as the knee bends and straightens.

Ligaments are like strong ropes that help connect bones and provide stability to joints. In the knee, there are four main ligaments. On the inner (medial) aspect of the knee is the medial collateral ligament (MCL) and on the outer (lateral) aspect of the knee is the lateral collateral ligament (LCL). The other two main ligaments are found in the center of the knee. These paired ligaments are called the anterior (cranial) cruciate ligament (ACL) and the posterior (Caudal) cruciate ligament (PCL). They are called cruciate ligaments because the ACL "crosses" in front of the PCL.

Two structures called menisci sit between the femur and the tibia. These structures act as "cushions" or "shock absorbers". They also help provide stability to the knee. There is a medial meniscus and a lateral meniscus.

Tendons connect muscles to bone. The strong quadriceps muscles on the front of the thigh attach to the top of the patella via the quadriceps tendon. This tendon covers the patella and continues down to form the "rope-like" patellar tendon. The patellar tendon in turn, attaches to the front of the tibia. The hamstring muscles on the back of the thigh attach to the tibia at the back of the knee. The quadriceps muscles are the main muscles that straighten the knee. The hamstring muscles are the main muscles that bend the knee.