Unstable Knee

Anatomy of the knee

knee anatomyThe knee is a complex joint composed bone, cartilage, ligaments, and tendons.  The bones are the tibia and the fibula on the lower leg, and the femur from the upper leg, and the patella.  Many issues with stability can manifest in the joint itself or the patella. The bones rest against each other with a piece of cartilage called the meniscus in-between them.  There are four ligaments of the knee: The ACL, PCL, MCL, and LCL.  There are also ligaments that attach the muscles of the leg to the bones to allow movement of the joint.  The bones of the knee offer rigid structure, the ligaments are connective tissue to hold the bones to each other, and the ligaments to attach muscle to bone to move the joint.  

Causes of an Unstable knee

Unstable knee because of bones

Bones are ridged structures and susceptible to fracture if energy is applied to them in an unusual way or in a capacity larger than they can withstand.  Fractures of the bone will destabilize the knee and require medical intervention.  Some fractures of the knee require casting, some require just time, and some require surgical intervention to stabilize the joint.

Unstable knee because of ligaments

Medial cruciate ligament PCLThe ligaments of the knee attach the bones of the lower leg to the meniscus and the upper leg.  There are four ligaments of the knee that can be partially or completely torn due to abnormal forces.  When these ligaments are torn the knee becomes unstable during specific motions.  The ACL and PCL are commonly torn in sports.  The ACL keeps the front of the knee in place and the PCL keeps the back of the knee in place.  The MCL and LCL are rarely torn by themselves and will accompany large amounts of structural damage to the knee in most cases.  The tear of any of the ligaments will require bracing to stabilize the knee with many people considering a surgical correction to reconstruct the ligament.  Additionally there are ligaments that hold the position of the kneecap.  If these ligaments are either too loose or too tight then kneecap misalignment or subluxation may ensue.

Unstable knee because of Muscles and Tendons

The muscles of the leg attach to bone in the hip, knee, and ankle joints.  If either the muscle or tendon are torn or ruptured the tension on the joint will become unbalanced leading to joint instability.  Issues with muscle often include unbalanced strength training, contusions, and sprains.  Issues with the tendons can include inflammation called tendonitis, or tears of the tendon itself, or the anchor it has to the bone.

Unstable knee because of the meniscus

The meniscus is prone to injury from twisting forces that can cause it to tear.  This can cause swelling, pain, and instability of the knee.  Some injuries may need surgical intervention while others have mild symptoms that people choose to live with.

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