Knee (human anatomy)
The knee is the largest and one of the most complex joints in the human body, playing a crucial role in mobility. It is composed of three primary bones: the tibia (shinbone), femur (thighbone), and patella (kneecap), along with cartilage, ligaments, tendons, and menisci that work together to allow smooth movement and stability. Ligaments, including the collateral and cruciate ligaments, provide support and control both lateral and rotational movements. Injuries to the knee, such as fractures, dislocations, or ligament tears, are common, especially among athletes, and may lead to significant pain and mobility issues.
Treatment for knee injuries can vary from physical therapy and bracing to surgical interventions, including the potential for knee replacement, particularly in cases of severe osteoarthritis, often seen in older adults. Strengthening the muscles around the knee, like the quadriceps and hamstrings, can help improve function and reduce stress on the joint. Overall, maintaining knee health is essential for overall mobility and quality of life.
Knee (human anatomy)
The largest joints in the human body, the knees are also among the most complex and delicate.
A healthy knee is composed of several parts. Bones in the knee and in the area surrounding it provide rigid structure. Ligaments in the knee provide stability, and muscles allow the joint to move. Should any of these parts become damaged by an injury, however, the entire knee may stop functioning properly. Many knee injuries require surgical repair. In some cases, the entire knee joint may need to be replaced by an artificial reconstruction.
Anatomy of the Knee
Knee joints are among the most complicated joints in the human body and the most important for general mobility. A weakened, unstable, or chronically painful knee can quickly become debilitating.
Knees are composed of three bones: the tibia (shinbone), the femur (thighbone), and the patella (kneecap). These three bones are supported by cartilage, a tough connective tissue. Cartilage covers the ends of the shinbone, the femur, and the patella and allows them to slide smoothly over each other without grinding away bone. Two other pieces of cartilage, called the meniscus, act as a cushion to absorb the shock of running and jumping.
Strings of connective tissue, the ligaments keep all the parts of the knee in place and stable. Two primary sets of ligaments are in the knee: the collateral ligaments and the cruciate ligaments. The collateral ligaments are located on the sides of the knee. They control the sideways motion of the knee, and stop it from rotating in unexpected ways. The cruciate ligaments form an X shape on the inside of the knee, keeping everything tightly pressed together. These ligaments control the forward and backward motion of the knee.
Tendons are strong fibers that connect muscle to bone. They are found throughout the body. There are two major sets of tendons in the knee. The quadriceps tendons connect the thigh to the kneecap. The patellar tendons connect the patella to the shinbone. If these tendons are injured, the knee will cease to function properly. The knee may feel unstable or off balance and extend far beyond its normal range.
While the ligaments and cartilage making up the knee are difficult or impossible to modify through exercise, strengthening the surrounding muscles significantly aids in knee function. Stretching and strengthening the stabilizing muscles, such as the quadriceps and the hamstring, takes stress off weakened or stretched ligaments. Some knee-strengthening exercises recommended by orthopedic experts include the straight-leg lift, the single-leg dip, hamstring curls, wall squats, and step ups. Experts also recommend stretching the quadriceps and hamstring before rigorous exercise.
Common Knee Injuries
Knees are very delicate joints and injure easily. In many cases, knee injuries fail to heal properly on their own. Some require specialized rehabilitation techniques.
A knee fracture occurs when one of the bones supporting the knee is broken. The patella is the most commonly broken bone in the knee. However, the ends of the femur and tibia that connect to the knee can also be broken. These breaks often require surgery to repair.
A knee dislocation occurs when the patella is moved out of its proper place. If a person with a knee dislocation quickly receives care, the dislocation is usually resolved without surgical correction. Sixty to 70 percent of people who have suffered a knee dislocation will regain full function without surgery. The remaining will retain a lesser degree of function or have a permanently painful and unstable knee.
Damage to the anterior cruciate ligament (ACL) is one of the most common injuries among athletes. Because of its role in stabilizing the knee, the ACL is vulnerable to sudden changes of direction. If too much stress is placed on the ACL, it may tear or even snap. Because a weakened ACL is no longer performing its primary function, the other parts of the knee are often injured as well. Specifically, the meniscus and articular cartilage are often injured along with the ACL.
ACL injuries are divided into three grades. In a grade 1 sprain, the ligament is only slightly stretched and is still able to keep the joint stable. In a grade 2 strain, the ligament is slightly torn, and the joint becomes loose. In a grade 3 sprain, the ACL is torn into two pieces, and the knee is unstable. Unfortunately, most ACL injuries are grade 3 sprains. While grade 1 sprains may be treated through bracing and physical therapy, a badly torn ACL will not heal without surgical intervention.
Injuries to the collateral ligaments are graded identically to ACL injuries. However, unlike ACL injuries, collateral ligaments are usually only injured when the knee has been impacted in some way. They also heal more easily than ACL injuries, and only require surgical repairs when torn.
In cases involving severe knee injury and long-term chronic pain, doctors may replace the knee. In most cases, the recipients of a knee replacement surgery are more than 50 years of age and suffer from severe osteoarthritis. In a knee replacement surgery, the damaged joint is cut out and removed. The shin bone, thigh bone, and patella are then reshaped to allow the insertion of a plastic or metal joint, which is secured with a type of cement.
Bibliography
Ivy Sports Medicine. "Knee Join Function." Ivy Sports Medicine, Ivy Sports Medicine, LLC, 2016, ivysportsmed.com/en/knee-pain/knee-joint-function. 21 Oct. 2016.
OrthoInfo. "Anterior Cruciate Ligament (ACL) Injuries." OrthoInfo, American Academy of Orthopaedic Surgeons, 2016, orthoinfo.aaos.org/topic.cfm?topic=A00549. Accessed 20 Oct. 2016.
OrthoInfo. "Collateral Ligament Injuries." OrthoInfo, American Academy of Orthopaedic Surgeons, 2016, orthoinfo.aaos.org/topic.cfm?topic=A00550. Accessed 20 Oct. 2016.
OrthoInfo. "Common Knee Injuries." OrthoInfo, American Academy of Orthopaedic Surgeons, 2016, orthoinfo.aaos.org/topic.cfm?topic=a00325. Accessed 20 Oct. 2016.
OrthoInfo. "Knee Exercises." OrthoInfo, American Academy of Orthopaedic Surgeons, 2016, orthoinfo.aaos.org/topic.cfm?topic=a00564. Accessed 20 Oct. 2016.
WebMD. "Knee Pain Health Center." WebMD, WebMD, LLC, 2016, webmd.com/pain-management/knee-pain/picture-of-the-knee. Accessed 21 Oct. 2016.
WebMD. "Knee Replacement Surgery for Arthritis." WebMD, WebMD, LLC, 2016, webmd.com/osteoarthritis/guide/knee-replacement-surgery#1. Accessed 21 Oct. 2016.