The knee joint has three compartments: medial, lateral, and
patellofemoral.
Causes of knee pain
include injury, degeneration, arthritis, infrequently infection, and rarely
bone tumors.
Ligaments within the
knee (cruciate ligaments) and on the inner and outer sides of the knee
(collateral ligaments) stabilize the joint.
Surgical repair of
ligament injury can involve suturing, grafting, and synthetic graft repair.
Some patients require total knee replacement.
Routine X-rays do not
reveal meniscus tears but can be used to exclude other problems of the bones
and other tissues. Arthroscope and MRI studies are used most frequently to
diagnose knee ailments; occasionally, a needle aspiration of fluid is done.
The knee joint is one of the most commonly
involved joints in rheumatic diseases (over 100 disease types). Rheumatic
diseases are immune diseases that affect various tissues of the body, including
the joints, by causing arthritis (pain, swelling, stiffness, and limited joint
movements).
How is the
knee designed, and what is its function?
The knee is a joint that has three compartments. This joint has
an inner (medial) and an outer (lateral) compartment. The kneecap (patella)
joins the femur to form a third compartment called the patellofemoral joint.
The thighbone (femur) meets the large shinbone (tibia), forming the main knee
joint.
The knee joint is surrounded by a joint capsule with ligaments
strapping the inside and outside of the joint (collateral ligaments) as well as
crossing within the joint (cruciate ligaments). These ligaments provide
stability and strength to the knee joint.
The meniscus is a thickened cartilage pad between the two joints
formed by the femur and tibia. The meniscus acts as a smooth surface for motion
and absorbs the load of the body above the knee when standing. The knee joint
is surrounded by fluid-filled sacs called bursae, which serve as gliding
surfaces that reduce friction of the tendons. Below the kneecap, there is a
large tendon (patellar tendon) which attaches to the front of the tibia bone.
There are large blood vessels passing through the area behind the knee
(referred to as the popliteal space). The large muscles of the thigh move the
knee. In the front of the thigh, the quadriceps muscles extend the knee joint.
In the back of the thigh, the hamstring muscles flex the knee. The knee also
rotates slightly under guidance of specific muscles of the thigh.
The knee functions to allow movement of the leg and is critical
to normal walking. The knee flexes normally to a maximum of 135 degrees and
extends to 0 degrees. The bursae, or fluid-filled sacs, serve as gliding
surfaces for the tendons to reduce the force of friction as these tendons move.
The knee is a weight-bearing joint. Each meniscus serves to evenly load the
surface during weight-bearing and also aids in disbursing joint fluid for joint
lubrication.
The goal of this article is to give the reader an overview of
causes of knee pain. Most of the topics covered in this article are further
expanded in detail as separate articles. For example, bursitis, types of
arthritis, total knee replacement, and others are covered in articles devoted
to knee pain-related topics that include specifics on diagnosis, tests,
treatments, and other details.
What injuries
can cause knee pain, and what are symptoms? How is knee pain with injury
diagnosed and treated?
Injury can affect any of the ligaments, bursae, or tendons
surrounding the knee joint. Injury can also affect the ligaments, cartilage,
menisci (plural for meniscus), and bones forming the joint. The complexity of
the design of the knee joint and the fact that it is an active weight-bearing
joint are factors in making the knee one of the most commonly injured joints.
Ligament
injury
Trauma can cause injury to the ligaments on the inner portion of
the knee (medial collateral ligament), the outer portion of the knee (lateral
collateral ligament), or within the knee (cruciate ligaments). Injuries to
these areas are noticed as immediate pain but are sometimes difficult to
localize. Usually, a collateral ligament injury is felt on the inner or outer
portions of the knee. A collateral ligament injury is often associated with
local tenderness over the area of the ligament involved. A cruciate ligament
injury is felt deep within the knee. It is sometimes noticed with a
"popping" sensation with the initial trauma. A ligament injury to the
knee is usually painful at rest and may be swollen and warm. The pain is
usually worsened by bending the knee, putting weight on the knee, or walking.
The severity of the injury can vary from mild (minor stretching or tearing of
the ligament fibers, such as a low grade sprain) to severe (complete tear of
the ligament fibers). Patients can have more than one area injured in a single
traumatic event.
Ligament injuries are initially treated with ice packs,
immobilization, rest, and elevation. It is generally recommended to avoid
bearing weight on the injured joint, and crutches may be required for walking.
Some patients are placed in splints or braces to immobilize the joint to
decrease pain and promote healing. Arthroscopic or open surgery may be
necessary to repair severe injuries.
Surgical repair of ligaments can involve suturing alone,
grafting, and synthetic graft repair. These procedures can be done by either
open knee surgery or arthroscopic surgery (described in the section below). The
decision to perform various types of surgery depends on the level of damage to
the ligaments and the activity expectations of the patient. Many repairs can
now be performed with arthroscopic surgery. However, certain severe injuries
will require an open surgical repair. Reconstruction procedures for cruciate
ligaments are increasingly successful with current surgical techniques.
Meniscus
tears
The meniscus can be torn with the shearing forces of rotation
that are applied to the knee during sharp, rapid motions. This is especially
common in sports requiring reaction body movements. There is a higher incidence
with aging and degeneration of the underlying cartilage. More than one tear can
be present in an individual meniscus. The patient with a meniscal tear may have
a rapid onset of a popping sensation with a certain activity or movement of the
knee. Occasionally, it is associated with swelling and warmth in the knee. It
is often associated with locking or an unstable sensation in the knee joint.
The doctor can perform certain maneuvers while examining the knee which might
provide further clues to the presence of a meniscal tear.
Routine X-rays, while they do not reveal a meniscal tear, can be
used to exclude other problems of the knee joint. The meniscal tear can be
diagnosed in one of three ways: arthroscopy, arthrography, or an MRI.
Arthroscopy is a surgical technique by which a small diameter
video camera is inserted through tiny incisions on the sides of the knee for
the purposes of examining and repairing internal knee joint problems. Tiny
instruments can be used during arthroscopy to repair the torn meniscus.
Arthrography is a radiology technique whereby a contrast liquid
is directly injected into the knee joint and internal structures of the knee
joint thereby become visible on X-ray film.
An MRI scan is another radiology technique whereby magnetic
fields and a computer combine to produce two- or three-dimensional images of
the internal structures of the body. It does not use X-rays and can give
accurate information about the internal structures of the knee when considering
a surgical intervention. Meniscal tears are often visible using an MRI scanner.
MRI scans have largely replaced arthrography in diagnosing meniscal tears of
the knee. Meniscal tears are generally repaired with arthroscopic surgery.
Tendinitis
Tendinitis of the knee occurs in the front of the knee below the
kneecap at the patellar tendon (patellar tendinitis) or in the back of the knee
at the popliteal tendon (popliteal tendinitis). Tendinitis is an inflammation
of the tendon, which is often produced by a strain event, such as jumping.
Patellar tendinitis, therefore, also has the name "jumper's knee."
Tendinitis is diagnosed based on the presence of pain and tenderness localized
to the tendon. It is treated with a combination of ice packs, immobilization
with a knee brace as needed, rest, and anti-inflammatory medications.
Gradually, exercise programs can rehabilitate the tissues in and around the
involved tendon. Cortisone injections, which can be given for tendinitis
elsewhere, are generally avoided in patellar tendinitis because there are
reports of risk of tendon rupture as a result of corticosteroids in this area.
In severe situations, surgery can be required. A rupture of the tendon below or
above the kneecap can occur. When it does, there may be bleeding within the
knee joint and extreme pain with any knee movement. Surgical repair of the
ruptured tendon is often necessary.
Fractures
With severe knee trauma, such as motor vehicle accidents and
impact traumas, bone breakage (fracture) of any of the three bones of the knee
can occur. Bone fractures within the knee joint can be serious and can require
surgical repair as well as immobilization with casting or other supports.
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