1) You may come back to this page and read the article as many times as you would like. 2) When you are ready to proceed to the test, just click on the "Take the test" link at the bottom of the page. 3) If you are not registered or logged in, you will be prompted to do so at that time. 4) Once you are registered you may take the test. 5) When you have passed the test you will be instructed on how to pay for your CEU in order to receive your certificate of completion. 6) If you choose not to pay at this time, you can log back in anytime in the future (your data is saved for your convenience), though
you will not receive the ARRT CEU numbers until after you pay.
Knee Anatomy and Imaging
Knee Anatomy and Imaging
Author: Tiffany Ohl R.T. (R) and Jenny Werner R.T. (R), written on Monday June 23rd 2008 - 6:20 PM Credits: 1.5
The A.R.R.T. Continuing Education Requirements for Renewal of Registration states that Internet activities reported in a biennium may not be repeated for credit in the same or subsequent biennium. If you have already completed this article, DO NOT take this CEU article again.
Upon Completion, the reader will be able to:
Identify the boney structures of the distal femur, proximal tibula, and patella.
Identify the soft tissue structures of the knee joint.
List the 3 main trauma views of the knee.
List the different radiographic views of the knee and patella.
List the different types of fractures of the knee and patella.
Discuss common conditions of the knee such as a Bakerís cyst, Bursitis, Osgood Schlatters disease
Discuss how an arthrogram is performed.
List common conditions that are evaluated utilizing ultrasound.
List anatomy that is demonstrated on MRI images
Discuss the importance of a CT scan for certain fractures of the knee or patella.
Identify how osteoarthritis and rheumatoid arthritis disrupt the knee.
List what anatomy can be evaluated and repaired during arthroscopic surgery of the knee.
List the differences between a total knee replacement (TKR) or a partial knee replacement (PKR).
Soft tissue structures
Exams for x-ray
Bilateral Weight Bearing
PA Tunnel View
Fractures and Common Conditions
Closed fracture/ Simple fracture
Dislocation of Patella
Tibial Plateau fracture
Single Contrast (Just contrast)
Single Contrast (Just air)
Double Contrast (Both)
Hydrogen Protons and Magnetic Field
Three different planes
CT vs. MRI
Bone vs. Soft tissue
Pain Relief Injections
The injection process
Knee Replacement Surgery
Pre Surgery Preparation
Total Knee Replacement vs. Partial (Unicompartmental) Knee Replacement
Post Surgery Recovery
The adult human body is comprised of 206 bones. These bones form the strong skeletal framework that supports the body and protects the internal organs. There are four types of bones: long bones (humerus and femur), short bones (carpal bones), flat bones (sternum or skull), and irregular bones (pelvis or facial bones).
An articulation or joint is where two or more bones meet. A joint may be fixed or movable. A fixed joint has a seam between the bones. This seam usually contains a thin layer of connective tissue. Although this type of joint does not permit movement, upon impact the fixed joint may allow enough shock absorption to keep the bones from breaking. The sutures of the cranium are a good example of a fixed joint.
There are three main types of movable joints. These are the ball and socket, pivot, and hinge joints. The ball and socket joint allows the greatest freedom of movement. These joints allow the swinging and rotating movements of the hip and shoulder. The pivot joint allows the rotating movements of the elbow and the side to side motion of the head. Hinge joints are those that permit the forward and backward movement of the finger and the knee.
Being the largest joint in the human body, the knee is more likely to sustain damage from trauma or injury from normal wear and tear. The daily repetitive impact of climbing stairs, running, twisting, walking and even standing can cause degenerative damage to the structure of the joint. Since the knee joint bears weight, an over weight or obese individual has an increased potential of developing structural problems with the knee. Even though the adult knee dominates with its size, at birth this hinge joint isn't fully formed.
All the components of the knee can be viewed in different modalities. Although a standard x-ray may start the clinical exam process, it may be necessary to obtain a computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, or nuclear medicine scan of the knee to get a definitive diagnosis. These specialty exams can highlight information that might not be seen on a conventional x-ray. After a diagnosis has been established, a treatment plan can be developed resulting in the optimal prognosis.
The knee is an essential hinge joint that the body utilizes everyday. This joint contains a combination of bone structures and multiple soft tissue groupings. The involved bone structures are the distal aspect of the femur, the proximal aspect of the tibia, and the patella. The fibula is in close proximity to the joint because of the articulation with the tibia. The fibula doesn't articulate with the knee joint, but it does act as a stabilizer for the body as a whole.(Bontrager, 202-5; Ballinger 10th ed., 236-7; Ballinger 9th ed., 291-315)
The femur is the longer, proximal portion of the lower extremity (leg). The distal portion of this bone contains important components that contribute to the knee joint. This includes the medial and lateral condyles which are located on either side of the distal femur. Each condyle has its own mini condyle that lays just proximal to the main condyle. These are known as the epicondyles, which are the connection site for the collateral ligaments. The collateral ligaments run on either aspect of the knee.(Bontrager, 204-5; Ballinger 10th ed., 236-7; Ballinger 9th ed., 291-315)
The distal femur is also home to the intercondylar fossa (notch) and the intercondylar sulcus (trochlear groove), which lie between the two condyles. The purpose for the intercondylar fossa is to allow a space for all of the soft tissue structures of the knee joint to pass through. This fossa lies in the posterior aspect of the knee. The trochlear groove is in the anterior portion of the knee. This is the track that the patella glides across when the knee is flexed and extended.(Bontrager, 204; Ballinger 10th ed., 236-7; Ballinger 9th ed., 291-315)
The lower half of the hinge joint is the proximal tibia. The tibia has two condyles which are located at their respective sides, the medial and the lateral. On the anterior portion of the tibia is a protrusion that is called the tibial tuberosity. This tuberosity connects the insertion of the patellar tendon to the bone. Between these two condyles there are also tubercles, medial and lateral, which are also known as the intercondylar eminence. The tubercles protrude upward from a surface known as the tibial plateau. The tibial plateau is a common fracture site.
Connected to the tibia, but not considered part of the hinge joint, is the proximal fibula. The proximal fibula consists of the articulation with the tibia at the apex of the fibula. The apex is the most proximal point. The fibula also has a head and a neck, which leads down the shaft and the distal portion of the fibula. (Bontrager, 202-5; Ballinger 10th ed., 236-7; Ballinger 9th ed., 291-315)
The patella is considered the largest sesamoid bone in the body. It is a small, triangular-shaped bone which glides anteriorly to the knee joint itself. The patella serves to protect the knee joint from direct trauma and helps improve the mechanics of knee extension. The patella consists of a convex anterior surface, posterior surface, three borders, and an apex. The thick superior border or base is sloped down and forward. The apex is the pointed inferior or distal portion. The lateral and medial borders make up their respective sides.
Along with bony structures, there are soft tissue structures that hold the knee together. On the sides of the joint are collateral ligaments. These ligaments are made to help the knee move from side to side, either laterally or medially. There are also two cruciate ligaments. The anterior cruciate ligament (ACL) starts at the anterior aspect of the tibia and runs to the posterior aspect of the femur. The posterior cruciate ligament (PCL) runs from the anterior aspect of the femur to the posterior portion of the tibia. Both of the cruciate ligaments run through the intercondylar fossa of the femur and prevent the knee from dislocating in the anterior/ posterior movement.
The patella is strategically held in place with the help of one major ligament, the patellar ligament, and many minor ligaments. The patellar ligament runs across the anterior surface of the patella. Just below the patella and behind the patellar ligament is a fat pad. This fat pad protects the knee joint as a whole. The tibial tuberosity is a connection site for the patellar tendon. To aid in the movement of the knee, there are capsules and cartilage. These capsules are called bursas which are located both inferior (infrapatellar bursa) and superior (suprapatellar bursa). The bursa appears as a pouch containing a jell-like fluid. The function of the bursa is to decrease friction between two surfaces. The bursa is located at points where the muscles and tendons glide over bones. Without a bursa, movements would be painful. The cartilage that helps the joint glide smoothly between the femur and the tibia are known as the meniscus. The meniscus is a C-shaped fibrocartilage which is located at the peripheral aspect of the joint between both the condyles of the femur and on the tibial plateau. The majority of the meniscus has no blood supply. For that reason, when damaged, the meniscus is unable to undergo the normal healing process. The meniscus will also deteriorate as an individual ages, often developing degenerative tears. The menisci which are located both medial and lateral provide shock absorption which helps prevent impact injuries to the knee joint.
EXAMS FOR GENERAL DIAGNOSTIC
There are three main views of the knee that have taken on the name of trauma views of the knee. These are the:
AP medial oblique
Patient is supine with leg extended
Central Ray (CR) perpendicular to Image Receptor (IR)
CR one inch below the apex of the patella
A 5-7 degree cephalic angle should be utilized
Patient is supine with leg internally rotated 45 degrees
CR is perpendicular to the IR
CR is 1/2 inch below the apex of patella
Medial Oblique View
The knee will be in a true lateral position, whether the patient is rolled on affected side or a cross-table lateral is shot
Condyles are superimposing on each other
Flex knee 20-30 degrees if possible
CR is perpendicular to the IR
CR is one inch below apex of patella
Cross-Table Lateral View
External Oblique (Lateral Oblique)
Patient is supine with leg externally rotated 45 degrees
CR is perpendicular to the IR
CR is one inch below the apex of patella
External Oblique View
Bilateral Weight Bearing (AP)
Patient is upright in an AP position and weight bearing on both knees equally
CR is perpendicular to the IR
CR is one inch below apex of patella
Arthritis is best demonstrated in the tibiofemoral joints
Bilateral Weight Bearing (AP) View
AP Axial (Intercondylar fossa)
Patient is supine
Knee flexed 40-45 degrees
Cassette under the posterior aspect of knee
CR is perpendicular to the tibula/fibula
CR is one inch distal to apex of patella
The intercondylar fossa and joint mice (loose bodies, often pieces of torn cartilage or bone chips, floating within the knee) are best demonstrated on this view
AP Axial (Intercondylar fossa)
PA Tunnel View (Axial)
Knee flexed 40-50 degrees resting up on sponge
Foot will rest on a sponge to keep knee bent
CR perpendicular to tibula/fibula
Cassette will rest under patella
Patient in kneeling position
From kneeling the patient will lean forward approximately 20-30 degrees
CR perpendicular to IR and lower leg
Cassette placed beneath patella
CR is perpendicular to the IR
CR is to knee joint/mid patella area
Done PA versus AP because there is less distance and increased boney detail
PA Patella View
CR is perpendicular to the IR
Flex knee 5-10 degrees
Knee is in true lateral position
CR to the mid patellofemoral joint
Horizontal fracture of the patella are best demonstrated on this view
Lateral Patella View
Patient is supine
Knees flexed 40 degrees over the end of the table
Cassette placed between feet and knees
CR is perpendicular to the IR
CR angled caudad 30 degrees from horizontal
CR between the patellaes
Merchant (Bilateral) Patella View
Patient is supine
Knees together with 40 degree sponge underneath
Cassette is placed mid thigh positioned almost vertically
CR is perpendicular to the IR
Vertical fracture of patella is best demonstrated on this view
The knee joint is used in virtually every daily activity. It is essential to the human body to be able to perform such tasks as walking, standing, and running. This leads to the knee joint being highly vulnerable to many types of injuries and susceptible to many different degenerative conditions.
FRACTURES AND COMMON CONDITIONS OF THE KNEE
There are many fractures that can affect the knee joint. Some are more common than others. Mild injuries may involve a bone breaking that stays contained within the skin. This is known as a closed fracture.
The closed fracture may also be known as a simple fracture. The surrounding skin will seem to be virtually unaffected by the fracture inside.
A patient may have trauma that could result in an oblique fracture. The oblique fracture tends to run at an angle through the bone, not straight across. This fracture is often mistaken for a spiral fracture. The spiral fracture has a definite corkscrew effect which is readily seen on imaging.
Many fractures are more complex than the closed fractures. Some injuries may cause the bones to break into two or more pieces which could protrude through the surface of the skin. This type of fracture is referred to as an open or compound fracture. These fractures are considered unstable. An unstable fracture is considered an emergent condition that requires prompt treatment to prevent lasting tissue, nerve or bone damage. The compound fracture would require surgical repair. ("Classification of Broken Bones and Fractures", Bontrager, 596)
FRACTURES OF THE PATELLA
The patella is known to be susceptible to three main fractures; the stellate, horizontal or transverse and vertical. These fractures are most often caused by trauma. The stellate fracture is generally caused by a direct blow which causes the patella to burst into a star-like pattern. This fracture is best visualized on an AP/PA view of the knee.
A horizontal or transverse fracture of the patella tends to occur in the central or distal one third of the patella. With this type of patella fracture, the crack runs across the knee cap within the medial and lateral borders. This fracture is best seen on a lateral view of the knee.
Horizontal or Transverse Fracture
The vertical fracture of the patella is considered relatively rare. This type of fracture runs from the superior aspect or base of the patella to the inferior aspect or the apex of the patella. This fracture is best seen on the sunrise view of the patella. ("Fractures of the Patella")
These fractures are all treated with surgical fixation around the patella.
DISLOCATION OF THE PATELLA
An injury to the knee may cause a patellar dislocation. Patellar dislocations tend to be laterally dislocated, resulting from a medial structure failing, muscle imbalance or leg mal-alignment. The patella can be reduced with the knee in flexion. Once reduced, flexion and extension of the knee can be resumed after the pain and swelling are under control. Non-operative treatments involve muscle exercises. These exercises strengthen the quadriceps after a period of immobilization. The surgical treatment consists of soft tissue repairs, bone realignment procedures or patellectomy. ("Subluxation/Dislocation of the Patella")
TIBIAL PLATEAU FRACTURE
Fractures of the tibial plateau are quite common. This type of fracture involves damage to the proximal portion of the tibia, the condyles and plateaus. While this injury is easily identified on trauma views of the knee, CT and MRI correlation is used extensively. The attending physician or radiologist may request a CT scan with coronal and axial slices. Frequently, the orthopedic surgeon may request a MRI to aid in surgical planning. Since the MRI is time consuming, it is usually considered after a trauma patient is stabilized and can tolerate the lengthy procedure.("Radiographic Studies for Tibial Plateau Fractures")
Tibial Plateau fracture
A common condition that can cause discomfort or pain in the posterior aspect of the knee is a Popliteal or Baker's cyst. The Baker's cyst is a swelling or fluid-filled mass protruding from the back or popliteal area of the knee that can be felt as a hard lump. This can occur when an excess of synovial fluid is compressed between the bones of the knee joint causing some of the fluid to separate from the knee joint. This fluid becomes trapped outside the joint to form a fluid-filled sac or Baker's cyst. Most Baker's cysts can be diagnosed upon physical examination. The cyst should feel soft and somewhat tender, like a water-filled balloon. Unless the cyst has ruptured, no additional imaging may be required. If the cyst has ruptured, there could be painful swelling, redness and bruising behind the knee into the calf of the leg. Since pain, swelling and bruising can also be symptoms of a blood clot, immediate medical attention is required.
Although most Baker's cysts cannot be identified on conventional radiographs because they are fluid-filled, a multi-lobular (many chambers) cyst can show up on x-ray as little dense balls posterior to the knee joint on a lateral projection. This type of popliteal cyst should be positively identified utilizing ultrasound to differentiate between a fluid-filled or solid mass. Magnetic resonance imaging (MRI) can also be obtained. The MRI provides excellent soft-tissue detail which can determine if a palpable mass is a fluid-filled sac or solid mass.
By name, bursitis is known as inflammation (-itis) of the bursa (-burs). This inflammation could be caused by several different factors. There may have been a traumatic incidence, overuse, or an underlying infection which could result in bursitis. The fluid surrounding the joint can be identified most prominently on MRI. After diagnosis, the patient and their physician may choose to treat the inflammation with rest, ice, elevation, and a compression pack. Others could choose to get the fluid aspirated in clinic or with the guidance of fluoroscopy.("Bursae and Bursitis of the Knee")
With Osgood Schlatter disease, the quadriceps muscle (patellar tendon) that attaches to the tubercle of the tibia has a tendency to pull the tubercle away from the tibia. This happens before the tubercle is completely fused with the anterior portion of the tibia. Osgood Schlatter disease is more common with people who are extremely active. This can be easily identified on a lateral x-ray view of the knee. This is the most practical way to diagnose and also the least expensive since the condition is rarely treated with more than decreased activity.("Osgood Schlatter Lesion")
Osgood Schlatter Disease
While the majority of diagnostic x-rays of the knees are ordered for acute trauma, a clinician would request AP and lateral views when a patient presents with persistent pain to the surrounding bone or joint with no known or apparent trauma. These radiographs could reveal an inflammatory or degenerative disease process such as arthritis, gout, Paget's disease, osteomalacia, osteoporosis, or Rickets. These radiographs could also provide evidence of ischemic necrosis of the bone, a benign cyst or a possible malignant metastases or tumor such as osteogenic sarcoma, chondrosarcoma, Ewing's sarcoma, and multiple myeloma to name a few.
While the AP and lateral knee radiographs can provide an initial diagnosis, CT, MRI, and nuclear medicine imaging would be utilized to obtain additional diagnostic information to help the attending clinicians determine the appropriate course of treatment.
While the bone structures of the knee can usually be adequately evaluated on a conventional radiograph, an arthrogram may be indicated. An arthrogram is an exam done to view the soft tissue aspects of the knee. It is an intra-articular injection with fluoroscopic guidance of a contrast medium to highlight the internal and surrounding tissue.
After the risks and benefits of the exam are explained, the patient will need to sign a consent form allowing the Radiologist to perform the exam. According to "Arthrography", by Robert H. Freiberger (MD) and Jeremy J. Kaye (MD), the main risks involved are allergic reaction, infection, and joint effusion. An allergic reaction from the contrast could range from simple hives to anaphylactic shock. When a patient has a known contrast allergy, it is imperative they be pre-medicated with a steroid and Benedryl prior to the exam. There is always a possibility of the patient developing an infection. Even though a sterile technique is utilized; anytime the skin is punctured there is a risk for a potential infection. Once the contrast is injected, the patient may experience discomfort and inflammation around the joint. If this is severe, it could indicate a synovial effusion which is the result of excessive fluid collecting in the joint. If this condition does not resolve, an additional needle puncture could be necessary to aspirate the extra fluid to provide pain relief.
There are three different varieties of arthrograms that can be performed. There is a single contrast with the use of a contrast medium, single contrast with air used as the contrast, and there is a double contrast which uses both a contrast medium and air. The contrast media used has a water-soluble iodinated base. Whichever exam is chosen, there are positives and negatives, to each arthrogram. The different types of arthrograms that are preformed all highlight soft tissue with different densities. The bone will be apparent and easily visible as in a conventional radiograph. The negatives of the single contrast with a contrast media: the Radiologist could inject too much contrast and the soft tissue structures trying to be viewed would be obscured. Also if there happens to be loose articles in the joint, the excessive contrast might cause the radiologist to overlook the loose bodies which could result is a misdiagnosis. The arthrogram performed with air only can also provide a variable diagnosis depending on where the air is injected into the joint, and how much air is injected. With these factors involved, the negatives are that there may not be enough of a density difference for the Radiologist to make an accurate reading. The double contrast arthrogram has been proven to be the most beneficial in providing a clear and accurate diagnosis. When the double contrast technique is utilized, the soft tissue (cruciate ligaments and menisci) will be outlined with contrast media and air providing more diagnostic information. The draw back is the possibility of air bubbles being visible in the joint which may cause an inconclusive diagnosis. Films may be taken pre and post exercise once the injection has been completed. Additional views may also be taken while the knee joint is being stressed by the attending Radiologist. Several different types of patient immobilizers are available to secure the leg while the knee is being stressed. Any combination of the different views taken may demonstrate a loose body floating in the joint or a possible ligament or meniscus tear. When the Radiologist looks at the final films, he/she will usually determines if there is a finding that could warrant additional imaging with CT or MRI.(Freiberger and Kaye, 1-11)
According to Arthrography, by Robert H. Freiberger (MD) and Jeremy J. Kaye (MD), an arthrogram under fluoroscopy is performed as follows:
Have the patient lay on their back on the fluoroscopy table
Under the affected knee should be a radiolucent sponge
The sterile arthrogram tray should be opened utilizing sterile technique
The affected knee is prepped and draped using sterile technique
Depending on the Radiologist preference local analgesic could be used to anesthetize the affected knee for comfort of the patient
The Radiologist will use fluoroscopy to view the knee joint and determine whether a medial or lateral approach would be more beneficial for injecting the contrast into the joint. It is recommended that the needle be inserted directly into the femoropatellar joint for best access.
Ultrasound is not a modality used for the visualization of the bony anatomy of the knee. Regardless, it is frequently used to highlight the soft tissue, veins and arteries around the knee joint. Ultrasound imaging is based on waveforms made by the fluid in the extremities.
The waveforms produce different frequencies that all together make up the spectral window. According to Ultrasound, by Alfred B. Kurtz (MD) and William D. Middleton (MD), the Doppler waveform shows a clear space between the arterial signal and the baseline. This is referred to as the spectral window. (Ultrasound, 464) The spectral window all depends on the velocities of blood flow throughout the vessels being viewed. There is a narrow range and a wide range of velocities that together help complete the spectral window. Some factors have the ability to alter the outcome of an ultrasound exam. One such factor is that ultrasound has angles which are highly involved. The high angles could elevate the risk of errors when measuring velocity.
This modality is greatly used for viewing the following:
Deep vein thrombosis
Obese patients' veins
(Kurtz and Middleton, 464-487; "Deep Venous Thrombosis"; "Venogram")
Deep vein thrombosis (DVT) is a condition in which a blood clot (thrombus) forms in a vein that is deep inside the body. A DVT is the main pathology that can be seen in the vicinity of the knee joint. Deep vein thrombosis is a relatively common condition affecting the veins in the legs. This condition is most common in adults over age 60, but it can occur in any age group. The formation of a DVT can be brought on by many factors. These factors include prolonged sitting or bed rest. A DVT may also be caused by recent surgery, fractures, childbirth, and the use of medications such as estrogen and birth control pills. The patient with a potential DVT may experience swelling, pain or tenderness, increased warmth or color change to the extremity. These clots can travel to the heart, lungs or brain which has the potential to be life threatening if not found and treated within a reasonable amount of time.(Kurtz and Middleton, 464-487; "Deep Venous Thrombosis"; "Venogram")
Advancement in doppler imaging has made the tradition venogram almost obsolete. The use of ultrasound provides the clinician with a diagnosis of a DVT without any risk to the patient.
While diagnostic radiographs seem to fail on providing a diagnosis for the soft tissue aspects of the knee, arthrography was the next best thing. MRI soon replaced arthrograms or was used in conjunction with arthrography.
MRI has become possible because of hydrogen protons and the use of magnetic fields. A normal hydrogen proton becomes altered when introduced to magnetic fields. When a proton is in its original state, it has a certain amount of energy stored up. This energy is lost during the MRI in an effort from the protons to accommodate to the magnetic field. The field allows the protons to put out a radiofrequency which in turn creates the very detailed images.(Munk and Helms, 1; UNICARE; "MRI of Knee")
Before a MRI is considered, a short patient history should be obtained. There are some contraindications for MRI including: certain implanted hardware in patients, pacemakers, patients who have a history of welding (may have metal in eye), and most surgical and/or aneurysm clips. (MRI of the knee, 2-3) Patients who have a history of working with metal may be allowed to proceed with the MRI after x-rays of the orbits, and/or the affected joint are cleared by a Radiologist. The scanner for the MRI has confined quarters, so some patients may have an issue with their weight or size, and be unable to proceed with a MRI. Other patients may be claustrophobic and will need to be sedated prior to the exam.
Different imaging planes can be utilized; this would be determined by the anatomy being imaged. Three-dimensional (3-D) imaging provides images in all three planes-sagittal, coronal and axial-from a single set of data. This data can be reformatted by the computer creating a 3-D image reconstruction. This type of MRI imaging is frequently requested by orthopedic surgeons. Since the iodinated contrast agents that are widely used throughout radiology are not effective with MRI, a contrast agent made especially for use with MRI has been developed. This substance is called gadolinium (Gd-DTPA). The side effects of gadolinium include mild headache, rash, gastrointestinal upset, nausea, vomiting, hypotension, and a slight increase in serum bilirubin. Gadolinium can be injected intra-articular during a fluoroscopic arthrogram, which was discussed earlier, and MRI imaging then obtained. Even without the administration of this contrast, MRI will provide very detailed imaging of the knee.(Munk and Helms, 2-3; UNICARE; "MRI of Knee")
Anatomy Demonstrated on Sagittal Plane Images
Anatomy Demonstrated on Coronal Plane Images
Collateral Ligaments (Only seen on coronal)
Anatomy Demonstrated on Axial Plane Images
Brings the other planes all together
When the MRI scan is complete, the technologist may alter the images to better demonstrate significant structures to accommodate the clinic/hospital protocol or at the Radiologists' request.
In conjunction with x-rays of the knee, CT can be beneficial in certain circumstances. A CT scan is frequently ordered when a patient has a fracture. The scans obtained can be useful in planning strategies for surgeries to reduce and repair the fracture site. The multiple planes offered would provide more diagnostic information of the fracture than a one dimensional x-ray would provide. Also when there are contraindications present for MRI, CT can gain information that may have been lost without the MRI. As with MRI, CT can also be used in correlation with arthrography. The CT arthrogram will not provide the same detailed imaging as the MRI arthrogram, but seems to show sufficient information to help make a diagnosis especially when soft tissue injuries and tears would be a concern. If a patient has had a knee replacement or significant hardware surgically placed, there will be streaking on the scan. This artifact creates a potential for misdiagnosis or an inconclusive study(MRI and CT of the Musculoskeletal System, 662-8; "CT/MRI Hips, Pelvic Bones, Knee, Ankle, Foot")
As with MRI, CT imaging can produce a three-dimensional or multiplanar image utilizing all three planes-sagittal, coronal and helical-from a single set of data.
KNEE INJECTION FOR PAIN RELIEF
The knee is a joint that is susceptible to the painful degenerative changes of both osteoarthritis and rheumatoid arthritis. Osteoarthritis is a degenerative joint disease that tends to predominately affect weight-bearing joints and the interphalangeal joints of the fingers. Although osteoarthritis is considered a wear and tear aging process, it can also develop in a joint after an injury or trauma. With osteoarthritis, there is a significant asymmetrical narrowing of the joint space caused by the thinning of the articular cartilage and the development of small bony spurs, osteophytes along the edges of the bone. The surface of the cartilage becomes rough and pitted so the joint no longer moves smoothly. Symptoms of osteoarthritis include pain, swelling, grinding sensation, stiffness after periods of rest and limited range of motion in the affected joint. As the damage worsens, the affected joint becomes more painful, less movable and unstable as the ligaments surrounding it stretch.
Rheumatoid arthritis is a chronic systemic disease that appears as an inflammatory arthritis starting in the small joints of the hands and feet. In rheumatoid arthritis, the joint spaces tend to have smooth, even narrowing with eventual joint fusions and deformities as the disease progresses. Rheumatoid arthritis is the most debilitating form of arthritis. Rheumatoid arthritis can progress until every joint in the body is involved or may undergo remissions of varying lengths. The average age of onset for rheumatoid arthritis is 40 years. Women are affected more frequently than men.
While these debilitating conditions can make standing and walking unbearable for the inflicted individual, an intra-articular injection of a combination of corticosteroids (steroids) and a long-lasting analgesic can provide temporary relief while providing the attending clinician valuable diagnostic information. If the patient's pain decreases after the injection, it is believed the source of the pain is the affected joint.
The knee injection for pain relief is a procedure similar to that of the knee arthrogram. The attending Radiologist will obtain an informed consent explaining the risks and benefits. The sterile tray is set up with betadine solution, local analgesic, sterile drapes, extension tubing, and at the Radiologists' preference, x-ray contrast, steroids, and a needle to get into the joint space. This exam can be done with fluoroscopy guidance by the Radiologist or in a clinical environment with the attending physician's expertise.
The standard knee injection can also include an aspiration if there is suspicion of an infection or excess fluid in the joint. The synovial fluid removed would be sent to the laboratory for specific diagnostic tests. The results of these tests could confirm or rule-out a diagnosis. There are different methods or approaches a physician might use to gain access to the knee joint. These include the medial approach, the medial suprapatellar approach, and the inferior approach. ("Knee Joint Injection") The Radiologist or attending physician will decide which approach would be appropriate based on the patient's knee anatomy.
While intra-articular joint injections with steroids may help with pain management, its effectiveness is limited. It is also widely recommended that these injections should not exceed four injections per joint per year. Exceeding this recommendation could cause a weakening of the bone, ligaments and tendons in the treated area. In addition to the joint injections that contain a combination of analgesic medication (Lidocaine, Xylocaine, Bupivicaine, Marcaine, etc...) and steroid, (Depomedrol, Kenalog, Celestone, etc...), there are alternatives that have been introduced which many individuals have benefited from. This new therapeutic joint injection provides lubrication for the joint, while the steroid injection does not.
Sodium Hyaluronate (Synvisc, Orthovisc, NeoVisc) injected into the joint space works as a viscosupplement by improving the natural viscosity and elasticity of the synovial fluid. This joint treatment will increase the lubrication in the joint which in turn increases joint motility and decreases pain. Viscosupplementation is considered a therapy not a drug. The Sodium Hyaluronate injections are typically given seven days apart for a total of three injections. This therapy is used to alleviate pain in the patient trying to prevent surgery or in patients who have already had surgery and continue to experience pain. Most individuals will get significant pain relief for up to six months. These injections can drastically improve the quality of a patient's life. Elderly patients suffering from osteoarthritis seem to benefit the most.(Euflexxa; Supartz: Joint Fluid Therapy; Family Practice Notebook)
Arthroscopy of the knee is a procedure typically done in a surgery suite by a skilled orthopedic surgeon. This procedure not only provides a detailed view of the knee and its soft tissue structures, it allows the attending physician an opportunity to surgically repair many conditions. Arthroscopic surgery is made possible by inserting a small diameter fiber optic camera into the knee joint, which is attached to a video monitor, into the knee. Generally, only local or regional anesthesia is required. The patient remains awake and able to respond. In some facilities, the patient can choose to watch the monitor as well. After the camera is inserted, saline is pumped into the knee under pressure to expand the joint and help control bleeding. During the course of the arthroscopy, the surgeon will make additional incisions to insert small instruments into the knee to complete the procedure. Commonly used instruments include a blunt hook to retract tissues, a shaver to remove damaged tissues, and a burr to remove bone. A cauterizing heat probe may also be used.
Most patients who undergo arthroscopic surgery will have had previous knee imaging. With the information provided by x-rays, CT, MRI or arthrograms, the surgeon is able to plan a surgical strategy prior to the arthroscopic procedure. Arthroscopic knee surgery is frequently implemented to repair or remove a torn meniscus, reconstruct ligaments, remove loose debris and trim damaged cartilage. While the arthroscopic approach is less traumatic to the muscles, ligaments and tissues than surgically opening the knee, the orthopedic physician will determine the best surgical option based on clinical exam, condition/age of patient and diagnostic imaging results.
KNEE REPLACEMENT SURGERY
Often, a patient with persistent knee pain will undergo numerous diagnostic tests, physical therapy, and intra-articular injections trying to prevent the inevitable, surgical joint replacement. A surgical knee replacement actually resurfaces the damaged bony aspects of the knee. The worn articular cartilage, end of the femur, top of the tibia, and the back portion of the patella are resurfaced with a metal or plastic device (prothesis). These prostheses are fixed to the healthy bone by plastic cement. The metal and plastic counterparts will simulate a healthy, active knee joint.
Since knee replacements first became available in the 1970's, they have become a common surgery performed on patients to improve quality of life by reducing pain and increasing mobility. Depending on the patient's joint condition, a total knee replacement (TKR) or a partial knee replacement (PKR) can be performed. The total knee consists of replacing the distal aspect of the femur, the proximal aspect of the tibia, and sometimes the patella. With the TKR, both condyles on the distal aspect of the femur are reshaped and replaced. A metal and plastic counterpart is placed in the joint. The counterpart is shaped with two femoral condyles and a simulated trochlear sulcus. The proximal tibia is fitted for a plate that fits into the space where the tibial plateau lies.
The PKR, unlike the TKR, usually involves resurfacing just one of the femoral condyles and the adjacent tibial plateau. With the unicompartmental knee replacement, the surgeon has decided that one side of the knee is salvageable. Since only the damaged side of the knee joint is replaced, the PKR allows more natural knee movements by retaining more of the natural joint lubrication. Whether the total knee replacement or the unicompartmental knee replacement is performed, the prothesis needs to be secured to the existing bone. The plates can be fixed into place by cement, non-cemented, or a combination. The way the plate is secured into the joint determines when the patient can start bearing weight on the joint. The non-cemented joint will need a little more healing before the patient can walk, because the bone grows around the plate to secure it.
The orthopedic surgeon will determine which type of knee replacement would be most beneficial for the patient. For both of these replacement surgeries, the surgeon may choose to leave the original patella or it may be resurfaced.(Get Bonesmart; Total Joint Replacement; Knee-Replacement Surgery, the Knee Society; "Knee Replacement")
After the decision has been made to proceed with the knee replacement, the patient would need a pre-operative physical exam which could include a variety of blood tests and additional x-rays. It is also suggested that the patient prepare their homestead for post surgery care. Change the sheets of the bed, keep the remote control handy, and make sure someone is available to assist them immediately following discharge from the hospital.(The Knee Society; Knee-Replacement Surgery; "Total Knee Replacement")
The patient should be NPO since midnight prior to exam. The surgeon will obtain an informed consent explaining the risks and benefits of the surgery. An anesthetist will determine which anesthesia will be best suited for the patient.
Following the surgery, the patient will be given pain medication, as needed. The patient will be encouraged to get out of bed as soon as possible. With increased bed rest, there is always a possibility of blood clots post surgery. This is also known as a Deep Vein Thrombosis (DVT), diagnosed by ultrasound. To prevent a DVT, the surgeon may prescribe blood thinners. The patient will be instructed on wound care and the prevention of infection. Preventative antibiotics may be prescribed. The average hospital stay is two to four days. A short recuperative stay in a nursing care facility could be required. To help with the recovery, the patient will receive physical therapy and occupational therapy. The patient should be able to resume normal activities within six to twelve weeks.(Knee-Replacement Surgery; Get Bone Smart)
The ball and socket, pivot, and hinge joints are the three main types of moveable joints.
Hinge joints are those that permit the forward and backward movement of the finger and the knee.
Being one of the largest joints in the human body, the knee is more likely to sustain damage from trauma or injury than from normal wear and tear.
The bone structures of the knee are the distal aspect of the femur, the proximal aspect of the tibia, and the patella. The fibula doesn't articulate with the knee joint, but it does act as a stabilizer for the body as a whole.
The epicondyles are the connection site for the collateral ligaments.
The purpose for the intercondylar fossa (notch) is to allow a space for all of the soft tissue structures of the knee joint to pass through. The intercondylar sulcus (groove) is the track that the patella glides across when the knee is flexed and extended.
The intercondylar sulcus lies in the anterior portion of the knee and the intercondylar fossa lies in the posterior portion of the knee, both of which lies between the two condyles of the femur.
On the anterior portion of the tibia is a protrusion that is called the tibial tuberosity. This tuberosity connects the insertion of the patellar tendon.
Between the two condyles are also tubercles, medial and lateral, which are also known as the intercondylar eminence. The tubercles protrude upward from a surface known as the tibial plateau. The tibial plateau is a common fracture site.
The anterior cruciate ligament (ACL) starts at the anterior aspect of the tibia and runs to the posterior aspect of the femur. The posterior cruciate ligament (PCL) runs from the anterior aspect of the femur to the posterior portion of the tibia. Both of the cruciate ligaments run through the intercondylar fossa of the femur and prevent the knee from dislocating in the anterior/ posterior movement.
The patella is strategically held in place with the help of one major ligament, the patellar ligament, and many minor ligaments. The patellar ligament runs across the anterior surface of the patella.
The tibial tuberosity is a connection site for the patellar tendon.
Bursas which are located both inferior (infrapatellar bursa) and superior (suprapatellar bursa) are capsules that aid in the movement of the knee.
The meniscus is a C-shaped fibrocartilage which is located at the peripheral aspect of the joint between both the condyles of the femur and on the tibial plateau.
The routine trauma views of the knee are the AP, AP medial oblique, and lateral.
For the AP view of the knee the central ray (CR) is centered one inch below the apex of the patella.
On the AP medial oblique view the patient is supine with the leg internally rotated 45 degrees.
On the lateral view, the knee needs to be flexed 20-30 degrees.
On the bilateral weight bearing AP view of the knee, arthritis is best demonstrated in the tibiofemoral joints.
In comparing the PA versus the AP Patella, the PA is preferred because there is less distance resulting in less magnification on the radiograph and increased boney detail.
A horizontal fracture of the patella is best demonstrated on the lateral patella view with the knee flexed 5-10 degrees.
A vertical fracture of the patella is best demonstrated on the Inferosuperior/ Sunrise/Skyline view.
The closed fracture may also be known as a simple fracture.
The oblique fracture tends to run at an angle through the bone, not straight across. This fracture is often mistaken for a spiral fracture. The spiral fracture has a definite a corkscrew effect which is readily seen on imaging.
Some injuries may cause the bones to break into two or more pieces which could protrude through the surface of the skin. This type of fracture is referred to as an open or compound fracture.
The patella is known to be susceptible to three main fractures, the stellate, horizontal, and vertical.
Patellar dislocations tend to be laterally dislocated, resulting from a medial structure failing, muscle imbalance or leg mal-alignment.
Fractures of the tibial plateau are quite common which involves damage to the proximal portion of the tibia, the condyles and plateaus. While this injury is easily identified on trauma views of the knee, CT and MRI correlation is used extensively.
A Popliteal or Baker's cyst is a swelling or fluid-filled mass protruding from the back or popliteal area of the knee that can be felt as a hard lump.
With Osgood Schlatter disease, the quadriceps muscle (patellar tendon) that attaches to the tubercle of the tibia has a tendency to pull the tubercle away from the tibia.
An arthrogram is an exam done to view the soft tissue aspects of the knee. It is an intra-articular injection with fluoroscopic guidance of a contrast medium to highlight the internal joint space and surrounding tissue.
Once the contrast is injected during an arthrogram the patient may experience discomfort and inflammation around the joint. If there is severe discomfort and inflammation around the joint space following the injection of contrast, a synovial effusion may be indicated. A synovial effusion is the result of excessive fluid collecting in the joint.
Ultrasound is greatly used for viewing the following:
Deep vein thrombosis
Obese patients' veins
The formation of a DVT can be brought on by many factors include prolonged sitting or bed rest., recent surgery, fractures, childbirth, and the use of medications such as estrogen and birth control pills.
The side effects of gadolinium used during an MRI include mild headache, rash, gastrointestinal upset, nausea, vomiting, hypotension, and a slight increase in serum bilirubin.
In conjunction with x-rays of the knee, CT can be beneficial in certain circumstances and is frequently ordered when a patient has a severe fracture. The scans obtained can be useful in planning strategies for surgeries to reduce and repair the fracture site.
Osteoarthritis is a degenerative joint disease that tends to predominately affect weight-bearing joints and the interphalangeal joints of the fingers.
With osteoarthritis, there is a significant asymmetrical narrowing of the joint space caused by the thinning of the articular cartilage and the development of small bony spurs (osteophytes) along the edges of the bone.
Rheumatoid arthritis is a chronic systemic disease that appears as an inflammatory arthritis starting with the small joints of the hands and feet. In rheumatoid arthritis, the joint spaces tend to have smooth, even narrowing with eventual joint fusions and deformities as the disease progresses.
When Sodium Hyaluronate (Synvisc, Orthovisc, NeoVisc) is injected into the joint space it works as a viscosupplement by improving the natural viscosity and elasticity of the synovial fluid. This joint treatment will increase the lubrication in the joint which in turn increases joint motility and decreases pain.
Arthroscopy not only provides a detailed view of the knee and its soft tissue structures, it allows the attending physician an opportunity to surgically repair many conditions such as a torn meniscus, reconstruct ligaments, remove loose debris and trim damaged cartilage.
A surgical knee replacement actually resurfaces the damaged bony aspects of the knee. The worn articular cartilage, end of the femur, top of the tibia, and the back portion of the patella may be resurfaced with a metal or plastic device (prothesis).
The total knee consists of replacing the distal aspect of the femur, the proximal aspect of the tibia, and sometimes the patella. With the TKR, both condyles on the distal aspect of the femur are reshaped and replaced.
The PKR, unlike the TKR, usually involves resurfacing just one of the femoral condyles and the adjacent tibial plateau. With the unicompartmental knee replacement, the surgeon has decided that one side of the knee is salvageable.
Arthroscopy. Rosemont: American Academy of Orthopedic Surgeons, 1995.
Arthroscopy of Your Knee. St. John Companies, 1998.
"Avulsion of the Tibial Tubercle". Wheeless' Textbook of Orthopedics. 11 Sept. 2007