The term ‘knee pain’ can be used to describe a wide variety of conditions. Pain can be located in the front, sides, back, or throughout the entire knee. It may be acute or chronic. It can be caused by traumatic injury such as a fall or motor vehicle accident. Pain may also develop slowly over time. The intensity of pain can range from mild to severe. Various imaging techniques can be useful in determining the cause of knee pain regardless of the location, onset, or intensity of pain. This study will focus on how imaging can be useful for different specific conditions where pain in the knee. We will be able to use a range of imaging techniques to determine if they are acute or chronic, helping us to determine the cause of the pain. The more common conditions include ligament and meniscal injuries, osteoarthritis, stress fractures and bone bruises, and problems involving the patella. We will discuss these conditions individually throughout the study.
The objective of this study is to describe and analyze the role of diagnostic imaging in the assessment and treatment of pain in the knee. We will clearly define how different imaging techniques can be used to help diagnose problems that can occur in the knee. As a patient, you may be unsure what is causing your pain. This is a common issue for many patients with various knee problems. Making an accurate diagnosis is very important because it will direct the course of treatment. Patients will receive the most appropriate treatment if the correct diagnosis is made. In some cases, determining the cause of your pain may not be so straightforward. This is where different imaging techniques can be very useful.
Common Causes of Knee Pain
Meniscus tears are one of the most common knee injuries. Each knee has two menisci, which are crescent-shaped and sit on top of the tibia. The role of the menisci is to distribute the weight of the body and to provide stability to the joint. The menisci are often torn when there is a sudden twist to the knee while the foot is planted on the ground. This is very common in sports such as football, tennis, and basketball. Older patients are at risk of a tear due to degeneration of the meniscus. The symptoms of a torn meniscus are pain on the side or center of the knee, swelling, stiffness, and the knee giving way. Locking and instability of the knee may also be felt. An accurate diagnosis and assessment of the tear is important in determining the most suitable treatment. High-resolution ultrasound is effective for assessing a recent or traumatic tear; however, an MRI is the most effective method of diagnosis. This is crucial for older patients who have a degenerative tear, as the tear can be difficult to assess and symptoms may be similar to those of osteoarthritis. A patient with an unclear diagnosis may require an arthroscopy so that the surgeon can look inside the knee and assess the damage to the meniscus. A diagnosis provided by an MRI can reduce the number of unnecessary arthroscopies.
Knee ligament injuries are another common cause of knee pain. The cruciate ligaments are found inside the knee joint. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) sit in the center of the knee joint and cross over each other to form an “X”. The ACL prevents the tibia from moving forwards on the femur, as well as providing stability to the knee. The ACL is often torn when there is a sudden change in direction or pivot against a locked knee. This is a common injury for athletes. The PCL, on the other hand, is often injured from a direct blow to the front of the tibia, such as landing badly from a jump. A blow to the knee can also cause damage to the other ligaments in the knee. Symptoms of a knee ligament injury are swelling, instability, and pain. However, the extent and the location of the injury can be difficult to assess. Often the diagnosis is unclear and includes assessment of the patient’s symptoms and an examination of the knee. Imaging is usually required to confirm a diagnosis and to assess the severity of the injury. High-resolution ultrasound is usually effective for diagnosing damage to the collateral ligaments. However, an MRI scan is the best option for taking images of the cruciate ligaments and providing an overall assessment of the knee. This is important to help the patient understand their injury and to make decisions regarding the necessity of surgery and the type of therapy that they will require.
Osteoarthritis refers to the degenerative condition of the joints and is one of the most common causes of knee pain. Weight-bearing joints, like the knees, are often affected by osteoarthritis. Symptoms of osteoarthritis in the knee are pain, swelling, and stiffness. The patient may feel the pain more often after physical activity. Occasionally, the pain may be felt at rest and disturb sleep. An accurate evaluation of the severity and the site of the cartilage damage can assist the patient in choosing the most appropriate therapy. High-resolution ultrasound and MRI are the most effective ways of diagnosing osteoarthritis in the knee. They provide pictures of the soft tissues in the body, which are not provided by an x-ray. Using these images, an accurate assessment of the amount and location of the damage to the cartilage can be made. This information can be crucial in deciding whether the patient will require surgery, such as a total knee replacement, or if less invasive therapies such as physiotherapy and medication may be effective.
Osteoarthritis
In the past, plain film radiography was the definitive way to diagnose OA. It remains an inexpensive and useful tool that can also be utilized to monitor progression of the disease. Recommended views include standing anteroposterior weight bearing, tunnel skyline, and lateral views. Unfortunately, OA may have significant symptoms and findings on physical examination without any obvious findings on plain films. In these cases, other imaging modalities such as MRI may be used to make the diagnosis. OA is a progressive disease and the earlier it is diagnosed, the easier it is to halt the damage and attempt to repair.
In the healthy knee, a coating of articular cartilage lines the ends of the bones that form the joint. This cartilage serves as a cushion and allows the joint to glide easily during motion. In the arthritic knee, this surface is damaged which leads to symptoms of pain, swelling, and disability. The diagnosis of OA is often clinically based with history and physical examination. Symptoms include generalized knee pain, stiffness, swelling, giving-way, and local tenderness. Duration and pattern of the symptoms is important as well. Morning stiffness lasting less than 30 minutes and stiffness after prolonged inactivity is often a sign of OA. Symmetrical pain focally located to the inner or outer knee is often indicative of medial or lateral compartment OA.
Osteoarthritis, often abbreviated as OA, is a common disease that is most noticeable in the knee joint. The disease process involves damage to the articular cartilage, leading to functional disability and often times pain. The cause of OA is unknown, but certain people are more likely to develop it due to a genetic predisposition. In these people, joint abnormality or instability, such as a torn meniscus or a ligament injury, may lead to the development of OA. There is also an inflammatory condition that may accelerate the cartilage loss. It is important to understand that OA is not an inevitable part of aging. It is a disease process that may be preventable and ultimately repairable with future technology.
Ligament Injuries
Knee ligament injuries are a very common cause of knee pain, especially in athletes involved in sports that require running, jumping, and sudden changes in direction. The most common knee ligament injuries are to the ACL and MCL. A tear to the MCL is typically caused by a direct impact to the outer part of the knee. It usually does not require surgery and can be rehabilitated with the use of a knee brace, limiting movement, and physical therapy. An ACL injury often occurs suddenly during activities that involve jumping or sudden changes in direction. Changing direction rapidly, slowing down when running, landing from a jump incorrectly, or direct contact or collision, often times a non-contact injury will be the cause of a tear to the ACL. This type of injury is very common in athletes. The patient may feel or hear a “pop” at the time of the injury, and typically the knee will swell immediately in a few hours because of bleeding into the joint. An ACL tear will most likely require surgery and extensive physical therapy to regain full function of the knee. Unfortunately, a surgical reconstruction will not reliably restore normal stability and full function of the knee in the long term. After 15 years from an ACL injury, up to 50% of individuals will have developed some degree of knee osteoarthritis. Some research has shown damage to the articular cartilage in the knee can occur within 6 weeks of an ACL injury. This will increase the likelihood of developing osteoarthritis in the knee. A prolonged period of disability and extensive rehabilitation can also take its toll on the mental health of the patient. This can lead to chronic stress, anxiety, or even depression.
Meniscus Tears
No matter what caused the injury, symptoms commonly experienced are: pain, stiffness, swelling, catching or locking of the knee, and the sensation of your knee giving way. The best way to know for sure if you have a torn meniscus is to have a diagnostic test done by a knee pain specialist. Testing the areas where your meniscus is located, the doctor will let you know whether there is extreme pain. At the time the pain becomes intense, it may be an indication that the edges of your meniscus have moved into the joint space, are catching in the joint, or are actually torn. Around the time of this diagnosis your knee will be very tender and move less than normal, not to mention the pain and swelling will increase. He may say you need meniscus surgery, meniscal repair operation, or have torn cartilage removed.
The pain and swelling can be quite severe. If the tear is large, pieces of the shredded cartilage can catch in the joint causing it to “lock up”. The knee may not straighten and may give way without warning. This is because the displaced meniscal fragment disrupts smooth joint movement and causes the knee to get “stuck”. An additional factor that increases the risk for a meniscus tear is an old knee injury.
Each of your knees has two C-shaped pieces of cartilage that act like a cushion between your shinbone and your thighbone. These are called the menisci. They can tear. A torn meniscus causes pain, swelling, and stiffness. You also might feel a block to knee motion and have trouble extending your knee fully.
Meniscus tears are among the most common knee injuries. Athletes, particularly those who participate in contact sports, are at risk for meniscus tears. However, anyone at any age can tear a meniscus. When people talk about “torn cartilage” in the knee, they are usually referring to a torn meniscus.
Importance of Imaging in Diagnosing Knee Pain
X-rays of the knee are the first imaging tests used to help diagnose knee problems. Plain radiographs of the knee are taken to evaluate the bones and to check for any breaks or fractures. Water on the knee (an accumulation of fluid) and some disorders that affect the patella (kneecap) do not show up well on x-ray, and an MRI scan or bone scan may be needed for further diagnosis. Arthritis is best seen on x-ray, and an increase in the density of the bone beneath the cartilage is an indicator of the early stages of arthritis. If surgery is being considered to treat the knee problem, x-rays will be used to evaluate the alignment of the knee and the success of the procedure.
An injury to the knee can lead to arthritis and cause significant pain. There are various tools that assist the physician in diagnosing the cause of knee pain. The clinical examination is the most important tool in diagnosing the cause of knee pain. However, the proper use of imaging can be equally important. The information from an x-ray can be quite useful. If the x-rays fail to provide a diagnosis, then an MRI may be needed. An MRI can provide the most complete information about the structures of the knee. Ultrasound is also useful in providing images of the soft tissues of the knee.
X-ray Imaging
X-ray technology has been utilized to diagnose knee pain for numerous years and is the most common kind of imaging to consider knee joint pain, stiffness, and swelling. The use of X-ray on knee pain can help rule in or out certain conditions, thus providing a proper diagnosis and treatment plan. X-rays can be used to identify patellofemoral malalignment, primarily through the utilization of a skyline view. Despite MRI being the gold standard for meniscal pathologies, a recent study has shown that MRI can still misinterpret meniscal pathology and that nearly 50% of meniscal tears seen on MRI are also visible on X-ray. The high incidence of meniscal tears found on MRI are often operated on but may not be the cause of a patient’s pain. X-ray is the most effective way to judge the degree of osteoarthritis (OA) in a knee. It is widely known that OA is one of the most common knee disorders and that it is a leading cause of chronic disability. A study found that OA may be present for many years before it becomes symptomatic, thus making it difficult to determine the cause of OA symptoms. X-ray’s ability to show osteophytes and joint space narrowing helps confirm that a patient’s symptoms are due to OA. This, in turn, allows the correct treatment to be carried out to minimize symptoms and disability. For example, if a patient’s pain is due to medial compartment OA and is not relieved by other treatments, a medial unicompartmental knee replacement can be done.
Magnetic Resonance Imaging (MRI)
MRI uses a powerful magnetic field and radio waves to produce detailed pictures of the knee joint anatomy. The images can be viewed on a computer monitor, printed on film or transferred to a CD. This examination is non-invasive and does not use ionizing radiation. An MRI helps the doctor determine the cause of the problem within the knee. The images can be used to plan a treatment based on the specific findings. An MRI provides a very detailed look at the tendons and ligaments, an area where ultrasound or X-ray may not be able to do. The MRI provides imaging that can help differentiate an old injury from a new one. This is very important in making the correct diagnosis when the physician is uncertain about the clinical findings. An MRI is often the best choice when unexplained pain persists after other diagnostic tests and the cause is still unclear. Utilization of the knowledge gained from an MRI can provide quicker and more accurate treatment.
Ultrasound Imaging
Ultrasound imaging should be considered as an imaging method for the knee, mainly because it is non-invasive, it has multi-planar capabilities, it is dynamic, it has no ionizing radiation, and it is the cheapest of all the imaging techniques. It is also specific in the diagnosis of soft tissue lesions, in particular, differentiating various types of meniscal tears, detection of patellar tendon lesions, assessment of Baker’s cysts (with the ability to assess internal derangement of the knee), and ligament tears, in particular injuries to the Medial Collateral Ligament (MCL). It is reliable and produces accurate diagnoses for medial or lateral collateral ligament tears, with reports of up to 98% sensitivity for diagnosing ACL ruptures. Dynamic ultrasound is a useful tool for confirming a clinical diagnosis of patella-femoral pain as well as assessment of the Vastus Medialis Obliquus (VMO) and tracking the patella-femoral joint during movement with the use of real-time ultrasound. This study demonstrated the abilities of MRI and ultrasound in the assessment of patellar tendon abnormalities, showing that ultrasound is sensitive and specific in diagnosing tendinopathies and partial or full thickness tears of the patellar tendon (compared to surgery or clinical outcome as a gold standard), and reasonably reliable at assessing location, size, and depth of patella-femoral cartilage defects, with direct comparison to arthroscopy.
Availability of Imaging Technologies in Singapore
The range of imaging modalities available in the public sector is dwarfed by that of the private sector, where patients can expect expedited access and high-quality facilities. More specifically, X-ray and MRI waiting times are markedly shorter in the private sector, ranging from a few days to a week. The choice of imaging modality is also largely left to the patient and his doctor, and cost considerations mean that the full range of available modalities can be utilized. A significant part of the population in Singapore has integrated shield plans which provide additional coverage for treatment in private institutions, and this will often influence the decision regarding the choice of imaging facility.
Ultrasound is less popular in public institutions but is becoming increasingly available as a form of soft tissue visualization and is useful for guiding injections. The availability and waiting times for these procedures on the whole are largely determined by the clinical indication and the urgency of the case. In knee pain Singapore, having procedures done in public institutions is generally more affordable for the average citizen due to heavy government subsidization. This includes imaging investigations; for example, an X-ray of the knee can cost as low as $10 at some institutions.
Public healthcare institutions use radiography as the primary mode of imaging investigation. These are widely available at all restructured hospitals, with most satellite outpatient clinics equipped with radiography services. Magnetic resonance imaging (MRI) is also readily available at larger institutions like Singapore General Hospital, and is considered the most useful mode of investigation when an accurate diagnosis is required. It is especially useful for internal derangement of the knee such as ligament, meniscus, and cartilage injuries. However, MRI waiting periods can range from a few weeks to a few months, with priority given to more urgent cases and inpatients.
Public Healthcare Institutions
Until 2000, imaging services in public healthcare institutions were provided by general radiography and ultrasound. With the setting up of NHG Diagnostics in 2003, a wide range of imaging services are now available to outpatients and inpatients at subsidized rates. NHG Diagnostics is a cluster-wide unit set up by the National Healthcare Group to coordinate and improve imaging services. Imaging services are available in selected public healthcare institutions under the National Healthcare Group. NHG Diagnostics has also set up a research and development unit to explore ways to improve imaging diagnosis. This unit focuses on developing new techniques and applications for medical imaging. In addition, it is working on improving the accessibility and cost-effectiveness of imaging services. The research findings will be used to review and draw up new clinical guidelines for imaging. This is to ensure that the right type of examination is carried out for the right group of patients to achieve the best clinical outcome. Other public healthcare institutions such as Singapore General Hospital and National University Hospital have also upgraded their imaging services to offer patients the best care. The Society of Radiographers in Singapore and the College of Radiologists work together with the Ministry of Health to ensure the continual improvement of imaging services in public healthcare institutions.
Private Medical Centers
Though private medical centers score better in availability of MRI units, ultrasound and plain film imaging services are quite on par with what is available at public institutions. This is because the cost-effectiveness of both these imaging modalities makes them more viable in the sense that a patient can get the same ultrasound or plain film imaging service at a cheaper rate in the public hospital specialty outpatient clinics and polyclinics. The quality of the ultrasound and plain film imaging services will also not differ much when compared to what is available in the private sector.
When compared to public institutions, availability of MRI units in private institutions is better. Many private orthopaedic clinics and private hospital-based orthopaedic departments have their own MRI units. The waiting time for an MRI scan appointment may only be a day or at most, a week. According to a study done by Lo, in the polyclinics and public hospital specialist outpatient clinics, the waiting time for an MRI appointment may be 4 to 12 weeks. This actually reflects the actual waiting time for public institutions in general. This is because the MRI unit is shared with other medical specialties in the public healthcare institutions.
