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Common Causes of Knee Pain: Expert Analysis from Singaporean Specialists

The knee joint is a complex one with many components, making it vulnerable to a variety of injuries. These injuries can be the result of overactivity (such as work or sports) or a specific injury. Out of all the injuries that can cause knee pain, the most common one is an anterior cruciate ligament (ACL) injury. This is an injury that can occur as a result of the knee joint being twisted the wrong way. This is a common injury among sportspeople, particularly basketball and soccer players. Another common injury is a meniscal injury. This injury is often caused by forceful twisting or rotating of the knee, often when the knee is bent. The risk of a meniscal injury increases with age. Other than these specific injuries, overuse injuries are common in people who do repetitive activities such as stair climbing, cycling, or jogging. These activities put repetitive stress on the knee, which can cause an overuse injury.

Without question, knee pain is one of the most common health problems affecting people of all age groups. In the US, it’s the cause for about 1/3 of all knee pain specialist‘s visits for muscle and bone pain. Knee pain is a common problem with many causes, from acute injuries to complications of medical conditions.

Overview of Knee Pain

Often in chronic conditions, prevention and better understanding can pave the way for better treatment with a tailored approach. Understanding your problem is the first step to recovery. Symptoms will vary with the cause of the knee pain and sometimes an individual’s experience of the pain. Generally, it depends on the nature of the injury. People usually feel pain, tenderness, and swelling. Sudden acute pain may be due to a simple injury such as a sprained ligament or pulled muscle. This, in turn, leads to bruising as blood from the internal injury seeps into the skin. Coming a few hours or days after the initial injury, swelling often reflects the amount of bleeding and seriousness of the injury. A feeling of instability or weakness in the knee may be due to a swollen ligament or tendon, and inability to straighten or bend the knee will be due to a failure to move the joint due to muscle/tendon or cartilage damage. Popping or crunching noises are a sure sign of something going wrong within the knee joint. If you ever feel or hear something like that, it is best to cease whatever activity you were doing and consult a specialist. A general ache after activity may be due to overuse of a particular part of the knee and might be an early sign of osteoarthritis. Osteoarthritis is the most common form of arthritis and is a result of the gradual breakdown of joint cartilage. Finally, people with systemic disease may have their knee symptoms related to what is known as referred pain. This is the pain felt in an area other than where the cause is situated, such as the spine or hip, from which the pain is referred to the knee.

Importance of Seeking Specialist Advice

An accurate assessment of the problem is needed so that the most effective treatment can be given. Self-diagnosis always runs the risk of incorrect identification of the problem. An example of this is a person who has weak thigh muscles and a slightly unstable knee. He feels a clicking inside the knee and tightness around the kneecap, having previously been able to walk or run with no pain at all. He may wrongly think that he has arthritis, whereas what is likely to be going on is damage to the articular surface of the kneecap due to the kneecap not tracking properly in the thigh groove. Seeking advice could prevent further damage to the knee.

Knee pain often results from an injury, such as a torn cartilage or a ruptured ligament. Many medical conditions, including arthritis, gout, and infection, can also cause knee pain. Some injuries or medical conditions, such as a torn cartilage or certain types of arthritis, can result in a gradual onset of pain and swelling. In this situation, it is all too easy for a person to think that nothing can be done and it is best to ignore the pain. However, it is always important to seek advice to confirm exactly what the problem is and to find out whether something can be done to improve the condition. This is particularly relevant with knee pain, as there is a lot that can be done to improve various different conditions, but a health professional will only be able to advise this after making a diagnosis.

Musculoskeletal conditions affect many people in the world. Among the many different conditions that can affect the musculoskeletal system, one of the most common ones is knee pain. Knee pain is experienced by people of all ages, and it may be sudden in onset or develop over a period. This essay explains the common causes of knee pain: when it is due to a serious injury or a medical condition, and when it needs no specialist treatment.

Common Causes of Knee Pain

Overuse injury: Some knee pain is caused by an overuse injury. This is often related to the pain coming from the patellofemoral pain syndrome. People who have overuse injuries report that pain increases when they are using the part of the leg that is associated with the injured part of the knee. It also increases during activity and often decreases after the activity is stopped. Pain may not be felt until after the activity is over. An example of this is pain coming from patellofemoral pain syndrome where a person may feel pain in the front of the knee after running.

Sudden injury: A sudden injury may cause severe pain, swelling, and bruising around the knee. In some cases, patients may hear or feel a ‘pop’. Injuries that cause sudden knee pain include ligament injuries, such as an anterior cruciate ligament (ACL) injury, and fractures, such as a fracture in the knee cap. Tears of the meniscus can also cause sudden knee pain.

Knee pain can be caused by a sudden injury, an overuse injury, or by an underlying condition, such as arthritis.

Osteoarthritis

Osteoarthritis is a degenerative wear and tear of the cartilage with age. It is the most common cause of knee pain. There may not be any incident which directly leads to the onset of pain. The patient may begin to notice pain and stiffness in the knee and it may be difficult to localize. The pain often increases with certain activities. At times, people will complain of pain in the knee at night or in cold weather. Swelling may occur in the knee but is usually painless. This is recurrent and is due to the knee ‘giving way’. This occurs due to muscle weakness and hindrance in the normal function of the knee. Finally, due to the breakdown of the cartilage and bone, there may be crepitus in the knee (a creaking feeling or grating sound). Flexion of the knee is usually painful, there may be a restriction in movement and in chronic cases there may be knee deformity. An x-ray is usually sufficient to diagnose the condition. An MRI may show up areas of partial thickness cartilage loss and or the presence of a meniscal tear within the arthritic knee. Osteoarthritis cannot be reversed and treatment is aimed at pain relief and improving the function of the knee. Physiotherapy, weight loss, activity modification and strengthening the muscles around the knee have a positive effect on the symptoms of OA. Topically, heat or ice may be soothing and the use of a walking aid reduces the load put through the knee. Simple analgesia such as paracetamol is usually tried first and if pain persists nonsteroidal anti-inflammatory drugs may be considered. Glucosamine sulfate is a relatively safe adjunct which is tried by some. Corticosteroid injections are usually avoided but can provide good relief in acute episodes of pain. High tibial osteotomy may be carried out in younger, active patients with significant pain. The aim is to correct a varus deformity and to offload the damaged part of the knee. Joint replacement is a good option for older patients with severe pain and limitation. The decision to progress to surgery should consider the age, occupation, expectations, and general health of the patient.

Ligament Injuries

The knee joint is designed to be quite stable, resisting varus (bow-legged) and valgus (knock-kneed) stress. The main stabilizers against varus stress are the MCL and the Posterior Oblique Ligament (POL). The MCL is a broad thick band on the inside of the knee. It is the most commonly injured ligament in the knee. Usually, it occurs in isolation and the knee reaches a point of maximal valgus stress and the MCL tears at its midpoint off the femur attachment. Sometimes the MCL tears off the tibia taking a piece of bone with it. The POL is a very strong ligament running from the lateral femoral epicondyle to the back of the tibia. It is the main stabilizer against the knee developing a recurvatum deformity. Sudden forceful varus stress to a flexed knee or forceful hyperextension can cause the POL to avulse a bony chip off the femoral insertion. This can cause great pain and instability in the knee.

Knee ligament injuries certainly rank as one of the most frequent causes of knee pain. Patients often recall a specific traumatic incident, usually involving a change in direction or a sudden stop, and feel the knee gave way. It is not uncommon for an ACL tear to occur in combination with tears to other ligaments such as the MCL or meniscus. These injuries often occur during sporting activities and can be quite debilitating. In severe cases, the patient may not be able to continue the activity. At the time of injury, the patient may hear a popping sound and the knee will usually become quite swollen within a few hours.

Meniscal Tears

The symptoms of a torn meniscus are swelling and stiffness in the knee, pain, especially when twisting or rotating the knee, difficulty straightening the knee fully, and a tendency for it to lock, catch, or give way. If the tear is minor, the symptoms may go away after 2-3 weeks. People with long-term symptoms can experience episodes where the symptoms “come and go” for years. This can lead to further deterioration of the meniscus and an increased risk of developing osteoarthritis. This symptom, a clicking sensation, is mostly caused by a small loose piece of cartilage interfering with the smooth motion of the knee joint. An individual with a severe meniscus tear is likely to experience pain and swelling of the knee and have problems straightening the knee.

Meniscus is a hose-shaped fibrous cartilage that is located between the thighbone and shinbone. The meniscus acts as a cushion and helps to distribute the weight of the body as evenly as possible across the knee. Each individual has two menisci in each knee. One is located on the inner half of the knee and is called the medial meniscus, and the other is located on the outer half of the knee and is called the lateral meniscus. Meniscal tears are one of the most common knee injuries. The meniscus can be torn during activities that cause direct contact or pressure from a forced twist or rotation. Older individuals are more susceptible to a meniscus injury because the cartilage weakens and wears thin over time. While young people can tear a meniscus, it is more common to occur in men and women over 30. A sudden meniscus tear can occur when lifting something heavy or playing an aggressive sport. Often times, a meniscus tear is accompanied by a feeling of the knee giving way.

Patellofemoral Pain Syndrome

This refers to pain experienced behind and around the patella. It is the most common cause of chronic knee pain. The onset is usually insidious, the pain is often activity-related and may be present in a broad area around the patella. Often it is increased after sitting for prolonged periods with the knees flexed, and during activity that increases the load on the patellofemoral joint. It may be painful when walking up or down hills or stairs. There are a number of different causes of PFPS and often a number of factors are involved. These may include overuse – physical activities that involve repetitive knee motion such as running, stair climbing, cycling and rowing can place extra stress on the patellofemoral joint. High-impact sports such as basketball and volleyball can increase the stress on the joint. Muscle imbalance – the vasti muscles in the quadriceps are the main knee extensors. Weakness in the vastus medialis obliquus (VMO) and tight lateral restraints can cause maltracking of the patella and increased pressure between the patella and femur. This can cause irritation to the undersurface of the patella and pain.

Diagnostic Approaches for Knee Pain

All of these questions aim to form a ‘picture’ in the physician’s head as to what the possible causes of the knee problem are. For example, a sudden injury involving a twisting/rotational movement of the knee, followed by swelling and difficulty weight bearing may suggest an injury to the anterior cruciate ligament. Whereas a history of gradual onset pain located at the front of the knee in an athlete may indicate patellofemoral pain syndrome. Accurate diagnosis is also important for the patient’s understanding and expectations of their knee problem. Often, a definitive diagnosis will aid a patient’s decision as to whether to undergo surgery or not.

The most important step a physician must take is to understand the patient’s knee problem. This will involve a thorough history and examination to help the physician decide what further investigation is required or what the probable diagnosis is. The patient will be asked about the onset of the problem, when and how the injury occurred, if there was any previous injury, if the knee ‘gives way’, and other possible symptoms elsewhere that may be connected with the knee problem. Often advice from the patient regarding what he or she does for a living and the level of sporting activities participated in can be useful.

Physical Examination and Medical History

The assessment of knee pain begins by obtaining a detailed history of the symptoms and events that led to the present condition. It is crucial to establish a timeline of the onset of the pain, the mode of onset (i.e. traumatic, gradual), and the progression of the pain. The changes in activity level and participation in various sports or occupations should be documented. A detailed history of any former injuries to the knee, and the treatments that followed, is also important. Any orthopaedic operations or treatments to other regions of the body should be disclosed as they may have implications on the present condition. If the knee pain is purported to be of systemic nature, then questions about the patient’s general health, including recent illnesses, fevers, weight loss, and medical history may also be relevant. Information on current medications or allergies is often overlooked but crucial. Finally, it is important to establish the patient’s goals and expectations from treatment of the knee pain. The physician should encourage the patient to do most of the talking in the interview, as this will improve the accuracy of the information collected.

Imaging Techniques

Imaging techniques are a significant part of the investigations used to diagnose knee problems. The two types of imaging are plain x-rays and complex imaging (either ultrasound or MRI). X-rays provide details of the bones of the knee, which is helpful for diagnosing fractures or arthritis. However, the menisci, cruciate ligaments, and other structures do not appear on x-rays. Complex imaging is often requested to provide more information and to assess soft tissues. Ultrasound is occasionally useful, but MRI is generally a more reliable and accurate test. It provides a three-dimensional image of the knee, and the information obtained can be very helpful if surgery is indicated. Because an MRI scan provides so much information, not all of it is significant, and sometimes it can be difficult to say which part of the knee is causing the symptoms. This is where the correlation with a clinical examination is particularly important.

Laboratory Tests

Finally, if there is suspicion of a malignancy, this can be confirmed with a tissue biopsy. If a soft tissue tumor is present around the knee, a biopsy can be performed under image guidance. For bony lesions, a referral should be made to an orthopedic oncologist.

Rheumatoid factor is a blood test for the diagnosis of rheumatoid arthritis. The test is positive in 80% of patients with rheumatoid arthritis, but may also be positive in other conditions or in the elderly. If there is suspicion of a connective tissue disorder, tests for specific autoimmune diseases can be performed. These tests are not usual and should be discussed with a rheumatologist. They include ANA, dsDNA, ENA panel. Biochemistry and serum urate can be performed to support a diagnosis of crystal-induced arthritis. Biochemistry is not specific, but gout is likely if there is an elevated serum urate and the patient has a typical clinical picture.

Laboratory tests are not specific for diagnosing the cause of knee pain, but they can be helpful to detect infection or support the diagnosis of inflammatory conditions. A complete blood count is a simple and common test to detect infection or anemia. Blood culture and ESR are tests for systemic infection or inflammation. In acute infection of the knee joint, the white cell count of the joint aspirate will be raised and the organism may be grown on culture.

Treatment Options for Knee Pain

Medications and Pain Management

Medications are prescribed to control the pain and provide relief from knee arthritis. Talk to your doctor about when and how to use both prescription and over-the-counter pain medications. Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to treat arthritis pain. They are available both over-the-counter, such as aspirin, ibuprofen, and naproxen sodium, and as a prescription, such as celecoxib. Several studies have shown that acetaminophen is as effective as NSAIDs for control of knee pain caused by osteoarthritis. Use of the safest dose is recommended. Follow the instructions of your orthopaedic surgeon and the manufacturer. If you have other health problems or are pregnant, talk to your doctor before taking any medications. Corticosteroids, also called glucocorticoids or just “steroids,” are powerful anti-inflammatory drugs. Given by mouth or injection, they are often used to treat short-term inflammatory problems, such as acute gout or an acute flare of rheumatoid arthritis.

Physical Therapy and Rehabilitation

Treatment of recently sustained knee injuries such as ligament or meniscal tears will vary depending on the specific nature of the damage but usually begins with an even shorter period of protection and offloading. The aim is to control pain and swelling and limit further damage to the injured structures. In some cases, surgery may be required. Physiotherapy can be beneficial both before and after surgery. If surgery is not required, then the therapist will educate the patient on the nature of the injury and how to protect the affected structures during healing. A progressive rehabilitation program will follow with the aims of restoring normal joint motion, muscle bulk and strength, and proprioception to provide the patient with a good level of function for return to normal daily activities and more demanding physical activities.

Physical therapists treat discomfort, pain, and loss of strength by using a variety of therapies and techniques to help you move better and feel better. Physical therapy is an important part of the rehabilitation process. Your treatment may involve only you, a therapist, and an exercise program or it may involve an adjunct to therapy such as hydrotherapy (water) or it may involve more invasive procedures provided by a therapist with special training. Some therapists are specialized in certain areas such as knee rehabilitation.

Minimally Invasive Procedures

High tibial osteotomy involves cutting and realigning the tibia. This is done for patients with early arthritis isolated to one side of the knee. The aim is to unweight the damaged portion of the knee and transfer the load to the undamaged or less damaged area. High tibial osteotomy can be an effective procedure; however, it requires significant rehabilitation and may be associated with complications. As a result, it is generally reserved for younger patients with significant functional disability.

Arthroscopic surgery is the most common minimally invasive knee surgery and is performed to see, diagnose, and treat problems inside the knee joint. The procedure is done through small incisions and the use of a camera attached to a pencil-sized instrument (arthroscope). This allows the surgeon to view the inside of the knee on a screen, and if necessary, a clear diagnosis of the problem can be obtained. The mini-incisions used in arthroscopy can be less traumatic to the soft tissues than the incisions used in traditional surgery. This can lead to less pain postoperatively, a quicker recovery, and a better final outcome. While most patients with knee pain will not require surgery, arthroscopy can be a very effective treatment for conditions such as torn cartilage or ligament damage.

Surgical Interventions

Surgical treatments are typically only considered after lengthy periods of medication and physical therapy have failed. Surgical options range from arthroscopic debridement and meniscectomy to open-wedge high tibial osteotomy, various meniscal procedures, and resection of osteophytes. There are three main types of surgery for knee OA. These are: arthroscopy, where the damaged parts of the knee are washed out; high tibial osteotomy, which involves reshaping the knee to relieve pressure on the damaged area; and knee replacement. What type of surgery best suits a patient depends on factors such as age, weight, occupation, activity level, alignment of the knee, and location and severity of damage. Selected patients with unicompartmental OA can achieve substantial improvement in pain and function after high tibial osteotomy. The two main aims of arthroscopic surgery are to decrease symptoms and to delay the progression of the osteoarthritic process. Knee replacement might rarely be considered for rheumatic conditions in patients aged <55 years who are sufficiently disabled. It is an effective treatment for advanced knee OA, but due to the likely risk of future prosthesis revision, it should be advised for patients who are >60 years. Osteoarthritis is the most common reason for total knee replacement and the primary reason for the large increase in TKR in patients in their later years. High rates of patient satisfaction and improved function and decreased pain have been reported, but objective physical function does not improve significantly in all patients. Satisfaction rates in TKR do not differ greatly between patients with severe and less severe radiographic evidence of the disease.

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