This piece was written by one of our contributors; Specialist Registrar in Trauma and Orthopaedics – Laura Fahey.
Knee pain is one of the leading joint and bone conditions that patients attend their GP about 1. Approximately 25% of adults are affected by knee pain with various conditions that can be responsible for this pain 2. While the majority of knee pain arises from the joint itself, occasionally knee pain can be referred from the hip joint or the lumbar spine.
The main symptoms that people experience when they have problems with joints can include pain, swelling, heat and stiffness or loss of function. Redness (known as erythema) is also a feature of inflammation which can sometimes be present after injury or due to ongoing knee pain. However, the presence of erythema, particularly spreading erythema accompanied by feeling unwell or with a fever may suggest an infection of the joint which should be promptly assessed by a healthcare professional 2.
Based upon a person’s age, certain conditions are more likely than others. For instance, a person aged 20-40 who has suffered a twisting knee injury and complains of medial sided pain and a “locking” sensation is more likely to have a meniscal injury. A 65-year-old person with medial sided pain and stiffness in the absence of trauma is more likely to have pain secondary to arthritis, commonly referred to wear and tear. Osteoarthritis is the commonest cause of knee pain in people over the age of 50 4.
Several injuries can be related to overuse of the joint and are known as overuse injuries. Regular gym work, running and jumping can lead to such injuries which are often referred to as “runner’s knee”, “jumper’s knee” or “tendonitis”. Such injuries are common in athletes, particularly runners, with patellofemoral pain being twice as common in females as males1. It commonly presents with anterior knee pain around the region of the patella (knee cap) which is provoked on activities that load the joint such as running, squatting and ascending and descending stairs1. Short periods of overuse such as overdoing it in the gym/training or an increase in physical activity are thought to be particular risk factors for patella-femoral pain1.
Cruciate ligament injuries
Cruciate ligament injuries are commonly sustained in sports, particularly those with a twisting element such as rugby, soccer and skiing 5. In simple terms, our cruciate ligaments function to keep our tibia (main shin bone) in normal alignment with our femur (thigh bone). The cruciates prevent excessive forward or backward motion of the tibia relative to the femur, thus keeping our knee stable. Anterior cruciate ligament (ACL) injuries are more common than posterior cruciate ligament injuries 5. As soon as this injury occurs, the person usually gets severe pain at the time of injury followed by gross swelling of the knee joint known as haemarthrosis. After the initial injury settles, ACL injury tends to give rise to knee symptoms where the person feels that their knee “gives way” or goes from under them whilst running, sometimes preventing them from returning to sports requiring twists/pivots which is why many people who sustain this injury who wish to return to sport opt for surgery known as ACL reconstruction where typically the patient’s own hamstrings or part of their patellar tendon is used to reconstruct a “new” ACL 5.
Meniscal injuries are a common cause of knee pain, frequently a twisting knee injury will result in a torn meniscus. The meniscus is a shock absorbing structure which is normally firmly attached to the underlying tibia 6. However, it can tear if injured giving rise to symptoms including pain and/or a “locking” sensation where the person will describe that they are unable to straighten their knee fully or they may have to do a certain manoeuvre to get it unlocked or straight again2. The knee has a medial and lateral meniscus so pain is usually felt on the side that is injured. The medial meniscus is more commonly injured than the lateral meniscus 7.
Collateral ligament rupture
Collateral ligament ruptures are another knee injury commonly sustained in sports. In the same way that the ACL and PCL ligaments act to constrain our knees by preventing too much forward/backward movement, our collateral ligaments act to prevent our knees going into excessive sideways movement known as varus/valgus movement. Any injury that results in excessive varus or valgus strain can result in a medial or lateral collateral ligament sprain or rupture. MCL injuries are the most common ligamentous knee injury sustained, accounting for almost 8% of all knee injuries sustained by athletes 8.
MCL and LCL injuries tend to occur following either direct trauma in athletes or due to a sudden change in speed or direction8. They can also occur in combination with injuries to other structures, for example, MCL injuries often occur in combination with ACL and medial meniscus ruptures8. Most collateral ligament injuries can be treated conservatively, however the more severe injuries may require surgical intervention, particularly if they occur in combination with other ligamentous/structural injuries3,8. Multi-ligamentous knee injuries where a combination of ACL, PCL, MCL and LCL injuries occur together tend to be rare injuries which often necessitate surgical intervention.
Quadriceps tendon rupture
A quadriceps tendon rupture is a rare knee injury9 that results from a rupture of the quadriceps tendon before it attaches to the patella (the kneecap). Here, patients tend to have a swelling above the patella with a palpable dip where the tendon has ruptured. Classically this injury is diagnosed when the patient is unable to extend their knee following a knee injury9. Such injuries generally require surgical repair.
A common cause for knee pain after an injury is a fracture. There can be some confusion around terminology regarding fractures/breaks. The medical community refers to any broken bone as a fracture regardless of whether the fracture is a “hairline crack” to the opposite extreme of a broken bone protruding out through the person’s skin (termed an open fracture). The force required to sustain a fracture of the femur/tibia in healthy non-osteoporotic bone is significant. The resulting pain from such an injury generally results in a person seeking immediate medical care at the time of injury. However, occasionally non-displaced fractures can give a more niggling pain that sometimes only causes the patient to seek help a few weeks or occasionally months after the injury or onset of pain2.
Osteochondral lesions (osteo=bone, chondral=cartilage) are similar to fractures in that a person usually sustains this injury in a similar way to a fracture. However, the difference here is that whereas a fracture results in a break in the bone, in osteochondral lesions the injury mainly occurs in the cartilage that lines the ends of our bones at the joint surfaces. This is known as hyaline cartilage. The injured piece of cartilage (which may be attached to a fragment of underlying bone) can fracture off, commonly as a result of a sporting injury10. Traumatic cartilage injuries often occur in association with other knee injuries10.
Hip and back problems
It is important to note that any problem with the hip such as hip arthritis can present with only knee pain as the primary symptom. Similarly, herniated discs in the lumbar spine pressing on nerves that supply sensation to the knee can also present with knee pain due to the organization of our sensory nerves. This is why doctors and physiotherapists will often examine these joints when someone presents with knee pain.
Osteoarthritis and other types of arthritis
Knee pain in the absence of trauma is commonly due to osteoarthritis, occasionally due to inflammatory arthritis or infection and very rarely due to sinister pathology such as cancer. There are various types of arthritis which can cause knee or other joint pain, the most common is osteoarthritis (OA), often referred to as “wear and tear”. This occurs usually as a gradual process where the hyaline cartilage that lines our joints gradually wears away. This type of arthritis is more common as people get older11. The presence of a previous knee injury increases the risk of developing OA significantly11.
Other risk factors include increasing age, increased BMI, female gender and occupations that involve over 2 hours per day of repetitive squatting or kneeling11. Patients with knee OA typically have persistent knee pain, stiffness and reduced function of the knee. Some patients also get a cracking/grating sensation on movement known as crepitus. Over time the range of movement can decrease as the OA progresses. There are also other types of arthritis that can cause pain in the knee and/or other joints such as rheumatoid arthritis and psoriatic arthritis. These types of arthritis, known as inflammatory arthritis, often display strong family links and tend to display features such as multiple joint involvement, early morning stiffness that gets better as the day goes on and inflamed swollen joints are often a hallmark feature.
These are some causes of knee pain that are routinely encountered in clinics. If you have queries or concerns, you should consult your own GP for advice and further management.
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(8) Andrews, K., Lu, A., McKean, L. & Ebraheim, N. Review: Medial collateral ligament injuries. Journal of orthopaedics 14, 550-554, doi:10.1016/j.jor.2017.07.017 (2017).
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