Knee Injuries: Symptoms, Causes, Risk Factors & Prevention

Published: 13 December, 2024 | 14'

The knee is the largest joint in the body and thus one of the most complex. It is directly responsible for our ability to move and, precisely for this reason, is one of those that most frequently experiences discomfort, as it is involved in numerous movements of the body in our day-to-day lives, especially for those who engage in regular physical activity.

Let us examine the different types of injuries that can occur and how to prevent them, as well as the specific care that helps keep our knees in good condition with the help of Dr José Luis Castilla, a specialist in physical medicine and rehabilitation.

Structure of the Knee

The knee joint is primarily composed of bone, cartilage, and ligaments, while the muscles and tendons surrounding it allow for movement, enabling us to flex, extend, and rotate it. “When any of these components are affected by an external or internal cause, an injury arises that causes discomfort and difficulty in movement,” explains Dr Castilla.

The Key Components of the Knee

Firstly, the knee has a bony component made up of the following bones: the femur (which runs from the knee joint to the hip joint), the tibia (the main bone below the knee that supports the weight of the body), and the patella (a small bone that protects the joint and aids in its movement).

The menisci are crescent-shaped cartilage structures that increase the joint surface area, provide joint lubrication, and therefore dampen the friction that may occur between the surfaces of the bones. This way, they act as shock absorbers and stabilize the knee.

The ligaments involved in this joint include four: the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), which provide stability and control forward and backward movement, along with the medial collateral ligament (MCL) and lateral collateral ligament (LCL) for lateral stability. The tendons also play an essential role as they assist in extending the knee. Finally, the knee joint contains a viscous, transparent fluid, synovial fluid, which lubricates the joint and modulates friction between the bones and cartilages of the knee during movement.

Additionally, the knee has sensory receptors that send information to the brain about its position and movement, which are fundamental in coordinating movement and maintaining balance.

How the Knee Functions: Movement and Stability

All the components of the knee work together to allow for flexion and extension movement:

• Flexion occurs when the quadriceps (the muscle located at the front of the thigh) relaxes and the hamstrings at the back contract.
• Extension occurs conversely when the quadriceps of the thigh contract while the hamstrings relax.

“The function of the ligaments is to stabilise the joint and also limit movements such as excessive twisting, while the menisci absorb shock and distribute the weight of the bones during movement,” explains the doctor. Thanks to this synergistic action, the knee can bear significant weight and adapt to different movements such as jumping and running.

Common Knee Injuries: How to Identify the Cause

“The main knee injuries primarily depend on the age of the patient,” asserts Castilla, “in younger individuals, they tend to be inflammatory, either in the tendons, or traumatic, such as sprains.” Knee sprains arise from a ligament injury caused by forcing the joint through twisting or impact.

Let’s look at some of the main knee injuries and their causes.

Ligament Injuries: Sprains and Tears

There are two very common injuries affecting the ligaments, which are those affecting the anterior cruciate ligament and the medial collateral ligament injury. These occur due to tearing of the specific ligament from a sprain or trauma. Typically, they happen during sports where you change direction abruptly or stop suddenly, such as football.

Meniscus Injuries: Tears and Symptoms

Meniscus injuries generally arise from traumatic causes, typically in younger persons who make a sudden twist of the knee during sports or hit the area, often resulting in tears in these cases. Normally, this type of meniscus injury manifests with symptoms like intense discomfort when rotating the knee and stiffness, along with swelling in the area.

“As we age, due to age-related changes, wear and tear injuries can occur at the meniscal level, which, although not traumatic, can lead to a tear in the meniscus,” continues Castilla, “especially if the person engages in work that involves climbing and descending stairs, or other similar movements that exert a high impact on the joint.”

Patellar Tendinitis: Discomfort at the Front of the Knee

Patellar tendinitis is commonly known as “jumper’s knee”, as it is very frequent in sports like basketball or volleyball. It occurs due to injury in the tendon that connects the patella to the tibia, responsible for extending the knee to jump and run.

Knee Bursitis: Inflammation of the Synovial Bags

Bursitis consists of the inflammation of the small synovial fluid sacs located near the knee joint, known as bursae, which reduce friction and cushion pressure. It can cause discomfort and limit the mobility of the knee.

Patellar Chondromalacia: Cartilage Wear

Cartilage wear in the area behind the patella leads to the occurrence of patellar chondromalacia. It causes discomfort in the knee, typically felt in the anterior area and commonly affects athletes, with a sensation of grinding against other bones when bending the knee.

Knee Arthritis and Osteoarthritis: Chronic Discomfort and Cartilage Wear

As we age, “degenerative injuries due to osteoarthritis will occur,” informs the doctor, “a condition of progressive cartilage wear.” Additionally, we may also encounter rheumatoid arthritis at older ages, an autoimmune condition that can affect any joint. Both present continuous pain in the knee with variable intensity and swelling in the joint.

Symptoms of Knee Injuries: When to Worry?

Knee discomfort depends primarily on the cause and the speed of onset, as injury signs can appear suddenly after a blow, for example in a sports setting, or gradually progressively in cases of certain conditions at older ages.

Discomfort, Swelling, and Stiffness: Early Warning Signs

The initial symptoms of an injury are generally inflammation of the area, redness or increased temperature, and discomfort. Depending on the severity and cause, the knee may feel unstable or limit its movement with the inability to fully extend.

Instability, Joint Sounds, and Movement Limitations: How Can I Tell If My Knee Injury Is Serious?

Depending on the type of injury and its severity, and considering the age of the patient, there are signs of a knee injury that determine whether we are facing a more or less serious situation. It is advisable to consult your physician if you notice any of these symptoms:

• Inability to bear weight on the knee.
• Instability or pronounced weakness.
• Sensation of clicking or grinding when moving the knee.
• Inability to fully extend or flex the joint.
• Deformity or swelling.
• You have fever in addition to numbness.
• Following trauma, the pain increases in the following days or does not subside.

Causes of Knee Injuries: Why Do They Occur?

A knee injury can affect connective tissue, bones, and even synovial bags as we saw earlier, and can arise from various reasons. Dr Castilla confirms that “one of the most common causes is mechanical problems such as a fall or blow, or alternatively from other risk factors like age, intrinsic genetic factors or the practice of certain sports.”

Common Mechanical Problems

Some of the most common mechanical problems that can cause a knee injury include:

Accidents and Falls

A knee injury can occur from a fall or accidental blow at any time in life. Depending on the distance to the ground and the position when falling, among many other factors like the person's age or weight, a fall can cause anything from a minor discomfort, such as a bruise, to more severe injuries like dislocations, tendon ruptures, or bone fractures.

High-Impact Sports

Continuous training in certain sports involves repeated stress on the joint and can lead to knee wear and injury. These are impact and contact sports like football, basketball, rugby, running or others that require rapid changes of pace, turns, and jumps with impact. Typically, these injuries affect the menisci and ligaments.

Incorrect Leg Alignment

When the patella does not fit into the groove of the joint, it tends to be pushed outwards, resulting in friction in the tissues and increased pressure at the back. This patellofemoral malalignment can be caused by poor alignment between the hip and ankles or by muscle weakness, such as in the quadriceps, which can help the patella maintain its position.

IT Band Syndrome

The IT band is tissue that runs along the outside of the leg from the knee to the hip. It can become tight and rub against the outer femur, causing IT band syndrome. This commonly occurs in athletes such as long-distance runners and cyclists.

Patellar Dislocation

A sudden change in direction of the leg can lead to a dislocation of the patella, causing it to shift out of place, typically towards the outside of the leg. This can happen in sports like basketball. Signs of dislocation include a knee that appears deformed or is flexed and cannot be straightened.

Risk Factors

Knee discomfort can be exacerbated by some intrinsic factors such as:

• Overweight, as it increases the strain and pressure on the knees during any physical activity.
• Muscle weakness, since the muscles are responsible for stabilising and supporting the well-being of the joints.
• A previous injury also raises the likelihood of experiencing it again.
• As we have seen, certain sports or specific jobs that involve greater physical exertion and movement are significant factors, as they require continuous effort on the knees in sports that involve jumps and twists, or in jobs such as construction or the agri-food industry.

Return to activity: How long do I need?

The return to normal conditions after any knee injury is unpredictable and largely depends on the individual patient and their lifestyle. The extent of the injury will also be decisive in determining the course of action.

“If the discomfort causes a significant limitation in daily or sporting activities, then it is recommended to pursue a more invasive procedure,” advises the doctor, “especially if it is a traumatic or unstable injury and in cases of older age when we have a more advanced wear condition and no alternative with conventional methods.”

Depending on the type of injury, how long could it take to return to normal?

The estimated time to return to normal following an injury will vary depending on its origin and extent, as some only require rest at home and physiotherapy follow-up, while others need a more invasive approach. Moreover, “the capacity for recovery decreases with age, both metabolically and in terms of circulation and muscle mass,” informs the doctor.

For instance, a meniscus tear or an injury to the anterior cruciate ligament may take several months to resume normal physical activity, while a sprain (if it does not require an invasive procedure) may only take a few weeks.

When can I return to sport? Advice for a safe reintegration

After any type of injury, resuming sporting activity should be guided by a healthcare professional who, depending on the injury and whether there has been intervention or not, could be a rehabilitation specialist and/or physiotherapist. They will be responsible for indicating the best time to return to any type of activity, as well as providing guidelines that tailor the exercises to our situation and gradually return to the previous pace.

Thus, the ideal course of action for any discomfort is to consult a specialist for effective recovery that promotes complete mobility in the knee.

How to take care of your joints

Although completely eliminating any discomfort or injury is nearly unavoidable due to various factors, there are some guidelines we can implement in our lifestyle to promote the health of our joints, particularly in the case of the knee. Dr. Castilla recommends the following:

Maintain a healthy weight

Keeping a healthy weight is one of the main guidelines, as extra weight on the joints can increase the risk of injuries and conditions related to excess strain on the knee.

Warm up before exercising and stretch afterwards

It is important to prepare the muscle and our body for any moderate or intense physical activity with specific dynamic warm-ups for that activity. This will help us gradually adapt to the required movements and reduce the likelihood of potential injuries afterwards due to poor practice or incorrect techniques.

On the other hand, cooling down with static stretches helps alleviate muscle tension and relax the body in preparation for recovery.

Strengthen your leg muscles

Muscle weakness is one of the main causes of knee injuries, so strengthening the quadriceps and hamstring muscles is key to caring for the joint, as these muscles support the knees. Additionally, engaging in exercises that focus on balance and stability will also contribute to ensuring effective muscle function.

Use appropriate footwear and correct techniques when playing sports

Ideally, footwear should fit well and be comfortable during any movement or impact in physical activity. While every individual has a different physiology and the choice of footwear is based on personal experience and comfort during sporting activities, it also depends on the sport in question. For example, running requires good cushioning, while for strength exercises, a flat sole will provide stability. Therefore, we can consult specialists and our trainer, who will be familiar with our history and specific needs.

Also, it's important to be aware of personal limitations and adapt exercise accordingly, especially if experiencing discomfort over prolonged periods or recurring injuries. Limiting high-impact activities during recovery from an injury and following healthcare professional’s recommendations will be beneficial in alleviating discomfort.

Relief from knee discomfort

Knee injuries should be treated individually and always following the guidelines of a healthcare professional to achieve a specific diagnosis with the necessary tests, as well as subsequent follow-up with a planned rehabilitation.

Rehabilitation exercises: Strength and mobility

Rehabilitation for any injury is key to recovering functionality and alleviating discomfort. As the doctor states, “thanks to rehabilitation, we can achieve the level prior to the injury by employing physiotherapy techniques.”

The type of rehabilitation and the timing to commence it will depend on the injury, as “if the injury requires invasive intervention, we must provide rehabilitation before and after”, continues Castilla, and “if it is of an inflammatory nature of any tendon or a ligament sprain that does not require that type of procedure, that rehabilitation can help prevent it from lasting longer than necessary”.

For a comprehensive approach to a knee injury, the rehabilitation guidelines would be:

1. The initial evaluation by a specialist to determine the extent, following the necessary tests that guide to a specific diagnosis.
2. Address the initial phase of the injury if there is discomfort and swelling with rest, ice, and compression of the area, immobilising it.
3. In cases where invasive intervention is not required, start with mobility and muscle strengthening exercises for the area, as well as balance exercises, under the guidance of a healthcare professional.
4. Begin with low-impact aerobic exercises such as swimming or cycling to gently resume physical activity and strengthen the muscles. If engaging in any sport prior to the injury, gradually return to this activity while always following the guidelines of the rehabilitator.
5. In light of possible future relapses of the injury, focus on performing exercises prioritising technique and continue with specific strength exercises.

To ensure that the rehabilitation process is appropriate, it is advisable to consider the input of a physiotherapist, who will help personalise and supervise the progress.

Nutrition and Supplements that Support Joint Wellbeing

“A healthy and balanced diet is fundamental to bone and muscle wellbeing”, states Dr. Castilla, “but it is now common to engage in high-intensity sports that can lead to wear and tear on the joints.” There are certain nutrients that are highly useful in this area and will help ensure that the skeletal system remains in optimal condition.

Thus, he recommends “maintaining a balanced and healthy diet, which can be complemented with collagen and glucosamine and chondroitin sulfate supplements, which can aid in lubricating the joint area, as well as alleviate the impact of sporting activities on the joint and modulate those effects in the area typical of older ages.”

Glucosamine and Chondroitin

Glucosamine and chondroitin are also naturally present in our bodies, specifically in the structures of cartilage, providing elasticity and are key in its formation. They are usually found in dietary supplements focused on the care of bones and joints in the form of chondroitin sulfate and glucosamine.

Collagen

Collagen is a protein that is naturally present in the body, found in the skin, cartilage, and connective tissues, making it a fundamental part of the joints. As we age, the reserves of collagen in our body decrease and it is essential to include it in the diet.

Magnesium and Calcium

Calcium is stored in over 90% in the skeleton and is primarily involved in the formation of the skeletal system, in addition to aiding mineralisation and its concentration being related to bone density.

Meanwhile, magnesium also plays a key role in maintaining bones and muscle function. Magnesium is predominantly deposited in the bone, with the rest residing in metabolically active tissues such as muscle. The body does not produce these minerals, so we must obtain them through our diet.

Vitamins

In the case of vitamin C, it contributes to the normal formation of collagen for the normal functioning of bones and cartilage, while vitamin D helps maintain bones under normal conditions, as it is strongly linked to calcium intake. Vitamin D contributes to the normal absorption and utilisation of calcium, and supports the functioning of these organs and tissues.

Additionally, vitamin K2 also contributes to the maintenance of bones under normal conditions.

Turmeric

Turmeric is widely used by Eastern cultures and is standardised for its main bioactive, curcumin. Turmeric helps to reduce inflammation in joints and muscles (EFSA ON HOLD (2030, 2598))¹⁴.

If you want to know more about injuries...

• Training in the cold, is there a higher risk of injuries?

• Plantar Fasciitis: what it is and how to relieve discomfort

Content created with the collaboration of Dr. José Luis Castilla. This article is informative and does not replace consultation with a specialist.

Health specialists