Knee

As a leading Perth orthopaedic surgeon, Rhys performs a range of knee surgeries – from knee replacements and partial knee replacements to knee arthroscopies.

Understanding the knee joint

The knee joint, one of the largest and most complicated joints in the human body, is essential for mobility. It is the crucial link between the thigh bone (femur) and the shin bone (tibia), functioning similarly to a hinge on a door. This design allows your leg to bend, allowing you to perform everyday tasks including walking, standing, running, and sitting.

The knee joint is constructed of bone, ligaments, tendons, and cartilage, and it is supported by massive muscle groups that cross it.

The knee’s ability to support forces larger than your body weight demonstrates its power. However, this capability exposes the knee to potential injury. Its role in absorbing enormous mechanical stress makes it one of the most injury-prone joints.

Understanding the form and function of the knee can help you recognise potential problems and make proactive efforts to keep your knee healthy. Whether it’s through preventive maintenance, regular exercise, or recognising the early signs of knee strain, caring for your knee joint is critical for maintaining an active and healthy lifestyle.

The fundamental structure of the knee joint (knee anatomy)

The knee joint is a critical component of the musculoskeletal system, allowing for movement and supporting the body’s weight. Anatomically, it is essentially made up of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). The femur’s rounded ends, known as condyles, rest against the tibia’s flat surface, whilst the patella sits in front of the joint, providing protection and leverage. This configuration enables the knee to operate efficiently as a hinge, allowing for necessary actions such as bending, straightening, and small rotation.

Supportive structures enhancing stability

Ligaments, tendons, and cartilaginous tissues all work together to keep the knee stable. The knee’s stability is dependent on four key ligaments: the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL), all of which prevent excessive movement that could result in injury. The menisci are two crescent-shaped cartilage pads that sit between the femur and tibia. They cushion the joint, absorb shock, and improve stability. Tendons, notably the large quadriceps tendon that connects the quadriceps muscle group to the patella, and the patellar tendon, which connects the patella to the tibia, are essential for movement and stability.

Synovium and joint fluid

The knee joint’s motion is supported by the synovial membrane, which secretes synovial fluid. This fluid lubricates the joint, minimising friction and wear on the articulating surfaces. The synovial fluid also nourishes the cartilage, preserving its health and function. Furthermore, the joint capsule encloses the knee, keeping the joint structures and fluid in place and allowing the knee to function smoothly and efficiently.

Muscles controlling knee motion

The dynamic movement of the knee is primarily regulated by strong muscle groups that surround and support the joint. The quadriceps muscles, positioned in the front of the thigh, are amongst the most important for knee mobility. They are made up of four muscles: the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. These muscles work together to extend the leg at the knee and are essential for straightening the leg from a bent position. On the posterior (back) side, the hamstring muscles — the biceps femoris, semitendinosus, and semimembranosus — aid in knee flexion (bending) and thigh extension at the hip. The calf muscles, which include the gastrocnemius and soleus, link to the knee via tendons and aid in bending and stabilising it whilst walking, running, and jumping.

Why does my knee swell after an injury?

Swelling is frequent after a knee injury. Depending on the intensity and nature of the injury, this swelling may be mostly composed of synovial fluid or blood. In cases of severe trauma, such as a fracture or ligament rupture (e.g., ACL), a blood vessel may be injured, resulting in bleeding into the joint space. In contrast, less severe injuries, such as a meniscus tear or arthritis, cause the body to produce more synovial fluid. This increased fluid helps to lubricate the joint and separate the injured surfaces, minimising friction and discomfort.

However, if the underlying cause of the swelling is not addressed, the body will continue to create fluid, resulting in persistent swelling. Rapid swelling can raise pressure within the knee capsule, causing significant pain. If the knee swells frequently, the excess fluid may eventually drain into the back of the knee, causing a Baker’s cyst.

Common knee problems

Osteoarthritis

A degenerative condition that causes the cartilage in the knee joint to wear away over time.

Meniscal tear

Injury to the shock-absorbing cartilage (meniscus) between the bones of the knee, which frequently occurs during sport. A knee meniscus injury is one of the most prevalent cases presented to an orthopaedic surgeon.

Ligament injuries

• ACL (anterior cruciate ligament) injury: common in sport, causing severe stretching or rupture of the ACL.
• PCL (posterior cruciate ligament) injury: often caused by a direct impact to the front of the knee.
• MCL (medial collateral ligament) injury: caused by a force pushing the knee sideways.
• LCL (lateral collateral ligament) injury: injury to the ligament on the outside of the knee, less common than MCL injuries.

Patellar tendinitis (jumper’s knee)

Inflammation of the tendon that links the patella to the shinbone; commonly found in athletes who jump frequently.

Patellofemoral pain syndrome (runner’s knee)

A condition that causes pain at the front of the knee and around the patella. It is common amongst runners and cyclists.

Dislocated kneecap

This occurs when the patella moves out of its normal place in the knee joint.

Fractures

• Patellar fractures: breaks in the kneecap caused by falls or direct impact.
• Distal femur fracture: a break at the bottom of the thighbone near the knee.

Iliotibial band syndrome (ITBS)

An overuse injury that causes pain on the outside of the knee, particularly amongst distance runners.

Diagnostic tools for knee problems

Physical examination

• Visual inspection: the doctor examines the knee for symptoms of swelling, redness, or deformity.
• Palpation: feeling the knee to detect soreness or abnormal swelling.
• Range of motion tests: bending and straightening the knee to determine the joint’s mobility and the presence of pain whilst moving.
• Special tests: various manoeuvres (e.g. McMurray’s test, Lachman test) are used to assess the integrity of knee structures such as ligaments and meniscus.

Imaging tests

• X-rays: provide images of the bones and can help detect fractures, misalignments, or degenerative changes.
• MRI (magnetic resonance imaging): uses powerful magnets and radio waves to provide detailed images of both hard and soft tissues — especially useful for soft tissue injuries such as ligament tears, meniscus tears, and cartilage damage.
• CT scan (computed tomography): combines X-rays taken at various angles to provide cross-sectional images, particularly useful when assessing complex fractures.
• Ultrasound: uses sound waves to image soft tissues, useful for examining tendons and ligaments and guiding procedures such as injections.

Laboratory tests

• Synovial fluid analysis: fluid is sometimes collected from the knee (aspiration) to look for evidence of infection or disease (such as gout or rheumatoid arthritis), or to determine the origin of fluid build-up.

Treatment options for knee problems

Knee problems can be effectively managed with several treatment options tailored to the severity and nature of the injury or condition. Non-surgical treatments are frequently the first step and may include physiotherapy to strengthen the muscles around the knee and improve flexibility; medications such as anti-inflammatories and analgesics to reduce pain and swelling; and corticosteroid injections to provide temporary relief from arthritis symptoms. A knee brace or support can help stabilise the area and prevent further injury.

When non-surgical measures are insufficient, surgical options may be considered. Arthroscopic surgery, a minimally invasive approach, is commonly used to repair or remove damaged cartilage, reconstruct torn ligaments, and remove loose bodies from the knee joint. In more serious cases, partial or total knee replacement may be required to replace damaged elements of the knee with artificial components, restoring function and relieving discomfort.

Preventive care and knee health

Regular exercise

• Strength training: strengthening the muscles surrounding the knee, particularly the quadriceps and hamstrings, helps to stabilise and protect the joint.
• Flexibility and stretching: regular stretching helps maintain range of motion and flexibility, lowering the risk of injury.
• Low-impact aerobics: activities like swimming, cycling, and walking keep joints in good working order without causing additional stress.

Weight management

Every time you take a step, around three times your body weight goes through your knee joint, so even carrying a small amount of extra weight can greatly increase these forces. Maintaining a healthy weight is vital, as excess body weight increases stress on the knee joints — particularly during daily activities like walking or climbing stairs. Losing weight can greatly reduce the chance of developing osteoarthritis and improve existing knee discomfort.

Injury-prevention techniques

To avoid putting too much strain on your knees, use proper technique and form when participating in sport or exercising. Suitable sports gear and personal protective equipment can also help to reduce risk.

Understanding body signals

It is critical to be aware of signs of discomfort and pain that may signal overuse or potential injury. Early attention can prevent more serious injuries and longer recovery times.