Knee radiograph

During knee X-rays, the knee can be examined in an anterior-posterior view (front view), sunrise view (when the knee is bent), and lateral view (side view)⁽²⁾.

In general, X-rays or radiographs are diagnostic tools with a high frequency and extremely short wavelength of electromagnetic waves⁽³⁾. They allow a view of the differentiation of soft tissues and bones⁽⁴⁾.

During knee radiographs or X-rays, the causes of several conditions’ symptoms are assessed through a two-dimensional, black and white image⁽⁵⁾. These symptoms include knee pain, deformity, swelling, or tenderness.

These X-ray images can help assess dislocated knee joints, broken bones in the knees, and proper alignment of the knee bones. The diagnostic imaging procedure also evaluates if a previous fracture or dislocation has properly healed⁽⁶⁾.

Notably, the standing knee anterior-posterior view (AP) X-ray can indicate the knee alignment and the presence of degenerative diseases⁽⁷⁾. Whereas the standing long leg alignment view of the knee radiograph helps measure the lower limbs’ alignment⁽⁸⁾. 

This view shows any deformities after a knee replacement⁽⁹⁾.

The Anatomy of the Knee

The knee, a synovial joint, is the largest joint in the body⁽¹⁰⁾. The femur, patella, and tibia are connected via the knee joints⁽¹¹⁾.

The femur bone is located between the knees and hip in the lower limb⁽¹²⁾. This bone is the largest and strongest bone in the body⁽¹³⁾. It supports various ligament attachments and muscular attachments in this area of the body⁽¹⁴⁾.

Next to the femur, the tibia is the second largest bone in the body⁽¹⁵⁾. It is called the shinbone and the weight-bearing bone because its primary function is to carry the body’s weight^(16-17).

Lastly, the patella or knee cap serves to protect the knee joint from damage⁽¹⁸⁾. It is located in front of the knee joint and the largest sesamoid bone⁽¹⁹⁾.

A sesamoid bone is embedded within a muscle or tendon.

Moreover, the knee joint consists of two joints: the patellofemoral joint and the tibiofemoral joint⁽²⁰⁾. The patellofemoral joint is the hinge between the femur and patella, while the tibiofemoral joint is the hinge between the femur and tibia⁽²¹⁾.

Hinge joints allow a variety of movements, such as extension and flexion motion⁽²²⁾. These knee joints are essential for bipedal movements, like running, jumping, and walking⁽²³⁾.

Healthy muscles, bones, synovial tissue and fluids, cartilage, and ligaments are needed to maintain the knee’s stability and anatomical functions⁽²⁴⁾. 

There are four stabilizing ligaments are that help maintain knee joint wellness⁽²⁵⁾:

• Anterior Cruciate Ligament (ACL)
• Posterior Cruciate Ligament (PCL)
• Medial Collateral Ligament (MCL)
• Lateral Collateral Ligament (LCL)

These ligaments have their respective functions. The ACL is responsible for preventing anterior translation of the femur to the tibia⁽²⁶⁾. Meanwhile, the PCL prevents the forward displacement of the tibia on the femur. 

Furthermore, the MCL prevents valgus stress or oblique displacement away from the midline of the knee, while the LCL prevents varus stress or oblique displacement of the knee towards the knee’s midline⁽²⁷⁾.

Knee Radiographs for Bone and Joint Disorders

An article published in Harvard Health Publishing cited that a simple X-ray can be a better diagnostic tool in knee pain and injuries due to its efficiency in cost and time⁽²⁸⁾.

Strenuous activities associated with the overuse of the structures at the anterior knee and patellar loading are the common causes of knee pain⁽²⁹⁾. These activities which can take a toll on the knees include running or climbing the stairs.

In some cases, inflammatory and degenerative diseases manifest as knee pain symptoms⁽³⁰⁾. 

Osteoarthritis, the most common form of arthritis, is typically diagnosed using a radiograph or X-ray⁽³¹⁾. This degenerative joint disease, which involves chronic pain and stiffness of the knee joints, gradually worsens over time⁽³²⁾.

According to a study on osteoarthritis, the fixed flexion view X-ray is useful in examining the severity of osteoarthritis by assessing joint spaces in the knee⁽³³⁾. 

The study also mentioned that a radiographic classification called Kellegren-Lawrence (KL) classification helps assess and determine the appropriate treatment and time for treatment of osteoarthritis⁽³⁴⁾.

Moreover, knee dislocations in the tibiofemoral and patellar-femoral joint are also assessed with X-rays and magnetic resonance imaging (MRI)⁽³⁵⁾. The tibiofemoral joint dislocation is a more severe injury resulting from the damage of multiple knee structures due to a massive force⁽³⁶⁾.

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