Knee Osteoarthritis

Introduction and Facts

Osteoarthritis (OA) is a joint condition that experiences a degenerative process. This causes pain, swelling and stiffness, affecting a person's ability to move freely. Osteoarthritis can attack the entire joint, including the surrounding tissue. This most often occurs in the knees, hips, spine, and hands. Osteoarthritis affects approximately 3.3% to 3.6% of the population globally. The disease causes moderate to severe disability in 43 million people, making it the 11th most debilitating disease worldwide.

Pathophysiology

Articular cartilage mainly consists of type II collagen, proteoglycans, chondrocytes and water. Healthy cartilage will constantly maintain a balance between each component, so that any degradation will be balanced by the formation of cartilage again, so that the health of the articular cartilage is maintained. In osteoarthritis, matrix metalloproteinases (MMPs), or degradative enzymes, are overexpressed, disrupting the balance and resulting in complete loss of collagen and proteoglycans. In the early stages of osteoarthritis, chondrocytes secrete tissue inhibitor MMPs and attempt to increase proteoglycan synthesis to match the degradation process. However, this reparative process is not enough. Loss of balance results in a decrease in the amount of proteoglycans despite increased synthesis, an increase in water content, an irregular collagen pattern, and ultimately a loss of elasticity of the articular cartilage. Macroscopically, these changes result in cracking and rupture of the cartilage and ultimately erosion of the articular surfaces.

Although knee osteoarthritis is closely correlated with aging, it is important to note that knee osteoarthritis is not simply a result of aging but rather a disease in itself. This is supported by the differences seen in cartilage in osteoarthritis and aging. In addition, enzymes responsible for cartilage degradation are expressed in higher amounts in knee osteoarthritis, whereas they are at normal levels in aging cartilage.

Etiology

Knee osteoarthritis is classified into primary and secondary depending on the cause. Primary knee osteoarthritis occurs due to degeneration of the articular cartilage without a known cause. This is usually thought of as degeneration that occurs due to age and wear. Secondary knee osteoarthritis is the result of degeneration of the articular cartilage due to known causes.

Possible causes of secondary knee OA:

• Post-trauma
• Post-surgery
• Congenital or malformation of limbs
• Malposition (varus/valgus)
• Scoliosis
• Rickets
• Hemochromatosis
• Chondrocalcinosis
• Ochronosis
• Wilson's disease
• Gout
• Pseudogout
• Acromegaly
• Avascular necrosis
• Rheumatoid arthritis
• Psoriatic arthritis
• Hemophilia
• Paget's disease
• Sickle cell disease

Risk Factors

Can be modified:

• Articular bone trauma
• Occupation
• Weakness in muscles or balance
• Weight
• Health (metabolic syndrome)

Cannot be modified:

• Gender
• Age
• Descendants
• Race

Diagnosis

Patients usually come to the doctor with knee pain as the main complaint. Therefore, it is important to have a detailed history of symptoms. Pay close attention to the history because knee pain can originate from the lumbar spine or hip joints. Obtaining a detailed medical and surgical history is also important to identify any risk factors associated with secondary knee osteoarthritis.

The history of the current illness should include the following:

• The onset of symptoms
• Specific location of pain
• Duration of pain and symptoms
• Characteristics of pain
• Mitigating and aggravating factors
• All the pain that radiates
• Time of onset of specific symptoms
• Severity of symptoms
• Patient's functional activity

Clinical Symptoms of Knee OA

In general, the symptoms experienced in OA are joint pain or knee pain, which has the following criteria:

• Usually starts gradually
• Worse with prolonged activity
• Worse with repeated bending or stairs
• Worsen if not active
• Worsens over time
• Better with rest
• Better with ice or anti-inflammatory medication
• Knee stiffness
• Swollen knees
• Decreased road capacity

Physical examination of the knee begins with a visual inspection. When the patient stands, look for erythema (redness) and periarticular swelling, atrophy (loss of muscle tissue) of the quadriceps, and varus or valgus deformity*. Observe gait for signs of pain or abnormal movement in the knee joint that could indicate ligament instability. Next, examine the surrounding skin for the presence and location of scars from previous surgical procedures if any, evidence of trauma, or soft tissue lesions.

Range of motion (ROM) testing is an important aspect of knee examination. Active and passive ROM related to knee flexion and extension must be assessed and data collected.

*The terms valgus and varus refer to angulation (or bowing) within a bony shaft or at a joint in the coronal plane. If the distal part is more lateral it is called valgus. If the distal part is more medial, it is called varus.

Palpation along the bony and soft tissue structures is an important part of any knee examination. The palpation examination can be broken down into the medial, midline, and lateral structures of the knee.

In addition to a thorough history and physical examination, radiographic imaging is required. The recommended images are standing anteroposterior (AP), standing sideways and extended, and showing a clearly visible image of the patella. A 45-degree standing posteroanterior (PA) view of the knee can be obtained, which provides a better view of the weight-bearing surface of the patella.

Management and Treatment

Management of knee OA includes non-surgical and surgical treatment. Typically, healthcare providers try non-surgical treatments first before recommending surgery.

Non-surgical management:

• Using pain relievers
• Doing physical therapy
• Maintain a healthy weight
• Using a knee brace
• Using orthotics such as special insoles or footwear
• Cortisone (steroid) injections

Surgical management:

• Cartilage grafting. Healthy cartilage is used to fill holes in diseased cartilage
• Knee osteotomy
• Partial knee replacement
• Total knee replacement

References:

1. Hsu H, Siwiec RM. Knee Osteoarthritis. National Library of Medicine [Internet]. 2023. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507884/
2. Cleveland Clinic. Osteoarthritis of the Knee [Internet]. 2021. Available from: https://my.clevelandclinic.org/health/diseases/21750-osteoarthritis-knee