Osteoarthritis of the Knee: Understanding, Causes, Symptoms, and Management

What is osteoarthritis of the knee?

Osteoarthritis (OA) of the knee is a common degenerative joint disease characterized by the breakdown of articular cartilage, leading to pain, stiffness, and reduced mobility in the knee joint.

Understanding Osteoarthritis (OA)

Osteoarthritis, often referred to as "wear-and-tear arthritis," is the most prevalent form of arthritis, predominantly affecting the weight-bearing joints such as the knees. It is a progressive condition where the smooth, slippery articular cartilage that cushions the ends of bones within the joint gradually erodes. This erosion leads to increased friction between the bones, causing inflammation, pain, and the formation of bone spurs (osteophytes). As the condition advances, the subchondral bone (bone beneath the cartilage) can become thickened and sclerotic, further contributing to joint dysfunction.

Anatomy of the Knee Joint

To comprehend knee OA, it's essential to understand the basic anatomy of the knee. The knee is a complex hinge joint formed by the articulation of three bones:

• Femur: The thigh bone.
• Tibia: The shin bone.
• Patella: The kneecap.

The ends of the femur and tibia, as well as the back of the patella, are covered with articular cartilage—a highly specialized connective tissue that provides a low-friction surface for smooth movement and acts as a shock absorber. The knee joint is enclosed by a joint capsule lined with a synovial membrane, which produces synovial fluid to lubricate the joint and nourish the cartilage. The joint also contains menisci (C-shaped cartilage pads that provide shock absorption and stability) and numerous ligaments (e.g., ACL, PCL, MCL, LCL) that stabilize the joint. In OA, the primary pathology involves the degradation of the articular cartilage.

Causes and Risk Factors

Knee OA can be broadly categorized into primary and secondary forms, though often a combination of factors contributes to its development.

• Age: The risk of OA significantly increases with age, as cartilage naturally degenerates over time.
• Genetics: A family history of OA can increase an individual's susceptibility, suggesting a genetic predisposition.
• Obesity: Excess body weight places significantly greater mechanical stress on the knee joints, accelerating cartilage wear. Adipose tissue also produces inflammatory cytokines that can contribute to cartilage degradation.
• Previous Knee Injury: Trauma to the knee, such as fractures, meniscal tears, ligamentous injuries (e.g., ACL tears), or repeated microtrauma, can predispose the joint to early onset OA.
• Repetitive Stress: Certain occupations or sports involving repetitive kneeling, squatting, or heavy lifting can increase the risk.
• Joint Malalignment: Congenital or acquired deformities, such as bowlegs (genu varum) or knock-knees (genu valgum), can cause uneven stress distribution across the joint, leading to localized cartilage wear.
• Muscle Weakness: Weakness in the quadriceps and hamstring muscles can compromise knee stability and shock absorption, increasing stress on the joint.
• Inflammatory Joint Diseases: While OA is primarily degenerative, chronic inflammation from conditions like rheumatoid arthritis can damage cartilage, leading to secondary OA.

Common Symptoms

The symptoms of knee OA typically develop gradually and worsen over time.

• Pain: This is the most common symptom, often described as a deep ache. It tends to worsen with activity (e.g., walking, climbing stairs) and improves with rest, especially in the early stages. As the condition progresses, pain may become constant, even at rest or during sleep.
• Stiffness: Patients often experience stiffness in the knee, particularly after periods of inactivity, such as first thing in the morning or after sitting for a long time (known as "gelling"). This stiffness usually lessens with movement.
• Reduced Range of Motion: The ability to fully bend or straighten the knee may become limited due to pain, swelling, or the presence of osteophytes.
• Swelling: Fluid accumulation (effusion) in the joint can occur, leading to visible swelling around the knee.
• Crepitus: A grinding, clicking, crackling, or popping sensation and sound may be felt or heard during knee movement as rough cartilage surfaces rub against each other.
• Tenderness: The joint line may be tender to the touch.
• Instability or Buckling: In some cases, the knee may feel unstable or give way, especially if muscle weakness is present.
• Muscle Weakness and Atrophy: Disuse due to pain can lead to weakening and wasting of the muscles surrounding the knee, particularly the quadriceps.
• Joint Deformity: In advanced stages, the knee joint may appear enlarged or develop a bowed or knock-kneed appearance.

Diagnosis of Knee OA

Diagnosis of knee OA typically involves a combination of clinical assessment and imaging:

• Medical History: The physician will inquire about symptoms, their onset, severity, and factors that worsen or alleviate them, as well as past injuries and family history.
• Physical Examination: A thorough physical assessment of the knee involves checking for tenderness, swelling, crepitus, range of motion, stability, and gait abnormalities. Muscle strength and alignment are also assessed.
• Imaging Tests:
  • X-rays: These are the primary imaging tool to diagnose OA. They can show joint space narrowing (indicating cartilage loss), bone spur formation (osteophytes), and changes in the subchondral bone.
  • Magnetic Resonance Imaging (MRI): While not routinely used for OA diagnosis, MRI can provide detailed images of cartilage, menisci, ligaments, and other soft tissues, which can be useful in complex cases or to rule out other conditions.
• Laboratory Tests: Blood tests are generally not used to diagnose OA but may be ordered to rule out other forms of arthritis, such as rheumatoid arthritis, which are inflammatory in nature.

The Role of Exercise and Kinesiology in Management

From a kinesiology perspective, exercise is a cornerstone of managing knee OA. It is crucial for pain relief, functional improvement, and slowing disease progression. The goal is to optimize joint health and function without exacerbating symptoms.

• Pain Management: Regular, appropriate exercise can help reduce pain by improving joint lubrication, strengthening supporting musculature, and potentially altering pain perception.
• Improving Function: Exercise directly enhances joint flexibility, range of motion, balance, and the strength of muscles surrounding the knee (quadriceps, hamstrings, glutes, calves), which are vital for stability and shock absorption.
• Weight Management: Exercise contributes to weight loss or maintenance, significantly reducing the load on the knee joint and alleviating stress on damaged cartilage.
• Enhanced Proprioception: Specific exercises can improve the body's awareness of joint position and movement, leading to better balance and reduced risk of falls.

Recommended Exercise Types:

• Low-Impact Aerobic Activities: These activities elevate heart rate without excessive stress on the joints. Examples include walking (especially on softer surfaces), cycling (stationary or outdoor), swimming, water aerobics, and elliptical training.
• Strength Training: Focusing on the muscles that support the knee is paramount.
  • Quadriceps strengthening: Exercises like straight leg raises, wall slides, partial squats, and leg presses.
  • Hamstring strengthening: Hamstring curls.
  • Gluteal strengthening: Glute bridges, clam shells, side leg raises.
  • Calf strengthening: Calf raises.
  • Prioritize closed kinetic chain exercises (e.g., squats, lunges) where the foot is fixed, as they are often more functional and provide greater joint compression and stability compared to open kinetic chain exercises (e.g., leg extensions).
• Flexibility and Range of Motion Exercises: Gentle stretches to maintain or improve the knee's ability to bend and straighten fully, such as hamstring stretches, quadriceps stretches, and heel slides.
• Balance and Proprioception Training: Exercises like single-leg stands, tandem walks, and use of wobble boards can improve stability and reduce fall risk.

Key Principles for Exercise with Knee OA:

• Start Gradually: Begin with low intensity and short durations, progressively increasing as tolerated.
• Listen to Your Body: Pain is a signal. While some discomfort during exercise is acceptable, sharp or increasing pain warrants modification or cessation.
• Proper Form: Incorrect technique can exacerbate joint stress. Seek guidance from a qualified exercise professional (e.g., physical therapist, certified personal trainer with experience in clinical populations).
• Consistency: Regular exercise, even in short bouts, is more beneficial than sporadic intense sessions.

Other Management Strategies

While exercise is key, a multi-faceted approach often yields the best outcomes:

• Lifestyle Modifications:
  • Weight Loss: Even a modest reduction in body weight can significantly decrease stress on the knee.
  • Activity Modification: Identifying and modifying activities that aggravate symptoms while maintaining overall activity levels.
• Physical Therapy: A physical therapist can design a personalized exercise program, provide manual therapy, and educate on pain management techniques and proper body mechanics.
• Medications:
  • Over-the-counter pain relievers: Acetaminophen (Tylenol) and NSAIDs (ibuprofen, naproxen).
  • Prescription NSAIDs: Stronger anti-inflammatory drugs.
  • Topical agents: Creams or patches containing NSAIDs or capsaicin.
• Injections:
  • Corticosteroid injections: Provide temporary pain relief and reduce inflammation.
  • Hyaluronic acid injections (viscosupplementation): Supplement the natural lubricating fluid in the joint.
  • Platelet-Rich Plasma (PRP) or Stem Cell Injections: Newer, experimental treatments with varying evidence.
• Assistive Devices: Canes, walkers, or knee braces can help reduce stress on the joint and improve stability.
• Surgical Options: Reserved for severe cases when conservative treatments fail.
  • Arthroscopy: Minimally invasive procedure to remove loose cartilage or bone fragments.
  • Osteotomy: Reshaping of bone to shift weight from the damaged part of the knee.
  • Total Knee Arthroplasty (TKA) / Total Knee Replacement: Replacement of the damaged joint surfaces with artificial components.

Prevention and Prognosis

While OA is a progressive condition, its progression can often be slowed, and symptoms effectively managed. Prevention focuses on minimizing risk factors:

• Maintaining a healthy body weight.
• Protecting joints from injury through proper sports technique and safety measures.
• Engaging in regular, appropriate exercise that strengthens supporting muscles without overloading the joints.
• Addressing joint malalignment early if possible.

With appropriate management, including consistent adherence to an exercise program, individuals with knee OA can significantly improve their quality of life, reduce pain, and maintain functional independence for many years.