Knee Pain: Causes, Symptoms, and Management When Bending and Straightening

Why does my knee hurt when I straighten it and bend it?

Knee pain experienced during both bending (flexion) and straightening (extension) often indicates an issue affecting the joint's mechanics, cartilage, or surrounding soft tissues, ranging from overuse injuries and inflammation to structural damage within the joint.

Understanding Knee Anatomy and Biomechanics

To comprehend why knee pain occurs during movement, a basic understanding of its complex structure is essential. The knee is a hinge joint, primarily allowing flexion and extension, but also some rotational movement.

• Bones: The knee connects the femur (thigh bone), tibia (shin bone), and patella (kneecap).
• Articular Cartilage: The ends of the femur and tibia, and the underside of the patella, are covered with smooth articular cartilage. This low-friction surface allows bones to glide effortlessly against each other.
• Menisci: Two C-shaped pieces of fibrocartilage, the medial and lateral menisci, sit between the femur and tibia. They act as shock absorbers, distribute weight, and enhance joint stability.
• Ligaments: Strong fibrous bands connect bones, providing stability:
  • Cruciate Ligaments (ACL & PCL): Inside the joint, crossing over, preventing excessive front-to-back and back-to-front movement.
  • Collateral Ligaments (MCL & LCL): On the sides of the joint, preventing excessive side-to-side movement.
• Tendons: Connect muscles to bones. The quadriceps tendon connects the quadriceps muscles to the patella, which then continues as the patellar tendon to the tibia. These are crucial for knee extension. The hamstring tendons attach to the tibia and fibula, facilitating knee flexion.
• Bursae: Small, fluid-filled sacs that reduce friction between bones, tendons, and muscles.

Knee Biomechanics: When you bend your knee (flexion), the tibia slides backward on the femur, and the patella glides downwards along the femoral groove. When you straighten your knee (extension), these movements reverse. Any interference with this precise gliding motion, or compromise to the joint's structures, can lead to pain.

Common Causes of Knee Pain During Movement

Pain during both bending and straightening is a hallmark of conditions that affect the general integrity or smooth operation of the knee joint.

• Osteoarthritis (OA): This is a degenerative joint disease where the articular cartilage wears down over time. As cartilage thins, bone-on-bone friction increases, leading to pain, stiffness, and reduced range of motion, especially after rest or with activity. Pain is often worse with weight-bearing movements.
• Patellofemoral Pain Syndrome (PFPS) / Runner's Knee: Characterized by pain around or behind the kneecap. It's often caused by poor patellar tracking within the femoral groove, leading to excessive friction. This can be due to muscle imbalances (weak VMO, tight IT band, weak glutes), overuse, or biomechanical issues. Pain is common with activities involving knee flexion and extension, such as squatting, climbing stairs, or prolonged sitting.
• Meniscus Tears: Tears in the menisci can occur acutely (e.g., twisting injury) or degeneratively (e.g., with age). Depending on the size and location of the tear, it can cause pain, swelling, clicking, catching, or even "locking" of the knee, limiting full extension or flexion.
• Tendinopathies (Patellar or Quadriceps Tendinopathy): Inflammation or degeneration of the tendons connecting muscles to the knee bones.
  • Patellar Tendinopathy (Jumper's Knee): Pain below the kneecap, common in activities involving repetitive jumping or landing.
  • Quadriceps Tendinopathy: Pain above the kneecap, often from repetitive knee extension activities. Both can hurt during the loading phase of flexion and the concentric/eccentric phases of extension.
• Bursitis: Inflammation of one of the bursae around the knee (e.g., prepatellar, infrapatellar, pes anserine). It typically causes localized pain, swelling, and tenderness, which can be exacerbated by movement that compresses the inflamed bursa.
• Ligament Sprains/Tears: While often causing instability, ligament injuries (e.g., ACL, MCL) can also cause pain during movement, especially if the joint is not stable or if there is associated swelling and inflammation.
• Plica Syndrome: The plica are normal folds in the synovial membrane (lining of the knee joint). If a plica becomes irritated or inflamed, it can get pinched during knee movement, causing pain, clicking, or a catching sensation, particularly during flexion and extension.
• Generalized Synovitis: Inflammation of the synovial membrane lining the joint, which produces synovial fluid. This can be due to injury, infection, or systemic conditions like rheumatoid arthritis, leading to diffuse pain and swelling with movement.

When Pain Occurs Primarily During Bending (Flexion)

If pain is most prominent during knee flexion (e.g., squatting, sitting down, climbing stairs, cycling), consider:

• Patellofemoral Pain Syndrome: Often worse with loading the patellofemoral joint during deep flexion.
• Meniscus Tears: Especially posterior horn tears, which get compressed during flexion. May present with clicking or catching.
• Osteoarthritis: Pain and stiffness increase as the joint compresses, particularly with weight-bearing flexion.
• Patellar Tendinopathy: Pain below the kneecap, especially during the eccentric phase of flexion (e.g., lowering into a squat).
• Bursitis (e.g., prepatellar, pes anserine): Direct compression or stretching of the bursa during bending.

When Pain Occurs Primarily During Straightening (Extension)

If pain is most prominent during knee extension (e.g., kicking, standing up, walking on flat ground, end-range leg extension), consider:

• Patellofemoral Pain Syndrome: Pain as the patella tracks up the femoral groove, especially with resisted extension or at the end range of motion.
• Meniscus Tears: Can cause mechanical block or locking, preventing full extension.
• Osteoarthritis: Stiffness and pain, particularly after prolonged sitting or rest, when attempting to straighten the knee.
• Quadriceps Tendinopathy: Pain above the kneecap, especially during the concentric phase of extension (e.g., pushing up from a chair).
• Plica Syndrome: The inflamed plica can get caught or irritated as the knee extends.

Risk Factors for Knee Pain

Several factors can increase your susceptibility to knee pain:

• Age: Increased risk of degenerative conditions like osteoarthritis.
• Obesity: Places increased stress on knee joints.
• Previous Injuries: A history of knee injuries (e.g., sprains, fractures) can predispose you to future pain.
• Certain Sports/Occupations: Activities involving repetitive stress, jumping, pivoting, or heavy lifting (e.g., running, basketball, construction).
• Muscle Imbalances and Weakness: Weak glutes, quadriceps, or hamstrings, or imbalances between them, can affect knee tracking and stability.
• Poor Biomechanics: Incorrect form during exercise or daily activities.
• Foot Mechanics: Overpronation or supination of the foot can alter lower limb alignment and put stress on the knee.

Self-Care Strategies and When to Seek Professional Help

For mild, acute knee pain without signs of severe injury, self-care can be beneficial.

Self-Care Strategies:

• R.I.C.E. Protocol:
  • Rest: Avoid activities that worsen the pain.
  • Ice: Apply ice packs for 15-20 minutes several times a day to reduce inflammation.
  • Compression: Use a bandage to help reduce swelling.
  • Elevation: Elevate your leg above your heart to minimize swelling.
• Activity Modification: Temporarily reduce or modify activities that trigger pain.
• Over-the-Counter Pain Relievers: NSAIDs (e.g., ibuprofen, naproxen) can help manage pain and inflammation.
• Gentle Movement and Strengthening: Once acute pain subsides, incorporate gentle, pain-free exercises to maintain range of motion and strengthen surrounding muscles (e.g., quadriceps, hamstrings, glutes, calves).
• Stretching: Address any muscle tightness (e.g., hamstrings, quadriceps, IT band, hip flexors).
• Proper Footwear: Ensure your shoes provide adequate support and cushioning, and consider orthotics if you have significant foot biomechanical issues.

When to Seek Professional Help:

It's crucial to consult a healthcare professional (e.g., physician, physical therapist, sports medicine specialist) if you experience any of the following:

• Severe pain that prevents you from bearing weight or performing daily activities.
• Sudden, significant swelling or bruising around the knee.
• Deformity of the knee or lower leg.
• A popping or snapping sound at the time of injury, followed by pain and swelling.
• Inability to fully bend or straighten the knee.
• Clicking, catching, or locking sensations that impede movement.
• Fever, redness, or warmth around the knee, which could indicate infection.
• Pain that worsens or does not improve after a few days of self-care.
• Pain that recurs frequently or interferes with your quality of life.

Prevention Strategies

Proactive measures can significantly reduce your risk of developing knee pain:

• Maintain a Healthy Weight: Reducing excess body weight decreases the load on your knee joints.
• Strengthen Supporting Muscles: Focus on balanced strength training for the quadriceps, hamstrings, glutes, and core muscles to improve knee stability and tracking.
• Improve Flexibility and Mobility: Regular stretching can prevent muscle imbalances and maintain healthy joint range of motion.
• Use Proper Technique: Ensure correct form during exercises, sports, and daily activities to avoid undue stress on the knees. Consider professional coaching or guidance.
• Gradual Progression: When starting a new exercise program or increasing intensity, do so gradually to allow your body to adapt. Avoid sudden increases in training volume or intensity.
• Listen to Your Body: Pay attention to early signs of discomfort or pain and address them promptly before they escalate into more significant issues.
• Warm-Up and Cool-Down: Always perform a dynamic warm-up before activity and a static cool-down afterward.

Conclusion

Knee pain during both bending and straightening can stem from a variety of causes, often indicating mechanical issues, inflammation, or structural damage within the joint. Understanding the intricate anatomy and biomechanics of the knee is key to identifying potential culprits. While many mild cases can be managed with self-care, persistent or severe symptoms warrant a professional evaluation to obtain an accurate diagnosis and develop an appropriate, evidence-based treatment plan. By prioritizing proper movement mechanics, muscle balance, and smart training strategies, you can significantly reduce your risk of knee pain and maintain optimal knee health.