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Understanding Knee Pain

The most common joint pain affecting 1 in 4 Americans

27M+ Americans affected annually
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Understanding the Joint

Knee Anatomy

Knee anatomy illustration

The knee is a complex hinge joint connecting the femur (thigh bone) to the tibia (shin bone). It is stabilized by ligaments, cushioned by cartilage, and powered by surrounding muscles.

Key Structures

  • ACL and PCL ligaments (front-back stability)
  • MCL and LCL ligaments (side stability)
  • Meniscus cartilage (shock absorption)
  • Patella/kneecap (protects joint)
  • Synovial membrane (produces lubricating fluid)
Common Causes

Knee Pain Conditions

Osteoarthritis

Most common (85%)

Progressive cartilage breakdown causing bone-on-bone friction. The most common reason for knee replacement surgery.

Symptoms

  • Stiffness after rest or in morning
  • Grinding or crackling sensation
  • Reduced range of motion
  • Pain that worsens with activity
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Meniscus Tear

Common in athletes

Torn cartilage cushion usually from twisting injury while bearing weight.

Symptoms

  • Popping sensation at time of injury
  • Swelling within 24 hours
  • Locking or catching sensation
  • Difficulty fully straightening knee

ACL Injury

200,000/year in US

Anterior cruciate ligament tear from sudden stops, direction changes, or landing from jumps.

Symptoms

  • Audible pop at injury
  • Rapid swelling within hours
  • Severe pain
  • Knee instability or giving way

Patellofemoral Syndrome

Common in runners

Pain behind or around kneecap from tracking issues. Often called runner's knee.

Symptoms

  • Pain climbing or descending stairs
  • Pain after prolonged sitting
  • Grinding or popping sound
  • Pain with squatting

Bursitis

Common

Inflammation of fluid-filled sacs (bursae) that cushion the knee.

Symptoms

  • Localized swelling
  • Warmth over affected area
  • Pain with pressure or movement
  • Tenderness to touch
Physical Therapy

Recommended Exercises

Consult a healthcare provider before starting any exercise program.

Straight Leg Raises

3 sets of 10 Quadriceps

Lie on back, bend one knee, keep other leg straight. Lift straight leg to height of bent knee. Hold 3 seconds, lower slowly.

Hamstring Curls

3 sets of 10 Hamstrings

Stand holding chair for balance. Bend knee bringing heel toward buttock. Hold 3 seconds, lower slowly.

Wall Squats

3 sets of 10 Quads and Glutes

Stand with back against wall. Slide down until knees are at 45-degree angle. Hold 5-10 seconds, slide back up.

Step-Ups

2 sets of 10 each leg Overall stability

Step up onto 6-inch step with one foot. Bring other foot up, then step back down. Alternate legs.

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Red Flags

When to See a Doctor

  • ! Severe swelling within hours of injury
  • ! Inability to bear weight on the leg
  • ! Visible deformity of knee or leg
  • ! Fever accompanied by redness and swelling
  • ! Significant instability (knee gives out)
  • ! Pain persisting more than 2 weeks despite rest
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