Common Knee Injuries

1. Anterior Cruciate Ligament (ACL) Tear

• Area of Pain: Deep within the knee, usually accompanied by an audible "pop" sensation, immediate swelling, and a feeling that the knee is "giving out" or unstable.

• Affected Anatomy: The anterior cruciate ligament (ACL), one of two major cruciate ligaments crossing inside the joint center to prevent the tibia from sliding too far forward relative to the femur.

• Explanation: Frequently occurs during sports involving sudden stops, rapid changes in direction, jumping, or direct impact (e.g., soccer, basketball, skiing).

2. Meniscus Tear (Medial or Lateral)

• Area of Pain: Sharp pain localized along the inner (medial) or outer (lateral) joint line. It is often accompanied by clicking, catching, locking, or an inability to fully straighten the leg.

• Affected Anatomy: The meniscus—two wedge-shaped pieces of C-shaped fibrocartilage (medial and lateral menisci) that sit between the femur and tibia to act as shock absorbers.

• Explanation: Can happen traumatically through forceful twisting of the knee while the foot is planted (common in athletes), or degeneratively over time as cartilage weakens with age.

3. Patellar Tendonitis ("Jumper's Knee")

• Area of Pain: Tenderness and aching right at the front of the knee, specifically focused on the tendon just below the kneecap. Pain typically worsens with jumping, running, or squatting.

• Affected Anatomy: The patellar tendon, which connects the bottom of the patella (kneecap) to the tibial tuberosity (shin bone).

• Explanation: An overuse injury caused by repetitive stress and micro-tears in the patellar tendon, common in sports that involve frequent explosive jumping or landing.

4. Medial Collateral Ligament (MCL) Sprain

• Area of Pain: Pain and tenderness directly on the inner (medial) side of the knee joint, especially when pressure is applied outward against the joint.

• Affected Anatomy: The MCL, a band of tissue running along the inner edge of the knee that stabilizes the joint against sideways forces from the outside.

• Explanation: Typically caused by a direct blow to the outer side of the knee (such as a tackle in contact sports), which stretches or tears the ligament on the inner side.

5. Chondromalacia Patellae ("Runner's Knee")

• Area of Pain: A dull, aching pain behind, around, or directly under the kneecap (patella). Pain typically intensifies when walking down stairs, squatting, kneeling, sitting for extended periods with knees bent ("theater sign"), or during running.

• Affected Anatomy: The articular cartilage lining the backside (posterior surface) of the patella (kneecap) where it glides against the femoral groove (trochlea) of the thigh bone.

• Explanation:

  • Characterized by the softening, fraying, and gradual breakdown of the smooth articular cartilage underneath the kneecap.

  • Frequently stems from poor patellar tracking—where the kneecap does not slide smoothly in the femoral groove—caused by muscle imbalances (such as weak vastus medialis/quadriceps or tight IT bands), abnormal hip alignment, or repetitive overuse from running and jumping sports.

  • As the cartilage wears thin, friction increases between the kneecap and thigh bone, triggering localized inflammation, pain, and sometimes a grinding or crunching sensation (crepitus) during knee movement.

6. Iliotibial Band (ITB) Syndrome

• Area of Pain: Sharp or burning pain localized specifically on the outer (lateral) side of the knee, just above the joint line. Pain often intensifies when the foot strikes the ground while running or when walking down stairs/hills.

• Affected Anatomy: The iliotibial band (ITB)—a thick, fibrous band of connective tissue (fascia) running down the outside of the thigh from the pelvis/hip to the top of the shin bone (tibia)—and the lateral femoral epicondyle (the bony prominence on the outer side of the lower thigh bone).

• Explanation:

  • ITB Syndrome is one of the most common overuse injuries in runners and cyclists.

  • As the knee repeatedly bends and straightens (specifically around a 30-degree flex angle), the tight IT band slides back and forth across the lateral femoral epicondyle.

  • This repetitive friction causes irritation, micro-inflammation, and pain in the fat pad and tissue underlying the band on the outer edge of the knee.

  • It is often exacerbated by weak hip abductors (gluteus medius), sudden increases in running volume/downhill running, or worn-out footwear.