The knee primarily moves through flexion and extension, acting like a hinge joint. This means it bends (flexion) and straightens (extension).
Knee Joint Mechanics
The knee joint is a complex structure involving the interaction of the femur (thigh bone), tibia (shin bone), and patella (kneecap). As described in Physiopedia and other sources, during flexion and extension, the tibia and patella move as a unit relative to the femur. The articular surfaces of the femur roll and glide over the tibial surface, enabling this hinge-like motion.
- Flexion: Bending the knee. This reduces the angle between the thigh and lower leg.
- Extension: Straightening the knee. This increases the angle between the thigh and lower leg, returning the leg to a straight position.
While flexion and extension are the primary movements, minor rotational movements are also possible, especially when the knee is flexed. However, these are less significant compared to the hinge-like motion. Damage to the ligaments or other structures in the knee can restrict this range of motion. For example, a torn meniscus, as noted by the Mayo Clinic, can limit the ability to move the knee normally and cause pain.
Impact of Injury and Surgery
Injuries like a dislocated kneecap (patella) significantly impact knee movement. A dislocated kneecap, as detailed by sources like the NHS and Penn Medicine, causes the patella to slide out of its normal position, disrupting the smooth motion of the joint and leading to pain and inability to move the knee freely. Similarly, knee surgery, such as ligament repair (as described by Johns Hopkins Medicine) or knee replacement (as discussed by Mount Sinai) can temporarily or permanently limit the range of motion depending on the procedure and recovery.
