Trauma
Articular cartilage injury can occur by direct of indirect mechanisms
Direct Injury
Fractures of the bone that extend into the knee joint can injure articular and meniscal cartilage, often leaving irregularities of the joint surfaces and sometimes loose fragments of cartilage. These irregularities and loose fragments can cause painful locking or grinding within the knee, resulting in irregular wear on the joint surfaces and post-traumatic arthritis.
When blunt trauma occurs to the knee without fracture, abnormal compression forces applied to the articular cartilage can result in microscopic injury to cartilage and underlying bone (bone bruise). This lessens the ability of the articular cartilage to handle normal joint forces and may lead to changes in the knee similar to osteoarthritis.
Indirect Injury
Ligament injury results from abnormal rotational or bending stress applied to the knee. Residual instability of the knee produces abnormal translational stresses to the articular and meniscal cartilage causing pain and swelling. Over time, these abnormal stresses can lead to degeneration of the joint surfaces.
Injury to the meniscal cartilage can occur with fractures, blunt trauma, or ligament injuries. The torn meniscus may get caught within the joint causing painful snapping or locking of the knee. After being torn, the
meniscus is less able to equally distribute the normal joint forces, leading to microscopic injury and eventual degeneration of the articular cartilage.
Osteoarthritis is the most common joint disease. It is characterized by progressive loss of articular cartilage and formation of bone and cartilage at the joint margins. Symptoms include pain in the involved joint that is typically worse with activity and relieved by rest, stiffness after periods of immobility, instability, limitation of motion, muscle atrophy and weakness. Osteoarthritis can result from ligament or meniscal injury and can be hereditary. Repetitive use, such as athletics, may be implicated as well. However, there is no clear, convincing evidence to support this theory at this time.
Osteonecrosis is a generic term used to describe the death of the cellular elements of bone. It can be associated with high dose steroid use, pregnancy, trauma, alcohol abuse, or not have any predisposing factor or condition (idiopathic). Symptoms are abrupt onset of pain initially only during weight bearing and later during non-weight bearing and even while at rest. In some patients, the pain becomes unbearable as the disease progresses, whereas in others, it does not.
