Osteonecrosis of the Knee

Few people have most likely heard of knee osteonecrosis, but it can be a serious condition. In addition to the sudden onset of pain, it can lead to permanent joint damage and the need for joint replacement. Early detection and treatment can help prevent bone and cartilage deterioration. Diagnosis and treatment of osteonecrosis of the knee are quite challenging, given the insidious and nonspecific onset of the condition. Consulting with the first-class orthopedic surgeons at the Colorado Center of Orthopaedic Excellence in Colorado Springs, Colorado, will ensure you get the finest diagnosticians, the best of care, and the most successful outcomes. There is no need to suffer from pain or lose functionality of your knee.

OVERVIEW

Like any other part of the body, bone is a living tissue that requires blood and oxygen to survive. In osteonecrosis of the knee, the blood supply to an area of bone is interrupted, resulting in death of that segment of bone. The term “osteonecrosis” is a Latin term for “bone death,” and the condition is also referred to as avascular necrosis (or AVN). Spontaneous osteonecrosis of the knee (SONK) is a painful knee condition of idiopathic or unknown cause that occurs spontaneously. It is a distinct clinical entity with no consensus regarding the condition’s etiology. SONK stands for Spontaneous Osteonecrosis of the Knee and is the most common type of osteonecrosis in the knee. Ninety-nine percent of patients have only one joint involved. Women are more commonly affected, typically three times that of males, and it is more common in those 60+ years of age.

ABOUT THE KNEE

The knee joint is the largest and arguably the most stressed joint in the body, receiving four times the amount of stress for every pound one weighs. Four bones meet to form the knee: the thighbone (femur), shinbone (tibia), the smaller bone that runs alongside it (fibula), and kneecap (patella). The ends of the bones are covered with articular cartilage, which helps the bones glide against each other. Two crescent-shaped cartilage pads called the menisci sit between the tibia and femur, acting as shock absorbers. The knee is held together by a joint capsule, which has an outer layer of dense connective tissue and an inner membrane that secretes fluid to lubricate the joint. The knee is a hinge joint that allows the leg to bend and straighten, and it’s essential for many movements, like walking, running, and jumping. It supports the body and helps with balance. Because the knee is used so much, it’s vulnerable to injury.

WHAT IS OSTEONECROSIS OF THE KNEE?

When an area of bone loses its blood supply due to osteonecrosis, the body tries to replace it with living bone in a process sometimes referred to as “creeping substitution.” However, in this progression, the softening and absorption of necrotic bone outpaces new bone formation. During this replacement process, there is a temporary weakening – and the possibility of collapse – of this segment of bone. When osteonecrosis involves a weight-bearing surface near a joint such as the knee, the weakened surface may break or collapse under normal loading. This surface fracture, called a subchondral fracture, may cause sudden, acute pain in the joint. There are 5 stages to osteonecrosis of the knee:

• Stage I: symptoms are most intense in the earliest stage and may continue for six to eight weeks before subsiding. The patient has a symptomatic knee, but the findings were normal on the X-ray.
• Stage II: it may take several months for the disease to progress to Stage II. At this point, X-rays will show that the rounded edge of the thighbone is starting to flatten out.
• Stage III: by the time the disease reaches stage III (three to six months after onset), it is clearly visible on X-rays, and no other diagnostic tests are needed. The articular cartilage covering the bone begins to loosen as the bone itself begins to die.
• Stage IV: at this point, the bone begins to collapse. The articular cartilage is destroyed, the joint space narrows, and bone spurs may form. Severe osteoarthritis results and joint replacement surgery may be necessary.

Read more about Osteonecrosis of the Knee on our new Colorado Springs Orthopedic News Site – Colorado Springs Orthopedic News. Schedule an appointment with a knee specialist today.