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 OCC – Advanced Orthopedic & Sports Medicine Specialists in Denver, Parker, or Aurora, 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.

CAUSES

In most patients, the exact cause of the osteonecrosis is unknown; this is referred to as idiopathic AVN. Idiopathic avascular necrosis. (AVN) is a rare bone disease that occurs when there’s no known cause for a disruption in blood supply to the bone, resulting in bone death. Although the exact mechanism is not fully understood, idiopathic AVN is associated with certain disease conditions:

• Kidney transplant and dialysis patients
• Patients with HIV
• Obesity
• High alcohol intake
• Patients with fat-storage diseases
• Patients who receive steroid treatment for various medical conditions
• Sickle cell anemia
• Thalassemia (a blood disorder that prevents the body from producing enough hemoglobin, a protein that carries oxygen in red blood cells)

SYMPTOMS

• Gradual onset pain
• Localized pain is usually felt on the inner side of the knee but that can spread across the knee as the condition worsens
• Pain aggravated by weight-bearing activities such as walking, climbing stairs, or standing for extended periods
• Swelling
• Tenderness
• Stiffness
• Joint instability or sense of knee “giving way” during movement
• Reduced mobility
• Catching or locking
• Limping
• Progressive worsening

NON-SURGICAL TREATMENT

In the early stages of the disease, treatment is non-operative and the following may help :

• Activity modification
• Crutches or a knee brace
• A conditioning program with exercises to increase the strength of the muscles in the thighs. Over-the-counter non-steroidal medications (NSAIDs) like aspirin, ibuprofen, or naproxen may help with pain.
• Treatment with bisphosphonates (an antiresorptive medication such as Fosamax) to try and prevent excessive resorption and weakening of the bone, and/or fat metabolism-altering drugs known as statins. These medications theoretically affect fat metabolism, which can cause the disease, and treat the bony issues as well.

WHEN IS SURGERY INDICATED?

Surgical treatment is considered in advanced stages and when symptoms fail to respond to non-surgical treatment. Surgical treatment options include:

• Arthroscopic debridement or cleansing of the joint
• Drilling the area of osteonecrosis of the knee to decrease pressure on the bone surface
• Procedures to lessen the weight from the affected area
• Unicompartmental or total knee replacement
• High-tibial osteotomy, a procedure to realign the knee joint

For younger patients, typically under the age of 50 and depending on the area and extent of involvement, various surgical procedures may also be indicated.

GETTING THE RIGHT DIAGNOSIS. GETTING THE RIGHT DOCTOR.

Because of the difficulty in diagnosing osteonecrosis of the knee, it is imperative to find an orthopedic surgeon who can confidently diagnose and treat the widest range of cases of osteonecrosis of the knee with the deepest expertise. You won’t find more experienced specialists than those at Advanced Orthopedics in Denver, Parker, or Aurora, Colorado. Typically, in early-stage disease (also known as stage I) the symptoms may be quite intense and, because routine X-rays are normal, a positive bone scan or MRI is needed to make the diagnosis. As the disease progresses, X-rays and MRIs can show more detailed damage and a CAT scan can be used to delineate the area of necrosis further. Definitively identifying the extent and location of the osteonecrotic area is key in determining a unique treatment plan for each patient’s condition. The compassionate and approachable surgeons at Advanced Orthopedic can answer all your questions, help alleviate any anxiety, and build trust, making your journey to recovery smoother and easier.