What Is Osteonecrosis

 Osteonecrosis (ON) is a condition in which our bone tissue dies and decays. Osteo means bone, and necrosis means death; therefore, ON translates to ‘bone death’.

ON can occur due to various reasons. Some of the most common ones are:

• Injury to the bone
• Loss of blood supply (avascular necrosis)
• Infection
• Chronic alcohol intake
• Certain medications, including glucocorticoids¹
• Connective tissue disorders

Any bone in the body can be affected by ON. Similarly, any person can be affected. However, it is most common in those aged between 30 and 50 years old. This article will go into more depth about ON, including discussing the causes, symptoms, and treatment.

Overview

ON can occur in any of our bones. When the affected area is small, our body can repair the damaged bone itself, and the problem is solved. However, repair mechanisms are not always successful, especially in weight-bearing bones like the hip joint, knee joint, or shoulder joint. Physical activity can cause those affected by ON to feel severe pain.

The symptoms are very simple and common and, therefore, difficult to diagnose as ON. Similar pain may occur due to various reasons, such as fractures or arthritis. -This often causes a delay in diagnosis, leading to the progression of the condition. The treatment of ON is complicated and invasive. Therefore, it's best to diagnose and treat it in its initial stages.

Causes of osteonecrosis

ON can be caused by many reasons. Our bones are in a constant cycle of being created (by cells called osteoblasts)and destroyed (by cells called osteoclasts). When there is an imbalance in this cycle to favour destruction, it can cause an overall loss of bone, which can result in ON.2 When bone is deprived of blood supply, osteocytes cannot work and fail to modify bone. ON can be broadly divided into:

1. Avascular necrosis - When ON occurs due to loss of blood supply, it is called avascular osteonecrosis.
2. Aseptic necrosis - When it is caused by any infection, it is called aseptic osteonecrosis.
3. Traumatic necrosis - Trauma results in bone dislocation, thereby affecting the blood supply.  This causes deprivation of oxygen and other nutrients, ultimately causing necrosis.
4. Atraumatic necrosis - Atraumatic is associated with other reasons such as medications or radiotherapy.

When the pressure in the bone increases, it can also result in ON. The normal pressure in bone is 15-30mm Hg. 

Other risk factors include:

• Intake of alcohol
• Fatty deposits in blood vessels - this can block blood from reaching the bone
• Certain diseases - such as Gaucher’s disease and sickle cell anaemia (these can also reduce blood flow to the bone)
• Steroid medications -  can cause fat buildup 
• Bisphosphonate use - they cause an increase in bone density and therefore decrease the chance of free flow of blood
• Certain cancer treatments - radiotherapy (where ionizing radiation is given) can disrupt the balance of bone morphology and cause ON. When ON occurs due to radiotherapy, it is called Radio Osteonecrosis.³

Signs and symptoms of osteonecrosis

The symptoms of ON depend on the bone affected. When the dying bone is a weight-bearing bone, the patient can get severe pain during any sort of physical activity.

However, in initial cases of ON, it can be completely asymptomatic. The most common symptoms are:

• Intense pain (especially when bearing weight), which can be relieved by removing the stress
• Stiffness in joint movements
• Limited range of movements
• Limping of the hip or knee joint
• Difficulty in simple tasks like standing, walking, and climbing stairs.

Management and treatment for osteonecrosis

Once the bone has died, it begins to decay. There is no way to regenerate the part that has died. So, treatment of ON involves prevention of further spread and preservation of joint structure as far as possible. It often also involves pain control and reducing the stress on affected bones. 

The main goal is to preserve joint function as much as possible and as effectively as possible.

Treatment can be broadly divided into:

• Surgical approach
• Non-surgical approach 

Your treatment plan can be decided based on:

• Extent of the disease
• Age
• Other medical conditions
• Which bone is affected

Surgical approach - The main goal is to remove the dead bone without breaking the entire bone structure. If the condition is severe and the joint cannot be restored, joint replacement surgery has to be performed. Various surgical approaches are:

1. Core decompression surgery - In this procedure, professionals drill into the affected bone, relieving bone internal pressure, thereby reducing pain, discomfort and disease progression. This procedure is combined with bone grafting to promote bone repair.
2. Osteotomy - when the affected bone is small, this procedure can be used. Surgeons reorient the healthy bone into the affected bone so that healthy tissue supports the weight, thereby relieving the pain.
3. Bone grafting - In this procedure, the affected bone is removed, and healthy bone (including its blood supply) from another part of the body (or from a donor) is inserted in its place to restore the affected bone.
4. Joint replacement - When the joint is completely damaged, the entire joint has to be replaced with an artificial joint made up of plastic, metal, or ceramic. It may relieve pain and increase the joint range of motion.

Non-surgical approach - these mainly aim to reduce the symptoms rather than prevent the spread or treat the damaged bone.

They involve:

1. Non-steroidal anti-inflammatory drugs (e.g. ibuprofen) for pain control
2. Physical therapy - to reduce joint tenderness and increase joint movements.
3. Use of crutches (if bone is affected is a weight-bearing joint) to support the joints and relieve pain
4. Corticosteroid injection to relieve pain and swelling in the joint

FAQs

Where does osteonecrosis occur

ON can occur in any bone of the body, depending upon the causes.  When it occurs in small areas, the body can repair itself.  But when they occur in weight-bearing bones, it will be problematic. The most common bones to be affected by ON are long bones such as femoral bone, knee bone, and shoulder bones. Pain is also often very severe when ON occurs at these joints.

How is osteonecrosis diagnosed?

ON is diagnosed with the help of X-rays in later stages. Initially, magnetic resonance imaging (MRI) has higher sensitivity than X-ray. MRI identifies any minor bone changes. However, your doctor may take an x-ray initially to rule out other potential causes, such as fractures or arthritis. Computed tomography (CT scans) can also be used to assess the extent of bone damage in latent cases.

How can I prevent osteonecrosis?

ON can be prevented by leading a healthy lifestyle. Reducing Alcohol and tobacco usage and doing regular exercise can help your joints to be in good, healthy condition. Certain medications like corticosteroids and bisphosphonates should be used under medical supervision. If you think you are at risk of getting ON, it is best to seek medical advice as soon as symptoms start.

Who are at risk of osteonecrosis

ON can occur in anyone. The most common age of occurrence is 30-50 years of age, and it is most commonly seen in those assigned female at birth (AFAB). But, there are also some medical conditions where the risk of ON is increased. They include:

• Sickle cell anemia
• Leukaemia
• Gaucher's disease
• Gout
• HIV
• Pancreatitis
• Rheumatoid arthritis
• Lupus

Patients who use corticosteroids, bisphosphonates, or those who are undergoing radiotherapy for cancer treatment are also more prone to develop ON.

How common is osteonecrosis

The prevalence of ON has been estimated to be around 4.7 cases/10000 person-years. This is based on a study conducted in 2019, which found that among those assigned male at birth (AMAB), the incidence was 3.5 /10000 person-years, and among those AFAB, it was 5.7 cases/10000 person-years.⁴

When should I see a doctor?

Severe pain in joints or bones can be caused by many different conditions, such as myalgia, myositis, fractures, arthritis, and autoimmune conditions. Some types of ON, such as traumatic and avascular necrosis of bone, are so unpredictable that it further complicates diagnosis. Therefore, if you are experiencing severe bone or joint pain, it's always best to visit the doctor as soon as possible so that investigation, diagnosis, and treatment can begin immediately.

Summary

Osteonecrosis is a debilitating condition that can deteriorate the quality of life of the patient. The symptoms are also very common and can be mistaken for many other muscle, joint, and bone disorders. The treatment of ON involves removing the dead bone and restoring the function of the joint. So far, there is no medication that can control the progression or prevention of the disease. Therefore, it is important to be careful, reduce your risk if possible, and seek medical advice as soon as you see symptoms.