Avascular necrosis/osteonecrosis is a degenerative bone disease characterized by the death of bone cellular components secondary to disruption of subchondral blood supply. It usually affects the epiphyses of long bones at weight-bearing joints. Advanced disease may cause The subchondral collapses, threatening the viability of the associated joint. Nontraumatic cases typically present with mechanical pain of variable onset and severity and are often difficult to localize. In the early stages of the disease, physical examination is usually normal, which inevitably delays diagnosis. 
This short video sums up the situation well
See Avascular Necrosis Femoral Head
Osteonecrosis most commonly occurs in the hip joint, but can also occur in the humerus, knee, and talus, and more rarely in the smaller bones of the wrist, such as the lunate  or scaphoid.
It can be caused by traumatic or nontraumatic events
- Joint or bone trauma
- Injuries such as joint dislocations can damage nearby blood vessels.
- Fractures, such as the femoral head.
- Cancer treatments that involve radiation can also weaken bones and damage blood vessels.
- Heavy alcohol consumption  and steroid abuse have been identified as major risk factors
- Many studies have also concluded that hyperlipidemia of the femoral head caused by steroid and alcohol use is associated with osteonecrosis. Both of these factors lead to increased fat volume in the bone marrow and lipid levels in the blood, leading to increased fat and fatty deposits. Interrupt blood flow to the femoral head.
- A stronger association was found for glucocorticoid intake than for alcohol consumption.
- Smoking: increased levels of oxidative stress and endothelial dysfunction due to changes in nitric oxide bioavailability
- Obesity: Osteonecrosis was positively correlated with BMI. Overweight and obesity like steroid and alcohol use are often associated with hyperlipidemia.
- Conditions such as sickle cell anemia or systemic lupus erythematosus.
Studies have shown that men have a higher prevalence, which may be attributed to higher levels of smoking and alcohol consumption. Greater fluctuations in climate temperature may also lead to higher rates of non-traumatic osteonecrosis. 
Symptoms include pain and decreased range of motion in the affected joint. In some cases, the disorder is diagnosed during routine X-ray imaging due to the lack of overt symptoms . The most common site for this condition is the head or neck of the femur or humerus and the knee United .
At first the disease is asymptomatic. It is also possible that there is segmental collapse that is not felt by the patient. As the disease progresses, the hip becomes more rigid, which is seen in the patient’s gait when they begin to limp. Pain is also observed in support On the buttocks groin and thighs.
Avascular necrosis can be divided into five distinct stages:
- Stage 1: No radiographic changes or showing mild osteopenia. An MRI scan is needed for identification (can show edema). The onset of the disease is asymptomatic.
- Stage 2: The first stage has radiographic changes. This stage is characterized by sclerosis and/or osteopenia and/or subchondral cysts in the upper central part of the articular head.
- Stage 3: In this stage, the articular surface is depressed and the circular contour is compromised, but there is no significant deformation. This results in a narrowing of the joint space. Plain radiographs show a crescent sign.
- Stage 4: This stage is characterized by extensive collapse of the subchondral bone and destruction of the underlying trabecular structure. This can lead to secondary arthritis.
- Stage 5: The final stage involving both joints resulting in joint dysfunction.
For example if there is a case where the patient has osteonecrosis of the femoral head. Avascular necrosis commonly affects the hip in more than 72% of cases. The patient will have mild chronic pain in the pelvis and normality of the spine around the pelvis and antero-medial thigh radiograph should be treated as ONFH and Hip joints MRI. This pain is often exacerbated by activity and internal rotation in flexion. As the disease progresses the pain may also occur at rest. Without treatment 85% will progress to articular collapse surface and will ultimately require a complete hip arthroplasty.  .
Osteonecrosis can be diagnosed by careful evaluation of the patient’s history combined with physical examination. Steroid use and alcohol abuse are important risk factors. The age of the patient can also be diagnostic because patients with osteoporosis are like that generally younger than those with osteoporosis. Locking popping or a painful click when mobilizing the affected joint may indicate the presence of loose osteochondral fragments. In another stage of the disease, loss of motion and increased pain may be observed. Once osteonecrosis is diagnosed the physician should look for other potentially dangerous joints such as the hip shoulder and knee.
In the early stages, the condition is asymptomatic, making diagnosis nearly impossible. However, early screening using MRI is currently the best diagnostic modality due to its sensitivity. Double lines are MRI findings seen around areas of osteonecrosis. it includes Inner bright lines representing granulation tissue and outer dark lines representing sclerotic bone. Measuring the size and location of necrotic lesions is a key prognostic parameter to predict collapse and can be better defined on MRI. 
At a more advanced time point, standard radiographs can confirm the diagnosis. Tissue affected by avascular necrosis will appear thickened (increased white) and possibly sclerotic (mottled) on the radiograph. MRI can help with the diagnosis. It can show a subchondral radiolucency called a “crescent sign” indicates immediate root collapse.
Functional outcome measures are useful for establishing baseline patient functioning and establishing measurable goals. See Outcome Measures Database for more.
The outcome chosen will depend on the affected joint.
1. The Harris Hip Score
2.4 Item Pain Intensity Measure (P4) Numeric Pain Rating Scale or Visual Analog Scale (if patient reports pain symptoms)
3. Hip Disability and Osteoarthritis Outcome Score (HOOS)
- Pharmacological Therapy
Medical treatment with anticoagulants statins and vasodilators appears to be effective in delaying the progression of early joint degeneration in avascular necrosis. Although there is little evidence to support the use of these drugs in the treatment of osteonecrosis. Another treatment that is still being tested is bisphosphonates. It is hypothesized that in the early stages of AVN, administration of bisphosphonates could inhibit osteoclast activity and thus prevent subchondral bone collapse. 
- Surgical Treatment
Core decompression (for stages 1 and 2 of the disease) creates a canal in, for example, the femoral head, which decompresses the head. This promotes increased blood flow, which in turn promotes new blood vessel formation, which may stimulate new bone growth. along with
advent of microsurgery this surgery can also be performed with bone grafts. Once you have debrided the necrotic array you replace the necrotic bone with viable bone (usually 15 cm of the fibula and the peroneal artery that connects to the ascending branch of the
lateral femoral circumflex artery and vein) to initiate callus formation in the femoral head.
An osteotomy is a surgical cut to shorten or lengthen a bone or to alter its alignment reducing the load from the dead bone by rotating the femoral head and neck or having varus or valgus angulation the proximal femur. This treatment is reserved for young patients with co-morbidities that preclude orthopedic healing. In the United States, angular osteotomy for diseases that are stage II or III at the time of intervention has had modest success rates ranging from 70% to 90% at follow-up from 3 to 18 years.
When all else fails, a total hip arthroplasty (typically at stages 3 and 4) is the only option. In this total hip replacement, damaged bone and cartilage are removed and replaced with prosthetic material.
• The damaged femoral head is removed and replaced with a metal rod placed in the middle of the femur with the hole.
• A metal or ceramic ball is placed at the top of the stem (replacing the femoral head) .
• The bony defect of the socket (acetabulum) is removed and replaced with a metal socket.
• A plastic ceramic or metal spacer is inserted between the new ball and the socket to create a smooth gliding surface.
Studies show that total hip arthroplasty (32-mm alumina-on-alumina ) in patients with avascular necrosis of the femoral head after 2 to 10 years of follow-up shows better outcomes in terms of cargo will be replaced in a long-term. It shows a better Harris hip score and decreased pain after surgery.  .
Physical Therapy Management
Appropriate treatment of avascular necrosis is essential to prevent further joint damage. If left untreated most patients become severely ill and immobile within two years. Although physical therapy cannot cure avascular necrosis it can slow the progression of disease and associated pain reduction. It is suggested that patients with Stage 1 and 2 osteonecrosis may benefit from a physical therapy program. Ultimately, most patients will require surgical treatment such as core decompression or arthroplasty.
Nonoperative treatment involves three main goals:
- Relief of symptoms
- Prevention of disease progression
- Improvement of functionality
Non-surgical treatment begins with patient education and addressing known risk factors such as smoking and alcohol abuse. In addition corticosteroids should be avoided.
To help the patient regain function and relieve pain symptoms, a cane or other walking aids may be introduced. The physical therapist should teach the patient how to use this device properly.By using a cane the load carried by the hip joint will be reduced. This burden-bearing restriction is an important conservative treatment. In the literature it is considered that weight restriction as a stand-alone treatment is insufficient in preventing disease progression but is a reasonable treatment when combined with pharmacologic or surgical regimens the.  .
Physical therapy focuses on exercises to maintain joint movement and strengthen the muscles surrounding the damaged joint. During exercises, excessive tensile and flexural forces on the joints should be avoided. The outcome depends on the size and stage of the lesion at the time of onset of the treatment of the disease.
To maintain joint mobility, both passive and active exercises should be initiated. Passive exercises contain passive hip movements and extension exercises. Dynamic exercises consist of 3dimensional motions of the hip joint and can be used while standing sitting in a chair or while lying on the ground. In the next phase, strengthening exercises are added. This exercise will focus on the hip and thigh muscles but will also include exercises for the core area as it plays a large supporting role. To improve performance it is necessary to use endurance training and systematic training in a more comprehensive phase of treatment. Endurance can be trained by walking on a treadmill or riding a bike on a home trainer. To improve systematic walking exercises of high intensity and balance exercises can be adopted in physical therapy sessions.  .
Exercise after surgery is also an important part of recovery. It starts the day after surgery. Patients are prepared for discharge by teaching them how to perform daily activities such as getting in and out of bed and using a walker or cane. (section 5) .
In a more advanced stage of treatment, the therapist instructs the patient to perform exercises without straining their muscles to improve the movement function in terms of balance and speed of walking. The patient learns specific movements while maintaining caution at the hips. The rehabilitation protocol is combined with a home exercise program. Below is an example of a comprehensive recovery training program .
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