Avascular necrosis (AVN) is a debilitating progressive condition associated with loss of blood flow to the subchondral bone leading to bone necrosis. While AVN is most often associated with the femoral head, it may occur at multiple sites (femoral condyle, humeral head, talus, calcaneus, etc.). The etiology of AVN is most often described as a loss of blood flow of the terminal vascular bed in a bony structure. If not treated timely and appropriately, AVN can lead to joint pain, joint dysfunction, and irreversible damage. Appropriate staging of AVN is critical to treatment planning with the goal being joint preservation.  The hypoxia associated with AVN may be mediated by hyperbaric oxygen therapy.[3][4]

Goals of HBOT

• Stimulation of angiogenesis and vasculogenesis in the affected bone to mitigate ischemia
  
• Stimulate bone remodeling (osteoclasts and osteoblasts)
• Edema reduction

Diagnosis

• Early diagnosis of avascular necrosis is crucial, as the success of treatment largely depends on the stage at which it is initiated. Various diagnostic tools are available to aid in detecting and staging avascular necrosis. These include histological examination, scintigraphy, functional bone assessments, radiography, magnetic resonance imaging (MRI), and computed tomography (CT).
• Common differential diagnosis include mid- to late-stage osteoarthritis, acetabular dysplasia with secondary osteoarthritis, hip involvement in ankylosing spondylitis, idiopathic transient osteoporosis of the hip, chondroblastoma of the femoral head, subchondral insufficiency fractures, pigmented villonodular synovitis, synovial herniation, bone infarction, and femoroacetabular impingement syndrome.[5][6] 

Hyperbaric Criteria

• The Ficat classification is one of the most widely used staging systems for AVN of the femoral head. Patients are classified into four stages based on the plain radiograph or most preferably, MRI.
• I.  Pain but no radiographic abnormalities
• II. Increased  density, cystic changes, or porosity
• III. Flattening of the  femoral head or crescent sign
• IV. Full Collapse of the femoral head with decrease in joint space
• Intervention with HBOT, depends on two possible opportunities:
• Early stages of the disease (Ficat I and II): complete recovery can be achieved in imaging and functional improvement from the injury and pain control.
• Pre-collapse stage of the articulation (Ficat stage III, early stage): This will give more time as preparations are made before a patient must undergo total hip arthroplasty (THA), which is the usual course of the disease without  HBOT. [3]

Evaluation 

Treatment

HBOT treatment protocol for Avascular Necrosis

• Prerequisite 1: Patient Selection - proper staging of the patient will allow for appropriate management strategies. HBOT should be considered in the initial stage of the disease.
• Prerequisite 2: Lifestyle changes -  patients with involvement of weight bearing areas should avoid joint overload during treatment, such as crutches, and take measures to improve physical health with weight reduction and smoking cessation.

Treatment Schemes (applied according to the different Ficat classification for the femoral head)

• Scheme 1: Ficat Stage 1 (early disease)
• Goal: Full healing
• 2.0-2.5 ATA for 60-70 minutes of 100% oxygen breathing
• Daily treatment for 30-40 treatments
• Comment: several studies show 90 minutes of oxygen breathing with an added 10 minute air-break
• Follow up: MRI and orthopedic evaluation at 1 month.
• Scheme 2: Ficat Stage II (early disease)
• Goal: Lesional resolution
• 2.0-2.5 ATA for 60-70 minutes of 100% oxygen breathing
• Daily treatment for 30-40 treatments followed by a pause of 20 -30 days, then 20 additional treatments.
• Follow up: MRI and orthopedic evaluation at 1 month
• Scheme 3: Ficat Stage IIIA or worse (late disease)
• Goal: cost-benefit assessment of HBOT to delay the need for surgery, which must be weighed against the urgency and feasibility of prosthesis placement.
• Follow Scheme 2 which may be repeated once or twice at four to six months from the MRI/orthopedic assessment (for example, pediatric patients with avascular necrosis femoral head (AVNFH) related to extensive use of corticosteroids in the course of chemotherapy). 
• Evaluation of tympanic membranes pre- and/or post- HBOT as needed
• Smoking cessation is highly encouraged.

Follow-Up

• Obtain MRI at least 1 month after completion of HBOT and assess for improvement [3]

Treatment Threshold

• Refer to the ICD-10 Guideline for the appropriate ICD-10 Code
  
• Most common ICD-10 codes are:
• M87.051 Idiopathic aseptic necrosis of right femur
• M87.052 Idiopathic aseptic necrosis of left femur

• If diabetes is present, blood glucose should be checked within an hour prior to treatment and immediately post-HBOT by unit personnel. 
• If petroleum based dressings and ointments are a necessary part of the surgical dressing, ensure that they are not exposed and are completely covered with a moistened 100% cotton airtight dressing.