Introduction

Avascular necrosis (AVN), also referred to as aseptic osteonecrosis (AO), can develop in several osseous districts of the body. Most commonly described is avascular necrosis of the femoral head (AVNFH), a debilitating and progressively disabling condition with partially understood, wide-ranging etiology and pathogenesis. Pathology is chiefly caused by a reduced vascularization of a terminal vascular bed, such as the one perfusing the femoral head, or similar vascular distributions such as femoral condyles, humeral head, the talus, the calcaneus, the navicularis, and other bony structures. Hypoxic conditions mediate the condition and can improve with a course of hyperbaric oxygen (HBO₂).

The Ficat classification is one of the most widely used staging systems for AVN of the femoral head. It classifies patients with osteonecrosis into four stages based on the appearance on a plain radiograph, at least before the advent of MRI, the ultimate golden standard for the specific case.

1. Pain but no radiographic anomalies
2. Increased density, cystic changes, or porosity
3. Flattening of the femoral head and crescent sign
4. Full collapse of the femoral head with decrease in joint space

Many of the treatment options proposed aim to achieve joint preservation. However, when the radiological signs progress to advanced bone collapse in the articular capsule, the single mandatory surgery approach is a femoral head replacement with total hip arthroplasty (THA).

There are two possible opportunities for intervention with HBO₂:

• Early stages of the disease (Ficat l and ll): complete recovery can be achieved in imaging and functional improvement from the injury and pain control.
• Pre-collapse stage of the articulation (Ficat lll, early stage): “buying time” before a patient must undergo THA, which is the usual clinical course of disease without HBO₂

All bones can develop an osteonecrotic lesion, but the segments most frequently affected are undoubtedly the terminal portions of the long bones (epiphyses), especially that of the femoral head. This pathology usually affects the age range of the most active population (40-50 years old), with repercussions both on the patient’s quality of life (as it is often progressively disabling, leading to femoral head collapse if left untreated and eventual surgery) and on the general economy as well (due to its reduction in the ability and work performance of those affected).

An estimated 20,000-30,000 cases of osteonecrosis are reported in the United States per year, and the percentage of patients requiring THA has increased from 54.2/100,000 hospital admissions in 2001 to 60.6/100,000 hospital admissions in 2010._1,2