In the earliest stage of Osteonecrosis, x-rays will appear normal and an accurate diagnosis can rarely be made without using MRI. It is only after weeks, perhaps months that the patient may develop an ill-defined mottling of the trabecular pattern as the earliest evidence of osteonecrosis that can be seen on a standard x-ray. The mottling seen is not actually dead bone, but the healing response of the living bone to the area of necrosis or tissue death as the body strives to revive and repair the injury.
As the disease continues to progress the dead bone and the new, softer repair bone begins to fail mechanically through a process of microfractures of the bone. If the necrotic area of bone is located in the medullary space, well away from the joint, a classic pattern of dense, serpiginous calcification will begin to be visible on imaging studies. However, if the necrosis occurs in the subchondral bone, which is frequently the case, a different distinctive pattern begins to emerge. That pattern is the classic crescent sign, a visible indication several microfractures that have occurred between the subchondral line and the area of dead bone tissue. As the body continues to attempt to repair and revascularize necrotic bone tissue, subchondral collapse and arthritic processes occur.
A discontinuity in the subchondral line forms a thick, sclerotic zone between the living and the dead as the living bone around the area reacts to the presence of the dead bone tissue. The timeframe for these imaging patterns to emerge are months after the necrosis begins. These image patterns serve as a precursor to the growing damage that is accumulating along the shared surface of the joint. The presence of these microfractures on the bone lead to a rough surface, causing further injury by a process of cartilage breakdown and even painful bone on bone friction. Without early treatment and sometimes despite early aggressive intervention the accumulating damage will require major joint reconstruction (Richardson, 2003).
Staging of a hip injury is the prelude to treatment. Staging systems examine how far the disease has progressed, the degree of bone damage, and the diagnostic imaging evidence. Using the information obtained from the diagnostic process a clinician can map out a plan of care based on the individual characteristics, and damage present. Several formal staging systems are in use. Radiologists and Orthopedic Surgeons rarely use the same system (Lee, Chang, Chao, &, 2002).
The Ficat Classification System can be employed before any evidence of injury is visible. In the preclinical stage, or Stage 0, a suspected diagnosis of hip osteonecrosis can be made based on the knowledge of pre-existing disease in the opposite hip joint. There is a high incidence of bilateral involvement. Almost 50% of the cases of osteonecrosis in one hip eventually progress to the second hip (Levine, Rajadhyaksha, & Mont, 2004).
Ficat Classification System Stages of Bone Necrosis of the Femoral Head
Stage 0 – Pre-clinical
Stage I – Pre-radiographic
Stage II – Pre-collapse
Stage III – Collapse
Stage IV – Osteoarthritis
The Steinberg Staging System, or S-3, is a useful tool in establishing the age and extent of injury from a particularly radiographic viewpoint. The Steinberg System has some advantages over the Ficat Classification System in that it portrays a greater level of detail and a more accurate prediction of outcome.
Steinberg Staging System
Stage 0 - Normal or nondiagnostic radiographic, bone scan, and MRI findings
Stage 1 - Normal radiographic findings, abnormal bone scan and/or MRI findings
Stage 2 - Lucent and sclerotic changes in femoral head
Stage 3 - Subchondral collapse (crescent sign) without flattening
Stage 4 - Flattening of femoral head
Stage 5 - Joint narrowing and/or acetabular changes
Stage 6 - Advanced degenerative changes
Nonsurgical treatment of osteonecrosis is limited; but, some interventions are important. This is especially true in the early stages (Ficat Stage 0 or Stage 1) of disease progression. Protected weight bearing is the first and for most non-surgical intervention. Protected weight bearing is the use of stability assistance devices such as a walker. The damaged and fragile bone surface of the hip should be protected from the pressures found in regular articulation and ambulation. This gives the bone an opportunity to repair itself.
Bone remodeling is the replacement of existing bone, mostly primary bone, by more precisely ordered lamellar or secondary bone. As resorption progresses, long cylindrical cavities housing blood vessels and embryonic bone marrow develop. This remodeling process continues throughout life, allowing an organism to conduct its usual skeletal and metabolic functions and allowing repair, or adjustment to new conditions (Zipfel, Guiot, & Fessler, 2003).
Both physical therapy and a form of electrical stimulation for the promotion of bone healing have been found to be helpful adjuncts to the wait-and-see approach. Atmospheric pressure has been used to promote oxygenation of the necrotic area in the effort to aid healing. In one study, this hyperbaric form of conservative approach proved quite successful with Ficat Stage 1 injuries, leading to a 94% success rate of all hips scored as less then Stage 2 on the Ficat scale. Of the hips rated Ficat 2 or greater, 96% needed surgical interventions. This demonstrates the importance of accurate staging of osteonecrosis to determine a treatment path (Montanari & Bronzini, 2003). No matter what supportive interventions are added to conservative treatment, close observation and the use of adequate pain control measures are needed for successful healing to be achieved.
There is a risk to using the conservative approach. Most studies indicate that the risk for disease progression is greater with nonsurgical treament than with surgical intervention (Levine, Rajadhyaksha, & Mont, 2004). It is especially important to weigh out the possibility that the osteonecrotic process could get worse, versus the hope that conservative measures will bring healing.
Unfortunately, the type and severity of damage present in osteonecrosis of the hip usually leads to little recourse except surgical intervention. Preoperative staging, especially when there is a collapse of the femoral head and/or acetabular involvement, determines which of the numerous surgical procedures are best.
For Ficat Stage 2a or earlier stages the best choices are core decompression or cancellous or cortical bone grafting. Trapdoor procedures with allografts are indicated for Ficat Stage 2b or early Stage 3 lesions (Levine, Rajadhyaksha, & Mont, 2004). Trapdoor procedures are an open excision of the necrotic bone by elevation of the cartilage. One approach for Stage 3 disease is an Osteotomy. A more aggressive Arthrodesis and Arthroplasty procedure is also a choice for Ficat Stage 3 or Stage 4. Arthrodesis and arthroplasty are occasionally seen for Stage 1 and Stage 2 (Levine, Rajadhyaksha, & Mont, 2004).
Core decompression is used primarily to stimulate the process of revascularization while decreasing pressure within the femoral head. This is one of the lesser of the invasive procedures used for avascular necrosis, and is sometimes used as a diagnostic test in order to see just what is going on inside the core of the hip. In this procedure, a lateral incision is made just above the trochanteric ridge and, using image intensification, an 8-10 millimeter core of bone is removed from the femoral lesion. The removal of this section of necrotic lesion serves to take pressure from the area, allowing white blood cells and other blood components to make their way into the dead tissue and begin the process of repair. Core decompression has few complications serves to greatly improve the speed of recovery (Mont, Ragland, & Garcia, 2004).
Cancellous or cortical bone grafting provides healthy bone material to the area. Many clinicians are adamant that simple decompression just will not do. While accessible, they advocate the placement of new bone to further aid the healing process. When discussing bone grafting, it is important to be specific as there are several techniques in use.
Types of Graphs
Bone grafts that are transplanted directly from one area of an individual’s skeleton to another are called autogenous bone grafts, or bone autografts. In most cases, these are the preferred bone grafts to use. The graft bone is harvested, or taken, from the bones of the hip, the ribs or the leg most commonly.
Autograft bone is one of the safest to use due to the low risk of disease transmission. It also offers a better chance of acceptance and effectiveness in the transplant site, since it contains the greatest amount of the patient’s own bone growing cells and proteins. Autograft bone provides a strong framework for the new bone to grow into.
The downside of autograft bone is the fact that it adds another surgical site to a procedure and therefore another location to feel postoperative pain and discomfort (Bone Graft Alternatives, 2005).
Bone that comes from a donor is called allograft bone. Allograft bone usually comes from bone banks that harvest the bone from cadavers. The types of allograft bone used for surgery include fresh frozen and lyophilized (freeze-dried). The bone is cleaned and disinfected to reduce the possibility of disease transmission from donor to recipient. Allograft bone provides a framework for the new bone to grow on and into.
Unlike autograft bone, allograft bone does not always have the same strength properties or the cells and proteins that can influence the growth of new bone (Bone Graft Alternatives, 2005).
The techniques involved with osteotomy focuses on rotating a specific area of the femoral head away from weight bearing surfaces. Bone of either the acetabulum or the femur is removed to change the areas of pressure within the hip joint. During an osteotomy, flexion of the hip is usually performed to rotate the head of the femur, exposing the damaged bone surface for grafting and repair. Plate and screws are used to hold the new material in its proper position. Bone may be removed from either the acetabulum (hip socket), or the femoral head in order to change the fit or existing pressure points present on the hip. This puts new cartilage in contact with new bone surface and allows the point of injury to heal without the weight of the body on it. Unfortunately, osteotomy is a procedure for the young, under 30. Older patients fail to receive any lasting benefit from this procedure statistically, and usually progress to the point of requiring total hip surgery (Alternative Hip Surgeries, 2005).
AGE at Osteotomy
% Converted to total hip within 10 years
Mean 30 years
Age > 55 years
(Alternative Hip Surgeries, 2005)
In osteonecrosis, it often comes down to a decision for replacement of the damaged tissue of the hip. The artificial components of the hip come in two basic types; the acetabular component (or hip socket portion) is designed to replace the natural acetabulum, while the femoral component (or hip stem portion) will replace the pivoting femoral head. Diseased bone may be replaced with a wide variety of materials, including other pieces of bone, shaped metal, polyethylene, or even ceramic held in place either with or without forms of cement.
A completely artificial replacement of the damaged joint, known as a joint prosthesis, is classified as a Total Hip Arthroplasty or simply Total Hip. This means that the articular surfaces of the acetabulum and the femur are replaced.
Total Hip Arthroplasty Frequency
In the US: More than 120,000 total hip arthroplasties are performed annually
When only the femoral head is replaced and no alteration is made to the natural acetabulum, the procedure and resulting prosthesis is referred to as a half, or Hemiarthroplasty.
Total hip arthroplasty can be broken down into the following sequential procedures.
Femoral Head Removal
Care following surgical procedures to the hip differs according to the type of procedure. Often, even the most extensive procedures warrant only a few days as a hospital inpatient. The length of stay after a total hip is typically 3 to 5 days after hip surgery (Leopold, 2003).
Physical Therapy is a part of virtually every hip procedure, and often begins before the actual surgical treatment occurs in order to prepare and train the person undergoing surgery in just what will be expected of them afterwards. Physical therapy techniques differ with procedures, and with individual patient tolerances and abilities. They are an integral part of the pre and post surgical recovery process.
With core decompression, patients are asked to ambulate in a non-weight bearing manner for between six to twelve weeks. They are then advised to resume their normal activities as tolerated.
As bone grafting often accompanies core decompression procedures, consideration is often included in the basic expectations for aftercare. Depending on the amount and nature of grafts used, the original non-weight bearing ambulation remains the same: however, resumption of normal activities occurs at a slower pace, and in a progressive manner. Full weight bearing and activities should be resumed within six months of the procedure.
Trapdoor procedures to remove and replace necrotic bone are followed by initial non-weight bearing, twenty percent weight bearing within the first six weeks, fifty percent weight bearing within ten weeks, and then on to full weight bearing as that individual tolerates.
Patients who have more extensive hip procedures get up and around after surgery faster because more diseased bone is replaced. After Osteotomy, protected weight bearing can be initiated soon after surgery and continues for the first six weeks of recovery. After that interval, as that person is able, full independent ambulation can be gained. With arthroplasty, including Total Hip Arthroplasty, weight bearing can resume immediately after surgery, taking into account surgeon preferences and that person’s individual considerations.
All invasive procedures carry risk. Looking at Total Hip Arthroplasty for example, as the most invasive of the treatments for osteonecrosis, the possibilities include infection, blood clots, bleeding, anesthesia risks, and medical risks not directly due to the invasive procedure. Certain hip-specific risks, like infection at the surgical site, are typically less than 1.5 percent for total hip replacement. The complication of dislocation, where the femoral head comes out of joint, is reported to be less than 1 percent. Overall, the frequency of major complications following total hip replacement surgeries is regarded as low (Leopold, 2003).
Later risks associated with total hip surgery include the possibility that the prosthetic device may loosen from the bone and that late infections or dislocations may occur. However, numerous studies have shown that a technically well-performed total hip replacement is more than 90 percent likely to be in service and functioning well more than 10 years after the surgery, and some sources report full function in as much as 80 percent 20 years after surgery (Leopold, 2003), (Total Hip Replacement, 2003).
Osteonecrosis, bone death, of the hip is a painful crippling disease. Once the blood flow to the bone ceases, the living tissue that composes the bone dies. Often, the injury is not noticed until later, when the living tissue around the necrotic area attempts to repair the damage. Sudden pain in groin or hip signals the bone and cartilage destruction caused by microfractures and arthritic changes. Once pain brings attention, diagnostic staging can help map out a plan of treatment specific to the amount of bone injury present.
Nonsurgical treatment can often be used with good success on Ficat Stage 0 or Stage 1 areas of hip avascular necrosis. On higher stages, more invasive procedures such as core decompression and osteotomy show better results. Hemiarthroplasty and Total Hip Arthroplasty are options wherein the bone and cartilage components of the hip socket are replaced with artificial materials. Hip replacement allows renewal of movement in the largest joint of the body and comes as a true blessing to many who otherwise find their lives limited by pain and immobility. Ninety percent or more of patients having hip replacement surgery report having significant pain relief and improved range of motion. Truly, this is a blessing to those significantly affected by the crippling effects of osteonecrosis of the hip.
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