Osteonecrosis of the Hip

Key Points

Characteristics common among patients with avascular necrosis (AVN) of the hip:
- Present at a younger age than patients with osteoarthritis (OA) of the hip
- Systemic disease or condition associated with the osteonecrosis
- Abnormal bone quality of the hip and femur
Total hip arthroplasty (THA) poses a unique set of challenges in patients with AVN:
- Poor bone quality of the hip and femur
- Previous surgical procedures involving the hip and femur
The results of THA for patients with AVN have improved greatly over the past several decades. However, they still tend to have slightly worse outcomes and increased complications compared with patients undergoing THA for OA.

Total hip arthroplasty (THA) for osteonecrosis of the hip can greatly improve the quality of life for patients afflicted with this disease. However, there are several unique challenges when comparing total hip replacement for osteonecrosis with THA for osteoarthritis (OA). These include abnormal bone quality associated with osteonecrosis, the young age of the patient that typically develops osteonecrosis, and the underlying diseases associated with osteonecrosis. The acetabular and femoral bone in patients with osteonecrosis is often of poor quality; the surgeon must be careful in reaming the acetabulum and during broaching and placement of the femoral component. Surgical challenges may also be present because of previous hip surgery performed to help prevent femoral head collapse. Surgery to preserve the femoral head via core decompression with or without adjunct bone graft or tantalum inserts is commonplace and can be difficult to address during THA. An osteotomy to rotate the osteonecrotic segment away from the weight-bearing area of the femoral head may have been performed as well, altering the proximal femoral anatomy, which can also be challenging during THA. The purpose of this chapter is to provide essential information to assist in the management of patients with osteonecrosis of the femoral head. This includes the defining features and teaching points relevant to THA for patients with osteonecrosis.

The age of patients with osteonecrosis of the hip is one of the challenging factors that affects the results of total hip replacement for this patient population. In general, patients with osteonecrosis are younger than those undergoing total hip replacement for OA. Younger patients have historically had poorer results following THA compared with an older population. By definition, this group is more active than their elderly counterparts, which may account for some of the difference in results.

There are several systemic diseases associated with osteonecrosis that contribute to the poorer results of THA in this patient population. Steroids, alcoholism, connective tissue disease, sickle cell disease, end-stage renal failure, human immunodeficiency virus (HIV), autoimmune diseases, and trauma all increase risk of osteonecrosis and all possess characteristics that may compromise early and long-term results of THA. Furthermore, the complications associated with THA in these patients are unique and occur more frequently than complications of THA in patients with OA.

The quality of acetabular and proximal femoral bone in patients with osteonecrosis is different than those with normal bone. Arlot and associates evaluated bone histomorphometry in 77 patients with osteonecrosis of the femoral head. In this study, all patients were ambulatory, and none were confined to a bed or wheelchair. Factors associated with osteonecrosis in these patients included steroids (15 patients) and alcoholism (33 patients) and were unknown in the remaining patients (29). Bone biopsy and histomorphometric analysis were performed on horizontal transiliac crest bone. Trabecular bone volume, trabecular osteoid volume, trabecular osteoid surface, thickness index of osteoid seams, total resorption surfaces, calcification rate, tetracycline-labeled surfaces, and bone formation rates at the basic multicellular unit level and at the tissue level were determined. Results suggested a marked decrease in osteoblastic appositional rate and in bone formation rate at cell and tissue levels.

Several studies have also investigated the anatomic extent of the disease. Calder et al. examined 16 patients with advanced osteonecrosis of the hip (Ficat III and IV) and compared them with 19 patients with OA who had undergone THA. Histologic specimens from the hip and the proximal femur were examined. They identified that changes related to osteonecrosis extended down to 4 cm below the lesser trochanter. Overall, a statistically significant difference in extent of disease was noted between the 2 groups ( P < .001). A more recent prospective study by Tingart et al. compared 20 patients with osteonecrosis of the femoral head (ONFH) with 20 patients with OA, and examined the histologic characteristics of samples of cancellous bone taken from the greater and lesser trochanters as well as the medullary canal 4 cm below the lesser trochanter during THA. They found that the gene expression of BMP-2 was significantly higher in the femoral metaphysis of patients with ONFH compared with those with OA. They also found that the greater trochanter region of patients with ONFH demonstrated a significantly increased number of osteoblasts/osteocytes compared with patients with OA. Another interesting finding was the altered microarchitecture of the trabecular bone in the metaphysis of patients with ONFH compared to those with OA. These results demonstrated that the disease process includes abnormal bone turnover, remodeling, and architecture that is not limited to the femoral head but also extends down into the metaphysis of those patients with ONFH. Although these two studies from Tingart et al. and Calder contradict each other in some of their results, they both emphasize the fact that the bone quality in patients with ONFH is significantly different from those with OA. These reports may explain in part why patients with osteonecrosis are more likely to develop early aseptic loosening of the femoral prosthesis.

Surgery to prevent the collapse of the femoral head in osteonecrosis is not always successful, often leading to THA. Alterations to the surgical site caused by previous surgery may pose a substantial challenge to the surgeon at the time of joint replacement and may contribute to the poorer results of total hip replacement in this population. Core decompression with placement of a fibular strut graft, tantalum construct, or dowel pose unique challenges. Intertrochanteric osteotomy may result in abnormal anatomy. Finally, because of abnormalities related to age, bone quality, and previous surgery, thorough preoperative planning, meticulous surgery, and selection of the correct implant are imperative for achieving a good result in this patient population.

Indications and Contraindications

Disabling pain and loss of function are two of the main indications for THA for osteonecrosis and are present in this population of patients at an average age that is younger than patients with OA. Heavy demand over a longer period of time requires that the prosthesis be durable, thus minimizing the risk of early revision. Modest expectations and a lower level of activity may increase implant durability and longevity. Unfortunately, it is unlikely that this population will become less active after surgery because one of their main goals is to obtain relief from pain to achieve a higher level of activity.

There are several relative and absolute contraindications to hip replacement for patients with osteonecrosis of the hip. It is important to keep in mind that many of these patients at baseline are at increased risk for infection. The presence of active infection must be ruled out before elective hip replacement, as it is an absolute contraindication to surgery. One example of this is the patient on dialysis, who is especially prone to infection. It is incumbent on the treating surgeon to make certain that infection is not present before elective hip replacement is performed. The same is true for patients on steroids and for those who are immunocompromised because of medications used to treat their underlying disease process. Retained hardware after osteotomy or fracture fixation also increases the risk for infection. Low-grade or active infection may be present in these patients. If an infection is suspected, staged surgical removal of the retained hardware, debridement, antibiotics, and confirmed eradication of the infection are necessary before total hip replacement is performed.

Osteonecrosis of the hip is often seen in those patients with end-stage renal disease. In this population of patients, peripheral vascular disease is not uncommon. Evaluation of peripheral arterial blood flow should be performed preoperatively to assess the presence of peripheral vascular disease. This may be considered a relative contraindication to surgery and could necessitate an intervention by the vascular surgeon before THA. In addition to systemic and diffuse disease processes that require preoperative evaluation, local problems can add to the challenge of surgical reconstruction and may be a contraindication to hip replacement.

Preoperative Planning

Preoperative planning for THA in patients with osteonecrosis focuses on optimizing their underlying medical conditions and on the orthopedic evaluation. In addition, it is important to perform appropriate preoperative templating for the hip surgery. This process of preoperative planning and templating helps identify technical factors that may require special attention. Dong et al. described a novel hip templating technique that incorporated adjustments for conditions common to osteonecrosis—including external rotation of the femur, osteoporosis of the femur, osteosclerosis of the acetabulum—and type of stem used. Adjustments in femoral component size were made based on measurements including thickness of the lesser trochanter and the canal bone ratio 10 cm below the lesser trochanter. Adjustments to the acetabular component size were made based on the amount of sclerosis and size of osteophytes present. Before the adjustments, the accuracy was 69% and 70% for the stem and cup, respectively. After adjustments were made, the accuracy improved to 83% for the stem and 79% for the cup. Accurate templating of the hip improves the surgeon's ability to restore limb length and offset and select the appropriate implants for the patient's anatomy. This often translates to improved outcomes and increased patient satisfaction.

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