Bone marrow is an environment rich in its diversity of cell types and niches. Both hematopoietic and osteogenic stromal cells are present and have been studied extensively. Less is known about the function of one of the most abundant cell types in the bone marrow: adipocytes. There are several hypotheses that have been proposed including: passive role as a space filler; active role in the body's general lipid metabolism; role in providing a localized energy reservoir for emergency situations affecting the bone or hematopoiesis; support of differentiation or function of other cell types (such as bone, endothelial, and other stromal cells). There are several human pathologies associated with increases in adipocyte hypertrophy or proliferation including changes associated with aging, osteoporosis, and osteonecrosis. The reasons for these changes are poorly understood. One etiology associated with both osteoporosis and osteonecrosis, corticosteroid therapy, has been shown to increase the lipid content of osteoblasts and adipocytes. With osteonecrosis, several pathogenetic mechanisms involving adipocytes have been proposed: Mechanical - increased size and number cause increased intraosseous pressure and decreased venous outflow Direct precursor cells away from osteoblastogenesis towards adipogenesis Liquid fat causing a hypercoagulable state Osteocyte dysfunction or apoptosis Adipocyte and bone marrow necrosis Release adipokines and other factors that have an effect on the cells within the bone marrow (inhibiting angiogenesis, e.g.) The possibility that adipocytes may actually play an active role in propagating specific pathologic features has only recently been discussed. This is in part due to our increasing understanding that adipocytes have an endocrine role in metabolism. Only recently have scientists tried to identify specific cellular mechanisms that may be involved in the pathogenesis of osteonecrosis. Results from these studies will not only contribute to our understanding of the disease of osteonecrosis (and other diseases such as osteoporosis) but will also help us to appreciate the multiple functionalities of the heretofore unappreciated adipocyte.
Core decompression is a common treatment for early stage osteonecrosis of the femoral head due to the simplicity of the procedure and the positive results of this intervention. A number of different core decompression methods exist: including methods backfilled by a bone graft material and those without filling. Due to the inherent desire that the core decompression defect regenerate healthy bone, reduce pain, and stave off the need for total hip arthroplasty for some period of time, this surgically created defect is an excellent application for the use of a bone graft substitute. Recently, an injectable calcium sulfate (CaSO4)/calcium phosphate (CaPO4) composite graft has become available for use in the treatment of surgically created defects. The synthetic graft is an injectable composite of CaSO4, tricalcium phosphate (TCP) granules, and brushite that hardens Early clinical series have indicated similar results to the canine studies. Reports of early clinical findings have included a 12 patient benign bone tumor series with 4–12 month follow up and a core decompression series of 38 Ficat stage I–III hips with 6–16 month follow up. Preliminary radiological results in the bone tumor series showed peripheral resorption of the injectable CaSO4/CaPO4 composite with new bone formation along the resorbing edge. Clinically, patients in the bone cyst series have not experienced fractures or additional surgery and all patients have displayed full functional recovery. In the core decompression series, 32 of the 38 hips experienced pain relief and within the subset of 30 symptomatic hips, 24 had pain relief. These results, although preliminary, are promising outcomes. Collectively, the pre-clinical and preliminary clinical results indicate that the use of an injectable CaSO4/CaPO4 composite could prove to be of benefit in core decompression of the femoral head. The staged resorption and dense bone formation evidenced in canine studies would be desirable in core decompression techniques where healthy bony ingrowth is the goal. Due to the straightforward compilation and use of this composite, the incorporation of this material as a backfill matrix into the core decompression procedure is technically simple. Although additional studies are certainly merited, these early clinical results are encouraging.
The Johns Hopkins University Department of Orthopaedics at the Good Samaritan Hospital, Baltimore, Maryland USA
Imaging techniques continue to gain in sophistication. Gd-enhanced MRI can be used to assess perfusion of the diseased tissue. Doppler ultrasonography has also been used to estimate blood flow noninvasively. Near Infrared Spectroscopy (NIRS) can be used to measure tissue oxygenation. While there has been recent interest in using biomarkers or genetic markers in the diagnosis and analysis of disease progression, more research is needed to determine the sensitivity and specificity of these techniques with respect to osteonecrosis.
Osteonecrosis (ON) of the femoral head is a condition that afflicts approximately 20 000 new patients per year, at an average age of 38. Twenty-five percent of the patients seen in our institution are under 25. Without treatment, most of these patients can be expected to need a total hip replacement (THR). However preservative procedures have a significant failure rate, and some, significant morbidity. It is desirable to avoid or delay THR, because most of the patients with ON will outlive the prosthesis, at the current state of the art. There are four issues that need to be weighed to arrive at a reasonable algorithm for the preservative treatment of ON; patient risk factors, morbidity of the proposed procedure, size of the lesion, and stage of the lesion. Risk – risk of outliving a THR. Age, sex, weight, general health, associated diseases, and level of activity all influence the longevity of a THR. The greater the risk, the greater the indication for a preservative procedure. Morbidity – There is a big difference between core decompression and a complex osteotomy. The overall risk of the procedure and the impact on THR must be considered. Size – Large lesions do much worse than small lesions at any stage. Stage – Pre-collapse lesions do better than post-collapse lesions. Using the above issues might lead the surgeon to do a THR on a 25-year old with a large post-collapse lesion or a core decompression on a 60-year old with a small symptomatic pre-collapse lesion. All of the issues must be considered to make sense out of a complex clinical situation.
Many of our most important pharmaceuticals have their origins in plants, such as digoxin, penicillin and coumadin. However, many physicians are deeply sceptical about the use of natural remedies. This scepticism is based on the concerns about patient self-diagnosis and treatment as well as the lack of scientific testing of claims. Nonetheless, a new class has emerged called nutraceuticals – nutritional supplements with pharmaceutical properties. Because these substances are relatively unregulated, there is no requirement for rigorous scientific testing prior to marketing. This lack of regulation also poses problems with purity and quality control. Even so, patients are being bombarded with, and responding to, claims of the results of these of herbs, nutraceuticals, and nutritional supplements. Glucosamine and chondroitin sulfate sales alone in the USA are estimated at $600 million. Sales of all neutraceuticals and vitamin supplements in the USA exceeded $12 billion in 1999. Many physicians took offence at the title of the book by Theodaskis et al., The Arthritis Cure, because they know no cure exists. Patients, on the other hand, pushed sales of the book to the best-seller list. Moreover, glucosamine and chondroitin have been widely studied in tissue culture, animal models of arthritis, veterinary clinical trials, and human comparative or placebo controlled trials. No published study has failed to show a positive effect and no trial has shown significant side affects. These nutraceuticals have become our first line of treatment for osteoarthritis.