Biosynthetic bone grafting

The regeneration of bone remains an elusive yet important goal in the field of orthopaedic surgery. Despite its limitations, autogenous cancellous bone grafting continues to the most effective means by which bone healing is enhanced clinically. Biosynthetic bone grafts currently are being developed as an alternative to autogenous bone grafting. These grafts generally contain one or more of three critical components: (1) osteoprogenitor cells; (2) an osteoconductive matrix; and (3) osteoinductive growth factors. The importance of each of these components based on preclinical data supports their use in biosynthetic bone grafts. The use of growth factors such as bone morphogenetic proteins, transforming growth factor, platelet derived growth factor, and fibroblastic growth factor is reviewed in preclinical long bone defect and spinal fusion models. The use of bone marrow in preclinical and clinical settings is presented with specific emphasis given to the use of bone marrow as a source of osteoprogenitor cells and how the use of these cells can be enhanced with the use of bone morphogenetic protein-2. These data support the concept that although products that contain only one of the three key components of a bone graft may regenerate bone successfully, composites of the three key components will be more successful clinically.

Bone marrow and recombinant human bone morphogenetic protein-2 in osseous repair

Bone marrow stem cells and recombinant human bone morphogenetic protein-2 each has the capacity to repair osseous defects. Recombinant human bone morphogenetic proteins require the presence of progenitor cells to function. It is hypothesized that a composite graft of recombinant human bone morphogenetic protein-2 and marrow would be synergistic and could result in superior grafting to autogenous bone graft. Syngeneic Lewis rats with a 5-mm critical sized femoral defect were grafted with recombinant human bone morphogenetic protein-2 and marrow, recombinant human bone morphogenetic protein-2, marrow, syngeneic cancellous bone graft, or carrier alone (control). Serial radiographs (3, 6, 9, 12 weeks) and torque testing (12 weeks) were performed. Bone formation and union were determined. The recombinant human bone morphogenetic protein-2 and marrow composite grafts achieved 100% union at 6 weeks. Recombinant human bone morphogenetic protein alone achieved 80% union by week 12. Both groups yielded a higher union rate and superior mechanical properties than did either syngeneic bone graft (38%) or marrow (47%) alone. The superior performance of recombinant human bone morphogenetic protein-2 combined with bone marrow in comparison with each component alone strongly supports a biologic synergism. This experimentation shows the clinical importance of establishing operative site proximity for the osteoinductive factors and responding progenitor cells.

Intravertebral body reconstruction with an injectable in situ-setting carbonated apatite: biomechanical evaluation of a minimally invasive technique

The ability to mechanically reinforce an osteoporotic vertebral body could impede spinal compression fracture and the associated pain and complications. Previous studies have shown that reinforcement of fractured vertebrae with conventional acrylic cement can relieve symptoms and avoid further collapse. In this study, we explored the use of a carbonated apatite cement combined with a minimally invasive injection technique to improve the compressive mechanical properties of cadaveric vertebral bodies. After establishing the biomechanical characteristics of cement formulations intended to have appropriate viscosities, we evaluated the infiltration of the cements into thoracic vertebral bodies using a combined suction-injection technique. The energy-absorption capabilities of the reinforced vertebral bodies were then measured during axial compressive tests and compared with those of nonreinforced vertebrae. The ultimate compressive strength of the cement formulations averaged from 11.6 to 17.7 MPa, depending on curing conditions. The suction-injection technique allowed from one-half to two-thirds of each vertebral body to be infiltrated with cement. Energy absorption was significantly higher (p < 0.05) between 25 and 70% collapse of the vertebral body in the specimens that received the apatite injection as compared with the controls. These results suggest that osteoporotic vertebral-body augmentation with the injection of apatite cement could prevent further collapse after initial failure has occurred. The osteoconductive nature of the cement and its ability to be remodeled by bone, together with its compressive strength, which is higher than that of cancellous bone, could provide better clinical results than those of current treatments with acrylic cement.

Osteoporosis: current modes of prevention and treatment

The most common metabolic bone disorder is osteoporosis, which affects 25 million Americans, of whom 80% are women. Bone loss in women occurs most commonly after menopause, when the rate of loss may be as high as 2% per year. Bone mass can be determined with dual-energy x-ray absorptiometry. The rate of active loss can be assayed by the detection of bone collagen breakdown products (e.g., N-telopeptide, pyridinoline) in the urine. Although it has been suggested that white women are most commonly affected, Hispanic and Asian women are also affected. Strategies for the prevention and treatment of osteoporosis are directed at maximizing peak bone mass by optimizing physiologic intake of calcium, vitamin D therapy, exercise, and maintenance of normal menstrual cycles from youth through adulthood. Coupled with drug therapy should be a comprehensive approach to exercise and fall prevention. Stretching, strengthening, impact, and balance exercises are effective. Of the balance exercises, tai chi chuan has proved to be the most successful in decreasing falls. Prevention of bone loss is obviously preferable to any remedial measures, but new therapeutic strategies provide a means of restoring deficient bone.

Current understanding of osteoconduction in bone regeneration

Bone tissue is osteoconductive. In particular, cancellous bone with its porous and highly interconnected trabecular architecture allows easy ingrowth of surrounding tissues. When placed in an osseous environment, living tissue for the host bed migrates into the cancellous structure, which results in new bone formation and incorporation of that structure. This is the process of osteoconduction. The mineral and collagenous components of bone are osteoconductive. Osteoconduction also is observed in fabricated materials that have porosity similar to that of bone structure. Corallin ceramics, hydroxyapatite beads, and combinations of hydroxyapatite and collagen all have osteoconductive properties, and porous metals and biodegradable polymers. Osteoconduction appears to be optimized in devices that mimic not only bone structure, but also bone chemistry. The incorporation of calcium salts and collagen by osteoconductive matrices leads to more complete ingrowth with new bone formation.

Prosthetic knee replacement after resection of a malignant tumor of the distal part of the femur. Medium to long-term results

We evaluated the medium to long-term results of treatment with a custom prosthetic knee replacement after wide resection of a primary malignant tumor of the distal part of the femur in forty consecutive patients. The duration of follow-up ranged from five to seventeen years (median, eight years). At the time of the latest follow-up, thirty-five (88 per cent) of the forty patients were free of disease and five (13 per cent) were alive with metastatic disease. No local recurrence was observed. Twenty early complications occurred in eighteen patients (45 per cent). Aseptic loosening of the femoral component, which necessitated a revision in eleven patients at an average of fifty-one months, was the most frequent mode of failure. The rate of prosthetic survival, as estimated with use of the Kaplan-Meier method, was 85, 67, and 48 per cent at three, five, and ten years. Univariate analysis demonstrated that the rate of prosthetic survival was significantly worse for male patients, for those in whom at least 40 per cent of the femur had been resected, for those who had had total resection of the quadriceps muscles or subtotal resection (preservation of only the rectus femoris muscle), and for those in whom a straight femoral stem had been used (p < 0.05 for all comparisons). Multivariate analysis showed that the independent adverse prognostic factors for prosthetic survival were male gender, resection of at least 40 per cent of the femur, and fixation of the femoral stem with cement. The rate of limb salvage was calculated, with use of the Kaplan-Meier method, to be 93 per cent at three years and 90 per cent at five and ten years. At the latest follow-up examination, the functional scores according to the classification system of the Musculoskeletal Tumor Society ranged from 14 to 29 points; the mean was 24 points, which represents function that is 80 per cent that of normal. The mean scores in the categories of walking supports and gait were better for the patients in whom the quadriceps muscles had been preserved than for those who had had total or subtotal resection of those muscles. Although advances in imaging and local therapy narrow the indications for an extra-articular resection of a tumor, the implant that was used in the present study continues to be used in approximately 15 per cent of patients who have a fracture or an intra-articular extension of the tumor that necessitates extensive extra-articular resection.

Traumatic lumbar pseudomeningocele occurring with spina bifida occulta

Pseudomeningocele in the lumbar spine due to spinal fractures or surgical procedures are well-recognized complications. We treated a 24-year-old man who fell from a horse, landing on his buttocks, and developed headaches, back pain, and a large lumbar subcutaneous fluid collection. Plain radiographs and magnetic resonance (MR) imaging revealed a midline defect in the sacral lamina and a large fluid collection in the subcutaneous space consistent with cerebrospinal fluid (CSF). He was treated conservatively, his symptoms resolved, and follow-up MR imaging showed resolution of the CSF accumulation. To our knowledge, there have been no cases of traumatic pseudomeningocele related to spina bifida occulta reported in the literature. The authors postulate that congenital defects in the neural arch contribute to the occurrence of this entity, and nonsurgical treatment should be the initial course.

Future directions. Augmentation of osteoporotic vertebral bodies

Because current medical and surgical treatments of vertebral body fractures are less than adequate, there is a need for interventions that decrease the likelihood of occurrence of these fractures and improve the treatment options once they have occurred. One such broad category of intervention involves the fortification or augmentation of the vertebral bodies. In addition to prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture, augmentation of vertebral bodies that have already fractured may prove to be useful by reducing pain, improving function, and preventing further collapse and deformity. Vertebral body augmentation can also be used as an adjunct to fixation of internal hardware--for example, pedicle screws-in osteoporotic spines. A number of products are now available or are in clinical trials. The most promising products are injectable materials-polymethylmethacrylate or mineral bone cement. The early clinical results using polymethylmethacrylate in percutaneous vertebroplasty for fractured vertebral bodies and the results in vitro using an injectable mineral cement for vertebral body fortification are encouraging. Although the principle of vertebral body augmentation remains encouraging, data to support the widespread use of these techniques remain sparse, and the indications for their use should be more clearly defined.

Osteoporosis. Medical prevention and treatment

Osteoporosis is a bone disorder characterized by deficient bone mass and fragility fractures of the hip, wrist, and spine. The therapeutic strategies for treating osteoporosis are designed to maximize peak bone mass through proper nutrition, appropriate intake of calcium and vitamin D, maintenance of physiologic menstrual cycles, and a program of weight bearing and strengthening exercises. For the conditions of high bone turnover--osteoporosis in which osteoclastic resorption is increased--efficacious treatment options include hormone replacement therapy, calcitonin, and bisphosphonates. Osteoporosis with low bone turnover results from deficient osteoblastic bone formation and responds to the experimental drug programs of fluoride, parathyroid hormone, and parathyroid hormone related peptide analogues. Determination of bone density defines the patient's current condition, measurement of the level of N-telopeptides (collagen breakdown products) predicts the patient's future regarding osteoporotic fractures, and the presence of risk factors for hip fracture establish the therapeutic window for treatment.

Use of bone morphogenetic protein 2 on ectopic porous coated implants in the rat

The ability of recombinant human bone morphogenetic protein 2 to remain osteoinductive and stimulate appositional bone formation on a porous coated implant was tested in a rat quadriceps muscle pouch. Implants with or without hydroxyapatite were used to compare the effects on bone formation of two different does (23 micrograms or 46 micrograms) of recombinant human bone morphogenetic protein 2 against controls as evidenced by contact radiography, histologic examination, and backscatter scanning electron microscopic analysis. Cylindrical plasma sprayed porous titanium implants were placed bilaterally within a muscle pouch surgically created in 48 Lewis rats. Implants treated with recombinant human bone morphogenetic protein 2 formed significantly more bone than did control implants independent of the dose or presence of hydroxyapatite. In all implants with bone formation, osteoinduction via endochondral ossification began within 7 days. By 21 days, cartilage largely was replaced by bone and marrow. The results of this ectopic, nonweightbearing in vivo assay suggest that recombinant human bone morphogenetic protein 2 remains biologically active after application to a titanium implant and may be used to enhance appositional bone formation by direct application to the implant surface.

Estrogen affects the cellular metabolism of the anterior cruciate ligament. A potential explanation for female athletic injury

Investigations from this laboratory have established the presence of estrogen receptors in the human anterior cruciate ligament. This study further investigates the effects of 17 beta-estradiol on the cellular proliferation and collagen synthesis of fibroblasts derived from the rabbit anterior cruciate ligament. Fibroblast proliferation and collagen synthesis in response to near log concentrations of 17 beta-estradiol (at 0.0029, 0.025, 0.25, 2.5, and 25 ng/ml) were assessed by measuring [3H]thymidine and [14C]hydroxyproline incorporation, respectively. Collagen synthesis was significantly reduced with increasing local estradiol concentration (P < 0.001). Declining collagen synthesis was first noted at a 17 beta-estradiol concentration of 0.025 ng/ml. Within normal physiologic levels of estrogen (0.025 to 0.25 ng/ml), collagen synthesis was reduced by more than 40% of control, and at pharmacologic levels of 2.5 and 25 ng/ml, by more than 50% of control. A significant reduction of fibroblast proliferation was also observed with increasing estradiol concentrations (P = 0.023). Clinically, alterations in anterior cruciate ligament cellular metabolism caused by estrogen fluctuations may change the composition of the ligament, rendering it more susceptible to injury.

Fibroblast growth factor and epidermal growth factor receptors in ligament healing

Although recent in vivo studies indicate that basic fibroblast growth factor hastens the healing and strength of the medical collateral ligament after injury, in vitro studies with epidermal growth factor and basic fibroblast growth factor have shown increased fibroblast proliferation with the exogenous administration of these growth factors. Using an established spontaneously healing rabbit injury model, the surgical transection of the medial collateral ligament was undertaken in 12 anesthetized male adult rabbits. Immunohistochemical localization using monoclonal antibodies to the basic fibroblast growth factor receptor and epidermal growth factor receptor were used to identify the distribution and relative concentrations of the individual receptors at 3, 7, 14, and 28 days after surgery. Realizing that the trophic effects of basic fibroblast growth factor and epidermal growth factor are determined exclusively by their individual receptors, this study confirms the hypothesis that basic fibroblast growth factor and epidermal growth factor receptor proteins are present and increase during the early stages of medial collateral ligament healing. The understanding of this rabbit ligament injury model has far reaching implications to ligament healing seen in humans. By elucidating the spatial and temporal regulation of the basic fibroblast growth factor and epidermal growth factor receptor proteins, exogenous growth factor therapy, once approved for human use, potentially can be synchronized with maximal protein receptor levels.

Increased sodium appetite stimulates c-fos expression in the organum vasculosum of the lamina terminalis

The relation between c-fos expression in the forebrain of Lister hooded rats and water and NaCl intakes was examined in response to systemic injection of angiotensin II, desoxycorticosterone, angiotensin II and desoxycorticosterone together, frusemide or low sodium diet, all treatments that induce a sodium appetite. Angiotensin II (1 mg/kg subcutaneously) caused significant increases in the 1-h intakes of water and 1.8% NaCl compared to controls, the effect on water intake being the greater. There was a similar increase in NaCl intake after four days' treatment with desoxycorticosterone (20 mg pellet subcutaneously) but water intake was not increased. The NaCl intake of rats given angiotensin II following desoxycorticosterone treatment was approximately the sum of the intakes after angiotensin II or desoxycorticosterone alone, but the water intake was slightly less than after angiotensin II alone. Frusemide pretreatment (4 mg/kg subcutaneously) caused an NaCl intake similar to that following angiotensin II and desoxycorticosterone but water intake was little affected. Low dietary sodium also increased salt appetite, as expected. These treatments were repeated in rats that were not allowed to drink NaCl, after which the brains were processed for c-fos immunocytochemistry. This showed intense staining of the subfornical organ, median preoptic nucleus, organum vasculosum of the laminal terminalis, paraventricular nucleus and supraoptic nucleus after subcutanous angiotensin II. Animals given angiotensin II following desoxycorticosterone pretreatment showed patterns of c-fos expression that did not differ from those of angiotensin II alone. Treatment with desoxycorticosterone alone produced intense staining in the organum vasculosum of the laminal terminalis and some staining in the median preoptic nucleus. Frusemide gave a similar pattern of staining to desoxycorticosterone, stimulating c-fos expression in the same regions but to a lesser extent. A low salt diet resulted in increased c-fos expression only in the organum vasculosum of the laminal terminalis. Therefore, five different treatments that induced increased sodium appetite evoked distinct patterns of c-fos expression in the anteroventral region of the third ventricle of the rat forebrain. Since the common feature was induction of c-fos in the organum vasculosum of the laminal terminalis, these results suggest a key role for this structure in the development of increased sodium appetite.

Stride analysis after proximal tibial replacement

Ten patients who had undergone primary intraarticular proximal tibial replacement between April 1985 and December 1994, and had a minimum of 2 years of followup, were available for stride analysis. Mean age, time since intraarticular proximal tibial replacement, height, and weight were 23.8 years, 6.5 years, 167 cm, and 63 kg, respectively. A volunteer control group of five male patients who had undergone above knee amputation was obtained from the local community. The mean age, time since above knee amputation, height, and weight were 43.6 years, 24.1 years, 165 cm, and 70 kg, respectively. Stride analysis was performed over the central 6-m portion of a 10-m walkway at a self selected, comfortable pace. Gait velocity, stride length, cadence, and stance time symmetry were measured. Velocity after intraarticular proximal tibial replacement versus above knee amputation was 79.2 +/- 7.6 m per minute versus 71.4 +/- 5.4 m per minute. Cadence after intraarticular proximal tibial replacement versus above knee amputation was 112.4 +/- 10.6 steps per minute versus 110.1 +/- 2.4 steps per minute. There were no significant differences between stride length (1.41 +/- 0.13 m versus 1.43 +/- 0.12 m) and stance time symmetry (0.90 +/- 0.07 versus 0.87 +/- 0.11) for intraarticular proximal tibial replacement versus above knee amputation. The results suggest that endoprosthetic reconstruction resulted in a gait comparable with that after above knee amputation with an external prosthesis.

Morphology and matrix composition during early tendon to bone healing

This study outlines the early morphologic phenomenon of tendon to bone healing in the rabbit model. Twelve skeletally mature, male New Zealand White rabbits received transplantation of the hallucis longus tendon into a 2-mm calcaneal bone tunnel. The morphologic characteristics of the healing tendon to bone interface were evaluated at 1, 2, 4, and 6 weeks after surgery by the use of conventional histology and immunohistochemical localization of collagen Types I, II, and III. Histologic analysis illustrated progressive maturation and reorganization of the tendon to bone interface with subsequent development of tissue collagen fiber continuity between the tendon and bone. Initially, diffuse immunolocalization of all three collagen types was observed within the scar tissue filling the space between the tendon and bone. During a 6-week period, reorganization of the scar tissue into an interface occurred, similar to an indirect insertion. Although a definitive fibrocartilage region did not form, Type II collagen was localized at the remodeling insertion site throughout the first 6 weeks of repair. In addition, Type III collagen fibers, resembling Sharpey's fibers, were noted to span this interface. The characterization of the insertion between tendon and bone is important to the understanding of healing in commonly used orthopaedic grafting procedures, such as anterior cruciate ligament reconstructions.

Dizocilpine maleate, an N-methyl-D-aspartate antagonist, inhibits dipsogenic responses and C-Fos expression induced by intracerebral infusion of angiotensin II

The interactions between dizocipline, an N-methyl-D-aspartate open channel antagonist, and the induction of water drinking and c-fos expression by intracerebroventricular (i.c.v.) infusion of angiotensin II have been studied. Pretreating male rats with i.c.v. dizocilpine maleate (100 or 300 nmol) or tenocyclidine (150 nmol), both non-competitive N-methyl-D-aspartate antagonists, inhibited the subsequent dipsogenic response to i.c.v. angiotensin II (125 or 50 pmol, 5-10 min later). Dizocilpine also decreased the angiotensin II-evoked expression of c-fos in the median preoptic nucleus, supraoptic nucleus and the medial (parvicellular) and lateral (magnocellular) parts of the hypothalamic paraventricular nucleus, as well as in the nucleus of the solitary tract and the lateral parabrachial nucleus. Double staining showed that suppression of c-fos expression occurred in N-methyl-D-aspartate R1 receptor containing neurons in the hypothalamus. Pretreating rats with any of three competitive glutamate antagonists (2-amino-5-phosphonopentanoic acid, 60 or 160 nmol; gamma-D-glutamylglyine, 400 nmol; (DL-3/(R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid, 0.1 nmol) or the glycine site antagonist 7-chlorokynurenic acid had no effects on angiotensin II-induced drinking. Neither did pretreating rats with the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid antagonist 6-cyano-7-nitroquinoxaline-2,3-dione [two infusions, 30 min (240 nmol) and 5 min (160 nmol) before angiotensin II]. To eliminate cross-reactivity of dizocilpine with nicotinic receptors, animals were pretreated with nicotinic acetylcholine blocker mecamylamine (250 nmol, i.c.v.), but this had no effect on angiotensin II-dependent drinking or c-fos expression. These results suggest that an N-methyl-D-aspartate-type glutamate receptor is implicated in the dipsogenic and cellular responses to i.c.v. angiotensin II, and point to the existence of a novel set of interactions between excitatory amino acids and this neuropeptide.

Treatment of femoral Ewing's sarcoma

BACKGROUND

The treatment of Ewing's sarcoma consists of chemotherapy for systemic and local disease. However, the role of radiation therapy, and/or surgical resection for definitive local treatment has yet to be determined.

METHODS

A retrospective review of 32 patients (24 males and 8 females) treated for femoral Ewing's sarcoma between 1970 and 1985 was performed. Patients were divided into 3 treatment groups: chemotherapy and radiotherapy (CR) (10); chemotherapy and surgery (CS) (9); and chemotherapy, surgery, and radiotherapy (CSR) (13). Patients in the CR group received a mean of 5320 centigray (cGy) of radiation and patients in the CSR group received a mean of 3590 cGy. Multiagent cyclophosphamide/doxorubicin based chemotherapy was used in all cases. Surgery consisted of wide resection or amputation.

RESULTS

Patients in the CR group had a higher risk of local recurrence than patients in the CS and CSR groups (P=0.02, log rank). The combination of local recurrences and treatment complications necessitated surgery for 7 of 10 CR patients, whereas 1 of 9 and 4 of 13 in the CS and CSR groups required additional surgery. The median survival for the entire group was 39 months. Minimum follow-up for surviving patients was 45 months. Five-year survival consisted of 1 of 10 patients in the CR group, 2 of 9 in the CS group, and 7 of 13 in the CSR group. There were no statistically significant differences among the three survival curves. Tumor location within the femur was a significant prognostic variable. Distal femoral location had a survival advantage compared with proximal and mid-femur locations (P = 0.049, log rank).

CONCLUSIONS

Femoral Ewing's sarcoma remains a disease with a poor prognosis. Radiation alone for local treatment results in a high rate of local recurrence and complications. Our current local treatment strategy for femoral Ewing's sarcoma includes surgery in all and adjuvant radiotherapy in many of the patients.