Aaron Daluiski

The role of growth factors in the repair of bone. Biology and clinical applications.

•: Growth factors (bone morphogenetic protein, transforming growth factor-beta, fibroblast growth factor, platelet-derived growth factor, and insulin-like growth factor) are proteins secreted by cells that act on the appropriate target cell or cells to carry out a specific action. •: Because growth factors are expressed during different phases of fracture-healing, it has been thought that they may serve as potential therapeutic agents to enhance bone repair. •: The selection of an appropriate carrier or delivery system for a particular growth factor is essential in order to induce a specific biologic effect. •: There are a number of potential clinical applications for growth factors in the enhancement of bone repair, including acceleration of fracture-healing, treatment of established nonunions, enhancement of primary spinal fusion or treatment of established pseudarthrosis of the spine, and as one element of a comprehensive tissue-engineering strategy that could include gene therapy to treat large bone-loss problems. Growth factors are proteins that serve as signaling agents for cells. They function as part of a vast cellular communications network that influences such critical functions as cell division, matrix synthesis, and tissue differentiation. The results of experimental studies have established that growth factors play an important role in bone and cartilage formation, fracture-healing, and the repair of other musculoskeletal tissues. Recently, with the advent of recombinant proteins, there has been considerable interest in the use of growth factors as therapeutic agents in the treatment of skeletal injuries. As growth factors become available as therapeutic agents, it is essential that orthopaedic surgeons understand their biological characteristics and clinical potential. The purpose of this review is to define the mechanisms of action, functions, and potential clinical applications of a variety of growth factors that may be used clinically to treat problems associated with the repair of bone. Growth factors are proteins secreted …

Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development

Coordinated production and remodeling of the extracellular matrix is essential during development. It is of particular importance for skeletogenesis, as the ability of cartilage and bone to provide structural support is determined by the composition and organization of the extracellular matrix. Connective tissue growth factor (CTGF, CCN2) is a secreted protein containing several domains that mediate interactions with growth factors, integrins and extracellular matrix components. A role for CTGF in extracellular matrix production is suggested by its ability to mediate collagen deposition during wound healing. CTGF also induces neovascularization in vitro, suggesting a role in angiogenesis in vivo. To test whether CTGF is required for extracellular matrix remodeling and/or angiogenesis during development, we examined the pattern of Ctgf expression and generated Ctgf-deficient mice. Ctgf is expressed in a variety of tissues in midgestation embryos, with highest levels in vascular tissues and maturing chondrocytes. We confirmed that CTGF is a crucial regulator of cartilage extracellular matrix remodeling by generating Ctgf-/- mice. Ctgf deficiency leads to skeletal dysmorphisms as a result of impaired chondrocyte proliferation and extracellular matrix composition within the hypertrophic zone. Decreased expression of specific extracellular matrix components and matrix metalloproteinases suggests that matrix remodeling within the hypertrophic zones in Ctgf mutants is defective. The mutant phenotype also revealed a role for Ctgf in growth plate angiogenesis. Hypertrophic zones of Ctgf mutant growth plates are expanded, and endochondral ossification is impaired. These defects are linked to decreased expression of vascular endothelial growth factor (VEGF) in the hypertrophic zones of Ctgf mutants. These results demonstrate that CTGF is important for cell proliferation and matrix remodeling during chondrogenesis, and is a key regulator coupling extracellular matrix remodeling to angiogenesis at the growth plate.

The Effect of Regional Gene Therapy with Bone Morphogenetic Protein-2-Producing Bone-Marrow Cells on the Repair of Segmental Femoral Defects in Rats*

BACKGROUND Recombinant human bone morphogenetic proteins (rhBMPs) can induce bone formation, but the inability to identify an ideal delivery system limits their clinical application. We used ex vivo adenoviral gene transfer to create BMP-2-producing bone-marrow cells, which allow delivery of the BMP-2 to a specific anatomical site. The autologous BMP-2-producing bone-marrow cells then were used to heal a critical-sized femoral segmental defect in syngeneic rats. METHODS Femoral defects in five groups of rats were filled with 5 x 10(6) BMP-2-producing bone-marrow cells, created through adenoviral gene transfer (twenty-four femora, Group I); twenty micrograms of rhBMP-2 (sixteen femora, Group II); 5 x 10(6) beta-galactosidase-producing rat-bone-marrow cells, created through adenoviral gene transfer of the lacZ gene (twelve femora, Group III); 5 x 10(6) uninfected rat-bone-marrow cells (ten femora, Group IV); or guanidine hydrochloride-extracted demineralized bone matrix only (ten femora, Group V). Guanidine hydrochloride-extracted demineralized bone matrix served as a substrate in all experimental groups. Specimens that were removed two months postoperatively underwent histological and histomorphometric analysis as well as biomechanical testing. RESULTS Twenty-two of the twenty-four defects in Group I (BMP-2-producing bone-marrow cells) and all sixteen defects in Group II (rhBMP-2) had healed radiographically at two months postoperatively compared with only one of the thirty-two defects in the three control groups (beta-galactosidase-producing rat-bone-marrow cells, uninfected rat-bone-marrow cells, and guanidine hydrochloride-extracted demineralized bone matrix alone). Histological analysis of the specimens revealed that defects that had received BMP-2-producing bone-marrow cells (Group I) were filled with coarse trabecular bone at two months postoperatively, whereas in those that had received rhBMP-2 (Group II) the bone was thin and lace-like. Defects that had been treated with bone-marrow cells producing beta-galactosidase (Group III), uninfected bone-marrow cells (Group IV), or guanidine hydrochloride-extracted demineralized bone matrix only (Group V) demonstrated little or no bone formation. Histomorphometric analysis revealed a significantly greater total area of bone formation in the defects treated with the BMP-2-producing bone-marrow cells than in those treated with the rhBMP-2 (p = 0.036). Biomechanical testing demonstrated no significant differences, with the numbers available, between the healed femora that had received BMP-2-producing bone-marrow cells and the untreated (control) femora with respect to ultimate torque to failure or energy to failure. CONCLUSIONS This study demonstrated that BMP-2-producing bone-marrow cells created by means of adenoviral gene transfer produce sufficient protein to heal a segmental femoral defect. We also established the feasibility of ex vivo gene transfer with the use of biologically acute autologous short-term cultures of bone-marrow cells.

Bone morphogenetic protein-3 is a negative regulator of bone density

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β (TGF-β) superfamily. Many BMPs are produced in bone and show osteogenic activity, suggesting that they may be determinants of bone mass. BMP3 was originally purified from bone as osteogenin, which induces osteogenic differentiation. Recombinant BMP3 (rhBMP3) has no biological activity, however, leaving its role in skeletal growth unclear. Here we show that BMP3 is an antagonist of osteogenic BMPs: BMP3 dorsalizes Xenopus laevis embryos, inhibits BMP2-mediated induction of Msx2 and blocks BMP2-mediated differentiation of osteoprogenitor cells into osteoblasts. These effects appear to be mediated through activin receptors. Finally, Bmp3−/− mice have twice as much trabecular bone as wild-type littermates, indicating that BMP3, the most abundant BMP in adult bone, is a negative determinant of bone density.

Complications After Flexor Tendon Repair: A Systematic Review and Meta-Analysis

PURPOSE Although outcomes after flexor tendon repair have reportedly improved with modern treatment, complications are common. The purpose of this study was to determine the incidence of these complications and the potential contributory factors within the published literature. METHODS We performed a systematic review of the available literature to identify publications in which patients with flexor tendon ruptures were surgically treated. We extracted demographics, zone of injury, core suture technique (only modified Kessler or a combination of techniques), use of epitendinous suture, and date of publication (before or after January 1, 2000). We excluded articles if they did not report information on reoperation, rupture, or adhesions. We used unadjusted pooled meta-analysis to report the incidence of complications, and meta-regression to describe the potential contributory factors for each complication while controlling for age, gender, and zone of injury. RESULTS Unadjusted meta-analysis revealed rates of re-operation of 6%, rupture of 4%, and adhesions of 4%. Meta-regression analysis of 29 studies showed that core suture technique or use of an epitendinous suture does not influence rupture. However, the presence of an epitendinous suture decreases re-operation by 84%. Adhesion development is 57% lower when the modified Kessler technique is used. The incidence of complications did not vary with publication date. CONCLUSIONS The published literature supports use of the modified Kessler repair technique with an epitendinous suture to minimize complications. Although complication rates are low, our data suggest that there has been no definitive improvement in reported complications before and after 2000.

Transient Production of Bone Morphogenetic Protein 2 by Allogeneic Transplanted Transduced Cells Induces Bone Formation

The aim of this study was to evaluate the use of transplantation of genetically modified allogeneic cells as a method to induce bone formation. In this study, we infected a murine osteoprogenitor cell line with a retroviral vector containing the human bone morphogenic protein 2 (BMP2) gene. Transduced cells exhibited more alkaline phosphatase activity than cells treated with any of the tested doses of recombinant human BMP2 protein (rhBMP2). The transduced cells were suspended in a collagen solution and injected into the quadriceps muscle in immunocompetent outbred mice. Radiographic and histological examinations demonstrate abundant ectopic bone formation in 85% of the transplanted animals (n = 13). PCR and Southern blot analysis for the puromycin resistance gene revealed that the transplanted cells were detectable for up to 1 week, but not at later time points. None of the animals developed tumors. Our results suggest that allogeneic BMP2-expressing transduced cells may have therapeutic potential for enhancing new bone formation. This model also provides a simple, inexpensive, and sensitive assay for evaluating in vivo the osteoinductive potentials of secreted proteins without the requirement of protein purification or the use of immunodeficient animals.

Indications and Reoperation Rates for Total Elbow Arthroplasty: An Analysis of Trends in New York State

BACKGROUND Total elbow arthroplasty was originally used to treat patients with arthritis. As familiarity with total elbow arthroplasty evolved, the indications were expanded to include other disorders. There continues to be a low number of total elbow arthroplasties performed each year in comparison with hip, knee, and shoulder arthroplasties, and few large studies have examined the indications and associated complications of total elbow arthroplasty. The purposes of this study were to evaluate the changes with time in the indications for total elbow arthroplasty and to examine the complications of this procedure in a large database. METHODS The Statewide Planning and Research Cooperative System database from the New York State Department of Health, a census of all ambulatory and inpatient surgical procedures in the state of New York, was used to identify individuals who underwent primary total elbow arthroplasty during the time period of 1997 to 2006. These total elbow arthroplasties were evaluated for admitting diagnoses, sex and age of patient, readmission and complication data, and time to subsequent elbow surgery. RESULTS From 1997 to 2006, there were 1155 total elbow arthroplasties performed in New York State. In 1997, 43% of the total elbow arthroplasties were associated with trauma and 48%, with inflammatory conditions. In 2006, this changed to 69% and 19%, respectively. Within ninety days after the primary total elbow arthroplasty, 12% of the patients were readmitted to the hospital with approximately one-half (5.6%) admitted for problems related to the total elbow arthroplasty. The overall revision rate was 6.4%. The revision rates for the traumatic, inflammatory arthritis, and osteoarthritis groups were 4.8%, 8.3%, and 14.7%, respectively. Of particular interest, 90.5% of the total elbow arthroplasties were performed by surgeons with no recorded experience in the database, which began collecting these data in 1986. CONCLUSIONS This study provides useful information regarding patients undergoing total elbow arthroplasty in New York State. During the study period, the most common indication for total elbow arthroplasty changed from inflammatory arthritis to trauma. Although the number of total elbow arthroplasties being performed each year has increased, there continues to be a high complication and revision rate.

Publication of abstracts submitted to the annual meeting of the Pediatric Orthopaedic Society of North America.

A computerized MEDLINE search was performed to determine the publication pattern of the abstracts submitted for podium presentation at the 1991-1994 annual meetings of the Pediatric Orthopaedic Society of North America (POSNA). The publication percentage for all papers submitted to the POSNA meetings from 1991 through 1994 was 45%. Fifty-three percent of papers accepted for podium presentation were ultimately published in comparison with 38% of those not accepted for presentation (p < 0.001). The mean time to publication was 29 months and did not differ significantly for the two groups. The majority of papers (65%) were published in either Journal of Pediatric Orthopaedics (48%) or The Journal of Bone and Joint Surgery (American) (17%). The frequency of ultimate publication of abstracts submitted to the annual POSNA meetings compares favorably with the rates for other medical subspecialties.

Hinged elbow external fixators: indications and uses.

Abstract Hinged external fixation of the elbow joint can play an important role in managing complicated fracture‐dislocations, joint instability after extensive contracture release, and distraction interposition arthroplasty. Application of these devices requires accurate alignment of the fixator axis with the anatomic axis of the elbow. The primary therapeutic goal is to allow joint motion while protecting the healing ligaments. Common complications include pin loosening, injury to adjacent neurovascular structures, cellulitis, and loss of reduction. Although reported data are limited, this technique is a useful adjunct in patients with complex elbow instability.

An Online Video Investigation Into the Mechanism of Elbow Dislocation

PURPOSE Acute elbow instability leading to dislocation is thought to be a spectrum initiated by an injury to the lateral stabilizing structures of the elbow. Previous cadaveric studies have shown elbow dislocations to occur in flexion. The purpose of this study was to analyze videographic evidence of the deforming forces and upper extremity position during elbow dislocations. We sought to corroborate previous biomechanics studies with in vivo observations. METHODS We included 62 YouTube.com videos with a clear videographic view of an elbow dislocation. Three senior elbow surgeons independently evaluated arm position at the time of dislocation, along with the suspected deforming forces at the elbow based on these positions. RESULTS Of the 62 visualized elbow dislocation events, the vast majority (92%) dislocated at or near full extension. The most common arm positions were forearm pronation (68%) with shoulder abduction (97%) and forward flexion (63%). The typical elbow deforming forces were a valgus moment (89%), an axial load (90%), and progressive supination (94%). We identified 4 discrete patterns of arm position and deforming forces. CONCLUSIONS Acute elbow dislocations in vivo occur in relative extension irrespective of forearm position, a finding distinct from previous cadaveric studies. The most common mechanism appears to involve a valgus moment to an extended elbow, which suggests a requisite disruption of the medial collateral ligament, the known primary constraint to valgus force. These videographic findings suggest that some acute elbow dislocations may result from acute valgus instability and therefore are distinct in nature and mechanism from posterolateral rotatory instability. This information could lead to improved understanding of the sequence of structural failure, modification of rehabilitation protocols, and overall treatment.