Dose and time-dependent effects of cyclooxygenase-2 inhibition on fracture-healing

Extracellular signaling molecules to promote fracture healing and bone regeneration

To date, the delivery of signaling molecules for bone regeneration has focused primarily on factors that directly affect the bone formation pathways (osteoinduction) or that serve to increase the number of bone forming progenitor cells. The first commercialized growth factors approved for bone regeneration, Bone Morphogenetic Protein 2 and 7 (BMP2 and BMP7), are direct inducers of osteoblast differentiation. As well, newer generations of potential therapeutics that target the Wnt signaling pathway are also direct osteoinducers. On the other hand, some signaling molecules may play a role as mitogens and serve to increase the number of bone producing cells or may increase vascularization. This is true for factors such as Platelet Derived Growth Factor (PDGF) or Fibroblast Growth Factor (FGF). Vascular Endothelial Growth Factor (VEGF) likely has a special role. Not only does it induce new blood vessel formation, it also has direct effects on osteoblasts through endothelial cell-based BMP production. In addition to these pathways that classically have targeted bone production, there are also opportunities to target other aspects of the bone healing process such as inflammation, vascularization, and cell ingress to the fracture site. Bone regeneration is highly complex with defined, yet overlapping stages of healing. We will review established and novel extracellular signaling factors associated with various stages of fracture healing that could be targeted to promote enhanced bone regeneration. Importantly, multiple potential cell and tissues could be targeted to enhance healing in addition to focusing solely on osteoinductive therapeutics.

Trends of non-union and prescriptions for non-steroidal anti-inflammatory drugs in the United States, 1993-2012

BACKGROUND AND PURPOSE

Surgical care and pain management for patients with fractures have evolved over the years. We wanted to ascertain if there were any changes in the incidence of non-unions and, if so, whether the use of non-steroidal anti-inflammatory drugs (NSAIDs), including COX-2 selective inhibitors, might have an effect.

PATIENTS AND METHODS

We used the National Inpatient Sample (NIS) to estimate the annual number of patients hospitalized for surgical treatment of a non-union between 1993 and 2012, and calculated age-adjusted rates of non-union. We estimated the prevalence of prescriptions for NSAIDs from 1996 through 2012 using the Medical Expenditure Panel Survey (MEPS). The interrupted time-series analysis was used to relate quarterly rates of non-union to changes in prescriptions for NSAIDs between 1996 and 2009.

RESULTS

The annual estimate of non-unions in the USA declined 30% from 25,634 in 1993 to 17,815 in 2012 (p < 0.001). Specifically, the age-adjusted rate of non-unions decreased by 44% from 8.6 per 10(5) persons in 1996 to 4.8 per 10(5) persons in 2012 (p < 0.001). However, there was an 8% increase in the incidence rate of non-unions (p = 0.003) between 2000 and 2004, when certain COX-2 selective inhibitors were on the market and their prescriptions were prevalent at around 6% among those with fractures. A drop in non-union estimates from 22,321 in 2010 to 18,789 in 2011 (p = 0.04) also coincided with a marked decrease in prescriptions for NSAIDs in patients with fractures, from 22% to 14% (p = 0.02).

INTERPRETATION

Non-unions in the USA declined substantially between 1993 and 2012, but this was interrupted by changes in prescriptions for NSAIDs, with sustained increases between 2000 and 2004 followed by transient decreases in 2005 and 2011.

Effects of Diclofenac Sodium on BMP-induced Inflammation in a Rodent Model

STUDY DESIGN

Prospective in vivo rodent model of bone morphogenetic protein (BMP)-induced inflammation.

OBJECTIVE

To evaluate the effects of the coadministration of the nonsteroidal anti-inflammatory drug, diclofenac, on BMP-induced inflammation using our rodent model.

SUMMARY OF BACKGROUND DATA

The use of BMP-2 is associated with inflammation in the neck and back. We have previously reported on a rodent model of BMP-2-induced inflammation.

METHODS

Seven treatment groups were: Surgery alone; absorbable collagen sponges (ACS) alone; 20 μg rhBMP-2 on ACS with no diclofenac; 20 μg rhBMP-2 on ACS+50 mg diclofenac injections; 20 μg rhBMP-2 on ACS+75 mg diclofenac; 20 μg rhBMP-2 on ACS+100 mg diclofenac; and 20 μg rhBMP-2 on ACS+125 mg diclofenac. Using magnetic resonance imaging, inflammation (soft tissue edema volume) was assessed at 3 hours and at 2, 7, and 14 days after implantation. Western blot analysis, histology, and immunohistochemical staining were performed to compare the inflammatory response between groups. The mass size and tissue density of bone formation were compared between groups using plain radiography.

RESULTS

Soft-tissue edema volumes in all diclofenac-treated groups were significantly lower than those observed in the rhBMP-2 alone. There was no significant difference in soft tissue edema volumes between 4 diclofenac-treated groups. The expression of NF-κB signaling pathway related proteins (p65 and p-p65) were increased in the rhBMP-2+ACS group and decreased in diclofenac treatment groups. Histological findings and immunohistochemical staining were consistent with the Western blot results. There was no significant difference between the rhBMP-2+ACS group and diclofenac treatment groups in terms of the mass size and tissue density of bone formation.

CONCLUSION

Coadministration of diclofenac sodium can reduce the inflammatory response to BMP-2 without impairing heterotopic bone formation in our rodent model of BMP-2-induced inflammation.

LEVEL OF EVIDENCE

N/A.

Salicylic Acid-Based Polymers for Guided Bone Regeneration Using Bone Morphogenetic Protein-2

Bone morphogenetic protein-2 (BMP-2) is used clinically to promote spinal fusion, treat complex tibia fractures, and to promote bone formation in craniomaxillofacial surgery. Excessive bone formation at sites where BMP-2 has been applied is an established complication and one that could be corrected by guided tissue regeneration methods. In this study, anti-inflammatory polymers containing salicylic acid [salicylic acid-based poly(anhydride-ester), SAPAE] were electrospun with polycaprolactone (PCL) to create thin flexible matrices for use as guided bone regeneration membranes. SAPAE polymers hydrolyze to release salicylic acid, which is a nonsteroidal anti-inflammatory drug. PCL was used to enhance the mechanical integrity of the matrices. Two different SAPAE-containing membranes were produced and compared: fast-degrading (FD-SAPAE) and slow-degrading (SD-SAPAE) membranes that release salicylic acid at a faster and slower rate, respectively. Rat femur defects were treated with BMP-2 and wrapped with FD-SAPAE, SD-SAPAE, or PCL membrane or were left unwrapped. The effects of different membranes on bone formation within and outside of the femur defects were measured by histomorphometry and microcomputed tomography. Bone formation within the defect was not affected by membrane wrapping at BMP-2 doses of 12 μg or more. In contrast, the FD-SAPAE membrane significantly reduced bone formation outside the defect compared with all other treatments. The rapid release of salicylic acid from the FD-SAPAE membrane suggests that localized salicylic acid treatment during the first few days of BMP-2 treatment can limit ectopic bone formation. The data support development of SAPAE polymer membranes for guided bone regeneration applications as well as barriers to excessive bone formation.

The Effect of Cyclooxygenase Inhibition on Tendon-Bone Healing in an In Vitro Coculture Model

The effects of cyclooxygenase (COX) inhibition following the reconstruction of the anterior cruciate ligament remain unclear. We examined the effects of selective COX-2 and nonselective COX inhibition on bone-tendon integration in an in vitro model. We measured the dose-dependent effects of ibuprofen and parecoxib on the viability of lipopolysaccharide- (LPS-) stimulated and unstimulated mouse MC3T3-E1 and 3T3 cells, the influence on gene expression at the osteoblast, interface, and fibroblast regions measured by quantitative PCR, and cellular outgrowth assessed on histological sections. Ibuprofen led to a dose-dependent suppression of MC3T3 cell viability, while parecoxib reduced the viability of 3T3 cultures. Exposure to ibuprofen significantly suppressed expression of Alpl (P < 0.01), Bglap (P < 0.001), and Runx2 (P < 0.01), and although parecoxib reduced expression of Alpl (P < 0.001), Fmod (P < 0.001), and Runx2 (P < 0.01), the expression of Bglap was increased (P < 0.01). Microscopic analysis showed a reduction in cellular outgrowth in LPS-stimulated cultures following exposure to ibuprofen and parecoxib. Nonselective COX inhibition and the specific inhibition of COX-2 led to region-specific reductions in markers of calcification and cell viability. We suggest further in vitro and in vivo studies examining the biologic and biomechanical effects of selective and nonselective COX inhibition.

Axial strain enhances osteotomy repair with a concomitant increase in connexin43 expression

The mechanical environment is known to influence fracture healing. We speculated that connexin43 (Cx43) gap junctions, which impact skeletal homeostasis, fracture healing and the osteogenic response to mechanical load, may play a role in mediating the response of the healing bone to mechanical strain. Here, we used an established rat fracture model, which uses a 2 mm osteotomy gap stabilized by an external fixator, to examine the impact of various cyclical axial loading protocols (2%, 10%, and 30% strain) on osteotomy healing. We examined the presence of Cx43 in the osteotomy-healing environment and assessed how mechanical strain modulates Cx43 expression patterns in the callus. We demonstrated that increased cyclical axial strain results in increased radiographic and histologic bone formation. In addition, we show by immunohistochemistry that Cx43 is abundantly expressed in the healing callus, with the expression most robust in samples exposed to increased cyclical axial strain. These data are consistent with the concept that an increase in Cx43 expression by mechanical load may be part of the mechanisms by which mechanical forces enhances fracture healing.

Method for measuring lipid mediators, proteins, and messenger RNAs from a single tissue specimen

This article describes a new method for extracting RNA, protein, and lipid mediators from a single tissue specimen. Specifically, mouse bone fracture callus specimens were extracted into a single solution that was processed using three different procedures to measure messenger RNA (mRNA) levels by reverse transcription-quantitative polymerase chain reaction (RTqPCR), cytokines and growth factors using an xMAP method, and lipid mediators by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method has several advantages because it decreases the number of animals necessary for experimentation, allows division of the sample from a homogeneous mixture that reduces sample variability, and uses a solution that protects the integrity of the macromolecules during storage.

Perioperative use of non-steroidal anti-inflammatory drugs might impair dental implant osseointegration

OBJECTIVE

To appraise whether adverse biological events following oral implant placement may be associated with perioperative use of non-steroidal anti-inflammatory drugs (NSAIDs).

METHODS

All patients treated in a university faculty postgraduate dental clinic between 1979 and 2012 that had experienced a failing and surgically removed dental implant (292 implants in 168 patients) were contacted to solicit additional information about their present dental and medical status and frequency of current and past use of NSAIDs. Potential associations between perioperative NSAIDs use and the occurrence of adverse biological events were explored by the use of 2 × 2 tables and two-tailed Fisher's exact tests.

RESULTS

One hundred and four patients with initially 468 implants had experienced 238 implant failures, of which 197 were due to failing osseointegration (42%). Sixty of the participants, initially with 273 implants, had used NSAIDs perioperatively and experienced 44% implant failures, versus 38% in the non-NSAID cohort. The NSAID cohort experienced 3.2 times more cases of radiographic bone loss greater than 30% of the vertical height of their remaining implants and 1.9 times more cases of cluster failures, defined as failure of 50% or more of the implant(s) placed.

CONCLUSIONS

Notwithstanding that a retrospective study design is open to potential bias, the current data indicate that dental implant osseointegration may be affected negatively by an inhibitory effect of NSAIDs on bone healing in vulnerable patients. Future and better clinical studies than the current should be designed to appraise more precisely the potential effects of NSAIDs on implant osseointegration in study populations that are not limited by stringent medical inclusion and exclusion criteria.

Dipyrone has no effects on bone healing of tibial fractures in rats

OBJECTIVE:

To evaluate the effect of dipyrone on healing of tibial fractures in rats.

METHODS:

Fourty-two Wistar rats were used, with mean body weight of 280g. After being anesthetized, they were submitted to closed fracture of the tibia and fibula of the right posterior paw through manual force. The rats were randomly divided into three groups: the control group that received a daily intraperitoneal injection of saline solution; group D-40, that received saline injection containing 40mg/Kg dipyrone; and group D-80, that received saline injection containing 80mg/Kg dipyrone. After 28 days the rats were sacrificed and received a new label code that was known by only one researcher. The fractured limbs were then amputated and X-rayed. The tibias were disarticulated and subjected to mechanical, radiological and histological evaluation. For statistical analysis the Kruskal-Wallis test was used at a significance level of 5%.

RESULTS:

There wasn't any type of dipyrone effect on healing of rats tibial fractures in relation to the control group.

CONCLUSION:

Dipyrone may be used safely for pain control in the treatment of fractures, without any interference on bone healing. Level of Evidence II, Controlled Laboratory Study.

The detrimental effects of systemic Ibuprofen delivery on tendon healing are time-dependent

BACKGROUND

Current clinical treatment after tendon repairs often includes prescribing NSAIDs to limit pain and inflammation. The negative influence of NSAIDs on bone repair is well documented, but their effects on tendon healing are less clear. While NSAIDs may be detrimental to early tendon healing, some evidence suggests that they may improve healing if administered later in the repair process.

QUESTIONS/PURPOSES

We asked whether the biomechanical and histologic effects of systemic ibuprofen administration on tendon healing are influenced by either immediate or delayed drug administration.

METHODS

After bilateral supraspinatus detachment and repair surgeries, rats were divided into groups and given ibuprofen orally for either Days 0 to 7 (early) or Days 8 to 14 (delayed) after surgery; a control group did not receive ibuprofen. Healing was evaluated at 1, 2, and 4 weeks postsurgery through biomechanical testing and histologic assessment.

RESULTS

Biomechanical evaluation resulted in decreased stiffness and modulus at 4 weeks postsurgery for early ibuprofen delivery (mean ± SD [95% CI]: 10.8 ± 6.4 N/mm [6.7-14.8] and 8.9 ± 5.9 MPa [5.4-12.3]) when compared to control repair (20.4 ± 8.6 N/mm [16.3-24.5] and 15.7 ± 7.5 MPa [12.3-19.2]) (p = 0.003 and 0.013); however, there were no differences between the delayed ibuprofen group (18.1 ± 7.4 N/mm [14.2-22.1] and 11.5 ± 5.6 MPa [8.2-14.9]) and the control group. Histology confirmed mechanical results with reduced fiber reorganization over time in the early ibuprofen group.

CONCLUSIONS

Early administration of ibuprofen in the postoperative period was detrimental to tendon healing, while delayed administration did not affect tendon healing.

CLINICAL RELEVANCE

Historically, clinicians have often prescribed ibuprofen after tendon repair, but this study suggests that the timing of ibuprofen administration is critical to adequate tendon healing. This research necessitates future clinical studies investigating the use of ibuprofen for pain control after rotator cuff repair and other tendon injuries.

Fracture healing and lipid mediators

Lipid mediators regulate bone regeneration during fracture healing. Prostaglandins and leukotrienes are well-known lipid mediators that regulate inflammation and are synthesized from the Ω-6 fatty acid, arachidonic acid. Cyclooxygenase (COX-1 or COX-2) and 5-lipoxygenase (5-LO) catalyze the initial enzymatic steps in the synthesis of prostaglandins and leukotrienes, respectively. Inhibition or genetic ablation of COX-2 activity impairs fracture healing in animal models. Genetic ablation of COX-1 does not affect the fracture callus strength in mice, suggesting that COX-2 activity is primarily responsible for regulating fracture healing. Inhibition of cyclooxygenase activity with nonsteroidal anti-inflammatory drugs (NSAIDs) is performed clinically to reduce heterotopic ossification, although clinical evidence that NSAID treatment impairs fracture healing remains controversial. In contrast, inhibition or genetic ablation of 5-LO activity accelerates fracture healing in animal models. Even though prostaglandins and leukotrienes regulate inflammation, loss of COX-2 or 5-LO activity appears to primarily affect chondrogenesis during fracture healing. Prostaglandin or prostaglandin analog treatment, prostaglandin-specific synthase inhibition and prostaglandin or leukotriene receptor antagonism also affect callus chondrogenesis. Unlike the Ω-6-derived lipid mediators, lipid mediators derived from Ω-3 fatty acids, such as resolvin E1 (RvE1), have anti-inflammatory activity. In vivo, RvE1 can inhibit osteoclastogenesis and limit bone resorption. Although Ω-6 and Ω-3 lipid mediators have clear-cut effects on inflammation, the role of these lipid mediators in bone regeneration is more complex, with apparent effects on callus chondrogenesis and bone remodeling.

Influence of non-steroidal anti-inflammatory drugs (NSAIDs) on osseointegration of dental implants in rabbit calvaria

AIM

Until recently, adverse effects of non-steroidal anti-inflammatory drugs (NSAIDs) on osseointegration of dental implants were unknown. Hence, this study investigated the short- and long-term effects of a 7-day regimen of parecoxib and diclofenac sodium on osseointegration of dental implants in calvarial bone.

MATERIAL AND METHODS

Eighteen New Zealand White rabbits were randomly allocated into three groups (each n = 6): Control group with no postoperative pain killers (Group A), diclofenac group (Group B) and parecoxib group (Group C). In each animal, one dental implant was placed into the calvarial bone (total n = 18). Three rabbits from each group were sacrificed in Week 4. The other three rabbits from each group were sacrificed in Week 12 postoperatively. The implant together with the calvarial bone and dura mater was harvested and subjected to micro-computed tomography (micro-CT) and histomorphometric analysis.

RESULTS

Quantitative analysis of micro-CT data and histomorphometric data neither revealed any statistically significant (P ≤ 0.05) differences between the three different groups related to osseointegration nor between different time points of observation.

CONCLUSION

In rabbits, a 7-day regimen of appropriate doses of diclofenac sodium and parecoxib did not adversely affect osseointegration of dental implants and bone healing in calvaria, neither short nor long term (12 weeks).

Immunohistochemical localization of key arachidonic acid metabolism enzymes during fracture healing in mice

This study investigated the localization of critical enzymes involved in arachidonic acid metabolism during the initial and regenerative phases of mouse femur fracture healing. Previous studies found that loss of cyclooxygenase-2 activity impairs fracture healing while loss of 5-lipoxygenase activity accelerates healing. These diametric results show that arachidonic acid metabolism has an essential function during fracture healing. To better understand the function of arachidonic acid metabolism during fracture healing, expression of cyclooxygenase-1 (COX-1), cyclooxygenase -2 (COX-2), 5-lipoxygenase (5-LO), and leukotriene A4 hydrolase (LTA4H) was localized by immunohistochemistry in time-staged fracture callus specimens. All four enzymes were detected in leukocytes present in the bone marrow and attending inflammatory response that accompanied the fracture. In the tissues surrounding the fracture site, the proportion of leukocytes expressing COX-1, COX-2, or LTA4H decreased while those expressing 5-LO remained high at 4 and 7 days after fracture. This may indicate an inflammation resolution function for 5-LO during fracture healing. Only COX-1 was consistently detected in fracture callus osteoblasts during the later stages of healing (day 14 after fracture). In contrast, callus chondrocytes expressed all four enzymes, though 5-LO appeared to be preferentially expressed in newly differentiated chondrocytes. Most interestingly, osteoclasts consistently and strongly expressed COX-2. In addition to bone surfaces and the growth plate, COX-2 expressing osteoclasts were localized at the chondro-osseous junction of the fracture callus. These observations suggest that arachidonic acid mediated signaling from callus chondrocytes or from callus osteoclasts at the chondro-osseous junction regulate fracture healing.

Compensatory cellular reactions to nonsteroidal anti-inflammatory drugs on osteogenic differentiation in canine bone marrow-derived mesenchymal stem cells

The suppressive effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on the bone healing process have remained controversial, since no clinical data have clearly shown the relationship between NSAIDs and bone healing. The aim of this study was to assess the compensatory response of canine bone marrow-derived mesenchymal stem cells (BMSCs) to several classes of NSAIDs, including carprofen, meloxicam, indomethacin and robenacoxib, on osteogenic differentiation. Each of the NSAIDs (10 µM) was administered during 20 days of the osteogenic process with human recombinant IL-1β (1 ng/ml) as an inflammatory stimulator. Gene expression of osteoblast differentiation markers (alkaline phosphatase and osteocalcin), receptors of PGE₂ (EP2 and EP4) and enzymes for prostaglandin (PG) E2 synthesis (COX-1, COX-2, cPGES and mPGES-1) was measured by using quantitative reverse transcription-polymerase chain reaction. Protein production levels of alkaline phosphatase, osteocalcin and PGE₂ were quantified using an alkaline phosphatase activity assay, osteocalcin immunoassay and PGE₂ immunoassay, respectively. Histologic analysis was performed using alkaline phosphatase staining, von Kossa staining and alizarin red staining. Alkaline phosphatase and calcium deposition were suppressed by all NSAIDs. However, osteocalcin production showed no significant suppression by NSAIDs. Gene expression levels of PGE₂-related receptors and enzymes were upregulated during continuous treatment with NSAIDs, while certain channels for PGE₂ synthesis were utilized differently depending on the kind of NSAIDs. These data suggest that canine BMSCs have a compensatory mechanism to restore PGE₂ synthesis, which would be an intrinsic regulator to maintain differentiation of osteoblasts under NSAID treatment.

Dual effect of platelet lysate on human articular cartilage: a maintenance of chondrogenic potential and a transient proinflammatory activity followed by an inflammation resolution

Platelet-rich plasma (PRP), a cocktail of platelet growth factors and bioactive proteins, has been proposed as a therapeutic agent to restore damaged articular cartilage. We report the biological effect of the platelet lysate (PL), a PRP derivative, on primary human articular chondrocytes cultured under both physiological and inflammatory conditions. When added to the culture medium, PL induced a strong mitogenic response in the chondrocytes. The in vitro expanded cell population maintained a chondrogenic redifferentiation potential as revealed by micromass culture in vitro and ectopic cartilage formation in vivo. Further, in chondrocytes cultured in the presence of the proinflammatory cytokine interleukin-1α (IL-1α), the PL induced a drastic enhancement of the synthesis of the cytokines IL-6 and IL-8 and of neutrophil-gelatinase associated lipocalin, a lipocalin expressed during chondrocyte differentiation and inflammation. These events were mediated by the p38 MAP kinase and NF-κB pathways. We observed that inflammatory stimuli activated phospo-MAP kinase-activated protein kinase 2, a direct target of p38. The proinflammatory effect of the PL was a transient phenomenon; after an initial upregulation, we observed significant reduction of the NF-κB activity together with the repression of the inflammatory enzyme cyclooxygenase-2. Moreover, the medium of chondrocytes cultured in the simultaneous presence of PL and IL-1α, showed a significant enhancement of the chemoattractant activity versus untreated chondrocytes. Our findings support the concept that the platelet products have a direct beneficial effect on articular chondrocytes and could drive in sequence a transient activation and the resolution of the inflammatory process, thus providing a rational for their use as therapeutic agents in cartilage inflammation and damage.

Therapeutic doses of nonsteroidal anti-inflammatory drugs inhibit osteosarcoma MG-63 osteoblast-like cells maturation, viability, and biomineralization potential

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used to reduce pain and inflammation. However, their effect on bone metabolisms is not well known, and results in the literature are contradictory. The present study focusses on the effect of dexketoprofen, ketorolac, metamizole, and acetylsalicylic acid, at therapeutic doses, on different biochemical and phenotypic pathways in human osteoblast-like cells. Osteoblasts (MG-63 cell line) were incubated in culture medium with 1-10 μM of dexketoprofen, ketorolac, metamizole, and acetylsalicylic acid. Flow cytometry was used to study antigenic profile and phagocytic activity. The osteoblastic differentiation was evaluated by mineralization and synthesis of collagen fibers by microscopy and alkaline phosphatase activity (ALP) by spectrophotometric assay. Short-term treatment with therapeutic doses of NSAIDs modulated differentiation, antigenic profile, and phagocyte activity of osteoblast-like cells. The treatment reduced ALP synthesis and matrix mineralization. However, nonsignificant differences were observed on collagen syntheses after treatments. The percentage of CD54 expression was increased with all treatments. CD80, CD86, and HLA-DR showed a decreased expression, which depended on NSAID and the dose applied. The treatments also decreased phagocyte activity in this cellular population. The results of this paper provide evidences that NSAIDs inhibit the osteoblast differentiation process thus reducing their ability to produce new bone mineralized extracellular matrix.

NSAID therapy effects on healing of bone, tendon, and the enthesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of skeletal injuries. The ability of NSAIDs to reduce pain and inflammation is well-established. However, the effects of NSAID therapy on healing of skeletal injuries is less defined. NSAIDs inhibit cyclooxygenase activity to reduce synthesis of prostaglandins, which are proinflammatory, lipid-signaling molecules. Inhibition of cyclooxygenase activity can impact many physiological processes. The effects of NSAID therapy on healing of bone, tendon, and the tendon-to-bone junction (enthesis) have been studied in animal and cell culture models, but human studies are few. Use of different NSAIDs with different pharmacological properties, differences in dosing regimens, and differences in study models and outcome measures have complicated comparisons between studies. In this review, we summarize the mechanisms by which bone, tendon, and enthesis healing occurs, and describe the effects of NSAID therapy on each of these processes. Determining the impact of NSAID therapy on healing of skeletal tissues will enable clinicians to appropriately manage the patient's condition and improve healing outcomes.

Ketorolac administration does not delay early fracture healing in a juvenile rat model: a pilot study

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective at controlling pain in children, especially in the treatment of fractures. Adult animal and adult clinical studies demonstrate conflicting evidence for the inhibitory relationship between NSAIDs and fracture healing. Published pediatric orthopaedic clinical studies do not demonstrate an inhibitory effect of ketorolac on bone healing. Little is known about the effects of any NSAID on bone formation in juvenile animals. This study investigates the effects of the NSAID ketorolac on fracture healing in a juvenile rat model.

METHODS

Unilateral surgically induced and stabilized tibial shaft fractures were created in 45 juvenile (3 to 4 wk old) male Sprague-Dawley rats. Either ketorolac (5 mg/kg; n=24) or saline (0.9% normal saline; n=21) was then administered to the rats 6 d/wk by intraperitoneal injections. Animals were then randomly assigned into time groups and euthanized at 7 days (n=8 ketorolac, n=7 saline), 14 days (n=8 ketorolac, n=7 saline), or 21 days (n=8 ketorolac, n=7 saline) postfracture. Biomechanical analysis was performed using a custom-designed 4-point bending loading apparatus. Statistics for tibial stiffness and strength data were performed using software package Systat 11. Specimens were also evaluated histologically using hematoxylin and eosin staining.

RESULTS

Strength and stiffness of all fractured tibiae increased over time from day 7 to day 21 regardless of treatment type. No statistical difference was found between the fractured tibiae strength or stiffness in the ketorolac or control-treated specimens at the same time point. In addition, the quality of the fracture callus was similar in both groups at each of the time points.

CONCLUSIONS

In this study of a juvenile rat model with a stabilized tibia fracture, fracture callus strength, stiffness, and histologic characteristics were not affected by the administration of ketorolac during the first 21 days of fracture healing.

CLINICAL RELEVANCE

The absence of inhibitory effects of ketorolac on early juvenile rat fracture healing supports the clinical practice of utilizing NSAIDs for analgesia in children with long bone fractures.

The effect of nonsteroidal anti-inflammatory drugs on tissue healing

PURPOSE

Non-selective (NSAIDs) and selective (COX-2) nonsteroidal anti-inflammatory drugs are commonly used for their analgesic and anti-inflammatory effects. Their role after orthopaedic surgery has been infrequently described and remains controversial because of unclear effects on soft tissue and bone healing. This study critically reviews the available literature to describe the effects of NSAIDs and COX-2 inhibitors on soft tissue and bone healing.

METHODS

A Medline search was performed using NSAIDs or COX-2 inhibitors and tissue healing. The combined search yielded 637 articles. Following exclusion, 44 articles were deemed relevant with 9 articles on soft tissue healing and 35 articles on bone healing. The available evidence is based primarily on animal data (39 studies), with considerable variation in study methods.

RESULTS

In regard to soft tissue healing, there is insufficient evidence of a detrimental effect when using either NSAIDs or COX-2 inhibitors at standard doses for ≤2 weeks. For soft tissue to bone healing, a limited number of studies demonstrate impairment in healing. However, with respect to bone healing, indomethacin appears to have a clear detrimental effect, with less substantial evidence for other NSAIDs.

CONCLUSIONS

Short-term, low-dose use of NSAIDs and COX-2 inhibitors does not appear to have a detrimental effect following soft tissue injury, but is inhibitory in cases involving bony healing. However, additional well-controlled human studies are necessary to draw more definitive conclusions regarding their role. Clinically, the prudent use of anti-inflammatory medications following sports medicine injuries and surgeries appears to be a reasonable option in clinical practice unless bone healing is required.

LEVEL OF EVIDENCE

III.

Selective and non-selective cyclooxygenase inhibitors delay stress fracture healing in the rat ulna

Anti-inflammatory drugs are widely used to manage pain associated with stress fractures (SFxs), but little is known about their effects on healing of those injuries. We hypothesized that selective and non-selective anti-inflammatory treatments would retard the healing of SFx in the rat ulna. SFxs were created by cyclic loading of the ulna in Wistar rats. Ulnae were harvested 2, 4 or 6 weeks following loading. Rats were treated with non-selective NSAID, ibuprofen (30 mg/kg/day); selective COX-2 inhibition, [5,5-dimethyl-3-3 (3 fluorophenyl)-4-(4 methylsulfonal) phenyl-2 (5H)-furanone] (DFU) (2.0 mg/kg/day); or the novel c5a anatagonist PMX53 (10 mg/kg/day, 4 and 6 weeks only); with appropriate vehicle as control. Quantitative histomorphometric measurements of SFx healing were undertaken. Treatment with the selective COX-2 inhibitor, DFU, reduced the area of resorption along the fracture line at 2 weeks, without affecting bone formation at later stages. Treatment with the non-selective, NSAID, ibuprofen decreased both bone resorption and bone formation so that there was significantly reduced length and area of remodeling and lamellar bone formation within the remodeling unit at 6 weeks after fracture. The C5a receptor antagonist PMX53 had no effect on SFx healing at 4 or 6 weeks after loading, suggesting that PMX53 would not delay SFx healing. Both selective COX-2 inhibitors and non-selective NSAIDs have the potential to compromise SFx healing, and should be used with caution when SFx is diagnosed or suspected.

Local inhibition of 5-lipoxygenase enhances bone formation in a rat model

Objectives

Recent studies have shown that modulating inflammation-related lipid signalling after a bone fracture can accelerate healing in animal models. Specifically, decreasing 5-lipoxygenase (5-LO) activity during fracture healing increases cyclooxygenase-2 (COX-2) expression in the fracture callus, accelerates chondrogenesis and decreases healing time. In this study, we test the hypothesis that 5-LO inhibition will increase direct osteogenesis.

Methods

Bilateral, unicortical femoral defects were used in rats to measure the effects of local 5-LO inhibition on direct osteogenesis. The defect sites were filled with a polycaprolactone (PCL) scaffold containing 5-LO inhibitor (A-79175) at three dose levels, scaffold with drug carrier, or scaffold only. Drug release was assessed in vitro. Osteogenesis was assessed by micro-CT and histology at two endpoints of ten and 30 days.

Results

Using micro-CT, we found that A-79175, a 5-LO inhibitor, increased bone formation in an apparent dose-related manner.

Conclusions

These results indicate that 5-LO inhibition could be used therapeutically to enhance treatments that require the direct formation of bone.

Effects of a selective cyclooxygenase-2 inhibitor (celecoxib) on fracture healing in rats

BACKGROUND

Several studies suggested that celecoxib interferes with bone healing while others contradict these findings. This study was conducted to investigate the effects of celecoxib on bone healing in rats femur mold with a dose based on body surface area conversion.

MATERIALS AND METHODS

72 adult female Sprague Dawley rats were randomly divided into three groups after the internal fixation operation of nondisplaced transverse mid diaphyseal fractures of the right femurs. Each group was treated with 1% methylcellulose, celecoxib (21 mg/kg/d) for 1 week, or celecoxib (21 mg/kg/d) for 4 weeks after surgeries respectively. Bone healing scores and callus formation were evaluated by radiographs at 3, 4, 6 weeks after surgeries. Half of these rats were sacrificed for histological analysis at 4 weeks after surgery. The remaining fractured femurs were evaluated by biomechanical tests at 6 weeks after surgery.

RESULTS

The mean radiographic scores for fracture healing of both short and long term groups were lower than that of the control group and the differences among the three groups were statistically significant (P < 0.05) at 3, 4, 6 weeks after surgery. The mean bone trabecula density of both groups was smaller than that of the control group and the differences were also statistically significant (P < 0.05) at 4 week. The maximum load, total energy and stiffness in both the short term and long term groups were significantly decreased compared with those in the control group (P < 0.05) at 6 week.

CONCLUSION

Both short term and long term sustained use of celecoxib in rat models has significantly inhibitory effects on rat fracture healing.

MMP9 regulates the cellular response to inflammation after skeletal injury

Like other tissue injuries, bone fracture triggers an inflammatory response, which plays an important role in skeletal repair. Inflammation is believed to have both positive and negative effects on bone repair, but the underlying cellular mechanisms are not well understood. To assess the role of inflammation on skeletal cell differentiation, we used mouse models of fracture repair that stimulate either intramembranous or endochondral ossification. In the first model, fractures are rigidly stabilized leading to direct bone formation, while in the second model, fracture instability causes cartilage and bone formation. We compared the inflammatory response in these two mechanical environments and found changes in the expression patterns of inflammatory genes and in the recruitment of inflammatory cells and osteoclasts. These results suggested that the inflammatory response could influence skeletal cell differentiation after fracture. We then exploited matrix metalloproteinase 9 (MMP9) that is expressed in inflammatory cells and osteoclasts, and which we previously showed is a potential regulator of cell fate decisions during fracture repair. Mmp9(-/-) mice heal stabilized fractures via endochondral ossification, while wild type mice heal via intramembranous ossification. In parallel, we observed increases in macrophages and T cells in the callus of Mmp9(-/-) compared to wild type mice. To assess the link between the profile of inflammatory cells and skeletal cell fate functionally, we transplanted Mmp9(-/-) mice with wild type bone marrow, to reconstitute a wild type hematopoietic lineage in interaction with the Mmp9(-/-) stroma and periosteum. Following transplantation, Mmp9(-/-) mice healed stabilized fractures via intramembranous ossification and exhibited a normal profile of inflammatory cells. Moreover, Mmp9(-/-) periosteal grafts healed via intramembranous ossification in wild type hosts, but healed via endochondral ossification in Mmp9(-/-) hosts. We observed that macrophages accumulated at the periosteal surface in Mmp9(-/-) mice, suggesting that cell differentiation in the periosteum is influenced by factors such as BMP2 that are produced locally by inflammatory cells. Taken together, these results show that MMP9 mediates indirect effects on skeletal cell differentiation by regulating the inflammatory response and the distribution of inflammatory cells, leading to the local regulation of periosteal cell differentiation.

Tunable drug release profiles from salicylate-based poly(anhydride-ester) matrices using small molecule admixtures

Poly(anhydride-esters) with salicylic acid, a nonsteroidal anti-inflammatory drug, chemically incorporated into the polymer backbone provide high inherent drug loading. These poly(anhydride-esters) hydrolytically degrade to release salicylic acid over extended time periods (>30 days); however, an initial lag period of no salicylic acid release is observed. This lag period could be unfavorable in applications where immediate salicylic acid release is desired. Poly(anhydride-esters) with short (2 days) and long (11 days) lag periods were admixed with various small molecules as a means to shorten or eliminate the lag period. Salicylic acid, larger salicylic acid prodrugs, and 1:1 combinations of the two were physically admixed, each at 1%, 5%, and 10% (w/w). All admixtures resulted in immediate salicylic acid release and a decrease in glass transition temperatures compared to polymer alone. By varying the amounts of salicylic acid and salicylic acid prodrugs incorporated into the polymer matrix, immediate and constant salicylic acid release profiles over varied time periods were achieved.

Arachidonic acid: a bridge between traumatic brain injury and fracture healing

Traumatic brain injury (TBI) is associated with enhanced osteogenesis. The aim of this study was to investigate the effect of serum from TBI rats on fracture healing. Results from this study showed that the serum from TBI rats enhanced the expression of bone gamma carboxyglutamate protein (BGLAP), and promoted in vitro proliferation of MC3T3-E1 cells, a mouse osteoblastic cell line. Furthermore, gas chromatography/mass spectrometry (GC/MS) coupled with multivariate statistical analysis was used to identify the changes in global serum metabolites after TBI. We found that arachidonic acid (AA) was significantly enhanced in serum metabolites in TBI subjects, while hydroxybutyric acid, leucine, malic acid, 5-oxyproline, isocitric acid, mannose, and uric acid were reduced. Finally, we examined the effects of AA on BGLAP expression and cell proliferation in MC3T3-E1 cells. We found that BGLAP expression and proliferation of osteoblasts were positively regulated in the presence of AA. These findings suggest that the increased AA in serum after TBI may play a key role in enhancing the speed of fracture healing.

Anti-inflammatory treatment increases angiogenesis during early fracture healing

OBJECTIVES

Both inflammation and angiogenesis are crucial for normal fracture healing. The goal of this work was to determine how anti-inflammatory treatment affects angiogenesis during early stages of fracture repair.

METHODS

Tibia fractures were created in adult mice and animals were treated with indomethacin (2 mg/kg/day), a non-steroidal anti-inflammatory drug, or PBS once a day beginning from 1 day before fracture and continuing to 6 days after fracture. Animals were killed at 7, 14, and 28 days after injury for histomorphometric analysis of fracture healing. A second group of animals were killed at 3 and 7 days after injury to measure tissue levels of VEGF and interleukin-1 beta (IL-1β). A third group of animals were killed at 3 and 7 days after injury for stereology analysis of macrophage and neutrophil infiltration and tissue vascularization.

RESULTS

Indomethacin significantly decreased bone and cartilage formation at 7 days after fracture compared to controls. Indomethacin decreased the tissue levels of IL-1β at 3 days after fracture but did not affect the recruitment of macrophages or neutrophils to injured limbs. Indomethacin-treated fractures had similar length density and surface density of vasculature as the controls at 3 days after injury. At 7 days after fracture, vasculature in indomethacin-treated fractures exhibited higher length density and surface density than that in controls. By 28 days after injury, indomethacin-treated fractures still exhibited defects in fracture repair.

CONCLUSIONS

Anti-inflammatory treatments using indomethacin impair bone and cartilage formation and increase tissue vascularization in the callus during early fracture healing.

The effect of nonsteroidal anti-inflammatory drug administration on acute phase fracture-healing: a review

BACKGROUND

The analgesic efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) is well established, and these agents often form an integral part of posttraumatic pain management. However, potentially deleterious effects of resulting prostaglandin suppression on fracture-healing have been suggested.

METHODS

A systematic literature review involving searches of electronic databases and online sources was performed to identify articles exploring the influence of NSAIDs on fracture-healing.

RESULTS

A structured search approach identified 316 papers as potentially relevant to the topic, and these were manually reviewed. The majority described small-scale studies that were retrospective or observational in nature, with limited control of potentially confounding variables, or presented little key information that was not also present in other studies.

CONCLUSIONS

Although increasing evidence from animal studies suggests that cyclooxygenase-2 (COX-2) inhibition suppresses early fracture-healing, in vivo studies involving human subjects have not provided convincing evidence to substantiate this concern. We found no robust evidence to attest to a significant and appreciable patient detriment resulting from the short-term use of NSAIDs following a fracture. The balance of evidence in the available literature appears to suggest that a short-duration NSAID regimen is a safe and effective supplement to other modes of post-fracture pain control, without a significantly increased risk of sequelae related to disrupted healing.

Assessment of compromised fracture healing

No standard criteria exist for diagnosing fracture nonunion, and studies suggest that assessment of fracture healing varies among orthopaedic surgeons. This variability can be problematic in both clinical and orthopaedic trauma research settings. An understanding of risk factors for nonunion and of diagnostic tests used to assess fracture healing can facilitate a systematic approach to evaluation and management. Risk factors for nonunion include medical comorbidities, age, and the characteristics of the injury. The method of fracture management also influences healing. Comprehensive evaluation includes an assessment of the patient's symptoms, signs, and immune and endocrine status as well as the biologic capacity of the fracture, presence of infection, and quality of reduction and fixation. Diagnostic tests include plain radiography, CT, ultrasonography, fluoroscopy, bone scan, MRI, and several laboratory tests, including assays for bone turnover markers in the peripheral circulation. A systematic approach to evaluating fracture union can help surgeons determine the timing and nature of interventions.

Perioperative care for the older outpatient undergoing ambulatory surgery

As the number of ambulatory surgery procedures continues to grow in an aging global society, the implementation of evidence-based perioperative care programs for the elderly will assume increased importance. Given the recent advances in anesthesia, surgery, and monitoring technology, the ambulatory setting offers potential advantages for elderly patients undergoing elective surgery. In this review article we summarize the physiologic and pharmacologic effects of aging and their influence on anesthetic drugs, the important considerations in the preoperative evaluation of elderly outpatients with coexisting diseases, the advantages and disadvantages of different anesthetic techniques on a procedural-specific basis, and offer recommendations regarding the management of common postoperative side effects (including delirium and cognitive dysfunction, fatigue, dizziness, pain, and gastrointestinal dysfunction) after ambulatory surgery. We conclude with a discussion of future challenges related to the growth of ambulatory surgery practice in this segment of our surgical population. When information specifically for the elderly population was not available in the peer-reviewed literature, we drew from relevant information in other ambulatory surgery populations.

Activation of NF-κB/p65 facilitates early chondrogenic differentiation during endochondral ossification

BACKGROUND

NF-κB/p65 has been reported to be involved in regulation of chondrogenic differentiation. However, its function in relation to key chondrogenic factor Sox9 and onset of chondrogenesis during endochondral ossification is poorly understood. We hypothesized that the early onset of chondrogenic differentiation is initiated by transient NF-κB/p65 signaling.

METHODOLOGY/PRINCIPAL FINDINGS

The role of NF-κB/p65 in early chondrogenesis was investigated in different in vitro, ex vivo and in vivo endochondral models: ATDC5 cells, hBMSCs, chicken periosteal explants and growth plates of 6 weeks old mice. NF-κB/p65 activation was manipulated using pharmacological inhibitors, RNAi and activating agents. Gene expression and protein expression analysis, and (immuno)histochemical stainings were employed to determine the role of NF-κB/p65 in the chondrogenic phase of endochondral development. Our data show that chondrogenic differentiation is facilitated by early transient activation of NF-κB/p65. NF-κB/p65-mediated signaling determines early expression of Sox9 and facilitates the subsequent chondrogenic differentiation programming by signaling through key chondrogenic pathways.

CONCLUSIONS/SIGNIFICANCE

The presented data demonstrate that NF-κB/p65 signaling, as well as its intensity and timing, represents one of the transcriptional regulatory mechanisms of the chondrogenic developmental program of chondroprogenitor cells during endochondral ossification. Importantly, these results provide novel possibilities to improve the success of cartilage and bone regenerative techniques.

Do nonsteroidal anti-inflammatory drugs affect bone healing? A critical analysis

Nonsteroidal anti-inflammatory drugs (NSAIDs) play an essential part in our approach to control pain in the posttraumatic setting. Over the last decades, several studies suggested that NSAIDs interfere with bone healing while others contradict these findings. Although their analgesic potency is well proven, clinicians remain puzzled over the potential safety issues. We have systematically reviewed the available literature, analyzing and presenting the available in vitro animal and clinical studies on this field. Our comprehensive review reveals the great diversity of the presented data in all groups of studies. Animal and in vitro studies present so conflicting data that even studies with identical parameters have opposing results. Basic science research defining the exact mechanism with which NSAIDs could interfere with bone cells and also the conduction of well-randomized prospective clinical trials are warranted. In the absence of robust clinical or scientific evidence, clinicians should treat NSAIDs as a risk factor for bone healing impairment, and their administration should be avoided in high-risk patients.

Osteoimmunology and osteoporosis

The concept of osteoimmunology is based on growing insight into the links between the immune system and bone at the anatomical, vascular, cellular, and molecular levels. In both rheumatoid arthritis (RA) and ankylosing spondylitis (AS), bone is a target of inflammation. Activated immune cells at sites of inflammation produce a wide spectrum of cytokines in favor of increased bone resorption in RA and AS, resulting in bone erosions, osteitis, and peri-inflammatory and systemic bone loss. Peri-inflammatory bone formation is impaired in RA, resulting in non-healing of erosions, and this allows a local vicious circle of inflammation between synovitis, osteitis, and local bone loss. In contrast, peri-inflammatory bone formation is increased in AS, resulting in healing of erosions, ossifying enthesitis, and potential ankylosis of sacroiliac joints and intervertebral connections, and this changes the biomechanical competence of the spine. These changes in bone remodeling and structure contribute to the increased risk of vertebral fractures (in RA and AS) and non-vertebral fractures (in RA), and this risk is related to severity of disease and is independent of and superimposed on background fracture risk. Identifying patients who have RA and AS and are at high fracture risk and considering fracture prevention are, therefore, advocated in guidelines. Local peri-inflammatory bone loss and osteitis occur early and precede and predict erosive bone destruction in RA and AS and syndesmophytes in AS, which can occur despite clinically detectable inflammation (the so-called 'disconnection'). With the availability of new techniques to evaluate peri-inflammatory bone loss, osteitis, and erosions, peri-inflammatory bone changes are an exciting field for further research in the context of osteoimmunology.

Infection, inflammation, and bone regeneration: a paradoxical relationship

Various strategies have been developed to promote bone regeneration in the craniofacial region. Most of these interventions utilize implantable materials or devices. Infections resulting from colonization of these implants may result in local tissue destruction in a manner analogous to periodontitis. This destruction is mediated via the expression of various inflammatory mediators and tissue-destructive enzymes. Given the well-documented association among microbial biofilms, inflammatory mediators, and tissue destruction, it seems reasonable to assume that inflammation may interfere with bone healing and regeneration. Paradoxically, recent evidence also suggests that the presence of certain pro-inflammatory mediators is actually required for bone healing. Bone injury (e.g., subsequent to a fracture or surgical intervention) is followed by a choreographed cascade of events, some of which are dependent upon the presence of pro-inflammatory mediators. If inflammation resolves promptly, then proper bone healing may occur. However, if inflammation persists (which might occur in the presence of an infected implant or graft material), then the continued inflammatory response may result in suboptimal bone formation. Thus, the effect of a given mediator is dependent upon the temporal context in which it is expressed. Better understanding of this temporal sequence may be used to optimize regenerative outcomes.

Harnessing and modulating inflammation in strategies for bone regeneration

Inflammation is an immediate response that plays a critical role in healing after fracture or injury to bone. However, in certain clinical contexts, such as in inflammatory diseases or in response to the implantation of a biomedical device, the inflammatory response may become chronic and result in destructive catabolic effects on the bone tissue. Since our previous review 3 years ago, which identified inflammatory signals critical for bone regeneration and described the inhibitory effects of anti-inflammatory agents on bone healing, a multitude of studies have been published exploring various aspects of this emerging field. In this review, we distinguish between regenerative and damaging inflammatory processes in bone, update our discussion of the effects of anti-inflammatory agents on bone healing, summarize recent in vitro and in vivo studies demonstrating how inflammation can be modulated to stimulate bone regeneration, and identify key future directions in the field.

High-dose ketorolac affects adult spinal fusion: a meta-analysis of the effect of perioperative nonsteroidal anti-inflammatory drugs on spinal fusion

STUDY DESIGN

Meta-analysis of literature.

OBJECTIVE

To evaluate the effect of perioperative nonsteroidal anti-inflammatory drugs (NSAIDs) on the success rate of adult spinal fusion.

SUMMARY OF BACKGROUND DATA

NSAIDs are commonly used to treat postsurgical orthopedic pain. Studies on animal models have shown a significant inhibiting effect of NSAIDs on osteogenesis process, on which spinal fusion also depends. Recently, great interest has been shown in the effect of NSAIDs on the success rate of adult spinal fusion. Clinical trials have tested the effect of perioperative NSAIDs in spinal fusion procedures. A cumulative result of these studies would give more credit to the final conclusions.

METHODS

A systematic search of electronic databases and references from eligible articles was conducted. Comparative studies reporting on the results of primary spinal fusion including treatment group of NSAIDs perioperatively were regarded eligible. A pooled estimate of effect size was produced using both random and fixed effect model.

RESULTS

Five retrospective comparative studies (n = 1403 participants) were included in the present study. The mean age of these patients was more than 40 years and none of them had NSAIDs for longer than 14 days following spinal fusion surgery. High-dose ketorolac showed a statistically significant adverse effect on spinal fusion (P = 0.001, RR = 2.87, 95% CI = 1.53 = - 5.38) with no statistical heterogeneity (I = 3%, P = 0.38), whereas normal-dose NSAIDs (ketorolac, diclofenac sodium, celecoxib, or rofecoxib) did not appear to produce inferior results than the no-NSAIDs group (P = 0.30, RR = 1.39, 95% CI = 0.74 - 2.61) with no statistical heterogeneity (I² = 0%, P = 0.50).

CONCLUSION

Although randomized controlled trials would be optimal for meta-analyses, the data of this review revealed that short-time (<14 days) exposure to normal-dose NSAIDs (ketorolac, diclofenac sodium, celecoxib, or rofecoxib) were safe after spinal fusion, whereas short-time (<14 days) exposure to high-dose ketorolac increased the risk of nonunion, which meant that the effect of perioperative NSAIDs on spinal fusion might be dose-dependent. Further studies would be needed to find out whether long-time exposure to normal-dose NSAIDs could also increase the risk of nonunion and which type of NSAIDs would like to have a worse effect on spinal fusion.

EP1(-/-) mice have enhanced osteoblast differentiation and accelerated fracture repair

As a downstream product of cyclooxygenase 2 (COX-2), prostaglandin E(2) (PGE(2)) plays a crucial role in the regulation of bone formation. It has four different receptor subtypes (EP1 through EP4), each of which exerts different effects in bone. EP2 and EP4 induce bone formation through the protein kinase A (PKA) pathway, whereas EP3 inhibits bone formation in vitro. However, the effect of EP1 receptor signaling during bone formation remains unclear. Closed, stabilized femoral fractures were created in mice with EP1 receptor loss of function at 10 weeks of age. Healing was evaluated by radiographic imaging, histology, gene expression studies, micro-computed tomographic (µCT), and biomechanical measures. EP1(-/-) mouse fractures have increased formation of cartilage, increased fracture callus, and more rapid completion of endochondral ossification. The fractures heal faster and with earlier fracture callus mineralization with an altered expression of genes involved in bone repair and remodeling. Fractures in EP1(-/-) mice also had an earlier appearance of tartrate-resistant acid phosphatase (TRAcP)-positive osteoclasts, accelerated bone remodeling, and an earlier return to normal bone morphometry. EP1(-/-) mesenchymal progenitor cells isolated from bone marrow have higher osteoblast differentiation capacity and accelerated bone nodule formation and mineralization in vitro. Loss of the EP1 receptor did not affect EP2 or EP4 signaling, suggesting that EP1 and its downstream signaling targets directly regulate fracture healing. We show that unlike the PGE(2) receptors EP2 and EP4, the EP1 receptor is a negative regulator that acts at multiple stages of the fracture healing process. Inhibition of EP1 signaling is a potential means to enhance fracture healing.

The effect of Cox-2 specific inhibition on direct fracture healing in the rabbit tibia

OBJECTIVE

The purpose of this study was to evaluate the effect of Cox-2 administration on direct (primary) fracture healing.

METHODS

A transverse tibial osteotomy was created in adult male rabbits and rigidly fixed in compression using a 2.7-mm dynamic compression plate. Animals were randomized to receive either rofecoxib (12.5 mg orally per day) or placebo. Animals were killed at 4 weeks and fracture healing assessed by mechanical testing.

RESULTS

There were no significant differences between the control and Cox-2 treated animals in terms of mechanical strength at 4 weeks. There was a high complication rate of peri-implant fractures during the daily medication administration.

CONCLUSION

The immediate administration of a Cox-2 specific inhibitor did not impair primary (direct) bone healing at the dose administered in this rabbit tibial osteotomy model.

Accelerated fracture healing in mice lacking the 5-lipoxygenase gene

BACKGROUND AND PURPOSE

Cyclooxygenase-2 (COX-2) promotes inflammation by synthesizing pro-inflammatory prostaglandins from arachidonic acid. Inflammation is an early response to bone fracture, and ablation of COX-2 activity impairs fracture healing. Arachidonic acid is also converted into leukotrienes by 5-lipoxygenase (5-LO). We hypothesized that 5-LO is a negative regulator of fracture healing and that in the absence of COX-2, excess leukotrienes synthesized by 5-LO will impair fracture healing.

METHODS

Fracture healing was assessed in mice with a targeted 5-LO mutation (5-LO(KO) mice) and control mice by radiographic and histological observations, and measured by histomorphometry and torsional mechanical testing. To assess effects on arachidonic acid metabolism, prostaglandin E2, F2α, and leukotriene B4 levels were measured in the fracture calluses of control, 5-LO(KO) COX-1(KO), and COX-2(KO) mice by enzyme linked immunoassays.

RESULTS

Femur fractures in 5-LO(KO) mice rapidly developed a cartilaginous callus that was replaced with bone to heal fractures faster than in control mice. Femurs from 5-LO(KO) mice had substantially better mechanical properties after 1 month of healing than did control mice. Callus leukotriene levels were 4-fold higher in mice homozygous for a targeted mutation in the COX-2 gene (COX-2(KO)), which indicated that arachidonic acid was shunted into the 5-LO pathway in the absence of COX-2.

INTERPRETATION

These experiments show that 5-LO negatively regulates fracture healing and that shunting of arachidonic acid into the 5-LO pathway may account, at least in part, for the impaired fracture healing response observed in COX-2(KO) mice.

Trauma-induced inflammation and fracture healing

Fracture healing is an extremely complex interaction of cells, biologic pathways, and molecules. Certainly, the inflammatory response is one of the initiating factors for bone healing. The inflammatory phase is a critical period characterized by low oxygen tension, impaired perfusion, and the migration of a wide array of cells and release of active molecules. Systemwide inflammatory conditions also modulate the primary processes of fracture management. Osteoprogenitor cells, mesenchymal cells, osteoblasts, and chondrocytes contribute to the healing and inflammatory response at the bone level. The inflammatory process is dependent on and propagates through proinflammatory cytokines, the transforming growth factor-beta superfamily with other growth factors, and the metalloproteinases and angiogenic factors. Interference with any of these pathways or proteins either promotes or more likely decreases fracture healing. This article reviews the initial inflammatory response to trauma as it pertains to musculoskeletal healing.