Quantitative analysis of angiogenesis and growth of bone: effect of indomethacin exposure in a combined in vitro-in vivo approach

The avascular talus: revascularization in an animal model

Avascular necrosis of bone such as the talus can lead to collapse and loss of function. To avoid this, early revascularization has been proposed as an important event. Revascularization can occur either by vessel growth directly through the bony surface, or by vessel growth into the periosteum or ligaments with secondary reconnection to the bone. The ability to attract new vessels (angiogenesis) of the bony surface and the connective tissue was compared in an animal model. A talus isograft (all cortical surface, periosteum, and ligaments remaining; n = 11) or a sector of a femoral head isograft (cancellous surface, no connective tissue; n = 12) of adult mice was implanted into dorsal skinfold chambers of mice of the same strain. The implants were observed by intravital microscopy every 12 hours. First indicators of angiogenesis were hemorrhages around the implants (tali: 11 of 11, 72 +/- 12 hours; femoral heads: 6 of 12, 84 +/- 24 hours). Next, a sudden redness of the transplant indicated marrow hemorrhage (tali: 9 of 11 after 84 +/- 36 hours; femoral heads: 10 of 12 after 96 +/- 36 hours). Histology showed clear growth of capillaries into the cancellous surface of the femoral heads and possible growth of capillaries into the ligament stumps (tali). However, there was widespread necrosis of the marrow cells indicating failure of recirculation. A cancellous bony surface as well as the soft tissues attached to the bone provided a stimulus to rapid revascularization of the grafts. This model was able to evaluate differing rates of early partial revascularization for various bone surfaces, which may have implications for studying treatment options for certain fracture dislocations (e.g., in the talus).

Short-term load bearing capacity of osteochondral autografts implanted by the mosaicplasty technique: an in vitro porcine model

Articular surface congruency and graft stability are considered essential factors in the success of osteochondral grafting; however, quantitative measures of short-term load bearing capacity of grafts implanted by the mosaicplasty technique have not been reported. The purpose of this study was to develop a live tissue in vitro model to examine short-term fixation strength of mosaicplasty autografts immediately after and 1 week following graft implantation. Cylindrical osteochondral autografts were implanted in vitro by the mosaicplasty technique on five pairs of porcine femoral condyles within one and a half hours of animal sacrifice. Immediately following the surgical procedure, graft push-in and pull-out strength tests as well as indentation tests to determine modulus of the surrounding cancellous bone were performed on half of the specimens from the distal femurs of each animal. The remaining specimens, matched for location in the contralateral leg, were incubated in culture medium for 7 days prior to performing the same set of mechanical tests. Averaged push-in and pull-out graft fixation strength decreased 44% from 135.7 to 75.5N over the 7-day period, while no change in modulus was detected in the surrounding cancellous bone. These in vitro results demonstrate a substantial deterioration of short-term fixation strength of mosaicplasty grafts from the immediate post-operative state. Such a reduction in short-term graft load bearing capacity may pose a threat to the surgically established articular surface congruency and blood vessels formed during the early stages of the healing response.

Effect of tenoxicam on fracture healing in rat tibiae

BACKGROUND

Nonsteroidal anti-inflammatory drugs have been implicated in the development of delayed unions and nonunion after fractures in animal models. Previous investigations have identified two important factors as determinants of delayed fracture healing: early drug administration and a dose-dependent effect.

OBJECTIVE

The purpose of this investigation was to study the effect of tenoxicam, a nonsteroidal anti-inflammatory drug, on the fracture healing process in rat tibiae.

METHODS

Fifty-eight Wistar rats were randomly divided in four groups (I, II, III, and IV). Group I (control group, n=12) was given 0.1ml saline solution per day intramuscularly. Groups II (n=12), III (n=12), and IV (n=12) were administered 10mg per kg per day of tenoxicam intramuscularly. Administration of substances was begun on a week before to 48h after the fracturing procedure and continued during the entire experiment. Callus formation was studied histologically and histomorphologically, using light microscopy. In addition, a histologic grading based on the morphologic stage of fracture healing was carried out at 4 weeks, according to the criteria proposed by Allen et al.

RESULTS

There was a significant difference in treatment effect between Group I (saline solution) and Groups II, III, and IV (tenoxicam) (P=0.07). Histologically and histomorphologically, there were qualitative and quantitative delay in callus formation at all tenoxicam groups. This was more pronounced the earlier the nonsteroidal anti-inflammatory drug was started, although no significant difference could be detected between Groups II, III, and IV (P>(alpha=10%)). Four weeks after fracture, Group I (n=3) showed complete osseous union, Groups II (n=3) and III (n=3), complete cartilaginous union, and Group IV (n=3), incomplete osseous union, according to Allen et al. By using this rating scale, the difference between control and drug-treated groups was statistically significant (P<0.1).

CONCLUSION

Under studied conditions, this investigation shows that administration of tenoxicam intramuscularly delays fracture healing process in rat tibiae. These results suggest the hypothesis that early drug administration may delay bone healing after experimental fractures in animals, although it could not be detected statistically significant.

Heating or freezing bone. Effects on angiogenesis induction and growth potential in mice

We have characterized the effect of bone graft treatment by heating or freezing (with or without dimethyl sulfoxide (DMSO)). Tissue culture and dorsal skin-fold chambers in mice were used as sites to quantify the effect on angiogenesis, growth and calcification of neonatal femora. Fresh femora increased in both length and cartilage diameter (calcification in vivo only), but cryopreservation or heating abolished the increase in femoral dimensions. In vivo, femora of all experimental groups elicited an angiogenic response from the host tissue, which was most pronounced for fresh femora, weaker for DMSO-preserved frozen bone and poor for unprotected frozen bone and boiled femora. Freezing in the presence of a cryopreservative (DMSO) was found to preserve the angiogenic potential of frozen bone, whereas unprotected heating or freezing significantly impaired angiogenesis induction and growth potential.