Introduction: Monobutyrin (MB) has been shown to be a potent angiogenic factor for adipose tissue. It is one of the many compounds secreted from adipocytes adding to the knowledge that adipose tissue is not merely a storage unit but has an endocrine function. Adipocytes and osteoblasts share a common precursor. In osteoporosis the proportion of fat in bone increases. As both are present at a fracture site the addition of MB may enhance fracture healing by stimulating angiogenesis.

Method: 138 Sprague Dawley rodents were ovarect-omised at 12 weeks of age. After a further 24 weeks each animal underwent a right closed femoral fracture stabilized with a retrograde k-wire using a standard model (Walsh et al. 1997). Animals were randomised into control (empty or substrate only) or MB of varying concentrations (2.5μg, 7.5μg, 25μg, 75μg). A percutaneous injection of 0.2mls of each of the above was then injected into the fracture site. Animals were culled at 1, 3 and 6 week time points post surgery. The right and left femurs were dissected out and analyzed using radiographic, mechanical testing, micro computed tomography and histology endpoints. Statistical analysis was perfomed with SPSS for windows.

Results: All animals recovered well from the procedure and no adverse reactions were noted following the addition of MB. A progression to union was seen with time in all groups. Mechanical testing did not result in a statistical difference between groups, however the trend showed improved healing in the 7.5μg Monobutyrin group. Radiographic grading again showed no statistical difference however, interestingly micro CT data showed an increasing trend in both trabecular number and bone surface area to volume with increasing concentrations of MB.

The histology results implied a potential acceleration in the early stage of fracture healing in the high dose (75 μg) MB group. However progression to union following this initial early phase acceleration was delayed as callus volume increased rather than union according to micro CT and histological data.

Discussion: The ability to augment fracture healing has significant clinical implications considering the “greying of society”. This study investigated the possibility of improving fracture healing by incorporating the angiogenic factor, Monobutyrin in an estrogen deficient animal model. Although the results do not conclusively demonstrate an improvement in fracture healing, they do imply that MB does affect the early phase of fracture healing in the estrogen deficient model. This study is limited in that the effects of MB on fracture healing in a non-estrogen deficient model was not considered. The ideal release kinetics for Monobutyrin as well as other factors remains unknown.

Introduction: The use of bioabsorbable devices in sports medicine surgery in the shoulder and knee continues to evolve as new designs, devices and materials become available. Concerns over potential problems associated with metal artifacts and permanent metal devices continue to motivate the development and use of polymeric based devices. Calaxo interference screws (Smith & Nephew Endoscopy, Andover, MA) are composed of a novel bioabsorbable material blend of poly DL- lactide – co – glycolide 85:15 (65%) and calcium carbonate (35%). These screws have been shown to be osteoconductive when placed in the centre of a 4 stranded tendon graft in an ovine ACL reconstruction [1]. The screws are fully resorbed at 26 weeks with new bone formation in the tunnel. In general, osteoconductive materials are often more effective when placed adjacent to a bony bed. This study investigated whether positioning the Calaxo screw adjacent to the bone tunnel was superior to screw placement within the tendon as in our previous study [1].

Materials and Methods: An intra-articular anterior cruciate ligament (ACL) reconstruction model using 2 doubled over tendon autografts whip stitched and inserted into the right hind limb of 8 sheep were used. Animals were culled at 26 or 52 weeks following surgery (n=4 per time point) and data was compared using the same surgical model but with screws placed in the center of the 4 stranded graft (Walsh et al., 2006). The tibias were CT scanned and processed for paraffin histology along the axis of the bone tunnel. Three dimensional models using the DICOM data obtained from the CT where made using MIMICS (Materialise, Belgium).

Result & Discussion: Results showed excellent biocompatibility of the screws with no adverse reactions at 26 and 52 weeks as in our previous study [1]. The screws were fully resorbed by 26 weeks with new bone replacing the PLC material. Similarly, the screws were not detectable at 52 weeks with new bone formation where the screw had previously resided. The intra-articular portion of the graft, articular cartilage and synovium was normal at 26 and 52 weeks as previously reported [1]. Tendon – bone healing proximal to the screw progressed in a normal fashion. No calcification of the intraarticular portion of the graft was noted. Computed tomography, 3D models and histology revealed an osteoconductive response to the PLC material with new bone formation as the material degraded in vivo.

Placement of the screw adjacent to the tendon graft and thus against the bone tunnel appears to provide superior results compared to screw placement in the middle of the graft sleeve device. This effect may be due to direct contact of the osteoconductive material to the adjacent bone bed.

[1] Walsh et al., Arthroscopy 2006, in press.