This study investigated the quality and quantity of healing of a bone defect following intramedullary reaming undertaken by two fundamentally different systems; conventional, using non-irrigated, multiple passes; or suction/irrigation, using one pass. The result of a measured re-implantation of the product of reaming was examined in one additional group. We used 24 Swiss mountain sheep with a mean tibial medullary canal diameter between 8 mm and 9 mm. An 8 mm ‘napkin ring’ defect was created at the mid-diaphysis. The wound was either surgically closed or occluded. The medullary cavity was then reamed to 11 mm. The Reamer/Irrigator/Aspirator (RIA) System was used for the reaming procedure in groups A (RIA and autofilling) and B (RIA, collected reamings filled up), whereas reaming in group C (Synream and autofilling) was performed with the Synream System. The defect was allowed to auto-fill with reamings in groups A and C, but in group B, the defect was surgically filled with collected reamings. The tibia was then stabilised with a solid locking Unreamed Humerus Nail (UHN), 9.5 mm in diameter. The animals were killed after six weeks. After the implants were removed, measurements were taken to assess the stiffness, strength and callus formation at the site of the defect.

There was no significant difference between healing after conventional reaming or suction/irrigation reaming. A significant improvement in the quality of the callus was demonstrated by surgically placing captured reamings into the defect using a graft harvesting system attached to the aspirator device. This was confirmed by biomechanical testing of stiffness and strength. This study suggests it could be beneficial to fill cortical defects with reaming particles in clinical practice, if feasible.

Movement between an implant surface and overlying soft tissue gives rise to fibrous capsule formation with a liquid filled void. Clinically, this situation is more prevalent with electropolished stainless steel (EPSS) implants compared to commercially pure titanium (CpTi) implants. We hypothesise this is mainly due to lack of microtopography on the EPSS.

Four experimental EPSS surfaces with varying microtopographies were selected by a combination of morphological analysis using the scanning electron microscope and quantitative roughness analysis using laser profilometry. Standard treated EPSS (ISO 5832/1) and CpTi (ISO 5832/2) surfaces were also used. The plates had only one screw hole at either end so that the interaction of the tissue with an intact surface could be evaluated. Six plates of each type were implanted on both the left and right tibia, randomly, of 18 white New Zealand rabbits under the muscle for 12 weeks.

After sacrifice samples underwent standard histological processing. Briefly, fixation, dehydration, embedding in methyl methacrylate, sectioning at 250μm slices (with implant), grinding to 50μm and staining with Giemsa. Digital images were taken with a light microscope and the size of thickening of connective tissue on the implant surface and the presence or absence of a liquid filled void was observed.

Results showed no voids present on the CpTi samples. The standard EPSS had 3/6 plates with a void. The experimental EPSS surfaces were in-between these results. There was no relationship between quantitative measurements of average roughness (Ra) and the presence or absence of a void. There was a relationship between lack of fine microroughness of a surface (as seen with the SEM) and the presence of a void. The size of capsular thickening was not related to the Ra of the surface. These results support that void formation is mainly due to lack of microtopography on the plates.