In vivo assessment of the Reamer-Irrigator-Aspirator (RIA)

RIA vs unreamed nailing
The purpose of this part of the study was to compare the effects of reamed intramedullary (IM) nailing using a new reaming system which uses irrigation and suction (RIA: Reamer-Irrigator-Aspirator; Synthes USA) with unreamed IM nailing; the goal being reduction of fat emboli in the blood, and coincidentally preventing occlusion of intracortical vessels. Sheep were treated with reamed (RIA) and unreamed (UR) intramedullary nailing on both unfractured femora. Blood samples were taken from both femoral veins during consecutive steps of IM nailing: UR: nail insertion; RIA: guide wire insertion, reaming, and nail insertion. They were assessed for fat content using a modified Gurd Test. Number and size of fat droplets was measured and data expressed as differences between nail insertion on the UR side and each step on the RIA side. In histological cross-sections intra-vital staining and fat staining, indicating functioning cortical perfusion and distribution of fat in cortical vessels, was evaluated. Ratios of perfused and fat containing vessels out of the total number of cortical vessels were then calculated.

Fracture healing was studied in the tibia. The procedure was first performed in the left tibia, with an observation period of ten weeks. Bone remodeling was labeled with Calcein green, Xylenol orange and Tetracycline. Pre-terminally the same nailing procedures were performed in the right tibia, followed by intravitam staining with Procion red, and an ink perfusion of the left tibia. The fractured left tibia was embedded in polymethylmethacrylate and histological sections and contact radiographs were evaluated with respect to callus development, cortical remodeling and ink perfusion. In the right tibia acute effects on cortical perfusion (Procion red staining) were evaluated in polymer embedded sections. Cryocuts were evaluated with respect to fat distribution (Sudan III staining).

Blood samples from the RIA side contained significantly less fat than the samples from the UR side (Fig 1b). After irrigation and suction little fat was observed in the cortex of RIA specimens, whereas after unreamed nailing the endosteal third of the cortical bone was infused with fat (Fig 2). Unreamed nailing acutely showed signs of remaining perfusion in the endosteal tenth and periosteal third of the cortical bone, after irrigation and suction-reaming perfusion was preserved to a lesser degree due to ablation (Fig 3). After ten weeks callus development and perfusion was similar in both groups. Cortical remodelling was the same in both groups after four weeks and was three times larger in the unreamed group after six weeks, indicating a more pronounced reaction to intracortical damage.

Irrigation and suction significantly reduces fat intravasation, and thus the danger of adverse systemic effects, while fracture healing is comparable to unreamed nailing.

Upper pictures (Fig 2)
a Typical specimen of unreamed nailing with a red seam of stained medullary fat on the endosteal side of the cortex (left).
b Typical specimen of RIA nailing with no medullary fat visible in the cortex. The correct functioning of the staining technique is illustrated in the attached soft tissues on the right.

Lower pictures (Fig 3)
Perfusion did not show dramatic differences between the two nailing techniques, and disturbances covered a wide range.
a Example for a cortical region with relatively good blood supply.
b Example for an almost nonperfused cortical region.

RIA as a bone harvesting device
The RIA system permits the collection of bone particles which are produced by the reaming process. This system was used to study the influence of such bone particles, and of platelet rich plasma (PRP) on fracture healing. The results were compared to those of the SynReam (SYN) system.

In sheep, a defect of 8 mm was created in the left tibia at the midshaft. The RIA system was used in the groups RIA (no defect filling), RIA+B (bone particles) and RIA+B+PRP (bone particles+PRP), and the Syn-Ream system in group SYN. The medullary cavity was reamed to 11 mm in all four groups prior to implantation of an UHN (9.5 mm x 190 mm). After 6 weeks both tibia were harvested. Evaluation included mechanical testing, quantitative radiological evaluation and histomorphological analysis of newly formed bone.

For stiffness and strength the highest values were found in the group RIA+B, and they differed significantly (p<0.05) from group RIA. The values of RIA+B+PRP and RIA+B were significantly higher (p<0.01) than the values of SYN. After 4 weeks the radiological evaluation of callus area showed significant differences (p<0.05) between the two groups RIA+B+PRP and RIA+B and the two groups without bone reimplantation (RIA, SYN) but this difference was no longer visible at a later stage. No difference between RIA and SYN was found.

Callus formation can be significantly stimulated by the reimplantation of bone particles which are produced and collected by the RIA system. A clinical use of such techniques therefore seems to have an interesting potential.