Quantitative Analysis of Growth Factors from a Second Filter Using the Reamer-Irrigator-Aspirator System: Description of a Novel Technique

Use of the Reamer-Irrigator-Aspirator (RIA) as a source of autogenous bone graft in the treatment of nonunions is increasing. We report on our novel technique of using a second filter containing beta-tricalcium phosphate (TCP) as a graft extender while using the RIA system. We also quantify growth factor concentrations in the collections from the TCP filter. A second filter attached in series with the standard RIA filtration system yields TCP with substantial concentrations of bioactive proteins that are equal to those seen in the bone graft that is harvested in the first filter.

In the United States 7.9 million fractures occur annually. Between 5% and 10% of these fractures result in delayed or impaired healing. More than 1.5 million bone-grafting procedures are performed each year. Iliac crest bone graft has long been considered the gold standard for autogenous bone graft because of its osteoconductive, osteoinductive, and osteogenic properties ; however, it is associated with significant donor site morbidity and increased operative time. The Reamer-Irrigator-Aspirator (RIA; Synthes, USA, Paoli, PA) was initially developed to potentially reduce the embolic load associated with reaming the femur for intramedullary nailing in trauma. Subsequently it has been noted that the reamings are biologically active and may provide a source of autogenous bone similar to iliac crest in efficacy, but with fewer donor site complications. The RIA system typically uses a single filter to capture the bony reaming debris from the RIA cutting head. Recently it has been noted that the irrigating fluid effluent may also contain significant amounts of growth factors and mesenchymal stem cells.

The purpose of this paper is twofold. First, we report on our novel technique of using a second filter containing beta-tricalcium phosphate (TCP) as a graft extender while using the RIA system. Second, we sought to identify whether growth factors known to be present in the bony reaming debris and fluid effluent are also present in the collections from the TCP filter.

Materials and methods

This study was approved by our Institutional Review Board (IRB). Informed consent was obtained from 16 patients who were prospectively enrolled between February 2007 and May 2007. Inclusion criteria included age older than 19 years and nonunion of a long bone requiring bone grafting; exclusion criterion was active infection at the time of the bone-grafting procedure. Patients could be enrolled if they had a history of prior infection, but no signs of active infection. There were eight males and eight females enrolled with an average age of 40 years (range 22 to 60 years). Seven (44%) of the 16 patients were smokers, 1 (6%) had diabetes, and 9 (56%) had an open fracture with their initial injury. All patients underwent bone harvest and grafting using the RIA system as well as iliac crest aspiration. Samples from the TCP filter were analyzed and compared with the patient’s iliac crest bone marrow aspirate.

Operative RIA technique

Patients were placed supine on a radiolucent table. Bone was harvested using the RIA system through a trochanteric entry portal over a guide wire designed for this system. Access to the trochanteric portal was through a 25- to 30-mm incision that ended approximately 2 cm proximal to the tip of the greater trochanter. The technique is identical to trochanteric intramedullary nailing until the reamer is placed. A threaded wire was placed at the tip of the greater trochanter and drilled into the proximal femur. A cannulated opening reamer was then used to open the proximal femur. A ball-tipped guide wire was then inserted and passed into the distal femur. It is critical to make sure that the guide wire is centered distally. Two 750-μm sterile filters were attached to the suction tubing in series ( Fig. 1 ). The reamer head diameter was determined using intraoperative fluoroscopy. The reamer was used in a single-pass fashion using a slow, deliberate advance/withdrawal maneuver. The first filter collected the bony reamings and the second filter contained either large (2.8–5.6 mm) or medium (1.4–2.8 mm)-sized TCP granules that were washed with aspiration fluid. For all subjects, three stratified (top, middle, and bottom) samples ( Fig. 2 ) were taken from the TCP-containing second filter for quantitative analysis of various growth factors. The factors analyzed were vascular endothelial growth factor (VEGF), bone morphogenetic protein-2 (BMP-2), transforming growth factor-beta (TGF-beta), and total protein (TP). Each patient also had iliac crest bone marrow aspirate sent for quantification of these same growth factors. The entry portal was then plugged with a piece of tricalcium phosphate.

Operative RIA technique

Patients were placed supine on a radiolucent table. Bone was harvested using the RIA system through a trochanteric entry portal over a guide wire designed for this system. Access to the trochanteric portal was through a 25- to 30-mm incision that ended approximately 2 cm proximal to the tip of the greater trochanter. The technique is identical to trochanteric intramedullary nailing until the reamer is placed. A threaded wire was placed at the tip of the greater trochanter and drilled into the proximal femur. A cannulated opening reamer was then used to open the proximal femur. A ball-tipped guide wire was then inserted and passed into the distal femur. It is critical to make sure that the guide wire is centered distally. Two 750-μm sterile filters were attached to the suction tubing in series ( Fig. 1 ). The reamer head diameter was determined using intraoperative fluoroscopy. The reamer was used in a single-pass fashion using a slow, deliberate advance/withdrawal maneuver. The first filter collected the bony reamings and the second filter contained either large (2.8–5.6 mm) or medium (1.4–2.8 mm)-sized TCP granules that were washed with aspiration fluid. For all subjects, three stratified (top, middle, and bottom) samples ( Fig. 2 ) were taken from the TCP-containing second filter for quantitative analysis of various growth factors. The factors analyzed were vascular endothelial growth factor (VEGF), bone morphogenetic protein-2 (BMP-2), transforming growth factor-beta (TGF-beta), and total protein (TP). Each patient also had iliac crest bone marrow aspirate sent for quantification of these same growth factors. The entry portal was then plugged with a piece of tricalcium phosphate.